Integrase strand transfer inhibitors (INSTIs) are key components of antiretroviral therapy (ART), blocking the integration of viral DNA into host chromatin and halting replication. Among these, the second-generation INSTI dolutegravir (DTG) has become a standard first-line treatment due to its potency, tolerability, and high genetic barrier to resistance. However, drug resistance mutations (DRMs) in HIV-1 integrase (IN) continue to emerge under therapeutic pressure. The R263K substitution alone confers low-level resistance to DTG, but when combined with accessory mutations M50I and S119R, the resulting triple mutant (R263K/M50I/S119R) further reduces DTG susceptibility while retaining ∼60%–70% replication capacity relative to wild type. To investigate how these mutations alter integrase function and contribute to resistance, we have initiated a series of structural and biochemical studies. Mutant IN proteins and viral DNA are purified and assembled into intasomes for high-resolution structural analysis by cryo-electron microscopy (cryo-EM), aimed at resolving mutation-induced structural changes and inhibitor interactions. These efforts are complemented by integration assays to quantify catalytic activity and drug susceptibility. Although DTG is the primary focus of this study, the findings may elucidate how specific integrase mutations influence susceptibility across second-generation INSTIs, including bictegravir (BIC), which shares key structural features with DTG and exhibits a similar mechanism of action. Understanding how R263K-based mutations affect inhibitor binding will inform ongoing efforts to optimize INSTI design and improve treatment durability against emerging resistance.
Olvera et al. (Sun,) studied this question.