Abstract

Mutations of the FLT3 receptor tyrosine kinase consisting of internal tandem duplications (ITD) have been detected in blasts from 20% to 30% of patients with acute myeloid leukemia (AML) and are associated with a poor prognosis. FLT3/ITD results in constitutive autophosphorylation of the receptor and factor-independent survival in leukemia cell lines. The C-28 methyl ester of the oleane triterpenoid (CDDO-Me) is a multifunctional molecule that induces apoptosis of human myeloid leukemia cells. Here, we report that CDDO-Me blocks targeting of NFkappaB to the nucleus by inhibiting IkappaB kinase beta-mediated phosphorylation of IkappaBalpha. Moreover, CDDO-Me blocked constitutive activation of the signal transducer and activator of transcription 3. We report the potent and selective antiproliferative effects of CDDO-Me on FLT3/ITD-positive myeloid leukemia cell lines and primary AML cells. The present studies show that CDDO-Me treatment results in caspase-3-mediated induction of apoptosis of FLT3/ITD-expressing cells and its antiproliferative effects are synergistic with PKC412, a FLT3-tyrosine kinase inhibitor currently in clinical trials. Taken together, our studies indicate that CDDO-Me greatly enhanced the efficacy of the FLT3 inhibitor PKC412, suggesting that combining two separate pathway inhibitors might be a viable therapeutic strategy for AML associated with a FLT3/ITD mutation.