Telix Pharmaceuticals (TLX) Study update summary

Study background, design, and objectives

• ProstACT Global Phase III Part 1 evaluated TLX591 (TLX591-Tx) in combination with standard of care for metastatic castration-resistant prostate cancer, focusing on safety, dosimetry, and feasibility as required by the FDA to proceed to Part 2.

• The study included three cohorts: TLX591 with abiraterone, enzalutamide, or docetaxel, reflecting real-world clinical practice and accommodating global differences in standard of care.

• 36 patients were enrolled after screening 57, all with prior ARPI treatment; mean age was 75 years, median 77, range 59–88, with balanced demographics and prior treatments.

• The two-dose regimen (76 mCi each, 14 days apart) supports patient compliance and ease of integration with standard therapies.

Safety and tolerability results

• No new or unexpected safety signals were observed; adverse events were manageable and consistent with expectations for this therapy class.

• Most non-hematologic adverse events were mild (Grade 1/2), including fatigue (53%), nausea (28%), dry mouth (25%), and only one Grade 3 dizziness event.

• Hematologic events (thrombocytopenia and neutropenia) were transient, manageable, and resolved spontaneously in most cases, with platelet counts recovering to Grade 1 or better within ~15 days post-nadir.

• No treatment-related deaths occurred; 32 of 36 patients remained alive at data cutoff, with 26 continuing on study.

Dosimetry and pharmacokinetics

• TLX591 showed favorable and predictable pharmacokinetics, with sustained tumor uptake and low normal organ exposure, and low inter-patient variability.

• Lesion dosimetry demonstrated consistent and meaningful radiation delivery to tumor sites across all cohorts.

• Organ radiation exposure was well below established safety limits, with low radiation to kidneys and salivary glands, reducing risk of long-term toxicity.

• No significant differences in absorbed dose profiles or drug-drug interactions were observed between cohorts or with ARPI/docetaxel.

• The antibody-based approach resulted in prolonged tumor retention compared to small molecule radioligands, with retention up to 15 days.