A First-in-human, Dose-escalation Study of the Methionine Aminopeptidase 2 Inhibitor M8891 in Patients with Advanced Solid Tumors

Methionine aminopeptidase 2 (MetAP2) is essential to endothelial cell growth and proliferation during tumor angiogenesis. M8891 is a novel orally bioavailable, potent, selective, reversible MetAP2 inhibitor with antiangiogenic and antitumor activity in preclinical studies. The safety, tolerability, pharmacokinetics, and pharmacodynamics of M8891 monotherapy were assessed in a phase I, first-in-human,multicenter, openlabel, single-arm, dose-escalation study (NCT03138538). Patients with advanced solid tumors received 7-80 mg M8891 once daily in 21-day cycles. The primary endpoint was dose-limiting toxicity (DLT) during cycle 1, with the aim to determine the maximum tolerated dose (MTD). Twenty-seven patients were enrolled across six dose levels. Two DLTs (platelet count decrease) were reported, one each at 60 and 80 mg/once daily M8891, resolving after treatment discontinuation. MTD was not determined. The most common treatment-emergent adverse event was platelet count decrease. M8891 plasma concentration showed dose-linear increase up to 35 mg and low-to-moderate variability; dose-dependent tumor accumulation of methionylated elongation factor 1α, a MetAP2 substrate, was observed, demonstratingMetAP2 inhibition. Pharmacokinetic/ pharmacodynamic response data showed that preclinically defined target levels required for in vivo efficacy were achieved at safe, tolerated doses. Sevenpatients (25.9%) had stable disease for 42-123 days.We conclude that M8891 demonstrates a manageable safety profile, with dose-proportional exposure and low-to-moderate interpatient variability at target pharmacokinetic/ pharmacodynamic levels at ≤35 mg M8891 once daily. On the basis of the data, 35mgM8891 once daily is the recommended phase II dose forM8891 monotherapy. This study forms the basis for future development of M8891 in monotherapy and combination studies. Significance: M8891 represents a novel class of reversible MetAP2 inhibitors and has demonstrated preclinical antitumor activity. This doseescalation study assessedM8891 treatment for patients with advanced solid tumors. M8891 demonstrated favorable pharmacokinetics, tumoral target engagement, and a manageable safety profile, and thus represents a novel antitumor strategy warranting further clinical studies.