Differential effect of protein-bound polysaccharide (PSK) on survival of experimental murine tumors

The effect of protein-bound polysaccharide (PSK) on the survival of BALB/c and C57BL/6 mice after intravenous injections of syngeneic murine sarcomas (GR9.B9 and Meth-A), LSTRA lymphoma and B16 melanoma cells was studied. Pretreatment of mice with PSK significantly increased survival after the injection of either type of sarcoma cells, although the effect was attenuated when high numbers of cells were injected. Survival was not modified significantly in LSTRA lymphoma or B16 melanoma. Mice pretreated with anti-asialo GMI serum showed significantly decreased survival from all tumors in comparison with untreated mice injected with tumors, regardless of cell dose used. We observed an inverse correlation between H-2 antigen expression and in vitro NK sensitivity of tumor cells from all lines except B16 melanoma cells. These results clearly suggest that pretreatment of mice with PSK prolongs survival and inhibits metastasis formation in mice injected with sarcoma cells, being this effect highly selective, since survival was not improved in mice injected with LSTRA lymphoma or B16 melanoma.