Structures of Tyr188Leu mutant and wild-type HIV-1 reverse transcriptase complexed with the non-nucleoside inhibitor HBY 097: Inhibitor flexibility is a useful design feature for reducing drug resistance

The second generation Hoechst-Bayer non-nucleoside inhibitor, HBY 097 (S-4-isopropoxycarbonyl-6-methoxy-3-(methylthiomethyl)-3,4-dihydroquinoxalin-2(1H)-thione), is an extremely potent inhibitor of HIV-1 reverse transcriptase (RT) and of HIV-1 infection in cell culture. HEY 097 selects for unusual drug-resistance mutations in HIV-1 RT (e.g. Gly190Glu) when compared with other non-nucleoside RT inhibitors (NNRTIs), such as nevirapine, alpha-APA and TIBO. We have determined the structure of HEY 097 complexed with wild-type HIV-1 RT at 3.1 Angstrom resolution. The HIV-1 RT/KBY 097 structure reveals an overall inhibitor geometry and binding mode differing significantly from RT/NNRTI structures reported earlier, in that HEY 097 does not adopt the usual butterfly-like shape. We have determined the structure of the Tyr188Leu HIV-1 RT drug-resistant mutant in complex with HEY 097 at 3.3 Angstrom resolution. HEY 097 binds to the mutant RT in a manner similar to that seen in the wild-type RT/HBY 097 complex, although there are some repositioning and conformational alterations of the inhibitor. Conformational changes of the structural elements forming the inhibitor-binding pocket, including the orientation of some side-chains, are observed. Reduction in the size of the 188 side-chain and repositioning of the Phe227 side-chain increases the volume of the binding cavity in the Tyr188Leu HIV-1 RT/HBY 097 complex. Loss of important protein-inhibitor interactions may account for the reduced potency of HEY 097 against the Tyr188Leu HIV-1 RT mutant. The loss of binding energy may be partially offset by additional contacts resulting from conformational changes of the inhibitor and nearby amino acid residues. This would suggest that inhibitor flexibility can help to minimize drug resistance. (C) 1998 Academic Press.