Noninvasive imaging of c(RGD) 2 ‐9R as a potential delivery carrier for transfection of siRNA in malignant tumors

The purpose of our study was to develop and evaluate a novel integrin α v β 3 ‐specific delivery carrier for transfection of siRNA in malignant tumors. We adopted arginine‐glycine‐aspartate (RGD) motif as a tissue target for specific recognition of integrin α ν β 3 . A chimaeric peptide was synthesized by adding nonamer arginine residues (9‐arginine [9R]) at the carboxy terminus of cyclic‐RGD dimer, designated as c(RGD) 2 ‐9R, to enable small interfering RNA (siRNA) binding. To test the applicability of the delivery carrier in vivo, c(RGD) 2 ‐9R was labeled with radionuclide of technetium‐99m. Biodistribution and γ‐camera imaging studies were performed in HepG2 xenograft‐bearing nude mice. As results, an optimal 10:1 molar ratio of 99m Tc‐c(RGD) 2 ‐9R to siRNA was indicated by the electrophoresis on agarose gels. 99m Tc‐c(RGD) 2 ‐9R/siRNA remained stable under a set of conditions in vitro. For in vivo study, tumor radioactivity uptake of 99m Tc‐c(RGD) 2 ‐9R/siRNA in nude mice bearing HepG2 xenografts was significantly higher than that of control probe ( P  < .05). The xenografts were clearly visualized at 4 hours till 6 hours noninvasively after intravenous injection of 99m Tc‐c(RGD) 2 ‐9R/siRNA, while the xenografts were not visualized at any time after injection of control probe. It was concluded that c(RGD) 2 ‐9R could be an effective siRNA delivery carrier. Technetium‐99m radiolabeled‐delivery carrier represents a potential imaging strategy for RNAi‐based therapy.