Tropism-independent protection of macaques against vaginal transmission of three SHIVs by the HIV-1 fusion inhibitor T-1249

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Abstract
We have assessed the potential of the fusion inhibitory peptide T-1249 for development as a vaginal microbicide to prevent HIV-1 sexual transmission. When formulated as a simple gel, T-1249 provided dose-dependent protection to macaques against high-dose challenge with three different SHIVs that used either CCR5 or CXCR4 for infection (the R5 virus SHIV-162P3, the X4 virus SHIV-KU1 and the R5X4 virus SHIV-89.6P), and it also protected against SIVmac251 (R5). Protection of half of the test animals was estimated by interpolation to occur at T-1249 concentrations of ≈40–130 μM, whereas complete protection was observed at 0.1–2 mM. In vitro, T-1249 had substantial breadth of activity against HIV-1 strains from multiple genetic subtypes and in a coreceptor-independent manner. Thus, at 1 μM in a peripheral blood mononuclear cell-based replication assay, T-1249 inhibited all 29 R5 viruses, all 12 X4 viruses and all 7 R5X4 viruses in the test panel, irrespective of their genetic subtype. Combining lower concentrations of T-1249 with other entry inhibitors (CMPD-167, BMS-C, or AMD3465) increased the proportion of test viruses that could be blocked. In the PhenoSense assay, T-1249 was active against 636 different HIV-1 Env-pseudotyped viruses of varying tropism and derived from clinical samples, with IC50 values typically clustered in a 10-fold range ≈10 nM. Overall, these results support the concept of using T-1249 as a component of an entry inhibitor-based combination microbicide to prevent the sexual transmission of diverse HIV-1 variants.