Specific-SPECT imaging of vulnerable atherosclerotic lesions of a novel Tc-99m labeled cRGD peptide (99mTc-labeled NO2-D-[c(RGDfK)]2) in ApoE KO mice model

1599 Objectives Increased expression of αvβ3 integrin is involved in the inflammatory process in atherosclerotic lesions as well as tumor-induced angiogenesis. Previous studies have demonstrated that Tc-99m labeled NO2-D-[c(RGDfK)]2 showed high binding affinity and clearly visible with high contrast for αvβ3 integrin receptor. In this study, we evaluated Tc-99m labeled cRGD peptide for SPECT imaging of αvβ3 integrin expression in atherosclerotic plaques. Methods Tricarbonyl Tc-99m-labeled cRGD peptide was synthesized by incorporating [99mTc(CO)3]+ into the precursor. For scintigraphic imaging study, male hypercholesterolemic ApoE KO mice on a western diet and normally fed adult control mice were injected with Tc-99m-labeled cRGD peptide and obtained SPECT images. The aorta CT image was obtained with contrast agent. The aorta was dissected for autoradiography study and histology (H&E, confocal, Masson trichrome, and Oil Red O staining). Results This radiotracer binding to HUVE was inhibited by excess cRGDyV in a dose dependent manner, with a calculated IC50 value of 0.4 nM. Fenestra VC provided a very constant and high level of image with maximum enhancement of approximately 680 HU (aorta) and approximately 110 HU (kidney) in CT image. SPECT image of Tc-99m labeled cRGD peptide was colocalized with calcified lesion of the aortic arch as seen in contrast-enhanced CT image and atherosclerotic plaques uptake was 3.4±0.3 %ID/g. Authoradiography measurement demonstrated the preferential accumulation of Tc-99m labeled cRGD peptide in the atherosclerotic plaques when compared with the adjacent normal vessel wall and this uptake region was consistent with in vivo SPECT image. Atherosclerotic plaques were confirmed by histology and stained the tissue. Conclusions Our results show that Tc-99m labeled NO2-D-[c(RGDfK)]2 demonstrates visible SPECT uptake in atherosclerotic mice, which may make it a promising radiotracer for specific atherosclerotic lesions