Novel polysaccharide extracted from Sipunculus nudus inhibits HepG2 tumour growth in vivo by enhancing immune function and inducing tumour cell apoptosis

A novel polysaccharide was extracted from Sipunculus nudus (SNP). The molecular weight (MW) of SNP was determined to be 9223 Da by high-performance gel permeation chromatography analyses, and the structure of the SNP repeat units was determined to be →3,4-β-D-GlcpNAC (1→ and →4) -α-D-Glcp (1→ in the ratio of 15:1; →2) -α -D-Galp - (1→ as a side chain; and β-D-Galp-(1→ and α- D-Glcp - (1→ as end groups by GC-MS analysis and NMR assays. The effect of SNP on hepatoma HepG2-bearing mice was analysed to verify its potential in the clinical treatment of liver cancer. A total of 90 male athymic nu/nu mice were divided into therapeutic and preventive groups and fed with different amounts of SNP. The antitumour effect of SNP on HepG2-bearing mice and mechanism of such were studied by analysing the tumour size, spleen index, thymus index, immune factors in the blood, tumour apoptosis factors, etc. The results suggest that SNP not only increased the index of immune organs in the body, but also enhanced the secretion of immune factors, including interleukin-2, interferon gamma and tumour necrosis factor-alpha in the serum. SNP induced the apoptosis of tumour cells via the mitochondrial apoptosis pathway, which upregulated caspase-3, caspase-8, caspase-9 and BCL2-associated X, but downregulated B-cell lymphoma-2 and vascular endothelial growth factor protein expression. In conclusion, SNP inhibited tumour growth by enhancing immune function and inducing tumour cell apoptosis in HepG2-bearing mice. Therefore, SNP may be further investigated as a promising candidate for future antitumour drugs.