Automated radiosynthesis of [⁶⁴Cu]Cu-FAPI-2286 for FAP-targeted PET imaging

Fibroblast Activation Protein (FAP) is a critical target for imaging cancer-associated fibroblasts and active hepatic stellate cells in liver fibrosis. While FAPI-2286 has been widely explored with ⁶⁸Ga and ¹⁷⁷Lu, the use of copper-64 offers unique advantages for theranostics due to its amenable half-life and chemical pairing with therapeutic copper-67. This study focuses on the automated radiosynthesis of [⁶⁴Cu]Cu-FAPI-2286 in a green synthetic route, detailed physicochemical characterization, quality control analysis, and initial clinical evaluation of [⁶⁴Cu]Cu-FAPI-2286 in liver fibrosis.

The [⁶⁴Cu]Cu-FAPI-2286 was synthesized via manual and automated modules using aqueous solution of [⁶⁴Cu]CuCl₂. The reaction conditions (solvent, temperature, time) were optimized. Physicochemical evaluation included lipophilicity (logD_7.4) and stability challenges against EDTA, physiological media, and human serum. A pilot PET/CT scan was performed on a patient with HCV-related decompensated cirrhosis complicated by Grade III ascites to assess biodistribution and hepatic uptake.

Optimized automated synthesis in aqueous medium at 40 °C yielded [⁶⁴Cu]Cu-FAPI-2286 with >95% radiochemical purity and an apparent molar activity (AMA) of 258 ± 5 MBq/μmol. The radiotracer demonstrated high hydrophilicity with a logD_7.4 value of -2.38 ± 0.01. The complex exhibited excellent stability (>95%) in serum and saline over 24 h and showed strong resistance to transchelation against a 500-fold excess of EDTA. Clinically, the patient with liver fibrosis demonstrated intense, diffuse hepatic uptake with a SUV_max(lbm) of 17.54, significantly higher than background, confirming active fibrogenesis.

We successfully established a robust, green, automated synthesis route for [⁶⁴Cu]Cu-FAPI-2286. The tracer's favorable hydrophilicity and stability make it a promising agent. The high uptake observed in the fibrotic liver highlights its potential as a non-invasive biomarker for staging liver fibrosis and for guiding future [⁶⁷Cu]Cu-FAPI-2286 therapies.