In vivo analysis of the effect of panobinostat on cell-associated HIV RNA and DNA levels and latent HIV infection

Abstract

BackgroundThe latent reservoir in resting CD4+ T cells presents a major barrier to HIV cure. Latency-reversing agents are therefore being developed with the ultimate goal of disrupting the latent state, resulting in induction of HIV expression and clearance of infected cells. Histone deacetylase inhibitors (HDACi) have received a significant amount of attention for their potential as latency-reversing agents.ResultsHere, we have investigated the in vitro and systemic in vivo effect of panobinostat, a clinically relevant HDACi, on HIV latency. We showed that panobinostat induces histone acetylation in human PBMCs. Further, we showed that panobinostat induced HIV RNA expression and allowed the outgrowth of replication-competent virus ex vivo from resting CD4+ T cells of HIV-infected patients on suppressive antiretroviral therapy (ART). Next, we demonstrated that panobinostat induced systemic histone acetylation in vivo in the tissues of BLT humanized mice. Finally, in HIV-infected, ART-suppressed BLT mice, we evaluated the effect of panobinostat on systemic cell-associated HIV RNA and DNA levels and the total frequency of latently infected resting CD4+ T cells. Our data indicate that panobinostat treatment resulted in systemic increases in cellular levels of histone acetylation, a key biomarker for in vivo activity. However, panobinostat did not affect the levels of cell-associated HIV RNA, HIV DNA, or latently infected resting CD4+ T cells.ConclusionWe have demonstrated robust levels of systemic histone acetylation after panobinostat treatment of BLT humanized mice; and we did not observe a detectable change in the levels of cell-associated HIV RNA, HIV DNA, or latently infected resting CD4+ T cells in HIV-infected, ART-suppressed BLT mice. These results are consistent with the modest effects noted in vitro and suggest that combination therapies may be necessary to reverse latency and enable clearance. Animal models will contribute to the progress towards an HIV cure.

HIV signaling through CD4 and CCR5 activates Rho family GTPases that are required for optimal infection of primary CD4+ T cells

“…Acetylation and methylation of histone residues on viral-associated nucleosomes impact chromatin structure and accessibility of the viral promoter to cellular transcriptional machinery [10, 11]. For instance, histone deacetylase (HDAC) inhibitors promote viral reactivation from latency both in vitro and in vivo and are being investigated as potential latency reversing agents in strategies to eliminate latent viral reservoirs [12–15]. Recently, we reported an unanticipated effect of HDAC inhibitors on HIV infection that was independent of its effects on nuclear histones: pre-treatment of primary CD4+ T cells with drugs that inhibited the cytoplasmic HDAC6 enhanced the kinetics and efficiency of reverse transcription, nuclear import, and integration and led to a significant increase in susceptibility to HIV infection [16].…”

Humanized mice for HIV and AIDS research

“…Exposure of latently infected resting CD4+ T cells isolated from suppressed patients to panobinostat also resulted in a modest induction of replication competent HIV. Administration of panobinostat to BLT mice resulted in robust increases in the levels of histone acetylation in all tissues evaluated confirming its in vivo activity [63]. Despite clear systemic bioactivity of panobinostat, no increases in HIV-RNA were noted in cells isolated from tissues of suppressed BLT mice.…”

“…Specifically, this model has been used to 1) demonstrate that systemic and topical tenofovir is highly effective at preventing rectal HIV transmission, 2) investigate the stability of drug resistance mutations in vivo , and 3) evaluate transmission of drug resistant viruses [41,62]. The availability of efficient drug regimens capable of effectively suppressing HIV replication in BLT mice have made this model useful for the study of HIV persistence [42,53,63,64]. Currently, BLT mice are being used to investigate HIV persistence in the GI tract.…”

“…Administration of a toxin conjugated to an antibody targeting the HIV Env protein to ART-treated and suppressed animals resulted in a dramatic decrease in the systemic levels of residual HIV-infected cells [53]. Recently Tsai et al evaluated the effect of panobinostat on HIV persistence in vitro and in BLT mice [63]. In vitro administration of panobinostat resulted in modest increases in the levels of HIV-RNA in peripheral blood cells from HIV-infected and suppressed patients.…”

Clinical pharmacology in HIV cure research – what impact have we seen?

“…However, there is not an agreement about the dose regimen to apply in order to obtain a complete depletion of the reservoirs [40,41]. Another potent member of these series is panobinostat, A c c e p t e d M a n u s c r i p t 9 which demonstrated to be able to reverse latency with a high level both of cell-associated unspliced HIV RNA and plasma viremia other than to increase the amount of sytemic histone acetilation both in vitro and in BLT (bone marrow, liver, thymus) mice [42,43]. Despite these promising results, panobinostat has not proved to obtain a drop in the levels of latent-infected CD4+ T cells suggesting that a combination therapy may be necessary [42,43].…”