Induction of apoptosis and inhibition of DNA topoisomerase-I in K-562 cells by a marine microalgal polysaccharide.

We have previously purified an extracellular polysaccharide, D-galactan sulfate associated with L(+)-lactic acid, produced from a marine microalga Dinoflagellate Gymnodinium sp. A3 (GA3). The GA3 polysaccharide, irrespective of presence or absence of lactic acid, exhibited significant cytotoxicity, which is based on an induction of apoptotic cell death, toward human myeloid leukemia K562 cells. Furthermore, we found that the GA3 polysaccharide with or without lactic acid possesses an inhibitory effect on topoisomerase-I (topo-I). The potent cytotoxic effect of GA3 polysaccharide may result from its inhibitory effect on topo-I, because the topo-I inhibition is known to trigger apoptotic cell death.