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Blood, 1 March 2006, Vol. 107, No. 5, pp. 2094-2097. Prepublished online as a Blood First Edition Paper on November 22, 2005; DOI 10.1182/blood-2005-08-3317.
NEOPLASIA FLT3-ITD, but not BCR/ABL-transformed cells require concurrent Akt/mTor blockage to undergo apoptosis after histone deacetylase inhibitor treatmentFrom the Universitätsklinikum Marburg und Gießen, Standort Marburg, Klinik für Hämatologie, Onkologie, und Immunologie, and Institut für Pathologie, Marburg; and University Hospital Frankfurt, Medizinische Klinik III, Frankfurt, Germany.
Leukemias are differentially sensitive to histone deacytelase inhibitor (HDI)induced apoptosis, but molecular reasons for this remain unclear. We here show that BCR/ABL-, but not FMS-like tyrosine kinase 3 (FLT3)internal tandem duplication (ITD)transformed 32D cells or primary acute myeloid leukemia (AML) blasts undergo apoptosis after treatment with the HDI valproic acid (VPA) plus all-trans retinoic acid (VPA/ATRA). A particular VPA/ATRA responsiveness of Philadelphia chromosomepositive (Ph+) acute lymphatic leukemia (ALL) was confirmed in a therapy-refractory patient in vivo. HDI-stimulated apoptosis in Ph+ cells was caspase dependent, but independent from Akt pathway inhibition. Conversely, separate blockage of the Akt/mTor-signaling pathway was a prerequisite for overcoming apoptosis resistance to VPA/ATRA in FLT3-ITD cells, and primary AML blasts (n = 9). In conclusion, constitutive Akt activation causes apoptosis resistance to VPA/ATRA in AML, but not in Ph+ leukemia. This warrants the application of HDI-based therapies in poor-risk Ph+ ALL, and the use of Akt/mTor inhibitors to overcome HDI resistance in AML.
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