A novel Tc‐99m and fluorescence‐labeled arginine‐arginine‐leucine‐containing peptide as a multimodal tumor imaging agent in a murine tumor model

We developed a Tc‐99m and TAMRA‐labeled peptide, Tc‐99m arginine‐arginine‐leucine (RRL) peptide (TAMRA‐GHEG‐ECG‐RRL), to target tumor cells and evaluated the diagnostic performance of Tc‐99m TAMRA‐GHEG‐ECG‐RRL as a dual‐modality imaging agent for tumor in a murine model. TAMRA‐GHEG‐ECG‐RRL was synthesized using Fmoc solid‐phase peptide synthesis. Binding affinity and in vitro cellular uptake studies were performed. Gamma camera imaging, biodistribution, and ex vivo imaging studies were performed in murine models with PC‐3 tumors. Tumor tissue slides were prepared and analyzed with immunohistochemistry using confocal microscopy. After radiolabeling procedures with Tc‐99m, Tc‐99m TAMRA‐GHEG‐ECG‐RRL complexes were prepared in high yield (>96%). The K d of Tc‐99m TAMRA‐GHEG‐ECG‐RRL determined by saturation binding was 41.7 ± 7.8 nM. Confocal microscopy images of PC‐3 cells incubated with TAMRA‐GHEG‐ECG‐RRL showed strong fluorescence in the cytoplasm. Gamma camera imaging revealed substantial uptake of Tc‐99m TAMRA‐GHEG‐ECG‐RRL in tumors. Tumor uptake was effectively blocked by the coinjection of an excess concentration of RRL. Specific uptake of Tc‐99m TAMRA‐GHEG‐ECG‐RRL was confirmed by biodistribution, ex vivo imaging, and immunohistochemistry stain studies. In conclusion, in vivo and in vitro studies revealed substantial uptake of Tc‐99m TAMRA‐GHEG‐ECG‐RRL in tumors. Tc‐99m TAMRA‐GHEG‐ECG‐RRL has potential as a dual‐modality tumor imaging agent.