HDAC9 and cancer: Similarly, treatment of T47D/WT cancer cells with the HDAC inhibitor, trichostatin A significantly increased the expression of MRP1, MRP2, MRP4, and BCRP. In other words, contrary to what occurs in cancer induced by epigenetic gene silencing, overexpression of MRP1, MRP2, MRP3, MRP4, and BCRP might be caused by DNA demethylation and histone acetylation.