gamma-Propoxy-sulfo-lichenin, an antitumor polysaccharide derived from lichenin

A water-soluble semisynthetic polysaccharide, gamma-propoxy-sulfo-lichenin (PSL), was prepared by reaction of propansultone with lichenin, a natural occurring beta-1.3/1.4-linked glucan originating from Cetraria sp. PSL represents a class of mixed-linked beta-glucans with long and hydrophilic side chains in position C-6 of the glucan backbone. PSL with a degree of substitution of 0.8 and an average molecular weight of 250 kDa exhibited a strong antitumor activity in doses of 25 and 5 mg/kg against solid sarcoma 180 (100% resp. 82% tumor inhibition). The antitumor activity of PSL was shown to be dependent on the dimension of the molecule: the higher the average molecular weight, the higher was the inhibition rate obtained in the antitumor assay. No antitumor effect was observed by using a pretreatment of animals prior to transplantation of sarcoma 180. On syngenic DBA/2-MC.SC1 fibrosarcoma PSL inhibited tumor growth by about 88% at a concentration of 25 mg/kg. PSL failed to exhibit any direct cytotoxic effects on hormone-independent MDA-MB 231 mammacarcinoma. For PSL an indirect antitumor effect via modulation of the host mediate immune defence is postulated.