HDACs regulate gene transcription, producing disparate effects on cell growth and survival. Vorinostat, an HDAC inhibitor, was approved by the kinase inhibitor MEK162 FDA as therapy for cutaneous T cell lymphomas. Pracinostat is an oral HDAC inhibitor that is currently in phase II clinical trials. We also reported previously that another HDAC inhibitor, depsipeptide, an acetylated intracellular protein, is effective against BCR ABL positive blastic crisis cells. Because vorinostat and other HDAC inhibitors induce cell cycle ar rest and apoptosis in tumor cells, we investigated whether vorinostat or pracinostat would inhibit growth in BCR ABL expressing cells. K562 and Ba F3 T315I cells were treated with vorinostat or pracinostat, and cell prolif eration was investigated.

Treatment with vorinostat or pracinostat for 72 h strongly and significantly inhibited the growth of K562 and Ba F3 T315I cells in a dose dependent manner. HDAC inhibitors have been reported to induce the degradation of both Aurora A and B kinases through a proteasome mediated pathway. Because ab errant expression and activity of Aurora kinases occur in a wide range of human tumors, inhibition or depletion of Aurora kinases may provide a promising method to delay the growth of leukemia cells. In this study, we investi gated the effects of vorinostat and pracinostat on Aurora kinase expression by using K562 cells. K562 cells were treated with vorinostat or pracinostat at the indicated con centration for 48 h and analyzed by immunoblotting. The expression of Aurora A and B was dose dependently re duced after treatment with vorinostat or pracinostat.

Analysis of the effects of an Aurora kinase inhibitor on intracellular signaling in K562 cells Because HDAC proteins are aberrantly expressed in many types of cancers and have nonredundant functions in con trolling the hallmark phenotypes of cancer cells, we ex amined HDAC expression after treatment with an Aurora kinase inhibitor in K562 cell lines using DNA and antibody microarray techniques. We found that the relative levels of HDAC gene expression in K562 cell lines were decreased after tozasertib treatment. In contrast, expression of apoptosis related genes, including Bim, was increased. We next examined results of the protein array studies. In K562 cells, we found that HDAC protein levels were decreased and apoptosis related protein expression was increased after 24 h treatment with 1 uM tozasertib.

To confirm these findings, we performed im munoblotting analysis. Additionally, after tozasertib treat ment, the expression of HDAC1, 2, 5, and ?7 proteins was significantly reduced, while that of Bim was increased. Activity of the Aurora kinase inhibitor in wild type and mutant BCR ABL expressing cells We next Anacetrapib investigated the activity of tozasertib against wild type and mutant BCR ABL expressing cells.