Class I Histone Deacetylase Inhibitor Entinostat Suppresses Regulatory T Cells and Enhances Immunotherapies in Renal and Prostate Cancer Models

Abstract

BackgroundImmunosuppressive factors such as regulatory T cells (Tregs) limit the efficacy of immunotherapies. Histone deacetylase (HDAC) inhibitors have been reported to have antitumor activity in different malignancies and immunomodulatory effects. Herein, we report the Tregs-targeting and immune-promoting effect of a class I specific HDAC inhibitor, entinostat, in combination with either IL-2 in a murine renal cell carcinoma (RENCA) model or a survivin-based vaccine therapy (SurVaxM) in a castration resistant prostate cancer (CR Myc-CaP) model.Methods and ResultsRENCA or CR Myc-CaP tumors were implanted orthotopically or subcutaneously, respectively. Inoculated mice were randomized into four treatment groups: vehicle, entinostat, cytokine or vaccine, and combination. Tregs in the blood were assessed by FACS analysis. Real time quantitative PCR and Western blot analysis of isolated T cell subpopulations from spleen were performed to determine Foxp3 gene and protein expression. The suppressive function of Tregs was tested by T cell proliferation assay. Low dose (5 mg/kg) entinostat reduced Foxp3 levels in Tregs and this was associated with enhanced tumor growth inhibition in combination with either IL-2 or a SurVaxM vaccine. Entinostat down-regulated Foxp3 expression transcriptionally and blocked Tregs suppressive function without affecting T effector cells (Teffs). In vitro low dose entinostat (0.5 µM) induced STAT3 acetylation and a specific inhibitor of STAT3 partially rescued entinostat-induced down-regulation of Foxp3, suggesting that STAT3 signaling is involved in Foxp3 down-regulation by entinostat.ConclusionsThese results demonstrate a novel immunomodulatory effect of class I HDAC inhibition and provide a rationale for the clinical testing of entinostat to enhance cancer immunotherapy.

ENGAGE- 501: phase II study of entinostat (SNDX-275) in relapsed and refractory Hodgkin lymphoma

“…In particular, recent publications show synergism between PD-1 blockade and HDAC inhibitor, possibly through the enhanced modulation of myeloid-derived suppressor cells, increased expression of PD-1 mediated by HDAC inhibitors, and alteration of the tumor immune microenvironment. 12,13,25 Consistent with the growing experience of HDAC inhibitors in HL, entinostat demonstrates clinical activity with a well-tolerated clinical profile suitable for combination therapy. Entinostat appears well tolerated, with only C.L.…”

Prognostic and biological significance of survivin expression in patients with diffuse large B-cell lymphoma treated with rituximab-CHOP therapy

“…SVN53-67/M57 (SurVaxM) has demonstrated its clinical potential in the treatment of gliomas and, more importantly, this vaccine contains multiple HLA epitopes that may be applicable to a large patient population. [78][79][80] DPX-Survivac vaccine, which has been proved to be well tolerated and shows the clinical benefits in ovarian cancer in phase I clinical trial, 81 is currently being examined in diffuse large B-cell lymphoma patients with survivin expression in a phase II clinical trial. 82 Furthermore, incomplete Freund's adjuvant and type-I interferon (IFNα) are two adjuvants that can enhance survivin-specific antitumor immunity.…”

The immune microenvironment in Hodgkin lymphoma: T cells, B cells, and immune checkpoints

“…126,127 The multiple pleiotropic effects of HDAC inhibition may collectively tip the balance towards deeper responses to checkpoint blockade.…”