In Vitro HIV-1 Resistance Selections with Combinations of Tenofovir and Emtricitabine or Abacavir and Lamivudine

Gilead Sciences, Inc., 333 Lakeside Drive, Foster City, CA, 94404 USA

^* To whom correspondence should be addressed. Email: Michael.Miller{at}gilead.com.

	Abstract

HIV-1 resistance development was evaluated in vitro using drug combinations of tenofovir and emtricitabine or abacavir and lamivudine, as well as using the compounds individually. Emtricitabine- and lamivudine-resistant HIV-1 with the M184I or M184V mutation in reverse transcriptase was readily selected in the emtricitabine, lamivudine, and both combination cultures and conferred high-level resistance to emtricitabine and lamivudine. Tenofovir-resistant HIV-1 with the K65R mutation occurred in both the tenofovir alone and the emtricitabine + tenofovir combination culture. The mutations S68N and S68K were also observed in the tenofovir cultures with no detectable impact on resistance, suggesting a possible compensatory role in viral fitness. At low concentrations of emtricitabine and tenofovir, the M184I mutation appeared first, followed by the K65R mutant in a subset of viruses. At intermediate concentrations of emtricitabine and tenofovir, viruses harboring K65R or a novel K65N+K70R double mutation grew before giving rise to K65R+M184V/I double mutants at higher emtricitabine concentrations. Abacavir resistance was characterized by the accumulation of the M184V, Y115F and K65R mutations in the abacavir culture, while the M184V and L74V mutations were selected in combination with lamivudine. In the presence of the abacavir resistance mutations viral growth was strong even in the presence of high concentrations of abacavir. In contrast, viral growth was markedly impaired in the cultures at high tenofovir concentrations even in the presence of K65R. In conclusion, these studies show that HIV-1 mutants with a K65R+M184V genotype are generated under maximum selection pressure from the combination of tenofovir and emtricitabine.