Towards HIV eradication using a novel Tat inhibitor

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 DESCRIPTION (provided by applicant): Antiretroviral therapy (ART) effectively blocks viral replication, although it fails to eradicate the virus. A small population of latently infected restng memory CD4+T cells still persists in patients on suppressive therapy. The most explored strategy for HIV eradication is dubbed "shock and kill", which attempts to purge the viral reservoir by reactivating the virus using anti-latency agents in the presence of ART. The expectation is that reactivation will prompt elimination of infected cells by cytopathic effects and/or by cytolytic T-lymphocyte lysis (1). This approach is challenging and has been unsuccessful thus far. Right now, we need new therapeutic agents that target different stages of the virus life cycle and limit latent HIV disease. The viral protein Tat binds HIV mRNA and promotes viral transcription. Compounds that block Tat activity have been highly sought after; however, none is yet in the clinic. We reported that Cortistatins, steroid-like alkaloids isolated from the marine sponge corticium simplex, represent a novel class of anti- Tat drug candidates. Didehydro-Cortistatin A (dCA) potently and selectively inhibits Tat-activity with no cellular associated toxicity (2). dCA binds specifically to the RNA-binding domain of Tat reducing HIV-1 RNA production in infected cultured and primary cells at an EC50 as low as 0.7 pM. Treatment of HIV-1 infected cells with dCA drives viral gene expression into an induced state of persistent deep latency in vitro, refractory to viral reactivation by the usual panel of activators (cytokines HDAC inhibitors, PKC activators). Discontinuation of dCA treatment does not result in viral rebound, suggesting the chromatin environment of the HIV promoter is epigenetically repressed. Importantly, dCA abrogates antigenic virus reactivation from latently infected CD4+T primary cells explanted from patients receiving suppressive ART. We propose an alternative approach to the "shock and kill" strategy. Specifically, using a Tat-inhibitor to target HIV-1 transcription rather than activating the endogenous latent reservoir, we propose to drive the residual transcription that occurs during ART into long-term latency or deep latency. A Tat-inhibitor combined with ART could reduce the size of the latent reservoir pool by blocking ongoing viral replication, reactivation and replenishment of the latent viral reservoir. Thus, the latent pool of cells in an infected individual would be stabilized, and death of the long-lived infected memory T-cells would result in a continuous decay of this pool over time, possibly culminating in the long-awaited sterilizing cure. Here we propose to: 1) fully characterize the molecular epigenetic events set in place at the HIV promoter in the presence of dCA and how these modifications impact HIV transcriptional activity; 2) establish a robust primary cellular model of latency that wll allow for confirmation of dCA mediated epigenetic modifications and 3) understand the molecular mechanism of viral resistance to dCA.