Background— The α_vβ₃ integrin plays a critical role in cell proliferation and migration. We hypothesized that vascular cell proliferation, a hallmark of injury-induced remodeling, can be tracked by targeting α_vβ₃ integrin expression in vivo.

Methods and Results— RP748, a novel ¹¹¹In-labeled α_vβ₃-specific radiotracer, was evaluated for its cell-binding characteristics and ability to track injury-induced vascular proliferation in vivo. Three groups of experiments were performed. In cultured endothelial cells (ECs), TA145, a cy3-labeled homologue of RP748, localized to α_vβ₃ at focal contacts. Activation of α_vβ₃ by Mn²⁺ led to increased EC binding of TA145. Left common carotid artery wire injury in apolipoprotein E^−/− mice led to vascular wall expansion over a period of 4 weeks. RP748 (7.4 MBq) was injected into groups of 9 mice at 1, 3, or 4 weeks after left carotid injury, and carotids were harvested for autoradiography. Relative autographic intensity, defined as counts/pixel of the injured left carotid area divided by counts/pixel of the uninjured right carotid area, was higher at 1 and 3 weeks (1.8±0.1 and 1.9±0.2, respectively) and decreased significantly by 4 weeks after injury (1.4±0.1, P<0.05). Carotid α_v and β₃ integrin expression was maximal at 1 week and decreased by 4 weeks after injury. The proliferation index, as determined by Ki67 staining, followed a temporal pattern similar to that of RP748 uptake. Dynamic gamma imaging demonstrated rapid renal clearance of RP748.

Conclusions— RP748 has preferential binding to activated α_vβ₃ integrin and can track the injury-induced vascular proliferative process in vivo.