Cu-SAR-Bombesin Faces Validation Hurdles Despite Promising Prostate Cancer Detection

A New Diagnostic Frontier in Prostate Cancer

Clarity Pharmaceuticals (ASX, CU6) has announced encouraging topline results from its Phase II SABRE trial evaluating Cu-SAR-Bombesin, a novel PET imaging agent designed to detect prostate cancer recurrence in patients whose disease is not visible on standard-of-care (SOC) scans. This development addresses a critical gap in prostate cancer diagnostics, particularly for patients with biochemical recurrence (BCR) who test negative or equivocal on conventional imaging such as PSMA PET scans.

Cu-SAR-Bombesin targets the gastrin-releasing peptide receptor (GRPR), a receptor found in up to 100% of prostate cancers, including those that do not express PSMA. This biological heterogeneity in prostate cancer has long challenged clinicians, as PSMA-negative lesions often evade detection, delaying diagnosis and treatment.

Trial Design and Key Findings

The SABRE trial enrolled 53 patients with BCR and negative or equivocal SOC imaging results. Participants underwent PET/CT scans using Cu-SAR-Bombesin at one to four hours and again approximately 24 hours post-dose. The imaging was independently reviewed by blinded central readers and compared against a composite reference standard including histopathology, follow-up imaging, and PSA response.

Cu-SAR-Bombesin detected lesions in roughly 35% of patients on same-day imaging and 28% on next-day imaging, despite prior negative SOC scans. Importantly, biopsies performed on a subset of lesions confirmed a 100% true-positive rate, underscoring the agent’s diagnostic accuracy. The most common lesion sites were lymph nodes and prostate regions, areas critical for staging and treatment planning.

Safety and Clinical Implications

The agent was well tolerated, with only two mild adverse events reported, both resolving quickly. Clarity’s Executive Chairperson Dr Alan Taylor highlighted the significance of these findings, emphasizing that Cu-SAR-Bombesin could reveal otherwise hidden metastatic disease, enabling more informed and effective treatment decisions for patients who currently have limited diagnostic options.

One illustrative case involved a patient with a high PSA level and negative PSMA PET scans, where Cu-SAR-Bombesin revealed extensive metastatic disease confirmed by biopsy. Follow-up PSMA imaging failed to detect these lesions, demonstrating the potential of Cu-SAR-Bombesin to fill a critical diagnostic void.

Looking Ahead

Building on these promising results, Clarity is engaging with medical experts and regulatory authorities to chart a pathway for registration and commercialization. The company is also exploring Cu-SAR-Bombesin’s application in other cancers expressing GRPR, such as breast and ovarian cancers, supported by encouraging data from related trials.

While the SABRE trial’s conservative analysis approach and limited biopsy verification reflect the complexities of this patient population, the data strongly suggest that Cu-SAR-Bombesin could become a best-in-class diagnostic tool. Its ability to detect lesions missed by current SOC imaging positions it as a potential game-changer in prostate cancer management.