Abstract B74: The dual FLT3-Aurora inhibitor CCT241736 overcomes resistance to selective FLT3 inhibition driven by FLT3 ligand and FLT3 point mutations in acute myeloid leukemia.

Internal tandem duplication or kinase domain point mutations of the fms-like tyrosine kinase 3 gene (FLT3-ITD, -TKD) result in constitutive FLT3 kinase activation and promote leukemic proliferation. FLT3-ITD occurs in 20–35% of adults and 15% of children with acute myeloid leukemia and confers a poor prognosis in both age groups. Activated FLT3 therefore represents a valid therapeutic target and several FLT3 inhibitors are currently in phase II-III clinical trials. The clinical impact of FLT3 inhibitors has thus far been limited by transient responses when used as single agents due to lack of sustained FLT3 inhibition and the emergence of secondary acquired resistance following treatment. Aurora kinases are a family of serine-threonine kinases that play a key role in several stages of mitosis. Although studies in leukemia have been limited to cell lines and small patient cohorts, over-expression of Aurora A has been consistently demonstrated and Aurora kinase inhibitors show potential in the treatment of AML. Our hypothesis is that simultaneous FLT3 / Aurora inhibition will improve single-agent efficacy and reduce susceptibility to FLT3-ligand-driven and FLT3 mutation-driven resistance in FLT3-ITD positive AML. In addition, we have generated a model of FLT3 inhibitor resistance by prolonged treatment of MOLM-13 cells with the selective FLT3 inhibitor MLN518. These resistant cells, termed MOLM-13-RES, are doubly-mutated with FLT3-ITD and a FLT3-TKD (D835Y) point mutation and over-express Survivin. Here we demonstrate that such doubly-mutated AML cells are sensitive to the dual FLT3-Aurora inhibitor CCT241736. CCT241736, an imidazo[4,5-b]pyridine derivative discovered at our Institution, is a novel, orally bioavailable, potent and highly selective FLT3 and pan-Aurora inhibitor [S(10) = 0.057; a fraction of 386 kinases inhibited >90% when screened at 1 μM of CCT241736]. In biochemical assays, CCT241736 has IC50 values against FLT3, Aurora A and Aurora B of 0.035, 0.015 and 0.1 μM respectively. Furthermore, CCT241736 inhibits a wide range of FLT3 mutants, including FLT3-ITD, -D835Y, -D835H, -K663Q and -N841I. In cellular assays, CCT241736 inhibits viability of the human FLT3-ITD positive AML cell lines MOLM-13 and MV-4;11 with EC50 values of 0.1 and 0.27 M respectively. In vivo, mouse tumor xenograft models of MOLM-13, MV-4;11 and the doubly-mutated cell line, MOLM-13-RES, are also sensitive to CCT241736, with biomarker modulation consistent with dual inhibition of FLT3 and Aurora kinases. In summary, dual inhibition of FLT3 and the critical mitotic kinase Aurora by CCT241736 may represent a novel treatment strategy for FLT3-mutated AML by overcoming the effects of high FL levels and limiting resistance caused by secondary mutations of the FLT3 gene. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B74.