Class I histone deacetylase inhibitor entinostat suppresses regulatory T cells and enhances immunotherapies in renal and prostate cancer models.
BACKGROUND
Immunosuppressive 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.


RESULTS
RENCA 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.


CONCLUSIONS
These 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.
Department of Medicine, Roswell Park Cancer Institute, Buffalo, New York, United States of America.
Li
L
Shen
Michael
M
Ciesielski
Swathi
S
Ramakrishnan
Kiersten M
KM
Miles
Leigh
L
Ellis
Paula
P
Sotomayor
Protul
P
Shrikant
Robert
R
Fenstermaker
Roberto
R
Pili
D000107:Acetylation / Q000187:drug effects; D000818:Animals; D001549:Benzamides / Q000494:pharmacology / Q000627:therapeutic use*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology; D002292:Carcinoma, Renal Cell / Q000188:drug therapy* / Q000235:genetics / Q000276:immunology / Q000473:pathology; D002369:Castration; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology / Q000627:therapeutic use*; D006655:Histone Deacetylases / Q000378:metabolism*; D006801:Humans; D007109:Immunity / Q000187:drug effects; D007167:Immunotherapy; D007371:Interferon-gamma / Q000276:immunology; D007376:Interleukin-2 / Q000627:therapeutic use; D007680:Kidney Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000276:immunology / Q000473:pathology; D008212:Lymphocyte Depletion; D008297:Male; D051379:Mice; D011471:Prostatic Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000276:immunology / Q000473:pathology; D011725:Pyridines / Q000494:pharmacology / Q000627:therapeutic use*; D050796:STAT3 Transcription Factor / Q000378:metabolism; D050378:T-Lymphocytes, Regulatory / Q000187:drug effects / Q000276:immunology*; D022223:Vaccines, Subunit / Q000276:immunology / Q000627:therapeutic use
D001549:Benzamides; D051858:Forkhead Transcription Factors; C498833:Foxp3 protein, mouse; D056572:Histone Deacetylase Inhibitors; D007376:Interleukin-2; D011725:Pyridines; D050796:STAT3 Transcription Factor; D022223:Vaccines, Subunit; C118739:entinostat; D007371:Interferon-gamma; D006655:Histone Deacetylases