Antitumor immunity of alcohol-soluble polysaccharide from Nostoc sphaeroides in non-small cell lung cancer.

Nostoc sphaeroides is a species of edible blue-green alga (cyanobacterium) that forms large, spherical colonies and has been used for centuries as a food. Alcohol-soluble polysaccharides exhibit diverse bioactivities such as antitumor, immunomodulatory, and antioxidant effects. However, their extraction and functions in N. sphaeroides remain unreported. To extract alcohol-soluble polysaccharides from N. sphaeroides and explore its antitumor effect and potential mechanism on lung cancer. The alcohol-soluble polysaccharide named NSAP was isolated from N. sphaeroides using hot water extraction, enzymatic hydrolysis, and 80 % ethanol precipitation followed by purification with a DEAE-Sepharose A25 dextran gel chromatography column. Subsequently, its structural characterizations were explored and anti-lung cancer effects were evaluated in vitro and in vivo experiments. Structural characterization revealed that NSAP is an acidic polysaccharide with a molecular weight ranging from 7 × 104-3 × 105 Da, which mainly composed of glucose, galactose, mannose, xylose, glucuronic acid, and rhamnose. Methylation analysis indicated that the glycosidic linkages were 4-linked glucose (4-Glc(p), 21.62 %), 3,4-linked glucuronic acid (3,4-Glc(p)-UA, 15.55 %), 4-linked mannose (4-Man(p), 7.81 %), and 4,6-linked galactose (4,6-Gal(p), 11.74 %). Functionally, NSAP suppressed cell viability, DNA replication, and cell migration, while inducing apoptosis and lactose dehydrogenase release in H157 and A549 lung cancer cells, without affecting normal BEAS-2B and NIH/3T3 cells. NSAP also promoted cytokine secretion from RAW264.7 macrophages and splenic lymphocytes, and enhanced macrophage phagocytosis in zebrafish. In vivo, NSAP inhibited tumor growth and infiltration in lung cancer-bearing mice. Mechanistically, NSAP exerted antitumor immunity by upregulating NFKBIZ expression and inhibiting the NF-κB/PD-L1 pathway. Moreover, NSAP could overcome resistance in osimertinib-resistant lung cancer cells. This study identifies NSAP as a novel alcohol-soluble polysaccharide from N. sphaeroides, with potential as a therapeutic agent for lung cancer via modulation of the NFKBIZ/NF-κB/PD-L1 pathway.