Differential activity of saporin 6 on normal and leukemic hemopoietic cells

The antiproliferative effect of saporin 6 (SO6), a ribosome-inactivating protein (RIP) purified from the seeds of Saponaria officinalis has been tested on three leukemic cell lines (K562, U937, and HL60), human normal bone marrow, and peripheral blood hemopoietic progenitor cells from normal subjects. In leukemic cell lines, SO6 appeared much more effective against erythrocytic than against monocytic and promyelocytic leukemic cells, as shown by protein synthesis assays carried out after up to 72 h of culture. Among the normal hemopoietic progenitor cells, erythroid burst-forming units were the most affected, with results similar to those observed in the erythroid leukemic cell line, both in treated and in pretreated cultures, with strong damage after 24 h of exposure to SO6. On the other hand, granulocyte-macrophage colony-forming units (CFU-GM) from bone marrow were significantly more affected than the myeloid leukemic cell lines after permanent treatment with the inhibitor, the damage being significantly lower after an exposure of 24 h. CFU-GM from peripheral blood and megakaryocyte CFU showed an intermediate sensitivity after 24 h of exposure to SO6, similar to that of the other normal precursors after permanent treatment with the drug.