Induction of differentiation of human myeloid leukemias by phorbol diesters: phenotypic changes and mode of action.

Treatment with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) of acute myeloblastic leukemia cells halts proliferation and induces expression of monocyte/macrophage markers. Surface characteristics of leukemic HL60 cells, as defined using a panel of monoclonal antibodies, were found to be similar to those of normal human promyelocytes. TPA treatment, however, induced a phenotype that, unlike normal monocytes, contained several myeloid-specific markers and lacked several monocyte-specific markers. TPA treatment of HL60 cells causes the rapid disappearance of the transferrin receptor from the cell surface. Because transferrin is essential for HL60 cell proliferation in culture, the disappearance of this receptor is followed by an irreversible accumulation of the cells in the G1 phase of the cell cycle. The TPA-induced arrest of cell proliferation suggests the potential of this agent in experimentally treating myeloblastic leukemias.