ara-Cytidine acylates. Use of drug design predictors in structure-activity relationship correlation

5′Prime;-Ester Prodrugs of the Varicella-Zoster Antiviral Agent, 6-Methoxypurine Arabinoside

The potent and selective activity of 6-methoxypurine arabinoside (9-[β-D-arabinofuranosyl]-6-methoxy-9H-purine; 1) and its pharmacokinetic limitations have been described previously. In an attempt to circumvent first-pass catabolism following oral administration, a series of 5′-esters (2a-t) was prepared by dicyclohexyl-carbodiimide-promoted condensation with formic acid in the case of 2a, or by direct acylation of the parent nucleoside with the corresponding acyl chloride. These compounds were evaluated in rats for efficacy as oral prodrugs of 1 by measuring the amount of 1 excreted in the urine. Both aliphatic and aromatic esters exhibited a range of systemic availabilities. The substituted benzoate esters showed a correlation between the amount of 1 excreted and the electron-donating properties of the substituent. A similar relationship was observed for the relative stabilities of this series of esters to non-enzymatic hydrolysis at neutral pH. No clear relationship between systemic availability and solubility, partition coefficient, or stability was observed for the remaining esters of 1. Although significant enhancements in systemic availability were observed with some of the 5′-esters of this series, their limited water solubility precluded their use in intravenous formulations.

2-Ester Prodrugs of the Varicella-Zoster Antiviral Agent, 6-Methoxypurine Arabinoside

6-Methoxypurine arabinoside [9-(β-D-arabinofuranosyl)-6-methoxy-9H-purine; 1] is a potent and selective agent against varicella-zoster virus in vitro. Studies in the rat indicated that extensive first pass metabolism of this nucleoside occurred after oral dosing, presumably from high levels of adenosine deaminase in the intestine. Only 3.8% of an oral dose of 6-methoxypurine arabinoside was recovered in the urine. In an attempt to improve these unfavourable pharmacokinetics, a series of twenty-five 2′-esters of 6-methoxypurine arabinoside were prepared either by direct acylation or by a protection, acylation, and deprotection sequence. These esters were evaluated in the rat for their suitability as prodrugs on the basis of urinary recovery of 1 after oral dosing. The straight-chain aliphatic esters, but not the branched chain or aromatic esters, improved this urinary recovery. The 2′-valerate, hexanoate, heptanoate, and octanoate esters (2d–g, respectively) were the most effective, with urinary recoveries of 1 above 15%. The water solubility of the valerate ester was high (107 mM at 37°C and pH 7.2), but solubilities progressively decreased with the longer chain esters. The combination of high water solubility and improved metabolic stability upon oral dosing made 2d the prodrug of choice for both oral and intravenous dosing.

Highly enhanced leukemia therapy and oral bioavailability from a novel amphiphilic prodrug of cytarabine

Highly enhanced leukemia therapy and oral bioavailability are demonstrated for a new amphiphilic prodrug of cytarabine.

Spiral assembly of amphiphilic cytarabine prodrug assisted by probe sonication: Enhanced therapy index for leukemia

In order to overcome the drawbacks of cytarabine (Ara-C), such as low lipophilicity as well as short plasma half-life and rapid inactivation, a new derivative of Ara-C was designed by incorporation into the non-toxic material, oleic acid (OA), obtaining an amphiphilic small molecular weight prodrug (OA-Ara). By a simple amidation reaction, OA-Ara was synthesized successfully with a yield up to 61.32%. It was for the first time to see that the novel prodrug molecules could assemble into the unexpectedly spiral assembly under probe ultrasonication in aqueous solution. The oil/water partition coefficient (Ko/w) and the permeability of cell membrane of the prodrug were significantly increased compared with Ara-C molecules. In addition, OA-Ara molecules were stable in various pH solutions and artificial digestives, which indicated that it could be administrated orally. Cell viability assay showed that the prodrug displayed much higher antiproliferative effect against K562 and HL60 cells due to its improvement of the lipophilicity and penetrability of cell membrane. These findings demonstrate the feasibility of utilizing structural modification to broaden the clinic application of Ara-C and thus provide an effective new therapeutic alternative for leukemia.

Lipid-based drug carriers for prodrugs to enhance drug delivery

The combination of lipid drug delivery systems with prodrugs offers several advantages including improved pharmacokinetics, increased absorption, and facilitated targeting. Lipidization and use of lipid carriers can increase the pharmacological half-life of the drug, thus improving pharmacokinetics and allowing less frequent dosing. Lipids also offer advantages such as increased absorption through the intestines for oral drug absorption and to the CNS for brain delivery. Furthermore, the use of lipid delivery systems can enhance drug targeting. Endogenous proteins bind lipids in the blood and carry them to the liver to enable targeting of this organ. Drugs with significant side effects in the stomach can be specifically delivered to enterocytes by exploiting lipases for prodrug activation. Finally, lipids can be used to target the lymphatic system, thus bypassing the liver and avoiding first-pass metabolism. Lymphatic targeting is also important for antiviral drugs in the protection of B and T lymphocytes. In this review, both lipid-drug conjugates and lipid-based carriers will be discussed. An overview, including the chemistry and assembly of the systems, as well as examples from the clinic and in development, will be provided.

A facile whole-cell biocatalytic approach to regioselective synthesis of monoacylated 1-β-D-arabinofuranosylcytosine: influence of organic solvents

The lyophilized Pseudomonas fluorescens cell was an efficient alternative catalyst to enzymes for highly regioselective acylation of a polar nucleoside, 1-β-D-arabinofuranosylcytosine (ara-C). The cells showed an evident solvent dependence in the reaction. Among the tested solvents except for acetonitrile-pyridine, catalytic activity of the cells clearly increased with increasing the polarity of the organic solvents used. Among all the tested solvents both pure and binary, the best results were observed in isopropyl ether-pyridine system, in which the catalyst also showed good thermal and operational stabilities. For the biocataylsis in isopropyl ether-pyridine, the optimal isopropyl ether concentration, water content, acyl donor/ara-C ratio, biocatalyst dosage and reaction temperature were 30% (v/v), 4%, 45, 50mg/mL and 30 °C, respectively, under which the initial rate, yield and 5'-regioselectivity were 2.93 mM/h, 77.1% and 97.3%, respectively. The bacterial cells exhibited comparable 5'-regioselectivity to the expensive immobilized enzyme, which could also have environmental and cost advantages.

LbL coated microcapsules for delivering lipid-based drugs

Nowadays, more than 40% of new pharmacologically active compounds exhibit poor water solubility, which requires the development of the new methods for their administration and delivery. One of the most promising approaches for the development of such delivery systems is the use of layer-by-layer assembly technology for encapsulation of the lipid-based drugs. This technique permits the step-wise adsorption of various components as the layer growth is governed by their electrostatic attraction and allows the formation of multilayer shells with nanometer-scale precision. The proposed review surveys the application of layer-by-layer assembly for emulsions, nanoparticles, and capsule-based delivery systems for lipid-based drugs.

Synthesis and in vitro antitubercular activity of some 1-[(4-sub)phenyl]-3-(4-{1-[(pyridine-4-carbonyl)hydrazono]ethyl}phenyl)thiourea

Various isonicotinyl hydrazones were prepared by reacting isonicotinyl hydrazide [INH] with 1-(4-acetylphenyl)-3-[(4-sub)phenyl]thiourea and were tested for their antimycobacterial activity in vitro against Mycobacterium tuberculosis H37Rv and INH-resistant M. tuberculosis using the BACTEC 460 radiometric system. Among the synthesized compounds, 1-(4-fluorophenyl)-3-(4-{1-[(pyridine-4-carbonyl)-hydrazono]ethyl}phenyl)thiourea (4d) was found to be the most potent compound with a minimum inhibitory concentration of 0.49 microM against M. tuberculosis H37Rv and INH-resistant M. tuberculosis. When compared to INH, 4d was found to be 3 and 185 times more active against M. tuberculosis H37Rv and INH-resistant M. tuberculosis, respectively, with a selectivity index of >300.

Synthesis and in vitro and in vivo antimycobacterial activity of isonicotinoyl hydrazones

The purpose of this study was to prepare various isoniazid derivatives by introducing the isoniazid pharmacophore into several molecules and screening for antimycobacterial activity. Ortho-hydroxy acetophenone reacts with isoniazid to form acid hydrazones. The C-Mannich bases of the above acid hydrazones were prepared by reacting them with formaldehyde and various secondary amines. The synthesized compounds were screened against M. tuberculosis H(37)R(v) using the alamar blue susceptibility test. The synthesized compounds inhibit Mycobacterium tuberculosis strain H(37)R(v) with minimum inhibitory concentrations ranging from 0.56 to 4.61 microM. Compound N'-{1-[2-hydroxy-3-(piperazin-1-ylmethyl)phenyl]ethylidene}isonicotinohydrazide 8 was found to be the most active compound with an MIC of 0.56 microM, and was more potent than isoniazid (MIC of 2.04 microM). After 10 days of treatment, compound 8 decreased the bacterial load in murine lung tissue by 3.7-log10 as compared to controls, which was equipotent to isoniazid. The results demonstrate the potential and importance of developing new isoniazid derivatives against mycobacterial infections.

Quantitative structure-metabolism relationships: steric and nonsteric effects in the enzymatic hydrolysis of noncongener carboxylic esters

An attempt to quantitatively describe human blood in vitro hydrolysis data for more than 80 compounds belonging to seven different noncongener series of ester-containing drugs is presented. A parameter not yet explored in pharmaceutical studies, the inaccessible solid angle Omega(h), calculated around different atoms was used as a measure of steric hindrance, and the steric hindrance around the carbonyl sp(2) oxygen (Omega(h)(O=)) proved the most relevant parameter. The obtained final equation, log t(1/2) = -3.805 + 0.172Omega(h)(O=) - 10.146q(C=) + 0.112QLogP, also includes the AM1-calculated charge on the carbonyl carbon (q(C=)) and a calculated log octanol-water partition coefficient (QLogP) as parameters and accounts for 80% of the variability in the log half-lives of 67 compounds. A number of structures are still mispredicted, but the equation agrees very well with a recently proposed mechanism for hydrolysis by carboxylesterases. The model, with a predictive power tested here on three unrelated structures, should be useful in estimating approximate rates of hydrolysis for prodrug or soft drug candidates ahead of their synthesis.

Synthesis and biological evaluation of some phosphate triester derivatives of the anti-cancer drug araC

A number of novel phosphate triester derivatives of the anti-cancer nucleoside analogue araC have been prepared by a rapid 2-step procedure, not necessitating prior sugar protection. Spectroscopic and lipophilicity data have been collected on these compounds. An in vitro assay indicated inhibition of thymidine incorporation by mammalian epithelial cells, by each of these compounds, in the range 3-300 microM. Moreover, the degree of inhibition showed a close correlation to chemical structure; in particular, there was a clear relationship between inhibition of thymidine incorporation and log(P). These results are consistent with cellular penetration by the intact phosphate triesters and intracellular action by an unspecified mechanism. Triethyl phosphate is inactive under the conditions of the test.

Synthesis and antiviral activity of various esters of 9-[(1,3-dihydroxy-2-propoxy)methyl]guanine

The synthesis and in vivo biological activity of a series of mono-O-, di-O-, and N2-acyl derivatives of 9-[(1,3-dihydro-2-propoxy)-methyl]guanine (DHPG) are described.

Synthesis of some 5'-amino-2',5'-dideoxy-5-iodouridine derivatives and their antiviral properties against herpes simplex virus

In an attempt to improve the antiviral efficacy of 5'-amino-2',5'-dideoxy-5-iodouridine (AIdU) the N-acetyl and N,3'-O-diacetyl derivatives were prepared. N-Acetylation of AIdU increased its ability to inhibit the phosphorylation of thymidine by the deoxypyrimidine kinase of herpes simplex virus type 1 (HSV1) while diacetylation had the converse effect. The affinity of the corresponding compounds containing uracil or thymine for virus deoxypyrimidine kinase was also determined. A range of N-acyl-, N-sulphonyl- and N,3'-O-diacyl- derivatives of AIdU were synthesized; enhanced inhibition of deoxypyrimidine kinase by a number of these compounds was observed. The previous observation that 5'-azido-2',5'-dideoxy-5-iodouridine has antiherpetic activity in vivo led us to investigate its 3'-O-acetyl derivative as well as the corresponding compound containing uracil. None of the derivatives described showed antiviral activity in cell culture against HSV1; acylation failed to enhance the potency of AIdU against HSV1 in vivo.

Derivatives of 4-dihydro-4-deoxy-4(R)-amino spectinomycin and their activity against susceptible and resistant Escherichia coli strains

A number of alkyl and acyl derivatives of 4-dihydro-4-deoxy-4(R)-amino spectinomycin were tested against various Escherichia coli strains, possessing different susceptibilities to spectinomycin. The influence of the lipophilicity and the length of the side chain substituents of the derivatives was compared to both minimal inhibitory concentration values and stability to adenyltransferase. Derivatives with a chain length of more than 10 carbon atoms demonstrated a significantly higher activity against all investigated strains, whether susceptible or resistant. The same inhibitory effect was achieved with short-chain aminoacyl derivatives only against susceptible strains. Other short-chain derivatives possessed no advantage to spectinomycin. A 10-fold decrease in the affinity for adenyltransferase was achieved in compounds with a high lipophilicity (log P), i.e., in aliphatic substituted derivatives with a log P greater than 4 and in benzoyl-substituted derivatives with a log P greater than 2. Derivatives with branched alkyl chains and long side chains displayed a different mode of action than spectinomycin. They possessed strong activity against strains with an altered ribosomal binding site and a decreased influence of pH on antimicrobial activity.

Cytotoxic liponucleotide analogs. II. Antitumor activity of CDP-diacylglycerol analogs containing the cytosine arabinoside moiety

Among events limiting the effectiveness of cancer chemotherapy are the general lack of preferential uptake of anticancer drugs by tumor cells and the occurrence of drug resistance. An approach has been undertaken to explore whether or not such events can be favorably altered or circumvented therapeutically by development of a new class of anticancer molecules, cytotoxic liponucleotide analogs. The design of cytotoxic liponucleotide analogs encompasses both biochemical and biophysical aspects of liponucleotide and glycerophospholipid structure and metabolism. Several cytotoxic liponucleotide analogs of cytidine diphosphate diacylglycerol (CDPdiacylglycerol/dCDPdiacylglycerol), containing the 1-beta-D-arabinofuranosyl moiety, were tested for antitumor activity. Multispecies ara-CDPdiacylglycerol (1-beta-D-arabinofuranosylcytosine 5'-diphosphate diacylglycerol), which contains egg lecithin-derived mixed fatty acyl chains, was more active than 1-beta-D-arabinofuranosylcytosine (ara-C), a clinically used anticancer drug, against leukemia L5178Y and P388 ascites cells in mice. At identical single doses (50 mg/kg per day times 4) administered intraperitoneally, ara-CDPdiacylglycerol prolonged the life spans of L5178Y tumor-bearing mice 93%, while ara-C prolonged life by 18%. Ara-CDPdiacylglycerol increased life spans of P388 tumor-bearing mice by 357% at doses of 50 mg/kg per day times 4; the maximum increase with ara-C was 159% (85 mg/kg per day times 4). Against a P388 ara-C-resistant cell line (P/Ara-C, kinase deficient) in mice, ara-CDPdiacylglycerol prolonged survival times by 34% at a dose of 50 mg/kg per day times 4 and by 55% at 75 mg/kg per day times 4; the drug was not active against two other ara-C-resistant murine leukemia mutants (CA 55, CA5b). With cell line-derived human colon carcinoma HCT-15 grown in mice immunosuppressed with anti-thymocyte serum, ara-CDPdiacylglycerol at a single daily dose of 50 mg/kg per day times 4 significantly reduced tumor weights to 21% of the controls; the same dose schedule of ara-C caused no observable reduction of tumor weights. Results of these preliminary antitumor evaluations indicate that cytotoxic liponucleotide analogs should be investigated further to determine their potential as antineoplastic molecules.

Effects of different buffer species on partition coefficients of drugs used in quantitative structure-activity relationships

A study was conducted in which the same organic solvent, 1-octanol, and different buffer systems were used to obtain intercorrelations among log Pcorr values given by log P (octanol-water) = a log P (octanol-buffer) + b, where a and b are different constants for the different systems used. The range of a was 0.418-1.156 and that of b was -1.962-1.176 for the four buffer systems examined. Only with neutral drugs was the slope (a) close to 1.0 and the intercept (b) close to 0.0 for the three buffer systems studied. For acidic drugs, only 1-octanol-phosphate buffer gave a 1:1 correlation with 1-octanol-water partition coefficients. Acetate and bicarbonate buffer systems gave different correlations. For basic drugs, none of the three systems examined gave a 1:1 correlation with 1-octanol-water partition coefficients.

Hydrolysis of an orally active platelet inhibitory prostanoid amide in the plasma of several species

The prostanoid 3-oxa-4,5,6-trinor-3,7-inter-m-phenylene-PGE1-amide (OI-PGE1-amide) has a prolonged duration of oral platelet aggregation inhibitory activity when compared to the parent free acid (OI-PGE1) in the rat. When incubated in rat plasma at 1 microgram/ml for 30 seconds prior to addition of ADP, OI-PGE1-amide inhibits in vitro rat platelet aggregation approximately 50%. OI-PGE1 inhibits at 1 ng/ml. Inhibition of platelet aggregation by plasma incubated with OI-PGE1-amide (1 microgram/ml) increases with time and the rate of this increase differs with species. Incubation of OI-PGE1 in plasma does not result in an increase of platelet inhibitory activity with time. The increase of platelet inhibitory activity was assumed to indicate hydrolysis of OI-PGE1-amide to the more active OI-PGE1. A compound, different from OI-PGE1-amide, was isolated by an ion exchange/silica gel separation sequence from an incubation of OI-PGE1-amide in rat plasma. It had potent platelet aggregation inhibitory activity. This material was shown to be OI-PGE1 by thin-layer chromatography, gas chromatography and mass spectral analysis. Studies with [3H]-OI-PGE1-amide confirmed the formation of OI-PGE1 in plasma incubations. Amide hydrolytic activity was significantly different between species, the rank order being: rat greater than guine pig greater than monkey = human greater than dog. This relationship corresponded with that determined by measuring the increase in platelet inhibitory activity with time in plasma incubations of OI-PGE1-amide reported above. Present data indicate that (a) OI-PGE1-amide is hydrolyzed to the parent acid by plasma enzymes of several species and (b) hydrolytic activity of plasma varies widely between species.