Peter Samuel

In Vivo Antiretroviral Activity of Stampidine in Chronically Feline Immunodeficiency Virus-Infected Cats

ABSTRACT Here we report the antiretroviral activity of the experimental nucleoside reverse transcriptase inhibitor (NRTI) compound stampidine in cats chronically infected with feline immunodeficiency virus (FIV). Notably, a single oral bolus dose of 50 or 100 mg of stampidine per kg resulted in a transient ≥1-log decrease in the FIV load of circulating peripheral blood mononuclear cells in five of six FIV-infected cats and no side effects. A 4-week stampidine treatment course with twice-daily administration of hard gelatin capsules containing 25 to 100 mg of stampidine per kg was also very well tolerated by cats at cumulative dose levels as high as 8.4 g/kg and exhibited a dose-dependent antiretroviral effect. One of three cats treated at the 25-mg/kg dose level, three of three cats treated at the 50-mg/kg dose level, and three of three cats treated at the 100-mg/kg dose level (but none of three control cats treated with placebo pills) showed a therapeutic response, as evidenced by a ≥1-log reduction in the FIV load in peripheral blood mononuclear cells within 2 weeks. The previously documented in vitro and in vivo antiretroviral activity of stampidine against primary clinical human immunodeficiency virus type 1 isolates with genotypic and/or phenotypic NRTI resistance, together with its favorable animal toxicity profile, pharmacokinetics, and in vivo antiretroviral activity in FIV-infected cats, warrants further development of this promising new NRTI compound.

PHI-443: A Novel Noncontraceptive Broad-Spectrum Anti-Human Immunodeficiency Virus Microbicide

Abstract PHI-443 (N′-[2-(2-thiophene)ethyl]-N′-[2-(5-bromopyridyl)] thiourea) is a rationally designed novel thiophene thiourea nonnucleoside reverse transcriptase inhibitor (NNRTI) with potent anti-HIV activity against the wild-type and drug-resistant primary clinical human immunodeficiency virus (HIV-1) isolates. This study examined the potential utility of PHI-443 as a nonspermicidal microbicide for prevention of sexual transmission of HIV. Our goal in this study was to test the effects of PHI-443 on in vivo sperm functions under conditions shown to inactivate viruses in human cells. PHI-443 completely prevented the vaginal transmission of a genotypically and phenotypically drug-resistant HIV-1 isolate in the humanized severe combined immunodeficient (Hu-SCID) mouse model of sexually transmitted AIDS. Exposure of human sperm to PHI-443 at doses 30 000 times higher than those that yield effective concentrations against the AIDS virus had no adverse effect on sperm motility, kinematics, cervical mucus penetrability, or the viability of vaginal and cervical epithelial cells. Exposure of rabbit semen to PHI-443 either ex vivo or in vivo had no adverse impact on in vivo fertilizing ability in the rabbit model. Reproductive indices (i.e., pregnancy rate, embryo implantation, and preimplantation losses) were not affected by pretreatment of rabbit semen with PHI-443. Likewise, intravaginal application of 2% PHI-443 via a self-emulsifying gel at the time of artificial insemination resulted in healthy offspring with no apparent peri- or postnatal repercussions. Repeated intravaginal administration of 0.5%– 2% PHI-443 gel was found to be safe in rabbits and lacked systemic absorption. PHI-443 has clinical potential as a prophylactic broad-spectrum anti-HIV microbicide without contraceptive activity.

Effects of Aryl Substituents on the Anti-HIV Activity of the Arylphosphoramidate Derivatives of Stavudine

We compared the anti-HIV activity of 13 phenyl phosphate derivatives of stavudine (2′,3′-didehydro-2′,3′-dideoxythymidine/d4T) by examining their ability to inhibit HIV-1 replication in human peripheral blood mononuclear cells. Our results show that the introduction of electron-withdrawing substituents enhances the activity of these phosphoramidate derivatives. The rate of chemical hydrolysis under alkaline conditions (but not the lipophilicity) predicted the potency of the compounds.

Conceival, a novel noncontraceptive vaginal vehicle for lipophilic microbicides

The objective of this study was to develop a nontoxic and noncontraceptive vaginal drug delivery vehicle for lipophilic anti-human immunodeficiency virus (HIV) microbicides. Three representative poorly water-soluble novel broad-spectrum anti-HIV microbicides, PHI-113, PHI-346, and PHI-443, were evaluated in 11 different solvent systems. Based on their solubility profiles, a novel non-spermicidal self-emulsifying gel (viz Conceival) composed of pharmaceutical excipients, sorbitol, polyethylene glycol 400, polysorbate 80, microcrystalline cellulose, xanthan gum, and water was optimized. Conceival enhanced the solubility of these poorly water-soluble (<0.001 mg/mL) anti-HIV drugs by at least 150- to 270-fold. Conceival was evaluated in vivo in the New Zealand white rabbit model for the preservation of sperm function based on pregnancy outcome and the potential for vaginal irritation following single and multiple intravaginal applications, respectively. Conceival administered intravaginally immediately prior to artificial insemination with semen had no adverse effects on subsequent reproductive performance, neonatal survival, or pup development when compared with untreated control group. Histologic evaluation of vaginal tissues of rabbits exposed intravaginally to Conceival for 14 consecutive days revealed lack of epithelial, submucosal, and vascular changes at the gel application site (total irritation score <3 out of a possible 16). These findings indicate that Conceival has potential to become a clinically useful, safe noncontraceptive vaginal vehicle for lipophilic microbicides.

Development and Evaluation of a Thermoreversible Ovule Formulation of Stampidine, a Novel Nonspermicidal Broad-Spectrum Anti-Human Immunodeficiency Virus Microbicide

Abstract Stampidine [2′,3′-didehydro-2′,3′-dideoxythymidine 5′-[p-bromophenyl methoxyalaninyl phosphate], a prodrug of stavudine (STV/d4T) with improved anti-HIV activity, is undergoing development as a novel nonspermicidal microbicide. Here, we report the stability of stampidine as a function of pH, preparation of a novel thermoreversible ovule formulation for mucosal delivery, its dissolution profile in synthetic vaginal fluid, and its mucosal toxicity potential as well as systemic absorption in the rabbit model. Stampidine was most stable under acidic conditions. Stampidine was solubilized in a thermoreversible ovule formulation composed of polyethylene glycol 400, polyethylene glycol fatty acid esters, and polysorbate 80. Does were exposed intravaginally for 14 days to an ovule formulation with and without 0.5%, 1%, or 2% stampidine corresponding to 1 × 107- to 4 × 107-fold higher than its in vitro anti-HIV IC50 value. Vaginal tissues harvested on Day 15 were evaluated for mucosal toxicity and cellular inflammation. Additionally, does were exposed intravaginally to stampidine, and plasma collected at various time points was assayed by analytical HPLC for the prodrug and its bioactive metabolites. Stampidine did not cause mucosal inflammation. The vaginal irritation scores for 0.5–2% stampidine were within the acceptable range for clinical trials. The prodrug and its major metabolites were undetectable in the blood plasma. The marked stability of stampidine at acidic pH, its rapid spreadability, together with its lack of mucosal toxicity or systemic absorption of stampidine via a thermoreversible ovule may provide the foundation for its clinical development as an easy-to-use, safe, and effective broad-spectrum anti-HIV microbicide without contraceptive activity.

In vivo evaluation of a gel formulation of stampidine, a novel nonspermicidal broad-spectrum anti-HIV microbicide

IntroductionStampidine (2′,3′-didehydro-2′,3′-dideoxythymidine 5′-[p-bromophenyl methoxyalaninyl phosphate]), a novel aryl phosphate derivative of stavudine (STV/d4T), is a potent, broad-spectrum anti-HIV agent with potential as a new class of nonspermicidal microbicide. As part of an effort to develop an acceptable formulation for the clinical use of stampidine as a microbicide, we developed a vaginal gel formulation of stampidine and evaluated its potential to cause mucosal toxicity in the New Zealand white rabbit vaginal irritation model.MethodsStampidine was solubilized in a gel formulation composed of microcrystalline cellulose, xanthan gum, macrogol (polyethylene glycol [PEG]) 400, sorbitol, and polysorbate 80. Rabbits in groups of four were exposed intravaginally to a gel with 0.5, 1, or 2% stampidine or no active drug for 14 consecutive days. The rabbits were euthanized on day 15 and their vaginal tissues were evaluated for histologic evidence of mucosal toxicity and immunohistochemical evidence of cellular inflammation or hyperplasia. Additionally, rabbits in groups of three were exposed intravaginally to a 2% stampidine gel, and plasma samples collected at various timepoints were assayed for stampidine and its major metabolites, alaninyl-stavudine-monophosphate and stavudine by analytical high performance liquid chromatography (HPLC).ResultsWith application of 0.5–2.0% stampidine, only minimal-to-mild vaginal irritation was observed, which is within the acceptable range for clinical trials (total score <4 out of a possible 16). Repeated intravaginal treatment with stampidine gel caused no inflammation or hyperplasia in the vaginal epithelium and submucosa. Stampidine and its major metabolites were not detectable in the plasma of rabbits given 2% stampidine-containing gel intravaginally.ConclusionsThe favorable toxicity profile of intravaginally administered stampidine-containing gel may provide the foundation for its clinical development as a safe and effective broad-spectrum anti-HIV microbicide without contraceptive properties.

Synthesis and Anti-HIV Activity of Carbamates of Antiviral Agent Stavudine

An efficient synthesis of carbamate analogues of the NRTI compound stavudine, has been achieved in five steps starting from commercially available thymidine. The synthesis involves conversion of thymidine into stavudine followed by condensation with carbaimidazole derivative obtained from various aromatic and heterocyclic amines in dimethylformamide solvent. The analogues thus obtained were further purified by crystallization to furnish analytically pure products. Examination of biological activity of these carbamate derivatives of stavudine showed that they inhibited HIV replication only at micro-molar concentrations.