Blockade of MEK/ERK signaling enhances sunitinib-induced growth inhibition and apoptosis of leukemia cells possessing activating mutations of the FLT3 gene

The FMS-like tyrosine kinase 3 (FLT3) is a cell surface receptor tyrosine kinase. Activating mutations of this gene occur in nearly 30% of acute myelogenous leukemia (AML) patients. These mutations, in part, result in activation of mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathways. In this study, we found that AZD6244 (ARRY-142886), a novel inhibitor of MEK1/2 kinases, effectively inhibited the proliferation of acute biphenotypic leukemia MV4-11 and acute monocytic leukemia MOLM13 cells. The concentrations that inhibited 50% growth were approximately 0.3 and 1.2 μM, respectively, as measured by thymidine uptake on day 2 of culture. AZD6244 potently down-regulated the levels of phospho-ERK1/2 and its downstream effector, p-p70S6K, in the MV4-11 and MOLM13 cells as measured by Western blot analysis. Interestingly, when AZD6244 was combined with sunitinib, a FLT3 kinase inhibitor, growth inhibition and apoptosis of both MV4-11 and MOLM13 cells were synergistically enhanced in association with further down-regulation of phospho-ERK1/2 and p-p70S6K in these cells. Taken together, concomitant blockade of FLT3 and MEK signaling represents a promising treatment strategy for individuals with leukemia who possess activating mutations of FLT3.