Dual‐labeled prostate‐specific membrane antigen (PSMA)‐targeting agent for preoperative molecular imaging and fluorescence‐guided surgery for prostate cancer

The objective of this study was to report the synthesis and characteristics of a dual modality imaging agent, Tc‐99m GRFLTGGTGRLLRIS‐GHEG‐ECG‐K(‐5‐carboxy‐X‐rhodamine)‐NH2 (GRFLT‐ECG‐ROX), and to verify its feasibility as both molecular imaging and intraoperative guidance agent. GRFLT‐ECG‐ROX was synthesized using Fmoc solid‐phase peptide synthesis. Radiolabeling of GRFLT‐ECG‐ROX with Tc‐99m was accomplished using ligand exchange via tartrate. Binding affinity and in vitro cellular uptake studies were performed. Gamma camera imaging, biodistribution, and ex vivo imaging studies were performed using LNCaP and PC‐3 tumor‐bearing murine models. Surgical removal of tumor nodules in murine models with peritoneal carcinomatosis was performed under a fluorescence imaging system. After radiolabeling procedures with Tc‐99m, Tc‐99m GRFLT‐ECG‐ROX complexes were prepared in high yield (>96%). The binding affinity value (Kd) of Tc‐99m GRFLT‐ECG‐ROX for LNCaP cells was estimated to be 9.5 ± 1.3 nM. In gamma camera imaging, the tumor to normal muscle uptake ratios of Tc‐99m GRFLT‐ECG‐ROX increased with time (3.1 ± 0.2, 4.0 ± 0.4, and 6.3 ± 0.9 at 1, 2, and 3 h, respectively). Under real‐time optical imaging, the removal of visible nodules was successfully performed. Thus, Tc‐99m GRFLT‐ECG‐ROX could provide both preoperative molecular imaging and fluorescence imaging guidance for tumor removal.