Antiviral activity and resistance profile of phosphazid--a novel prodrug of AZT

[The experience in the application of nikavir in the schemes of perinatal chemoprophylactics of HIV infection: evaluation of the immunological and virusological effectiveness.]

OBJECTIVES

The goal of this work was to study the immunological and virological efficacy of the domestic antiretroviral drug nicavir (at the optimal dose, as proven by previous clinical studies) with lamivudine, in comparison with other drugs of the group of nucleoside reverse transcriptase inhibitors in combination with kaletra in perinatal HIV chemoprophylaxis regimens.

METHODS

658 pregnant women aged 16-39 years and children born to them were examined. The first group (281 people) and the third group (66 people) received the nicavir (manufactured by AZT PHARMA KB LLC) with lamivudine in combination with calyx; the second (281 people) and the fourth (30 people) of the comparison group, stag and zidovudine, respectively, with lamivudine in combination with calyx. The effectiveness of CP was assessed from the increase in the number of CD4 lymphocytes, reduction of the viral load, and the number of children born without HIV DNA in the blood.

RESULTS

Against the backdrop of the therapy, the viral load below the detectable level and the positive dynamics of CD4 lymphocytes were registered in all examined women prior to childbirth. When applying the scheme of niacavir + lamivudine + kaletra, a more rapid decrease in the level of BH, most pronounced by week 4 of therapy, was found, as compared with the rate of decline of the same index in pregnant comparison groups.

CONCLUSIONS

The obtained results allow us to consider ART with the inclusion of nicavir effective and recommend its priority use in perinatal prevention of mother-to-child transmission of HIV.

5'-aminocarbonyl phosphonates as new zidovudine depot forms: antiviral properties, intracellular transformations, and pharmacokinetic parameters

The main disadvantages of 3'-azido-3'-deoxythymidine (zidovudine, AZT), the most common anti-HIV drug, are toxicity and a short half-life in the organism. The introduction of an H-phosphonate group into the AZT 5' position resulted in significant improvement of its therapeutic properties and allowed a new anti-HIV drug, Nikavir (AZT H-phosphonate). In this work, we described a new group of AZT derivatives, namely, AZT 5'-aminocarbonylphosphonates. The synthesized compounds displayed antiviral properties in cell cultures infected with HIV-1 and the capacity to release the active nucleoside in animals (rabbits and dogs) in a dose-dependent manner. The compounds were less toxic in MT-4 and HL-60 cell cultures and experimental animals compared with AZT. Major metabolites found in MT-4 cells after their incubation with AZT 5'-aminocarbonylphosphonate 1 were AZT and AZT 5'-phosphate (25 and 55%, respectively). Among the tested compounds, phosphonate 1 was the most effective AZT donor, and its longest t(1/2) and T(max) values in the line phosphonate 1--AZT H-phosphonate--AZT imply that compound 1 is an extended depot form of AZT. Although bioavailability of AZT after oral administration of phosphonate 1 was lower than those of AZT H-phosphonate and AZT (8 against 14 and 49%), we expect that this reduction would not cause essential decrease of antiviral activity but noticeably decrease toxicity as a result of gradual accumulation of AZT in blood and the absence of sharp difference between C(max) and C(min). Such a combination of properties makes the compounds of this group promising for further studies as extended-release forms of AZT.

New N4-Hydroxycytidine Derivatives: Synthesis and Antiviral Activity

Two series of N4-hydroxycytidine derivatives were synthesized and evaluated as potential antipox virus agents. Acylation of N4-hydroxycytidine (1) with an excess of acyl chloride or imidazolide yielded the corresponding N4-(acyloxy) derivatives. 5'-Phosphonates of 1 were prepared by the reaction of cytidine 5'-phosphonates with aqueous hydroxylamine hydrochloride (pH 6.0). Nucleoside 1 and its N4-(acyloxy) derivatives inhibited replication of pox viruses in cell cultures, N4-(pivaloyloxy)- and N4-(benzoyloxy)cytidines being the most potent. The synthesized 5'-phosphonates were more cytotoxic than the parent nucleoside.

Novel approach to nucleoside-5'-(1-hydroxymethylene-1, 1-bisphosphonates): synthesis of new AZT analogues

An efficient synthetic method of nucleoside-5'-(1-hydroxymethylene-1,1-bisphosphonates) is reported here. The procedure was optimized with 3'-protected thymidine and then applied to synthesis of new AZT analogues.

Intracellular metabolism and pharmacokinetics of 5'-hydrogenphosphonate of 3'-azido-2',3'-dideoxythymidine, a prodrug of 3'-azido-2',3'-dideoxythymidine

5'-Hydrogenphosphonate of 3'-azido-2',3'-dideoxythymidine (HpAZT), a novel anti-HIV drug approved for the treatment of HIV-infected patients in Russia, displays some clinical advantages over azidothymidine (AZT). Metabolism in the HL-60 cell culture and pharmacokinetics in mice of [6-3H]-HpAZT (in comparison with [6-3H-AZT) were studied to elucidate the metabolic basis of its lower clinical toxicity. Accumulation of [6-3H]-HpAZT-derived products in cells with time, distribution of its radioactive metabolites among blood and different mouse organs and dependence of drug accumulation on the route of administration were investigated. The rate of accumulation of [3H]-HpAZT metabolites in cells was slower than the rate of accumulation of [3H]-AZT metabolites. [3H]-AZTMP was the dominating metabolite at all time points, achieving the level of 15 +/- 3 pmol/10(6) cells after 25 h incubation. After oral or intravenous administrations of [3H]-HpAZT, the (radioactive) metabolites were rapidly distributed among blood, stomach, intestine and liver and were not found in brain, muscles and spleen. [3H]-HpAZT underwent rapid and extensive metabolism, [3H]-AZT being the dominating product at all time points. Administration of 180 nmol of [3H]-HpAZT resulted in an AZT concentration in blood of 1-3 microM after 5 min, which remained practically constant during the next 25 min and did not depend on the route of administration.

Uncharged AZT and D4T derivatives of phosphonoformic and phosphonoacetic acids as anti-HIV pronucleosides

Two series of new lipophilic phosphonoformate and phosphonoacetate derivatives of AZT and d4T were synthesized and evaluated as anti-HIV agents. The efficacy of some of the synthesized compounds in cell cultures infected with HIV-1 was higher than that of the parent nucleosides and only slightly correlated to their stability in the phosphate buffer and human blood serum. The synthesized phosphonates are most probably prodrug forms of the corresponding nucleosides.

In vitro study of resistance-associated genotypic mutations to nucleoside analogs

In spite of a rather long period of investigations, the problem of HIV drug resistance remains unsolved, and more that, at present HIV-1 mutants resistant to all known nucleoside inhibitors being used in clinical therapy against the human immunodeficiency syndrome are discovered. In this study we selected HIV-1 mutants resistant to the nucleoside inhibitors of HIV reverse transcriptase (NRTI): 3'-azido-2',3'-dideoxythymidine (AZT), 5'-phosphit 3'-azido-2',3'-dideoxythymidine (ph-AZT), dideoxyinosine (ddI) and didehydrodeoxythymidine (d4T). Selection of resistant mutants was carried out by gradually increasing of drug concentration in the culture medium during propagation of the HIV-1EVK on fresh MT-4 cells. Phenotypic resistance was defined as an increase in ID50 of 160-fold for AZT, 8 for ph-AZT, 10 for ddI, 7 for d4T. In comparison studies it was determined that the viral resistance to these drugs was appeared variously in a similar conditions and duration of selection. The nucleotide sequences of the RT region of the HIV-1 variants were compared with the HIV-1EVK from "0" passage. For some of selected HIV-1 mutants NRTI resistance mutations were detected. Selected AZT resistant variants contained amino acid substitutions in positions D67A and K70R. Our studies was not revealed substitution at position 75 for ph-AZT resistant variants, whereas substitution at position L214F have been observed in both experiments using AZT and ph-AZT. Selected d4T resistant mutants contained amino acid substitutions in positions N54D and P52R. Selected ddI resistant mutants contained only one amino acid substitution in position P143S. Collection of drug-resistant mutants should prove to be a convenient tool for rapid investigations a new antiretroviral agents on cross drug-resistance.

Synthesis, anti-HIV activity, and stability studies of 5'-phosphorofluoridate derivatives of AZT

The synthesis, in vitro anti-HIV activity and stability studies of the 5'-fluorophosphate derivative of 3'-azido-3'-deoxythymidine (AZT) are reported. The results support the hypothesis that this phosphorylated entity exerts its biological effect via the delivery of the corresponding 5'-mononucleotide through an enzymatic process. However, the antiviral evaluation in thymidine kinase-deficient CEM cells as well as the stability studies in culture medium and cell extract showed that this bioconversion is not specific to the intracellular medium. Attempts to improve the biological activity of mononucleoside 5'-fluorophosphates by the use of the S-pivaloyl-2-thioethyl (tBuSATE) group as biolabile phosphate protection are reported.

Anti-HIV activity of novel phosphonate derivatives of AZT, d4T, and ddA

Anti-HIV activity and cytotoxicity were tested for novel phosphonate derivatives of AZT, d4T and ddA. For d4T phosphonate derivatives the most active was 2',3'-Dideoxy-2',3'-didehydrothymidine 5'-isopropylphosphite and among the AZT phosphonate derivatives highest activity was shown by 2',3'-Dideoxy-3'-azidothymidine 5'-cyclohexylphosphite.

Development of novel nucleoside analogues for use against drug resistant strains of HIV-1

Nucleoside analogue inhibitors of the reverse transcriptase (RT) enzyme of HIV-1 were the first class of compounds to be used in anti-HIV-1 therapy and are a cornerstone in highly active antiretroviral therapy. Despite the number of inhibitors of HIV-1 RT available for clinical use at the present time and the effectiveness of these compounds in combination regimens, long-term exposure of patients to these drugs often results in the development of viral resistance or long-term toxicity. For this reason, efforts to identify new agents with activity against drug-resistant strains of HIV-1 and with a toxicity profile that allows for individual patient tolerance of the drugs are still warranted.

P-(alkyl)-nucleoside 5'-hydrogenphosphonates as depot forms of antiviral nucleotide analogues

P-(Alkyl)esters of AZT 5'-hydrogenphosphonate were synthesized and their stabilities in the phosphate buffer and human serum were evaluated. The esters bearing residues of primary and secondary alcohols were degraded to give AZT, whereas those containing tertiary alkyl groups yielded AZT 5'-hydrogenphosphonate. The corresponding derivatives of d2A and d4T showed the same properties.