Synthesis and positron emission tomography evaluation of 18F-Glu-Urea-Lys, a prostate-specific membrane antigen-based imaging agent for prostate cancer.

In recent years, single-photon emission computed tomography and positron emission tomography (PET) have also been used, in addition to computed tomography and magnetic resonance imaging, in targeting the diagnosis of prostate cancer. The aim of this study was to synthesize the prostate-specific membrane antigen (PSMA)-based imaging agent 2-{3-[1-Carboxy-5-(4-[18F] fluoro-benzoylamino)-pentyl]-ureido}-pentanedioic acid (18F-Glu-Urea-Lys, [18F]3) and to detect its PET imaging efficiency for high PSMA expression in prostate cancer. In this study, 18F-Glu-Urea-Lys was synthesized in two steps from the p-methoxybenzyl-protected Glu-Urea-Lys precursor using N-Hydroxysuccinimidyl-4-[18F] fluorobenzoate ([18F]SFB). PET imaging evaluation was conducted in nude mice using LNCaP (PSMA+), and PC-3, 231 and A549 (all PSMA-) xenograft models. The results indicated that 18F-Glu-Urea-Lys was produced in radiochemical yields of 28.7%. The radiochemical purity was 99.1% and the mean total synthesis time was 168 min. In nude mice models 18F-Glu-Urea-Lys clearly delineated PSMA+ LNCaP prostate tumor xenografts on PET imaging. At 4 h post-injection, the contrast agents were only observed in renal, liver, bladder and PSMA+ LNCaP tumors. The PSMA- tumor (PC-3, 231 and A549) was clear. In conclusion, 18F-Glu-Urea-Lys was found to be easily synthesized. This radiotracer demonstrated high tumor and low-to-normal tissue uptake, fast clearance from non-target tissues and retention in PSMA+ prostate tumor xenografts.