THE MOLECULAR BASIS OF HIV-1 PROTEASE DRUG RESISTANCE. Paul Ala, E. Huston, R. DeLoskey, J. Duke, B. Korant, C.-H. Chang, et al. The DuPont Merck Pharmaceutical Co., Wilmington, DE 19880

HIV-1 protease processes the gag and gag-pol polyproteins into mature structural and replicative proteins. Incomplete processing caused by disrupting the normal function of the protease results in the formation of immature (non-infectious) viral particles. Several potent synthetic compounds against the wild type enzyme currently exist, however, clinical studies have revealed the emergence of drug resistance during the course of treatment. Selective pressures created by treating patients with these inhibitors have caused the emergence of viruses that possess mutations in several regions of the protease sequence, most importantly in the substrate binding pocket and the flaps. We believe that all protease inhibitors will, to some degree, select for viruses which possess mutant proteases that will be able to process viral polyprotein precursors but exhibit reduced binding affinities for inhibitors. Therefore, we have attempted to identify the structural features of HIV-1 protease mutants that confer drug resistance and utilize this information to improve drug efficacy. We have crystallized wild type and several mutant HIV-1 proteases (V82I, V82F, I84V and V82F/I84V) complexed with cyclic urea inhibitors, DMP323 and DMP450. The structures indicate that a loss or gain of hydrophobic interactions between mutant proteases and inhibitors is in part responsible for altering the binding affinities for inhibitors. A detailed understanding of the structural changes caused by mutations, within the protease sequence, will be essential when designing new compounds to combat native and mutant HIV-1 proteases in future treatments.