Automated synthesis of [¹⁸F]DCFPyL via direct radiofluorination and validation in preclinical prostate cancer models

Prostate-specific membrane antigen (PSMA) is frequently overexpressed and upregulated in prostate cancer. To date, various ¹⁸F- and ⁶⁸Ga-labeled urea-based radiotracers for PET imaging of PSMA have been developed and entered clinical trials. Here, we describe an automated synthesis of [¹⁸F]DCFPyL via direct radiofluorination and validation in preclinical models of prostate cancer.

[¹⁸F]DCFPyL was synthesized via direct nucleophilic heteroaromatic substitution reaction in a single reactor TRACERlab FX_FN automated synthesis unit. Radiopharmacological evaluation of [¹⁸F]DCFPyL involved internalization experiments, dynamic PET imaging in LNCaP (PSMA+) and PC3 (PSMA−) tumor-bearing BALB/c nude mice, biodistribution studies, and metabolic profiling. In addition, reversible two-tissue compartmental model analysis was used to quantify pharmacokinetics of [¹⁸F]DCFPyL in LNCaP and PC3 tumor models.

Automated radiosynthesis afforded radiotracer [¹⁸F]DCFPyL in decay-corrected radiochemical yields of 23 ± 5 % (n = 10) within 55 min, including HPLC purification. Dynamic PET analysis revealed rapid and high uptake of radioactivity (SUV_5min 0.95) in LNCaP tumors which increased over time (SUV_60min 1.1). Radioactivity uptake in LNCaP tumors was blocked in the presence of nonradioactive DCFPyL (SUV_60min 0.22). The muscle as reference tissue showed rapid and continuous clearance over time (SUV_60min 0.06). Fast blood clearance of radioactivity resulted in tumor-blood ratios of 1.0 after 10 min and 8.3 after 60 min. PC3 tumors also showed continuous clearance of radioactivity over time (SUV_60min 0.11). Kinetic analysis of PET data revealed the two-tissue compartmental model as best fit with K ₁ = 0.12, k ₂ = 0.18, k ₃ = 0.08, and k ₄ = 0.004 min⁻¹, confirming molecular trapping of [¹⁸F]DCFPyL in PSMA+ LNCaP cells.

[¹⁸F]DCFPyL can be prepared for clinical applications simply and in good radiochemical yields via a direct radiofluorination synthesis route in a single reactor automated synthesis unit. Radiopharmacological evaluation of [¹⁸F]DCFPyL confirmed high PSMA-mediated tumor uptake combined with superior clearance parameters. Compartmental model analysis points to a two-step molecular trapping mechanism based on PSMA binding and subsequent internalization leading to retention of radioactivity in PSMA+ LNCaP tumors.