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Milademetan in Advanced Solid Tumors with MDM2 Amplification and Wild-type TP53: Preclinical and Phase II Clinical Trial Results

E. Dumbrava, T. Stinchcombe, M. Gounder, G. M. Coté, Glenn J. Hanna, Bradley Sumrall, Trisha M. Wise-Draper, Mohammed Kanaan et al.

Clinical Cancer Research, 2025

40 participants · 16 citations

Abstract

Abstract Purpose: Mouse double minute 2 (MDM2) is an E3 ubiquitin ligase that degrades the tumor suppressor p53. In cancers, MDM2 amplification (MDM2amp) leads to overexpression of MDM2, inducing p53 degradation and a p53-null phenotype even in the absence of TP53 mutations. We report here the preclinical and clinical activities of milademetan, a potent and selective oral small-molecule inhibitor of the MDM2–p53 interaction, in MDM2amp, TP53 wild-type (WT) solid tumors. Patients and Methods: Milademetan was tested against a variety of cell line and xenograft tumor models. This supported a phase II basket study (MANTRA-2) in patients with advanced MDM2amp, TP53-WT solid tumors. The primary endpoint was the objective response rate, and key secondary endpoints included progression-free survival and adverse events. Results: Milademetan showed potent activity against MDM2amp, TP53-WT laboratory models. In the phase II trial, 40 patients received milademetan, 31 of whom had centrally confirmed molecular testing. The best overall response was 19.4% (6/31) with one confirmed response (3.2%) and five unconfirmed partial responses, including a patient with endometrial stromal sarcoma who achieved a 100% target lesion reduction. The median progression-free survival was 3.5 months (95% confidence interval, 1.8–3.7). Grade 3 or 4 adverse events observed included thrombocytopenia, neutropenia, anemia, leukopenia, and diarrhea. Conclusion: Milademetan had a manageable safety profile and…

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