Clarity Pharmaceuticals Adds Two Complete Responses to SECuRE Trial Data

Clarity Pharmaceuticals (ASX: CU6) has reported two additional complete responses among participants receiving the 8 gigabecquerel (GBq) dose of 67Cu-SAR-bisPSMA in its ongoing SECuRE prostate cancer trial.

The preliminary assessment covered 19 participants, including three from the dose escalation phase and 16 from the cohort expansion phase, with responses continuing to mature among patients remaining on treatment.

Prostate-specific antigen (PSA) declines of at least 50% were recorded in 63% of evaluable participants, while 53% achieved PSA declines of at least 75% and 26% reached declines of at least 90%.

Among 16 participants evaluable by radiographic assessment, 81% achieved disease control comprising eight cases of stable disease and five cases of complete response or undetectable disease.

Deeper Responses Across Cohort

The two newly evaluable participants achieved complete responses under Response Evaluation Criteria in Solid Tumors 1.1 (RECIST), lifting the number of complete responses or undetectable disease cases across the 67Cu-SAR-bisPSMA program to seven.

Five of those seven participants received the 8GBq dose, representing 31% of all radiographically evaluable participants treated at that level.

The seven participants had received a median of five previous anti-cancer regimens, while 57% had bone metastases and all had previously received a second-generation androgen receptor pathway inhibitor.

Most of the broader 19-participant group was also heavily pre-treated, with 79% having received at least five previous anti-cancer regimens and 63% presenting with bone metastases before enrolment.

Manageable Safety Profile

Participants received a median of two 8GBq treatment cycles, with the group averaging 2.1 cycles and individual exposure ranging from one to four cycles at the 20 July data cut-off.

The most frequently reported related adverse events (AEs) were dry mouth in 47% of participants, nausea in 42%, fatigue in 26%, and anaemia or decreased neutrophil count in 21%.

Most AEs were mild or moderate and transient, with two Grade 3 events involving reduced lymphocyte and white blood cell counts recorded in one participant and no related Grade 4 or higher events reported.

Clarity found the prevalence and severity of treatment-related AEs among participants receiving 8GBq were generally lower than across the overall trial population.

Trial Expansion Continuing

SECuRE is a Phase I/IIa trial assessing the safety and efficacy of 67Cu-SAR-bisPSMA in people with prostate-specific membrane antigen (PSMA)-expressing metastatic castration-resistant prostate cancer.

The trial uses 64Cu-SAR-bisPSMA to identify PSMA-expressing lesions and select candidates for treatment, with recruitment continuing in a 24-participant cohort expansion phase that permits up to six 8GBq treatment cycles.

A subset of participants will receive 67Cu-SAR-bisPSMA alongside enzalutamide, while planning is continuing for a Phase III registrational trial based on the emerging data.

“The benefits we are seeing in the clinic, based on the treatment responses and favorable safety profile achieved with so few doses, are due to our unique combination of the optimised bivalent “bis” structure with the advantages offered by the beta emitter, copper-67, enabled by the proprietary sarcophagine (SAR) chelating technology,” executive chair Dr Alan Taylor said.

“Armed with the growing body of high-quality data, our team and collaborators continue to advance SAR-bisPSMA towards the paradigm shift it could bring to the prostate cancer space, aiming to improve the outcomes of so many patients with prostate cancer across multiple stages of their disease.”