99mTc-HYNIC-RGD analog for monitoring of integrin expression in ischemic animal model

Introduction: The development of new blood vessels, from existing network of angiogenesis, occurs during embryonic development, cancer, arthritis and in response to ischemia. Ischemia in muscle tissue increases expression of integrin in the form of proliferating endothelial cells, including the αvβ3 receptor. Cyclic peptides containing RGD sequences have high affinity and selectivity for αvβ3 integrin, and may thus be used for angiogenesis monitoring. Aim: The aim of this study was the investigation of neovascularization in an ischemic hindlimb model using RGD conjugated with HYNIC and labeled with technetium-99m. Methods: 99mTc-HYNIC-RGD analog was prepared using tricine and EDDA as coligands. Unilateral hindlimb ischemia was induced in Wistar rats by surgical ligation of the femoral artery. Radiolabeled RGD was injected in rats after 2 h, as well as 1, 3, 5, 7, 10 and 14 days of ischemic induction. Evaluation of uptake by ischemic limb and normal contralateral limb was done by planar imaging and biodistribution studies. Pertechnetate distribution, which has no affinity for regeneration tissue and in the circumstances indicates just blood flow, was also assessed for confirmation. Results: The highest uptake ratio between ischemic hindlimb and control side was achieved at the seventh day (2.62 ± 0.95), with substantial decreased by the fourteenth day. For pertechnetate the seventh day ratio was 0.87 ± 0.23, consistent with reduced perfusion following arterial ligation. Scintigraphic imaging confirmed the RGD results. Both renal and hepatic elimination was observed, with noticeable uptake also by intestine, spleen and bone. Conclusions: 99mTc-HYNIC-RGD analog corresponded to the expectations in this animal model, displaying elevated uptake in ischemic tissue by the time of widespread angiogenesis. Utilization in other ischemic models can be recommended. (author)