Susceptibility to HIV-1 integrase strand transfer inhibitors (INSTIs) in highly treatment-experienced patients who failed an INSTI-based regimen

The aim of this study was to characterize the genotypic and phenotypic resistance profile to the inte- grase strand transfer inhibitor (INSTI) bictegravir (BIC) and other INSTIs in patients who previously failed twice-daily raltegravir (RAL)-based or twice-daily dolutegravir (DTG)-based regimens. Twenty-two sam- ples were collected after failure on an INSTI-based regimen in 17 highly treatment-experienced patients with HIV-1 with multi-drug-resistant virus, recorded in the Italian PRESTIGIO registry. Genotypic resis- tance mutations and phenotypic susceptibility to INSTIs were detected by GeneSeqIN and PhenoSenseIN assays, respectively (Monogram Biosciences, San Francisco, CA, USA). The primary INSTI resistance sub- stitutions E138A/K, G140S, Y143C/H/R, Q148H and N155H were detected in 14 of 22 samples and were associated with resistance to one or more INSTIs, with G140S + Q148H present in 11 of 22 samples. Of these 14 samples, all showed high levels of resistance to elvitegravir (EVG) and RAL. Two isolates con- tained L74M, E138K, G140S and Q148H, or L74M, T97A, S119T, E138K, G140S, Y143R and Q148H, and had high-level resistance to all INSTIs, including BIC and DTG. Intermediate resistance was reported for eight of 14 isolates for BIC and nine of 14 isolates for DTG. Overall, for the 14 INSTI-resistant isolates, the median fold-change values in phenotypic susceptibility were: BIC 3.2 [interquartile range (IQR) 0.6–66], DTG 6.3 (IQR 0.8–> 186), EVG > 164 (IQR 2.6–> 164) and RAL > 188 (IQR 2.7–> 197). In conclusion, the study findings supported the in-vitro activity of BIC and DTG against most isolates derived from highly treatment-experienced patients who failed INSTI regimens.