Optimized Ga-Labeled Urea-Based PSMA-Targeted PET Tracers for Prostate Cancer.

Prostate-specific membrane antigen (PSMA)-targeting radiopharmaceuticals have become some of the most promising tools for the diagnosis and therapy prostate cancer (PCa). The structure of existing PSMA-targeted PET tracers still needs to be optimized to improve their pharmacokinetic properties and tumor-to-background ratio. In this study, we modified the structure of a well-studied PSMA tracer, and six novel tracers with variable hydrophilicity and pharmacokinetics were developed and evaluated both in vitro and in vivo. All of the novel tracers showed high hydrophilicity (log = -2.99 ± 0.33 to -3.49 ± 0.01), rapid clearance rates (elimination half-times = 15.55 to 35.97 min), and high affinity for PSMA (Ki = 8.11 ± 0.49 to 42.40 ± 2.11 nM) in vitro. Specific cell binding and micro-PET experiments showed that [Ga]Ga-PSMA-Q displayed the highest specific PSMA+ cell uptake (3.75 ± 0.35 IA%/10 at 60 min), tumor uptake (SUVmax = 0.97 ± 0.24 at 60 min p.i.), and tumor-to-muscle ratio (59.33 ± 5.72 at 60 min p.i.), while the tumor-to-muscle ratio was much higher than that of [Ga]Ga-PSMA-617. The results of this study validate the clinical potential of [Ga]Ga-PSMA-Q for PET imaging and further targeted therapy of prostate cancer.