A 13-week subchronic intravaginal toxicity study of pokeweed antiviral protein in mice

Pokeweed antiviral protein (PAP), a 29-kDa plant-derived protein isolated from Phytolacca americana, is a broad-spectrum antiviral agent. PAP shows unique clinical potential to become the active ingredient of a non-spermicidal microbicide because of its potent in vivo anti-HIV activity, non-interference with in vivo sperm functions, and lack of cytotoxicity to genital tract epithelial cells. Over 13 weeks the subchronic and reproductive toxicity potential of an intravaginally administered gel formulation of PAP was studied in mice to support its further development as a vaginal microbicide. Female B6C3F1 and CD-1 mice in subgroups of 20, were exposed intravaginally to a gel formulation containing 0, 0.025, 0.05, or 0.1% PAP, 5 days/week for 13 consecutive weeks. On a molar basis, these concentrations are 500- to 2000-times higher than the in vitro anti-HIV IC50 value. After 13 weeks of intravaginal treatment, B6C3F1 mice were evaluated for survival, body weight gain, and 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 PAP-dosed female CD-1 mice were mated with untreated males in order to evaluate if PAP has any deleterious effects on reproductive performance. There were no treatment-related mortalities. Mean body weight gain was not reduced by PAP treatment during the dosing period. The hemogram and blood chemistry profiles revealed lack of systemic toxicity following daily intravaginal instillation of PAP for 13 weeks. No clinically significant changes in absolute and relative organ weights were noted in the PAP dose groups. Extensive histopathological examination of tissues showed no increase in treatment-related microscopic lesions in any of the three PAP dose groups. Repeated intravaginal exposure of CD-1 mice to increasing concentrations of PAP for 13 weeks showed no adverse effect on their subsequent reproductive capability (100% fertile), neonatal survival (>90%) or pup development. Collectively, these findings demonstrate that repetitive intravaginal administration of PAP at concentrations as high as 2000 times its in vitro anti-HIV IC50 value was not associated with local or systemic toxicity and did not adversely affect the reproductive performance of mice. PAP may be useful as an active ingredient of a safe vaginal microbicide for prevention of the sexual transmission of viruses, particularly of HIV-1.