HDAC9 and acute promyelocytic leukemia: Interestingly, ATRA sensitization of non-APL cells has been induced by targeting epigenetic enzymes: inhibition of histone deacetylase (HDAC) with valproic acid [39] or inhibition of the histone demethylase LSD1/KDM1A [40] or by targeting SUMOylation [41].