Results from the second clinical trial to test the HDAC inhibitor vorinostat as a latency-reversing agent, first presented at CROI 2013, have now been published in the open access journal PLoS Pathogens. The study design differed from the first trial, involving a longer 14-day dosing period. The results are broadly consistent, with a significant increase in cell-associated HIV RNA documented, but no change in multiple measures of the HIV reservoir or HIV RNA as assessed by the standard viral load test. Side effects experienced by participants were grade 1 or 2 (mild or moderate in severity) with lethargy, diarrhea and thrombocytopenia being most common; all resolved after the drug was stopped. The researchers noted long-term changes in expression of multiple cellular genes and caution that this could present a safety concern, stating: “the prolonged changes in host gene expression require careful long term follow up.”
The paper adds to the evidence that HDAC inhibitors can activate at least some latent HIV, but do not shrink the HIV reservoir in most cases, suggesting additional interventions are needed to kill latently infected cells that are induced to produce virus. In terms of the latency-reversing potency of HDAC inhibitors, the results presented to date are consistent with in vitro studies indicating a hierarchy of vorinostat > panobinostat > romidepsin, with the latter mediating the greatest effect based on the detection of HIV RNA by standard viral load testing (these data were presented at the AIDS 2014 conference by Dr. Ole Schmeltz Søgaard and the presentation is available on YouTube). The safety concerns raised by the persistent alterations in host gene expression will require ongoing assessment in all the clinical trials that are being conducted.
HDAC inhibitors also have effects on the immune system, and this aspect is evaluated in study published recently in Blood. The research did not involve HIV-positive people but rather individuals undergoing hematopoietic cell transplantation who were receiving vorinostat to prevent graft-versus-host disease. The authors found increases in the numbers of immunosuppressive regulatory CD4 T cells (Tregs) and greater suppression by these cells on a per-cell basis, along with reduced inflammatory responses by peripheral blood mononuclear cells.
Similar anti-inflammatory effects were reported in an analysis of HIV-positive participants in a clinical trial of panobinostat that was presented at AIDS 2014; the presentation was covered by Jules Levin of NATAP and the abstract and slides are posted to the NATAP website. There are reasons to believe that the anti-inflammatory activity of HDAC inhibitors could be of some benefit in HIV, but Tregs have also been linked to lower HIV-specific immunity, which could potentially be a negative (particularly if HIV-specific immunity needs to be boosted to eliminate latently infected cells). There is already some evidence that HDAC inhibitors can suppress the killing of HIV-infected cells by virus-specific CD8 T cells in laboratory assays (this paper was published in PLoS Pathogens in August).
Complicating matters further, at the recent Strategies for an HIV Cure conference Jonathan Karn gave a presentation suggesting HDAC inhibitors may enhance natural killer (NK) cell responses by causing downregulation of MHC class I on target cells and upregulating NK cell receptors, possibly consistent with some preliminary evidence presented at the same conference indicating NK cell responses were associated with declines in HIV DNA levels in a few participants in the panobinostat trial.
Additional research will be needed to investigate how the various possible consequences of HDAC inhibition balance out in HIV-positive people, and to assess the extent to which these effects persist after dosing is stopped.
PLoS Pathog. 2014 Nov 13;10(10):e1004473. doi: 10.1371/journal.ppat.1004473. eCollection 2014.
Elliott JH, Wightman F, Solomon A, Ghneim K, Ahlers J, Cameron MJ, Smith MZ, Spelman T, McMahon J, Velayudham P, Brown G, Roney J, Watson J, Prince MH, Hoy JF, Chomont N, Fromentin R, Procopio FA, Zeidan J, Palmer S, Odevall L, Johnstone RW, Martin BP, Sinclair E, Deeks SG, Hazuda DJ, Cameron PU, Sékaly RP, Lewin SR.
Human immunodeficiency virus (HIV) persistence in latently infected resting memory CD4+ T-cells is the major barrier to HIV cure. Cellular histone deacetylases (HDACs) are important in maintaining HIV latency and histone deacetylase inhibitors (HDACi) may reverse latency by activating HIV transcription from latently infected CD4+ T-cells. We performed a single arm, open label, proof-of-concept study in which vorinostat, a pan-HDACi, was administered 400 mg orally once daily for 14 days to 20 HIV-infected individuals on suppressive antiretroviral therapy (ART). The primary endpoint was change in cell associated unspliced (CA-US) HIV RNA in total CD4+ T-cells from blood at day 14. The study is registered at ClinicalTrials.gov (NCT01365065). Vorinostat was safe and well tolerated and there were no dose modifications or study drug discontinuations. CA-US HIV RNA in blood increased significantly in 18/20 patients (90%) with a median fold change from baseline to peak value of 7.4 (IQR 3.4, 9.1). CA-US RNA was significantly elevated 8 hours post drug and remained elevated 70 days after last dose. Significant early changes in expression of genes associated with chromatin remodeling and activation of HIV transcription correlated with the magnitude of increased CA-US HIV RNA. There were no statistically significant changes in plasma HIV RNA, concentration of HIV DNA, integrated DNA, inducible virus in CD4+ T-cells or markers of T-cell activation. Vorinostat induced a significant and sustained increase in HIV transcription from latency in the majority of HIV-infected patients. However, additional interventions will be needed to efficiently induce virus production and ultimately eliminate latently infected cells.
Blood DOI: http://dx.doi.org/10.1182/blood-2014-10-605238
Sung Won Choi, Erin Gatza, Guoqing Hou, Yaping Sun, Joel Whitfield, Yeohan Song, Katherine Oravecz-Wilson, Isao Tawara, Charles A. Dinarello, and Pavan Reddy
- HDAC inhibition reduced pro-inflammatory cytokines and increased regulatory T cell number and function after allo-HCT.
- HDAC inhibition enhanced STAT-3 acetylation and induced IDO after allo-HCT.
We examined immunological responses in patients receiving histone deacetylase (HDAC) inhibition (vorinostat) for graft-versus-host disease (GVHD) prophylaxis following allogeneic hematopoietic cell transplant (allo-HCT). Vorinostat treatment increased histone acetylation in peripheral blood mononuclear cells (PBMC) from treated patients, confirming target HDAC inhibition. HDAC inhibition reduced pro-inflammatory cytokine levels in plasma and from PBMC, decreased ex vivo responses of PBMC to pro-inflammatory TLR-4 stimuli, but did not alter the number or response of conventional T cells (Tconv) to non-specific stimuli. However, the numbers of regulatory T cells (Tregs) were increased, which revealed greater demethylation of the Foxp3 T regulatory-specific demethylation region. Vorinostat-treated patients showed increased expression of CD45RA and CD31 on Tregs, and these Tregs demonstrated greater suppression on a per-cell basis. Consistent with preclinical findings, HDAC inhibition also increased STAT-3 acetylation and induced indoleamine-2,3-dioxygenase (IDO). Our data demonstrate that HDAC inhibition reduces inflammatory responses of PBMC but enhances Tregs after allo-HCT.