We have discovered and developed a novel anti-HIV chemotype, the 2-mercaptobenzamide thioesters, and have synthesized a large library of active compounds. They target the highly conserved zinc finger loops of the nucleocapsid protein, NCp7, that display structural features shared among essentially all retroviruses. A battery of in vitro, biological assays has been completed on several selected compounds. Two thioesters, that are relatively stable and also have good in vitro anti-HIV-1 activity and low cellular toxicity, show promising potential for development as HIV drugs. These are among the most potent S-acyl 2-mercaptobenzamide compounds that we have studied so far. They have low micromolar virucidal activity, inhibit HIV-1 infection in peripheral blood mononuclear cells (PBMC) and inhibit cell-to-cell transmission of HIV-1 as well as target early steps in reverse transcription. The virucidal activity and the inhibition of cell-to-cell transmission suggest that these compounds could be optimal for topical microbicide applications. Our in vivo studies in the mouse model strongly support a continued investigation of these compounds in the treatment of HIV infection. We have, therefore, initiated testing their antiviral efficacy in a non-human primate model against the highly related simian immunodeficiency virus (SIV). This work is required before consideration is given to S-acyl 2-mercaptobenzamide derivatives as systemic antiretroviral therapeutic in HIV-infected patients. The Primate Facility for Infectious Disease Research at the University of Pittsburgh is a state-of-the-art facility having a major interest in vaccine and pathogenicity studies using the non-human primate/SIV model. These studies have been done primarily in the rhesus macaque. However, since increased demand has escalated the costs of rhesus macaques, we have begun to investigate alternative, but related, breeds of monkeys for our SIV work. Accordingly, we have selected cynomolgus monkeys, a more inexpensive yet highly relevant model for SIV vaccination and therapy studies. We have purchased 8 cynomolgus monkeys, each of which was infected by intrarectal inoculation with a biological isolate of simian immunodeficiency virus called Delta/B670. The therapy consists of a constant delivery for 28 days of a potent the S-acyl 2-mercaptobenzamide derivative. This compound is being delivered at a concentration of 2 mg/kg/day by means of an osmotic pump placed subcutaneously between the shoulder blades. The course of treatment is currently ongoing, and monkeys have received the therapy for 28 days and are being followed for up to 70 days post inoculation. Viral loads have been determined initially to detect antiviral effect and anti-infectivity assays will be performed from frozen cells and serum at a later time. Serum chemistries and other clinical parameters are being measured to determine any toxic effects of the drug. Preliminary data indicate a reduction in the viral load approaching several orders of magnitude. These studies will complete the first phase of preclinical evaluation of these novel and promising zinc finger inhibitors, and will open the way for more in-depth preclinical evaluations in the coming year.
