Epigenetic Cooperativity as a Therapeutic Vulnerability in Cancer

NUT carcinoma (NC) is one of the most common types of undifferentiated carcinomas affecting young adults with a dismal prognosis. NUT carcinomas often involve chromosomal translocations, leading to the production of BRD4-NUT fusion protein that generates large domains of hyperactive chromatin and activates oncogenic gene expression. Bromodomain and extraterminal domain (BET) bromodomain inhibitors offer a direct means to block BRD4-mediated gene activation but have shown limited clinical efficacy in patients. In this issue of Cancer Research, Huang and colleagues report an unexpected discovery of a synthetic lethal NC dependency on Polycomb repressive complex 2 (PRC2)-mediated gene repression, including EZH2, the catalytic subunit of PRC2. EZH2 is highly expressed in NC patient tumors and a specific inhibitor of its methyltransferase activity, tazemetostat, exhibits potent antitumor cell activity. While the repressed and activated chromatin domains in NC cells are distinct, the resultant gene expression changes exhibit convergent features, including dysregulation of CDKN2A and the E2F-RB1 axis. As a result, combined treatment of NC tumors with tazemetostat and the BET inhibitor mivebresib produces marked antitumor therapeutic synergy in vitro and in vivo, associated with enhanced suppression of RB1 function through convergent remodeling of NC gene expression. This study advances epigenetic cooperativity as a distinct mode of gene expression dysregulation in NC and nominates a compelling combination epigenetic strategy for investigation in clinical trials for patients. See related article by Huang et al., p. 3956.