A polysaccharide of the marine alga Capsosiphon fulvescens induces apoptosis in AGS gastric cancer cells via an IGF‐IR‐mediated PI3K/Akt pathway

Because seaweed extracts have recently been found to have antioxidant and anti‐tumor activities, we analyzed a hot‐water‐soluble polysaccharide (PS) of the marine alga Capsosiphon fulvescens for its potential as a functional foodstuff by determining its effects on cell growth and DNA synthesis. MTS assays showed that the C. fulvescens PS ( Cf ‐PS) significantly inhibited the proliferation of cultured human cancer cells in a dose‐dependent manner. Cf ‐PS‐treated AGS cells exhibited a marked increase in caspase‐3 activation and a decrease in Bcl‐2 expression. In addition, phosphorylation of insulin‐like growth factor‐I receptor (IGF‐IR) was decreased in Cf ‐PS‐treated AGS cells as compared to non‐treated control cells, which is consistent with PI3‐kinase (PI3K)/Akt activation. Cf ‐PS also decreased IGF‐I‐stimulated recruitment of p85 to IGF‐IR and IRS‐1. These results indicate that Cf ‐PS inhibits cell proliferation and induces apoptosis by inhibiting IGF‐IR signaling and the PI3K/Akt pathway.