The tumor-promoting phorbol diester, 12-O-tetradecanoylphorbol-13-acetate (TPA), appears to induce a macrophage-mimicking transformation of cells in human promyelocytic leukemia continuous cultured lined HL-60, cells from normal human and chronic myeloid leukemia bone marrow, and cells from human acute leukemias. In the present experiments, peripheral blood and/or bone marrow nucleated cells from 12 patients with acute myeloblastic leukemia (AML), 1 with acute promyelocytic leukemia (APL), 1 with acute myelomonocytic leukemia, 3 with myeloid blastic crisis of chronic myelogenous leukemia (BI-CML), and 2 with acute lymphocytic leukemia (ALL) were exposed to TPA at concentrations from 10-7 to 10-9 m. After 1 to 4 days, in all cases except ALL, the cells acquired the peculiar morphology of macrophage-mimicking cells with multiple long or short thin pseudopods.
We studied the ability of leukemia promyelocytes from HL-60 cells and cells from AML, APL, and BI-CML to produce colony-stimulating activity (CSA) after treatment with TPA. Several samples of HL-60 cells and blasts from leukemic patients were treated with 10-8 m TPA in liquid culture for 2 to 6 days and transferred to semisolid agar in which they were maintained for 7 to 24 days. Afterwards, cells in semisolid agar were used as a feeder layer in double-layer semisolid agar colony-forming unit colony formation assay. The formation of normal granulocyte-macrophage colony-forming unit colonies was induced by feeder layers from leukemic cells treated with TPA. Depletion of adherent cells from leukemic cell buffy coats before treatment with TPA did not affect the production of CSA. The intensity of colony formation induced by feeder layers from TPA-treated leukemic cells was comparable to that induced by normal buffy coat feeder layers.
TPA-untreated leukemic cells (HL-60, AML, APL, and BI-CML) did not produce CSA in the same experiments. ALL cells, whether treated with 10-8 m TPA or left untreated, did not produce CSA. No CSA was shown by lymphocyte-enriched normal human buffy coats treated with 10-8 m TPA. The data showed that CSA production occurs in leukemic blasts treated with TPA themselves but not by some cellular minority present in leukemic blood and bone marrow buffy coats and possibly activated by TPA. TPA (10-8 m) itself incubated in culture medium without any cells up to 7 days did not possess any CSA.
These experiments show that TPA is able not only to transform leukemic myeloid cells to macrophage-mimicking cells but also to induce CSA production by these cells.
This work was supported by a grant from the Cancer Research Institute, Inc., a grant from the T. J. Martell Foundation for Leukemia Research, and National Cancer Institute Cancer Center Grant 5P11-CA 15936. A preliminary report of these findings has been made at the First International Conference on Immuno-Pharmacology, Brighton, United Kingdom, July 29 to August 1, 1980 (43).