Poly(N-vinylacetamide) chains enhance lectin-induced biorecognition through the reduction of nonspecific interactions with nontargets

Lectin-immobilized fluorescent nanospheres were designed with the aim of developing a novel endoscopic imaging agent for the detection of early colorectal cancer. Submicron-sized polystyrene nanospheres with surface poly(N-vinylacetamide) (PNVA) and poly(methacrylic acid) (PMAA) chains encapsulating fluorescein-labeled cholesterol were prepared as a platform of the imaging agent. Peanut agglutinin (PNA) was immobilized on the surface of fluorescent nanospheres through a chemical reaction with PMAA in order to recognize β-d-galactosyl-(1-3)-N-acetyl-d-galactosamine (Gal-β(1-3)GalNAc), which is the terminal sugar of the Thomsen–Friedenreich antigen that is specifically expressed on the mucosal side of colorectal cancer cells. The effect of surface structure of nanospheres on the affinity and specificity of immobilized PNA for Gal-β(1-3)GalNAc was examined. Agglutination of normal and Gal-β(1-3)GalNAc-expressed erythrocytes in the presence of nanospheres showed that PNA was immobilized actively on the nanosphere surface. Molecular weights of PNVA and PMAA affected the PNA activity most strongly. When the weight-average molecular weight of PNVA was nearly equal to that of PMAA, the affinity of PNA immobilized on the nanosphere surface for Gal-β(1-3)GalNAc was as strong as that of intact PNA; the specificity for the carbohydrate residue was higher than that of the PNA. Results indicated that PNVA enhanced the specificity of PNA through the reduction of nonspecific interactions between PNA and carbohydrates other than Gal-β(1-3)GalNAc on the erythrocyte surface without a significant decrease in the affinity.