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Session 75 Poster Session Resistance to Antiretroviral Chemotherapeutic Agents Session Time: 4:30-6:30 pm Room 4E-F

563-T. Molecular Mechanism of I50V, I54L, and I54M Resistance to Amprenavir and Other HIV-1 Protease Inhibitors R. Xu, W. Andrews, A. Spaltenstein, D. Danger, W. Dallas, L. Carter, M. Hanlon, L. Wright, and E. Furfine* GlaxoSmithKline, Res. Triangle Park, NC Background: The mutation I50V confers resistance to APV and minimal resistance to other clinically utilized HIVPIs. Similarly I54L and I54M confer resistance to APV in vivo, but this pathway is observed less frequently than I50V. We studied the molecular mechanism of I50V, I54L, and I54M virus resistance to amprenavir (APV) and minimal cross-resistance to nelfinavir (NFV) and indinavir (IDV). Methods: We determined the Ki values and X-ray structures for WT- and I50V-protease bound to APV, NFV, IDV, and for I54L and I54M bound to APV. Results: I50V-protease has increased KI values for APV, NFV, and IDV, compared to WT enzyme (80-, 10-, 15-fold, respectively). The decreased affinity to I50V protease correlates to I50V relative viral-resistance to these inhibitors. I50V resistance to HIVPIs is defined by the conformation of the P81 residue in WT enzyme inhibitor complexes. The P81 residue conformation in WT is defined by the conformation of I50 in WT, which is in turn defined by the structure of the respective inhibitor bound. In this model, the I50V protease the P81 residue and loop condenses around NFV or IDV to create compensatory interactions for those lost upon the changing I50 to 50V (losing the interaction of the methyl group). From these conformational shifts, the I50V enzyme maintains much of its affinity for either IDV or NFV. In the I50V-APV complex, the P81 loop does not shift in, thus the enzyme loses more affinity to APV. In the case of I54L or I54M bound to APV, the affinity is reduced by 15- and 25-fold, respectively. The mutations I54L or I54M both alter the conformation of the I50 residue, decreasing its interactions with APV, thus reducing enzyme affinity. Therefore, even mutations I54L and I54M exert their effects via the I50 residue. Conclusions: I50V resistance to APV is due to decreased hydrophobic interaction of the V residue. IDV and NFV are less affected by I50V because a shift in P81 forms compensatory hydrophobic interactions. Interestingly, I54L and I54M effect resistance to APV via conformational shifts of I50 residue (reduction of E-I interactions). Because I54L or I54M reduce affinity less than I50V, it is not surprising that clinical isolates that contain 54 mutations cause less resistance than those with I50V, on average. These data define a molecular rationale for resistance to APV and minimal cross-resistance to other clinically relevant HIVPIs.

©2002 9th Conference on Retroviruses and Opportunistic Infections