Long dissociation half-life (t1/2) of HIV integrase strand transfer inhibitors (INSTI) correlates with high antiretroviral activity and barrier to resistance. The dissociation t1/2 of bictegravir (BIC) from wild-type (WT) integrase (IN)/DNA complexes is longer than that of elvitegravir (EVG), raltegravir (RAL), and dolutegravir (DTG). BIC has improved activity against HIV isolates with INSTI resistance mutations, particularly the 140/148 combination. Here, we evaluate phenotypic resistance and dissociation kinetics using G140S+Q148H mutant IN.
INSTIs were phenotyped with 17 G140S+Q148H clinically-derived isolates with or without other IN mutations. The apparent association and dissociation t1/2 of 3H-labelled RAL, EVG, DTG, and BIC were measured using WT and G140S/Q148H mutant HIV IN/DNA complexes with a scintillation proximity assay. The association and dissociation kinetics were analyzed using both a single exponential decay function and an equilibrium binding model that generates half-lives that may be more representative of the t1/2 in cells.
HIV isolates with G140S+Q148H in IN had mean phenotypic fold-change values of 3.6±1.9 for BIC, 8.1±4.7 for DTG (p<0.01 for DTG vs BIC), and >100 for RAL and EVG. The apparent association t1/2 of BIC and DTG to G140S+Q148H mutant HIV IN/DNA complexes were 37±4 min and 34±5 min, respectively, and similar to that for WT. For BIC and DTG, the dissociation t1/2 from G140S+Q148H IN/DNA complexes were both shorter compared to WT (p≤0.01). The BIC apparent t1/2 from the mutant IN/DNA complexes using single exponential fit was longer than DTG (5.5±0.1 h vs 2.0±0.01 h, respectively, p<0.01). Similarly, dissociation t1/2 determined from equilibrium binding models were longer for BIC than DTG (2.5±0.07 h vs 0.65±0.2 h, respectively, p<0.01). In contrast, EVG and RAL had no measurable association or dissociation with the mutant IN/DNA, consistent with high-level resistance.
BIC has improved activity compared to DTG, EVG, and RAL against HIV isolates with the 140+148 INSTI resistance mutations. BIC dissociates more slowly than DTG from the G140S+Q148H mutant IN/DNA complex and may explain the improved in vitro activity of BIC compared to other INSTIs against this mutant.