Abstract 5636: Different characteristics of drug resistance in AML cell lines between a dual Flt3/CDK4 kinase inhibitor AMG 925 and Flt3 inhibitors.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Objectives: Flt3 inhibitors have shown clinical responses in Flt3 mutant acute myeloid leukemia (AML) but resistance develops rapidly. In order to improve the durability of clinical response of AMLFlt3 MUT, a small molecule inhibitor of Flt3 and CDK4/6 kinases, AMG 925, was developed. The primary purpose of this study is to compare the ability of AML cell lines to become resistant to AMG 925 and to other Flt3 inhibitors, and to elucidate the underlying molecular mechanisms. Methods: Drug resistant MOLM13 and Mv4-11 cell clones were isolated by prolonged exposure to increasing concentrations of AMG 925 and other Flt3 inhibitors. Cell proliferation was determined by CellTiter Glo. Protein expression levels were assessed by Western Blotting, IP Western Blotting and MSD assays. Flt3 mRNA levels were measured by RT-PCR. Results and Conclusions: Both MOLM13 and Mv4-11 cells developed resistance to all the inhibitors tested within 3-4 months. In contrast to AML cells resistant to other Flt3 inhibitors (IC50 increased by about 1000 fold), cells resistant to AMG 925 were only at much lower drug concentrations (IC50 increased by 3-5 fold). Mutations in the Flt3 kinase domains were found in cells resistant to the other Flt3 inhibitors but not in those resistant to AMG 925. P-Flt3 and P-STAT5 in AMG 925 resistant cells were less inhibited than in the sensitive parental cells, apparently as a result of an increased total Flt3 (2-3 fold) in the resistant cells. These results are consistent with the hypothesis that it is more challenging for AML cells to develop drug resistance against combined inhibition of Flt3 and CDK4/6 (AMG 925) than against inhibition of Flt3 alone. Citation Format: Cong Li, Lingming Liang, Darrin Beaupre, Katie Newhall, Zhihong Li, Queenie Wang, Zhen Xia, Qiang Liu, Larry McGee, Dineli Wickramasinghe, Kang Dai. Different characteristics of drug resistance in AML cell lines between a dual Flt3/CDK4 kinase inhibitor AMG 925 and Flt3 inhibitors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5636. doi:10.1158/1538-7445.AM2013-5636