Enhancement of colony formation of mouse bone marrow cells by ubenimex

Ubenimex enhanced colony formation of bone marrow cells from CDF1 mice induced by L920 cell supernatant, which shows a macrophage-colony-stimulating activity (M-CSA), and also enhanced the colony formation induced CDF1 mouse spleen cell conditioned medium, which shows a granulocyte and macrophage-colony-stimulating activity. The maximal effect was obtained at 0.01 microgram/ml. But, ubenimex showed no effect on the nature of the colonies induced by each CSA. By preincubation of the bone marrow cells with ubenimex, M-CSA-induced colony-forming and the M-CSA-binding activities of the cells were increased. These results suggest that ubenimex enhances the CSA-induced colony formation of bone marrow progenitor cells of CDF1 mouse by increasing the amount of the CSA-binding to the cells.