The Analysis of HDAC Inhibitor, Vorinostat Efficacy against Wild Type and BCR-ABL Mutant Positive Leukemia Cells in Monotherapy and in Combination with a Pan-Aurora Kinase Inhibitor, MK-0457

The use of imatinib, an ABL tyrosine kinase inhibitor, has led to a dramatic change in the management of BCR-ABL positive leukemia patients. However, the resistance to imatinib mediated by mutations in the BCR-ABL domain has become a major problem in the treatment. Histone deacetylase (HDAC) inhibitors have been shown to mediate the regulation of gene expression, induce cell growth, cell differentiation and apoptosis of tumor cells. Vorinostat (suberoylamide hydroxamic acid:SAHA) is a hydroxamic acid based polar HDAC inhibitor. Vorinostat have shown efficacy in a wide range of cancers such as cutaneous T-cell lymphoma (CTCL). However, efficacy of vorinostat against the BCR-ABL mutants has fully not known. Here we report on the studies performed against murine Ba/F3 cell line which was transfected wild type (Wt) p210 and p185 BCR-ABL or imatinib resistant BCR-ABL mutants such as G250E, Q252H, Y253F, E255K, M294V, T315I, T315A, F317L, F317V, M351T, H396P and T315I(p185). 48 hours treatment of vorinostat exhibits cell growth inhibition and proapoptotic activity murine Ba/F3 cells ectopically expressing Wt and imatinib resistant BCR-ABL mutants including T315I mutation in a dose dependent manner. IC50 of these cell lines are Wt(720nM), G250E(625nM), Q252H(220nM), Y253F(525nM), E255K(685nM), M294V(785nM), T315I(500nM), T315A(715nM), F317L(560nM), F317V(565nM), M351T(375nM) and H396P(485nM). Aurora kinases play a pivotal role in the regulator of mitotic processes during cell division. MK-0457 is a small molecule inhibitor of the Aurora kinase family and was found to be active against the cells from BCR-ABL positive patients with T315I mutation in clinical trial. Because vorinostat also depleted BCR-ABL, as well as induced apoptosis and sensitized BCR-ABL-expressing leukemia cells, we examined whether vorinostat and MK-0457 enhances the apoptosis in imatinib resistant BCR-ABL-expressing cells. 48 hours treatment of MK-0457 exhibits cell growth inhibition of Ba/F3 cells ectopically expressing Wt and imatinib resistant BCR-ABL mutants including T315I mutation. IC50 of MK-0457 is Wt(215nM), G250E(205nM), Q252H(185nM), Y253F(245nM), E255K(185nM), M294V(238nM), T315I(205nM), T315A(165nM), F317L(200nM), F317V(200nM), M351T(225nM) and H396P(195nM). We examined the intracellular signaling by using these cell lines. We found that caspase 3, and poly (ADPribose) polymerase (PARP) were activated after MK-0457 treatment in a dose dependent manner. Phosphorylation of BCR-ABL and Crk-L which is downstream target of BCR-ABL was reduced after MK-0457 treatment. We found that combination of vorinostat and MK-0457 synergistically cell growth inhibition of Wt and BCR-ABL mutants Ba/F3 cells in 48 hours treatment. Phosphorylation of Crk-L was reduced after vorinostat and MK-0457 treatment. Caspase 3 and PARP activation were also synergistically increased after vorinostat and MK-0457 treatment. We evaluated the activity of MK-0457 and vorinostat in primary BCR-ABL positive acute lymphoblastic leukemia (ALL) cells with the T315I mutation. We found that MK-0457 potently induced cell growth inhibition of primary T315I cells in 48 hours treatment. Moreover, combination of vorinostat and MK-0457 synergistically increased the cell growth inhibition in primary T315I cells. This study demonstrate monotherapy of vorinostat and the combination of vorinostat and MK-0457 are more potent efficacy not only wild type BCR-ABL but also imatinib resistant BCR-ABL mutants cells and represents a promising new strategy for treatment of imatinib resistant BCR-ABL positive leukemias, including those harboring the T315I mutation.