Abstract 1318: Preclinical characterization of quizartinib and AC886, a metabolite of quizartinib, in AML models, and anti-leukemic activity of quizartinib on midostaurin-resistant AML cells
Authors: Aikawa Tomoya , Togashi Noriko , Iwanaga Koichi , Okada Hiroyuki , Nishiya Yumi , Inoue Shinichi , Levis Mark J. , Isoyama Takeshi 
Published: August 2019

Abstract
FLT3 mutations have been found in about 30% of acute myeloid leukemia (AML) cases, and the most common form of FLT3 mutation is internal tandem duplication (ITD) in the juxtamembrane domain, which occurs in approximately 25% of adult AML patients and 10-15% of pediatric patients. FLT3-ITD is a driver mutation in AML and the FLT3-ITD presence is associated with poor prognosis in AML patients. Quizartinib is a second-generation small-molecule inhibitor of FLT3, and a phase 3, QuANTUM-R trial showed significantly prolonged overall survival in patients with FLT3-ITD-mutated relapsed/refractory AML. In this preclinical study, we characterized quizartinib and AC886, a metabolite of quizartinib, compared with other FLT3 inhibitors including midostaurin, gilteritinib, crenolanib and sorafenib, and then evaluated the anti-tumor effect of quizartinib on midostaurin-resistant AML cells. Selectivity profiling of the FLT3 inhibitors against over 400 kinases and over 80 non-kinases showed that quizartinib and AC886 were highly selective against FLT3. Quizartinib and AC886 clearly inhibited FLT3 signaling pathways such as STAT5, RAS/MAPK and PI3K/AKT cascades in FLT3-ITD-mutated AML cells, leading to potent growth inhibition of the AML cells with the IC50 values of &lt;1 nM. When quizartinib was orally administered once a day to mice bearing MV4-11 cells harboring FLT3-ITD mutation, AC886 was rapidly detected and the tumor regression was observed at doses of 1 mg/kg and over without severe body weight loss, while midostaurin and gilteritinib also showed the tumor regression at 30 mg/kg and 10 mg/kg, respectively. In addition, we evaluated the effect of quizartinib on midostaurin-resistant FLT3-ITD-mutated AML MOLM-14 cells, which were established after long term treatment of midostaurin, and acquired KRAS (G12A) or NRAS (G12C) mutation. Quizartinib inhibited the viability of the midostaurin-resistant MOLM-14 cells with the IC50 values of &lt;10 nM, and exerted potent anti-tumor activity in the xenograft models without severe body weight loss. On the other hand, midostaurin and gilteritinib did not show significant anti-tumor effect in the models. This is the first report on the detailed characterization of quizartinib and its metabolite AC886 in comparison with other FLT3 inhibitors. Preclinical anti-leukemic activity in midostaurin-resistant FLT3-ITD-mutated AML cells suggests the potential value of quizartinib for midostaurin failure in AML patients with FLT3-ITD mutations. Further clinical investigation is warranted to find the optimum treatment sequence with FLT3 inhibitors for the AML patients.
Citation Format: Tomoya Aikawa, Noriko Togashi, Koichi Iwanaga, Hiroyuki Okada, Yumi Nishiya, Shinichi Inoue, Mark J. Levis, Takeshi Isoyama. Preclinical characterization of quizartinib and AC886, a metabolite of quizartinib, in AML models, and anti-leukemic activity of quizartinib on midostaurin-resistant AML cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1318.