Entinostat is an oral, weekly or bi-weekly, selective histone deacetylase (HDAC) inhibitor that has been well-tolerated in clinical trials to date. HDACs are a class of enzymes with a predominant role in regulating gene expression through a chemical modification to DNA-associated proteins known as histones. This chemical modification is part of a regulatory system that controls gene expression, known as epigenetics. When the function of these epigenetic enzymes is altered, gene expression is changed in ways that often leads to disease. For example, specific HDACs are over-expressed in cancer cells, leading to improper gene regulation, which results in uncontrolled cell growth and resistance to cancer therapies. We believe that based upon our preclinical results entinostat is a potent inhibitor of these cancer-relevant HDACs, thereby restoring normal gene expression and protein function to slow cancer growth and turn off activated cancer therapy resistance pathways. We believe entinostat is differentiated through its selectivity for cancer-relevant HDACs and clinical activity profile, including convenient oral dosing and long half-life.

Entinostat targets cancer cell growth and the primary and acquired resistance pathways that limit the effectiveness and durability of cancer therapies. We observed in clinical trials that entinostat, in combination with other cancer therapies, may enhance and extend their therapeutic benefit resulting in prolonged progression-free survival and overall survival. We believe that our approach with entinostat is applicable to a broad range of cancer therapies and across a wide spectrum of tumor types. We have collected clinical data in both advanced breast and lung cancer, which we believe supports this approach and demonstrates the significant clinical and commercial potential for entinostat in targeting resistance to cancer therapies.