Anticancer activity of an aqueous mistletoe extract (AME) in syngeneic murine tumor models

Mistletoe extracts have been used for decades for nonspecific stimulation o f the immune system in cancer therapy. Mistletoe lectins (ML) have been ide ntified as the active principle with cytotoxic and immunomodulatory potenci es. In the present in viva experiments, the anticancer effects of an aqueou s mistletoe extract (AME) were investigated in different subcutaneously gro wing syngeneic murine tumors such as Renca renal cell carcinoma, C8 colon 3 8 carcinoma, F9 testicular carcinoma, B16 melanoma and Lewis lung carcinoma . The animals used were immunocompetent mice of different strains (C57BL/6, BALB/c), depending on the type of tumor tested. After tumor transplantatio n, the mice were treated with AME at dose levels corresponding to 0, 0.3, 3 , 30 or 300 ng ML/kg/d by the i.p. or s.c. route for a maximum of 4 consecu tive weeks. The tumor volume was determined by serial caliper measurements and expressed relative to controls. Significant tumor growth inhibition was observed with the Renca, C8 colon 38 and F9 testicular carcinomas at 30 an d 300 ng ML/kg/d. These findings were confirmed in independent repeat exper iments. No inhibitory effects were seen with the Lewis lung carcinoma and B 16 melanoma under the conditions described above. In conclusion, AME showed in vivo anticancer activity in different transplantable syngeneic murine t umor models following repeated parenteral treatment. In view of the low dos e levels used, the effects are most likely due to the immunostimulatory rat her than to the cytotoxic potencies of AME.