HIV-1 Reverse Transcriptase Still Remains a New Drug Target: Structure, Function, Classical Inhibitors, and New Inhibitors with Innovative Mechanisms of Actions
Nonnucleoside reverse transcriptase inhibitors (NNRTIs) are very potent and most promising anti-AIDS drugs that specifically inhibit HIV-1 reverse transcriptase (RT). However, to a great extent, the efficacy of NNRTI drugs is impaired by rapid emergence of drug-resistance mutations. Fortunately, detailed analysis of a wide range of crystal structures of HIV-1 RT/NNRTI complexes together with data on drug resistance mutations has identified factors important for design of inhibitors and resilience to mutations, such as, exhibiting conformational flexibility and positional adaptability of NNRTIs, forming extensive main chain hydrogen bonding, targeting highly conserved residues in HIV-1 RT and possessing unconventional mechanisms for NNRTI-mediated inhibition of RT. Besides, the plasticity of NNRTIs binding pocket (NNIBP) also provides a broad space for the discovery of new generations of NNRTIs. For instance, the composite binding pocket, integrated all available crystal structure information about the NNRTI binding site of HIV RT, was demonstrated to be an effective tool to better understand the flexible nature of the binding pocket and to identify specific inhibitors. The RT/solvent interface proved to be an attractive site for incorporating a moiety to improve water solubility and pharmacokinetics or introducing a second pharmacophore to construct multifunctional ligand. Totally, the characterization of NNRTIs and NNIBP may help in the design of more effective drugs that are potent toward wild type and drug-resistant strains of RT. In this paper we attempt to translate the general knowledge gained from a large number of related literature into a set of medicinal chemistry strategies to improve the drug resistance profile of NNRTIs.