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α_vβ₃ integrins play an important role in angiogenesis and cell migration in cancer and are highly expressed on the activated endothelial cells of newly formed blood vessels. Here, we compare the targeting characteristics of 4 ⁶⁸Ga-labeled multimeric cyclic arginine-glycine-aspartate (RGD)–based tracers in an α_vβ₃ integrin–expressing tumor model and a tumor model in which α_vβ₃ integrin is expressed solely on the neovasculature. Female BALB/c nude mice were subcutaneously injected with SK-RC-52 (α_vβ₃ integrin–positive) or FaDu (α_vβ₃ integrin–negative) tumor cells. ⁶⁸Ga-labeled DOTA-(RGD)₂, TRAP-(RGD)₃, FSC-(RGD)₃, or THP-(RGD)₃ was intravenously administered to the mice (0.5 nmol per mouse, 10–20 MBq), followed by small-animal PET/CT imaging and ex vivo biodistribution studies 1 h after injection. Nonspecific uptake of the tracers in both models was determined by coinjecting an …