A fast tumor-targeting near-infrared fluorescent probe based on bombesin analog for in vivo tumor imaging.

Bombesin (BBN), an analog of gastrin-releasing peptide (GRP), of which the receptors are over-expressed on various tumor cells, is able to bind to GRP receptor specifically. In this study, a near-infrared fluorescent dye (MPA) and polyethylene glycol (PEG) were conjugated to BBN analog to form BBN[7-14]-MPA and BBN[7-14]-SA-PEG-MPA. The successful synthesis of the two probes was proved by the characterization via sodium dodecylsulfate-polyacrylamide gel electrophoresis, infrared and optical spectra. Cellular uptakes studies indicated that BBN-based probes were mediated by gastrin-releasing peptide receptors (GRPR) on tumor cells and the PEG modified probe had higher affinity. The dynamic distribution and clearance investigations showed that the BBN-based probes were eliminated by the liver-kidney pathway. Furthermore, both of the BBN-based probes displayed tumor-targeting ability in GRPR over-expressed tumor-bearing mice. The PEG modified probe exhibited faster and higher tumor targeting capability than BBN[7-14]-MPA. The results implied that BBN[7-14]-SA-PEG-MPA could act as an effective fluorescence probe for tumor imaging.