Crystallography and the design of anti-AIDS drugs: conformational flexibility and positional adaptability are important in the design of non-nucleoside HIV-1 reverse transcriptase inhibitors.

Drug resistance is a key cause of failure for treatment of HIV infection. The efficacy of non-nucleoside reverse transcriptase inhibiting (NNRTI) drugs is impaired by rapid emergence of drug-resistance mutations. A multidisciplinary effort led to the discovery of the potent NNRTIs dapivirine and etravirine, both of which are diarylpyrimidine (DAPY) derivatives. Systematic structural and molecular modeling studies of HIV-1 reverse transcriptase (RT)/NNRTI complexes revealed different modes of inhibitor binding, and some of the DAPY inhibitors can bind to RT in different conformations. The torsional flexibility ("wiggling") of the inhibitors can generate numerous conformational variants and the compactness of the inhibitors permits significant repositioning and reorientation (translation and rotation) within the pocket ("jiggling"). Such adaptations appear to be critical for the ability of the diarylpyrimidine NNRTIs to retain their potency against a wide range of drug-resistant HIV-1 RTs. Exploitation of inhibitor conformational flexibility (such as torsional flexibility about strategically located chemical bonds) can be a powerful element of drug design, especially for the design of drugs that will be effective against rapidly mutating targets (which is a collection of related targets).