Anticancer activity in vitro of a fucoidan from the brown alga Fucus evanescens and its low-molecular fragments, structurally characterized by tandem mass-spectrometry

Fucoidan was isolated and purified from the brown algae Fucus evanescens and subjected to autohydrolysis to obtain low-molecular-weight fragments. MALDI-TOFMS analysis has shown that monosulfated fucose and more heavily sulfated (up to 5) fucooligosaccharides with polymerization degree (DP) 2, 4 and 6, including galactose-containing sulfated oligosaccharides were the products of autohydrolysis. The structural features of these fragments were elucidated by negative-ion potential lift tandem MALDI-TOF mass-spectrometry using arabinoosazone as a matrix, which allowed reducing the in-source fragmentation. Native fucoidan has been shown to exert anticancer activities in both human malignant melanoma cell lines SK-MEL-28 and SK-MEL-5. Low-molecular-weight fragments exhibited almost no action to cell proliferation in both cell lines and colony formation on SK-MEL-5 cells, but its inhibition activity to the colony formation of SK-MEL-28 cell lines was as high as was demonstrated by native fucoidan (70%). Probably, the inhibiting activity for SK-MEL-28 depended on the presence of sulfates and (1 → 4)-linked α-l-Fucp residues in the main chain of fucoidan/oligosaccharides.