Synergistic Activity of Combined FLT3-ITD and MDM2 Inhibition with Quizartinib and Milademetan in FLT3-ITD Mutant/TP53 Wild-type Acute Myeloid Leukemias.

Purpose: Acute myeloid leukemia (AML) is characterized by frequent mutations in FMS-like tyrosine kinase 3 (FLT3), overexpression of murine double minute 2 (MDM2), and TP53 wild-type (WT). Monotherapies targeting FLT3 frequently result in the development of resistant disease. In this study, we investigated the antileukemic efficacy of co-targeting FLT3 and MDM2 with quizartinib and milademetan (Q/M) in FLT3 internal tandem duplication (FLT3-ITD) AML cell lines, xenograft and patient-derived xenograft (PDX) models, and a phase I clinical trial.

Experimental Design: Preclinical studies used human and murine cell lines carrying FLT3-ITD and/or tyrosine kinase domain mutations, TP53 WT/knockdown, leukemia cell xenograft models, and a PDX model. Assays were conducted using milademetan (DS-3032b) and murine-specific MDM2 inhibitor (DS-5272). An open-label, phase I, dose-escalation clinical trial (ClinicalTrials.gov NCT03552029) was conducted.

Results: Dual inhibition of FLT3-ITD and MDM2 synergistically induced apoptosis in FLT3-ITD/TP53 WT AML and venetoclax-resistant cell lines, reduced tumor burden, and improved survival in xenograft and PDX models of FLT3-ITD AML. Phase I clinical data indicated favorable safety and tolerability for the Q/M combination treatment. Complete responses with incomplete hematologic recovery were achieved in 40% of patients with relapsed/refractory AML. Unsupervised single-cell proteomic analysis showed that Q/M treatment decreased the expression of prosurvival proteins (p-ERK, p-AKT, and Mcl-1) and activated protein signaling downstream of p53 including p53 upregulated modulator of apoptosis. YTHDF2 was increased after therapy in resistant cells. The Q/M combination demonstrated higher activity in CD34+ versus CD34- leukemia blasts.

Conclusions: Preclinical and mechanistic rationale and preliminary clinical data support the future development of MDM2/FLT3-targeting strategies for FLT3-mutant AML.