Evaluation of a dimeric-cRGD peptide for targeted PET-CT imaging of peripheral angiogenesis in diabetic mice

The α _V  β₃ integrin plays an important role in many physiological functions and pathological disorders. α _V  β₃ is minimally expressed in normal quiescent endothelial cells, but significantly upregulated during neovascularization. In this study, we evaluated a ⁶⁴Cu-labeled dimeric cRGD tracer targeted at α _V  β₃ integrin and report its applicability to assess peripheral angiogenesis in diabetes mellitus (DM). We established a murine model of type-1 DM characterized by elevated glucose, glycated serum protein (GSP), and glycated hemoglobin A1c (HbA1c). We demonstrated that our imaging probe is specific to α _V  β₃ integrin under both normo- and hyperglycemic conditions. We found that the analysis of in vivo PET-CT images correlated well with gamma well counting (GWC). Both GWC and PET-CT imaging demonstrated increased uptake of ⁶⁴Cu-NOTA-PEG4-cRGD₂ in the ischemic hindlimb in contrast to non-ischemic control. GWC of the distal ischemic tissue from DM mice showed significantly lower probe accumulation than in non-DM mice. The immunofluorescence staining of the ischemic tissues showed a 3-fold reduction in CD31 and 4-fold reduction in the α _V  β₃ expression in DM vs. non-DM animals. In conclusion, we successfully demonstrated that diabetes-associated reductions in peripheral angiogenesis can be non-invasively detected with PET-CT imaging using targeted dimeric-cRGD probe.