Histone deacetylases (HDACs) help control how accessible DNA is to the transcription machinery of the cell. They were the first enzymes to be targeted by drugs trying to affect cellular epigenetics, and multiple companies are in multiple clinical trials for multiple indications with drugs that hope to join FDA-approved HDAC inhibitors Istodax (romidepsin, Celgene Corp.) and Zolinza (vorinostat, Merck & Co Inc.) on the market.