A potent antitumor polysaccharide from the edible brown seaweed Hydroclathrus clathratus.

A sulfated polysaccharide H3-a1 [designated polysaccharide fraction, H3-a1, of Hydroclathrus clathratus (HCP)] was isolated and purified from an edible brown seaweed Hydroclathrus clathratus; HCP contained about 8.6% protein and a relatively high sulfur content (8.2%). HCP significantly affected the growth of human acute promyelocytic leukemia cells (HL-60), human breast carcinoma (MCF-7) and human hepatocellular carcinoma cancer cell lines. As revealed by flow cytometry, when HCP was co-incubated with HL-60 and MCF-7 cells for 72 h, it induced significant sub-G1 arrest (apoptosis) of these cells. HCP caused G1 phase arrest but did not induce terminal differentiation of these cancer cells. In vivo antitumor tests showed that HCP inhibited tumor growth at doses of 20 and 50 mg kg-1 in tumor-bearing BALB/c (supplied by the Laboratory Animal Services Centre of The Chinese University of Hong Kong) mice, but this effect was not due to an in vivo inhibitory effect on tumorigenesis. Nevertheless, HCP suppressed ascitic Sarcoma 180 tumor growth and prolonged the life span of the tumor-bearing mice by about 30–40%. HCP had no observed toxic side effects; it did not affect blood cells, or body, liver or spleen weights of mice 4, 7 and 10 days after treatment. This sulfated polysaccharide induced increased tumor necrosis factor-alpha (TNF-α) level in mouse serum. It also activated peritoneal macrophages to secrete TNF-α and nitric oxide. [ABSTRACT FROM AUTHOR]