Preparation and Biological Study of ⁹⁹Tc^m(N)(PNP6)(Cys-RGD) for Integrin α_vβ3-positive Tumor Imaging

Objective To investigate the possibility of Radiolabelled Cys-RGD peptides for tumor αvβ3 integrin receptor scintigraphy. Methods The Cys-RGD peptide conjugate Cys-RGD（c(Arg-Gly-Asp-D-Tyr-Lys)-Cys） was radiolabelled with 99Tcm-nitrido core combined with PNP6 ligand (PNP6=bis(diethoxypropylphosphino ethyl)ethoxy ethylamine), and the radiochemical purity was measured with HPLC. The in vitro stability was investigated at room temperature and incubated in the cystein and serum solution. Biodistribution studies and gamma camera imaging were performed in normal mice and nude mice bearing FWK-1 pancreatic tumor xenografts. Results The radiolabelling yield was over 90% under optimized preparation condition. The high in vitro stability was found for 99Tcm(N)(PNP6)(Cys-RGD). In vivo biodistribution studies indicated the radiolabelled peptides was cleared rapidly from blood and mainly excreted via urinary system. Tumour uptake was 2.92±0.71% ID/g at 1h post injection. The ratios of tumor/blood and tumor/muscle were 11.0 and 3.1 at 4h post injection, respectively. Scintigraphic imaging allowed contrasting visualisation of αvβ3-expressed tumors at 1h post injection. Conclusion The results suggest 99Tcm(N)(PNP6)(Cys-RGD) would be the potential agent for αvβ3-positive tumor imaging.