Detection of early colorectal cancer imaged with peanut agglutinin-immobilized fluorescent nanospheres having surface poly(N-vinylacetamide) chains

Peanut agglutinin (PNA)-immobilized fluorescent nanospheres were designed as a novel imaging agent for colonoscopy. PNA is a targeting moiety that binds to β-d-galactosyl-(1–3)-N-acetyl-d-galactosamine, which is the terminal sugar of the Thomsen-Friedenreich antigen that is specifically expressed on the mucosal side of colorectal cancer cells. The in vivo performance of the imaging agent was evaluated using a human colorectal cancer orthotopic animal model. Human colorectal adenocarcinoma cell lines, HT-29, HCT-116, and LS174T, were implanted on the cecal serosa of immune-deficient mice. A loop of the tumor-bearing cecum was made, and the luminal side was treated with the imaging agent. Strong fluorescence was observed at several sites of the cecal mucosa, irrespective of cancer cell type. Microscopic histological evaluation of the cecal mucosa revealed that bright areas with fluorescence derived from the imaging agent and dark areas without the fluorescence well denoted the presence and absence, respectively, of the invasion of implanted cancer cells on the mucosal side. This good correlation showed that PNA-immobilized fluorescent nanospheres recognized millimeter-sized tumors on the cecal mucosa with high affinity and specificity.