Death by HDAC Inhibition in Synovial Sarcoma Cells

Conventional cytotoxic therapies for synovial sarcoma provide limited benefit, and no drugs specifically targeting the causative SS18-SSX fusion oncoprotein are currently available. Histone deacetylase (HDAC) inhibition has been shown in previous studies to disrupt the synovial sarcoma oncoprotein complex, resulting in apoptosis. To understand the molecular effects of HDAC inhibition, RNA-seq transcriptome analysis was undertaken in six human synovial sarcoma cell lines. HDAC inhibition induced pathways of cell-cycle arrest, neuronal differentiation, and response to oxygen-containing species, effects also observed in other cancers treated with this class of drugs. More specific to synovial sarcoma, polycomb group targets were reactivated, including tumor suppressor CDKN2A, and proapoptotic transcriptional patterns were induced. Functional analyses revealed that ROS-mediated FOXO activation and proapoptotic factors BIK, BIM, and BMF were important to apoptosis induction following HDAC inhibition in synovial sarcoma. HDAC inhibitor pathway activation results in apoptosis and decreased tumor burden following a 7-day quisinostat treatment in the Ptenfl/fl; hSS2 mouse model of synovial sarcoma. This study provides mechanistic support for a particular susceptibility of synovial sarcoma to HDAC inhibition as a means of clinical treatment. (C) 2017 AACR.