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Combination antiretroviral therapy (cART) has been proven to efficiently inhibit ongoing replication of human immunodeficiency virus type 1 (HIV-1), and significantly improve the health outcome in patients of acquired immune deficiency syndrome (AIDS). However, cART is unable to cure HIV-1/AIDS. Even in presence of cART there exists a residual viremia, contributed from the viral reservoirs of latently infected HIV-1 proviruses; this constitutes a major hurdle. Currently, there are multiple strategies aimed at eliminating or permanently silence these HIV-1 latent reservoirs being intensely explored. One such strategy, a recently emerged “block and lock” approach is appealing. For this approach, so-called HIV-1 latency-promoting agents (LPAs) are used to reinforce viral latency and to prevent the low-level or sporadic transcription of integrated HIV-1 proviruses. Although several LPAs have been reported, there is still a question of their suitability to be further developed as a safe and valid therapeutic agent for the clinical use. In this study, we aimed to identify new potential LPAs through the screening an FDA-approved compound library. A new and promising anti-HIV-1 inhibitor, levosimendan, was identified from these screens. Levosimendan is currently used to treat heart failure in clinics, but it demonstrates strong inhibition of TNFα-induced HIV-1 reactivation in multiple cell lines of HIV-1 latency through affecting the HIV-1 Tat-LTR transcriptional axis. Furthermore, we confirmed that in primary CD4+ T cells levosimendan inhibits both the acute HIV-1 replication and the reactivation of latent HIV-1 proviruses. As a summary, our studies successfully identify levosimendan as a novel and promising anti-HIV-1 inhibitor, which should be immediately investigated in vivo given that it is already an FDA-approved drug.

IFI44 is an interferon-alfa inducible protein, and is associated with infection of several viruses. However, IFI44 elicits minimal antiviral effects on these viruses, and its exact role is still unknown. Here we show that IFI44 inhibits HIV-1 replication in vitro. Through depletion of endogenous IFI44 or overexpression of IFI44 we confirm that IFI44 suppresses HIV-1 LTR promoter activity and affects viral transcription. Furthermore, we find that IFI44 localizes to nuclei and binds to the HIV-1 LTR promoter in HIV-1 infected cells. Removing suppression of HIV-1 transcription benefits reactivation of HIV-1 proviruses for purging latent reservoirs. We demonstrate that depletion of endogenous IFI44 in J-LAT cells induces reactivation of latent HIV-1. Based on these results, we propose a model in which IFI44 is recruited to the HIV-1 LTR, which may suppress viral transcription and prevent reactivation of latent HIV-1. Our study suggests a previously unrecognized anti-HIV phenomenon for interferon-stimulated proteins.