Shares of Monte Rosa Therapeutics Inc (NASDAQ: GLUE) fell 4.8% on Monday after the company initiated a Phase 2 clinical study of its investigational drug MRT-2359 in combination with apalutamide for patients with metastatic castration-resistant prostate cancer (mCRPC) harboring androgen receptor (AR) mutations.
The MODeFIRe-1 trial will enroll up to 25 patients under a Simon’s two-stage design, with eligibility requiring prior treatment with a second-generation AR inhibitor and either measurable disease per RECIST criteria or rising PSA levels. Primary endpoints include PSA response, RECIST response, duration of response, radiographic progression-free survival, PSA progression-free survival, and safety. MRT-2359 will be administered orally at 0.5 mg on a 21-day-on, 7-day-off schedule across 28-day cycles.
The Phase 2 study follows earlier Phase 1/2 data showing that MRT-2359, in combination with enzalutamide, produced a 100% PSA response rate and disease control rate among five heavily pretreated mCRPC patients with AR mutations. Two patients also achieved RECIST responses. An expansion arm of six patients with AR mutations has since completed enrollment, and Monte Rosa expects to report an update on this subset by year-end.
MRT-2359 is an orally bioavailable, GSPT1-directed molecular glue degrader developed in-house by Monte Rosa. The biotech’s shares were trading down 4.8% at $11.25 in midday U.S. markets on Monday.
