herbimycin and Leukemia--Megakaryoblastic--Acute

Leukemia with megakaryocytic involvement has a poor prognosis. MX2 is a new morpholino anthracycline that is effective against various leukemic cell lines. This study examined the antitumor activity of MX2 against human megakaryocytic cell lines, including CMK, CMK11-5, MEG-01, and UT-7, and investigated the role of apoptosis in the cytotoxicity of this drug. To quantify the extent of apoptosis induced by MX2, we used the in situ terminal deoxynucleotide transferase assay and the histone-associated DNA fragmentation assay. The cytotoxic effect of MX2 on CMK cells was reduced by various inhibitors of apoptosis. To our knowledge, this is the first report showing that apoptosis is involved in the killing of megakaryocytic cell lines by an antileukemic agent. We suggest that MX2 may be useful for the treatment of megakaryocytic leukemia.

Topics: Antibiotics, Antineoplastic; Apoptosis; Benzoquinones; Carubicin; DNA Fragmentation; Enzyme Inhibitors; Humans; Ionomycin; Lactams, Macrocyclic; Leukemia, Megakaryoblastic, Acute; Megakaryocytes; Microscopy, Electron; Protein-Tyrosine Kinases; Quinones; Rifabutin; Staurosporine; Tumor Cells, Cultured

12-O-Tetradecanoylphorbol 13-acetate (TPA) induces rapid changes in the morphology of the human megakaryoblastic leukemia cell line, MEG-01, as well as changes in adhesion and megakaryocytic differentiation. To investigate the signal transduction pathway of these three phenomena, we studied the effect of herbimycin A, an inhibitor of tyrosine kinase (TK) and the effects of calphostin C, a specific inhibitor protein kinase C (PKC) on TPA treated MEG-01 cells. Both herbimycin A and calphostin C inhibited all three TPA-induced phenomena, suggesting that both pathways are required for these phenomena. Herbimycin A but not calphostin C blocked the tyrosine phosphorylation of cellular proteins. Immunohistochemical staining of PKC using an anti-PKC monoclonal antibody showed that herbimycin A did not interfere with the translocation and subsequent down regulation of PKC induced by TPA, suggesting that the TPA-induced effect on PKC (translocation and probably its activation) is not dependent on TK. Induction of c-fos and c-jun expression by TPA was inhibited by both herbimycin A and calphostin C, suggesting that both PKC and TK pathways are necessary for the induction of the TPA-induced transcription factor AP1, which is a known TPA-inducible early immediate gene product. Taken together, our results show that the tyrosine kinase signal transduction system as well as the PKC pathway is indispensable for the TPA-induced phenomena of morphologic change, cell attachment, early immediate gene expression, and lineage-specific phenotypic expression in the MEG-01 cell line.

Topics: Benzoquinones; Cell Adhesion; Cell Differentiation; Genes, fos; Genes, jun; Humans; Lactams, Macrocyclic; Leukemia, Megakaryoblastic, Acute; Megakaryocytes; Naphthalenes; Phosphotyrosine; Polycyclic Compounds; Protein Kinase C; Protein-Tyrosine Kinases; Quinones; Rifabutin; Tetradecanoylphorbol Acetate; Tumor Cells, Cultured; Tyrosine