Melbourne, Australia & Indianapolis, United States – March 10, 2026

Telix Pharmaceuticals has announced that Part 1 of the global Phase 3 ProstACT clinical study evaluating TLX591-Tx (lutetium-177 rosopatamab tetraxetan) has successfully achieved its primary safety and dosimetry objectives, reinforcing the potential of the investigational therapy as a promising treatment for metastatic castration-resistant prostate cancer (mCRPC). The study demonstrated an acceptable safety and tolerability profile with no new safety signals, supporting further development of the therapy in combination with current standard-of-care treatments. These findings mark an important milestone for the ProstACT Global trial and position TLX591-Tx as a potential first-in-class radio antibody-drug conjugate (rADC) designed to target prostate-specific membrane antigen (PSMA) in advanced prostate cancer patients.

Phase 3 ProstACT Study Demonstrates Safety and Tolerability

The ProstACT Global Phase 3 study is an international, multicenter clinical trial evaluating TLX591-Tx in combination with established prostate cancer therapies, including enzalutamide, abiraterone, and docetaxel. Part 1 of the study served as a safety and dosimetry lead-in stage involving 36 patients with PSMA-positive metastatic castration-resistant prostate cancer who had previously received treatment with one androgen receptor pathway inhibitor.

Results showed that all 36 patients received two doses of TLX591-Tx administered 14 days apart, confirming a consistent treatment protocol across the study cohorts. Importantly, investigators observed no unexpected safety issues or drug-drug interactions, indicating that the therapy can be safely combined with existing standard treatments. Most non-hematologic adverse events were mild to moderate (Grade 1 or Grade 2), with the most common symptoms including fatigue, nausea, and dry mouth.

Hematologic events such as thrombocytopenia and neutropenia were transient and manageable, aligning with the expected safety profile for therapies within this treatment class. Recovery rates across patient cohorts were consistent, further supporting the therapy’s manageable tolerability profile. These findings demonstrate that TLX591-Tx can potentially be integrated into current clinical treatment strategies for advanced prostate cancer without introducing significant new safety concerns.

Targeted Radiopharmaceutical Therapy for Prostate Cancer

TLX591-Tx is a targeted radiopharmaceutical therapy that combines a monoclonal antibody with the radioactive isotope lutetium-177, enabling highly precise delivery of radiation directly to cancer cells expressing prostate-specific membrane antigen (PSMA). This targeted approach allows the therapy to deliver radiation selectively to tumor tissue while minimizing exposure to healthy organs, improving the potential therapeutic index.

Dosimetry analysis conducted during the study demonstrated consistent radiation absorption across tumor lesions in all patient cohorts, with radiation exposure to critical organs remaining well below established safety thresholds. The therapy also showed limited uptake in salivary glands and kidneys, an important advantage over some existing radioligand therapies that often cause significant dry mouth or kidney toxicity.

Pharmacokinetic analysis further confirmed sustained therapeutic activity approximately 15 days after dosing, while imaging studies showed prolonged retention of the therapy within tumor sites, indicating effective targeting of cancerous tissue. These characteristics highlight the potential of TLX591-Tx to deliver durable tumor-directed radiation therapy with reduced off-target effects.

Expansion to Global Phase 3 Treatment Study

Following the successful completion of Part 1, the ProstACT Global trial has now advanced into Part 2, a randomized treatment expansion phase designed to compare PSMA-targeted TLX591-Tx therapy combined with standard of care versus standard of care alone. The expansion phase is expected to enroll approximately 490 patients worldwide, making it one of the largest global studies evaluating a radiopharmaceutical therapy for advanced prostate cancer.

The trial has already received regulatory approvals to initiate clinical recruitment across multiple international regions, including Australia, New Zealand, Canada, China, Singapore, South Korea, Türkiye, and the United Kingdom. Telix plans to present the Part 1 clinical data to the U.S. Food and Drug Administration (FDA) as part of an Investigational New Drug (IND) amendment, seeking approval to expand the trial into the United States.

Despite significant advances in prostate cancer treatment, patients with metastatic castration-resistant disease continue to face limited treatment options, particularly in the first- and second-line therapy settings. Researchers believe that PSMA-targeted radiopharmaceutical therapies such as TLX591-Tx may represent a transformative approach, enabling more precise targeting of cancer cells while preserving healthy tissue.

The early safety results from the ProstACT Global study therefore represent an important step toward developing next-generation targeted therapies for advanced prostate cancer. If further clinical trials confirm its safety and effectiveness, TLX591-Tx could potentially emerge as a new frontline treatment option for patients with PSMA-positive metastatic prostate cancer, helping address a major unmet medical need in oncology.

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Source: Telix Pharmaceuticals press release