Fig. 6. ST6GAL1 K.O. sensitizes ErbB2-positive gastric cancer cells to trastuzumab-induced cytotoxicity.

A Resazurin assay for the measurement of the metabolic activity of NCI-N87 WT and ST6GAL1 K.O. ErbB2-positive gastric cancer (GC) cells following the treatment with increasing doses of trastuzumab; H₂O₂—positive control; IgG1—trastuzumab isotype control; B Assessment of trastuzumab-induced cell death through the annexin V/propidium iodide (PI) staining of WT and ST6GAL1 K.O. cells treated with 10 μg/mL trastuzumab for 120 h; C Quantification of ErbB2 cell surface expression by trastuzumab-binding in WT and ST6GAL1 K.O. cells treated with 10 μg/mL trastuzumab for 12 and 24 h; D Western blot analysis and α-tubulin-normalized quantification of ErbB2 intracytoplasmic phosphorylation in WT and ST6GAL1 K.O. cells treated with 10 μg/mL trastuzumab for 120 h and stimulated with 10 ng/mL EGF; E Analysis of the phosphorylation status of 43 human kinases in NCI-N87 WT and ST6GAL1 K.O. cells treated with 10 μg/mL trastuzumab for 120 h; Western blot analysis and α-tubulin-normalized quantification of EGFR intracytoplasmic phosphorylation for array target validation in NCI-N87 WT and ST6GAL1 K.O. cells treated with 10 μg/mL trastuzumab for 120 h; Comparisons were made using one-way ANOVA analysis of variance (n = 3; mean ± SD; *p < 0.05; **p < 0.01; ***p < 0.001); n.s. nonsignificant, C1 clone 1, C2 clone 2, C3 clone 3.