HDAC9 and cancer: It is well known that butyrate is the primary energy source of colonocytes; moreover, several studies have shown that in high concentrations (~5 mM), butyrate is a potent HDAC inhibitor, resulting in expression of several genes involved in cancer or inflammation: cyclin-dependent kinase inhibitor 1A (p21WAF1/Cip1), mucin 2 (MUC-2), testin LIM domain protein (TES), and hypoxia-inducible factor 1 (HIF-1) (55, 56, 58, 59).