Abstract 2748: Antitumor activity of HDAC inhibition in bladder cancer mouse models correlates with enhanced immune response
Authors: Stewart Kyle G. , Truong Andrew S. , Krishnan Bhavani , Zhou Mi , Saito Ryoichi , Kardos Jordan , Manocha Ujjawal , Bailey Sean T. , Kim William Y. 
Published: August 2018

Abstract
Aberrant chromatin remodeling by epigenetic modifier proteins such as histone deacetylases (HDACs) is common within many types of cancer, including muscle-invasive bladder cancer (MIBC). The removal of acetyl groups from the lysine residues of histones leads to transcriptional silencing that promotes tumor growth and potentially enhances cancer cells' ability to evade the host immune response. Therefore, HDACs present themselves as attractive targets for cancer therapy. Histone deacetylase inhibitors (HDACi) demonstrate broad anti-cancer activity. Many proposed mechanisms exist to explain their effects, including those that involve the immune system. Here, we evaluated the efficacy and transcriptional effects of entinostat, a selective class 1 HDAC inhibitor (HDAC1 and HDAC3), in a novel preclinical murine model of high-grade MIBC.
BBN963 cells were derived from a primary bladder cancer GEM, cultured, and implanted subcutaneously into immunocompetent C57BL/6 mice and immunodeficient NOD scid gamma (NSG) mice. Animals were randomized to control or entinostat treatment. Tumor volume was recorded weekly and fresh tissue collected for RNAseq and Ingenuity Pathway Analysis (IPA). Entinostat exhibited in vivo activity in the BBN963 model in both C57BL/6 and NSG mice, however the anti-tumor response in B6 mice was significantly greater than the observed response in NSG mice. RNAseq analysis on tumor tissue collected from NSG mice indicated that entinostat treated tumors had distinct gene expression changes. Comparison of control to entinostat treated tumors revealed 4987 genes were significantly upregulated and 4112 genes were significantly downregulated (p-value &lt; 0.05). IPA contextualized these changes as an enhanced inflammatory response, as indicated by increased expression of upstream regulators TGFβ, LPS, and IFNγ. Additionally, hierarchical clustering using established immune gene signatures stratified entinostat treated and untreated tumors into two distinct groups.
Our results suggest that the anti-cancer properties of entinostat are in part immunologically mediated. BBN963 tumors in B6 mice displayed a more robust therapeutic response compared to their NSG counterparts. Transcriptional analysis of the tumor tissue indicated significant differences in immune gene signature levels as well as inflammatory pathway activation. Therefore, an intact immune system appears critical to achieve a maximal therapeutic response observed with HDAC inhibition. Together these results lay the foundation for further elucidating entinostat's mechanism of action in the context of high-grade MIBC.
Citation Format: Kyle G. Stewart, Andrew S. Truong, Bhavani Krishnan, Mi Zhou, Ryoichi Saito, Jordan Kardos, Ujjawal Manocha, Sean T. Bailey, William Y. Kim. Antitumor activity of HDAC inhibition in bladder cancer mouse models correlates with enhanced immune response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2748.