Abstract
Colorectal adenocarcinoma is the third most commonly diagnosed cancer and the third most deadly malignancy in the United States. Colonoscopies are a powerful tool for the early detection of the disease, as they readily facilitate the identification and resection of both carcinomas and precancerous lesions like tubular adenomas (TAs). However, the identification of another type of precancerous lesion-sessile serrated polyps (SSPs)-during colonoscopy is notoriously challenging, given their poor circumscription, concealment by mucous caps, and flat appearance. The development of effective molecular imaging agents for the delineation of SSPs requires the identification and characterization of biomarkers expressed by SSPs but not healthy colonic epithelium. In this investigation, we explore the expression of the glycoprotein MUC5AC in tissue samples of healthy colon, colorectal carcinoma, TAs, SSPs, and hyperplastic polyps (HPs). Immunohistochemistry revealed that the antigen is abundantly expressed in SSPs; completely absent in healthy colonic epithelium; and found to an intermediate degree in HPs, TAs, and carcinomas. In light of these promising data, we synthesized a near-infrared fluorescence (NIRF) imaging agent via the site-selective conjugation of a thiol-reactive variant of the fluorophore IR800CW (i.e., PODS-IR800) to the MUC5AC-targeting monoclonal antibody RA96. In order to interrogate the in vivo performance of this probe in the context of MUC5AC-expressing colorectal lesions, NIRF imaging experiments were performed in mice bearing both subcutaneous and orthotopic LS174T colorectal carcinoma xenografts. These data clearly show that the probe delineates MUC5AC-expressing xenografts with high target-to-background contrast, underscoring the promise of RA96-IR800 as a clinical tool for the visualization of precancerous and malignant colorectal lesions.