HK1004324B - Enzyme inactivators - Google Patents

Description

The present invention relates to certain enzyme inactivators which are especially useful for co-administration with other therapeutic compounds such as antiviral compounds in order to provide an improved therapeutic index by reducing the toxic side-effects.

A therapeutic nucleoside analogue that has been found to have a particularly beneficial clinical effect against a spectrum of conditions associated with Human Immunodeficiency Virus (HIV) infections such as Acquired Immune Deficiency Syndrome (AIDS), AIDS-related complex (ARC) and asymptomatic infections, is the compound 3'-azido-3'-deoxythymidine having the approved name zidovudine. This compound at low doses is generally very well tolerated by patients and is now widely used in the treatment of HIV infections. However, in certain patients treated with zidovudine, some haematological suppression including anaemia and neutropenia may be observed, presumably arising from a certain limited level of toxicity of zidovudine observed towards stem cells. Other less commonly observed side-effects have been described such as myopathy which may be related to intracellular activity of zidovudine.

It has now been found that the stem cell and haematological toxicity of zidovudine can be reduced by co-administration of 5-ethynyluracil as an inactivator of the enzyme uracil reductase (dihydropyrimidine dehydrogenase, EC 1.3.1.2) which reduces the degradation of uracil.

The present invention is thus based on the discovery that the use of an inactivator of uracil reductase in combination with zidovudine reduces the cellular toxicity of zidovudine.

According to the present invention therefore we provide 5-ethynyluracil for use in medical therapy, especially in combination with zidovudine or a pharmaceutically acceptable salt or ester thereof, for example in the treatment or prophylaxis of HIV infections such as AIDS, ARC and asymptomatic infections.

The present invention further provides :-

• a) a combination of 5-ethynyluracil as a uracil reductase inactivator and zidovudine or a pharmaceutically acceptable salt or ester thereof.

It should be noted that the references herein to uracil reductase inactivators refer to compounds that inactivate the uracil reductase enzyme, effectively acting as suicide substrates, in contrast to compounds that merely have an inhibiting effect on the enzyme.

In experiments in mice, it has been found that red-blood cell anaemia induced by treatment with zidovudine could be at least partially prevented by treatment with 5-ethynyluracil.

Other uracil reductase inactivators which may be employed in accordance with the present invention include compounds which generate the above 5-ethynyluracil in vivo. Such compounds include nucleoside derivatives which contain a nucleobase corresponding to the above 5- substituted uracil compounds, for example nucleoside derivatives containing a ribose, 2'-deoxyribose, 2',3'-dideoxyribose, arabinose or other cleavable sugar portion, which may additionally contain a 2'- or 3'-substituent such as halo, for example fluoro. Specific examples of such nucleoside derivatives are 2',3'-dideoxy-5-ethynyl-3'-fluorouridine.

Zidovudine or a pharmaceutically acceptable salt or ester thereof and the said uracil reductase inactivator may be employed in combination in accordance with the invention by administration of the components of the combination to an appropriate subject either concomitantly, for example in a unitary pharmaceutical formulation, or, more preferably, separately, or sequentially within a sufficient time period whereby the desired therapeutic effect of the combination is achieved.

Zidovudine or a pharmaceutically acceptable salt or ester thereof and 5-ethynyluracil may be administered respectively for therapy by any suitable route including oral, rectal, nasal, topical (including buccal and sublingual), vaginal and parenteral (including subcutaneous, intramuscular, intravenous and intradermal); the oral route is especially preferred. It will be appreciated that the preferred route will vary with the condition and age of the recipient, the nature of the infection and other clinical factors.

In general a suitable dose of zidovudine or a pharmaceutically acceptable salt or ester thereof will be in the range of 1.0 to 120 mg per kilogram body weight of the recipient per day, preferably in the range of 2 to 30 mg per kilogram body weight per day and most preferably in the range of 5 to 20 mg per kilogram body weight per day. The desired dose is preferably presented as two, three, four, five, six or more sub-doses administered at appropriate intervals throughout the day. These sub-doses may be administered in unit dosage forms, for example, containing 10 to 1500 mg, preferably 20 to 1000 mg, and most preferably 50 to 700 mg of active ingredient per unit dosage form.

Experiments with 3'-azido-3'-deoxythymidine suggest that a dose should be administered to achieve peak plasma concentrations of the active compound of from 1 to 75 µM, preferably 2 to 50 µM, most preferably 3 to 30 µM. This may be achieved, for example, by the intravenous injection of a 0.1 to 5% solution of the active ingredient, optionally in saline, or orally administered as a bolus containing 1 to 100 mg/kg of the active ingredient. Desirable blood levels may be maintained by a continuous infusion to provide 0.01 to 5.0 mg/kg/hour or by intermittent infusions containing 0.4 to 15 mg/kg of the active ingredient.

The 5-ethynyluracil may be administered in a dosage in the range of 0.01 to 50 mg per kilogram body weight of the recipient per day, preferably in the range of 0.01 to 10 mg per kilogram body weight per day, most preferably in the range of 0.01 to 0.4 mg per kilogram body weight per day; an alternative preferred administration regime is 0.5 to 10 mg/kg once per week.

The desired dose is preferably presented as one, two or more sub-doses administered at appropriate intervals throughout the day. These sub-doses may be administered in unit dosage forms for example containing 1 to 200 mg, preferably 2 to 100 mg, most preferably 2 to 50 mg of 5-ethynyluracil.

Zidovudine and 5-ethynyluracil are employed in an appropriate ratio whereby the above-mentioned toxic effects of zidovudine are reduced or obviated without significant reduction of the therapeutic effect of zidovudine; such a ratio (based on the respective weights of zidovudine and uracil reductase inactivator) is generally in the range 1:1 to 1000:1, preferably in the range 5:1 to 500:1 and particularly in the range 20:1 to 200:1.

Zidovudine and 5-ethynyluracil are preferably administered in a pharmaceutical formulation, either in a single pharmaceutical formulation containing both components or in separate pharmaceutical formulations each containing one of the components of the combinations.

The present invention thus includes as a further feature a pharmaceutical formulation comprising 5-ethynyluracil optionally in combination with zidovudine or a pharmaceutically acceptable salt or ester thereof together with at least one pharmaceutically acceptable carrier or excipient.

Each carrier must be "pharmaceutically acceptable" in the sense of being compatible with the other ingredients of the formulation and not injurious to the patient. Formulations include those adapted for oral, rectal, nasal, topical (including buccal and sublingual), vaginal and parenteral (including subcutaneous, intramuscular, intravenous and intradermal) administration. The formulations may conveniently be presented in unit dosage form and may be prepared by any methods well known in the art of pharmacy. Such methods include the step of bringing into association the active ingredient with the carrier which constitutes one or more accessory ingredients. In general, the formulations are prepared by uniformly and intimately bringing into association the active ingredient with liquid carriers or finely divided solid carriers or both, and then if necessary shaping the product.

Formulations of the present invention adapted for oral administration may be presented as discrete units such as capsules, cachets or tablets each containing a predetermined amount of the active ingredient; as a powder or granules; as a solution or a suspension in an aqueous (at pH 10) or non-aqueous liquid; or as an oil-in-water liquid emulsion or a water-in-oil liquid emulsion. The active ingredient may also be presented as a bolus, electuary or paste.

A tablet may be made by compression or moulding, optionally with one or more accessory ingredients. Compressed tablets may be prepared by compressing in a suitable machine the active ingredient in a free-flowing form such as a powder or granules, optionally mixed with a binder (e.g. povidone, gelatin, hydroxypropylmethylcellulose), lubricant, inert diluent, preservative, disintegrant (eg. sodium starch glycollate, cross-linked povidone, cross-linked sodium carboxymethylcellulose) surface-active or dispersing agent. Moulded tablets may be made by moulding in a suitable machine a mixture of the powdered compound moistened with an inert liquid diluent. The tablets may optionally be coated or scored and may be formulated so as to provide controlled release of the active ingredient therein using, for example, hydroxypropylmethyl cellulose in varying proportions to provide the desired release profile.

Formulations for topical administration in the mouth include lozenges comprising the active ingredient in a flavoured basis, usually sucrose and acacia or tragacanth; pastilles comprising the active ingredient in an inert basis such as gelatin and glycerin, or sucrose and acacia; and mouthwashes comprising the active ingredient in a suitable liquid carrier.

Formulations for rectal administration may be presented as a suppository with a suitable base comprising for example cocoa butter or a salicylate.

Formulation for vaginal administration may be presented as pessaries, tampons, creams, gels, pastes, foams or spray formulations containing in addition to the active ingredient such carriers as are known in the art to be appropriate.

Formulations for parenteral administration include aqueous (at pH 10) and non-aqueous isotonic sterile injection solutions which may contain anti-oxidants, buffers, bacteriostats and solutes which render the formulation isotonic with the blood of the intended recipient; and aqueous and non-aqueous sterile suspensions which may include suspending agents and thickening agents. The formulations may be presented in unit-dose or multi-dose sealed containers, for example, ampoules and vials, and may be stored in a freeze-dried (lyophilized) condition requiring only the addition of the sterile liquid carrier, for example water for injections, immediately prior to use. Extemporaneous injection solutions and suspensions may be prepared from sterile powders, granules and tablets of the kind previously described.

Preferred unit dosage formulations are those containing a daily dose or unit, daily sub-dose, as herein above recited, or an appropriate fraction thereof, of an active ingredient.

The above-mentioned uracil reductase inactivators which are employed in combination with zidovudine in accordance with the present invention may be prepared in conventional manner. For example, the 5-ethynyluracil inactivators and prodrug thereof referred to above may be prepared by the methods described in J. Heterocycl. Chem. 19(3) 463-4 (1982) for the preparation of 5-ethynyluracil.

The above nucleoside derivatives may also be prepared in conventional manner, for example in accordance with processes described in European Patent Specification No. 356166 for the preparation of 2',3'-dideoxy-5- ethynyl-3'-fluorouridine.

The following Examples illustrate the present invention.

Example 1 5-(Trimethylsilylethynyl)uracil

A solution of 5-iodouracil (8g, 30mmol) in redistilled triethylamine (500mL) and dry DMF (10mL) was degassed with oxygen-free nitrogen for 15 minutes. Bis(triphenylphosphine)palladium (II) chloride (0.5g), copper (I) iodide (0.5g) and trimethylsilylacetylene (10g, 102mmol) were then added and the mixture was heated with stirring at 50°C for 24 hours. The cooled reaction mixture was filtered, the filtrate evaporated to dryness and the residue dissolved in dichloromethane (500mL). The organic solution was washed with a 2% aqueous solution of disodium EDTA (3 x 250mL), water (3 x 200mL), dried (Na₂SO4) and evaporated to dryness. The residue was triturated with ethanol to give the first crop of the title compound. The solid filtered from the reaction mixture was also found to contain the required product but in a more impure form and so was worked up as above in a separate batch to give a second crop.

• 1H nmr δ (d6DMSO) 11.75-10.85 (2H, bs, NH), 7.75 (1H, s, H-6), 0.15 ppm (9H, m, SiCH3).

Example 2 5-Ethynyluracil

A solution of 5-(trimethylsilylethynyl)uracil (5.3g, 25.4mmol) in 0.2M solution of sodium methoxide in methanol (400 mL) was stirred at room temperature for 3 hours and neutralized to pH 7 with dilute hydrochloric acid. The precipitated product was filtered, washed with methanol and dried to give a first crop of the title compound. The filtrates and washings were combined, evaporated to dryness and the residue crystallised from methanol to give the second crop of product. Combination of both crops and a further recrystallisation from ethanol gave a pure product. M.pt. : 260°C (dec.) ¹H nmr δ (d₆DMSO) 11.6-10.8 (2H, bs, NH), 7.8 (1H, s, H-6), 4.03 ppm (1H, s, acetylenic H)

	C, 52.95;	H, 2.96;	N, 20.58
Found :	C, 52.04;	H, 2.92;	N, 20.3

Example 3

a) 2,4-Dimethoxy-5-iodo-pyrimidine A dry 1L round-bottomed flask was charged with 5-iodouracil (50 g, 0.21 mol), phosphorus oxychloride (300 ml), and N,N-diethylaniline (6 drops). The heterogenous mixture was heated in a 120°C oil bath under a nitrogen atmosphere for 24 hours. The phosphorus oxychloride was distilled off (some product co-distills off). The reaction solution was next slowly and cautiously poured over ice (1L) and solid sodium bicarbonate keeping the internal temperature at or below -20°C. (This was accomplished by cooling in a dry-ice acetone bath). Once the addition was complete, the reaction mixture was adjusted to pH 7 by addition of solid sodium bicarbonate. The mixture was extracted with methylene chloride and the organic fractions dried by passage through phase separator paper. The crude solution of 2,4-dichloro-5-iodopyrimidine was immediately added dropwise to a solution containing MeOH (400 ml) and sodium methoxide (28.8 g, 0.533 mol). This addition took 1 hour. The reaction was then stirred at room temperature overnight. The solution was neutralized with CO₂ (gas), extracted with methylene chloride, dried over anhydrous Na₂SO₄, filtered and concentrated. The crude product was adsorbed onto silica gel (100 g) and loaded onto a 400 g silica gel flash chromatography column. The column was eluted with 90:10 hexanes: ethyl acetate (v:v). The appropriate fractions were combined and concentrated to a white solid as the title compound.

• Yield 26.7 g (48%)
• 200MHZ NMR CDCl3 δ=3.97 (s, 3H); 4.02 (s, 3H), 8.43 (s, 1H).

b) 2,4-Dimethoxy-5-(β-trimethylsilyl)-ethynylpyrimidine A dry 1L round-bottomed flask under a nitrogen atmosphere was charged with the product of stage a) (26.7 g, 0.10 mol), dry methylene chloride (Aldrich, 150 mL), dry Et₃N (freshly distilled from KOH pellets, 250 mL). The system was evacuated and purged with nitrogen several times via a Firestone valve. Trimethyl-silylacetylene (21.2 mL, 0.15 mol; Aldrich) was added by syringe. Next were added bis(triphenylphosphine)palladium (II) chloride (Aldrich 5.84 g, 8.32 mmol) and copper (I) iodide (Aldrich 4.76 g, 25 mmol). The mixture was heated in a 60°C oil bath for 2 hours, cooled and filtered through Celite. The filtrate was concentrated in vacuo. The residue was diluted with toluene (100 mL) and then the toluene was removed in vacuo. The residue was taken up into methylene chloride (200 mL), filtered and the filtrate extracted with 5% aq. ethylenediaminetetraacetic acid, disodium salt dihydrate (3 x 100 mL Aldrich), H₂O (1 x 100 mL). The organic layer was dried via passage through phase separator paper and concentrated in vacuo. The product was purified on a Waters Prep 500 eluting with 95:5 hexanes: ethyl acetate (v:v). The crude product was adsorbed onto 100 g of silica gel and loaded onto a 400 g silica gel flash chromatography column. The column was eluted with 97.5:2.5 hexanes: ethyl acetate (v:v). The appropriate fractions were combined and concentrated.

• Yield 16.94 g (73%).

A 1.2 g sample of the resulting compound was bound to 6 g of silica gel and loaded onto a 50 g flash chromatography column. The column was eluted with hexanes: ethyl acetate 95:5 (v:v). The appropriate fractions were combined, concentrated, stripped with CH₂Cl₂ (2 x 30 mL), and dried in vacuo to yield

• 1.000 g of the title compound, m.p. 72.5-73°C
• Lit. m.p. 73-74°C J. Heterocyclic Chem., 19, 463 (1982).

c) 5-(β-trimethylsilyl)ethynyluracil A dry 3-necked round-bottomed flask under nitrogen was charged with 2,4-dimethoxy-5-(β-trimethylsilyl)ethynylpyrmidine (6.5 g, 27.5 mmol), dry acetonitrile (120 mL Aldrich), sodium iodide (oven dried in vacuo 80°C, 18 h, 12.4 g, 82.7 mmol) and chlorotrimethylsilane (10.5 mL, 82.7 mmol freshly distilled). The mixture was heated at reflux for 3 hours and then concentrated in vacuo. The residue was digested with a solution containing methanol (40 mL) and water (20 mL) and the product filtered off to give 1.48 g (26%). The product was dissolved in chloroform and the solution adsorbed onto silica gel 7 g) which was then loaded onto a 35 g silica gel flash chromotography column. Elution with chloroform:methanol 95:5 (v:v) followed by chloroform:methanol 90:10 (v:v) and evaporation of the product-containing fractions yielded 1.23 g of the title compound as a white solid. d) 5-Ethynyluracil A solution containing 5-(β-trimethylsilyl)ethynyluracil (3.85 g, 18.4 mmol) and methanol (370 mL) was treated with a second solution containing sodium hydroxide (2.3 g, 57.5 mmol) and water (18 mL). The mixture was stirred at room temperature for 2 hours and then concentrated in vacuo. The residue was suspended in water (35 mL) and the pH adjusted to 5 using 0.1 N HCl. The solids dissolved and then a second precipitate formed when the pH=5. The product was filtered, washed with H₂O, and then dried in vacuo to give 2.3 g (92%) of 5-ethynyluracil as a light beige powder.

	C, 52.95:	H, 2.96;	N, 20.58
Found:	C, 52.79;	H, 3.02;	N, 20.44

The following Examples illustrate pharmaceutical formulations. Example 4 Tablet Formulations

The following formulations 4A, 4B and 4C are prepared by wet granulation of the ingredients (except the magnesium stearate) with a solution of the povidone followed by drying of the granules, addition of the magnesium stearate and compression.

Formulation 4A	mg/tablet	mg/tablet
Active ingredient	5	2
Lactose, B.P.	205	75
Povidone, B.P.	15	10
Sodium starch glycollate	20	10
Magnesium stearate	5	3

Formulation 4B	mg/tablet	mg/tablet
Active ingredient	5	2
Lactose, B.P.	155	-
Avicel PH 101	50	25
Povidone, B.P.	15	10
Sodium starch glycollate	20	10
Magnesium stearate	5	3

Formulation 4C	mg/tablet
Active ingredient	5
Lactose, B.P.	205
Starch	50
Povidone, B.P.	6
Magnesium stearate	4

The following formulation 4D is prepared by direct compression of the admixed ingredients. The lactose used is of the direct compression type.

Formulation 4D	mg/tablet
Active ingredient	5
Lactose	155
Avicel PH 101	100

The following formulation 4E is a controlled release tablet and is prepared by wet granulation of the ingredients (except magnesium stearate) with a solution of the povidone, followed by drying of the granules, addition of the magnesium stearate and compression.

Formulation 4E	mg/tablet
Active ingredient	5
Hydroxypropylmethylcellulose (Methocel K4M Premium)	110
Lactose, B.P.	50
Povidone, B.P.	28
Magnesium stearate	7

Example 5 Capsule Formulations

The following formulations 5A and 5B are prepared by admixing the uncompressed ingredients ad filling into a two-part hard gelatin capsule.

Formulation 7A	mg/capsule
Active ingredient	10
Lactose, B.P.	250
Sodium starch glycollate	25
Magnesium stearate	5

Formulation 5B	mg/capsule
Active ingredient	5
Pregelatinized starch NF15	245

Formulation 5C	mg/capsule
Active ingredient	10
Macrogol 4000, B.P.	340

The Macrogol 4000, B.P. is melted and the active ingredient dispersed therein. The thoroughly mixed melt is then filled into a two-part hard gelatin capsule.

Example 6 Injectable Formulation

Active ingredient	10mg
Sterile, pyrogen free Pyrophosphate buffer (pH 10), q.s. to	10ml

The active ingredient is dissolved in most of the pyrophosphate buffer (35-40°C), then made up to volume and filtered through a sterile micropore filter into a 10 ml amber glass vial (type 1) and sealed with a sterile closure and overseal.

Example 7 Suppository Formulation

	mg/suppository
Active ingredient, 63 µm*	10
Hard fat, B.P. (Witepsol H15-Dynamit Nobel)	1790

*The active ingredient is used as a powder wherein at least 90% of the particles are of 63 µm or less.

Our-fifth of the Witepsol H15 is melted in a steam-jacketed pan at 45°C maximum. The active ingredient is sifted through a 200 µM sieve and added to the molten base with mixing, using a silverson fitted with a cutting head, until a smooth dispersion is achieved. Maintaining the mixture at 45°C, the remaining Witepsol H15 is added to the suspension and stirred to ensure a homogeneous mix. The entire suspension is passed through a 250 µM stainless steel screen and, with continuous stirring, is allowed to cool to about 40°C. At a temperature of 38°C to 40°C 1.80 g of the mixture is filled into suitable plastic moulds. The suppositories are allowed to cool to room temperature.

Determination of Uracil Reductase Inactivation

Uracil reductase (1µM) (dihydropyrimidine dehydrogenase, EC 1.3.1.2) purified from bovine liver was incubated with 100µM inactivator and 5mM dithiothreitol (enzyme reductant) at 37° for 30 minutes in 0.05 M Tris-HCl at pH 8.0. The enzyme and inactivator were diluted 100-fold into the assay buffer, which contained 200µM NADPH, 200µM thymine and 1mM dithiothreitol in Tris-HCl at pH 8.0. The velocity of the enzyme was determined spectrophotometrically. These velocities have been corrected for NADPH oxidase activity, which was less than 10% of the rate of thymine-dependent oxidation of NADPH. The % inactivation of the enzyme was equal to 100% minus the percent of enzymatic activity remaining. Enzyme incubated without inhibitor was stable under these conditions. Parenthetical values are the relative first-order rate constants for inactivation of enzyme determined from similar experiments where the fractional activity was measured as a function of the time of incubation of 50µM inactivator with enzyme.

The results are given below:-

Compound	% Inactivation
5-ethynyluracil	100 (100)

Protection from Zidovudine Toxicity

Male mice were dosed p.o. with 1000 mg/kg/day of zidovudine for 30 days either alone, or 1.5 hours after dosing with 2 mg/kg/day of 5-ethynyluracil (5-EU). Other groups of mice (a) were dosed with 2 mg/kg/day of 5-ethynyluracil alone; and (b) served as controls, receiving neither zidovudine nor 5-ethynyluracil. Levels of haematocrit, haemoglobin and red blood cells were determined.

The results are as follows:-

GROUP	HEMATOCRIT (%)	HEMOGLOBIN (g/dl)	RED BLOOD CELLS (million/ml)
Control	48.1	16.0	9.7
5-EU	45.9	15.1	9.1
Zidovudine	34.5	11.2	6.1
Zidovudine plus 5-EU	43.1	13.9	7.6

Claims (12)

1. 5-ethynyluracil for use in medical therapy.
2. A pharmaceutical formulation comprising 5-ethynyluracil together with at least one pharmaceutically acceptable carrier or excipient therefor.
3. A formulation as claimed in claim 2 in unit dosage form.
4. A formulation as claimed in claim 3 wherein each unit dosage contains 1 to 200mg of 5-ethynyluracil.
5. A formulation as claimed in claim 4 wherein each unit dosage form contains 2 to 50mg of 5-ethynyluracil.
6. A formulation as claimed in any one of claims 2 to 5 which is adapted for oral administration.
7. A formulation as claimed in claim 6 in the form of a tablet, capsule or cachet.
8. A formulation as claimed in any one of claims 2 to 7 in combination with zidovudine.
9. The use of 5-ethynyluracil in the preparation of a medicament for use as a uracil reductase inhibitor.
10. The use of a medicament as claimed in claim 9 in unit dosage form wherein the 5-ethynyluracil or prodrug thereof is present at 2 to 50mg and wherein the medicament is adapted for oral administration.
11. A process for preparing a formulation as claimed in any of claims 2 to 8 which comprises bringing 5-ethynyluracil into association with a pharmaceutically acceptable carrier.
12. A method of preparing a pharmaceutical formulation of 5-ethynyluracil, comprising preparing 5-ethynyluracil in conventional manner and mixing with a pharmaceutically acceptable carrier or excipient.