Abstract 2690: DCC-2618 is a potent inhibitor of wild-type and mutant KIT, including refractory Exon 17 D816 KIT mutations, and exhibits efficacy in refractory GIST and AML xenograft models (2015)

Abstract Introduction: KIT kinase mutations are causative of a number of human cancers, including gastrointestinal stromal tumors (GIST), systemic mastocytosis (SM), mast cell leukemia (MCL), and subtypes of melanoma and acute myeloid leukemia (AML). DCC-2618 is a robust Type II switch pocket control inhibitor which potently inhibits exon 17 KIT mutations that are resistant to conventional TKIs. Experimental procedures: DCC-2618 was tested for inhibition of KIT isoforms using a standard PK/LDH coupled spectrophotometric assay. CHO cells were transiently transfected to express mutant KIT or PDGFRα constructs. Transfected cells were treated with a range of DCC-2618 and levels of phosphorylated KIT or PDGFRα in cell lysates were determined by ELISA or western blot. Cell proliferation of several cell lines was measured using the fluorescent dye resazurin. Experiments were performed in triplicate. In vivo xenograft models were performed at Molecular Imaging, Inc. (Ann Arbor, MI) or Molecular Response, LLC (San Diego, CA). Summary of results: DCC-2618 inhibited various forms of KIT with nanomolar potency: WT (IC50 4 nM), V654A (8 nM), T670I (18 nM), D816H (5 nM), D816V (14 nM). In CHO cells transiently transfected with both single and double (primary/secondary) KIT mutants, DCC-2618 robustly inhibited exon 17, exon 9/13, exon 9/14, and exon 9/17 KIT mutants, as well as exon 11/17 KIT mutants, including exon 17 D816V, D816G, D820A, D820E, D820Y, N822K, N822Y, N822H, and Y823D primary or secondary mutations. DCC-2618 inhibited wild type KIT phosphorylation in the MO7e cell line (IC50 36 nM). DCC-2618 potently inhibited KIT activation in human GIST cell lines, including GIST T1 (exon 11 deletion, IC50 2 nM), GIST 430 (exon 11 deletion/exon 13 V654A, IC50 7 nM), and GIST 48 (exon 11 V560D/exon 17 D820A, IC50 53 nM). In the murine mastocytosis P815 cell line expressing the exon 17 D816Y mutation, DCC-2618 potently inhibited cell proliferation (IC50 2 nM). In vivo, DCC-2618 administration at 50 mg/kg afforded an ED90 for inhibition of KIT phosphorylation in the GIST T1 xenograft model, corresponding to an EC90 concentration of ∼ 470 ng/mL. When give twice daily, this oral dose resulted in almost complete tumor stasis. This dose of DCC-2618 produced tumor regressions in a patient derived xenograft (PDX) GIST expressing KIT exon 11 delW557K558/exon 17 Y823D, and also in a KIT exon 17 N822K AML xenograft model. Conclusion: DCC-2618 is a potent inhibitor of singly and doubly mutated KIT characterized by primary exon 9 or exon 11 mutations paired with secondary mutations in exons 13, 14 or 17. DCC-2618 inhibits exon 17 mutations, including the D816V mutation refractory to currently marketed KIT inhibitors. DCC-2618 has the potential to treat KIT mutant-driven cancers including GIST, systemic mastocytosis, AML, or melanoma. DCC-2618 has been selected for formal IND-enabling clinical development. Citation Format: Bryan D. Smith, Molly M. Hood, Scott C. Wise, Michael D. Kaufman, Wei-Ping Lu, Thomas Rutkoski, Daniel L. Flynn, Michael C. Heinrich. DCC-2618 is a potent inhibitor of wild-type and mutant KIT, including refractory Exon 17 D816 KIT mutations, and exhibits efficacy in refractory GIST and AML xenograft models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2690. doi:10.1158/1538-7445.AM2015-2690