Assessing phenotypic effect of integrase strand-transfer inhibitor (INSTI)-based resistance substitutions associated with failures on cabotegravir

Abstract

Objectives: International guidelines recommend integrase strand-transfer inhibitor (INSTI)-based regimens as initial and switch therapy in people with HIV. As novel INSTIs become available, understanding how emergence of resistance at virological failures and seroconversions affects subsequent treatment options is needed. For the latest approved INSTI, cabotegravir, resistance patterns comprising Q148K/R, N155H, R263K, G118R, E138A/K and G140A/S (alone or in combination) have been documented in virological failures and seroconversions. Here, the effect of these substitutions on antiviral activity of commercially approved INSTIs, bictegravir and elvitegravir, was assessed.

Methods: Antiviral testing was performed using person-derived clinical isolates (n = 52) with viral profiles similar to cabotegravir INSTI resistance patterns; susceptibility to cabotegravir, bictegravir and elvitegravir was measured using a phenotypic assay. Substitution patterns from isolates included triple [Q148K/H/R + E138A/K + G140A/C/S (n = 16)], double [Q148R + E138K (n = 3); Q148H/R + G140A/S (n = 24)] and single [N155H (n = 6); Q148R (n = 3)] resistance-associated mutations (RAMs).

Results: IC50 fold changes (FCs) for triple RAMs were the highest, at 47.0, 7.59 and >144 for cabotegravir, bictegravir and elvitegravir, respectively. For cabotegravir, bictegravir and elvitegravir, respectively, mean IC50 FCs were 9.5, 2.5 and >144 for double RAMs; and 3.3, 1.4 and >65 for single RAMs. When considering clinical/biological assay cut-offs, 54% (28/52) of isolates were susceptible to bictegravir, 40% (21/52) were partially susceptible and 6% (3/52) were resistant; for elvitegravir, 100% of isolates were resistant. Cabotegravir cut-offs were not available at the time of reporting.

Conclusions: Overall, clinical isolates with RAM patterns similar to clinically observed cabotegravir INSTI resistance showed meaningful increases in IC50 FCs, suggesting that cabotegravir-associated resistance may negatively affect efficacy of bictegravir- and elvitegravir-based regimens.