Differential susceptibility of cells infected with defective and intact HIV proviruses to killing by obatoclax and other small molecules.

OBJECTIVES: Some drugs that augment cell-intrinsic defenses or modulate cell death/survival pathways have been reported to selectively kill cells infected with HIV or Simian Immunodeficiency Virus (SIV), but comparative studies are lacking. We hypothesized that these drugs may differ in their ability to kill cells infected with intact and defective proviruses. DESIGN: To investigate this hypothesis, drugs were tested ex vivo on peripheral blood mononuclear cells (PBMC) from nine antiretroviral therapy (ART)-suppressed individuals. METHODS: We tested drugs currently in clinical use or human trials, including auranofin (p53 modulator), interferon alpha2A, interferon gamma, acitretin (RIG-I inducer), GS-9620/vesatolimod (TLR7 agonist), nivolumab (PD-1 blocker), obatoclax (Bcl-2 inhibitor), birinapant [inhibitor of apoptosis proteins (IAP) inhibitor], bortezomib (proteasome inhibitor), and INK128/sapanisertib [mammalian target of rapamycin mTOR] [c]1/2 inhibitor). After 6 days of treatment, we measured cell counts/viabilities and quantified levels of total, intact, and defective HIV DNA by droplet digital PCR (Intact Proviral DNA Assay). RESULTS: Obatoclax reduced intact HIV DNA [median = 27-30% of dimethyl sulfoxide control (DMSO)] but not defective or total HIV DNA. Other drugs showed no statistically significant effects. CONCLUSION: Obatoclax and other Bcl-2 inhibitors deserve further study in combination therapies aimed at reducing the intact HIV reservoir in order to achieve a functional cure and/or reduce HIV-associated immune activation.

Mechanisms and efficacy of small molecule "latency promoting agents" to inhibit HIV reactivation ex vivo.

HIV infection cannot be cured due to the persistence of a reservoir of latently infected cells. Furthermore, virally suppressed individuals experience chronic immune activation from ongoing low-level viral expression. Drugs that inhibit HIV transcription and/or reactivation of latent HIV have been proposed as a strategy to reduce HIV-associated immune activation and/or to achieve a functional cure. We evaluated 26 small molecules, both previously reported drugs and new drug candidates, for their ability to act as "latency promoting/silencing agents (LPAs)" that can reduce or prevent HIV expression after T cell activation. Using a panel of RT-ddPCR assays, we measured the progression through HIV transcription and pinpointed the step at which each of those drugs inhibited HIV transcription, with and without prior activation. While some drugs primarily inhibited one or two steps in HIV reactivation, other drugs (CDK inhibitors, splicing inhibitors, tanespimycin, and triptolide) inhibited multiple stages of HIV transcription and blocked the production of supernatant viral RNA. Dinaciclib, AZD4573, and pladienolide B also appeared to inhibit HIV splicing in unstimulated PBMC. By selecting drugs with known mechanisms of action, we specifically identified cellular factors and pathways that may be involved in regulation of HIV expression. These drugs/targets deserve further study in strategies aimed at reducing HIV-associated immune activation or achieving a functional cure.