Superior efficacy of a combined epigenetic therapy against human mantle cell lymphoma cells

Purpose: A deregulated epigenome contributes to the transformed phenotype of mantle cell lymphoma (MCL). This involves activity of the polycomb repressive complex (PRC) 2, containing three core proteins, EZH2, SUZ12, and EED, in which the SET domain of EZH2 mediates the histone methyltransferase activity. We determined the effects of 3-deazaneplanocin A (DZNep), an S - adenosylhomocysteine hydrolase inhibitor, and/or pan-histone deacetylase inhibitor panobinostat (PS) on cultured and primary MCL cells. Experimental Design: Following treatment with DZNep and/or PS, apoptosis and the levels and activity of EZH2 and PRC2 proteins in cultured and primary MCL cells were determined. Results: Treatment with DZNep depleted EZH2, SUZ12, and 3MeK27H3 in the cultured human MCL cells. DZNep also increased expression of p21, p27, and FBXO32, whereas it depleted Cyclin D1 and Cyclin E1 levels in MCL cells. In addition, DZNep treatment induced cell-cycle arrest and apoptosis in cultured and primary MCL cells. Furthermore, as compared with treatment with each agent alone, cotreatment with DZNep and PS caused greater depletion of EZH2, SUZ12, 3MeK27H3, and Cyclin D1 levels, whereas it induced greater expression of FBXO32, p16, p21, and p27. Combined treatment with DZNep and PS synergistically induced apoptosis of cultured and primary MCL cells while relatively sparing normal CD34 + cells. Cotreatment with DZNep and PS also caused significantly greater inhibition of tumor growth of JeKo-1 xenografts in NOD/SCID mice. Conclusions: These preclinical in vitro and in vivo findings show that cotreatment with DZNep and PS is an active combined epigenetic therapy worthy of further in vivo testing against MCL.