Targeting rectal cancer using fluorescent nanoparticles conjugated to a novel GRPR-Binding peptide for tumor imaging applications

• Gastrin-releasing peptide receptor is highly overexpressed in rectal cancer tissues, supporting its value as a target for molecular imaging. • A novel peptide specifically binding to the gastrin-releasing peptide receptor was developed and showed strong, selective targeting of rectal cancer cells in laboratory studies. • Nanoparticles made of biodegradable polymers and loaded with a fluorescent dye achieved better tumor localization and sustained dye release compared to the free dye. • Functionalizing these nanoparticles with the targeting peptide further improved tumor-specific fluorescence, potentially aiding precise surgical resection. Surgical treatment of rectal cancer is difficult due to anatomical complexity. To improve tumor resection, fluorescence-guided surgery (FGS) has been developed using near-infrared fluorescence (NIRF, approximately 800 nm) and a dedicated camera system. Indocyanine green (ICG), an FDA-approved NIRF probe, enables optical imaging. The gastrin-releasing peptide receptor (GRPR), a member of the G protein-coupled receptor family, is widely expressed in rectal cancer cells. This abundant expression makes GRPR an ideal biomarker for molecular targeting and imaging of rectal cancer. In this study, the location and expression levels of GRPR were measured by immunofluorescence, immunohistochemistry and western blot. Our data confirmed significant overexpression of GRPR in rectal cancer cells and tissue samples, providing a significant indication for GRPR targeting evaluation. We designed the novel GRPR-targeting peptide, GRP-derived peptide (GRP-DP) derived from the natural GRPR-binding gastrin-releasing peptide (GRP). The newly developed GRP-DP demonstrated strong in vitro GRPR-targeting capabilities for rectal cancer imaging, potentially aiding surgeons in achieving complete tumor resection. Additionally, we investigated the use of ICG encapsulated within poly(lactic-co-glycolic acid)-polyethylene glycol (ICG/PLGA-PEG) nanoparticles (NPs) as a vehicle for fluorescent tumor imaging in rectal cancer. The ICG-NPs were functionalized with GRP-DP, exhibiting favorable physicochemical properties, including controlled ICG release kinetics and biocompatibility.