Because of the reported immune-enhancing and anti-
tumor activities of some mushroom
polysaccharides, their applications as
biological response modifiers have attracted significant attention. We have purified a water-soluble
beta-glucan PCM3-II, comprising mainly 1right curved arrow 3 and 1right curved arrow 4 linkages, from the mycelia of Poria cocos (Schw.) Wolf (Fu-ling). In this study, the growth-inhibitory effect of
PCM3-II was further explored on the human
breast carcinoma MCF-7 cells in vitro. The dose effect of
PCM3-II was studied by incubating the
breast cancer cells with 12.5-400 microg/ml of the
glucan for 72 h. The MTT study showed that
PCM3-II reduced proliferation and viability of the MCF-7 cells dose-dependently, so that the
cancer-cell growth was decreased by 50% of the control level at 400 microg/ml of the
glucan. The time effect of
PCM3-II was then investigated by treating the
breast cancer cells with 400 microg/ml of the
glucan for 24, 48 and 72 h, respectively. Results from the flow cytometry study demonstrated that
PCM3-II induced cell-cycle G1 arrest time-dependently and about 90% of the cells in cell cycle were accumulated at G1 phase after 72 h of treatment. The G1 arrest was associated with downregulations of the unscheduled
cyclin D1 and
cyclin E expressions in the
breast cancer cells. Apoptosis was also induced by
PCM3-II in the MCF-7 cells, so that the subG1 cells in
DNA histogram of the flow cytometry were elevated by 5-fold of the control level at 48 h and by 24-fold at 72 h of treatment. The immunoblot study also showed that the
glucan induced depletion of the antiapoptotic Bcl-2
protein, but not the proapoptotic
Bax protein, so that the Bax/Bcl-2 ratio was elevated in the
breast cancer cells at the time when the most prominent apoptosis was also observed. In conclusion, although the detailed mechanism for the anti-
tumor activity of the P. cocos
beta-glucan still needs further investigation, this study provides preliminary insights into its mode of action and perspectives of its development as a water-soluble anti-
tumor agent.