Differential impact of the HIV-1 non-nucleoside reverse transcriptase inhibitor mutations K103N and M230L on viral replication and enzyme function.

Objectives: We wished to study the resistance profile of etravirine, a novel non-nucleoside reverse transcriptase inhibitor (NNRTI) active against common human immunodeficiency virus type-1 (HIV-1) drug-resistant strains.

Methods: We compared the effects of K103N, the most prevalent NNRTI resistance mutation, and M230L on enzyme function, virus replication and extent of biochemical inhibition by etravirine, efavirenz and nevirapine.

Results: Growth kinetics analyses in cord blood mononuclear cells (CBMCs) demonstrated that K103N-containing virus replicated as well as wild-type (WT) virus and that the M230L-containing virus was severely impaired in replication ability in the absence of NNRTIs. K103N-containing viruses replicated well in the presence of efavirenz and nevirapine, while virus containing M230L displayed substantial replication in the presence of all NNRTIs tested. RNA-dependent DNA polymerase assays using a heterogeneous HIV-1 RNA template and purified recombinant WT or mutated reverse transcriptase enzymes revealed that the fold change (FC) for etravirine was 0.7 for K103N and 8 for M230L. K103N and M230L conferred high-level resistance to both efavirenz (FC=39 and 15.3, respectively) and nevirapine (FC=43.5 and 33), confirming that M230L confers cross-resistance to both drugs while K103N-containing viruses remain susceptible to etravirine. In enzymatic assays, the K103N mutation was associated with moderate reductions in the efficiency of 3' DNA end-directed RNA template cleavage, while comparable efficiency to WT enzyme was observed with regard to minus-strand strong stop DNA synthesis and polymerase processivity.

Conclusions: These properties help to explain differences in the evolution and prevalence of these two NNRTI mutations.