Wnt/ß-catenin pathway is a key signaling pathway to trastuzumab resistance in gastric cancer cells.

BACKGROUND: Trastuzumab is the only approved target agent for the first-line treatment of human epidermal growth factor receptor-2 (HER-2) positive gastric cancer; however, trastuzumab resistance is a major problem in clinical practice. To comprehend the mechanism of trastuzumab resistance, we focused on the Wnt/ß-catenin signaling pathway and its influence on the phenotypes and behavior of trastuzumab-resistant gastric cancer cells. METHODS: Trastuzumab-resistant NCI-N87R cells were established in vitro from the human gastric cancer cell line NCI-N87 by dose-escalating repeated trastuzumab treatment. We investigated the phenotypes of NCI-N87R cells, including Wnt signaling pathway activity. Gastric cancer organoid cells were incubated with complete medium and Wnt3a-depletion medium, and their resistance to trastuzumab was compared. RESULTS: NCI-N87R exhibited stemness and epithelial-mesenchymal transition (EMT)-like phenotypes, along with decreased levels of the epithelial marker E-cadherin and increased levels of the mesenchymal markers Vimentin and Snail along with an increased Wnt signaling pathway activity. When gastric cancer cells were incubated in Wnt3a-conditioned medium. Wnt signaling pathway activity and resistance to trastuzumab increased. Gastric cancer patient-derived organoids incubated in Wnt3a-depletion medium were more susceptible to dose-dependent inhibition of cell viability by trastuzumab than those incubated in complete medium. CONCLUSIONS: Trastuzumab-resistant gastric cancer cells exhibited EMT-like phenotype, and trastuzumab resistance was promoted by the Wnt/ß-catenin signaling pathway. The Wnt/ß-catenin pathway is a key signaling pathway for trastuzumab resistance in gastric cancer cells.