Gold nanorods-bombesin conjugate as a potential targeted imaging agent for detection of breast cancer

• Bombesin was conjugated covalently with PEG-coated gold nanorods.
• Cell binding assay showed selective binding of new contrast agent to cancer cells.
• Biodistribution study showed accumulation of GNR–PEG–BBN in breast tumor.
• The conjugate showed potential as a targeted contrast agent for PIA of breast cancer.

Photoacoustic imaging (PAI) is a hybrid biomedical imaging modality that offers both strong optical absorption contrast and high ultrasonic resolution. PAI is capable of in vivo molecular imaging, thus facilitating further molecular and cellular characterization of cancer. In this study, Gold nanorods (GNRs) were synthesized and coated with polyethyleneglycol (PEG). Then, the PEG-GNRs were conjugated with bombesin (BBN), a cancer seeking peptide, for production of a potential photoacoustic targeting imaging agent for detection of breast cancer. The optical property, biocompatibility, stability and in vitro/in vivo binding affinities of GNR-PEG-BBN for breast cancer cells were investigated. UV–vis spectroscopy confirmed the conjugation of bombesin with PEG-coated GNRs. The stability assessment proved high optical stability of GNR-PEG-BBN in human blood serum up to 12 h. Cytotoxicity study showed biocompatibility of GNR–PEG–BBN conjugate. Molecular targeting ability was approved in cells over expressing gastrin-releasing peptide (GRP) receptor (breast cancer cell line) in comparison with cells that do not express GRP receptor (skin fibroblast cell line). The selective accumulation of GNR-PEG-BBN was demonstrated in breast tumor in comparison with unconjugated gold nanorods, following the intravenous administration of GNR-PEG-BBN to breast tumor-bearing mice. This study demonstrated the potential of GNR-PEG-BBN as a photoacoustic imaging agent that can provide improved specificity and sensitivity for breast cancer detection.