Abstract 804: Antitumor activity of the potent and novel FLT3 inhibitor HM43239 in acute myeloid leukemia
Authors: Lee Miyoung , Ha Young Eun , Moon Mi Jin , Byun Joo-Yun , Yu HyunKyung , Kang SeokJong , Lee JaeHo , Lee Kyuhang , Kim Eunkyung , Kim Eunyoung , Lee Ho Jeong , Kim YoungHoon , Ahn YoungGil , Suh KweeHyun , Kim Sun-Jin 
Published: August 2018

Abstract
Introduction: Acute myeloid leukemia (AML) with FMS-like tyrosine kinase 3 (FLT3) mutations is associated with poor prognosis with a high risk of relapse after therapy and reduced overall survival. Activating mutations of internal tandem duplication (ITD) and tyrosine kinase domain point mutations (TKD) of FLT3 have been reported in approximately 30% of AML as oncogenic driver mutations. Currently, FLT3 inhibitors showed clinical benefits in the corresponding AML patients. In this study, we have characterized a novel FLT3 inhibitor, HM43239, and assessed the potential as a novel therapy for AML patients. Materials and Methods: HM43239 is a novel, highly potent FLT3 kinase inhibitor. This compound showed tight binding to FLT3 kinase in in silico docking model as a reversible Type I inhibitor. In vitro kinase assay was performed to identify kinase selectivity of HM43239. Standard proliferation assay, immunoblotting, and apoptosis analysis were carried out to validate the potency of HM43239 in AML cell lines. HM43239 was evaluated in MV-4-11 and MOLM-13 xenograft mice models. Tumor sizes were measured and tumor samples were analyzed of the mechanisms of action. Results: Among 191 kinases biochemically assayed, HM43239 showed the high selectivity toward FLT3 and AML associated other kinases (e.g. SYK, JAK and TAK1). IC50s' of HM43239 against FLT3 WT, FLT3 ITD and FLT3 D835Y kinases were 1.1 nM, 1.8 nM and 1.0 nM, respectively. HM43239 potently inhibited the growth of AML cell lines harboring FLT3 ITD mutation, such as MV4-11 (IC50: 1.3 nM), MOLM-13 (5.1 nM) and MOLM-14 (2.9 nM). Furthermore, HM43239 effectively inhibited the phosphorylation levels of FLT3 and of downstream kinases related with cell proliferation. In addition, caspase 3/7-dependent apoptosis was induced by HM43239 in AML cell lines expressing FLT3 ITD mutant. And HM43239 inhibited proliferation and induced apoptosis of leukemic stem cell (LSC) marker-expressing KG1a cells (CD34+/CD38- cells) suggesting that the possibility for targeting LSC. HM43239 showed the excellent dose proportional antitumor activity in mouse models xenografted with both MV4-11 and MOLM-13 cell line without any significant toxicity. Moreover, we identified in vivo modulation of related targets (p-FLT3 & p-STAT5) in AML cell with FLT3 mutant. Conclusion: Taken together, HM43239 has demonstrated the potential therapeutic efficacy for the treatment of AML patients and implicated the mechanism of overcoming resistance and preventing relapse.
Citation Format: Miyoung Lee, Young Eun Ha, Mi Jin Moon, Joo-Yun Byun, HyunKyung Yu, SeokJong Kang, JaeHo Lee, Kyuhang Lee, Eunkyung Kim, Eunyoung Kim, Ho Jeong Lee, YoungHoon Kim, YoungGil Ahn, KweeHyun Suh, Sun-Jin Kim. Antitumor activity of the potent and novel FLT3 inhibitor HM43239 in acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 804.