Clinical study of 68Ga labeled homologue of gastrin-releasing peptide for PET/CT imaging of patient with prostate cancer

Objectives Gastrin-releasing peptide receptors (GRPRs) are highly overexpressed in 63-100% of human prostate cancers (PCs). In this study, we investigated a ⁶⁸Ga labeled amphibian homologue of mammalian gastrin-releasing peptide ⁶⁸Ga-RM1 that targets GRPRs for PCs detection of patients.

Methods A total of 7 pre-surgical men patients (mean age ± SD: 65.6±9.4 year-old) with newly diagnosed and biopsy-proven PCs were subjected to ⁶⁸Ga-RM1 positron emission tomography (PET) study. The prostate-specific antigen (PSA) levels of all patients were examined. PET/CT imaging started at 40-50 minutes after injection of 111-142 MBq (mean±SD: 127±6 MBq) of ⁶⁸Ga-RM1 (purity >98%) using a PET/CT scanner (Biograph 40, Siemens). Quantitative assessment of ⁶⁸Ga-RM1 uptake was performed by analysis of maximum standardized uptake value (SUVmax) and mean SUV (SUVmean) of tumor region and background in normal tissues. Subsequently, tumor to background ratios were calculated.

Results All patients had significant abnormal PSA levels (mean±SD: 19.5±13.1 ng/ml) and Gleason scores (6-9). The PET/CT images showed high physiologic uptake in the pancreas (SUVmean: 11.67±3.85) and quick renal clearance. Among the 7 patients, high and specific uptake in primary cancer lesions were found. The SUVmean and SUVmax of tumor region is 4.22±1.33 and 4.64±2.53. One patient (1/7) had 3 visible positive lymph nodes in the abdomen and one patient (1/7) had 4 metastases in bone. Quantitative assessment revealed excellent contrast between tumor lesions and normal tissues. Median tumor to background ratios were 15.29 (9.27-26.42).

Conclusions Preliminary clinical data indicate that the use of ⁶⁸Ga-RM1 in patients with prostate cancer is safe and feasible. ⁶⁸Ga-RM1 could be an optional imaging probe for the imaging of PCs. However, further study on the relationship between PSA level and SUV of tumor, the comparison with other PCs targeting probes should be performed in future. Research Support: This work was supported, in part, by the Key Program of National Natural Science Foundation of China (Grant No. 81230033) and the Office of Science (BER), U.S. Department of Energy (DE-SC0008397).