Novel Theranostic Radiopharmaceutical Detects Lesions in Patients With PSMA PET-Negative BCR Prostate Cancer

By Zachary Bessette - September 13, 2023

Results of the phase 2 diagnostic investigator-initiated trial of 64Cu SAR-Bombesin in prostate cancer (BOP) have shown the novel theranostic radiopharmaceutical can detect lesions in men with biochemically recurrent (BCR) prostate cancer that are either negative or equivocal on prostate-specific membrane antigen positron emission tomography (PSMA PET).

BOP preliminary trial results were presented at the European Association of Nuclear Medicine Congress 2023.

64Cu SAR-Bombesin targets the gastrin-releasing peptide receptor (GRPr) rather than PSMA. GRPr is present in most prostate cancers, including those that do not express PSMA.

Led by Louise Emmett, MBChB, MD, director of theranostics and nuclear medicine at St. Vincent’s Hospital in Australia, the BOP trial assessed the safety and diagnostic performance of 64Cu SAR-Bombesin in men with BCR prostate cancer who had negative PSMA PET imaging scans or low PSMA expression disease, as well as men with metastatic castration-resistant prostate cancer who were ineligible for PSMA therapy.

Ninety six percent of patients in the BCR cohort had undergone radical prostatectomy and had a prostate-specific antigen doubling time of 4.2 months (range, 2.8-7.5 months) prior to study initiation. Patients received a mean dose of 210 MBq of 64Cu SAR-Bombesin and underwent PET imaging at 1, 3, and 24 hours postadministration.

Researchers reported no adverse events from 64Cu SAR-Bombesin administration. Additionally, they noted that 64Cu SAR-Bombesin PET-avid disease was found in 32% of patients with negative or equivocal PSMA PET.

“We believe SAR-Bombesin has the potential to add value in biochemical recurrence of prostate cancer following definitive therapy,” said Prof. Emmett in a press release. “We look forward to continuing our collaboration with Clarity [Pharmaceuticals] and also exploring the diagnostic and therapeutic benefits of SAR-Bombesin in not only PSMA-negative prostate cancer, but also in other diseases such as breast cancer.”

“In essence, for the patients [who] have had a positive SAR-Bombesin scan, this is the difference between having an incorrect negative cancer diagnosis leading to cancer progression and now having an effective treatment plan that may lead to long-term remission,” added Alan Taylor, PhD, executive chairman of Clarity Pharmaceuticals, the developer of 64Cu SAR-Bombesin.

The product is being further assessed in the phase 2 SABRE trial and the theranostic phase 1/2a COMBAT trial.