According to the World Health Organization, 4.8 million people were newly infected with HIV in 2003 bringing the total number to some 37.8 million people who are living with HIV. Since the first cases of AIDS were identified in 1981, over 20 million have died by this disease. In spite of remarkable medical advances, HIV-1 infections continue to increase. Our goal is to identify drugs against a novel and unexploited target for the treatment of AIDS. The human immunodeficiency virus type 1 (HIV-1), the causative agent of AIDS, is a complex retrovirus that encodes six regulatory proteins, including Vif that is essential for viral replication in vivo. Since there are no known cellular homologs of HIV-1 Vif, this protein represents an extremely attractive, yet unrealized, target for antiviral intervention. Therefore, we propose to identify lead inhibitors of HIV-1 Vif function. Our specific aims are as follows: (1) Identification of Vif inhibitors. Experiments are proposed to develop highly robust and reproducible fluorescence-based assays to monitor HIV-1 Vif function in cellular environment. High throughput screening assays will be employed to identify small molecule inhibitors that can target Vif-APOBEC3G interactions. (2) Structure activity relation studies and validation of lead compounds. Experiments are proposed to characterize the efficacy and specificity of the compounds identified as Vif inhibitors from initial screening experiments. Selected compounds will be tested for their anti-HIV Vif activities in both permissive and non-permissive cells (Project #2). Antiviral activities of selected Vif antagonists against clinical HIV-1 isolates will be analyzed and the safety and stability profiles of these compounds will be determined (core B). Consequences of Vif antagonist's activities in chronically infected macaques will be investigated in project #3. As a support to pharmacology studies (project #3 and core B), we will measure the drug concentrations in plasma of drug treated animals. Based on the activity, stability, and toxicity data (projects 2 and 3, and core B), new compounds will be synthesized to improve the potency and selectivity of lead structures. (3) Mechanism(s) of Vif inhibition. Experiments will be performed to understand the mechanism of Vif inhibitors at molecular level.