Telix Pharmaceuticals has dosed the first patient in the Phase 3 ProstACT GLOBAL study of its radio-antibody drug conjugate (rADC) therapy, TLX591 (Lu-rosopatamab tetraxetan).

TLX591 is an investigational prostate-specific membrane antigen (PSMA) targeting antibody-based prostate cancer therapy candidate.

It is composed of a high-specificity PSMA-targeting antibody, chelator linker, and cytotoxic lutetium payload.

ProstACT GLOBAL is the first late-stage study to assess TLX591 in adult patients with PSMA-positive metastatic castrate-resistant prostate cancer (mCRPC) administered together with Standard of Care (SoC) against SoC alone.

Eight Phase 1 and 2 trials of TLX591, such as Telix’s ProstACT SELECT study, have treated 242 patients so far. This study validated the clinical validity of Telix’s optimal fractionated dosage and product safety profile.

Data from earlier Phase 2 studies that were published showed a satisfactory safety profile and an overall survival (OS) of 42.3 months when given under a fractionated dose regimen given in conjunction with docetaxel treatment.

In addition, collective long-term follow-up of patients treated with TLX591 has not shown evidence of severe acute or delayed nephrotoxicity in comparison to other radioligand treatments, the Australian radiopharmaceutical company said.

Early findings from the recently concluded ProstACT SELECT study showed minimal absorption and toxicity concerns in the kidney, salivary glands, and lacrimal glands.

It also showed strong on-target PSMA tumour-binding and radiation delivery to bone, nodal, and visceral metastases.

Telix Group chief medical officer Colin Hayward said: “Dosing a first patient in the ProstACT GLOBAL study is a significant milestone for Telix and will help build on an already extensive data set for this product candidate.

“The current TLX591 experience underlines the potential benefits of an antibody-based approach in combination with real-world standards of care, including physician choice of ARPI or taxane.”

ProstACT GLOBAL expands upon ProstACT SELECT and other Phase 1 and 2 TLX591 studies.

The purpose of this international, multicentre, prospective, randomised, controlled, open-label Phase 3 trial is to ascertain the risks and benefits for patients of administering TLX591 in addition to SoC as opposed to SoC alone.

Subject to regulatory permissions, the research is anticipated to spread globally, including to Europe and the US, where Telix’s investigational new drug (IND) application is still scheduled for submission to the US Food and Drug Administration (FDA) in Q4 2023.