Effects of levamisole on in vivo and in vitro murine host response to syngeneic transplantable tumor

The effects of levamisole were studied in vivo and in vitro on 2 murine tumors, B16 melanoma and adenocarcinoma 15091, syngeneic to the mouse strains used. Administration of levamisole before tumor transplantation enhanced the early appearance of neoplasms but did not affect the overall incidence or course of tumor growth as compared with that observed in controls given saline injections or animals given levamisole with lethally X irradiated tumor cells. Administration of the drug 1 day before iv injection of tumor cells significantly reduced the incidence of pulmonary nodules, but if the drug was given 3 to 5 days before tumor challenge, the incidence of nodules was increased. Lymphocytes or macrophages from normal mice given levamisole had no effect on tumor cells in vitro, whereas lymphocytes incubated with levamisole in vitro enhanced tumor cell growth. When lymphocytes and tumor cells were mixed in vitro, lymphocytes from animals treated with the drug formed larger multicell clumps with tumor cells than did those from normal controls. It is concluded that levamisole did not protect the mice against the tested tumors.