Synthesis and evaluation of a near-infrared fluorescent non-peptidic bivalent integrin α_vβ₃ 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 α_vβ₃ 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 α_vβ₃ 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.