[PSK-mediated growth suppression and enhancement of 5-FU/docetaxel-induced cytotoxicity in human esophageal cancer cell lines].

PSK, a protein-bound polysaccharide, is widely used for treating cancer patients as an immunostimulant. However, its direct action on cancer cells is not fully understood. In the present study, we investigated direct effects of PSK alone or in combination with 5-FU, CDDP and docetaxel on tumor growth by using esophageal cancer cell lines, KYSE170 and TE13. Cells were incubated with different concentrations of PSK for 72 hour, and cell viability was determined by WST-8 assay, and cell cycle was analyzed by flow cytometry. As a result, PSK of 100 microg/mL induced growth suppression dose-dependently in the both cell lines, and flow cytometric analysis showed a PSK dose-dependent increase of sub-G1 cells indicating apoptotic cells. In addition, when cells were incubated with different concentrations of 5-FU and docetaxel in the presence of PSK at the dose of 5 microg/mL showing no growth suppression, cytotoxicity induced by 5-FU and docetaxel was significantly enhanced. These results indicate that PSK not only shows tumor growth suppression by apoptosis induction, but also enhances 5-FU and docetaxel-induced cytotoxicity.