INHIBITORY EFFECTS OF CHOLERA-TOXIN ON IN-VITRO GROWTH OF HUMAN LUNG-CANCER CELL-LINES

Cholera toxin (CT) inhibited the growth of three out of 10 small cell lung cancer (SCLC) cell lines and two out of seven non-small cell lung cancer (NSCLC) cell lines when tested by [4,5-dimethylthiazol-2-yl]-2 ,5-diphenyltetrazolium bromide (MTT) assay. These CT-sensitive as well as CT-resistant cell lines bound well to the non-toxic CT-B subunit-f luorescein isothiocyanate conjugate (FITC-CTB) when assayed by flow cy tometry. Using the reaction of horseradish peroxidase-conjugated CT-B (HRP-CTB) on thin-layer chromatography (TLC), we analyzed gangliosides extracted from SCLC cell lines, CT-resistant SBC-1, minimally CT-sens itive SBC-S and CT-sensitive SBC-5. HRP-CTB was found to react not onl y with GM1, but also with Fuc-GM1, GD1b, and other gangliosides on TLC . Although CT-resistant SBC-1 cells bound well to FITC-CTB, the bindin g of gangliosides extracted from SBC-1 cells to HRP-CTB was markedly d ecreased when compared to those from CT-sensitive SBC-5 cells. The CT resistance of the minimally CT-sensitive SBC-3 cell lines, which binds weakly FITC-CTB and HRP-CTB, was partially reversed by exogenous GM1 pretreatment. These observations suggest that the amount of gangliosid es, such as GM1, Fuc-GM1 and GD1b, on the cells, rather than the CT-bi nding ability to the cells, plays a major role in cytotoxicity by CT.