Activation mutations of FLT3 contribute to the pathophysiology of approximately 30% of AMI cases. Internal tandem duplication mutations are associated with an adverse prognosis especially in the subgroup with normal cytogenetics. Work from the prior funding period of this application showed that activating mutations of FLT3 confer factor-independent growth in leukemic cell lines and lead to a fatal myeloproliferative syndrome in a murine bone marrow transplant model. Pharmacological inhibitors of the FLT3 tyrosine kinase specifically kill such transformed cell lines and prolong the survival of mice with this model neoplasm. In partnership with pharmaceutical companies and in close collaboration with our laboratory-based colleagues, the adult leukemia program at the Dana-Farber Cancer Institute has taken the lead in developing FLT3 inhibitors for clinical use in AML. We established that PKC412 and MLN518 were tolerated as single agents in patients with AML and produced a reduction in peripheral leukemic blast count in most patients whose leukemia was documented to have a FLT3 mutation. However, the experience with all the FLT3 inhibitors to date suggests that their utility as single agents will be limited, due in part to pharmacological considerations but also due to the relevance of other genetic legions in AML. It will be necessary to combine FLT3 inhibitors with agents which either enhance target inhibition or interfere with critical pathways. We have led two studies in which a FLT3 inhibitor is combined with chemotherapy in patients with newly diagnosed AML. We propose to extend the studies with FLT3 inhibitors plus chemotherapy (specific Aim 1) by leading a definitive phase III study of standard chemotherapy +/- PKC412 and to perform ancillary studies to determine the potential mechanisms of FLT3 resistance. Ancillary studies associated with this U.S. Intergroup phase III trial will include (Specific Aim 1b) the impact of baseline FLT3 autophosphorylation and downstream signaling on outcome and (Specific Aim 1c) the frequency of changes in FLT3 mutational patterns at relapse compared with diagnosis. We will work closely with Dr. Griffin in Project 1 who will assess killing of human leukemic cells in vitro by combinations of FLT3 inhibitors and inhibitors of other pathways/cellular processes. We will then perform (Specific aim 2) clinical trials to test promising combinations in patients with mutant FLT3 AML. [The first such trial, based on preclinical experiments in Project 1, will be a phase I study of PKC412 and the mTOR inhibitor RAD001. Ancillary studies will determine if this combination of tyrosine kinase inhibition with downstream signaling inhibition is feasible and can inhibit the expected targets.] Based on pre-clinical development in this and the other projects in this grant we anticipate being able to devise new and potentially effective therapies for patients with this type of poor prognosis AML.
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