A Phase 1 Study of Milademetan in Combination with Quizartinib in Patients with Newly Diagnosed (ND) or Relapsed/Refractory (R/R) FLT3-ITD Acute Myeloid Leukemia (AML)

Background: FMS-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) mutations occur in ≈ 25% of patients with AML and are associated with poor prognosis. Quizartinib is a once-daily, oral, highly potent and selective FLT3 inhibitor. In the phase 3 QuANTUM-R trial (NCT02039726; Cortes et al. Lancet Oncol 2019), quizartinib prolonged overall survival compared with salvage chemotherapy in patients with R/R FLT3-ITD AML. Murine double minute 2 (MDM2), an E3 ubiquitin ligase, negatively regulates the p53 tumor suppressor and has been shown to be upregulated in patients with AML; TP53 mutations in AML are infrequent except within complex karyotypes. Milademetan, a novel and specific MDM2 inhibitor, showed activity in an ongoing phase 1 trial in patients with AML or myelodysplastic syndromes (MDS) [DiNardo et al. ASH 2016, abstract 593]. Preclinical studies have shown that quizartinib plus milademetan may act synergistically to target FLT3-ITD and restore p53 activity in FLT3-ITD/TP53 wild-type AML [Andreeff et al. ASH 2018, abstract 2720]. Targeting MDM2 may restore p53 activity in cell signaling pathways altered by FLT3-ITD in patients with wild-type TP53 AML.

Methods: This open-label, 2-part, phase 1 study (NCT03552029) evaluates quizartinib in combination with milademetan in patients with FLT3-ITD AML. Key inclusion criteria comprise a diagnosis of FLT3-ITD AML (de novo or secondary to MDS) and adequate renal, hepatic, and clotting functions. Key exclusion criteria include acute promyelocytic leukemia, prior treatment with a MDM2 inhibitor, QTcF interval > 450 ms, significant cardiovascular disease, and unresolved toxicities from prior therapies. Dose-escalation (part 1) comprises patients with R/R AML. In part 1, quizartinib will be administered once daily in 28-day cycles, at 3 proposed levels (30, 40, and 60 mg) with appropriate dose modifications based on QTcF monitoring and concomitant use of strong CYP3A inhibitors. Milademetan will be administered on days 1-14 of each 28-day cycle, at 3 proposed levels (90, 120, and 160 mg). Dose escalation will be guided by modified continual reassessment with overdose control. The primary objectives of part 1 are to evaluate the safety and tolerability, optimum dosing schedule, maximum tolerated dose (MTD), and recommended dosing for the expansion (RDE) cohort.

Dose expansion (part 2) comprises a cohort of patients with R/R FLT3-ITD AML who have not received > 1 salvage therapy and not received > 1 prior FLT3 inhibitor, and a second cohort including ND patients with FLT3-ITD AML who are unfit for intensive chemotherapy. Patients in part 2 will be treated with quizartinib plus milademetan at the RDE doses identified in part 1. The objectives of part 2 are to confirm the safety and tolerability of quizartinib plus milademetan at RDE and identify the recommended phase 2 dose. Pharmacokinetics and preliminary assessment of efficacy are also being evaluated as secondary outcomes. Pharmacodynamic and biomarker assessments such as leukemic stem cell numbers, STAT5 downstream signaling, minimal residual disease measured by flow cytometry, and gene mutations will be evaluated as exploratory endpoints. Approximately 24 to 36 dose-limiting toxicity-evaluable patients are needed in part 1 to determine the MTDs and the RDE; approximately 40 patients per cohort will be treated at the RDE in part 2. This study is currently recruiting at multiple sites in the United States for part 1; recruitment for part 2 may be expanded to additional sites worldwide as necessary.