Purification, Identification And Antitumor Mechanism Studies Of A Marine Polysaccharide Isolated From A Marine Bacillus

Cancer is an enormous global health problem,there are a large number of patients died of cancer every year.In all cancers,lung cancer is one of the leading causes of death worldwide.Because of the complex etiology and pathology characteristics,no specific medicine is available in prevention and treatment of lung cancer till now.Therefore,it is urgent to find the risk-benefit ratio drugs against lung cancer.In the ocean,there is abandent microbial resource,which could produce a large number of natural products with new structures and high biological activities.These natural products differ widely from terrigenous products,providing lead compounds for drug development.Marine polysaccharide is a hotspot of research and shows good biological activities in anti-inflammatory,antiviral,and antitumor.In addition,marine polysaccharides are also widely used in the field of food,cosmetics and auxiliary medical,suggesting good biological safety.Therefore,in recent years,finding marine polysaccharides with antitumor activity has attracted more and more researchers’attention.In this study,we isolated a new polysaccharide from a marine Bacillus sp.and named it EPS11.We futher investigated the structure and antitumor mechanism of EPS11.The results show that it is a kind of heteropolysaccharide whose relative molecular weight was estimated to be 22.3 kDa.Monosaccharide components of EPS11 contain mannose,glucosamine,galacturonic acid,glucose and xylose（1:2.58:0.68:0.13:3.09:1.41 in mole ratio）.EPS11 showed cytotoxic effects,especially against lung cancer cells.When incubated with 90 nmol/L EPS11 for 48 h,inhibition rates of EPS11 towards A549,H1299 and H460 cells reached up to 80%,67%and 47%respectively.We further investigated the molecular mechanisms of EPS11.Firstly,we found that EPS11 could significantly block cell adhesion in lung cancer cells.We further demonstrated that the expression of several cell adhesion associated proteins was downregulated and the filiform structures of cancer cells were destroyed after EPS11 treatment.Interestingly,the destruction of filiform structures in lung cancer cells by EPS11 is in a dose-dependent manner,and the inhibitory tendency is very consistent with that observed in the cell adhesion assay,which confirmed that filiform structures play important roles in modulating cell adhesion.When detached from extracellular matrix plenty of cell trend apoptosis which called anoikis,but some cancer cells could resist to anoikis such as A549 cells.However,in this study,we proved that EPS11 induced apoptosis of A549 cells through stimulatingβIII-tubulin associated anoikis:（i）EPS11 inhibits the expression ofβIII-tubulin in both transcription and translation levels;and（ii）EPS11 treatment dramatically decreases the phosphorylation of protein kinase B（AKT）,a critical downstream effector ofβIII-tubulin.Importantly,EPS11 evidently inhibits the growth of A549-derived tumor xenografts in vivo.After intravenous injected with EPS11(2.24μmol/kg2 d^-1)for two weeks,the anti-tumor rate was 42.2%,while there was no significant side effect in mice.Thus,our results suggest that EPS11 may be a potential candidate for human non-small cell lung carcinoma treatment via blocking filiform structure mediated adhesion and stimulatingβIII-tubulin associated anoikis.