Abstract 2913: Entinostat (KHK2375), class I histone deacetylase inhibitor, regulates human Treg function by decreasing Foxp3 expression and effector Treg population
Authors: Kosaka Hiromichi , Nishimura Yozo , Kaneda Ayumi , Masuda Norikazu , Tamura Kenji , Saji Shigehira , Iwata Hiroji , Mori Kiyotoshi 
Published: September 2020

Abstract
Objective: Entinostat (KHK2375 also known as MS-275, SNDX-275 and ZN244894), a synthetic benzamide derivative, is a class I selective histone deacetylase inhibitor. Entinostat increases the acetylation of histone and non-histone proteins. Change of histone modification status leads to chromatin remodeling and alters gene expression resulting in the change of cellular phenotype. Also, it has been reported that entinostat decreased myeloid-derived suppressor cells (MDSCs) in both mice and humans, suggesting that entinostat may impact tumor immunology. In this study, we evaluated the effect of entinostat on CD4+ regulatory T cells (Treg) using human peripheral blood mononuclear cells (PBMCs).
Materials/methods: Protein lysine acetylation (Ac-K) status and Treg population were evaluated by flow cytometric analysis. Expression of FoxP3, a master regulator of Treg development and function, was evaluated by both mRNA and protein levels. Treg function was also evaluated in terms of IFNγ production from CD4+ T cells (Tconv) and CD8+ T cells, and proliferation of these cells under a co-culture condition with Treg. Furthermore, the effect of entinostat on Treg population in PBMCs obtained in a phase 1 trial with Japanese breast cancer patients was evaluated.
Results: Entinostat induced the accumulation of Ac-K signals in naive Treg (CD45RA+FoxP3low), effector Treg (CD45RA−FoxP3high) and non-Treg (CD45RA−FoxP3low). Interestingly, entinostat selectively reduced the proportion of effector Treg among CD4+ T cells in a dose dependent manner, while those of naive Treg and non-Treg, as well as total Treg defined by CD4+CD25+CD127low/− were not changed by entinostat. Entinostat showed the reduction of FoxP3 expression in total Treg in both mRNA and protein levels. Moreover, immuno-suppressive function of Treg as measured by T cell dependent IFNg production was cancelled by entinostat. Lastly, the decrease of effector Treg proportion was also observed in PBMCs on the day following the oral administration of entinostat in the phase 1 study (Cohort 1: 3 mg/day (N=3), Cohort 2: 5 mg/day (N=3), Cohort 3: 10 mg/day (N=2)).
Conclusion: Entinostat (KHK2375) showed an inhibitory effect on immuno-suppressive function of human Treg by decreasing FoxP3 expression and effector Treg proportion. These results support a potential role for entinostat mediated immunomodulatory effects in providing clinical benefit to patients.
Citation Format: Hiromichi Kosaka, Yozo Nishimura, Ayumi Kaneda, Norikazu Masuda, Kenji Tamura, Shigehira Saji, Hiroji Iwata, Kiyotoshi Mori. Entinostat (KHK2375), class I histone deacetylase inhibitor, regulates human Treg function by decreasing Foxp3 expression and effector Treg population [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2913.