On January 23, 2023 Rain Oncology Inc. (NasdaqGS: RAIN), ("Rain"), a late-stage company developing precision oncology therapeutics with its lead product candidate, milademetan, an oral, small molecule inhibitor of the p53-MDM2 complex that reactivates p53, reported the publication of a peer-reviewed article titled, "A First-in-Human Phase I Study of Milademetan, an MDM2 Inhibitor, in Patients with Advanced Liposarcoma, Solid Tumors or Lymphomas" in the Journal of Clinical Oncology (Press release, Rain Oncology, JAN 23, 2023, View Source [SID1234626454]). Phase 1 clinical data in the paper highlight the activity and tolerability using intermittent dosing of milademetan across a range of tumor types including dedifferentiated liposarcoma (DD LPS), which represented the largest proportion of patients enrolled in the study (n=53).
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"An intermittent dosing schedule (260 mg qd, 3/14 days) of our highly selective inhibitor of the p53-MDM2 complex, milademetan, resulted in favorable safety and clinical activity in the Phase 1 trial in DD LPS patients," said Robert Doebele, MD, Ph.D., co-founder, president and chief scientific officer of Rain. "We view the prior data leveraging the intermittent dosing schedule as potentially offering a compelling risk/reward benefit, laying the foundation for our registrational Phase 3 MANTRA trial."
"Historical challenges with MDM2 inhibition identified cytopenias as a concern, for which intermittent dosing may provide a solution," said Richard Bryce, MBChB, Rain’s chief medical officer. "The intermittent dosing schedule identified may provide for a more favorable tolerability profile that we would expect to translate across a multitude of future therapeutic indications."
Key Article Highlights Include:
All liposarcoma patients enrolled in the Phase 1 trial exhibited the DD LPS subtype
Among DD LPS patients in the Phase 1 trial, median progression-free survival (mPFS) outcomes were maintained with intermittent dosing schedules (once daily [qd] on days 1-3 and 15-17 every 28 days; eg, 3/14 days) compared with extended (qd on days 1-21) / continuous (qd on days 1-28) schedules:
mPFS of patients across all doses/schedules (n=53): 7.2 months
mPFS of patients with 260 mg qd 3/14 intermittent schedule (n=16): 7.4 months
mPFS of previously treated patients with 260 mg qd 3/14 intermittent schedule (n=11): 8.0 months
mPFS of treatment-naïve patients in all doses/schedules (n=17): 14.6 months
Although all tested DD LPS patients had MDM2 gene amplification (n=22), mPFS in DD LPS patients did not differ by levels of key biomarkers including MDM2 or CDK4 copy number or by mRNA expression levels of MDM2, CDK4, or MDM4.
The preferred intermittent dosing schedule of milademetan (260 mg qd 3/14 days) mitigates dose-limiting hematologic adverse events while maintaining activity, leading to:
Marked reductions in occurrence and severity of grade 3/4 drug-related thrombocytopenia (15.8%; n=38) compared to extended/continuous schedules (36.2%; n=69) and
Fewer dose reductions (21.1%; n=8) and dose interruptions (15.8%; n=6) compared with extended/continuous schedules (23.3%; n=16 and 34.8%; n=24, respectively).
Preliminary single-agent activity with milademetan in DD LPS prompted the ongoing, randomized Phase 3 MANTRA trial (NCT04979442), with topline data anticipated in the first quarter of 2023.
About Milademetan
Milademetan (also known as RAIN-32) is an oral small molecule inhibitor of the p53-MDM2 complex that reactivates p53. Milademetan has demonstrated antitumor activity in an MDM2-amplified subtype of liposarcoma (LPS) and other solid tumors in a Phase 1 clinical trial, supported by a rationally designed dosing schedule to mitigate safety concerns and widen the potential therapeutic window of inhibition of the p53-MDM2 complex. Rain has completed enrollment in a Phase 3 trial of milademetan (MANTRA) in patients with LPS, and is evaluating milademetan in a Phase 2 tumor-agnostic basket trial in certain solid tumors (MANTRA-2). Rain anticipates commencing a Phase 1/2 clinical trial to evaluate the safety, tolerability and efficacy of milademetan in combination with Roche’s atezolizumab in patients with loss of cyclin-dependent kinase inhibitor 2A (CDKN2A) and wildtype p53 advanced solid tumors (MANTRA-4), in the first quarter of 2023. Milademetan has received Orphan Drug Designation from the U.S. Food and Drug Administration (FDA) for the treatment of LPS.