Telix says ProstACT Global Phase 3 Part 1 met primary objectives
Telix said Part 1 of the ProstACT Global Phase 3 study met its primary objectives for TLX591-Tx in mCRPC. The company reported acceptable safety, no new safety signals and progression plans for Part 2.
Telix Pharmaceuticals said Part 1 of the ProstACT Global Phase 3 study, the safety and dosimetry lead-in for TLX591-Tx (lutetium-177 (177Lu) rosopatamab tetraxetan), achieved its primary objectives. The company said the study demonstrated an acceptable safety and tolerability profile with no new safety signals observed, and confirmed the safety profile, biodistribution and dosimetry of TLX591-Tx administered in two doses, 14 days apart, in combination with abiraterone, enzalutamide or docetaxel.
The patient population comprised prostate-specific membrane antigen positive metastatic castration resistant prostate cancer patients previously treated with one androgen receptor pathway inhibitor. ProstACT Global is a Phase 3 trial comparing PSMA-targeted 177Lu-rADC therapy administered with standard of care versus standard of care alone, a trial design intended to reflect current global clinical practice.
Part 1 dosed 36 patients allocated across three cohorts: 11 patients received TLX591-Tx plus enzalutamide, 11 patients received TLX591-Tx plus abiraterone, and 14 patients received TLX591-Tx followed by docetaxel. All 36 patients received both doses of TLX591-Tx per protocol, and no adverse drug-drug interactions were observed in TLX591-Tx combinations.
The company said almost all treatment-emergent non-hematologic events were Grade 1 or Grade 2. The most prevalent were fatigue at 53%, nausea at 28% and dry mouth at 25%. Hematologic events were described as transient and manageable, with Grade 3 thrombocytopenia in 14% and neutropenia in 22%, and Grade 4 thrombocytopenia in 31% and neutropenia in 25%.
Lesion dosimetry indicated no difference in absorbed dose profile across cohorts, while radiation exposure to key organs was well below established safety limits. The company said lesion dosimetry demonstrated uptake across tumor sites and across all cohorts, pharmacokinetics demonstrated sustained activity at 15 days corroborated by imaging which demonstrated prolonged tumor retention, and there was limited dose to salivary glands and kidneys.
Telix said the results from Part 1 are consistent with prior clinical studies of this first-in-class lutetium radio antibody-drug conjugate therapy. The company has already advanced the study into Part 2, a 2:1 randomized treatment expansion, in jurisdictions where the clinical trial has obtained approval from health authorities, and said Part 1 data will be presented to the U.S. Food and Drug Administration to seek an Investigational New Drug amendment to progress Part 2 in the United States.