Background:  S/GSK134957 is a potent once-daily unboosted integrase inhibitor (INI) under clinical development. Previous studies with a subset of clinically relevant integrase mutant virus demonstrated limited cross resistance to other integrase inhibitors in vitro. When virus was passaged in the presence of S/GSK134957, highly resistant mutants were not isolated, but mutations that conferred low-fold change (maximum fold change=4.1) were identified within and around the integrase active site. Herein, we demonstrate S/GSK134957 profile against a large panel of clinically relevant integrase mutants.

Methods:  Seventy integrase inhibitor-resistance associated site-directed molecular clones (SDM) were constructed from the wild-type molecular clone pNL432. Viral fitness was assessed with replication in PBMCs and/or with a HeLa-CD4 cell single round infection assay. Mutations assessed were primarily those associated with raltegravir (RAL) and elvitegravir (ELV)-resistant viruses (RVs) observed in clinical trials, and included double mutations in the 3 RAL resistance pathways (Y143C/H/R, Q148H/K/R and N155H). Novel triple-quintuple mutations identified during passage of Q148H/K/R clones in the presence of S/GSK134957 were also included. Ten site-directed molecular clones replicated poorly, and the fold change (FC) in susceptibility against the remaining 60 site-directed molecular clones was determined with a HeLa-CD4 cell assay.

Results:  In RAL-related resistant viruses, all 143 and 155 pathway viruses were still sensitive (FC<5) to S/GSK134957. G140S/Q148H, a significant RAL-RV in the Q148 pathway, was still sensitive to S/GSK134957. S/GSK134957 showed reduced activity against E138K/Q148K (fold change =19) and G140S/Q148R (fold change =8.4). Addition of T97A, M154I, or V201I, to G140S/Q148H increased S/GSK134957 resistance. Among ELV-related RVs, all viruses remained sensitive to S/GSK134957. For the 28 single mutant site-directed molecular clones, S/GSK134957 demonstrated low fold change (<5). For the 28 double mutant site-directed molecular clones, S/GSK134957 demonstrated low fold change (<5) in activity against all except E138K/Q148K, G140S/Q148R, and Q148R/N155H. These integrase inhibitor-resistant viruses had relatively low replication rates compared to wild-type virus.

Conclusions:  S/GSK134957 has a markedly different resistance profile, as evidenced by limited cross-resistance to RAL-resistant site-directed molecular clones. All single mutant and 25/28 double mutants did not alter fold change activity to S/GSK134957 >5. These data show that S/GSK134957 has a resistance profile distinct from RAL and ELV, and demonstrates the potential for S/GSK134957 to have a higher genetic barrier to resistance.