Targeting and imaging colorectal cancer by activatable cell-penetrating peptides.

While it has been a great challenge to determine the positive status of metastasis lesions, intraoperative tumor imaging, which can show tumor localization and facilitate intraoperative staging of nodal metastases, have enabled surgeons to quickly and accurately perform radical resections. However, to date, there is no accurate method for evaluating nodal status intraoperatively. In this study, we synthesized activatable cell-penetrating peptides (ACPPs) that can specifically recognize colorectal cancer and their nodal status. ACPPs were labeled with Cy5 dye at the C-terminal, and named ACPP-Cy5. Laser scanning confocal microscopy and flow cytometry were used to measure the change in intracellular fluorescence intensity between cancer cells and normal cells. The results showed while the intracellular Cy5 fluorescent intensity can be visualized in both cancer and normal cells by 8 h after adding ACPP-Cy5, the relative fluorescence intensity of colorectal cancer cells was significantly higher than the normal cells. In addition, IVIS spectrum imaging system was used to observe the fluorescence intensity of ACPP-Cy5 after tail vein injection of mice with subcutaneous tumor or orthotopic colorectal cancer and liver metastasis. We found in mice with colorectal cancer and liver metastasis the Cy5 fluorescence intensity of cancer was significantly increased compared to the organs including liver, colorectum, lung, spleen, and heart. It is demonstrated here, this ACPPs can target colorectal cancer and liver metastasis, therefore ACPP-Cy5 may be a promising tool used for the diagnoses of colorectal cancer and to assist in tumor localization during surgery.