A polysaccharide from Ganoderma atrum inhibits tumor growth by induction of apoptosis and activation of immune response in CT26-bearing mice.

Ganoderma atrum is one species of edible and pharmaceutical mushroom with various biological activities. Recently, a novel polysaccharide, PSG-1, was purified from G. atrum. The antitumor activity and its mechanism of action were studied. In vitro, PSG-1 has little effect on inhibiting proliferation of CT26 tumor cells. However, the tumor size was significantly decreased in PSG-1-treated mice. The results showed that PSG-1 induced apoptosis in CT26 cells. Moreover, the intracellular cyclic AMP (cAMP) level and protein kinase A (PKA) activity were markedly increased in PSG-1-treated mice. In contrast, the contents of cyclic GMP and DAG and the PKC activity were decreased. Similarly, the expression of PKA protein was upregulated, while PKC protein expression in PSG-1-treated group was lowered. Additionally, PSG-1 increased the immune organ index and serum biochemistry parameter. In general, PSG-1 enhances the antitumor immune response, induces apoptosis in CT26-bearing mice, and could be a safe and effective adjuvant for tumor therapy or functional food.