Mechanism by which PF-3758309, a Pan Isoform Inhibitor of p21-Activated Kinases, Blocks Reactivation of HIV-1 Latency
The "block and lock" strategy is one approach that might elicit a sterilizing cure for HIV-1 infection. The "block" refers to a compounds ability to inhibit latent HIV-1 proviral transcription, while the "lock" refers to its capacity to induce permanent proviral silencing. We identified PF-3758309, a pan-isoform inhibitor of p21-activated kinases (PAKs), as a potent inhibitor of HIV-1 latency reversal (Vargas et al., Antimicrob Agents Chemother. 2019;63(2):e01744-18). The goal of this study was to define the mechanism(s) involved. We found that both 24ST1NLESG cells (a cell line model of HIV-1 latency) and purified CD4+ naive and central memory T cells express high levels of PAK2, and lower levels of PAK1 and PAK4. Knockdown of PAK1 or PAK2, but not PAK4, in 24ST1NLESG cells resulted in a modest, but statistically significant decrease in the magnitude of HIV-1 latency reversal. Overexpression of PAK1 significantly increased the magnitude of latency reversal. A phospho-protein array analysis revealed that PF-3758309 down-regulates the NF-{kappa}B signaling pathway, which provides the most likely mechanism by which PF-3758309 inhibits latency reversal. Finally, we used cellular thermal shift assays combined with liquid chromatography and mass spectrometry to ascertain whether PF-3758309 off-target binding contributed to its activity. In 24ST1NLESG cells and in peripheral blood mononuclear cells, PF-3758309 bound to mitogen-activated protein kinase 1 and protein kinase A; however, knockdown of either of these kinases did not impact HIV-1 latency reversal. Collectively, our study suggests that PAK1 and PAK2 play a key role in the maintenance of HIV-1 latency. IMPORTANCEThe persistence of latent, replication-competent HIV-1 proviruses in resting CD4+ T cells, and other cellular reservoirs, represents a major barrier to a cure. The "block and lock" strategy is one approach proposed to elicit a sterilizing cure for HIV-1 infection. In this study, we define the mechanism by which PF-3758309, a pan-isoform p21-activated kinase (PAK) inhibitor, blocks the reversal of HIV-1 latency. Our data show that PAK1 and PAK2 play a role in the maintenance of HIV-1 latency, and further suggest that PAK inhibitors, such as PF-3758309, could form part of "block and lock" therapeutic strategies.