Site-specifically biotinylated VEGF(121) for near-infrared fluorescence imaging of tumor angiogenesis.

The vascular endothelial growth factor (VEGF)/VEGF receptor (VEGFR) pathway is considered to be one of the most important regulators of angiogenesis and a key target in anticancer treatment. Imaging VEGFR expression can serve as a new paradigm for assessing the efficacy of antiangiogenic cancer therapy, improving cancer management, and elucidating the role and modulation of VEGF/VEGFR signaling during cancer development and intervention. In this study we developed an Avi-tagged VEGF(121) protein, which is site-specifically biotinylated in the presence of bacterial BirA biotin ligase. BirA biotinylated VEGF(121)-Avi (VEGF(121)-Avib) forms a stable complex with streptavidin-IRDye800 (SA800) that retains high affinity for VEGFR in vitro and allows receptor specific targeting in vivo in a 67NR murine xenograft model. In contrast, chemical coupling of IRDye800 abrogated the VEGFR binding ability of the modified protein both in vitro and in vivo. The VEGF(121)-Avib/SA800 complex (VEGF-Avib/SA800) may be used for quantitative and repetitive near-infrared fluorescence imaging of VEGFR expression and translated into clinic for evaluating cancer and other angiogenesis related diseases.