Preparation of 68 Ga-PSMA-11 with a Synthesis Module for Micro PET-CT Imaging of PSMA Expression during Prostate Cancer Progression.

Objective. To synthesize Ga-68-Glu-urea-Lys(Ahx)-HBED-CC (Ga-68-PSMA-11) with a synthesis module and investigate PET-CT imaging to monitor PSMA expression during prostate cancer (PCa) progression and tumor growth in mice bearing subcutaneous PCa xenografts. Method. The radiochemical purity and stability of 68Ga-PSMA-11 were determined via radio-HPLC. The PCa cell lines of different PSMA expression levels (PC3, VCAP +/-, CWR22RV1+, and LNCaP++) were selected to mimic the PCa progression. Ga-68-PSMA-11 biodistribution was studied by dissection method and in vivo imaging with micro PET-CT. The expression levels of PSMA in tumor cells and tissues were analyzed by immunofluorescence, flow cytometry, and western blot. The correlation between PSMA expression and radio-uptake was also evaluated. 2-PMPA preadministration served as a block group. Results. The radiochemical purity of Ga-68-PSMA-11 was 99.6 +/- 0.1% and stable in vitro for 2 h. The equilibrium binding constant (Kd) of (68)GaPSMA-11 to LNCaP, CWR22Rv1, PC-3, and VCAP cells was 4.3 +/- 0.8 nM, 16.4 +/- 1.3 nM, 225.3 +/- 20.8 nM, and 125.6 +/- 13.1 nM, respectively. Results of tumor uptake (% ID and % ID/g or % ID/cm 3) of Ga-68-PSMA-11 in biodistribution and micro PET imaging were LNCaP > CWR22RV1 > PC-3 and VCAP due to different PSMA expression levels. It was confirmed by flow cytometry, western blot, and immunofluorescence. Tumor uptake (% ID/cm(3)) of Ga-68-PSMA-11 increased with the tumor anatomical volume in quadratic polynomial fashion and reached the peak (when tumor volume was 0.5 cm(3)) earlier than tumor uptake (% ID). Tumor uptake (% ID/cm(3)) of Ga-68-PSMA-11 based on functional volume correlated well with the PSMA expression in a linear manner (y - 9.35x + 2.59, R-2 - 0.8924, and p < 0.0001); however, low dose 2-PMPA causes rapid renal clearance of increased tumor/kidney uptake of Ga-68-PSMA-11. Conclusions. The Ga-68-PSMA-11 PET-CT imaging could invasively evaluate PSMA expression during PCa progression and tumor growth with % ID/cm(3) (based on functional volume) as an important index. Low dose 2-PMPA preadministration might be a choice to decrease kidney uptake of Ga-68-PSMA-11.