First participant treated at highest dose level in Clarity’s theranostic prostate cancer trial

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Clinical-stage radiopharmaceutical company Clarity Pharmaceuticals (ASX:CU6) has announced the dosing of the first participant at the highest dose level of 12GBq in the third cohort of its Phase 1/2 theranostic trial evaluating 67Cu SAR-bisPSMA in patients with metastatic, castrate-resistant prostate cancer (mCRPC).

The SECuRE trial (NCT04868604) is a theranostic trial for the identification and treatment of participants with Prostate-Specific Membrane Antigen (PSMA)-expressing mCRPC using 64Cu/67Cu SAR-bisPSMA.

64Cu SAR-bisPSMA is used to visualise PSMA-expressing lesions and select candidates for subsequent 67Cu SAR-bisPSMA therapy.

The trial is a multi-centre, single-arm, dose-escalation trial with a cohort expansion involving up to 44 participants in the US.

The overall aim of the trial is to determine the safety and efficacy of 67Cu SAR-bisPSMA for the treatment of prostate cancer.

Cohort 3 explores the effects of the highest dose of 12GBq on the SECuRE trial participants following a single administration of 67Cu SAR-bisPSMA. The third cohort will be the last to assess single doses of 67Cu SAR-bisPSMA and will be followed by a multi-dose cohort, pending safety evaluation.

The first two cohorts in the dose escalation phase of the trial were completed with no DLTs reported in any of the participants dosed.

The 3 participants in cohort 2, were administered a single dose of 8GBq of 67Cu SAR-bisPSMA, and have been monitored by their physicians for safety and treatment response per the trial protocol.

All 3 participants in cohort 2 remain on the trial following their administration of 8GBq of 67Cu SAR-bisPSMA, with all 3 participants exhibiting a greater than 50 per cent reduction in PSA, which is one of the primary endpoints of the SECuRE trial and a commonly used surrogate endpoint for efficacy in this patient population. The company said PSA levels continue to fall in all patients, with the first 2 showing reductions of greater than 95 per cent and the last participant showing a drop of approximately 70 per cent so far.

Clarity’s executive chairperson, Dr Alan Taylor, said, “Results from cohort 2 are incredibly exciting and we look forward to seeing data from the increased dosing of 12GBq as well as discover the potential positive effects of multi-dosing on prostate cancer patients.

“The fast pace of recruitment into the dose escalation phase of the trial is indicative of the high unmet need in the prostate cancer therapy space and we are thrilled to be working on a solution that has potential to not only offer treatment benefits to patients with mCRPC, but also resolve the logistical and manufacturing challenges of the current-generation radiopharmaceuticals, such as 177Lu PSMA-617, especially now with the availability of commercial quantities of the 67Cu radioisotope routinely produced domestically in the US and exclusively supplied to us by NorthStar.

“We look forward to sharing more data on 67Cu SAR-bisPSMA as we continue to recruit participants into the SECuRE trial and progress on our path towards commercialisation with the ultimate goal of improving treatment outcomes for people with cancer,” said Dr Taylor.