Abstract 25: CG′806, a first-in-class FLT3/BTK inhibitor, exerts superior potency against AML cells harboring ITD, TKD and gatekeeper mutated FLT3 or wild-type FLT3

• Published in: Clinical cancer research 2017-12, Vol.23 (24_Supplement), p.25-25
• Main Authors: Zhang, Weiguo, Zhang, Hongying, Local, Andrea, Rice, William G., Ly, Charlie J., Yu, Guopan, Howell, Stephen B., Andreeff, Michael
• Format: Article
• Language: English
• ISSN: 1078-0432; 1557-3265
• DOI: 10.1158/1557-3265.HEMMAL17-25

The receptor tyrosine kinase FLT3 can undergo a series of mutations, including the activating internal tandem duplication (ITD) in the juxtamembrane region and point mutations in the tyrosine kinase domain such as at the activation loop residue D835 (Thiede et al. 2002). FLT3 is widely accepted as a prime target for acute myeloid leukemia (AML) therapy, as the FLT3-ITD mutation is present in approximately 24% of AML patients and it is associated with very poor prognosis (Kottaridis et al. 2003). However, additional acquired mutations of FLT3, including D835 or “gatekeeper” F691 mutations that have been identified in clinical patients who showed resistance/relapse to FLT3 inhibitors sorafenib or quizartinib (Man et al. 2012; Smith et al. 2012), can render most FLT3 inhibitors ineffective. We also reported that aberrant upregulation of other parallel prosurvival signaling pathways may render AML resistant to FLT3-targeted therapy (Zhang et al. 2014). CG′806 is a small-molecule multi-kinase inhibitor against FLT3 and BTK kinases that is under development to treat FLT3-driven AML. A single test concentration of 25 nM in a 583-kinase panel, an IC50 analysis against 176 kinases, and a Kd analysis against 483 kinases illustrated the ability of CG′806 to target the entirety of FLT3-mutant enzymes and to inhibit additional kinases (e.g., BTK, AURK, STE group, and TRK/AXL/DDR group). CG′806 exerted potent picomolar IC50 antiproliferative activity against human AML cells and against Ba/F3 mouse AML cells with FLT3-ITD mutations (about 50 to 250-fold higher activity compared to quizartinib or gilteritinib). Specifically, compared to second-generation FLT3 inhibitors quizartinib or gilteritinib, CG′806 showed much more pronounced antiproliferative effects in leukemia cells with D835 mutations, the ITD plus F691I/Y842D/D835 mutations, or in FLT3 wild-type cells (IC50s were 0.17, 0.82, 9.49, 0.30, 8.26, 9.72, and 0.43 nM for human ITD-mutated AML cells MV4-11 (FLT3-ITD), MOLM13 (FLT3-ITD), murine ITD mutated leukemia cells Ba/F3 WT, Ba/F3-ITD, Ba/F3-D835Y, Ba/FLT3-ITD+D835Y, and “gatekeeper” mutation Ba/F3-ITD+F691L cells, respectively). Furthermore, CG′806 triggered profound apoptosis in cell lines and primary AML patient samples harboring FLT3-ITD mutations as well as WT. Mechanistically, CG′806 profoundly suppressed FLT3 and its downstream MAPK/AKT signaling, as well as phospho-Aurora, and/or phospho-BTK proteins, suggesting the ability of CG′806 to inhibit various ki