The lectin Griffonia simpucifolia I‐A4 (GS I‐A4) specifically recognizes terminal α‐linked N‐acetylgalactosaminyl groups and is cytotoxic to the human colon cancer cell lines LS174t and SW1116

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Abstract
The lectin GS I‐A4 binds to terminal α‐N‐acetylgalactosaminyl (GaINAc) groups (which include the Tn antigen), but not to the closely related tumor‐associated epitope, sialylated Tn antigen. The lectin also precipitates asialo OSM, but not its native sialylated form. Lectin histochemistry with human colonic tissues showed that GS I‐A4 specifically stained specimens of colon cancer and colonic tissues from individuals with FAP; however, normal colonic tissues from patients without colonic disease were rarely stained with this lectin. Glycoconjugates bound by GS I‐A4 were observed on the surface membranes of 2 human colon cancer cell lines, LS174t and SW1116, when fluorescein isothiocyanate (FITC)‐conjugated GS I‐A4 was used. GS I‐A4 was toxic to these 2 human colon cancer cell lines in monolayer culture, A dose‐response study conducted using 10‐160 μg/ml of GS I‐A4 demonstrated significant dose‐related toxicity against LS174t and SW1116 cells. At concentrations > 80 μg/ml, > 99% of LS174t and > 90% of SW1116 cells were killed. Four mM GaINAc specifically inhibited the cytotoxic effect of GS I‐A4 (p < 0.001), whereas 4mM N‐acetylglucosamine (GlcNAc) had no effect. Two other lectins that recognize terminal α‐GalNAc residues, DBA and LBL, were significantly less cytotoxic to the colon cancer cells than GS I‐A4. In the light of these findings, we speculate that GS I‐A4 may have potential use as a diagnostic agent against colorectal cancer.