A 13-Week Subchronic Intravaginal Toxicity Study of the Novel Broad-Spectrum Anti-HIV and Spermicidal Agent,N-[2-(1-cyclohexenyl)ethyl]-N'-[2-(5-bromopyridyl)]-thiourea (PHI-346) in Mice

Abstract

The nonnucleoside inhibitor (NNI) of HIV-1 reverse transcriptase, PHI-346 (N -[2-(1-cyclohexenyl)ethyl]- N'-[2-(5-bromopyridyl)]-thiourea), is a dual-function spermicidal agent with potent anti-HIV activity against drug-sensitive as well as drug-resistant HIV-1 strains with genotypic and phenotypic NNI resistance. PHI-346 was formulated via a lipophilic gel-microemulsion for intravaginal use as a potential dual-function microbicide. To evaluate the toxicity potential of short-term intravaginal exposure to PHI-346, groups of 15 female B₆C₃F₁ and CD-1 mice were exposed intravaginally to a gel-microemulsion containing 0, 0.5, 1.0, or 2.0% PHI-346, 5 days per week for 13 consecutive weeks. On a molar basis, these concentrations of PHI-346 are 350 to 1,400-times higher than its spermicidal EC₅₀ and nearly 5 × 10⁶ to 2 × 10⁷ times higher than its in vitro anti-HIV IC₅₀. After 13 weeks of intravaginal treatment, B₆C₃F₁ mice were evaluated for survival, body weight gain, absolute and relative organ weights. Blood was analyzed for hematology and clinical chemistry profiles. Microscopic examination was performed on hematoxylin and eosin-stained tissue sections from each study animal. Placebo control and PHI-346 dosed female CD-1 mice were mated with untreated males in order to evaluate if PHI-346 has any deleterious effects on the reproductive performance. There were no treatment-related mortalities. Mean body weight gain during the dosing period was not reduced by PHI-346 treatment. The hemogram or blood chemistry profiles revealed lack of systemic toxicity following daily intravaginal instillation of PHI-346 for 13 weeks. No clinically significant changes in absolute and relative organ weights were noted in PHI-346 dose groups. Extensive histopathological examination of tissues revealed no treatment-related abnormalities in any of the three PHI-346 dose groups. Repeated intravaginal exposure of CD-1 mice to increasing concentrations of PHI-346 for 13 weeks had no adverse effect on their subsequent reproductive capability, perinatal outcome, growth, and development of offspring. Collectively, these findings demonstrate that repetitive intravaginal administration of PHI-346 at concentrations as high as 1,400-times its spermicidal EC₅₀ and 2 ×10⁷ times its in vitro anti-HIV IC₅₀ was not associated with local or systemic toxicity and did not adversely affect the reproductive performance in mice. PHI-346 may be useful as an active ingredient of a safe vaginal microbicide for prevention of the sexual transmission of multidrug-resistant HIV-1.

Keywords

13-week intravaginal nonnucleoside inhibitor HIV/AIDS microbicide spermicide.

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