*3.1. Materials*

Adriamycin was purchased from Meilun Biological Technology Co., Ltd. (Dalian, China). Dexamethasone Acetate tablet (Lot No.170545) was purchased from Tianjin Tianyao Pharmaceutical Co. Ltd. (Tianjin, China). All other chemicals and reagents were obtained from general commercial sources.

#### *3.2. Preparation of Fucoidan and Its Depolymerized Fragment*

*Saccharina japonica* Aresch (Formerly name: *Laminaria japonica*, Laminariaceae), cultured in the coast of Rongcheng, Shandong Province, China, was collected in July 2017. The fresh seaweed was washed with clean seawater and sun dried. Fucoidan was extracted from *S. japonica* in hot water at 100 ◦C for 2 h. The extraction liquid was filtered and 1% CaCl2 was added to precipitate soluble alginate. After centrifugation, the supernatant was dialyzed using a dialysis membrane (molecular weight cuto ff (MWCO) 3500 Da) against pure water, concentrated under reduced pressure and finally precipitated with ethanol. The precipitate was washed twice with ethanol and dried to ge<sup>t</sup> fucoidan.

Low-molecular-weight fucoidan (LMWF) was prepared using free radical degradation with the combination of hydrogen peroxide and ascorbic acid. Briefly, fucoidan was dissolved in distilled water to a final concentration of 0.5%, ascorbic acid and hydrogen peroxide was added to the solution to a final concentration of 30 mM, and stirred at room temperature for 2 h. The solution was filtered, dialyzed against pure water (MWCO 3500 Da), concentrated under reduced pressure and subsequently precipitated with ethanol (75%, final concentration).
