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Recently, a  18 F-labeled derivative of the widely used  68 Ga-PSMA-11 was developed for PET imaging of prostate cancer. Although  18 F-PSMA-11 has already been evaluated in a Phase I and Phase II clinical trial, preclinical evaluation of this radiotracer is important for further understanding its dynamic behavior. Saturation binding experiments were conducted by incubation of LNCaP cells with  18 F-PSMA-11 or  68 Ga-PSMA-11 for 1 h, followed by determination of the specific and aspecific binding. Mice bearing LNCaP or PC-3 xenografts each received ± 3.7 MBq  18 F-PSMA-11 and  68 Ga-PSMA-11 followed by dynamic acquisition of 2.5 h as well as ± 15 MBq  18 F-FDG followed by static acquisition at 1 h post injection (p.i.). Uptake was evaluated by comparison of uptake parameters (SUV mean , SUV max , TBR mean  and TBR max ). Mice underwent ex vivo biodistribution where  18 F-PSMA-11 activity was measures in excretory organs (kidneys, bladder and liver) as well as bone fragments (femur, humerus, sternum and skull) to evaluate bone uptake. The dissociation constant (K d ) of  18 F-PSMA-11 and  68 Ga-PSMA-11 was 2.95 ± 0.87 nM and 0.49 ± 0.20 nM, respectively. Uptake parameters were significantly higher in LNCaP compared to PC-3 xenografts for both  18 F-PSMA-11 and  68 Ga-PSMA-11, while no difference was found for  18 F-FDG uptake (except for SUV max ). Tumor uptake of  18 F-PSMA-11 showed a similar trend over time as  68 Ga-PSMA-11, although all uptake parameter curves of the latter were considerably lower. When comparing early (60 min p.i.) to delayed (150 min p.i.) imaging for both radiotracers individually, TBR mean  and TBR max  were significantly higher at the later timepoint, as well as the SUV max  of  68 Ga-PSMA-11. The highest %ID/g was determined in the kidneys (94.0 ± 13.6%ID/g 1 h p.i.) and the bladder (6.48 ± 2.18%ID/g 1 h p.i.). No significant increase in bone uptake was seen between 1 and 2 h p.i. Both radiotracers showed high affinity for the PSMA receptor. Over time, all uptake parameters were higher for  18 F-PSMA-11 compared to  68 Ga-PSMA-11. Delayed imaging with the latter may improve tumor visualization, while no additional benefits could be found for late  18 F-PSMA-11 imaging. Ex vivo biodistribution demonstrated fast renal clearance of  18 F-PSMA-11 as well as no significant increase in bone uptake.

Intra-individual dynamic comparison of 18F-PSMA-11 and 68Ga-PSMA-11 in LNCaP xenograft bearing mice