Fluorescent Non-peptidic RGD Mimetics with High Selectivity for αVβ3 vs αIIbβ3 Integrin Receptor: Novel Probes for in Vivo Optical Imaging

Integrins are heterodimeric transmembrane protein receptors consisting of different alpha and beta subunits. alpha v beta(3) integrins are overexpressed on many tumor cells and tumor-associated angiogenic vessels, whereas alpha(IIb)beta(3) is a receptor for, e.g., fibrinogen and mediates platelet aggregation. In this study, a near-infrared fluorescent imaging probe has been designed and synthesized by conjugating fluorescent dyes to a non-peptidic, pharmacophore-based ligand, based on a molecular modeling design approach. Affinity values were determined, and in vitro cell binding assays and preliminary in vivo xenograft studies in nude mice were performed to evaluate target binding. Competition assays revealed excellent binding and selectivity to alpha(v)beta(3) compared to that for alpha(IIb)beta(3). In vitro, the probe showed high target binding on av beta 3-positive M-21 cells and negligible binding to alpha v beta 3-negative MCF-7 cells. In vivo, the tracer is able to image target expression in U-87 xenografts with a maximum signal-to-noise ratio (SNR) of 2.5:1 at 24 h after injection.