Thapsigargin Enhances Cell Death in the Gastrointestinal Stromal Tumor Cell Line, GIST-T1, by Treatment with Imatinib (Glivec)

Abstract

Imatinib is a specific inhibitor of c-KIT that has recently been approved for the treatment of chronic myeloid leukemia and gastrointestinal stromal tumor (GIST). Thapsigargin is an inhibitor of calcium transport to the endoplasmic reticulum (ER) and can inhibit protein maturation. In this study, we evaluated the synergistic cytotoxic effect of thapsigargin and imatinib on the GIST cell line, GIST-T1. Cell viability and cell death were determined by 3,-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry, respectively. In addition, the amount and activation of c-KIT on the cell surface were measured by flow cytometry and western blot analysis, respectively. Thapsigargin alone (for 5 hr incubation) was shown to decrease the amount of c-KIT on the GIST-T1 cell surface and to slightly inhibit the associated tyrosine kinase activity. Interestingly, thapsigargin significantly enhanced the cell death induced by imatinib compared with the effect of imatinib alone. The results further suggested that thapsigargin induced the increased cell death in GIST-T1 cells co-treated with imatinib, at least in part, via disrupting the translocation of c-KIT to the cell surface, and decreasing the activated c-KIT molecules.