Part 3 will evaluate the effect of an acidic beverage co-administered with entinostat in subjects with increased gastric pH due to omeprazole treatment. In Period 1, multiple oral doses of omeprazole will be administered with a single dose of entinostat co-administered with water. In Period 2, multiple doses of omeprazole will be administered with a single dose of entinostat co-administered with an acidic beverage.