Treatment with LAQ824 (Novartis Pharmaceutical, Inc.), a cinnamyl hydroxamic acid analogue inhibitor of histone deacetylases, depleted the mRNA and protein expression of Bcr-Abl in human chronic myeloid leukemia blast crisis (CML-BC) cells. Exposure to LAQ824 induced the expression of the cell cycle-dependent kinase inhibitors p21 and p27 and caused cell cycle G(1)-phase accumulation and apoptosis of CML-BC cells. LAQ824 also induced acetylation of heat shock protein 90. This inhibited the

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... rone association of Bcr-Abl with heat shock protein 90, thereby promoting the proteasomal degradation of Bcr-Abl. Cotreatment with LAQ824 increased imatinib mesylate-induced apoptosis of CML-BC cells. Additionally, LAQ824 down-regulated the levels of mutant Bcr-Abl possessing the T315I point mutation, as well as induced apoptosis of imatinib-refractory primary CML-BC cells. Therefore, LAQ824 may be a promising therapeutic agent in the treatment of imatinib-sensitive or -refractory human leukemia.