Clarity Pharmaceuticals is moving to the assessment of a second patient cohort for its Phase I/II theranostic trial, SECuRE.

SECuRE (NCT04868604) is evaluating safety and efficacy of Cu 64 SAR-bisPSMA therapy in prostate-specific membrane antigen (PSMA)-expressing metastatic castrate-resistant prostate cancer (mCRPC). The multi-centre, single arm, dose-escalation trial has cohort expansion involving up to 44 patients in the US.

In the now-completed first cohort, six participants received a single administration of 4GBq Cu 64 SAR-bisPSMA, the lowest dose. No dose limiting toxicities were reported and the trial will advance to cohort 2 after recommendation by the safety review committee. The dose will be increased to 8GBq.

Patients in cohort 1 have continued to have therapy cycles outside of the trial under an extended access programme (EAP).

In images collected 48 hours following a third therapy cycle in a patient in the EAP, a reduction in intensity of product uptake at the tumour sites was observed. More than a 50% reduction in PSA levels was seen following administration of Cu 64 SAR-bisPSMA at 4GBq dose. Clarity added that such a reduction is commonly used as a primary endpoint for efficacy in this patient population.

SAR-bisPSMA combines two PSMA binding motifs linked to Clarity’s SAR chelator technology, allowing for diagnostic (via Cu-64) and therapeutic applications (via Cu-67).

“We have not seen any safety issues in the patients treated so far and are already seeing clinical benefits in some patients,” said Dr Luke Nordquist, CEO, urologic medical oncologist and principal investigator at the Urology Cancer Center, Omaha.

“Outside of reductions in PSA levels and changes in tumour imaging, we have seen an improvement in quality-of-life measures such as reduction in pain and return of appetite and physical exercise.”