Inhibitory Effect of Fucoidan Analogs on Highly Metastatic Gastric Cancer Cells via Galectin-4 Inhibition

In malignant-type gastric cancer, peritoneal dissemination is the most frequent metastatic process and is an inoperable condition for which effective treatment is lacking. Our research has revealed that galectin-4 plays an important role in the peritoneal metastasis of gastric cancer cells. Based on this, we hypothesized that inhibiting galectin-4 could suppress peritoneal metastasis. The inhibitory activity towards galectin-4 binding was evaluated using an enzyme-linked immunosorbent assay, while the suppressive effect on gastric cancer cell proliferation was assessed using an adenosine triphosphate-based cell viability assay. Direct binding to galectin-4 was examined by surface plasmon resonance analysis. Chemically synthesized fucoidan analogs exhibited significant suppressive activity against the proliferation of gastric cancer cells, partly via a galectin-4-mediated pathway. Among the 13 fucoidan analogs tested, analog 10, whose sugar chains composed of repeating 2,3-O-sulfated α(1,4)-linked L-fucose, showed significant inhibitory activity against galectin-4 binding and cell proliferation. 14, the cholestanol-conjugated analog 10, exhibited a pronounced increase in inhibitory activity, consistent with potential multimerization. Molecular docking and site-directed mutagenesis studies revealed that Arginine-45 in galectin-4 is important for binding to fucoidan analogs. In conclusion, fucoidan analogs with a strong affinity for galectin-4 are promising candidates for inhibiting the peritoneal metastasis of galectin-4-positive gastric cancer cells.