Molecular mechanism of antagonism between the Y181C and E138K mutations in HIV-1 reverse transcriptase.

Etravirine (ETR) is an expanded-spectrum nonnucleoside reverse transcriptase inhibitor (NNRTI) approved for use as an antiretroviral agent in treatment-experienced patients. Y181C and E138K in HIV-1 RT are among 20 different drug resistance mutations associated with ETR. However, E138K can be consistently selected by ETR when wild-type viruses but not viruses containing Y181C are grown in tissue culture. This study was carried out to evaluate any possible mechanisms that might explain antagonism between the Y181C and E138K mutations. Accordingly, we performed tissue culture studies to investigate the evolutionary dynamics of E138K in both a wild-type (WT) and a Y181C background. We also generated recombinant enzymes containing Y181C and E138K alone or in combination in order to study enzyme processivity, rates of processive DNA synthesis, enzyme kinetics, and susceptibility to ETR. We now show that the presence of the Y181C mutation prevented the emergence of E138K in cell culture and that the simultaneous presence of E138K and Y181C impaired each of enzyme activity, processivity, rate of processive DNA synthesis, and deoxynucleoside triphosphate (dNTP) affinity. The addition of E138K to Y181C also decreased the level of resistance to ETR compared to that obtained with Y181C alone.