TY - JOUR T1 - GRPr antagonist <sup>68</sup>Ga-SB3 PET/CT-imaging of primary prostate cancer in therapy-naive patients JF - Journal of Nuclear Medicine JO - J Nucl Med DO - 10.2967/jnumed.120.258814 SP - jnumed.120.258814 AU - Ingrid L Bakker AU - Alida C Fröberg AU - Martijn B Busstra AU - J. Fred Verzijlbergen AU - Mark Konijnenberg AU - Geert J. L. H. van Leenders AU - Ivo G Schoots AU - Erik de Blois AU - Wytske M van Weerden AU - Simone U Dalm AU - Theodosia Maina-Nock AU - Berthold Artur Nock AU - Marion de Jong Y1 - 2021/03/01 UR - http://jnm.snmjournals.org/content/early/2021/03/31/jnumed.120.258814.abstract N2 - The gastrin releasing peptide receptor (GRPr) is overexpressed in prostate cancer (PCa) cells, making it an excellent tool for targeted imaging. The gallium-68 labeled GRPr antagonist SB3 (68Ga SB3) has shown excellent results in (pre)clinical studies and was selected for further clinical investigation. The aims of this phase I study were to investigate 68Ga SB3 PET/CT-imaging of primary PCa tumors and assess safety. More aims included biodistribution, dosimetry, comparison with pathology and GRPr expression. MATERIALS AND METHODS: Ten therapy-naive, biopsy-confirmed PCa patients planned for prostatectomy were included. A 3-hour extensive PET/CT-imaging protocol was performed, within 2 weeks prior to prostatectomy. Prostate tissue was evaluated for tumor localization, Gleason Score and in vitro autoradiography was performed to determine GRPr expression. Available MRI scans performed within 3 months prior to the study were matched. For dosimetry residence times were estimated and effective dose to the body as well as absorbed doses to organs were calculated using the IDAC dose 2.1 model. RESULTS: Administration of 68Ga SB3 (187.4 ± 40.0 MBq, 40±5 μg) was well tolerated, no significant changes in vital signs or laboratory results were observed. 68Ga SB3 PET/CT showed lesions in 8 out of 10 patients. Pathological analysis revealed a total of 16 tumor lesions of which PET/CT showed 14, resulting in a sensitivity of 88%. 68Ga SB3 PET/CT-imaging showed uptake in 2 large prostatic intraepithelial neoplasia foci, considered a precursor of PCa, resulting in an 88% specificity. Autoradiography of tumor lesions revealed heterogeneous GRPr expression and was negative in 4 patients. Both PET/CT-negative patients had a GRPr-negative tumor. In autoradiography-positive tumors, level of GRPr expression showed significant correlation to tracer uptake on PET/CT. Dosimetry calculations estimated the effective dose to be 0.0144 mSv/MBq, similar to other 68Ga labeled radiopeptides. Highest absorbed dose was detected in the physiological GRPr-expressing pancreas (0.198 mGy/MBq), followed by bladder wall and kidneys. CONCLUSION: 68Ga SB3 PET/CT is a safe imaging method and a promising tool for early PCa imaging. ER -