Biochemical studies suggest INSTI’s bind to HIV integrase in a two-step mechanism. this website Mutations may alter the second step and lead to fast INSTI dissociation kinetics that contribute to the development of integrase resistance. In biochemical analyses with wild-type integrase DNA complexes, DTG demonstrated a dissociative t 1/2 of 71 h as compared to 8.8 h for

RAL and 2.7 h for EVG; thus, DTG exhibited an off-rate 5–40 times slower than RAL and EVG (P < 0.0001) (Fig. 1) [20]. This slow dissociation may contribute to DTG’s high barrier to resistance and suggests that prolonged binding plays a role in its unique resistance profile [20, 21]. Single mutations of the major RAL pathway Y143, N155, and Q148 do not increase DTG-fold change, and have variable effect on the off-rate of DTG with half-lives of dissociation from ACY-1215 clinical trial 42 to 60 h for Y143 mutants, 9.6 h for N155H, and 5.2 to 11 h for Q148 mutants. Q148 plus additional mutations do increase the dissociative kinetics and impart a fold change. A fold change ≥3 as measured by change in Smoothened Agonist nmr half-maximal effective concentration (EC50) of mutant versus wild-type HIV-1 was considered resistant for in vitro studies [19, 21]. When mutations Q148H and G140S are present, the dissociative t 1/2 of DTG is reduced to 3.3 h [20] with a 2.6-fold change in EC50 [19]. The VIKING studies (discussed below; NCT01328041, NCT00950859) demonstrate that DTG maintains activity against RAL- and EVG-resistant

virus [22]; however, treatment-experienced participants with Q148 + ≥2 associated mutations had reduced potency when compared to no Q148 mutations at baseline

(P < 0.0001) [23]. The current FDA label cautions that poor virologic response has been observed in subjects with a Q148 substitution plus two or more additional INSTI-resistance substitutions [24] (Fig. 1). These data underpin the danger in maintaining a failing regimen that may lead to further accumulation of resistance mutations that can impact the efficacy of newer drug options. Fig. 1 INSTI pathways of HIV-1 resistance SPTLC1 with associated dissociative t 1/2 and fold change in EC50 [19] compared to wild-type virus. Diss t 1/2 dissociative values previously reported [20, 21]. Major integrase mutations are denoted in black bold: E92Q/V; Y143C/H/R; Q148H/K/R; N155H. Accessory mutations are denoted in gray: E138A/K; G140A/C/S [25]. DTG dolutegravir, EC 50 half-maximal effective concentration, EVG elvitegravir, FC fold change, INSTI integrase strand transfer inhibitor, ND not determined, RAL raltegravir, t 1/2 half-life Evaluation of 3,294 genotypic resistance tests ordered for clinical decision making from 2009 to 2012 at a United States national referral lab revealed that integrase resistance mutations were often paired with PI resistance [25]. Although the treatment regimen was not available, presumably subjects included in the database were receiving RAL based on the timing of FDA approvals.