[Experimental studies on the therapy of rat myelomonocytic leukemia with lipopolysaccharide (LPS) and daunomycin (DM)].

The aim is to examine experimentally whether injections of LPS in combination with Daunomycin are effective on a rat myelomonocytic leukemia. Effects of Lipopolysaccharide (LPS), one of the major differentiation-inducing agents in the mouse myeloid leukemia cell line M1, were investigated on the cells of a rat myelomonocytic leukemia cell line c-WRT-7 in vitro and in vivo. It was shown that sensitive cells of c-WRT-7 cells changed remarkably into macrophage-like cells, which lost the growth potential by LPS-treatment, whereas such change and growth inhibition in insensitive cells of c-WRT-7 were not so remarkable by LPS-treatment. Although the sensitive cells were extremely malignant in vivo, the sensitive cells treated with LPS in vitro lost the transplantability into the syngeneic rats. The sensitive cells by injections of LPS developed morphologically into macrophage-like cells in diffusion chamber i.p. in syngeneic rat. Injections of LPS inhibited the progression of leukemia in 60% of the rats which had been inoculated with the sensitive cells, whereas the leukemia-development was inhibited in only 20% of the rats which had been inoculated with the insensitive cells and i.p. treated with LPS. Daunomycin, Aclacinomycin A and Vincristine induced phagocytic activities in c-WRT-7 cells, whereas Actinomycin D and Cycloheximide showed no such effects. Daunomycin in combination with LPS increased the number of phagocytic cells, whereas cycloheximide inhibited the LPS induced phagocytosis. Injections of LPS in combination with Daunomycin inhibited doubtlessly the leukemia-development in rats which had been i.p. inoculated with the sensitive cells, compared to the injections of LPS or Daunomycin alone. In conclusion, it is suggested that the effects of LPS and Daunomycin on the inhibition of the leukemia-development could be associated in part with their differentiation-inducing activities.