Background:  Enzymes of the pol gene of HIV are important targets for the discovery of anti-HIV therapeutic agents. While reverse transcriptase and protease have been successfully targeted with a number of efficacious therapeutic agents, drug discovery efforts on HIV integrase have only recently produced favorable phase III clinical efficacy. Because toxicity and resistance are commonly encountered problems for all classes of anti-HIV drugs, the discovery of new classes of integrase inhibitors remains a significant scientific challenge. 

Methods:  Stability studies of INH-I001 in human liver cytosol and microsome were monitored by high performance liquid chromatography with retention time, ultraviolet, mass spectrometry, and nuclear magnetic resonance data used for identification. Cytochrome P450 data were obtained for the major human CYP isoforms. Pharmacokinetic data were determined from oral and intrvenous dosing in rodents.

Results:  The compound INH-I001, which inhibits both 3'-processing and strand transfer steps of HIV integrase, exhibits potent in vitro anti-HIV activity (IC₅₀ < 20 to 50 nM) against HIV-1 isolates in peripheral blood mononuclear cells (PBMC) with antiviral efficacy data (TI = CC₅₀/IC₅₀) of >10,000 (HIV-1_NL4-3). Cell viability data showed mild cellular cytotoxicity (CC₅₀ >200 μM). Carbonyl reduction and side-chain cleavage resulted in 2 metabolites, produced in cytosol. In liver microsomes, the stability of INH-I001 was as follows:  74% (1 hour), 58% (2 hours), 49% (3 hours). INH-I001 was not an inhibitor of CYP 1A1/2, 2A6, 2C19, 2D6, 2E1, and 3A4. For CYP 2C8 and 2C9, the IC₅₀ values were >400 µM. INH-I001 does not appear to be oxidized by CYP450 enzymes. Data from Caco-2 studies predicted moderately high oral absorption. Pharmacokinetic studies in rats at a 5 mg/kg oral dose gave the following results: >80% bioavailability; C_max of 2.3 mg/L^–kg; clearance of 8.4 mL/min^–kg; and half-life (t_1/2) of 4.4 hours.  

Conclusions:  The favorable in vitro anti-HIV activity profile of INH-I001—together with its low toxicity, microsome stability, P450 data, and favorable pharmacokinetics—suggest that it has potential for further preclinical studies and development as an anti-HIV agent.