Near Infrared Fluorescent Probe Based on Bombesin Analogue for Tumor Diagnosis in vivo

Gastrin-releaing peptide(GRP) receptors have over expression distribution on several type of human tumors and less distribution in health tissue. As an GRP analogue, 14 amino acid residues, bombesin has high specificity and affinity to GRPR, this study was about to design, synthesize, and characterize new target specific near infrared(NIR) fluorescent probe based on an 11-amino acid Bombesin analogue, H2N-Gly-Gly-Gly-Gln-Trp-Ala-Val-Gly-His-Leu-Met(NH2). In this study, a near infrared (NIR) fluorescent dyes, ICG-Der-02, was conjugated to BBN analogue to form ICG-Der-02-BBN and ICG-Der-02-PEG-SA-BBN respectively for NIR fluorescent imaging. Probe conjugates were prepared by reation of ICG-Der-02 succinimidyl ester to H2N-Gly-Gly-Gly-Gln-Trp-Ala-Val-Gly-His-Leu-Met(NH2) and ICG-Der-02 succinimidyl ester to PEG4000. The conjugates were purified by HPLC. Confocal fluorescence microscopy images of RhB-BBN and RhB-PEG-SA-BBN in human breast tumor MDA-MB-231 indicated specific uptake in vitro. In addition, the xenografts of MDA-MB-231 cancer cells using ICG-Der-02-BBN and ICG-Der-02-PEG-SA-BBN as near infrared fluorescent probes clearly visualized subcutaneous MDA-MB-231 cancer, also the ability of targeting to gastrin releasing peptide receptor(GRPR) was illustrated. Moreover, after 6h later of inject ICG-Der-02-BBN, high tumor/normal tissue ratios was illustrated by biodistribution experiment. Conclusion: the results suggested that ICG-Der-02-BBN and ICG-Der-02-PEG-SA-BBN were superior probes for in vivo optical imaging.