Clinical Response of Carcinomas Harboring the BRD4–NUT Oncoprotein to the Targeted Bromodomain Inhibitor OTX015/MK-8628

UNLABELLED: The antineoplastic, prodifferentiative effects of bromodomain and extra-terminal (BET) bromodomain (BRD) inhibitors were initially discovered in NUT midline carcinoma (NMC), an aggressive subtype of squamous cancer driven by the BRD4-NUT fusion oncoprotein. BRD4-NUT blocks differentiation and maintains tumor growth through a potent chromatin-modifying mechanism. OTX015/MK-8628, a novel oral BET inhibitor, targets BRD2/3/4/T with preclinical activity in NMC and several other tumor types and is currently in clinical development. Antitumor activity was evaluated in four patients with advanced-stage NMC with confirmed BRD4-NUT fusions who were treated with 80 mg OTX015/MK-8628 once daily in a compassionate-use context. Two patients responded rapidly with tumor regression and symptomatic relief, and a third had meaningful disease stabilization with a minor metabolic response. The main side effects were mild to moderate gastrointestinal toxicity and fatigue, and reversible grade 3 thrombocytopenia. This is the first proof-of-concept evidence of clinical activity of a BRD inhibitor in targeting BRD4-NUT. SIGNIFICANCE: We present the first clinical proof-of-concept that targeting BRD4-NUT with a BET inhibitor results in impressive and rapid antitumor activity in NMC. It offers strong potential for future clinical application in this rare patient population as either a single agent or in combination with other agents. Cancer Discov; 6(5); 492-500. ©2016 AACR.This article is highlighted in the In This Issue feature, p. 461.