GSK2838232 (GSK232; GlaxoSmithKline) is a novel maturation inhibitor that blocks the proteolytic cleavage of the HIV-1 Gag-Pol precursor, rendering newly-formed virions non-infectious. GSK232 is active against a broad range of HIV-1 Gag variants in culture, including brevirimat-resistant mutants, and was recently evaluated in a phase 2a clinical trial in HIV-1–infected individuals (NCT 03045861). To our knowledge, GSK232 has not been tested against HIV-2, and there are limited data regarding the susceptibility of HIV-2 to other compounds in the maturation inhibitor class.
We determined the activity of GSK232 against a panel of HIV-1, HIV-2, and SIV isolates using two culture-based methods: single-cycle assays, and 6-day spreading infections of an immortalized T cell line (CEMss). Single-cycle assays were initiated by transfecting GSK232-treated 293T-17 cells (and solvent-only controls) with full-length HIV or SIV-encoding plasmids. For the spreading (multi-cycle) assays, CEMss cells were treated with GSK232 and infected with cell-free virus stocks. To quantify replication-competent virus, supernatants from the 293T-17 and CEMss cultures were transferred to MAGIC-5A indicator cells. After ~44 h of growth, the MAGIC-5A monolayers were treated with lysis buffer, and HIV/SIV-induced ?-galactosidase activity was quantified via the addition of a colorimetric substrate (CPRG). The resultant dose-response data were plotted in Prism v. 6.0h (GraphPad Software). All GSK232 preparations used in these experiments were purchased from Cayman Chemical (Ann Arbor, Michigan).
GSK232 was highly active against HIV-1 isolates from group M subtypes A, B, C, D, F, and group O. IC50 values for HIV-1 ranged from 1.5–3.7 nM in the single-cycle assay and 0.23–0.93 nM in spreading infection assays. In contrast, GSK232 showed weak or no detectable activity (IC50 >40 nM) against HIV-2 isolates from groups A, B, and CRF01_AB; similar results were observed for SIVmac239, SIVmac251, and SIVagm (IC50 >40 nM).
GSK232 potently inhibited group M and group O isolates of HIV-1, but showed negligible activity against the HIV-2 and SIV strains tested in this study. The mechanism(s) responsible for the differential susceptibility of HIV-1 and HIV-2/SIV to GSK232 require further investigation. Our data suggest that GSK232 is not a suitable candidate for antiretroviral therapy of HIV-2 infection.