Monte Rosa Therapeutics Inc. (GLUE) released interim data from its ongoing Phase 1/2 clinical trial that's turning heads on Wall Street. The study is evaluating MRT-2359 combined with enzalutamide in patients with metastatic castration-resistant prostate cancer who've already been through multiple treatment rounds.
The trial tested two doses of MRT-2359, 0.5 mg and 0.75 mg, administered orally for 21 days followed by a 7-day break. The treatment was combined with Pfizer Inc. (PFE) and Astellas Pharma Inc. (ALPMF) (ALPMY) Xtandi (enzalutamide).
As of December 3, the study included 20 patients with advanced castration-resistant prostate cancer who had already undergone extensive prior treatment.
What the Trial Showed
All 20 enrolled patients were evaluated for safety, and the results look encouraging. The combination maintained what researchers call a "favorable safety profile," meaning side effects were manageable and mostly involved gastrointestinal issues classified as mild or moderate.
Among the 14 patients evaluable for efficacy, the results in patients with AR mutations were particularly striking. Two patients showed RECIST partial responses (one confirmed, one unconfirmed), and the disease control rate in this AR-mutant group hit 100%.
The broader results remained solid too. Five patients with wild-type AR or positive for ARV7 transcripts achieved stable disease, with several showing actual tumor size reductions. That brought the overall disease control rate to 64% across all 14 evaluable patients.
Perhaps most importantly, the treatment effects proved durable, especially in patients carrying AR mutations or those who hadn't previously received AR inhibitors.
Monte Rosa plans to share updated findings from the Phase 1/2 study at the ASCO Genitourinary Cancers Symposium in February.
What's Next
The company is preparing to launch a Phase 2 study of MRT-2359 combined with a second-generation AR inhibitor. The study will enroll up to 25 patients with metastatic castration-resistant prostate cancer and is designed to efficiently assess efficacy in patients with AR mutations, with the possibility of expanding into additional patient groups.
Researchers will evaluate PSA response, RECIST response, duration of response, progression-free survival, radiographic progression-free survival, and safety. The study is expected to begin in 2026.
The Phase 1/2 trial also included six patients with hormone receptor-positive breast cancer. While the safety profile remained favorable in this group, the results didn't show enough activity to justify continued development for that indication.
MRT-8102 Update
Monte Rosa also provided guidance on another program. The company plans to present interim Phase 1 data on MRT-8102 in early 2026.
The ongoing Phase 1 study includes single-ascending dose and multiple-ascending dose cohorts in healthy volunteers, plus a Part 3 cohort designed to evaluate potential early proof of concept in subjects at increased cardiovascular disease risk. The company has already started dosing in Part 3.
Price Action: GLUE stock traded up 11.43% at $18.33 on Tuesday.