Preliminary Evaluation of Ga-P16-093, a PET Radiotracer Targeting Prostate-Specific Membrane Antigen in Prostate Cancer.

Purpose: Prostate-specific membrane antigen (PSMA) is a promising molecular target for imaging of prostate adenocarcinoma. Ga-P16-093, a small molecule PSMA ligand, previously showed equivalent diagnostic performance compared to Ga-PSMA-11 PET/CT in a pilot study of prostate cancer patients with biochemical recurrence (BCR). We performed a pilot study for further characterization of Ga-P16-093 including comparison to conventional imaging.

Procedures: Patients were enrolled into two cohorts. The biodistribution cohort included 8 treated prostate cancer patients without recurrence, who underwent 6 whole body PET/CT scans with urine sampling for dosimetry using OLINDA/EXM. The dynamic cohort included 15 patients with BCR and 2 patients with primary prostate cancer. Two patients with renal cell carcinoma were also enrolled for exploratory use. A dynamic PET/CT was followed by 2 whole body scans for imaging protocol optimization based on bootstrapped replicates. Ga-P16-093 PET/CT was compared for diagnostic performance against available F-fluciclovine PET/CT, Tc-MDP scintigraphy, diagnostic CT, and MRI.

Results: Ga-P16-093 deposited similar effective dose (0.024 mSv/MBq) and lower urinary bladder dose (0.064 mSv/MBq) compared to Ga-PSMA-11. The kidneys were the critical organ (0.290 mSv/MBq). While higher injected activities were preferable, lower injected activities at 74-111 MBq (2-3 mCi) yielded 80% retention in signal-to-noise ratio. The optimal injection-to-scan interval was 60 min, with acceptable delay up to 90 min. Ga-P16-093 PET/CT showed superior diagnostic performance over conventional imaging with overall patient-level lesion detection rate of 71%, leading to a change in management in 42% of the patients.

Conclusions: Based on its favorable imaging characteristics and diagnostic performance in prostate cancer, Ga-P16-093 PET/CT merits further investigation in larger clinical studies.