herbimycin and Leukemia--Myelogenous--Chronic--BCR-ABL-Positive

Herbimycin A, a benzoquinonoid anasamycin antibiotic, has been shown to reserve the oncogenic phenotypes of p60v-src transformed cells by the virtue of the inhibition of src protein tyrosine kinase. Furthermore, we previously demonstrated that herbimycin A displayed the antitumor activity on Ph1-positive leukemia cells and bcr/abl oncoprotein-associated transformed murine hematopoietic cells with the transfection of a retroviral vector expressing bcr/abl. Herbimycin A showed preferential inhibition on the in vitro growth of Ph1-positive leukemia cells and bcr/abl oncoprotein-associated murine hematopoietic cells through the inhibition of bcr/abl tyrosine kinase activity and the reduction of subsequent phosphotyrosyl proteins. Recently, from the view of investigating the oncogenic significance or of developing a future clinical application in malignancies, several developing agents targeted against oncoprotein have been tried. We reviewed the present progress in the mechanism of oncoprotein-targeted antitumor effects and focused on herbimycin A-induced antitumor activity on Ph1-positive leukemia cells.

Topics: Animals; Antibiotics, Antineoplastic; Benzoquinones; Cell Division; Cell Survival; Cell Transformation, Neoplastic; Fusion Proteins, bcr-abl; Humans; Lactams, Macrocyclic; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Mice; Oligonucleotides, Antisense; Protein-Tyrosine Kinases; Quinones; Rifabutin; Tumor Cells, Cultured

We previously reported that herbimycin A (HMA) alters the mode of cell death of K562 cells induced by radiation and enhanced their radiosensitivity. In the present study, we explored the apoptosis-inducing activity of HMA and the fundamental mechanism via which it regulates radiation-induced cell death.. Chronic myelogenous leukemia (CML) cell line K562 was used. For X-irradiation and drug treatment, cells were plated at approximately 2x10(5) cells/ml. Exponentially growing cells were treated with 10 Gy of X-ray using a 6-MeV X-ray machine at a dose rate of 200-300 cGy/min. The cells were treated with 0.25 microM HMA immediately after irradiation and HMA remained for the entire culture period. The modes of cell death were discriminated by morphological changes, analysis of cell cycle, analysis of the mitochondrial events, and the expression of apoptosis-related proteins.. Our data demonstrates that radiation induced a significant time-dependent increase of cell death and failed to sustain a prolonged G2 arrest in K562 cells. Radiation-induced cell death caused the accumulation of cyclinB1 and weak nuclear fragmentation, suggesting a mitotic catastrophe. This mitotic catastrophe was dependent upon the mitochondrial permeability transition pore (PTP) opening and was independent of caspase-3. In contrast, K562 cells treated with radiation and HMA had an accelerated cell death and induced a p53-independent apoptosis. This apoptotic pathway was dependent upon an initial hyperpolarization of the mitochondrial inner membrane, following the release of cytochrome c and subsequent caspase-3 activation.. Two mechanisms of radiation-induced cell death in K562 cells, mitotic catastrophe and apoptosis, are regulated through distinct pathways, mitochondria and caspase-independent and -dependent, respectively. The findings of this study may provide new insights into improving the efficiency of radiotherapy in CML patients.

Topics: Apoptosis; Benzoquinones; Caspases; Enzyme Activation; Enzyme Inhibitors; G2 Phase; Humans; Lactams, Macrocyclic; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Membrane Potentials; Mitochondrial Membranes; Mitosis; Quinones; Rifabutin; Tumor Cells, Cultured; X-Rays

Chronic myelogenous leukemia (CML) is a clonal disorder of a pluripotent hematopoietic stem cells characterized by a chimeric bcr-abl gene giving rise to a p210(Bcr-Abl) protein with dysregulated tyrosine kinase activity. Radicicol, a macrocyclic antifungal antibiotic, binds to the N-terminal of heat shock protein 90 (Hsp90) and destabilizes Hsp90-associated proteins such as Raf-1. This study investigated the effect of radicicol, novel oxime derivatives of radicicol (KF25706 and KF58333), and herbimycin A (HA), a benzoquinoid ansamycin antibiotic, on the growth and differentiation of human K562 CML cells. Although KF25706 and KF58333 induced the expression of glycophorin A in K562 cells, radicicol and HA caused erythroid differentiation transiently. Cell cycle analysis showed that G(1) phase accumulation was observed in K562 cells treated with KF58333. KF58333 treatment depleted p210(Bcr-Abl), Raf-1, and cellular tyrosine phosphorylated proteins in K562 cells, whereas radicicol and HA showed transient depletion of these proteins. KF58333 also down-regulated the level of cell cycle-dependent kinases 4 and 6 and up-regulated cell cycle-dependent kinase inhibitor p27(Kip1) protein without an effect on the level of Erk and Hsp90 proteins. Immunoprecipitation analysis showed that p210(Bcr-Abl) formed multiple complexes with Hsp90, some containing p23 and others Hsp70; KF58333 treatment dissociated p210(Bcr-Abl) from Hsp90/p23 chaperone complexes. Furthermore, KF58333 induced apoptosis in K562 cells and administration of KF58333 prolonged the survival time of SCID mice inoculated with K562 cells. These results suggest that KF58333 may have therapeutic potential for the treatment of CML that involves abnormal cellular proliferation induced by p210(Bcr-Abl).

Topics: Animals; Antibiotics, Antineoplastic; Antifungal Agents; Benzoquinones; Cell Differentiation; Erythroblasts; Fusion Proteins, bcr-abl; G1 Phase; HSP90 Heat-Shock Proteins; Humans; K562 Cells; Lactams, Macrocyclic; Lactones; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Macrolides; Mice; Quinones; Rifabutin

Philadelphia chromosome (Ph)-positive leukaemia cells express the chimeric bcr/abl oncoprotein, whose deregulated protein tyrosine kinase (PTK) activity antagonizes the induction of apoptosis by DNA damaging agents. Treatment of Ph-positive K562, TOM 1 and KCL-22 cells with etoposide for 2d induced cytosolic vacuolation, but not nuclear condensation or DNA fragmentation. The bcr/abl kinase-selective inhibitor herbimycin A increased the induction of nuclear apoptosis by etoposide or gamma-radiation. The concentration of herbimycin required to synergize with etoposide was similar to that required to decrease the level of tyrosine phosphorylated proteins or of the protein tyrosine kinase activity of anti-abl immune complexes in K562 cells. The ability of herbimycin A to sensitize K562, TOM 1 or KCL-22 cells to apoptosis induction correlated with its ability to decrease the cellular content of phosphotyrosyl proteins in these Philadelphia-positive lines. Enhancement of nuclear apoptosis by herbimycin was not attributable to downregulation of the bcl-2 or bcl-XL anti-apoptotic proteins. In contrast, herbimycin protected Philadelphia-negative HL60 cells from apoptosis induction by etoposide and did not affect killing of NC37 and CEM cells. The data suggest that the induction of apoptosis is blocked in cells expressing the bcr/abl oncoprotein and that herbimycin A increases induction of programmed cell death following DNA damage. Selective PTK inhibitors may therefore be of value in securing the genetic death of Ph-positive leukaemia cells.

Topics: Antibiotics, Antineoplastic; Antineoplastic Agents, Phytogenic; Apoptosis; bcl-X Protein; Benzoquinones; Etoposide; Fusion Proteins, bcr-abl; Gamma Rays; HL-60 Cells; Humans; Lactams, Macrocyclic; Leukemia, Erythroblastic, Acute; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Proto-Oncogene Proteins c-bcl-2; Quinones; Rifabutin; Tumor Cells, Cultured

Activated human natural killer (NK) cells undergo rapid apoptotic cell death after ligand binding to the Fc receptor (CD16). We examined whether human NK cells die after engagement in cytolytic functions. Peripheral blood NK cells, with and without prior activation in vitro with interleukin-2 (IL-2), were tested for the occurrence of cell death after incubation with K562, the prototype NK-sensitive target cell. A proportion (15.2%) of NK cells that were stimulated for 3 days with IL-2 and then incubated for 4 hours with K562 cells showed rapid cell death, but NK cells not stimulated with IL-2 did not. This cell death was found to involve nuclear condensation and fragmentation and DNA cleavage, all of which are characteristic of apoptosis. These data indicate that a proportion of activated human NK cells undergo apoptosis as they engage in target cell lysis. Target-induced NK cell death may represent an important mechanism for regulation of inflammatory processes involving NK cells.

Topics: Apoptosis; Benzoquinones; Cells, Cultured; Cytotoxicity, Immunologic; Enzyme Inhibitors; Humans; Interleukin-2; Killer Cells, Natural; Lactams, Macrocyclic; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Lymphocyte Activation; Microscopy, Electron; Protein-Tyrosine Kinases; Quinones; Receptors, IgG; Rifabutin; Tumor Cells, Cultured

We previously reported that natural killer (NK)-sensitive target cells, K562, kill interleukin-2-stimulated (lymphokine-activated killer [LAK]) but not unstimulated NK cells. We have now investigated the molecular basis of this phenomenon. Soluble monoclonal antibody (MoAb) to CD18 inhibited 75% of K562-induced DNA fragmentation and membrane disruption, whereas blocking MoAb to Fas partially inhibited only the DNA fragmentation. MoAbs to CD2, CD11a, CD11b, B7, or CD16 had limited or no effect on K562-induced death of LAK cells. Receptor ligation with either immobilized MoAb to CD18 or Fas induced membrane disruption and DNA degradation in LAK cells independently of K562, and MoAb to CD18, CD11a, or CD11b enhanced DNA fragmentation induced by anti-Fas. Fas-L-transfected Raji cells also killed LAK cells, but only if Fas-L expression was amplified. K562 cells rapidly triggered protein phosphorylation in LAK cells, and the tyrosine kinase inhibitor, Herbimycin A, inhibited DNA fragmentation and membrane disruption. Protease inhibitors strongly suppressed K562-mediated DNA fragmentation of LAK cells, but not membrane disruption. In conclusion, (1) K562-induced death of LAK cells involves primarily CD18, although other molecules, such as Fas, may also be involved; (2) K562-mediated apoptosis of LAK cells requires tyrosine phosphorylation and protease activity; (3) engagement of Fas by immobilized MoAb or Fas-L on target cells can also kill LAK cells; and (4) Fas-immobilized MoAb synergizes with coimmobilized MoAb to CD11a, CD11b, or CD18 for LAK cell killing. Activation-induced death of NK cells may represent a mechanism for NK cell regulation.

Topics: Antibodies, Monoclonal; Antigens, CD; Apoptosis; Benzoquinones; CD18 Antigens; Cell Membrane; Cysteine Endopeptidases; Cytotoxicity, Immunologic; DNA; Fas Ligand Protein; fas Receptor; Humans; Interleukin-2; Killer Cells, Lymphokine-Activated; Killer Cells, Natural; Lactams, Macrocyclic; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Lymphoma, Non-Hodgkin; Melanoma; Membrane Glycoproteins; Protease Inhibitors; Quinones; Recombinant Fusion Proteins; Rifabutin; Serine Endopeptidases; Transfection; Tumor Cells, Cultured

The molecular basis of the Philadelphia chromosome (Ph1) is a structurally altered c-abl (bcr-abl) gene which encodes an abnormally large protein with protein tyrosine kinase activity. Herbimycin a, which effectively reduced intracellular phosphorylation by bcr-abl tyrosine kinase, preferentially inhibited the growth of Ph1-positive leukemia cell lines. Injection of Ph1-positive and -negative leukemia cell lines into mice with severe combined immunodeficiency (SCID) resulted in the death of all mice due to leukemia, although the severity of illness varied according to the cell lines used. Administration of herbimycin A significantly enhanced the survival of mice inoculated with the Ph1-positive leukemia cell lines tested but barely affected the survival of mice inoculated with the Ph1-negative leukemia cell lines tested. These results suggest that herbimycin A and related compounds may be useful for the treatment of Ph1-positive leukemia. The disease that developed using the Ph1-positive leukemia cell line NALM-20 resembled human Ph1-positive acute lymphoid leukemia. There was an inverse relationship between the survival time of mice and the number of cells inoculated. The SCID mouse-NALM-20 human leukemia chimera would be a good experimental model for screening tyrosine kinase inhibitors as therapeutic agents against Ph1-positive leukemia.

Topics: Animals; Benzoquinones; DNA, Neoplasm; Drug Screening Assays, Antitumor; Female; Fusion Proteins, bcr-abl; Lactams, Macrocyclic; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Leukemia, Myeloid, Chronic, Atypical, BCR-ABL Negative; Mice; Mice, SCID; Neoplasm Proteins; Neoplasm Transplantation; Phosphorylation; Protein Processing, Post-Translational; Protein-Tyrosine Kinases; Quinones; Rifabutin; Tumor Cells, Cultured

Herbimycin A, a benzoquinonoid anasamycin antibiotic, preferentially inhibited the in vitro growth of Ph1-positive leukemia cell lines. On the other hand, genistein, which was developed as an inhibitor of receptor-type tyrosine kinase, and other protein kinase inhibitors showed no selective inhibition of Ph1-positive leukemia cell growth. Herbimycin A also displayed an abrogative effect on the transformation of murine hematopoietic cells by transfection with a bcr/abl oncoprotein-expressing retroviral vector. The antitumor action of herbimycin A on Ph1-positive leukemia cells is related to an inhibition of activity of bcr/abl protein tyrosine kinase and a subsequent reduction of the constitutive phosphotyrosyl proteins, however, the antibiotic has no effect on the expression of bcr/abl mRNA and oncoprotein. Therefore, herbimycin A may provide an important insight into the oncogenic action of bcr/abl oncoprotein and the future development of oncoprotein-targeted therapeutic agents.

Topics: Antibiotics, Antineoplastic; Benzoquinones; Fusion Proteins, bcr-abl; Genistein; Humans; Isoflavones; Lactams, Macrocyclic; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Neoplasm Proteins; Phosphotyrosine; Protein-Tyrosine Kinases; Quinones; Rifabutin; Tumor Cells, Cultured; Tyrosine

Protein tyrosine kinase (PTK) inhibitor herbimycin A inhibited proliferation, induced accumulation of cells in the G0/G1 phase of the cell cycle and a marked increae of hemoglobin-producing human leukemic K-562 cells in vitro. The isoflavonoid PTK- and topoisomerase II inhibitor genistein produced a similar effect with the accumulation of cells in the G2/M phase of cell cycle. Genistein potentiated the effect of herbimycin A on the cell cycle (i.e. decreased the proportion of S-phase cells) and induced an increased proportion of hemoglobin-producing cells. Genistein, but not herbimycin A induced a marked increase in cell surface expression of CD15 (LewisX) antigen. Both of these agents down-regulated CD45 (leukocyte common antigen) and monocyte-associated CD14 antigen on K-562 cells. Neither genistein nor herbimycin A induced increased cell surface expression of glycophorin.

Topics: Animals; Antigens, Surface; Benzoquinones; Cell Cycle; Cell Differentiation; Genistein; Hemoglobins; Humans; Isoflavones; Lactams, Macrocyclic; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Mice; Phenotype; Protein-Tyrosine Kinases; Quinones; Rifabutin; Tumor Cells, Cultured

The molecular basis of the Philadelphia chromosome (Ph1) is a structurally altered c-abl (bcr/abl) gene which encodes an abnormally large protein with protein tyrosine kinase activity. Herbimycin A, an inhibitor of tyrosine kinase, preferentially inhibited the growth of Ph1-positive acute lymphoid leukemia (ALL) cell lines, as well as Ph1-positive chronic myeloid leukemia (CML) cell lines. Although noncytotoxic concentrations of herbimycin A induced erythroid differentiation of two CML-derived cell lines, K562 and KU812, in a previous study, the differentiation-inducing effect of herbimycin A on Ph1-positive ALL cell lines was less strong. Herbimycin A enhanced some differentiation-associated properties of one Ph1-positive ALL cell line, L2, but the effect of herbimycin A on the other Ph1-positive ALL cell lines was cytotoxic rather than cytostatic (differentiation-inducing). Several derivatives of herbimycin A were synthesized and their effects on the cell proliferation of Ph1-positive CML and ALL cell lines were examined. The sensitivities of the Ph1-positive cell lines to herbimycin A derivatives were different from the data on the rat kidney cell line infected with Rous sarcoma virus (v-src) derived from a previous study, suggesting bcr/abl kinase may differ in sensitivity from other tyrosine kinases. Moreover, the sensitivities of the ALL cell lines were not the same as those of the CML cell lines. These results suggest that a specific inhibitor of bcr/abl kinase could be an effective antileukemic agent against Ph1-positive CML or ALL.

Topics: Antibiotics, Antineoplastic; Benzoquinones; Cell Differentiation; Cell Division; Fusion Proteins, bcr-abl; Humans; Lactams, Macrocyclic; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Neoplasm Proteins; Philadelphia Chromosome; Phosphorylation; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Protein-Tyrosine Kinases; Quinones; Rifabutin; Tumor Cells, Cultured; Tyrosine

We report on the potency of two Tyrphostin tyrosine kinase blockers, AG 1112 and AG 568, to inhibit p210bcr-abl tyrosine kinase activity in K562 cells, concomitant with the induction of erythroid differentiation. AG 568 and especially AG 1112 represent a specific group of nontoxic protein tyrosine kinase blockers among more than 1,400 tested. These compounds possess therapeutic potential for purging Philadelphia chromosome-positive cells in preparation for autologous bone marrow transplantation in chronic myelogenous leukemia.

Topics: 3T3 Cells; Animals; Benzoquinones; Catechols; Cell Differentiation; Cell Division; Cell Line; ErbB Receptors; Fusion Proteins, bcr-abl; Humans; Kinetics; Lactams, Macrocyclic; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Mice; Molecular Structure; Nitriles; Phosphotyrosine; Protein-Tyrosine Kinases; Quinones; Receptors, Platelet-Derived Growth Factor; Rifabutin; Time Factors; Tumor Cells, Cultured; Tyrosine; Tyrphostins

We investigated whether antisense oligodeoxynucleotides complementary to bcr/abl mRNA or protein kinase antagonists display antitumor activity on Ph1-positive leukemia cell lines. bcr/abl antisense oligomers showed inhibitory effects on the in vitro growth of Ph1-positive leukemia cell lines in liquid culture, and further displayed an inhibitory effect on transformed murine hematopoietic cells using transfection with a retroviral vector expressing P210bcr/abl oncoprotein. However, in vitro treatment with a bcr/abl antisense oligomer did not completely abolish the expression of bcr/abl mRNA and did not display the desired "killing effect" on Ph1-positive leukemia cells. On the other hand, investigation of the effect on Ph1-positive leukemia cells by various types of protein kinase antagonists revealed that herbimycin A, a protein tyrosine kinase antagonist, displays preferential and remarkable suppression of the growth of Ph1-positive leukemia cells and P210bcr/abl associated transformed cells by virtue of suppressing bcr/abl protein tyrosine kinase activity. These results may provide important future insights in developing a new category of antitumor therapy by targeting oncogene products.

Topics: Antibiotics, Antineoplastic; Base Sequence; Benzoquinones; Cell Division; DNA, Antisense; Dose-Response Relationship, Drug; Fusion Proteins, bcr-abl; Humans; Lactams, Macrocyclic; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Molecular Sequence Data; Neoplasm Proteins; Philadelphia Chromosome; Polymerase Chain Reaction; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Protein-Tyrosine Kinases; Quinones; Rifabutin; RNA-Directed DNA Polymerase; Tumor Cells, Cultured

Accumulating evidence indicates that the activation of cellular oncogenes is a cause of some human cancers. ErbB-1, erbB-2 and abl oncogenes encoding tyrosine kinases, ras oncogenes encoding GTP binding proteins and myc oncogenes whose functions are not well understood are some examples. Therefore, agents which inhibit the activity of these oncogene products may provide new means to overcome certain human tumors. Herbimycin A and tyrphostins have been found and developed as inhibitors of tyrosine kinases and the effectiveness of these agents against tumors of Ph1-positive leukemia (CML, ALL) or squamous cell carcinomas has been reported. Although specific inhibitors of ras or myc oncogene products have not yet been described, recent studies on the processing of Ras proteins toward the cell membrane provide a strategy to search for inhibitors of ras functions.

Topics: Antibiotics, Antineoplastic; Benzoquinones; Carcinoma, Squamous Cell; Catechols; Cyclin D1; Female; Genes, ras; Humans; Lactams, Macrocyclic; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Male; Neoplasms; Nitriles; Protein-Tyrosine Kinases; Proto-Oncogene Proteins; Quinones; Rifabutin; Tyrphostins

Herbimycin A, a selective inhibitor of tyrosine kinase activity, induced differentiation of leukemia cells isolated from Philadelphia chromosome-positive chronic myelogenous leukemia patients. However, it did not induce differentiation of leukemia cells from acute myelogenous leukemia patients, although these cells could be induced to differentiate by treatment with appropriate compounds. A selective inhibitor of tyrosine kinase might be useful in chemotherapy of Philadelphia chromosome-positive leukemia.

Topics: Antibiotics, Antineoplastic; Benzoquinones; Cell Differentiation; Cell Division; Humans; Lactams, Macrocyclic; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Protein-Tyrosine Kinases; Quinones; Rifabutin

Herbimycin A, a benzoquinoid ansamycin antibiotic, was demonstrated to decrease intracellular phosphorylation by protein tyrosine kinase (PTK). In Philadelphia chromosome (Ph1)-positive leukemias such as chronic myelogenous leukemia (CML) and Ph1-positive acute lymphoblastic leukemia (ALL), both of which express bcr-abl fused gene products (P210bcr-abl or P190bcr-abl protein kinase) with augmented tyrosine kinase activities, herbimycin A markedly inhibited the in vitro growth of the Ph1-positive ALL cells and the leukemic cells derived from CML blast crisis. However, the same dose of herbimycin A did not inhibit in vitro growth of a broad spectrum of Ph1-negative human leukemia cells, and several other protein kinase antagonists also displayed no preferential inhibition. Furthermore, we demonstrated that herbimycin A has an antagonizing effect on the growth of transformed cells by a transfection of retroviral amphotrophic vector expressing P210bcr/abl into a murine interleukin (IL)-3-dependent myeloid FDC-P2 cell line. This inhibition was abrogated by the addition of sulfhydryl compounds, similar to the reaction previously described for Rous sarcoma virus transformation. The inhibitory effect of herbimycin A on the growth of Ph1-positive cells was associated with decreased bcr/abl tyrosine kinase activity, but no decrease of bcr-abl mRNA and protein, suggesting that the inactivation of bcr-abl tyrosine kinase activity by herbimycin A may be induced by its binding to the bcr-abl protein portion that is rich with sulfhydryl groups. The present study indicates that herbimycin A is a beneficial agent for the investigation of the role of the bcr-abl gene in Ph1-positive leukemias and further suggests that the development of agents inhibiting the bcr-abl gene product may offer a new therapeutic potential for Ph1-positive leukemias.

Topics: Benzoquinones; Cell Division; Cell Transformation, Neoplastic; Fusion Proteins, bcr-abl; Genetic Vectors; Humans; Lactams, Macrocyclic; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Protein-Tyrosine Kinases; Quinones; Retroviridae; Rifabutin; Sulfhydryl Compounds; Transfection

Herbimycin A, a benzoquinonoid ansamycin antibiotic, is found to reduce intracellular phosphorylation by tyrosine protein kinase. The human chronic myelogenous leukemia cell line K562 expresses a structurally altered c-abl protein with tyrosine kinase activity. When K562 cells are induced to undergo erythroid differentiation by hemin, reduction in the intracellular level of tyrosine phosphorylation occurs. In order to understand the relationship between induction of differentiation and reduction of tyrosine phosphorylation by the c-abl gene product, the effect that herbimycin A, a selective inhibitor of intracellular tyrosine kinase activity, exerts on the differentiation of K562 cells was examined. Reduction of tyrosine phosphorylation in K562 cells by herbimycin A was observed within 1 h. Noncytotoxic concentrations of herbimycin A induced erythroid differentiation of K562 cells but not of murine erythroleukemia 745A cells. The other human myeloid leukemia cell lines (HL-60, THP-1, and U937) tested were not induced to undergo cell differentiation by this antibiotic. Herbimycin A and the other well-known inducers such as hemin, butyric acid, Adriamycin, and 1-beta-D-arabinofuranosylcytosine had additive or more than additive effects on induction of erythroid differentiation of K562 cells. With respect to inhibition of cell growth, the sensitivity of K562 cells to herbimycin A was highest in the human leukemia cell lines we tested. Noncytotoxic concentrations of herbimycin enhanced the antiproliferative effect of Adriamycin or 1-beta-D-arabinofuranosylcytosine on K562 cells. Combination therapy with herbimycin A and its derivatives may be considered for use in the treatment of some types of leukemia where tyrosine kinase activities are implicated as determinants of the oncogenic state.

Topics: Benzoquinones; Cell Differentiation; Cell Division; Cell Line; Doxorubicin; Erythroblasts; Humans; Lactams, Macrocyclic; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Molecular Weight; Phosphorylation; Protein-Tyrosine Kinases; Quinones; Rifabutin