Is resistance futile?

A global effort has been undertaken to control human immunodeficiency virus (HIV) though the development of vaccines and pharmacologics. Current FDA approved pharmacological inhibitors target two of the three viral enzymes critical to replication and maturation of infectious viral particles: reverse transcriptase (RT) and protease (Pr). Although combination therapies targeting RT and Pr have significantly reduced AIDS related morbidity and mortality, resistance to individual inhibitors is a growing concern. Currently, there are six protease inhibitors in clinical use. These inhibitors target the active site of protease using peptidomimetic transition state analogs based on natural substrates. However, treatment failures arise as a lack of compliance due to HIV-inhibitor pharmacokinetics, toxicity, and tolerance. This allows reduced HIV-inhibitor pressure, increased viral replication, and the emergence of drug resistant mutations. Continued use of protease inhibitors in the face of incomplete viral suppression may result in HIV-1 escape mutants not only being resistant to the protease inhibitor used, but to all clinically available protease inhibitors. Thus, new broad-based protease inhibitors are needed to control the emerging multi-drug, cross-resistant HIV-1. Moreover, given the emergence of cross-resistant HIV-1, there is a need to target novel protease structural sites to reduce the risk of multi-drug cross-resistance. In this review, we discuss the resistance to protease inhibitors and the rationale for new strategies towards drug design for suppressing protease activity. We focus on the structure and function relationship and the influence that drug resistance mutants exert on the evolution of HIV-1 protease.