Construction of A Novel PSMA-targeted Radiotracer and Its Application in Prostate Cancer PET Imaging

OBJECTIVE To develop a prostate-specific membrane antigen(PSMA)-targeted PET probe based on a biorthogonal radiolabeling strategy, aiming to achieve high radiochemical yield and enhanced diagnostic performance.

METHODS Using glutamate-urea-lysine(Glu-Urea-Lys) as the PSMA targeting scaffold, an aryl tetrazine fragment was introduced via a succinic anhydride linker. Firstly, the radiolabeling precursor ¹⁸F-TCO was synthesized by nucleophilic ¹⁸F-fluorination. Subsequently, the novel probe ¹⁸F-TTCO-SA-PSMA was efficiently constructed via a tetrazine-trans-cyclooctene(Tz-TCO) click chemistry reaction between ¹⁸F-TCO and the PSMA-targeting precursor. Subsequently, the probe underwent small-animal PET/CT imaging and biodistribution assessment in prostate cancer xenograft mouse models.

RESULTS The labeling precursor was synthesized through an eight-step reaction sequence with an overall yield of 8.2%. ¹⁸F-TTCO-SA-PSMA was synthesized in three steps(fluorine-18 nucleophilic substitution, cyclization, and deprotection) with a total synthesis time of 1.25 h and a decay-corrected radiochemical yield of 30%. Following HPLC purification, the probe exhibited a radiochemical purity(RCP) >97% and a specific activity of (14±3)GBq·μmol⁻¹(n=3). It maintained >97% RCP throughout a 6 h incubation period in physiological saline at 37 °C, confirming its stability under biologically relevant conditions. In vivo studies revealed efficient tumor uptake(8.5±1.1)%ID·g⁻¹ at 0.5 h post-injection, rapid renal clearance(19.6±3.1)%ID·g⁻¹ at 0.5 h vs (6.1±1.8)%ID·g⁻¹ at 3.0 h, and a high tumor-to-muscle ratio(28∶1 at 0.5 h).

CONCLUSION In this study, a novel PSMA targeting probe ¹⁸F-TTCO-SA-PSMA based on biorthogonal labeling strategy is successfully constructed. This probe exhibits favorable characteristics including relatively short synthesis time, good radiochemical yield, excellent in vitro stability, and outstanding in vivo performance characterized by high tumor targeting, low renal retention, rapid clearance, and prominent tumor-to-background ratio, showing a good prospect of clinical transformation. Future research can further explore its application potential in the field of diagnosis and treatment integration.