Abstract
This study was designed to study the safety, biodistribution, radiation dosimetry of a gastrin-releasing peptide receptor (GRPR) antagonist positron emission tomography (PET) tracer 68Ga-RM26, to assess its clinical diagnostic value in prostate cancer patients, and to perform a direct comparison between GRPR antagonist 68Ga-RM26 and agonist 68Ga-BBN. Methods: Five healthy volunteers were enrolled to validate the safety of 68Ga-RM26 and calculate dosimetry. A total of 28 patients with prostate cancer (17 newly diagnosed and 11 post therapy) were recruited with written informed consent. All the cancer patients underwent PET/CT scans at 15-30 min after intravenous injection of 1.85 MBq (0.05 mCi) per kilogram body weight of 68Ga-RM26. Among them, 22 patients (11 newly diagnosed and 11 post therapy) accepted 68Ga-BBN PET/CT for comparison within 1 week. 99mTc-MDP bone scans were performed within 2 weeks for comparison. GRPR immunohistochemical staining of tumor samples was performed. Results: The administration of 68Ga-M26 was well tolerated by all subjects with no adverse symptoms being noticed or reported during the whole procedure and 2 weeks follow up. The total effective dose equivalent (EDE) and effective dose (ED) were 0.0912 ± 0.0140 and 0.0657 ± 0.0124 mSv/MBq, respectively. In the 17 patients with newly diagnosed prostate cancer, 68Ga-RM26 PET/CT showed positive prostate-confined findings in 15 tumors with SUVmax of 6.49 ± 2.37. In the 11 patients underwent prostatectomy or brachytherapy with/without androgen deprivation therapy (ADT), 68Ga-RM26 PET/CT detected 8 metastatic lymph nodes in three patients with SUVmax of 4.28 ± 1.25, and 21 bone lesions in 8 patients with SUVmax of 3.90 ± 3.07. Compared with 68Ga-RM26 PET/CT, GRPR agonist 68Ga-BBN PET/CT detected less primary lesions and lymph node metastases as well as lower tracer accumulation. There was a significant positive correlation between SUV derived from 68Ga-RM26 PET and the expression level of GRPR (P < 0.001). Conclusion: This study indicates the safety and significant efficiency of GRPR antagonist 68Ga-RM26. 68Ga-RM26 PET/CT would have remarkable value in detecting both primary prostate cancer and metastasis. 68Ga-RM26 is also expected to be better than GRPR agonist as an imaging marker to evaluate GRPR expression in prostate cancer.
- Copyright © 2017 by the Society of Nuclear Medicine and Molecular Imaging, Inc.