Clarity Pharmaceuticals has reported two additional complete responses among participants receiving its investigational radiopharmaceutical 67Cu-SAR-bisPSMA in the SECuRE trial, bringing the total number of complete responses or cases of undetectable disease across the company’s program to seven.
The preliminary update covers 19 participants treated at the 8 GBq dose level. Three came from the second cohort of the trial’s Dose Escalation phase and 16 from the ongoing Cohort Expansion phase. Recruitment and treatment continue.
The participants had advanced metastatic castration-resistant prostate cancer and had generally undergone extensive prior treatment. Nearly two-thirds had bone metastases, while 79 per cent had received at least five previous anti-cancer regimens. Previous treatments included androgen deprivation therapy, radiation, androgen receptor pathway inhibitors and, for some participants, taxane-based therapy or an experimental PSMA T-cell engager.
Participants received a median of two treatment cycles, with the number ranging from one to four. Three participants in the Cohort Expansion phase also received enzalutamide alongside 67Cu-SAR-bisPSMA.
The company said reductions in prostate-specific antigen were substantial. Among the 19 participants, 74 per cent achieved at least a 25 per cent reduction in PSA, 63 per cent achieved at least a 50 per cent reduction, 53 per cent achieved at least a 75 per cent reduction, and 26 per cent achieved at least a 90 per cent reduction. Responses were continuing to mature among participants who remained on treatment.
Radiographic assessments were available for 16 participants. Of these, 13, or 81 per cent, achieved disease control. Eight participants had stable disease, while five achieved a complete response or undetectable disease based on assessments using RECIST, bone scans or PSA measurements.
The two newly reported complete responses came from participants in the Cohort Expansion phase and were assessed using RECIST. Across the broader 67Cu-SAR-bisPSMA program, seven participants have now achieved a complete response or undetectable disease. Five of those participants received treatment at the 8 GBq dose level, representing 31 per cent of the participants evaluable for radiographic assessment at that dose.
The seven participants who achieved a complete response or undetectable disease had a median baseline PSA of 90.3 nanograms per millilitre, with results ranging from 3.3 to 490.3 nanograms per millilitre. They had received a median of five previous anti-cancer regimens, and four had bone metastases. All seven had previously received a second-generation androgen receptor pathway inhibitor.
Clarity said the safety profile among participants treated at 8 GBq was generally favourable. The most common treatment-related adverse events were dry mouth, reported in 47 per cent of participants, and nausea, reported in 42 per cent. Fatigue occurred in 26 per cent, while anaemia and reduced neutrophil counts each affected 21 per cent.
Clarity Executive Chairperson Dr Alan Taylor said, “The SAR-bisPSMA product continues to generate an impressive body of evidence in clinical trials and case studies, highlighting the strength of the evidence in both diagnostic and theranostic applications."
