Synthesis and Evaluation of a Near-Infrared Fluorescent Non-Peptidic Bivalent Integrin αvβ3 Antagonist for Cancer Imaging

Computer modeling approaches to identify new inhibitors are essentially a very sophisticated and efficient way to design drugs. In this study, a bivalent nonpeptide intergrin αvβ3 antagonist (bivalent IA) has been synthesized on the basis of an in silico rational design approach. A near-infrared (NIR) fluorescent imaging probe has been developed from this bivalent compound. In vitro binding assays have shown that the bivalent IA (IC50 = 0.40 ± 0.11 nM) exhibited improved integrin αvβ3 affinity in comparison with the monovalent IA (IC50 = 22.33 ± 4.51 nM), resulting in an over 50-fold improvement in receptor affinity. NIR imaging probe, bivalent-IA-Cy5.5 conjugate, also demonstrated significantly increased binding affinity (IC50 = 0.13 ± 0.02 nM). Fluorescence microscopy studies showed integrin-mediated endocytosis of bivalent-IA-Cy5.5 in U87 cells which was effectively blocked by nonfluorescent bivalent IA. We also demonstrated tumor accumulation of this NIR imaging probe in U87 mouse xenografts.