64Cu-SAR-Bombesin shows efficacy in detecting prostate cancer recurrence

Topline data from the phase 2 SABRE trial (NCT05407311) showed that ⁶⁴Cu-SAR-Bombesin was safe, well tolerated, and demonstrated the ability to detect prostate cancer recurrence in PSMA-negative patients who had negative or equivocal results on standard-of-care (SOC) imaging, Clarity Pharmaceuticals announced in a news release.¹

⁶⁴Cu-SAR-Bombesin works by targeting the gastrin-releasing peptide receptor.

⁶⁴Cu-SAR-Bombesin works by targeting the gastrin-releasing peptide receptor (GRPR), which is expressed in several malignancies, including prostate cancer, the company noted.

"The SABRE trial represents an important milestone for Clarity, setting a new benchmark by seeking to identify lesions that do not express PSMA,” said Clarity's executive chairperson, Alan Taylor, PhD, in the news release.¹ “This trial, which is Clarity's first sponsored study with ⁶⁴Cu-SAR-Bombesin, has now shown that this product can provide a solution where the current diagnostic options fall short and improve lesion detection beyond what is achievable with SOC PSMA-targeted imaging.”

At the time of data report, 47 patients in the study were evaluable for efficacy. Scans were interpreted by 3 blinded central readers.

Overall, the average detection rate across the 3 readers was 35.2% (range, 24.5% to 43.4%) on same-day imaging and 27.7% (range, 17.0% to 37.7%) on next-day imaging. Same-day imaging identified approximately 47 lesions (range, 40 to 59), and next-day imaging identified approximately 52 lesions (range, 24 to 95). The most common sites of lesion detection were in the lymph nodes and prostate regions.

Further, the participant-level correct detection rate (CDR) was 14.9% (95% CI, 6.2% to 28.3%) on same-day imaging and ranged from 4.3% to 14.9% (95% CI, 0.5% to 28.3%) on next-day imaging. The region-level positive predictive value (PPV) ranged from 22.6% to 47.1% (95% CI, 9.6% to 72.2%) on same-day imaging and from 22.2% to 37.5% (95% CI, 2.8% to 61.7%) on next-day imaging.

Clarity noted in the news release, “The CDR and PPV results were substantially impacted by the large number of lesions that were detected on the ⁶⁴Cu-SAR-Bombesin scans, but unable to be verified due to the lack of effective diagnostic options available for comparison and biopsy not being clinically appropriate in most cases.”

Positive ⁶⁴Cu-SAR-Bombesin PET/CT scans led to 4 biopsies in 3 patients. All biopsies were positive for prostate cancer, and included identification of 2 pelvic lymph nodes, 1 extra-pelvic lymph node, and 1 bone lesion.

Overall, ⁶⁴Cu-SAR-Bombesin was safe and well tolerated, Clarity noted. Adverse events related to ⁶⁴Cu-SAR-Bombesin occurred in 2 patients. These were all grade 1 and resolved within 2 days of onset.

According to Clarity, the results from the SABRE trial will be used to inform the design of a registrational trial of ⁶⁴Cu-SAR-Bombesin.

About the SABRE trial

In total, the single-arm, non-randomized, open-label SABRE study enrolled and imaged 53 patients across clinical trial sites in the US.²

To be eligible for enrollment, patients needed to have negative or equivocal findings on approved PSMA-PET imaging (⁶⁸Ga-PSMA-11 or 18F-DCFPyL), anatomical imaging (CT and/or MRI), and any other SOC imaging. Patients also needed to have a suspected recurrence of prostate cancer, an ECOG Performance Score of 0 to 2, adequate liver function, an estimated glomerular filtration rate of at least 30 mL/min, and a life expectancy of at least 12 weeks.

In the study, patients received a 200 MBq dose of ⁶⁴Cu-SAR-Bombesin before undergoing PET/CT scans at 1 to 4 hours (same-day imaging) and 24 ± 6 hours (next-day imaging) post-dose.

The primary end points for the trial were participant-level CDR (defined as the proportion of true-positive participants out of all scanned participants who had at least 1 evaluable reference standard datapoint collected) and region-level PPV (defined as the proportion of true-positive regions out of all positive regions on the ⁶⁴Cu-SAR-Bombesin PET/CT scan with corresponding evaluable composite reference standard data), both evaluated on same-day and next-day imaging.

Clarity noted, “If a lesion identified on the ⁶⁴Cu-SAR-Bombesin scan was not biopsied, and it was also not present on follow-up SOC imaging (a suboptimal reference standard with known low sensitivity and in a patient population that was negative on SOC imaging at screening), it was considered as false-positive in the analysis by default.”

Additional data on ⁶⁴Cu-SAR-Bombesin

⁶⁴Cu-SAR-Bombesin was previously assessed in the phase 2 BOP trial (NCT05613842), where the radiopharmaceutical detected disease recurrence in 44% of patients with biochemical recurrence of prostate cancer and negative or equivocal scans on ⁶⁸Ga-PSMA-11 PET/CT.

⁶⁴Cu-SAR-Bombesin has also showed encouraging preliminary efficacy in the C-BOBCAT trial, which is exploring the use of the agent in patients with breast cancer.

"These encouraging findings from the SABRE, BOP, and C-BOBCAT trials, as well as other trials with GRPR-targeted agents in other cancers, highlight the broad potential of ⁶⁴Cu-SAR-Bombesin to become a best-in-class diagnostic agent in a number of indications,” Taylor concluded in the news release.¹ “We look forward to working with key regulatory groups, such as the US Food and Drug Administration (FDA), to explore various avenues and indications with SAR-Bombesin further as we continually strive to improve diagnostic and theranostic options for patients and their clinicians."

REFERENCES

1. SABRE topline results: Cu-64 SAR-Bombesin is effective in detecting prostate cancer recurrence in patients with negative SOC imaging. News release. Clarity Pharmaceuticals. Published online and accessed June 13, 2025. https://www.prnewswire.com/news-releases/sabre-topline-results-cu-64-sar-bombesin-is-effective-in-detecting-prostate-cancer-recurrence-in-patients-with-negative-soc-imaging-302480940.html

2. 64Cu-SAR-BBN for identification of participants with recurrence of prostate cancer (SABRE) (SABRE). ClinicalTrials.gov. Last updated April 9, 2025. Accessed June 13, 2025. https://clinicaltrials.gov/study/NCT05407311