WO2025088105A1

WO2025088105A1 - Cancer treatment with anti-claudin 18.2 adc

Info

Publication number: WO2025088105A1
Application number: PCT/EP2024/080206
Authority: WO
Inventors: Bo Chen; Wei Liu; Chaohong Hu
Original assignee: Keymed Biosciences Chengdu Co Ltd; Shanghai Miracogen Inc; Couchman Edward
Current assignee: Keymed Biosciences Chengdu Co Ltd; Shanghai Miracogen Inc; Couchman Edward
Priority date: 2023-10-27
Filing date: 2024-10-25
Publication date: 2025-05-01
Anticipated expiration: 2026-04-27
Also published as: TW202535476A

Abstract

Provided herein is a method of treating cancer in a subject, comprising administering to the subject a therapeutically effective dose of an antibody-drug conjugate (ADC) comprising an antibody or antigen-binding fragment thereof that specifically binds claudin 18.2 (CLDN18.2) conjugated to a cytotoxic agent, wherein CLDN18.2 is expressed in the cancer at a level which indicates susceptibility to treatment with the ADC.

Description

CANCER TREATMENT WITH ANTI-CLAUDIN 18.2 ADC

FIELD

Provided herein are methods by which cancer patients susceptible to treatment with an antibody-drug conjugate (ADC) comprising an anti-claudin 18.2 antibody can be identified and treated.

BACKGROUND

The Claudin (CLDN) proteins participate in the formation of tight junctions between epithelial cells. CLDN proteins are transmembrane proteins with 4 transmembrane helices, with cytoplasmic N- and C-termini and two extracellular loops (ECLs). Different members of the Claudin family are expressed in different tissues.

Claudin 18 has two isoforms produced as a result of alternative splicing: CLDN18.1 and CLDN18.2. In healthy individuals, CLDN18.1 is expressed primarily in the lungs, in alveolar epithelial cells, whereas CLDN18.2 is expressed primarily in the stomach, in gastric mucosal membrane epithelial cells.

However, CLDN18.2 has been found to be expressed in a variety of cancers, including about 70 % of gastric cancers and 50 % of pancreatic cancers. Moreover, in healthy individuals CLDN18.2 is buried in tight junctions, but during malignant transformation is believed to become more exposed and thus therapeutically accessible. As a result, CLDN18.2 has been identified as a target for treatment of these cancers, particularly gastric cancer.

Gastric cancer is one of the most common cancers worldwide, with over a million cases diagnosed in 2020. Incidence of gastric cancer is particularly high in East Asia. The standard initial treatment for advanced or recurrent gastric cancer is chemotherapy. Although developments in treatment have improved the prognosis of gastric cancer patients in recent years, the 5-year overall survival rate is still only about 20 %.

Targeted therapy has brought new hope for the treatment of recurrent/advanced gastric cancer. The anti-HER2 antibody trastuzumab combined with chemotherapy can benefit patients with HER2-positive cancer, but only about 15 % of gastric cancers overexpress HER2. PD-1/PD-L1 inhibitors can also benefit gastric cancer patients, particularly those with PD-L1 -positive tumours. Nonetheless, new therapies remain needed, and CLDN18.2 is an attractive target.

The anti-CLDN18.2 monoclonal antibody zolbetuximab has been found to be effective in treating gastric cancer, improving survival rates when combined with either CAPOX (Shah et al., Nature Medicine 29: 2133-2141 , 2023) or mFOLFOX6 (Shitara et al., The Lancet 401 (10389): 1655-1668, 2023) compared to the chemotherapy alone, validating the approach of targeting CLDN18.2 in gastric cancer treatment. However, zolbetuximab has been found to display efficacy only in patients with moderate-to-strong CLDN18.2 expression (i.e. immunohistochemistry staining intensity of at least 2) in > 70 % of tumour cells (Sahin et a/., Annals of Oncology 32(5): 609-619, 2021 ).

WO 2020/211792 discloses a number of anti-CLDN18.2 antibodies that can be used in cancer therapy, including CM311 . Antibody-drug conjugates (ADCs) based on the same antibody are disclosed in WO 2022/078523, including an ADC comprising CM311 conjugated to the potent antineoplastic agent monomethyl auristatin E (MMAE), known as CMG901. A phase I, dose escalation/expansion study of CMG901 has now been completed.

SUMMARY

In a first aspect, provided herein is a method of treating cancer in a subject, comprising administering to the subject a therapeutically effective dose of an antibody-drug conjugate (ADC) comprising an antibody or antigen-binding fragment thereof that specifically binds claudin 18.2 (CLDN18.2) conjugated to a cytotoxic agent, wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region comprising VHCDR1 , VHCDR2 and VHCDR3 and a light chain variable region comprising VLCDR1 , VLCDR2 and VLCDR3, wherein:

VHCDR1 comprises the amino acid sequence set forth in SEQ ID NO: 1 ; VHCDR2 comprises the amino acid sequence set forth in SEQ ID NO: 2; VHCDR3 comprises the amino acid sequence set forth in SEQ ID NO: 3; VLCDR1 comprises the amino acid sequence set forth in SEQ ID NO: 4; VLCDR2 comprises the amino acid sequence set forth in SEQ ID NO: 5; and VLCDR3 comprises the amino acid sequence set forth in SEQ ID NO: 6; and wherein CLDN18.2 is expressed in the cancer at a level which indicates susceptibility to treatment with the ADC.

Relatedly, provided herein is an antibody-drug conjugate (ADC) comprising an antibody or antigen-binding fragment thereof that specifically binds claudin 18.2 (CLDN18.2) conjugated to a cytotoxic agent for use in a method of treating cancer in a subject, wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region comprising VHCDR1 , VHCDR2 and VHCDR3 and a light chain variable region comprising VLCDR1 , VLCDR2 and VLCDR3, wherein:

Also relatedly, provided herein is the use of an antibody-drug conjugate (ADC) comprising an antibody or antigen-binding fragment thereof that specifically binds claudin

18.2 (CLDN18.2) conjugated to a cytotoxic agent to treat cancer in a subject, wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region comprising VHCDR1 , VHCDR2 and VHCDR3 and a light chain variable region comprising VLCDR1 , VLCDR2 and VLCDR3, wherein:

VHCDR1 comprises the amino acid sequence set forth in SEQ ID NO: 1 ;

VHCDR2 comprises the amino acid sequence set forth in SEQ ID NO: 2;

VHCDR3 comprises the amino acid sequence set forth in SEQ ID NO: 3; VLCDR1 comprises the amino acid sequence set forth in SEQ ID NO: 4;

VLCDR2 comprises the amino acid sequence set forth in SEQ ID NO: 5; and VLCDR3 comprises the amino acid sequence set forth in SEQ ID NO: 6; and wherein CLDN18.2 is expressed in the cancer at a level which indicates susceptibility to treatment with the ADC.

18.2 (CLDN18.2) conjugated to a cytotoxic agent in the manufacture of a medicament for treating cancer in a subject, wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region comprising VHCDR1 , VHCDR2 and VHCDR3 and a light chain variable region comprising VLCDR1 , VLCDR2 and VLCDR3, wherein:

VHCDR1 comprises the amino acid sequence set forth in SEQ ID NO: 1 ;

VHCDR2 comprises the amino acid sequence set forth in SEQ ID NO: 2;

Also relatedly, provided herein is a pharmaceutical composition for use in treating cancer in a subject, wherein the composition comprises an antibody-drug conjugate (ADC) comprising an antibody or antigen-binding fragment thereof that specifically binds claudin

18.2 (CLDN18.2) conjugated to a cytotoxic agent, wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region comprising VHCDR1 , VHCDR2 and VHCDR3 and a light chain variable region comprising VLCDR1 , VLCDR2 and VLCDR3, wherein:

VHCDR1 comprises the amino acid sequence set forth in SEQ ID NO: 1 ;

VHCDR2 comprises the amino acid sequence set forth in SEQ ID NO: 2;

VHCDR3 comprises the amino acid sequence set forth in SEQ ID NO: 3;

VLCDR1 comprises the amino acid sequence set forth in SEQ ID NO: 4;

In a second aspect, provided herein is a method of identifying and treating a subject with cancer susceptible to treatment with an ADC as defined in the first aspect, the method comprising:

(a) assessing the level of CLDN18.2 expression in a tissue sample from the cancer;

(b) determining whether the subject is susceptible to treatment with the ADC based on the level of CLDN18.2 expression in the tissue sample; and

(c) when the subject is identified as susceptible to treatment with the ADC, administering an effective amount of the ADC to the subject.

In a third aspect, provided herein is a method of selecting a subject with cancer for treatment with an ADC as defined in the first aspect, the method comprising assessing the level of CLDN18.2 expression in a tissue sample from the cancer, wherein the subject is selected for treatment with the ADC when CLDN18.2 is expressed by at least 10 % of cells in the cancer.

In a fourth aspect, provided herein is a method of predicting whether a subject with cancer is likely to respond to treatment with an ADC as defined in the first aspect, the method comprising assessing the level of CLDN18.2 expression in a tissue sample from the cancer, wherein the subject is considered likely to respond to treatment with the ADC when CLDN18.2 is expressed by at least 10 % of cells in the cancer.

In a fifth aspect, provided herein is a method for identifying a subject with cancer who is likely to respond to treatment with an ADC as defined in the first aspect, the method comprising obtaining a tissue sample of the cancer from the subject and assessing the level of CLDN18.2 expression in the sample, wherein the subject is considered likely to respond to treatment with the ADC when CLDN18.2 is expressed by at least 10 % of cells in the cancer. In a sixth aspect, provided herein is a method for assessing the susceptibility of a cancer in a subject to treatment with an ADC as defined in the first aspect, comprising assessing the level of CLDN18.2 expression in a tissue sample from the cancer, wherein the cancer is considered susceptible to treatment with the ADC when CLDN18.2 is expressed by at least 10 % of cells in the cancer.

DETAILED DESCRIPTION

The present inventors have identified cancer patient populations particularly susceptible to treatment with an antibody-drug conjugate (ADC) targeting Claudin 18.2 (CLDN18.2), based on the level of CLDN18.2 expression in the target cancer. Unexpectedly, the level of CLDN18.2 expression required for susceptibility to treatment with the ADC is substantially lower than the level required for susceptibility to existing treatments which target CLDN18.2, opening up the possibility of such targeted therapy to a much wider pool of patients.

ANTIBODIES

The ADC for use herein comprises an antibody, or antigen-binding fragment thereof, that specifically binds to CLDN18.2.

As defined herein, in line with standard terminology in the art, an antibody is an antigen-binding protein comprising two heavy chains and two light chains. The light chains are shorter (and thus lighter) than the heavy chains. The heavy chains comprise an N- terminal heavy chain variable domain (VH), and the light chains comprise an N-terminal light chain variable domain (VL). The heavy and light chains each comprise constant domains C- terminal to the respective variable domain.

Both the light and heavy chains of an antibody comprise three hypervariable complementarity-determining regions (CDRs), as set out here below. In a pair of a light chain and a heavy chain, the CDRs of the two chains form the antigen-binding site. The CDR sequences determine the specificity of an antibody. The three CDRs of a heavy chain are known as VHCDR1 , VHCDR2 and VHCDR3, from N-terminus to C-terminus, and the three CDRs of a light chain are known as VLCDR1 , VLCDR2 and VLCDR3, from N-terminus to C-terminus. Framework regions are located in between the CDRs and between the CDRs and ends of the variable domains. Antigen-binding fragments of antibodies are fragments or synthetic constructs comprising one or more antigen-binding sites of an antibody, but not the entire antibody. Generally, an antigen-binding fragment of an antibody comprises the entire VL and VH domain sequences, but lacks at least part of the heavy and/or light chain constant domains.

The antibody, or antigen-binding fragment thereof (henceforth simply “fragment thereof’, or “antibody fragment”), used in the ADC specifically binds human CLDN18.2. Human CLDN18.2 has the UniProt accession number P56856-2, and the amino acid sequence set forth in SEQ ID NO: 11 . Thus the antibody or fragment thereof specifically binds a protein with the sequence of SEQ ID NO: 11.

An antibody which binds specifically to human CLDN18.2 is an antibody which binds to human CLDN18.2 with a greater affinity than that with which it binds to other molecules, or at least most other molecules. In particular, an antibody which binds specifically to human CLDN18.2 either does not bind human CLDN18.1 (UniProt P56856-1 , SEQ ID NO: 12), or binds human CLDN18.1 with much lower affinity than human CLDN18.2, e.g. it may bind human CLDN18.2 with an affinity which is one or more orders of magnitude higher than the affinity with which it binds human CLDN18.1.

An antibody which specifically binds human CLDN18.2 may display cross-reactivity with CLDN18.2 from other species. Regardless, the skilled person can readily determine whether an antibody or fragment thereof specifically binds human CLDN18.2 using standard techniques in the art, e.g. ELISA, Western-blot, surface plasmon resonance (SPR), etc.

The antibody or fragment thereof used in the present ADC comprises a heavy chain variable region comprising VHCDR1 , VHCDR2 and VHCDR3 and a light chain variable region comprising VLCDR1 , VLCDR2 and VLCDR3, wherein:

VHCDR1 comprises or consists of the amino acid sequence set forth in SEQ ID NO: 1 (GGSISSNYAWN);

VHCDR2 comprises or consists of the amino acid sequence set forth in SEQ ID NO: 2 (YIYYSGNTNYNPSLKS);

VHCDR3 comprises or consists of the amino acid sequence set forth in SEQ ID NO: 3 (SYYGNSFIY);

VLCDR1 comprises or consists of the amino acid sequence set forth in SEQ ID NO: 4 (KSSQSLLNSGNQKNYLT);

VLCDR2 comprises or consists of the amino acid sequence set forth in SEQ ID NO: 5 (WASTRES); and

VLCDR3 comprises or consists of the amino acid sequence set forth in SEQ ID NO: 6 (QNAYSFPWT).

The antibody or fragment thereof used in the ADC for use herein is capable of mediating endocytosis of CLDN18.2 expressed on the surface of a target cell. That is to say, upon binding of the antibody or fragment thereof to CLDN18.2 on the surface of a cell, the CLDN18.2 and bound antibody are internalised into the cell by endocytosis. Whether an antibody induces endocytosis upon binding to a cell surface protein can be determined by e.g. confocal microscopy using a fluorescent-tagged antibody.

As set out above, the present ADC comprises an antibody or fragment thereof. An “antibody” as referred to herein is an immunoglobulin having the features described hereinbefore. Antigen-binding fragments of antibodies are discussed in Rodrigo et al., Antibodies, Vol. 4(3), p. 259-277, 2015. Antibody fragments which may be used herein include, for example, Fab, F(ab')2, Fab' and Fv fragments. Fab fragments are discussed in Nelson, mAbs 2(1 ): 77-83, 2010. A Fab fragment consists of the antigen-binding domain of an antibody, i.e. an individual antibody may be seen to contain two Fab fragments, each consisting of a light chain and its conjoined N-terminal section of the heavy chain. Thus a Fab fragment contains an entire light chain and the VH and CH1 domains of the heavy chain to which it is bound. Fab fragments may be obtained by digesting an antibody with papain.

F(ab')2 fragments consist of the two Fab fragments of an antibody, plus the hinge regions of the heavy domains, including the disulphide bonds linking the two heavy chains together. In other words, a F(ab')2 fragment can be seen as two covalently joined Fab fragments. F(ab')2 fragments may be obtained by digesting an antibody with pepsin.

Reduction of F(ab')2 fragments yields two Fab' fragments, which can be seen as Fab fragments containing an additional sulfhydryl group which can be useful for conjugation of the fragment to other molecules.

Fv fragments consist of just the variable domains of the light and heavy chains. These are not covalently linked and are held together only weakly by non-covalent interactions. Fv fragments can be modified to produce a synthetic construct known as a single chain Fv (scFv) molecule. Such a modification is typically performed recombinantly, by engineering the antibody gene to produce a fusion protein in which a single polypeptide comprises both the VH and VL domains. scFv fragments generally include a peptide linker covalently joining the VH and VL regions, which contributes to the stability of the molecule. The linker may comprise from 1 to 20 amino acids, such as for example 1 , 2, 3 or 4 amino acids, 5, 10 or 15 amino acids, or other intermediate numbers in the range 1 to 20 as convenient. The peptide linker may be formed from any generally convenient amino acid residues, such as glycine and/or serine. One example of a suitable linker is Gly4Ser (Gly- Gly-Gly-Gly-Ser, SEQ ID NO: 13). Multimers of such linkers may be used, such as for example a dimer, a trimer, a tetramer or a pentamer, e.g. (Gly4Ser)2, (Gly4Ser)3, (Gly4Ser)4 or (Gly4Ser)₅. However, it is not essential that a linker be present, and the VL domain may be linked to the VH domain by a peptide bond. An scFv is herein defined as an antibody fragment, or antigen-binding fragment of an antibody.

The antibody or antibody fragment used in the ADC may be humanised. A “humanised” antibody is an antibody derived from non-human germline immunoglobulin sequences, but which has been modified to replace non-human sequences with human ones. A humanised antibody may be derived, for instance, from mouse, rat, rabbit, etc., germline immunoglobulin sequences. Indeed, a humanised antibody may be derived from the germline immunoglobulin sequences of any non-human animal. As defined herein, an antibody is considered humanised if at least one of the VH and VL domains is humanised. In particular, a humanised antibody may comprise a humanised VH sequence and a humanised VL sequence.

In a humanised variable domain, a non-human variable domain sequence is modified to replace the non-human (e.g. murine) framework sequences with human framework sequences, such that, generally, the only non-human sequences in the antibody are the CDR sequences (though the CDR sequences may also be modified during the humanisation process). Antibody humanisation is generally performed by a process known as CDR grafting, though any other technique in the art may be used. CDR grafting is well described in Williams, D.G. et al., Antibody Engineering Vol. 1 , edited by R. Kontermann and S. Dubel, Chapter 21 , pp. 319-339, 2010. In this process, humanisation of non-human variable domains involves intercalating the non-human CDRs from each immunoglobulin chain within the framework regions of the most appropriate human variable region. This is done by aligning the non-human variable domains with databases of known human variable domains (e.g. IMGT or Kabat). Appropriate human framework regions are identified from the best aligned variable domains, e.g. domains with high sequence identity between the human and non-human framework regions, domains containing CDRs of the same length, domains having the most similar structures (based on homology modelling), etc. The non-human CDR sequences are then grafted into the lead human framework sequences at the appropriate locations using recombinant DNA technology, and the humanised antibodies then produced and tested for binding to the target antigen. The process of antibody humanisation is known and understood by the skilled individual, who can perform the technique without further instruction. Antibody humanisation services are also offered by a number of commercial companies, e.g. GenScript (USA/China) and LifeArc (UK). Humanised antibody fragments can be easily obtained from humanised antibodies, as described above.

In the present case, the CDR sequences of SEQ ID NOs: 1-6 were originally derived from a murine antibody (though are slightly modified compared to the murine parent antibody). An antibody comprising the CDR sequences of SEQ ID NOs: 1-6 grafted into human framework sequences is a humanised antibody. Thus the antibody used in the ADC may comprise a VL and/or a VH comprising human framework sequences.

In particular embodiments, the antibody or fragment thereof comprises:

(a) a heavy chain variable domain comprising or consisting of the amino acid sequence set forth in SEQ ID NO: 7, or a variant thereof having at least 80, 85, 90 or 95 % identity to SEQ ID NO: 7; and (b) a light chain variable domain comprising or consisting of the amino acid sequence set forth in SEQ ID NO: 8, or a variant thereof having at least 80, 85, 90 or 95 % identity to SEQ ID NO: 8.

In particular, the antibody or fragment thereof may comprise a heavy chain variable domain comprising or consisting of the amino acid sequence set forth in SEQ ID NO: 7, and a light chain variable domain comprising or consisting of the amino acid sequence set forth in SEQ ID NO: 8.

When the antibody or antigen-binding fragment thereof comprises a VH with at least 80 % identity to SEQ ID NO: 7, but less than 100 % identity to SEQ ID NO: 7, this is subject to the proviso that the CDRs are as defined above, i.e. that VHCDR1 comprises or consists of the amino acid sequence of SEQ ID NO: 1 , VHCDR2 comprises or consists of the amino acid sequence of SEQ ID NO: 2 and VHCDR3 comprises or consists of the amino acid sequence of SEQ ID NO: 3. That is to say, when the heavy chain variable region comprises a variant of SEQ ID NO: 7, all variation in the heavy chain variable domain sequence relative to SEQ ID NO: 7 is found within the framework regions.

Similarly, when the antibody or antigen-binding fragment thereof comprises a VL with at least 80 % identity to SEQ ID NO: 8, but less than 100 % identity to SEQ ID NO: 8, this is subject to the proviso that the CDRs are as defined above, i.e. that VLCDR1 comprises or consists of the amino acid sequence of SEQ ID NO: 4, VLCDR2 comprises or consists of the amino acid sequence of SEQ ID NO: 5 and VLCDR3 comprises or consists of the amino acid sequence of SEQ ID NO: 6. That is to say, when the light chain variable domain comprises a variant of SEQ ID NO: 8, all variation in the light chain variable domain sequence relative to SEQ ID NO: 8 is found within the framework regions.

In embodiments in which the ADC comprises an antibody, the heavy and light chains of the antibody each comprise a constant region. The constant regions are generally human constant regions.

As is well known in the art, antibodies may belong to a number of different isotypes, with the isotype of an antibody being determined by the sequence of its heavy chain constant region. In humans, the antibody isotypes are IgG, IgE, IgM, IgA and IgD. Some isotypes may be divided into further subtypes, e.g. there are four sub-types of IgG antibodies: lgG1 , lgG2, lgG3 and lgG4. When an antibody is used in the methods herein, the antibody may be of any isotype, i.e. an IgG, IgE, IgM, IgA or IgD antibody may be used. In particular, the antibody may be an IgG antibody. When an IgG antibody is used it may be of any sub-type, i.e. IgG 1 , lgG2, lgG3 or lgG4 antibody may be used. In particular, the antibody may be an lgG1 antibody. In certain embodiments, the antibody is of the human lgG1 isotype (i.e. the antibody may comprise a human IgG 1 constant domain). In humans, the light chain constant region of an antibody may be a kappa or lambda (K or A) constant region, and thus a human antibody light chain may be a K or A light chain. An antibody used herein may comprise a K or A light chain. In particular, the antibody may comprise a K light chain. In certain embodiments, the antibody comprises a light chain comprising a human K constant domain.

The antibody for use herein may comprise:

(i) a heavy chain comprising or consisting of the amino acid sequence set forth in SEQ ID NO: 9, or a variant thereof having at least 80, 85, 90 or 95 % sequence identity thereto; and

(ii) a light chain comprising or consisting of the amino acid sequence set forth in SEQ ID NO: 10, or a variant thereof having at least 80, 85, 90 or 95 % sequence identity thereto.

As set out above, when the antibody comprises a heavy chain which is a variant of SEQ ID NO: 9, this is subject to the proviso that the CDRs are as defined above, i.e. that VHCDR1 comprises the amino acid sequence of SEQ ID NO: 1 , VHCDR2 comprises the amino acid sequence of SEQ ID NO: 2 and VHCDR3 comprises the amino acid sequence of SEQ ID NO: 3. That is to say, when the heavy chain comprises a variant of SEQ ID NO: 9, all variation in the heavy chain sequence relative to SEQ ID NO: 9 is found within the constant domain and the framework regions of the variable domain.

Similarly, when the antibody comprises a light chain which is a variant of SEQ ID NO: 10, this is subject to the proviso that the CDRs are as defined above, i.e. that VLCDR1 comprises the amino acid sequence of SEQ ID NO: 4, VLCDR2 comprises the amino acid sequence of SEQ ID NO: 5 and VLCDR3 comprises the amino acid sequence of SEQ ID NO: 6. That is to say, when the light chain comprises a variant of SEQ ID NO: 10, all variation in the light chain sequence relative to SEQ ID NO: 10 is found within the constant domain and the framework regions of the variable domain.

The antibody with the heavy chain amino acid sequence set forth in SEQ ID NO: 9 and the light chain amino acid sequence SEQ ID NO: 10 is referred to herein as CM311.

Sequence identity of variants of the sequences set out above may be assessed by any convenient method. However, for determining the degree of sequence identity between sequences, computer programmes that make pairwise or multiple alignments of sequences are useful, for instance EMBOSS Needle or EMBOSS stretcher (both Rice, P. et aL, Trends Genet. 16, (6) pp. 276-277, 2000) may be used for pairwise sequence alignments while Clustal Omega (Sievers F et aL, Mol. Syst. Biol. 7:539, 201 1) or MUSCLE (Edgar, R.C., Nucleic Acids Res. 32(5): 1792-1797, 2004) may be used for multiple sequence alignments, though any other appropriate programme may be used. Whether the alignment is pairwise or multiple, it must be performed globally (i.e. across the entirety of the reference sequence) rather than locally. Sequence alignments and % identity calculations may be determined using for instance standard Clustal Omega parameters: matrix Gonnet, gap opening penalty 6, gap extension penalty 1. Alternatively, the standard EMBOSS Needle parameters may be used: matrix BLOSUM62, gap opening penalty 10, gap extension penalty 0.5. Any other suitable parameters may alternatively be used.

For the purposes of this application, where there is dispute between sequence identity values obtained by different methods, the value obtained by global pairwise alignment using EMBOSS Needle with default parameters shall be considered valid.

Variants of the sequences set out herein (i.e. sequences with at least 80 % sequence identity to SEQ ID NO: 7, 8, 9 or 10) may be obtained by substitution, deletion or insertion of amino acid residues relative to the original sequences.

When a sequence is modified by substitution of a particular amino acid residue, the substitution may be a conservative amino acid substitution. The term "conservative amino acid substitution", as used herein, refers to an amino acid substitution in which one amino acid residue is replaced with another amino acid residue having a similar side chain. Amino acids with similar side chains tend to have similar properties, and thus a conservative substitution of an amino acid important for the structure or function of a polypeptide may be expected to affect polypeptide structure/function less than a non-conservative amino acid substitution at the same position. Families of amino acid residues having similar side chains have been defined in the art, including basic side chains (e.g. lysine, arginine, histidine), acidic side chains (e.g. aspartic acid, glutamic acid), uncharged polar side chains (e.g. asparagine, glutamine, serine, threonine, tyrosine), non-polar side chains (e.g. glycine, cysteine, alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan) and aromatic side chains (e.g. tyrosine, phenylalanine, tryptophan, histidine). Thus a conservative amino acid substitution may be considered to be a substitution in which a particular amino acid residue is substituted for a different amino acid in the same family. However, a substitution of an amino acid residue may equally be a non-conservative substitution, in which one amino acid is substituted for another with a side-chain belonging to a different family.

Where an antibody or fragment thereof is used which comprises a variant of the CM311 variable domain sequences (i.e. a variable domain which is a variant of SEQ ID NO: 7 or SEQ ID NO: 8, as set out above) or full chain sequences (i.e. a heavy or light chain which is a variant of SEQ ID NO: 9 or SEQ ID NO: 10), the variant may have equivalent activity to CM311 or a corresponding fragment thereof. For instance, an antibody which is a variant of CM311 (i.e. an antibody comprising a variant sequence as described above) may bind CLDN18.2 with an affinity which is equivalent to CM311 , which is not lower than the affinity with which CM311 binds CLDN18.2, or which is not substantially lower than the affinity with which CM311 binds CLDN18.2. For instance, a variant of CM311 may be considered to bind CLDN18.2 with an affinity which is not substantially lower than the affinity with which CM311 binds CLDN18.2 if the variant of CM311 binds CLDN18.2 with an affinity which is reduced by no more than 5 %, 10 %, 15 %, 20 % or 25 % compared to that of CM311.

The antibody or fragment thereof for use herein may be synthesised by any method known in the art. In particular, the antibody or fragment thereof may be synthesised using a protein expression system, such as a cellular expression system using prokaryotic (e.g. bacterial) host cells or eukaryotic (e.g. yeast, fungus, insect or mammalian) host cells. Cells which may be used in the production of the antibody or fragment thereof are discussed further below. An alternative protein expression system is a cell-free, in vitro expression system, in which a nucleotide sequence encoding the specific binding molecule is transcribed into mRNA, and the mRNA translated into a protein, in vitro. Cell-free expression system kits are widely available, and can be purchased from e.g. ThermoFisher Scientific (USA). Alternatively, antibodies and fragments thereof may be chemically synthesised in a non-biological system. Liquid-phase synthesis or solid-phase synthesis may be used to generate polypeptides which may form or be comprised within the antibody or fragment thereof used herein. The skilled person can readily produce antibodies or fragments thereof using appropriate methodology common in the art.

In particular, the antibody or fragment thereof may be recombinantly expressed in mammalian cells, such as CHO cells. Other suitable mammalian cells for production of the antibody or fragment thereof for use herein include monkey kidney cells (e.g. COS-7), HEK293 HeLa cells, baby hamster kidney (BHK) cells, human hepatocellular carcinoma cells (e.g. Hep G2), and a number of other cell lines including the mouse myeloma cell lines NSO and SP2/0.

The host cell, when cultured under appropriate conditions, synthesises the antibody or antigen-binding fragment thereof for use herein that can subsequently be collected from the culture medium (if the host cell secretes it into the medium) or directly from the host cell producing it (if it is not secreted). Thus the antibody or fragment thereof may be isolated from synthesis, as discussed above. The host cell line which produces the antibody or fragment thereof for use herein may stably express the antibody or fragment thereof or transiently express the antibody or fragment thereof.

ANTIBODY-DRUG CONJUGATES

The ADC for use herein comprises an antibody or fragment thereof, as described above, conjugated to a cytotoxic agent. That is to say, the antibody or fragment thereof is covalently joined to a cytotoxic agent. The cytotoxic agent may be referred to as the “payload” of the ADC. Throughout this section describing the ADC, the term “antibody” encompasses antibody fragments.

In line with its standard definition in the art, a cytotoxic agent, or cytotoxin, is an agent (or compound) which is toxic to cells. In the context of the ADC used herein, the cytotoxic agent is generally toxic to human cells. By “toxic to cells” is meant that the agent, when delivered to a cell, induces cell death, e.g. by apoptosis or necrosis.

An array of cytotoxic agents suitable for use as ADC warheads is known in the art. In particular embodiments, the cytotoxic agent is an antineoplastic drug. Examples of suitable antineoplastic drugs for use herein include SN-38, gemcitabine, monomethyl auristatin E (MMAE), monomethyl auristatin F (MMAF), doxorubicin, calicheamicin, duocarmycins and maytansinoids (e.g. maytansine DM1 , also referred to as mertansine; and maytansine DM4, also referred to as ravtansine), which are well known in the art.

For example, SN-38 has the structure set forth in Formula I:

Formula I

Gemcitabine has the structure set forth in Formula II:

Formula II

MMAE has the structure set forth in Formula III (in which the wavey line indicates the antibody or fragment thereof to which MMAE is bound, optionally including a linker between the antibody or antibody fragment and the MMAE): Formula III

MMAF has the structure set forth in Formula IV:

Formula IV

Doxorubicin has the structure set forth in Formula V:

Formula V

In other embodiments, the cytotoxic agent may be a toxin, e.g. a bacterial toxin, such as diphtheria toxin (produced by Corynebacterium diphtheriae) which has the UniProt accession number P00588; or a plant toxin, such as ricin (produced by the castor oil plant Ricinus communis), which has the UniProt accession number P02879.

In particular embodiments, the cytotoxic agent is MMAE. MMAE is a tubulin polymerisation inhibitor which is used in a number of existing approved ADCs, e.g. brentuximab vedotin and tisotumab vedotin. The term “vedotin” is used to refer to MMAE in the context of an ADC. Use of an ADC comprising the CM311 antibody conjugated to MMAE is described in the examples below.

The cytotoxic agent, e.g. MMAE, may be joined to the antibody by a linker. A linker, as defined herein, is any chemical group or entity (which may be a peptide) which joins the cytotoxic agent to the antibody. The linker may join the cytotoxic agent to any functional group on the antibody, e.g. an amino group, carboxyl group, hydroxyl group or thiol group. The linker may join the cytotoxic agent to a side chain of the antibody or to a terminus of an antibody chain. Generally, the cytotoxic agent is joined to the antibody via thiol groups.

Linkers suitable for use in ADCs are known in the art, and any suitable linker may be used herein. In some embodiments, the linker is protease-cleavable. That is to say, the linker may be susceptible to cleavage by an intracellular protease, particularly an endosomal or lysosomal protease, such that upon endocytosis of the ADC by a target cell, the linker is cleaved and the cytotoxic agent (e.g. MMAE) released. In some embodiments, the linker is a cathepsin-cleavable linker, i.e. a linker susceptible to cleavage by a cathepsin protease, e.g. cathepsin B. Where the cytotoxic agent is MMAE, following release from the antibody it is transported into the cytoplasm where it binds to tubulin and inhibits its polymerization, thereby blocking mitosis, inhibiting tumour cell proliferation and leading to tumour cell death.

In some embodiments, the linker is selected from 6-maleimidohexanoyl (MC), maleimidopropionyl (MP), N-succinimidyl 4-(2-pyridylthio) valerate (SPP), 4-(N-maleimidomethyl)-cyclohexan-1 -formyl (MCC), N-succinimidyl(4-iodo-acetyl)aminobenzoate (SIAB), and 6-maleimidocaproyl-valine- citrulline-p-aminobenzyloxycarbonyl (MC-vc-PAB). In particular embodiments, the linker is MC-vc-PAB. MC-vc-PAB has the structure set out in Formula VI below:

Formula VI

In some embodiments, the ADC comprises an antibody or fragment thereof as described above conjugated to MMAE by a MC-vc-PAB linker.

In some embodiments, the ADC comprises an antibody or fragment thereof comprising the heavy chain variable domain of SEQ ID NO: 7 and the light chain variable domain of SEQ ID NO: 8, conjugated to a cytotoxic agent by a MC-vc-PAB linker.

In some embodiments, the ADC comprises an antibody or fragment thereof comprising the heavy chain variable domain of SEQ ID NO: 7 and the light chain variable domain of SEQ ID NO: 8, conjugated to MMAE by a MC-vc-PAB linker.

In some embodiments, the ADC comprises an antibody comprising the heavy chain of SEQ ID NO: 9 and the light chain of SEQ ID NO: 10, conjugated to a cytotoxic agent by a MC-vc-PAB linker.

In some embodiments, the ADC comprises an antibody comprising the heavy chain of SEQ ID NO: 9 and the light chain of SEQ ID NO: 10, conjugated to MMAE by a MC-vc-PAB linker.

The antibody in the ADC may be conjugated to e.g. 3, 4 or 5 molecules of the cytotoxic agent (e.g. MMAE molecules). The number of molecules of the cytotoxic agent attached to the antibody in the ADC is referred to as the drug-antibody ratio (DAR). It should be noted that the ADC used herein is generally provided in a pharmaceutical composition containing multiple ADC molecules, which may have the same or different DAR values. That is to say, in some embodiments, provided herein are pharmaceutical compositions comprising the ADC described above, in which the ADC molecules all comprise the same number of cytotoxic agent moieties. In other embodiments, provided herein are pharmaceutical compositions comprising the ADC described above, in which the ADC molecules comprise different numbers of cytotoxic agent moieties.

The average number of cytotoxic agent moieties in the ADC molecules in a composition thereof is referred to herein as the average DAR. This may be referred to as the average DAR of a composition comprising the ADC, or as the average DAR of the ADC (i.e. reference to the average DAR of the ADC is shorthand for reference to the average DAR of a composition comprising the ADC, i.e. a composition comprising a population of the ADC). The average DAR for a composition of the ADC can be determined by any conventional means in the art, e.g. mass spectrometry or HPLC. WO 2022/078523 describes determination of the average DAR of a composition of the ADC by hydrophobic interaction chromatography-HPLC (HIC-HPLC).

In some embodiments, the ADC has an average DAR of 3 to 4.5, e.g. 3 to 4.4, 3 to 4.3, 3 to 4.2, 3 to 4.1 , 3 to 4, 3.1 to 4.5, 3.1 to 4.4, 3.1 to 4.3, 3.1 to 4.2, 3.1 to 4.1 , 3.1 to 4, 3.2 to 4.5, 3.2 to 4.4, 3.2 to 4.3, 3.2 to 4.2, 3.2 to 4.1 , 3.2 to 4, 3.3 to 4.5, 3.3 to 4.4, 3.3 to 4.3, 3.3 to 4.2, 3.3 to 4.1 , 3.3 to 4, 3.4 to 4.5, 3.4 to 4.4, 3.4 to 4.3, 3.4 to 4.2, 3.4 to 4.1 , 3.4 to 4, 3.5 to 4.5, 3.5 to 4.4, 3.5 to 4.3, 3.5 to 4.2, 3.5 to 4.1 , 3.5 to 4, 3.6 to 4.5, 3.6 to 4.4, 3.6 to 4.3, 3.6 to 4.2, 3.6 to 4.1 or 3.6 to 4.

In particular embodiments, the ADC has an average DAR of 3.3 to 4.3, 3.4 to 4.2, 3.5 to 4.1 , 3.6 to 4 or 3.7 to 3.9. In a particular embodiment, the ADC has an average DAR of about 3.8. An average DAR of about 3.8 may encompass an average DAR of e.g. 3.75 to 3.85, 3.76 to 3.84, 3.77 to 3.83, 3.78 to 3.82, 3.79 to 3.81. In some embodiments, the average DAR is 3.80.

As noted above, the cytotoxic agent is generally attached to the antibody via thiol groups of its cysteine residues. In naturally occurring antibodies, many cysteine thiol groups are unavailable for conjugation to other moieties (such as drug molecules) as they exist in the context of disulphide bridges. In some cases, additional reactive thiol groups can be generated by treating the antibody with a reducing agent such as dithiothreitol (DTT) or tris(2-carboxyethyl)phosphine (TCEP), thereby increasing the obtainable DAR.

The ADC may be used in the context of a salt of the ADC described above, e.g. a salt of an inorganic acid such as a hydrochloride, hydrobromide, hydroiodide, nitrate, bicarbonate, carbonate, sulfate or phosphate salt; or a salt of an organic acid salt such as a formate, acetate, propionate, benzoate, maleate, fumarate, succinate, tartrate, citrate, ascorbate, a-ketoglutarate, a-glycerophosphate, alkyl sulfonate or aryl sulfonate salt. Examples of suitable alkyl sulfonate salts include methanesulfonate and ethanesulfonate. Examples of suitable aryl sulfonate salts are benzenesulfonate and p-toluenesulfonate.

The ADC, or salt thereof, may be used in the context of a solvate. The term “solvate” refers to solid or liquid forms of the ADC formed by coordination of the ADC with solvent molecules. A particularly suitable form of the ADC for use herein is a hydrate, which is a solvate with coordinated water molecules.

SUBJECTS

The subject is a vertebrate animal suffering from cancer (i.e. that has been diagnosed with cancer). Generally, the subject is a human (who may be referred to as a patient), but may be a non-human animal diagnosed with cancer. For instance, the subject may be a domestic animal, particularly a companion animal, e.g. a dog, cat, horse or suchlike. The cancer is generally a solid cancer.

The cancer expresses CLDN18.2 (by which is meant that at least some of the cells of the cancer express CLDN18.2) at a level which indicates susceptibility to treatment with the ADC. Susceptibility to treatment with the ADC may be determined by the proportion of cells in the cancer which express CLDN18.2 and/or the strength or intensity of CLDN18.2 expression in the cancer. As discussed further below, the level of CLDN18.2 expression in a cancer (or by a cancer) may be determined by analysing a sample of the cancer, e.g. a biopsy. The sample of the cancer may be analysed by any suitable method known in the art capable of measuring the level of expression of a particular protein or gene, e.g. immunohistochemistry (IHC), qPCR or mass spectrometry. Thus expression of CLDN18.2 may be determined by detection of the CLDN18.2 protein itself, or by detection of mRNA encoding CLDN18.2.

Expression of CLDN18.2 at a level which indicates susceptibility to treatment with the ADC means that the level of expression of CLDN18.2 in the cancer is above a threshold whereby treatment with the ADC is deemed clinically worthwhile, i.e. the likelihood of the patient responding to the ADC is high enough to justify the risk of side effects. Such a threshold should be set to maximise the pool of eligible patients, to avoid excluding patients who are reasonably likely to benefit, while excluding patients who are not likely to respond.

In some embodiments, the threshold for CLDN18.2 expression is set such that at least about 25 %, 30 %, 35 % or 40 % of patients to whom the ADC is administered can be expected to respond to the treatment (by “response” here is meant a partial or complete response). In some embodiments, the threshold for CLDN18.2 expression is set such that at most 8 %, 10 %, 12 %, 14 %, 16 %, 18 % or 20 % of patients excluded from receiving therapy with the ADC would be expected to respond to it. In other embodiments, the threshold for CLDN18.2 expression may be set such that at least about 80 %, 82.5 %, 85 %, 87.5 %, 90 %, 92.5 %, 95 % or 97.5 % of patients expected to respond to the treatment are selected for treatment.

Generally, the threshold for CLDN18.2 is based on the proportion of cells in the cancer which express CLDN18.2. In some embodiments, the threshold is set at CLDN18.2 being expressed by at least 10 % of cells in the cancer. That is to say, a subject may be deemed susceptible to treatment with the ADC if at least 10 % of cells in their cancer express CLDN18.2. Thus, the subject treated according to the methods provided herein may have a cancer in which CLDN18.2 is expressed by at least 10 % of the cells.

In other embodiments, the threshold is set at CLDN18.2 being expressed by at least 20 % of cells in the cancer. That is to say, a subject may be deemed susceptible to treatment with the ADC if at least 20 % of cells in their cancer express CLDN18.2. Thus, the subject treated according to the methods provided herein may have a cancer in which CLDN18.2 is expressed by at least 20 % of the cells.

In other embodiments, the threshold is set at CLDN18.2 being expressed by at least 25 % of cells in the cancer. That is to say, a subject may be deemed susceptible to treatment with the ADC if at least 25 % of cells in their cancer express CLDN18.2. Thus, the subject treated according to the methods provided herein may have a cancer in which CLDN18.2 is expressed by at least 25 % of the cells. In other embodiments, the threshold is set at CLDN18.2 being expressed by at least 50 % or 75 % of cells in the cancer. That is to say, a subject may be deemed susceptible to treatment with the ADC if at least 50 % or 75 % of cells in their cancer express CLDN18.2. Thus, the subject treated according to the methods provided herein may have a cancer in which CLDN18.2 is expressed by at least 50 % or 75 % of the cells.

The examples below demonstrate that expression of CLDN18.2 by only a small percentage of cells in the cancer is sufficient for many patients to benefit from treatment with the ADC described above. In pancreatic cancer patients treated with the ADC, those with at least 10 % of cancer cells expressing CLDN18.2 had a median progression-free survival (PFS) more than twice as long as those with less than 10 % of cancer cells expressing CLDN18.2.

The examples below show that expression of CLDN18.2 at a relatively low level can distinguish effectively between patients likely and unlikely to respond to treatment with the ADC. While approximately 60 % of gastric cancers are estimated to display CLDN18.2 expression by at least 25 % of cells, setting a treatment threshold of at least 25 % of cells expressing CLDN18.2 is estimated to capture over 95 % of gastric cancer patients who will respond to therapy with the ADC.

As noted above, determination of the proportion of cells in a cancer which express CLDN18.2 can be made by analysis of a sample of cells (a tissue sample) from the cancer. Suitable tissue samples include biopsy samples and samples taken from tumours (or parts thereof) which have previously been surgically removed. It can be assumed that the proportion of cells in a cancer which express CLDN18.2 corresponds to the proportion of cells which express CLDN18.2 in a sample taken from that cancer. Thus if at least 20 % or 25 % of cells in a cancer sample express CLDN18.2, it can be assumed that at least 20 % or 25 % of cells in the cancer as a whole express CLDN18.2. Thus, the thresholds set out above refer to the proportion of cells in the cancer expressing CLDN18.2, the thresholds may instead be considered to refer to the proportion of cells in a sample of the cancer expressing CLDN18.2.

Any suitable technique can be used to determine the proportion of cells in a cancer which express CLDN18.2. Most commonly, immunohistochemistry (IHC) is used. Methods of performing IHC are well known in the art and are described in e.g. Kim et al., Journal of Pathology and Translational Medicine 50(6): 411-418, 2016; and in Immunohistochemistry, Hofman & Taylor, Current Protocols in Immunology 103:21.4.1-21.4.26, 2013, John Wiley & Sons, Inc.

CLDN18.2 can be detected by IHC using either a monoclonal or polyclonal anti- CLDN18.2 antibody, or an anti-pan-CLDN18 antibody which targets both CLDN18.1 and CLDN18.2. Suitable antibodies for detecting CLDN18.2 are commercially available from various sources, e.g.Abcam and Thermo Fisher Scientific. For instance, the Abeam anti- CLDN18.2 antibodies EPR19202 (catalogue # 222512) and EPR19202-244 (catalogue # 241330) are suitable for CLDN18.2 detection in IHC, and their use is exemplified and described in the examples below. Suitable anti-pan-CLDN18 antibodies include 34H14L15 (Thermo Fisher, catalogue # 700178), LS-B16145 (LSBio), NBP-32002 (Novus Biologicals), HPA018446 (Sigma-Aldrich) and 38-8000 (Thermo Fisher). Roche’s anti-pan-CLDN18 Ventana antibody (43-14A) is also suitable for CLDN18 detection in IHC. Other suitable antibodies for detecting CLDN18.2 by IHC may be generated by routine methods in the art, e.g. immunization of a small animal such as a mouse or rabbit to generate a polyclonal antibody, or via a hybridoma to obtain a monoclonal antibody. As is well known in the art, in IHC the target protein (e.g. CLDN18.2) is detected using a labelled antibody. The IHC may be performed using a single, labelled primary antibody, or using an unlabelled primary antibody and a labelled secondary antibody. Suitable detectable labels for IHC are known in the art and include fluorescent and chromogenic labels. IHC may be performed manually or may be automated.

Commonly, IHC staining is scored using a semi-quantitative technique, whereby the staining intensity is assigned a score (level) between 0 and 3. According to this scoring system, a score of ‘0’ indicates the staining is negative, i.e. the target protein is not detected; a score of T is defined as staining with weak intensity; a score of ‘2’ is defined as staining with moderate intensity; and a score of ‘3’ is defined as staining with strong intensity. This scoring system is well known in the art, as described in e.g. Kim et a!., supra; and Rizzardi et a!., Diagnostic Pathology 7: 42, 2012, and is used in the clinical practice guidelines of the American Society for Clinical Oncology and College of American Pathologist (ACO/CAP) guidelines (see e.g. Wolff et al., Journal of Clinical Oncology 36(20): 2105-2122, 2018), and can thus be routinely applied by a qualified pathologist, e.g. a pathologist certified by the American Board of Pathology, a member of the UK Royal College of Pathologists or a member of any equivalent body elsewhere. Indeed, the scoring system has been commonly used in this or similar form for over 3 decades (see e.g. McCarty et a!., Cancer Research 46(8-supplement): 4244s-4248s, 1986).

According to the present methods, the threshold for deeming a subject susceptible to treatment with the ADC may include a factor relating to the intensity of IHC staining for CLDN18.2 in the cancer, based on the scoring system described above. Intensity scoring of a cancer sample can readily be performed by a skilled pathologist.

In some embodiments, CLDN18.2 expression is analysed by IHC to determine the proportion of cells in a cancer which express CLDN18.2, but intensity staining is not performed, or is not factored into the assessment of whether a patient is likely to respond to treatment with the ADC. Thus, in these embodiments, susceptibility to treatment with the ADC is assessed purely based on the proportion of cancer cells which express CLDN18.2.

Thus in these embodiments, a subject may be deemed susceptible to treatment with the ADC if, for example, at least 10 %, 20 %, 25 %, 50 % or 75 % of cells in the cancer express CLDN18.2, regardless of IHC staining intensity, i.e. at an IHC staining intensity score of at least 1 (i.e. an IHC staining intensity score of 1 to 3, that is to say an IHC staining intensity score of 1 , 2 or 3). Thus, the subject treated according to the methods provided herein may have a cancer in which CLDN18.2 is expressed by at least 10 %, 20 %, 25 %, 50 % or 75 % of the cells at an IHC staining intensity of at least 1 .

In other embodiments, the staining intensity of CLDN18.2-positive cells is factored into the assessment of whether a subject is likely to respond to treatment with the ADC. For example, the assessment may be based on the proportion of cancer cells which express CLDN18.2 with a staining intensity score of at least 2 (i.e. a staining intensity score of 2 or 3), or a staining intensity score of 3.

In particular, in some embodiments a subject may be deemed susceptible to treatment with the ADC if, for example, at least 10 %, 20 %, 25 %, 50 % or 75 % of cells in the cancer express CLDN18.2 at a staining intensity level (or with a staining intensity score) of at least 2 (i.e. of 2 or 3). Thus, the subject treated according to the methods provided herein may have a cancer in which CLDN18.2 is expressed by at least 10 %, 20 %, 25 %, 50 % or 75 % of the cells at an IHC staining intensity level of at least 2.

As shown in the examples below, a threshold for a subject to be deemed susceptible to treatment with the ADC of at least 20 % or 25 % of cancer cells expressing CLDN18.2 at any staining intensity is highly effective in identifying gastric cancer patients who are likely to respond to therapy with the ADC. Likewise, a threshold of at least 10 %, 20 % or 25 % of cancer cells expressing CLDN18.2 at a staining intensity of at least 2 (i.e. of 2 or 3) is highly effective in identifying gastric cancer patients who are likely to respond to therapy with the ADC (see Figs. 9-12).

In particular, thresholds of at least 25 % of cancer cells expressing CLDN18.2 at any intensity, or of at least 10 or 20 % of cancer cells expressing CLDN18.2 at an intensity of at least 2, are estimated to include at least 90 % of likely responders to the ADC therapy while excluding at least 40 % of gastric cancer patients. In each of these 3 cases, the objective response rate (ORR) for selected patients is estimated to be at least 40 %, and the potential ORR for excluded patients is estimated to be less than 20 %.

Thresholds of at least 25 % of cancer cells expressing CLDN18.2 at any intensity, or of at least 20 % of cancer cells expressing CLDN18.2 at an intensity of at least 2, are particularly advantageous at distinguishing patients who will show an increased progression- free survival (PFS) following ADC treatment. As shown in Example 2, following treatment with the ADC, patients with at least 20 % of cancer cells expressing CLDN18.2 at an intensity of at least 2 have a median PFS 26 % longer than patients not meeting that threshold (140 days v. 111 days); patients with at least 25 % of cancer cells expressing CLDN18.2 at any intensity show a statistically significant improvement in median PFS of 41 % (p = 0.037) compared to patients not meeting that threshold (140 days v. 99 days).

Notably, a threshold of at least 25 % of cancer cells expressing CLDN18.2 at any intensity uniquely results in a treated population with an estimated ORR of over 40 % and an untreated population with an estimated hypothetical ORR (i.e. the ORR which would be seen if an untreated patient population were treated) of less than 10 %, while making the treatment available to an estimated 60 % of gastric cancer patients. Avoiding any need for staining intensity assessment is also advantageous as CLDN18.2 expression assessment is simplified compared to methods which include an intensity requirement in the threshold.

Another particularly useful threshold for treatment is of at least 20 % of cancer cells expressing CLDN18.2 at an intensity of at least 2. About 45 % of gastric cancer patients are estimated to display CLDN18.2 expression meeting this threshold, thus reducing the number of patients eligible for treatment by about 25 % compared to the threshold mentioned in the paragraph above while reducing the proportion of likely responders to the ADC selected by about 5 % (from about 97.5 % to 92.5 % overall).

Both these two thresholds are very useful for selecting cancer patients susceptible to treatment with the ADC described above. Selecting a threshold which maximises the number of eligible patients captures the highest proportion of likely responders to the ADC, while reducing the number of eligible patients enriches the treated population for likely responders but captures a smaller proportion of them.

Thus, in particular embodiments, the threshold at which a cancer patient is deemed susceptible to treatment with the ADC is set at CLDN18.2 expression by at least 25 % of cells in the cancer at any IHC staining intensity. That is to say, a subject may be deemed susceptible to treatment with the ADC if at least 25 % of cells in their cancer express CLDN18.2 at any IHC staining intensity. Thus, the subject treated according to the methods provided herein may have a cancer in which CLDN18.2 is expressed by at least 25 % of the cells at any IHC staining intensity.

In other particular embodiments, the threshold at which a cancer patient is deemed susceptible to treatment with the ADC is set at CLDN18.2 expression by at least 20 % of cells in the cancer at an IHC staining intensity of at least 2. That is to say, a subject may be deemed susceptible to treatment with the ADC if at least 20 % of cells in their cancer express CLDN18.2 at an IHC staining intensity of at least 2. Thus the subject treated according to the methods provided herein may have a cancer in which CLDN18.2 is expressed by at least 20 % of the cells at an IHC staining intensity level of at least 2. According to the therapeutic methods provided herein, the level of CLDN18.2 expression in the cancer may already have been determined, e.g. by IHC as described above. In this case, the therapy is for a subject with a cancer which has already been determined to express CLDN18.2 at a level which indicates susceptibility to treatment with the ADC.

Alternatively, the therapeutic methods provided herein may include a step of identifying whether a subject has a cancer which is likely to be susceptible to treatment with the ADC. Such a step includes:

(i) assessing the level of CLDN18.2 expression in a tissue sample from the cancer; and

(ii) determining whether the subject is susceptible to treatment with the ADC based on the level of CLDN18.2 expression in the tissue sample.

Suitable tissue samples for assessment of CLDN18.2 expression by the cancer are described above. Assessment of the level of CLDN18.2 expression may be performed by any suitable method, particularly IHC, as described above. Determination of whether the subject is susceptible to treatment with the ADC can be made based on whether the level of CLDN18.2 expression in the tissue sample is above a pre-defined threshold, as described above.

If the subject is to determined to be susceptible to treatment with the ADC, the subject is then treated with the ADC as described herein.

Accordingly, in one aspect provided herein is a method of identifying and treating a subject with cancer susceptible to treatment with the ADC described herein, the method comprising:

In some embodiments, such a method further comprises an initial step of obtaining the tissue sample from the cancer. As noted above, cancer tissue samples can be obtained e.g. by biopsy or surgery.

In particular embodiments, the cancer is gastric cancer or gastroesophageal junction (GEJ) cancer. In other embodiments, the cancer is pancreatic cancer. The cancer may be any type of cancer, particularly an adenocarcinoma, e.g. gastric adenocarcinoma, GEJ adenocarcinoma or pancreatic ductal adenocarcinoma. As noted above, these cancers express CLDN18.2 with high frequency. However, the thresholds for CLDN18.2 expression described above may indicate the susceptibility of any cancer to treatment with the ADC. In particular embodiments, the subject treated according to the methods provided herein has gastric cancer or GEJ cancer in which at least 25 % of cells express CLDN18.2 at any IHC staining intensity.

In other embodiments, the subject treated according to the methods provided herein has gastric cancer or GEJ cancer in which at least 20 % of cells express CLDN18.2 at an IHC staining intensity of at least 2.

In particular embodiments, the subject treated according to the methods provided herein has pancreatic cancer in which at least 50 % of cells express CLDN18.2 at any IHC staining intensity.

In other embodiments, the subject treated according to the methods provided herein has pancreatic cancer in which at least 75 % of cells express CLDN18.2 at any IHC staining intensity.

The cancer may be of any stage, but in particular may be an advanced cancer, e.g. a stage III or stage IV cancer. For example, the cancer may be a metastatic cancer or a locally unresectable cancer. In other embodiments, the cancer may be a borderline resectable cancer. Alternatively, the cancer may be an early-stage cancer, i.e. a non-metastatic and/or resectable cancer, e.g. a stage I or stage II cancer. Cancer stages referred to herein are those of the TNM staging system, which is well known in the art (see e.g. Rosen & Sapra, TNM Classification, in: StatPearls, Treasure Island (FL): StatPearls Publishing; 2023 Jan).

In some embodiments, the cancer does not express human epidermal growth factor receptor 2 (HER2). HER2 has the UniProt accession number P04626. HER2-positive cancers may be treated with drugs such as antibodies or ADCs which target HER2, e.g. trastuzumab or trastuzumab deruxtecan, and thus for HER2-positive cancers suitable, or even preferred, alternative treatment options may exist, at least in the first instance. Nonetheless, HER2 expression is not believed to impact efficacy of the ADC provided herein, which is thus suitable for treating HER2-positive and HER2-negative cancers. Indeed, treatment with the ADC provided herein may be agnostic of HER2 expression.

HER2 expression by the cancer may be determined by any suitable technique, e.g. IHC or qPCR as mentioned above.

The subject may be at any stage of treatment. For example, the ADC used herein may be used as a first line drug (i.e., the subject may not have received any prior cancer therapeutic/line of treatment for their cancer), a second line drug (i.e. the subject may have received one prior cancer therapeutic/line of treatment for their cancer) or a third or further line drug (i.e. the subject may have received two or more prior cancer therapeutics/lines of treatment for their cancer). TREATMENT REGIMENS

The subject treated with the ADC provided herein is administered a therapeutically effective dose of the ADC. The term “therapeutically effective” dose is defined as an amount sufficient to achieve or at least partially achieve a desired therapeutic effect. In particular, a therapeutically effective dose may be sufficient to at least temporarily halt disease progression (i.e. such that the cancer patient has stable disease), or alternatively to reduce the speed of disease progression. In some cases, a therapeutically effective dose induces disease regression, i.e. a partial or complete response. Exemplary effective doses are described below.

In particular embodiments the subject treated with the ADC is administered at least one dose of the ADC of about 1.8 to about 3.4 mg/kg. The dose may be about 1.8 mg/kg, 2.2 mg/kg, 2.6 mg/kg, 3 mg/kg or 3.4 mg/kg. Generally, the subject treated with the ADC is administered more than one dose of the ADC.

For subjects receiving more than one dose of the ADC, the frequency of the dosing may be determined by the subject’s physician, but in general a dose of the ADC may be administered to the subject about every 2 weeks, every 3 weeks, every 4 weeks, every 5 weeks or every 6 weeks. In some embodiments, a dose of the ADC is administered to the subject about every 3 to 6 weeks. In other embodiments, a dose of the ADC is administered to the subject about every 3 weeks.

By “about” a certain number of weeks, is meant that number of weeks plus or minus 3 days. Thus a second dose administered about 2 weeks after the first dose may be administered 11 to 17 days after the first dose; a second dose administered about 3 weeks after the first dose may be administered 18 to 24 days after the first dose. In other embodiments, the ADC may be administered to the subject every 2, 3 or 4 weeks plus or minus 2 days, or plus or minus one day. While in an ideal scenario the doses might be administered to the subject exactly every 2, 3 or 4 weeks, for example, in practice this is not always possible, e.g. if a subject is unwell or unavailable on a given date, and therefore some flexibility in the dosing schedule is advantageous.

In particular embodiments, the ADC is administered about every 3 to 6 weeks, in a dosing schedule whereby the ADC is administered every 3 weeks, unless a delay is necessitated by a treatment-related adverse event, in which case a dose delay of up to 3 weeks is permitted.

When determining a dosing schedule, the date of each dose may be calculated from the date of the prior dose. That is to say, where the ADC is administered about every 3 weeks, the second dose is administered 18 to 24 days after the first dose, the third dose is administered 18 to 24 days after the second dose, and so on. Alternatively, the date of each dose may be calculated from the date of the first dose. In this instance, where the date of the first dose is defined as day 0, and doses are administered about every 3 weeks, the second dose would be administered between days 18 and 24, the third dose would be administered between days 39 and 45, and so on.

In some cases, the lengths between doses in a particular dosing schedule may be altered, if judged to be indicated by the subject’s physician. For example the length of time between doses may be increased to reduce the level of side effects, or reduced for a greater effect, if considered appropriate.

As noted above, the subject treated with the ADC is administered at least one dose of the ADC of about 0.3 to about 3.4 mg/kg. Where the subject is administered more than one dose of the ADC, generally the same dosage is given each time. That said, the dosage may be increased or decreased if indicated, as judged by the subject’s physician. For example, the dosage may be decreased to reduce the level of side effects, or increased for a greater effect, if considered appropriate.

The dose, or each dose, administered to the subject, may be of about 0.6 to about

3.4 mg/kg, about 0.9 to about 3.4 mg/kg, about 1.2 to about 3.4 mg/kg, about 1.5 to about

3.4 mg/kg, about 1 .8 to about 3.4 mg/kg, about 1.8 to about 3 mg/kg, about 2 to about

3.4 mg/kg, about 2 to about 3 mg/kg, about 2.2 to about 3.4 mg/kg or about 2.2 to about 3 mg/kg. In particular, the subject may be administered one or more doses of the ADC of about 1.8 to about 3.4 mg/kg, or about 2.2 to about 3 mg/kg.

In some embodiments, the subject may be administered one or more doses of the ADC of about 0.3 mg/kg, about 0.6 mg/kg, about 0.9 mg/kg, about 1.2 mg/kg, about

1.5 mg/kg, about 1 .8 mg/kg, about 2.2 mg/kg, about 2.6 mg/kg, about 3 mg/kg or about 3.4 mg/kg. In particular, the subject may be administered one or more doses of the ADC of about 1.8 mg/kg, about 2.2 mg/kg, about 2.6 mg/kg, about 3 mg/kg or about 3.4 mg/kg.

In particular embodiments, the subject is administered a dose of the ADC of about 1.8 mg/kg, 2.2 mg/kg, 2.6 mg/kg, 3 mg/kg or 3.4 mg/kg, about every 3 weeks.

By “about” a certain dosage value is meant the specified value ± 10 %. All references to “about” a certain dosage specifically encompass the specified dosage, e.g. “about 2.2 mg/kg” specifically includes the value of 2.2 mg/kg.

As set out above, the dosages of the ADC used herein are defined as mg/kg. The ‘kg’ here refers to the body mass of the subject to be treated in kilograms. Thus for example, a dosage of 2.2 mg/kg means 2.2 mg per kg of the body mass of the subject. For example, a subject weighing 70 kg and receiving a dosage of 2.2 mg/kg would receive 154 mg of the ADC.

As noted above, the subject is generally administered more than one dose of the ADC, e.g. at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18 or 20 doses. For example, in particular embodiments, the subject is administered at least 5, 10, or 15 doses. The number of doses referred to here is the total number of doses administered to the subject through a course of therapy.

The subject may be administered the ADC for a duration of about 1 to 12 months. That is to say, the course of treatment with the ADC may last for about 1 to 12 months, i.e. the final dose of the ADC may be administered to the subject about 1 to 12 months after the first dose. For example, the subject may be administered the ADC for a duration of about 1 to 3, 1 to 4, 1 to 5, 1 to 6, 1 to 7, 1 to 8, 1 to 9, 1 to 10, 1 to 11 , 2 to 3, 2 to 4, 2 to 5, 2 to 6, 2 to 7, 2 to 8, 2 to 9, 2 to 10, 2 to 11 , 2 to 12, 3 to 4, 3 to 5, 3 to 6, 3 to 7, 3 to 8, 3 to 9, 3 to 10, 3 to 11 , 3 to 12, 4 to 5, 4 to 6, 4 to 7, 4 to 8, 4 to 9, 4 to 10, 4 to 11 , 4 to 12, 5 to 6, 5 to 7, 5 to 8, 5 to 9, 5 to 10, 5 to 11 , 5 to 12, 6 to 7, 6 to 8, 6 to 9, 6 to 10, 6 to 11 , 6 to 12, 7 to 8, 7 to 9, 7 to 10, 7 to 11 , 7 to 12, 8 to 9, 8 to 10, 8 to 11 , 8 to 12, 9 to 10, 9 to 11 or 9 to 12 months. In some cases the duration of treatment may be longer that 12 months, longer than 15 months or even longer than 18 months. The duration of treatment will vary between patients, with treatment being commenced and halted at the appropriate time for each subject, as determined by their physician. The longer the duration of treatment with the ADC, the more doses will be administered to the subject.

Generally, the course of treatment will last until confirmed disease progression in the subject, unacceptable toxicity to the subject or death of the subject. Confirmed disease progression may indicate that the ADC is not, or is no longer, effective in treating the subject’s cancer. Toxicity of the ADC to the subject may be considered unacceptable if the negative impact of the treatment side effects is greater than its anti-cancer benefit. In any event, confirmed disease progression or unacceptable toxicity can be readily determined by the subject’s physician.

The length of the course of treatment (e.g. the time until confirmed disease progression, unacceptable toxicity or death) may be dependent on the type of cancer suffered by the subject, the stage of the cancer at the beginning of therapy and/or the line of treatment for which the ADC is used. For example, on average, treatment of subjects with gastric cancer is likely to last for longer than treatment of subjects with pancreatic cancer. Subjects with pancreatic cancer may be treated with the ADC for a duration of about 1 to 12, 1 to 11 , 1 to 10, 1 to 9, 1 to 8, 1 to 7, 1 to 6, 1 to 4, 1 to 3, 2 to 4 or 2 to 3 months, though as set out above any individual subject may receive treatment with the ADC for longer (or indeed shorter) than this, if appropriate, depending on the overall health of the patient and their response to the treatment.

Subjects with gastric cancer or GEJ cancer may be treated with the ADC for a duration of about 3 to 9, 3 to 8, 3 to 7, 3 to 6, 4 to 8 or 4 to 6 months, though again, any individual subject may receive treatment with the ADC for longer (or indeed shorter) than this, if appropriate, depending on the overall health of the patient and their response to the treatment.

Generally, the length of the course of treatment (e.g. the time until confirmed disease progression, unacceptable toxicity or death) may also be dependent on how early in the course of the disease the ADC is administered to the subject. The earlier in treatment that the ADC is administered to the subject, the longer the treatment with the ADC will generally last. That is to say, where the ADC is administered as first line treatment, the treatment course is likely to last longer than where the ADC is administered as a second line treatment, and where the ADC is administered as a second line treatment, the treatment course is likely to last longer than where the ADC is administered as a third line treatment, etc. For example, where the ADC is administered as a first line treatment, the subject may be treated with the ADC for a duration of about 3 to 12, 3 to 11 , 3 to 10, 3 to 9, 3 to 8, 3 to 7, 3 to 6, 4 to 12, 4 to 11 , 4 to 10, 4 to 9, 4 to 8, 4 to 7, 4 to 6, 6 to 12, 6 to 9 or 6 to 8 months. Where the ADC is administered as a second line treatment, the subject may be treated with the ADC for a duration of e.g. about 1 to 9, 1 to 8, 1 to 7, 1 to 6, 1 to 5, 1 to 4, 2 to 9, 2 to 8, 2 to 7, 2 to 6, 2 to 5, 2 to 4, 3 to 9, 3 to 8, 3 to 7, 3 to 6, 4 to 9, 4 to 8, 4 to 7 or 4 to 6 months.

Indeed, the length of treatment duration is likely to be impacted by the combination of the line of treatment as which the ADC is used and the type of cancer to be treated, e.g. first line of treatment of gastric cancer is likely to have a much longer duration that second or subsequent line treatment of pancreatic cancer.

As shown in the examples below, treatment of cancer with the dosages of the ADC described above has been found to be effective. For example, in a given population of patients with gastric or GEJ cancer, the overall response rate (ORR, alternatively referred to as the objective response rate) may be at least 25 %, 30 %, 35 %, 40 %, 45 % or 50 %. The ORR is defined as the proportion of patients showing either a complete response (CR) or partial response (PR) to the treatment, according to RECIST classification (e.g. RECIST version 1 .1 , Eisenhauer et a!., European Journal of Cancer 45: 228-247, 2009). This may particularly be the case when the ADC is administered as a second or further line of therapy (i.e. in subjects who have already received at least one prior line of therapy).

In particular, treatment of subjects with gastric or GEJ cancer with the ADC described herein as a second or further line of treatment, at a dosage of 2.2 mg/kg to 3 mg/kg about every 3 weeks, may have an ORR of at least 25 %, 30 %, 35 %, 40 %, 45 % or 50 %. More specifically, treatment of such subjects at a dosage of 2.2 mg/kg, 2.6 mg/kg or 3 mg/kg of the ADC about every 3 weeks may have an ORR of at least 25 %, 30 %, 35 %, 40 %, 45 % or 50 %.

Alternatively or additionally, in a given population of patients with gastric or GEJ cancer, the disease control rate (DCR) may be at least 60 %, 65 %, 70 %, 75 %, 80 %, 85 % or 90 %. The disease control rate is defined as the proportion of patients showing a complete response (CR), partial response (PR) or stable disease (SD) to the treatment, according to RECIST classification (e.g. RECIST version 1.1 , Eisenhauer et al., supra). This may particularly be the case when the ADC is administered as a second or further line of therapy (i.e. in subjects who have already received at least one prior line of therapy).

In particular, treatment of subjects with gastric or GEJ cancer with the ADC described herein as a second or further line of treatment, at a dosage of 2.2 mg/kg to 3 mg/kg about every 3 weeks, may have a DCR of at least 60 %, 65 %, 70 %, 75 %, 80 %, 85 % or 90 %. More specifically, treatment of such subjects at a dosage of 2.2 mg/kg, 2.6 mg/kg or 3 mg/kg of the ADC about every 3 weeks may have a DCR of at least 60 %, 65 %, 70 %, 75 %, 80 %, 85 % or 90 %.

Alternatively or additionally, in a given population of patients with gastric or GEJ cancer, treatment with the ADC described herein may result in a median progression-free survival (PFS) of at least 3, 3.5, 4, 4.5, 5, 5.5 or 6 months. This may particularly be the case when the ADC is administered as a second or further line of therapy (i.e. in subjects who have already received at least one prior line of therapy).

In particular, treatment of subjects with gastric or GEJ cancer with the ADC described herein as a second or further line of treatment, at a dosage of 2.2 mg/kg to 3 mg/kg about every 3 weeks, may result in a median progression-free survival of at least 3, 3.5, 4, 4.5, 5, 5.5 or 6 months. More specifically, treatment of such subjects at a dosage of 2.2 mg/kg, 2.6 mg/kg or 3 mg/kg of the ADC about every 3 weeks may result in a median progression-free survival of at least 3, 3.5, 4, 4.5, 5, 5.5 or 6 months.

Alternatively or additionally, in a given population of patients with gastric or GEJ cancer, treatment with the ADC described herein may result in a median overall survival of at least 9, 10, 11 , 12, 13, 14 or 15 months. This may particularly be the case when the ADC is administered as a second or further line of therapy (i.e. in subjects who have already received at least one prior line of therapy).

In particular, treatment of subjects with gastric or GEJ cancer with the ADC described herein as a second or further line of treatment, at a dosage of 2.2 mg/kg to 3 mg/kg about every 3 weeks, may result in a median overall survival of at least 9, 10, 11 , 12, 13, 14 or 15 months. More specifically, treatment of such subjects at a dosage of 2.2 mg/kg, 2.6 mg/kg or 3 mg/kg of the ADC about every 3 weeks may result in a median overall survival of at least 9, 10, 11 , 12, 13, 14 or 15 months.

Progression-free survival (PFS) and overall survival (OS) as referred to herein are counted from the beginning of treatment with the ADC.

The ADC described herein may be administered in the context of a monotherapy, by which is meant that the ADC is not administered in combination with any other anti-cancer drug. That is to say, when the ADC is administered as a monotherapy, no other anti-cancer drug is administered to the subject during the course of therapy using the ADC.

Alternatively, the ADC described herein may be administered as part of a combination therapy with one or more other anti-cancer drugs, such as a chemotherapy drug or an immunotherapy drug. The ADC described herein may be administered in combination with other modes of cancer treatment, such as radiotherapy or surgery. For instance, the ADC may be administered to a subject prior to surgery (i.e. as a neoadjuvant), e.g. for the purpose of shrinking a tumour to improve the prospects of surgical treatment. The ADC can also be used as adjuvant therapy following surgery, or in combination with surgery where resectable tumours are surgically removed and unresectable tumours are treated with the ADC.

Administration of the ADC to the subject may be by any suitable route. Generally the ADC is administered parenterally, e.g. intravenously, intramuscularly, topically or subcutaneously. Generally, the ADC is administered intravenously.

COMPOSITIONS

The ADC for use herein is generally administered in the context of a pharmaceutical composition. A pharmaceutical composition may comprise at least one pharmaceutically acceptable diluent, carrier or excipient, in addition to the ADC. The term "pharmaceutically acceptable" as used herein refers to ingredients that are compatible with other ingredients of the compositions as well as physiologically acceptable to the recipient. The nature of the composition and carriers or excipient materials may be selected in routine manner.

The pharmaceutical composition may be in any form known in the art, but may particularly be a liquid solution of the ADC. Suitable pharmaceutically acceptable diluents, carriers and excipients for inclusion in such liquid solutions are well known in the art. For instance, suitable diluents, carriers and excipients include sucrose, lactose, trehalose, glucose (and other sugars), polyols, liposomes, polyvinyl alcohol, mannitol, gelatin and alcohols.

Liquid pharmaceutical compositions, whether they be solutions, suspensions or other like form, may include one or more of the following: sterile diluents such as water for injection, Ringer's solution, isotonic sodium chloride, polyethylene glycols, glycerin, propylene glycol or other solvents; antibacterial agents such as benzyl alcohol or methyl paraben; antioxidants such as ascorbic acid or sodium bisulfite; chelating agents such as EDTA; buffers such as acetates, citrates or phosphates and agents for the adjustment of tonicity such as dextrose. A parenteral preparation can be enclosed in ampoules, disposable syringes or multiple dose vials made of glass or plastic. METHODS OF IDENTIFYING OR SELECTING SUBJECTS, PREDICTING RESPONSES AND ASSESSING SUSCEPTIBILITY

The level of CLDN18.2 expression in a subject’s cancer can be assessed in order to select a subject for treatment with the ADC provided herein, to predict whether a subject with cancer is likely to respond to treatment with the ADC provided herein, to identify a subject with cancer who is likely to respond to treatment with the ADC provided herein, and/or to assess the susceptibility of a cancer to treatment with the ADC provided herein. Assessment of the level of CLDN18.2 expression in a subject’s cancer can be performed as described above. In particular the level of CLDN18.2 expression can be assessed in a tissue sample from the cancer. Generally, the level of CLDN18.2 expression is assessed by IHC.

A cancer is defined herein as susceptible to treatment with the ADC if the level of CLDN18.2 expression in the cancer is above a pre-defined threshold, as described above. A subject is defined as likely to respond to treatment with the ADC if their cancer is deemed susceptible to such treatment. Similarly, subjects can be selected for treatment with the ADC if their cancer is deemed susceptible to such treatment.

Subjects identified as or predicted to be likely to respond to treatment with the ADC, or with a cancer deemed susceptible to treatment with the ADC, can be selected for treatment with the ADC. Subjects selected for treatment with the ADC can be treated with the ADC, e.g. in a method as described above.

The therapies disclosed herein are exemplified in the non-limiting figures and examples below.

FIGURE LEGENDS

Figure 1 shows the efficacy of CMG901 in the dose escalation phase of the trial (Part A, N = 27). Panel A shows the change in target lesion size from baseline, horizontal dashed lines represent 20 % increase and 30 % reduction in tumour size; panel B shows responses and treatment duration. Measurable lesions were only present in 24/27 patients.

CR = complete response; PR = partial response; SD = stable disease, PD = progressive disease; NE - not evaluable.

Figure 2 shows the efficacy of CMG901 in the subgroup with CLDN18.2-positive gastric/GEJ cancer (N = 89). The graph shows the best percentage change from baseline in target lesion size in subgroup with CLDN18.2-positive G/GEJ cancer. Each bar represents an individual patient. Measurable lesions were only present in 89/93 patients receiving CMG901 at doses of 2.2, 2.6, and 3.0 mg/kg. Horizontal dashed lines represent 20 % increase and 30 % reduction in tumour size. G/GEJ=gastric/gastroesophageal junction. CR=complete response. PR=partial response. SD=stable disease. PD=progressive disease; NE - not evaluable.

Figure 3 shows the response and duration of treatment of CMG901 in the subgroup with CLDN18.2-positive G/GEJ cancer (n=93). G/GEJ=gastric/gastroesophageal junction. CR=complete response. PR=partial response. SD=stable disease. PD=progressive disease.

Figure 4 shows the survival outcomes for patients treated with CMG901 in subgroup with CLDN18.2-positive G/GEJ cancer (n=93). Panel A shows the PFS and OS data in all patients with gastric/GEJ cancer (2.0, 2.6, and 3.0 mg/kg doses; n=113). Panel B shows the PFS and OS data in a subgroup of gastric/GEJ cancer patients with CLDN18.2 expression of > 2+ in > 20 % of tumour cells (2.0, 2.6, and 3.0 mg/kg doses; n=93).

G/GEJ = gastric/gastroesophageal junction. PFS = progression-free survival. OS = overall survival.

Figure 5 shows subgroup analyses in patients with CLDN18.2-positive G/GEJ cancer. Panel A shows the confirmed objective response rate (ORR). Panel B shows progression-free survival (PFS). Dotted lines represent the ORR or median PFS for each study population receiving CMG901 at doses of 2.0, 2.6, and 3.0 mg/kg (33% for confirmed ORR and 4.8 months for median PFS). G/GEJ=gastric/gastroesophageal junction. ECOG PS=Eastern Cooperative Oncology Group performance status. PD-1=programmed cell death protein 1.

Figure 6 shows the efficacy of CMG901 in G/GEJ cancer patients. Panel A shows the best percentage change from baseline in target lesion size. Measurable lesions were only present in 109/113 patients receiving CMG901 at doses of 2.0, 2.6, and 3.0 mg/kg. Horizontal dashed lines represent 20% increase and 30% reduction in tumor size. Panel B shows the response and duration of treatment of CMG901 in all 113 patients. G/GEJ=gastric/gastroesophageal junction. CR=complete response. PR=partial response. SD=stable disease. PD=progressive disease; NE - not evaluable.

Figure 7 shows the survival outcomes of CMG901 in G/GEJ cancer patients. Panel A shows progression-free survival (PFS), while panel B shows the overall survival (OS). G/GEJ=gastric/gastroesophageal junction. PFS=progression-free survival. OS=overall survival. Figure 8 shows subgroup analyses of G/GEJ cancer patients. Panel A shows the objective response rate (ORR). Panel B shows progression-free survival (PFS). Dotted lines represent the ORR or PFS for each study population receiving CMG901 at doses of 2.0, 2.6, and 3.0 mg/kg (28% for confirmed ORR and 3.7 months for median PFS). G/GEJ=gastric/gastroesophageal junction. ECOG PS=Eastern Cooperative Oncology Group performance status. PD-1=programmed cell death protein 1.

Figure 9 shows confirmed best overall responses (cBOR) to CMG901 treatment in G/GEJ cancer patients stratified by CLDN18.2 expression levels, based on the proportion of tumour cells which are CLDN18.2-positive, as determined by IHC. Panel A shows stratification by CLDN18.2 expression at an IHC staining intensity of at least 1 ; panel B shows stratification by CLDN18.2 expression at an IHC staining intensity of at least 2.

Figure 10 shows confirmed and unconfirmed best overall responses (c+uBOR) to CMG901 treatment in G/GEJ cancer patients stratified by CLDN18.2 expression levels, based on the proportion of tumour cells which are CLDN18.2-positive, as determined by IHC. Panel A shows stratification by CLDN18.2 expression at an IHC staining intensity of at least 1 ; panel B shows stratification by CLDN18.2 expression at an IHC staining intensity of at least 2.

Figure 11 shows progression-free survival (PFS) for G/GEJ cancer patients treated with CMG901 stratified by CLDN18.2 expression levels, based on the proportion of tumour cells which are CLDN18.2-positive, as determined by IHC, at a staining intensity of at least

1.

Figure 12 shows progression-free survival (PFS) for G/GEJ cancer patients treated with CMG901 stratified by CLDN18.2 expression levels, based on the proportion of tumour cells which are CLDN18.2-positive, as determined by IHC, at a staining intensity of at least

2.

Figure 13 shows progression-free survival (PFS) for PDAC patients treated with CMG901 stratified by CLDN18.2 expression levels, based on the proportion of tumour cells which are CLDN18.2-positive, as determined by IHC, at a staining intensity of at least 1.

Figure 14 shows progression-free survival (PFS) for PDAC patients treated with CMG901 stratified by CLDN18.2 expression levels, based on the proportion of tumour cells which are CLDN18.2-positive, as determined by IHC, at a staining intensity of at least 2. Figure 15 compares H-scores for an anti-CLDN18.2-specific antibody (Ventana SP455) against another anti-CLDN18.2-specific antibody (Abeam EPR19202, shown in light grey) and an anti-pan-CLDN18 antibody (Ventana 43-14A, shown in dark grey) and demonstrates that all three antibody clones are analytically comparable.

Figure 16 compares the percentage of tumour cells expressing CLDN18.2 at a) any intensity ((+) TC, any intensity), or b) intensity scores 2-3+ ((+) TC, 2-3+) as detected by anti-CLDN18.2-specific antibody Ventana SP455 compared to anti-CLDN18.2 antibody (Abeam EPR19202, shown in light grey) and anti-pan-CLDN18 antibody (Ventana 43-14A, shown in dark grey).

EXAMPLES

Example 1 : Treatment of advanced gastric/gastroesophageal junction cancer using Anti-CLDN18.2 CMG901

BACKGROUND

CMG901 is a first-in-class CLDN18.2 specific antibody-drug conjugate (ADC) that consists of a humanized anti-CLDN18.2 immunoglobulin G1 antibody (CM311) attached via a protease- cleavable linker to the highly cytotoxic microtubule-disrupting agent monomethyl auristatin E (MMAE). Preclinical studies showed that CMG901 induced potent anti-tumour activity in gastric and pancreatic patient-derived xenograft (PDX) models (WO 2022/078523). To evaluate the safety/tolerability, preliminary efficacy, pharmacokinetics and immunogenicity of CMG901 in patients with advanced gastric/GEJ cancer, pancreatic cancer and other solid tumours, a phase 1 trial was conducted. Here, the findings from the overall population in the dose escalation phase (Part A), and from the gastric/GEJ cancer cohort in the dose expansion phase (Part B), are reported.

METHODS

Trial Design

KYM901 (NCT04805307) is a multicentre, phase 1 trial conducted in patients with advanced solid tumours. This trial included dose escalation (Part A: 0.3-3.4 mg/kg) and dose expansion (Part B: 2.2, 2.6 and 3.0 mg/kg) phases.

Part A consisted of eight dose-escalation cohorts, with the initial two CMG901 dose levels following an accelerated titration design, while the subsequent six dose levels followed traditional 3+3 dose escalation design. The planned sequential dose escalations were 0.3, 0.6, 1.2, 1.8, 2.2, 2.6, 3.0 and 3.4 mg/kg. In Part B, patients received CMG901 at assigned doses of 2.2, 2.6 and 3.0 mg/kg. CMG901 was administrated intravenously once every 3 weeks until confirmed disease progression, unacceptable toxicity, initiation of new antitumour therapy, withdrawal from the study, or death, whichever occurred first. Dose delay due to treatment-related adverse events (AEs) was permitted up to 3 weeks after the planned date of infusion.

T ai Procedures

The dose-escalation scheme of CMG901 was guided by the safety review committee based on evidence of all dose-limiting toxicities (DLTs) occurring within 21 days post CMG901 first infusion. A DLT was defined as a CMG901 -related occurrence of any pre-described adverse events (AEs), details of which were set out in the protocol (available at clinicaltrials.gov). If one patient in each cohort developed a DLT during the accelerated titration, the dose was switched to the traditional 3+3 dose-escalation. If one of 3 patients in each cohort developed a DLT during the traditional 3+3 dose escalation, then an additional 3 patients were to be treated at that dose level.

Blood samples were collected at protocol-specified timepoints for analyses of complete blood count, blood biochemistry, pharmacokinetics (after first and third infusions), and immunogenicity. Tumour responses were evaluated by computed tomography or magnetic resonance imaging of the chest, abdomen and pelvis using Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 by investigators at the end of week 3, every 6 weeks thereafter, and every 12 weeks after 1 year until radiological progression of disease, initiation of new anti-tumour therapy, withdrawal from the study or death, whichever occurred first. Responses to treatment visible at 2 sequential scans were deemed “confirmed”. Other responses were deemed “unconfirmed”.

AEs were monitored during the trial until the end of the safety follow-up (up to 4 weeks after the last administration), initiation of new anti-tumour therapy, withdrawal from the study or death, whichever occurred first. The severity of AEs was graded using Common Terminology Criteria for Adverse Events (CTCAE) v5.0.

Sample Size

The sample size for the dose-escalation phase (Part A) was determined using a modified 3+3 design, and additional patients could be enrolled to account for withdrawals that were unrelated to toxicity. For the dose-expansion phase (Part B), it was planned to enroll 50-150 patients for treatment in three cohorts (2.2, 2.6, and 3.0 mg/kg). Patients

Eligibility criteria included individuals aged 18 or older, with a diagnosis of advanced gastric/GEJ cancer, pancreatic cancer or other solid tumours, who demonstrated refractoriness and/or intolerance to standard therapies, and had an Eastern Cooperative Oncology Group (ECOG) performance status score of < 1 , a life expectancy of > 3 months, and either evaluable lesions (Part A) or a minimum of one measurable lesion (Part B) as per the Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1). CLDN18.2 expression was retrospectively assessed in Part A (as described below). For patient enrollment in Part B, a requirement of moderate-to-strong CLDN18.2 expression (defined as > 2 intensity) in > 5 % tumour cells for gastric/GEJ cancer was required. Patients were excluded if they had a known allergy to monoclonal antibodies or had received any antitumour treatments within 28 days. Full eligibility criteria are listed in the trial protocol.

Determination of CLDN18.2 expression

To detect CLDN18.2 expression, immunohistochemistry with an anti-CLDN18.2 antibody kit (either Abeam catalogue # 222512 or Abeam catalogue # 241330) was performed to assess the archival or fresh tissue specimens obtained prior to CMG901 treatment. Tumour tissue sections were fixed with 4 % formaldehyde solution and incubated with different antibodies at the manufacturer-specified concentrations at 4°C overnight, followed by incubation with HRP-conjugated secondary antibody at room temperature for 1 h. Chromogenic 3,3'- diaminobenzidine substrate was added to visualize the expression of CLDN18.2.

The IHC-score was based on tumour cells showing either strong (3+), intermediate (2+), weak (1+) or no (0) membranous staining for CLDN18.2. IHC-score 3+ was qiven if strong staining was circumferentially present in tumour cells. Partially present stroma staining or circumferential light staining was assessed with the IHC-score 2+. If faint staining was partially present, score 1+ was given. Tumour cells without detectable membranous staining were scored with 0. The percentage of positive tumour cells (either approximated to the nearest 10 %, or categorized by quartile (less than 25 %, at least 25 %, at least 50 % or at least 75 % of positive tumour cells)) showing the defined staining intensities (3+, 2+ 1+0) was gauged with respect to all tumour cells visible on each tissue specimen and always added up to a total of 100% tumour cells. Endpoints

The primary endpoints for Part A were safety/tolerability and determination of the maximum tolerated dose (MTD). The primary endpoints for Part B were the objective response rate (ORR) and identifying the recommended phase 2 dose (RP2D).

Secondary endpoints included disease control rate (DCR), duration of response (DOR), progression-free survival (PFS), overall survival (OS), and the correlation between the clinical response to CMG901 and CLDN18.2 expression. Additional secondary endpoints included pharmacokinetic parameters after single and multiple doses and anti-drug antibody (ADA) production.

Study Oversight

The trial was conducted following the Declaration of Helsinki, the International Conference on Harmonization of Good Clinical Practice guidelines, and applicable regulatory requirements. The trial received the ethics committee approvals of each trial centre, and written informed consents were obtained from all patients.

Statistical Analysis

DLT analyses were performed on DLT-evaluable patients (applicable only for Part A). The full analysis set included patients who received at least one administration of CMG901. The efficacy set comprised all gastric/GEJ cancer patients from Part A and Part B who received CMG901 at doses of 2.2, 2.6, and 3.0 mg/kg at least once, and for whom post-treatment imaging evaluation results were available. Additionally, a subgroup of patients selected from the efficacy set, who had detectable CLDN18.2 expression, were included in the biomarker set. The safety set, pharmacokinetic concentration set, pharmacokinetic analysis set and immunogenicity set included all patients who received one or more doses of CMG901 and had at least one corresponding qualified result.

SAS v9.4 was used for statistical analyses. Categorical variables were summarized by frequencies and percentages. Time to event endpoints were analyzed using Kaplan-Meier methods, with a two-sided 95 % confidence interval (Cl) calculated. Subgroups based on patient characteristics were analyzed for ORR. Pharmacokinetic parameters of serum CMG901 , total antibody and MMAE were determined using standard noncompartmental analysis (Phoenix WinNonlin v8.3).

RESULTS Trial Population

Between December 24, 2020, and July 24, 2023, 27 patients in Part A (13 for G/GEJ cancer and 14 for pancreatic cancer) and 149 patients in Part B (107 for G/GEJ cancer, 40 for pancreatic cancer and 2 for other solid tumours) were enrolled at 31 sites in China (Table 1 A). In Part A, 70 % of patients were ECOG score 1 , and the median number of lines of prior therapies was 3 (range 1 -5, Table 2). Among the 113 patients (including six from Part A) with G/GEJ cancer who received CMG901 at doses of 2.2, 2.6, and 3.0 mg/kg in this trial, the median prior lines of therapy was 2 (range 1 -6) (Table 1A). 74 % of patients had received prior anti-programmed cell death protein 1 (PD-1 ) or anti-programmed death ligand 1 (PD- L1 ) therapies, and 4 % had received prior CLDN18.2-targeting therapy (Table 1A). At the data cut-off date of July 24, 2023, 93 of 113 patients (82 %) had discontinued CMG901 treatment, with 64 (57 %) discontinuing due to progressive disease and 14 (12 %) discontinuing due to patient request.

Among the 47 patients with pancreatic cancer who received CMG901 at doses of 2.2, 2.6, and 3.0 mg/kg in this trial, 32 (68 %) had received at least one previous line of therapy. Exactly half of these (16 patients) had received prior immune checkpoint inhibitor therapy (Table 1 B).

Safety

In Part A, the MTD was not reached. At 2.2 mg/kg, one patient experienced a dose-limiting toxicity (DLT) with grade 3 pancreatitis, but no subsequent cases of pancreatitis were identified. All 27 patients reported at least one treatment-emergent adverse event (TEAE). Drug-related grade >3 TEAEs occurred in 5 patients (19 %) (Table 3). The most frequent TEAEs were vomiting, decreased appetite, proteinuria, and anaemia (Table 3; Table 4). Three patients had treatment discontinuation due to drug-related TEAEs: fatigue and pancreatitis. One death occurred due to grade 5 pneumonia, which was not considered drug related (Table 3).

Safety data were reported for the 113 patients with advanced G/GEJ cancer who received CMG901 at doses of 2.2-3.0 mg/kg and the 47 patients with PDAC who received the same doses. All patients had at least one TEAE. The most commonly reported TEAEs in the G/GEJ cancer group were anaemia (63 %), vomiting (58 %), hypoalbuminaemia (58 %), weight decreased (56 %), and nausea (55 %) (Table 5). Drug related grade >3 TEAEs occurred in 54 % (61/113) of patients in the G/GEJ cancer group (Table 3); neutrophil count decreased (19 %), vomiting (9 %), anaemia (7 %), white blood cell count decreased (7 %), and decreased appetite (6 %) were the most frequent. Serious AEs were reported in 47 % of patients in the G/GEJ cancer group (31 % were considered drug related) (Table 3). Similar results were seen in the Part A + Part B pancreatic cancer group, where 38 % of patients reported a serious AE, of which 32 % were considered treatment-related. Three deaths occurred due to TEAEs, of which one (cerebral haemorrhage) was considered to be related to CMG901 , while the other two patients died of unknown reasons. 15 patients (13 %) had a TEAE leading to dose reduction, and CMG901 -related AEs leading to treatment discontinuation occurred in nine patients (Table 3).

Among the 134 patients from Part A and Part B (G/GEJ cancer), 25 (19 %) had low grade peripheral neuropathy, with only three being classified as grade 2. The median time to the first onset of peripheral neuropathy was 2.1 months (range: 0.2-11.7). In addition, nine patients (8 %) experienced CMG901 -related infusion-related reaction, with three classified as grade 1 , four as grade 2, and two as grade 4 (resulting in treatment discontinuation).

Table 1A: Patient demographics and baseline characteristics in G/GEJ cancer cohort (Full Analysis Set)

Data are median (IQR) or n (%). ‘Includes 6 patients with G/GEJ cancer from Part A. ^#Sex was self- reported by the participants, with options "male" or "female". G/GEJ=gastric/gastroesophageal junction. ECOG PS=Eastern Cooperative Oncology Group performance status. PD-1 =programmed cell death protein 1. PD-L1 =programmed death ligand 1. Table 1 B: Patient demographics and baseline characteristics in pancreatic cancer cohort

Data are median (range) or n (%). ECOG PS = Eastern Cooperative Oncology Group performance status; ICI = immune checkpoint inhibitor.

Table 2 - Patient Demographics and Baseline Characteristics in Dose-escalation Phase (Full Analysis Set)

ECOG PS = Eastern Cooperative Oncology Group performance status; GEJ = gastroesophageal

5 junction; PD-(L)1 = programmed cell death protein 1 or programmed death ligand 1. Table 3 - Safety and Tolerability of CMG901 (Safety Set)

Data are presented as n (%). *Includes 6 patients with G/GEJ cancer from dose-escalation phase (Part A). The maximum severity of TEAE was classified by Common Terminology Criteria for Adverse Events. TEAE=treatment-emergent adverse event. SAE=serious adverse events.

Efficacy

Anti-tumor activity was observed at doses from 1.8 mg/kg upwards. One patient with peritoneal metastasis in the 1.8 mg/kg cohort achieved complete response following 5 cycles of CMG901 , with a PFS of 6.2 months. Detailed efficacy data of CMG901 in Part A is shown in Fig. 1.

For G/GEJ cancer patients with moderate-to-strong CLDN18.2 expression in < 20 %, > 20 %, > 30 %, > 40 %, > 50 % and > 60 % of tumour cells, confirmed ORRs were 5 %, 33 %, 34 %, 36 %, 36 % and 36 %, respectively. This suggested a possible correlation between CLDN18.2 expression and anti-tumor activity of CMG901. Therefore, we defined moderate-to-strong CLDN18.2 expression in > 20 % of tumor cells as CLDN18.2-positive, while anything below this threshold was not considered CLDN18.2-positive.

For 89 response-evaluable CLDN18.2-positive patients, the confirmed ORR was 33 % (95 % Cl 23.0-43.3; including two complete responses), with an ORR of 42 % in the 2.2 mg/kg cohort (Table 6). Confirmed disease control was seen in 62 patients (70 %; 95 % Cl 59.0-79.0). The median time to response was 2.0 months (95 % Cl 2.1-3.5), and the median duration of response (DOR) was 5.7 months (95 % Cl 4.2-8.1 ) (Table 6). Tumour shrinkage is shown in Fig. 2. In the 3.0 mg/kg cohort, one patient, who had previously received a first-line combination of PD-1 inhibitor and chemotherapy, achieved a 100 % reduction in the size of all target and non-target lesions following seven cycles of CMG901 administration.

As of the data cut-off date, 23 of 93 CLDN18.2-positive patients (25 %) continued CMG901 treatment (Fig. 3). After a median follow up of 6.0 months (IQR 4.2-8.3), the median PFS in the 2.2, 2.6, and 3.0 mg/kg cohorts were 4.8, 3.3, and 14.5 months, respectively (Fig. 4A). The median OS was not reached (95 % Cl 7.5-not reached [NR]) (Table 7; Fig. 4B). The estimated 6-month and 9-month OS rates were 69 % (95 % Cl 58.2- 78.1 ) and 56 % (95 % Cl 43.6-67.3), respectively. Among patients who had received > 2 prior lines of therapies, the median PFS was 4.8 months (95 % Cl 3.4-6.3), and the median OS was not reached (95 % Cl 6.8-NR), with a 9-month OS rate of 54 %.

Subgroup analyses were conducted to explore the association between confirmed ORR or PFS and baseline characteristics in the 93 patients with CLDN18.2-positive G/GEJ cancer (Fig. 5). Findings indicated similar ORR and PFS irrespective the number of prior lines of therapy. 18 (35 %) patients with peritoneal metastasis achieved a confirmed objective response, with a median PFS of 6.0 months.

Anti-tumour responses were also assessed across the cohort, in 109 of 113 patients with advanced gastric/gastroesophageal junction (G/GEJ) cancer. 30 patients (28 %; 95 % Cl 19.4-36.9) reached a confirmed objective response. The confirmed disease control rate was 65 % (n = 71 , 95 % Cl 55.4-74.0) (Fig. 6A, Table 8). The median duration of response was 5.6 months (95 % Cl 4.2-8.1) and the median time to response was 2.0 months (95 % Cl 2.2-not reached [NR]) (Table 8).

As of the data cut-off date, 26/113 patients with G/GEJ cancer (23 %) continued treatment (Fig. 6B). With a median follow-up of 5.7 months (IQR, 4.2-8.5), the median progression-free survival was 3.7 months (95 % Cl 3.3-4.9) (Fig. 7A), and the median overall survival was 9.8 months (95 % Cl 6.8-NR) (Table 9; Fig. 7B).

Subgroup analyses showed that the ORR and PFS remained consistent regardless of the number of prior lines of therapy and previous anti-PD-1 therapy. In addition, a high ORR (4/6, 67 %) and long median PFS (6.9 months) were observed in G/GEJ cancer patients with exclusively peritoneal metastasis (Fig. 8).

In patients with pancreatic cancer (pancreatic ductal adenocarcinoma, PDAC), confirmed responses were seen in 4/38 patients (10.5 %), see Tables 10 and 11 . In PDAC patients with cancers containing > 50 % CLDN 18.2-positive tumour cells median PFS was 3.3 months. The median overall survival was not reached at the data cut-off (Table 12).

Pharmacokinetics and Immunogenicity

The pharmacokinetics of CMG901 was assessed in the 134 G/GEJ cancer patients. The systemic exposure of CMG901 (defined as area under the concentration-time curve from time 0 to infinity in Cycle 1) showed a generally dose-proportional increase, while patients had typical low systemic exposure to unconjugated MMAE with the mean observed maximum concentration less than 10 ng/ml across all dose levels. 53 patients (40 %) were confirmed to be positive for ADA: three had pre-existing ADA, one had treatment-boosted ADA, and 49 had treatment-induced ADA. The impact of ADA on efficacy and safety was not observed.

Table 6: Best overall response evaluation of CMG901 in patients with CLDN18.2-positive G/GEJ cancer (Efficacy Set)

Data are presented as n (%) unless stated otherwise. Best responses of each patient were assessed according to RECIST v1 .1 by the investigator. *Includes 3 patients with G/GEJ cancer from the doseescalation phase, includes two patients who had the potential to achieve a confirmed PR. ⁶Calculated as the proportion of patients showing confirmed CR, PR, or SD for a minimum of 5 weeks from the first dosing date. ⁺10 partial responders had unconfirmed partial responses. G/GEJ = gastric/gastroesophageal junction; BOR = best overall response; CR = complete response; PR = partial response; SD = stable disease; PD = progressive disease; NE = not evaluable; ORR (CR+PR) = objective response rate; Cl = confidence interval; DCR (CR+PR+SD) = disease control rate; NR = not reached. Table 7: Efficacy outcomes in patients with claudin 18.2-positive G/GEJ cancer (Biomarker Set)

Data are presented as n (%) or median (interquartile range, IQR) unless stated otherwise. ‘Includes 3 patients with G/GEJ cancer from the dose-escalation phase. G/GEJ=gastric/gastroesophageal junction. Cl=confidence interval. NR=not reached.

Table 8. Best overall response evaluation of CMG901 in G/GEJ cancer cohort (Efficacy Set)

Data are presented as n (%) unless stated otherwise. Best responses of each patient assessed according to RECIST 1.1 by the investigator. ‘Includes 6 patients with G/GEJ cancer from the dose- escalation phase. #Includes two patients who had the potential to achieve a confirmed PR.

⁶Calculated as the proportion of patients showing confirmed CR, PR, or SD for a minimum of 5 weeks from the first dosing date. G/GEJ = gastric/gastroesophageal junction; BOR = best overall response; CR = complete response; PR = partial response; SD = stable disease; PD = progressive disease; NE = not evaluable; ORR (CR+PR) = objective response rate; Cl = confidence interval; DCR (CR+PR+SD) = disease control rate; NR = not reached. Table 9. Efficacy outcomes in G/GEJ cancer cohort (Full Analysis Set)

Data are presented as n (%) or median (interquartile range, IQR) unless stated otherwise. ‘Includes 6 patients with G/GEJ cancer from the dose-escalation phase. G/GEJ = gastric/gastroesophageal junction; Cl = confidence interval; NR = not reached.

Table 10. Confirmed Efficacy outcomes in PDAC cohort

Table 11. ORR in PDAC patients with > 50 % CLDN18.2-positive tumour cells

Data are presented as n (%) unless stated otherwise.

Table 12. Efficacy outcomes in PDAC patients with > 50 % CLDN18.2-positive tumour cells

Example 2: Investigation of CMG901 efficacy in G/GEJ cancer and PDAC patient populations stratified by CLDN18.2 expression In the 108 G/GEJ cancer cohort patients in Part B, further analysis was performed to investigate the efficacy of CMG901 when patients are stratified based on the proportion of cells that are CLDN18.2-positive, and optionally the intensity of CLDN18.2 expression in those cells.

Patient responses to treatment based on cut-offs of > 10 %, > 20 %, > 25 %, > 50 %, and > 75 % of tumour cells being CLDN18.2-positive, either at an IHC staining intensity of at least 1 or an IHC staining intensity of at least 2, were analysed to determine whether a particular level of CLDN18.2 expression is predictive for treatment efficacy. Analysis based on confirmed responses is shown in Fig. 9 and analysis based on unconfirmed responses is shown in Fig. 10.

Based on this analysis, optimal cut-offs appear to be > 25 % CLDN 18.2-positive tumour cells at a staining intensity of at least 1 and > 20 % CLDN18.2-positive tumour cells at a staining intensity of at least 2. A cut-off of > 25 % CLDN18.2-positive tumour cells at a staining intensity of at least 1 is estimated to encompass about 60 % of gastric/GEJ cancer patients (data not shown) and to capture over 95 % of responders (based on both confirmed and unconfirmed ORRs). A cut-off of > 20 % CLDN 18.2-positive tumour cells at a staining intensity of at least 2 is estimated to encompass about 45 % of gastric GEJ cancer patients and 90-95 % of responders (based on unconfirmed ORRs). A cut-off of > 20 % CLDN 18.2- positive tumour cells at a staining intensity of at least 2 therefore enriches the treated population for responders, but leaves more responders behind. Further increasing the cut-off in terms of the proportion of CLDN18.2-positive tumour cells (whether at a staining intensity of at least 1 or a staining intensity of at least 2) further enriches the treated population for responders while leaving additional responders behind.

Patient survival for the G/GEJ cancer cohort was also stratified using the same set of cut-offs, at > 10 %, > 20 %, > 25 %, > 50 %, and > 75 % CLDN 18.2-positive cells (Fig. 11). When including CLDN18.2 staining intensities of at least 1 , a significantly longer PFS was seen in patients above a cut-off of > 25% CLDN18.2-positive cells. No further increase in PFS was seen in patients at higher cut-offs. When restricting for moderate to high CLDN18.2 expression (staining intensity of at least 2), using a cut-off of > 20 % resulted in good differentiation between the two patient groups (Fig. 12).

Patient survival was also stratified for the PDAC cohort using the same set of cutoffs. A longer PFS was seen in patients with > 10 %, > 20 %, > 25 % or > 50 % tumour cells expressing CLDN18.2 at any staining intensity (Fig. 13). No improvement in differentiation was seen by restricting for moderate to high CLDN18.2 expression (Fig. 14). Example 3: Determination of CLDN18.2 expression using an anti-pan-CLDN18 antibody

METHODS

Determination of CLDN18.2 expression 91 primary gastric carcinoma (GC) FFPE (formalin-fixed paraffin-embedded) resection specimens were stained for CLDN18.2 expression using 3 different antibodies: a pan- CLDN18 antibody (Ventana 43-14A), and two anti-CLDN18.2 antibodies (Ventana CLDN18.2 SP455 and Abeam EPR19202). CLDN18 and CLDN18.2 expression were measured by manual scores and computational pathology scores (QCS) in parallel. 3 % (n=3) of the specimens were AJCC/UICC stage I, 57 % (n=52) were AJCC/UICC stage IIA-B, 37 % (n=34) were AJCC/UICC stage IIIA-C, and 2 % (n=2) were AJCC/UICC stage IV. Specimens were from Vietnam (62 %, n=56), Ukraine (37 %, n=34) and Russia (1 %, n=1 ).

Histologically, 32 % (n=29) of specimens were diffuse and 68 % (n=62) of specimens were non-diffuse.

To detect CLDN18 expression, immunohistochemistry with an anti-CLDN18 antibody kit (VENTANA CLDN18 (43- 14 A) Assay, Ref 790-7027) was performed to assess the archival tissue specimens. Ventana CLDN18 (43-14A) is a pan-CLDN18 antibody which detects both CLDN18.1 and CLDN18.2. Tumor tissue sections were fixed with 10 % formaldehyde solution and incubated with the pan CLDN18 (43-14A) antibody at the manufacturer-specified concentrations at 37 °C for 16 minutes, followed by incubation with OptiView HRP Linker and Multimer for 8 minutes each. Chromogenic 3,3'- diaminobenzidine substrate was added to visualize the expression of CLDN18 (both CLDN18.1 and CLDN18.2).

Immunohistochemistry with anti-CLDN18.2 antibody kits (Ventana SP455 and Abeam EPR19202 #22512) was also performed to assess the archival tissue specimens. Tumor tissue sections were fixed with 10 % formaldehyde solution and incubated with the CLDN18.2 Ventana SP455 and Abeam EPR19202 antibodies at the manufacturer-specified concentrations at 37 °C for 24 minutes and ambient temperature for 60 minutes, respectively. For Ventana SP455-stained slides, primary antibody incubation was followed by incubation with OptiView HRP Linker and Multimer. For EPR19202-stained slides, primary antibody incubation was followed by incubation with BOND Polymer Refine Detection. Chromogenic 3,3'- diaminobenzidine substrate was added to visualize the expression of CLDN18.2 for both methods. The IHC-score for pan-CLDN18 (43-14A) and CLDN18.2 (SP455 and EPR19202) IHC was based on tumor cells showing either strong (3+), intermediate (2+), weak (1+) or no (0) membranous staining for CLDN18/CLDN18.2. IHC-score 3+ was given if strong staining was circumferentially present in tumor cells. Circumferential moderate staining was assessed with the IHC-score 2+. Circumferential faint staining was given a score 1+. Tumor cells without detectable membranous staining were scored with 0. The percentage of positive tumor cells (either approximated to the nearest 10 %, or categorized by quartile (less than 25 %, at least 25 %, at least 50 % or at least 75 % of positive tumor cells)) showing the defined staining intensities (3+, 2+, 1+, 0) was gauged with respect to all tumor cells visible on each tissue specimen and always added up to a total of 100% tumor cells.

Statistical Analysis

To compare the H scores and fraction of positive tumour cells [at any intensity (1+ and above) or high intensity cut offs (2-3+)] derived from pan-CLDN18 (43-14A) and CLDN18.2 (SP455 and EPR19202) stained slides, simple linear regressions were applied to calculate the best-fit slope, intercept, and coefficient of determination.

RESULTS

Figure 15 compares the histochemical score (H-score) of Ventana SP455 CLDN18.2- specific antibody against both an anti-pan-CLDN18 (Ventana 43-14A) and another CLDN18.2-specific antibody (Abeam EPR19202). H-scores ranged from 0 to 300 and were calculated using the following formula: H scores = [% of (+) tumor cells with weak (1+) expression multiplied by 1] + [% of (+) tumor cells with moderate (2+) expression multiplied by 2] + [% of (+) tumor cells with strong (3+) expression multiplied by 3],

Figure 15 shows that the anti-CLDN18.2 clone Ventana SP455 and the anti-pan-CLDN18 clone (Ventana 43-14A) are analytically equivalent (slope = 1 , R = 0.94) across a range of intensities and expression levels. When using high intensity cut offs (2-3+), the positivity prevalence in pan-CLDN18 stained samples is only 5-10 % higher than CLDN18.2-stained samples. Furthermore, Figure 15 demonstrates that the CLDN18.2-specific clones (Ventana SP455 and Abeam EPR19202) are analytically comparable (slope = 0.8, R = 0.92), though when high intensity cut offs (2-3+) are used, the positivity prevalence is 5-10 % higher for staining with Ventana SP455 compared to Abeam EPR19202. Importantly, none of the specimens were identified as CLDN18.1-positive but CLDN18.2-negative. Figure 16 compares the percentage of tumor cells expressing CLDN18.2 (% TC(+)) at any intensity (Figure 16A), or at intensity scores 2-3+ ((+) TC, 2-3+) (Figure 16B), as detected by anti-CLDN18.2 clone Ventana SP455 compared to both anti-CLDN18 Ventana 43-14Aand anti-CLDN18.2 Abeam EPR19202 clones. There is a clear concordance between anti- CLDN18.2 (Ventana SP455) vs pan-CLDN18 (Ventana 43-14A) clones and anti-CLDN18.2 (Ventana SP455) vs anti-CLDN18.2 (Abeam EPR19202) clones when compared at any intensity (Figure 16A) or intensity scores 2-3+ ((+) TC, 2-3+) (Figure 16B).

These comparisons demonstrate that an anti-pan-CLDN18 antibody is analytically equivalent to an anti-CLDN18.2 antibody for the purpose of assessing CLDN18.2 expression on tumor tissue. Notably the variance in results between using an anti-pan-CLDN18 antibody and an anti-CLDN18.2 antibody was no greater than the variance between the results obtained with two different anti-CLDN18.2 antibodies. This shows that anti-pan-CLDN18 antibodies may be utilized in the identification of CLDN18.2-expressing cancers.

SEQUENCE LISTING

All sequences are amino acid sequences.

SEQ ID NO: 1 (CM311 VHCDR1 )

GGSISSNYAWN

SEQ ID NO: 2 (CM311 VHCDR2)

YIYYSGNTNYNPSLKS

SEQ ID NO: 3 (CM311 VHCDR3)

SYYGNSFIY

SEQ ID NO: 4 (CM311 VLCDR1 )

KSSQSLLNSGNQKNYLT

SEQ ID NO: 5 (CM311 VLCDR2)

WASTRES

SEQ ID NO: 6 (CM311 VLCDR3)

QNAYSFPWT

SEQ ID NO: 7 (CM311 VH)

QVQLQESGPGLVKPSETLSLTCTVSGGSISSNYAWNWIRQPPGKGLEWIGYIYYSGNTNYN

PSLKSRVTISRDTSKNQFSLKLSSVTAADTAVYYCATSYYGNSFIYWGQGTLVTVSS

SEQ ID NO: 8 (CM311 VL)

DIVMTQSPDSLAVSLGERATINCKSSQSLLNSGNQKNYLTWYQQKPGQPPKLLIYWASTRE

SGVPDRFSGSGSGTDFTLTISSLQAEDVAVYYCQNAYSFPWTFGQGTKVEIK

SEQ ID NO: 9 (CM311 heavy chain)

QVQLQESGPGLVKPSETLSLTCTVSGGSISSNYAWNWIRQPPGKGLEWIGYIYYSGNTNYN

PSLKSRVTISRDTSKNQFSLKLSSVTAADTAVYYCATSYYGNSFIYWGQGTLVTVSSASTKG

PSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSS

VVTVPSSSLGTQTYICNVNHKPSNTKVDKRVEPKSCDKTHTCPPCPAPELLGGPSVFLFPP

KPKDTLMISRTPEVTCVWDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSV LTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTC LVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSV

MHEALHNHYTQKSLSLSPGK

SEQ ID NO: 10 (CM311 light chain)

DIVMTQSPDSLAVSLGERATINCKSSQSLLNSGNQKNYLTWYQQKPGQPPKLLIYWASTRE

SGVPDRFSGSGSGTDFTLTISSLQAEDVAVYYCQNAYSFPWTFGQGTKVEIKRTVAAPSVFI FPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSS TLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC SEQ ID NO: 11 (human CLDN18.2)

MAVTACQGLGFWSLIGIAGIIAATCMDQWSTQDLYNNPVTAVFNYQGLWRSCVRESSGFT

ECRGYFTLLGLPAMLQAVRALMIVGIVLGAIGLLVSIFALKCIRIGSMEDSAKANMTLTSGIMFI

VSGLCAIAGVSVFANMLVTNFWMSTANMYTGMGGMVQTVQTRYTFGAALFVGWVAGGLT LIGGVMMCIACRGLAPEETNYKAVSYHASGHSVAYKPGGFKASTGFGSNTKNKKIYDGGAR TEDEVQSYPSKHDYV

SEQ ID NO: 12 (human CLDN 18.1 )

MSTTTCQVVAFLLSILGLAGCIAATGMDMWSTQDLYDNPVTSVFQYEGLWRSCVRQSSGF TECRPYFTILGLPAMLQAVRALMIVGIVLGAIGLLVSIFALKCIRIGSMEDSAKANMTLTSGIMF

IVSGLCAIAGVSVFANMLVTNFWMSTANMYTGMGGMVQTVQTRYTFGAALFVGWVAGGL

TLIGGVMMCIACRGLAPEETNYKAVSYHASGHSVAYKPGGFKASTGFGSNTKNKKIYDGGA RTEDEVQSYPSKHDYV SEQ ID NO: 13 (Gly₄Ser linker)

GGGGS

Claims

1 . A method of treating cancer in a subject, comprising administering to the subject a therapeutically effective dose of an antibody-drug conjugate (ADC) comprising an antibody or antigen-binding fragment thereof that specifically binds claudin 18.2 (CLDN18.2) conjugated to a cytotoxic agent, wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region comprising VHCDR1 , VHCDR2 and VHCDR3 and a light chain variable region comprising VLCDR1 , VLCDR2 and VLCDR3, wherein:

VHCDR1 comprises the amino acid sequence set forth in SEQ ID NO: 1 ; VHCDR2 comprises the amino acid sequence set forth in SEQ ID NO: 2; VHCDR3 comprises the amino acid sequence set forth in SEQ ID NO: 3; VLCDR1 comprises the amino acid sequence set forth in SEQ ID NO: 4;

2. The method of claim 1 , wherein the antibody or antigen-binding fragment thereof is humanized.

3. The method of claim 1 or 2, wherein the antibody or antigen-binding fragment thereof comprises:

(a) a heavy chain variable domain comprising the amino acid sequence set forth in SEQ ID NO: 7, or a variant thereof having at least 80, 85, 90 or 95 % identity to SEQ ID NO: 7; and

(b) a light chain variable domain comprising the amino acid sequence set forth in SEQ ID NO: 8, or a variant thereof having at least 80, 85, 90 or 95 % identity to SEQ ID NO: 8.

4. The method of claim 3, wherein the antibody or antigen-binding fragment thereof comprises:

(a) a heavy chain variable domain comprising the amino acid sequence set forth in SEQ ID NO: 7; and

(b) a light chain variable domain comprising the amino acid sequence set forth in SEQ ID NO: 8.

5. The method of any one of claims 1 to 4, wherein the ADC comprises an antibody comprising a human IgG constant domain, preferably a human IgG 1 constant domain.

6. The method of any one of claims 1 to 5, wherein the antibody comprises:

(a) a heavy chain comprising the amino acid sequence set forth in SEQ ID NO: 9, or a variant thereof having at least 80, 85, 90 or 95 % identity to SEQ ID NO: 9; and

(b) a light chain comprising the amino acid sequence set forth in SEQ ID NO: 10, or a variant thereof having at least 80, 85, 90 or 95 % identity to SEQ ID NO: 10.

7. The method of claim 6, wherein the antibody comprises:

(a) a heavy chain comprising the amino acid sequence set forth in SEQ ID NO: 9; and

(b) a light chain comprising the amino acid sequence set forth in SEQ ID NO: 10.

8. The method of any one of claims 1 to 7, wherein the cytotoxic agent is selected from monomethyl auristatin E (MMAE), monomethyl auristatin F (MMAF), gemcitabine, SN-38, a maytansinoid, calicheamicin, an MGBA, doxorubicin, ricin or a bacterial toxin.

9. The method of claim 8, wherein the cytotoxic agent is MMAE.

10. The method of any one of claims 1 to 9, wherein the cytotoxic agent is joined to the antibody or antigen-binding fragment thereof via a linker.

11. The method of claim 10, wherein the linker is 6-maleimidocaproyl-valine-citrulline-p- aminobenzyloxycarbonyl (MC-vc-PAB).

12. The method of any one of claims 1 to 11 , wherein the ADC has an average drug-to- antibody ratio (DAR) of 3.3 to 4.3.

13. The method of claim 12, wherein the ADC has an average DAR of 3.8.

14. The method of any one of claims 1 to 13, wherein CLDN18.2 is expressed by at least 10 % of cells in the cancer, or a sample thereof.

15. The method of claim 14, wherein CLDN18.2 is expressed by at least 20 % of cells in the cancer, or a sample thereof.

16. The method of claim 15, wherein CLDN18.2 is expressed by at least 25 % of cells in the cancer, or a sample thereof.

17. The method of claim 16, wherein CLDN18.2 is expressed by at least 50 % or at least 75 % of cells in the cancer, or a sample thereof.

18. The method of any one of claims 14 to 17, wherein CLDN18.2 expression has been determined by immunohistochemistry (IHC).

19. The method of claim 18, wherein the CLDN18.2 expression is at a staining intensity level of at least 1.

20. The method of claim 18 or 19, wherein the CLDN18.2 expression is at a staining intensity level of 2 or 3.

21. The method of claim 19, wherein CLDN18.2 is expressed at a staining intensity level of at least 1 by at least 25 % of cells in the cancer.

22. The method of claim 20, wherein CLDN18.2 is expressed at a staining intensity level of 2 or 3 by at least 20 % of cells in the cancer.

23. The method of any one of claims 1 to 22, wherein the cancer is a solid cancer.

24. The method of claim 23, wherein the cancer is gastric cancer or gastroesophageal junction cancer.

25. The method of claim 23, wherein the cancer is pancreatic cancer.

26. The method of any one of claims 1 to 26, wherein the cancer is locally unresectable or metastatic.

27. The method of any one of claims 1 to 26, wherein the cancer does not express HER2.

28. The method of any one of claims 1 to 27, wherein the subject is a human.

29. The method of any one of claims 1 to 28, wherein the subject has received at least 2 prior lines of treatment.

30. The method of any one of claims 1 to 29, wherein the subject is administered at least one dose of the ADC of about 1.8 to about 3.4 mg/kg.

31. The method of claim 30, wherein the subject is administered at least one dose of the ADC of about 1.8 mg/kg, 2.2 mg/kg, 2.6 mg/kg, 3 mg/kg or 3.4 mg/kg.

32. The method of claim 30 or 31 , wherein the subject is administered a dose of the ADC about every 2 weeks, every 3 weeks or every 4 weeks.

33. The method of any one of claims 30 to 32, wherein the subject is administered the ADC for a duration of 1 to 12 months.

34. The method of any one of claims 30 to 33, wherein the subject is administered a total of at least 2 doses, at least 3 doses or at least 4 doses of the ADC.

35. The method of claim 34, wherein the subject is administered a total of at least 14 doses of the ADC.

36. The method of any one of claims 1 to 35, wherein the subject is administered the ADC until confirmed disease progression, unacceptable toxicity or death.

37. The method of any one of claims 1 to 36, wherein the ADC is administered intravenously.

38. The method of claim 24, wherein the method has an overall response rate (ORR) of at least 30 %.

39. The method of claim 24 or 38, wherein the method has a disease control rate (DCR) of at least 70 %.

40. The method of claim 24, 38 or 39, wherein the method gives a median progression- free survival of at least 4 months.

41. The method of any one of claims 24 or 38 to 40, wherein the method is associated with a median overall survival of at least 9 months.

42. A method of identifying and treating a subject with cancer susceptible to treatment with an ADC, wherein the ADC is as defined in any one of claims 1 to 13, and the method comprises:

43. The method of claim 42, wherein the level of CLDN18.2 expression in the tissue sample is determined by immunohistochemistry (IHC).

44. The method of claim 42 or 43, wherein the subject is determined to be susceptible to treatment with the ADC if the level of CLDN18.2 expression is as defined in any one of claims 14 to 17 or 19 to 22.

45. The method of any one of claims 42 to 44, further comprising obtaining the tissue sample from the cancer.

46. The method of any one of claims 42 to 45, wherein the cancer and/or subject are as defined in any one of claims 23 to 29, and/or the ADC is administered in a method as defined in any one of claims 30 to 41.

47. An antibody-drug conjugate (ADC) as defined in claim 1 , for use in a method of treating cancer in a subject, wherein CLDN18.2 is expressed in the cancer at a level which indicates susceptibility to treatment with the ADC.

48. The ADC for use according to claim 47, wherein the level of CLDN18.2 expression in the cancer has been determined by immunohistochemistry (IHC).

49. The ADC for use according to claim 47 or 48, wherein CLDN18.2 is expressed in the cancer at a level as defined in any one of claims 14 to 17 or 19 to 22.

50. The ADC for use according to claim 47, wherein the method comprises:

51. The ADC for use according to claim 50, wherein the level of CLDN18.2 expression in the tissue sample is determined by immunohistochemistry (IHC).

52. The ADC for use according to claim 50 or 51 , wherein the subject is determined to be susceptible to treatment with the ADC if the level of CLDN18.2 expression is as defined in any one of claims 14 to 17 or 19 to 22.

53. The ADC for use according to any one of claims 47 to 52, wherein the ADC is as defined in any one of claims 2 to 13, the cancer and/or subject are as defined in any one of claims 23 to 29, and/or the treatment is as defined in any one of claims 30 to 41.

54. Use of an antibody-drug conjugate (ADC) as defined in claim 1 to treat cancer in a subject, wherein CLDN18.2 is expressed in the cancer at a level which indicates susceptibility to treatment with the ADC.

55. Use of an antibody-drug conjugate (ADC) as defined in claim 1 in the manufacture of a medicament for treating cancer in a subject, wherein CLDN18.2 is expressed in the cancer at a level which indicates susceptibility to treatment with the ADC.

56. The use of claim 54 or 55, wherein the ADC, cancer, subject and/or treatment are as defined in any one of claims 2 to 41 , and/or wherein the subject is identified by a method as defined in any one of claims 42 to 45.

57. A pharmaceutical composition for use in treating cancer in a subject, wherein the composition comprises an antibody-drug conjugate (ADC) as defined in claim 1 , and CLDN18.2 is expressed in the cancer at a level which indicates susceptibility to treatment with the ADC.

58. The pharmaceutical composition for use of claim 57, wherein the ADC, cancer, subject and/or treatment are as defined in any one of claims 2 to 41 , and/or wherein the subject is identified by a method as defined in any one of claims 42 to 45.

59. A method of selecting a subject with cancer for treatment with an ADC as defined in any one of claims 1 to 13, the method comprising assessing the level of CLDN18.2 expression in a tissue sample from the cancer, wherein the subject is selected for treatment with the ADC when the level of CLDN18.2 expression is as defined in any one of claims 14 to 17.

60. A method of predicting whether a subject with cancer is likely to respond to treatment with an ADC as defined in any one of claims 1 to 13, the method comprising assessing the level of CLDN18.2 expression in a tissue sample from the cancer, wherein the subject is considered likely to respond to treatment with the ADC when the level of CLDN18.2 expression is as defined in any one of claims 14 to 17.

61. A method for identifying a subject with cancer who is likely to respond to treatment with an ADC as defined in any one of claims 1 to 13, the method comprising obtaining a tissue sample of the cancer from the subject and assessing the level of CLDN18.2 expression in the sample, wherein the subject is considered likely to respond to treatment with the ADC when the level of CLDN18.2 expression is as defined in any one of claims 14 to 17.

62. A method for assessing the susceptibility of a cancer in a subject to treatment with an ADC as defined in any one of claims 1 to 13, comprising assessing the level of CLDN18.2 expression in a tissue sample from the cancer, wherein the cancer is considered susceptible to treatment with the ADC when the level of CLDN18.2 expression is as defined in any one of claims 14 to 17.

63. The method of any one of claims 60 to 62, wherein when the subject is considered likely to respond to treatment with the ADC or the cancer is considered susceptible to treatment with the ADC, the subject is selected for treatment with the ADC.

64. The method of any one of claims 59 to 63, wherein the level of CLDN18.2 expression in the tissue sample is assessed by IHC.

65. The method of claim 64, wherein the subject is selected for treatment with the ADC, the subject is considered likely to respond to treatment with the ADC and/or the cancer is considered susceptible to treatment with the ADC when the level of CLDN18.2 expression is as defined in any one of claims 19 to 22.

66. The method of any one of claims 59 to 65, wherein when the subject is selected for treatment with the ADC, the subject is considered likely to respond to treatment with the ADC and/or the cancer is considered susceptible to treatment with the ADC, the method further comprises administering the ADC to the subject.