Foretinib Is Effective in Acute Myeloid Leukemia by Inhibiting FLT3 and Overcoming Secondary Mutations That Drive Resistance to Quizartinib and Gilteritinib

Abstract FLT3 internal tandem duplication (FLT3-ITD) mutations are one of the most prevalent somatic alterations associated with poor prognosis in patients with acute myeloid leukemia (AML). The clinically approved FLT3 kinase inhibitors gilteritinib and quizartinib improve the survival of patients with AML with FLT3-ITD mutations, but their long-term efficacy is limited by acquisition of secondary drug-resistant mutations. In this study, we conducted virtual screening of a library of 60,411 small molecules and identified foretinib as a potent FLT3 inhibitor. An integrated analysis of the BeatAML database showed that foretinib had a lower IC50 value than other existing FLT3 inhibitors in patients with FLT3-ITD AML. Foretinib directly bound to FLT3 and effectively inhibited FLT3 signaling. Foretinib potently inhibited proliferation and promoted apoptosis in human AML cell lines and primary AML cells with FLT3-ITD mutations. Foretinib also significantly extended the survival of mice bearing cell-derived and patient-derived FLT3-ITD xenografts, exhibiting stronger efficacy than clinically approved FLT3 inhibitors in treating FLT3-ITD AML. Moreover, foretinib showed potent activity against secondary mutations of FLT3-ITD that confer resistance to quizartinib and gilteritinib. These findings support the potential of foretinib for treating patients with AML with FLT3-ITD mutations, especially for those carrying secondary mutations after treatment failure with other FLT3 inhibitors. Significance: Foretinib exhibits superior efficacy to approved drugs in AML with FLT3-ITD mutations and retains activity in AML with secondary FLT3 mutations that mediate resistance to clinical FLT3 inhibitors.