Inhibitory effects of cholera toxin on in vitro growth of human lung cancer cell lines : Kiura K, Watarai S, Shibayama T, Ohnoshi T, Kimura I, Yasuda T. Inst Cellular and Molecular Biology, Okayama University Medical School, 2-5-1 Shikata-cho, Okayama 700. Anti-Cancer Drug Res 1993;8:417–428

Abstract

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 3-[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-fluorescein isothiocyanate conjugate (FITC-CTB) when assayed by flow cytometry. 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-sensitive SBC-3 and CT-sensitive SBC-5. HRP-CTB was found to react not only 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 binding of gangliosides extracted from SBC-1 cells to HRP-CTB was markedly decreased 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 gangliosides, such as GM1, Fuc-GM1 and GD1b, on the cells, rather than the CT-binding ability to the cells, plays a major role in cytotoxicity by CT.