Association between [⁶⁸Ga]NODAGA-RGDyK uptake and dynamics of angiogenesis in a human cell-based 3D model

Radiolabeled RGD peptides targeting expression of α_vβ₃ integrin have been applied to in vivo imaging of angiogenesis. However, there is a need for more information on the quantitative relationships between RGD peptide uptake and the dynamics of angiogenesis. In this study, we sought to measure the binding of [⁶⁸Ga]NODAGA-RGDyK to α_vβ₃ integrin in a human cell-based three-dimensional (3D) in vitro model of angiogenesis, and to compare the level of binding with the amount of angiogenesis. Experiments were conducted using a human cell-based 3D model of angiogenesis consisting of co-culture of human adipose stem cells (hASCs) and of human umbilical vein endothelial cells (HUVECs). Angiogenesis was induced with four concentrations (25%, 50%, 75%, and 100%) of growth factor cocktail resulting in a gradual increase in the density of the tubule network. Cultures were incubated with [⁶⁸Ga]NODAGA-RGDyK for 90 min at 37 °C, and binding of radioactivity was measured by gamma counting and digital autoradiography. The results revealed that tracer binding increased gradually with neovasculature density. In comparison with vessels induced with a growth factor concentration of 25%, the uptake of [⁶⁸Ga]NODAGA-RGDyK was higher at concentrations of 75% and 100%, and correlated with the amount of neovasculature, as determined by visual evaluation of histological staining. Uptake of [⁶⁸Ga]NODAGA-RGDyK closely reflected the amount of angiogenesis in an in vitro 3D model of angiogenesis. These results support further evaluation of RGD-based approaches for targeted imaging of angiogenesis.