Abstract 4800: Covalent Flt3-Cys828 inhibition represents a novel therapeutic approach for the treatment of Flt3-ITD and Flt3-D835 mutant acute myeloid leukemia

Abstract

Abstract Inhibition of Flt3 kinase activity is a promising strategy for the treatment of Flt3 mutant acute myeloid leukemia (AML). However, clinical studies with Flt3 kinase inhibitors have shown that mutations of the gate keeper or an activation loop residue in the Flt3 catalytic domain limits the duration of response. Such mutations generally reduce kinase domain binding affinity and residence time of the kinase inhibitor, and consequently its efficacy. We therefore investigated whether covalent, irreversible binding to Flt3 could overcome some of the limitations of classic non-covalent Flt3 inhibitors. Here, we report for the first time on the high-affinity Cys828-covalent binding mode of a resorcylic acid lactone to the isolated Flt3 kinase domain using X-ray crystallography and kinetic binding assays. In a cellular context (Ba/F3-Flt3-ITD), mutation of Cys828 to Ala reduces potency (IC50) from low nM to microM, demonstrating all relevant Flt3 inhibition in cells critically depends on Cys828. Consistently, the molecule is a low nM inhibitor of both Flt3-ITD and Flt3D835Y in vitro and in BaF3 cells, translating to potent nM inhibition of Flt3-ITD driven AML cell line proliferation, with only microM antiproliferative activity in non-Flt3 driven AML and unrelated leukemia cell lines. Finally, in spite of its fast clearance when dosed to MV4-11 (Flt3-ITD AML) xenograft bearing mice, robust anti-tumor activity was observed using a once-daily treatment schedule. These data demonstrate the feasibility of covalent Flt3 inhibition, and suggest it represents an attractive novel therapeutic approach for the treatment of Flt3-driven AML. Citation Format: Matthias Versele, Burkhard Haefner, Berthold Wroblowski, Ian Stansfield, Laurence Mevellec, Ron Gilissen, Lars Neumann, Martin Augustin, Kris Jacobs, Jan Cools, S Barluenga, M Röthlingshöfer, G Karthikeyan, Ricardo Attar, Lieven Meerpoel, Nicolas Winssinger. Covalent Flt3-Cys828 inhibition represents a novel therapeutic approach for the treatment of Flt3-ITD and Flt3-D835 mutant acute myeloid leukemia. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4800.