Background: HIV-1 hypersusceptibility to non-nucleoside reverse transcriptase inhibitors (NNRTI) improves the response to NNRTI-containing regimens. The genetic basis for NNRTI hypersusceptibility was partly defined in our earlier analyses of a paired genotype-phenotype dataset of viral isolates from treatment-experienced patients, in which we identified reverse transcriptase mutations V118I, H208Y, and T215Y as being strongly associated with NNRTI hypersusceptibility.
Objectives: We evaluated the role of these mutations in NNRTI hypersusceptibility by site-directed mutagenesis and phenotypic analysis of HIV-1 recombinants.
Methods: Drug susceptibility and replication capacity were determined in single cycle assays. Hypersusceptibility was defined by a statistically significant (P < 0.01; Student's t-test) mean fold-change in 50% inhibitory concentration (IC50) of less than 0.4.
Results: The single mutations V118I, H208Y, and T215Y did not show hypersusceptibility to efavirenz with mean fold-change of 0.58, 0.55, and 0.70, respectively (P < 0.01 and P = 0.12). The H208Y/T215Y and V118I/H208Y/T215Y mutants showed marked hypersusceptibility to efavirenz, having mean fold-change values of 0.27 and 0.20, respectively (P < 0.001). In addition, H208Y/T215Y, V118I/T215Y, and V118I/H208Y/T215Y were hypersusceptible to delavirdine and nevirapine. The V118I/T215Y mutant was not replication impaired; whereas H208Y/T215Y and V118I/H208Y/T215Y had significantly (P < 0.01) reduced replication capacities of 40 and 35% of wild-type, respectively.
Conclusion: Different combinations of V118I, H208Y, and T215Y produce NNRTI hypersusceptibility. The V118I/T215Y mutant is hypersusceptible to delavirdine and nevirapine without reduced replication capacity, whereas the H208Y/T215Y and V118I/H208Y/T215Y mutants are hypersusceptible to all NNRTI and show impaired replication. These findings suggest that more than one mechanism is involved in NNRTI hypersusceptibility.