Studies of New Signal Transduction Modulators in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a life-threatening malignant disorder with dismal prognosis. AML is characterized by frequent genetic changes involving tyrosine kinases, normally acting as important mediators in many basic cellular processes. Due to the overexpression and frequent mutations of the FMS-like receptor tyrosine kinase 3 (FLT3) in AML, this tyrosine kinase receptor has become one of the most sought after targets in AML drug development. In this thesis, we have used a combination of high-throughput screens, direct target interaction assays and sequential cellular screens, including primary patient samples, as an approach to discover new targeted therapies. Gefitinib, a previously known inhibitor of epidermal growth factor receptor and the two novel tyrosine kinase inhibitors AKN-032 and AKN-028, have been identified as compounds with cytotoxic activity in AML. AKN-028 is a potent inhibitor of FLT3 with an IC50 value of 6 nM in an enzyme assay, but also displaying in vitro activity in a variety of primary AML samples, irrespective of FLT3 mutation status or quantitative FLT3 expression. AKN-028 shows a sequence dependent in vitro synergy when combined with standard cytotoxic agents cytarabine or daunorubicin, with better efficacy when cells are exposed to standard chemotherapy simultaneously or for 24 hours prior to adding AKN-028. Antagonism is observed when cells are pre-treated with AKN-028, possibly explained by the cell cycle arrest induced by the compound. In vivo cytotoxic activity and good oral bioavailability have made AKN-028 a candidate drug for clinical studies and the compound is presently investigated in an international two-part multicenter phase I/II study. Results from microarray studies performed to further elucidate the mechanism of action of AKN-028, revealed significantly altered gene expression induced by AKN-028 in both AML cell lines and in primary AML cells, with an enrichment of the Myc pathway among the downregulated genes. Furthermore, tyrosine kinase activity profiling shows a dose-dependent kinase inhibition by AKN-028 in all AML samples tested. Interestingly, cells with a high overall kinase activity were more sensitive to AKN-028. Provided conformation in a larger set of samples, kinase activity profiling may give useful information in individualizing treatment of patients with AML