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Telix Pharmaceuticals Begins Phase II Trial of Radiolabeled Prostate Cancer Antibody Treatment

NEW YORK – Telix Pharmaceuticals said Tuesday that it began enrolling patients with prostate-specific membrane antigen (PSMA)-positive prostate cancer in a Phase II trial of its antibody-based radiopharmaceutical TLX591.

In the ProstACT TARGET trial, Telix will enroll 50 patients with biochemically recurrent, oligometastatic prostate cancer and give them TLX591 with external beam radiation therapy. Eligible patients must experience recurrence on initial treatment as determined by elevated levels of prostate-specific antigen (PSA). Patients must also have PSMA-positive tumors on PET imaging scans.

TLX591, also known as 177-Lu-DOTA-rosopatamab, is a radiolabeled antibody that targets PSMA. In the ProstACT TARGET trial, Telix will track patients' progression-free survival and gauge if treatment with TLX591 and radiation therapy can defer the need for androgen deprivation therapy upon cancer recurrence. Telix's partner, GenesisCare, is enrolling patients in the trial at centers in Sydney and Perth, Australia.

Melbourne, Australia-based Telix is also conducting the Phase I ProstACT SELECT study to assess safety, tolerability, biodistribution, and dosimetry of TLX591 plus standard-of-care therapy in patients with metastatic castration-resistant prostate cancer that expresses PSMA and has progressed despite prior treatment with an androgen axis drug. The ProstACT SELECT study will also compare Telix's imaging agent Illuccix (68-Ga-PSMA-11) to TLX591 in a subset of patients to ensure equivalence of radiopharmaceutical localization and to demonstrate the utility of Illuccix to select patients for TLX591 therapy. The first patients have been dosed in this study.

In a third, pivotal trial underway, called ProstACT Global, Telix is comparing TLX591 plus standard-of-care treatment versus standard-of-care treatment alone in PSMA-positive, metastatic prostate cancer patients who have progressed on first-line androgen axis agents. The company is preparing to screen patients for this Phase III trial at sites in Australia and New Zealand and is aiming to enroll up to 390 patients who will be selected using Illuccix. Researchers will compare patients' radiographic progression-free survival in the two treatment arms.

"Alongside ProstACT SELECT, [the ProstACT TARGET trial] will add value and clinical insight to Telix's antibody therapy candidate TLX591, as we progress global regulatory submissions for the ProstACT GLOBAL Phase III study," said Telix Chief Medical Officer Colin Hayward in a statement.

Telix is also developing radiolabeled antibody therapeutics for kidney cancer, breast cancer, and glioblastoma. It is testing TLX250-CDx (89-Zr-DFO-girentuximab) as an imaging agent for kidney cancer patients in a Phase III trial, and it began a Phase II trial of TLX250 (177-Lu-DOTA-girentuximab) with Bristol Myers Squibb's Opdivo (nivolumab) using TLX250-CDx as a companion diagnostic.