Phenotypic susceptibility of HIV-2 to raltegravir: integrase mutations Q148R and N155H confer raltegravir resistance.

OBJECTIVES: Raltegravir is the first integrase strand transfer inhibitor approved for treating HIV-1 infection. Although emerging data suggest that raltegravir may also be useful for HIV-2 treatment, studies addressing the in-vitro susceptibility of HIV-2 to raltegravir are scarce, and the genetic pathways leading to raltegravir resistance in HIV-2 have not been adequately characterized. Our objectives were to directly compare the susceptibilities of HIV-1 and HIV-2 to raltegravir and to examine the role of mutations in HIV-2 integrase in emergent raltegravir resistance.

MATERIALS AND METHODS: Single-cycle and spreading infection assays were used to quantify the sensitivities of wild-type HIV-1 and HIV-2 strains to raltegravir. HIV-2 integrase mutants were constructed by site-directed mutagenesis, and the replication capacities and raltegravir susceptibilities of the resultant variants were analyzed in single-cycle assays.

RESULTS: Raltegravir showed comparable activity against wild-type HIV-1 and HIV-2 in both single-cycle and spreading infections, with EC(50) values in the low nanomolar range. Amino acid changes Q148R and N155H individually conferred resistance to raltegravir (14-fold and seven-fold, respectively), whereas the Y143C replacement had no statistically significant effect on raltegravir sensitivity. The combination of Q148R with N155H resulted in high-level raltegravir resistance (>1000-fold). In addition, all HIV-2 integrase variants tested showed impairments in replication capacity.

CONCLUSION: Our data support clinical studies of raltegravir for treating HIV-2 infection and show that the Q148R and N155H changes alone are sufficient for raltegravir resistance in HIV-2. Further efforts are needed to improve access to HIV-2-active antiretrovirals, including raltegravir, in resource-limited areas where HIV-2 is endemic.