Telix OPTIMAL-PSMA dosimetry data back TLX597-Tx dose push

Telix Pharmaceuticals has presented initial dosimetry results from the OPTIMAL-PSMA Phase 2 trial of its radioligand therapy (RLT) candidate TLX597-Tx at the 2026 International Prostate Cancer Symposium in Lugano, Switzerland. The data show markedly reduced radiation uptake in the salivary glands and kidneys relative to existing prostate-specific membrane antigen (PSMA) RLTs — an observation the company says could meaningfully expand the therapeutic window for patients with metastatic prostate cancer.

TLX597-Tx, chemically designated 177Lu-DOTA-HYNIC-panPSMA, is a small-molecule RLT designed to deliver higher tumour-absorbed doses while limiting exposure to healthy tissue. Xerostomia — dry mouth caused by salivary gland irradiation — and renal toxicity are recognised quality-of-life burdens that constrain the clinical uptake of currently approved PSMA-targeting RLTs, particularly in earlier-stage disease where patients may be fitter and expected to live longer. Telix positions TLX597-Tx's dosimetry profile as addressing exactly that gap.

Trial design and next steps

OPTIMAL-PSMA is an open-label, randomised, investigator-initiated Phase 2 study enrolling 120 men with metastatic castration-resistant prostate cancer (mCRPC), led by Professor Louise Emmett at St Vincent's Hospital in Sydney. Participants are randomised 2:1 to an intensified dosing schedule — 8.5 GBq per cycle delivered on days one, three and fifteen, followed by three further ten-weekly cycles — versus a standard dose schedule. The primary aim is to confirm that the intensified regimen maximises tumour radiation dose at periods of greatest cancer cell vulnerability without materially increasing toxicity.

Encouraged by the dosimetry readout, Telix says it will initiate OPTIMAL-E, a new Phase 2 study evaluating TLX597-Tx in metastatic hormone-sensitive prostate cancer (mHSPC) — an earlier disease setting with a larger addressable population.

Professor Emmett said the trial aims to "identify a dose regimen for TLX597-Tx that leads to deeper and longer responses without increasing toxicity for men with metastatic prostate cancer."

Dr David Cade, Group Chief Medical Officer at Telix, said the dosimetry findings, combined with earlier exploratory work presented at the European Association of Nuclear Medicine's 2025 annual congress, "highlight TLX597-Tx's potential to substantially increase the tumour dose while minimising radiation to sensitive organs."

Competitive and regulatory context

The RLT space for prostate cancer has been reshaped by the commercial success of lutetium-177 PSMA-617 (Pluvicto, Novartis), which received FDA approval in 2022 for mCRPC following the VISION trial. That approval, and subsequent label expansion efforts, have validated PSMA targeting as a therapeutic modality but also underscored the salivary-gland toxicity problem that Telix is seeking to engineer around. Several companies — including those developing PSMA-targeted alpha-particle emitters and bispecific constructs — are pursuing improved tolerability profiles, making the competitive field increasingly crowded.

Within its own pipeline, Telix is running two complementary prostate cancer programmes: TLX597-Tx for earlier-stage disease, and TLX591-Tx (lutetium-177 rosopatamab tetraxetan), a radio antibody-drug conjugate currently in the Phase 3 ProstACT Global trial in mCRPC. Neither candidate has received marketing authorisation in any jurisdiction. The portfolio approach — tailoring modality to disease stage — mirrors strategies adopted by larger oncology players seeking to capture patients across the treatment continuum.

The forthcoming OPTIMAL-E trial in mHSPC will be a critical test: the mHSPC setting is more competitive, patients are less heavily pre-treated, and any tolerability advantage over Pluvicto will need to be demonstrated in prospective data rather than dosimetry inference alone. Investors should watch for trial initiation timelines and, ultimately, efficacy endpoints before drawing conclusions about the candidate's commercial prospects.