Menin‑MLL inhibitors induce ferroptosis and enhance the anti‑proliferative activity of auranofin in several types of cancer cells

Menin‑mixed‑lineage leukemia (MLL) inhibitors have potential for use as therapeutic agents for MLL‑rearranged leukemia. They are also effective against solid cancers, such as breast cancer. The present study demonstrated that menin‑MLL inhibitors, such as MI‑463, unexpectedly induced the ferroptotic cell death of several cancer cell lines. MI‑463 at a double‑digit nM concentration markedly decreased the viable number of OVCAR‑8 ovarian cancer cells for 3 days. Ferrostatin‑1 (a ferroptosis inhibitor) almost completely abrogated the MI‑463‑induced decrease in viable cell numbers. Furthermore, the cancer cell‑killing activity was inhibited by N‑acetylcysteine [a scavenger of reactive oxygen species (ROS)], deferoxamine (DFO, an iron chelator), PD146176 (a specific inhibitor of arachidonate 15‑lipoxygenase), idebenone (a membrane‑permeable analog of CoQ10) and oleic acid [a monounsaturated fatty acid and one of the end products of stearoyl‑CoA desaturase 1 (SCD1)], whereas Z‑VAD‑FMK (an apoptosis inhibitor) had a negligible effect on cell death. It was also found that MI‑463 in combination with auranofin (a thioredoxin reductase inhibitor) synergistically increased cancer the death of breast, ovarian, pancreatic and lung cancer cell lines (88%, 14/16 cell lines). The synergistic induction of cell death was abrogated by ferroptosis inhibitor and DFO. Inhibitors of SCD1, similar to MI‑463, also enhanced cancer cell death synergistically with auranofin, while inhibitors of SCD1 and MI‑463 did not additively induce cell death. Treatment with zinc protoporphyrin‑9, a specific inhibitor of heme oxygenase‑1 (HO‑1), markedly attenuated the cell death induced by MI‑463 plus auranofin. On the whole, these results suggest that the MI‑463‑induced decrease in cell viability may be at least partly associated with the inhibition of SCD1 activity. In addition, the potent induction of HO‑1 contributed to the synergistic effects of MI‑463 plus auranofin. Therefore, menin‑MLL inhibitors, such as MI‑463, in combination with auranofin represent an effective therapeutic approach for several types of cancer via the induction of ferroptosis.

Effect of Cytokines and Hyperthermia on Phagocytosis and Phosphatidylserine Externalization: Implication for the Pathophysiology of Hemophagocytic Syndrome

OBJECTIVE

An aberrant production of inflammatory cytokines, with resultant febrile response, is a cardinal finding of hemophagocytic syndrome. A role of inflammatory cytokines on phagocytosis and clearance of apoptotic cells or particles has been shown, but effects of cytokines or hyperthermia on phagocytosis of viable blood cells were not fully understood. We examined effects of cytokines and hyperthermia on phagocytosis, and externalization of phosphatidylserine on the surface of phagocytosed blood cells, to clarify the pathophysiology of hemophagocytic syndrome.

METHODS

THP-1 macrophage cells were incubated with non-opsonized and opsonized sheep erythrocytes (SE) in the presence of tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), macrophage-colony stimulating factor (M-CSF), interleukin (IL)-6, IL-10 or IL-18, and phagocytic activity was analyzed. Co-operative effect between cytokines was also examined. In addition, SE were incubated at 37 or 39°C, and phagocytic activity was analyzed. After treatment of SE with cytokine or hyperthermia, phosphatidylserine expression of the cell surface was analyzed by detecting Annexin V-positive cells.

RESULTS

IL-6, IL-10 and IL-18 significantly increased phagocytosis of non-opsonized SE, but IFN-γ suppressed it. Phagocytosis of opsonized SE was significantly increased by any of the cytokines. IFN-γ suppressed and IL-10 enhanced phagocytic activity induced by other cytokines in non-opsonized SE, while in opsonized SE, both cytokines co-operated with other cytokines to enhance phagocytosis. Incubation of SE at a high temperature (39°C) resulted in increased phagocytic activity, as compared to SE incubated at 37°C. Cytokines and a high temperature did not increase the number of Annexin V-positive SE.

CONCLUSIONS

IL-6, IL-10 and IL-18 can augment phagocytosis of viable blood cells, whether cells are opsonized or not. Hyperthermia also enhances phagocytosis. These in vitro data suggest that therapy for targeting cytokine (IL-6, IL-10 or IL-18) by using biologics or small molecule drugs may be beneficial for the treatment of hemophagocytic syndrome. Unlike the case of apoptotic cells, phagocytosis of viable blood cells seems to be mediated via phosphatidylserine-independent manner.

Piperlongumine rapidly induces the death of human pancreatic cancer cells mainly through the induction of ferroptosis

Pancreatic cancer is one of the most lethal types of cancer with a mortality rate of almost 95%. Treatment with current chemotherapeutic drugs has limited success due to poor responses. Therefore, the development of novel drugs or effective combination therapies is urgently required. Piperlongumine (PL) is a natural product with cytotoxic properties restricted to cancer cells by significantly increasing intracellular reactive oxygen species (ROS) levels. In the present study, we demonstrated that PL induced cancer cell death through, at least in part, the induction of ferroptosis, as the cancer cell-killing activity was inhibited by the antioxidant, N‑acetylcysteine, ferroptosis inhibitors (ferrostatin‑1 and liproxstatin‑1) and the iron chelator, deferoxamine (DFO), but not by the apoptosis inhibitor, Z-VAD-FMK, or the necrosis inhibitor, necrostatin‑1. Cotylenin A (CN‑A; a plant growth regulator) exhibits potent antitumor activities in several cancer cell lines, including pancreatic cancer cell lines. We found that CN‑A and PL synergistically induced the death of pancreatic cancer MIAPaCa‑2 and PANC‑1 cells for 16 h. CN‑A enhanced the induction of ROS by PL for 4 h. The synergistic induction of cell death was also abrogated by the ferroptosis inhibitors and DFO. The present results revealed that clinically approved sulfasalazine (SSZ), a ferroptosis inducer, enhanced the death of pancreatic cancer cells induced by PL and the combined effects were abrogated by the ferroptosis inhibitors and DFO. SSZ further enhanced the cancer cell-killing activities induced by combined treatment with PL plus CN‑A. On the other hand, the synergistic induction of cell death by PL and CN‑A was not observed in mouse embryonic fibroblasts (MEFs), and SSZ did not enhance the death of MEFs induced by PL plus CN‑A. These results suggest that the triple combined treatment with PL, CN‑A and SSZ is highly effective against pancreatic cancer.

TH588, an MTH1 inhibitor, enhances phenethyl isothiocyanate-induced growth inhibition in pancreatic cancer cells

Chemotherapy and radiotherapy are the most common approaches in cancer therapy. They may kill cancer cells through the generation of high levels of reactive oxygen species (ROS), which leads to oxidative DNA damage. However, tumor resistance to ROS is a problem in cancer therapy. MTH1 sanitizes oxidized dNTP pools to prevent the incorporation of damaged bases during DNA replication. Although MTH1 is non-essential in normal cells, cancer cells require MTH1 activity to avoid the incorporation of oxidized dNTPs, which would result in DNA damage and cell death. By targeting a redox-adaptation mechanism, MTH1 inhibition represents a novel therapeutic strategy against cancer. However, recent reports have indicated that growth inhibition by MTH1 inhibitors may be due to off-target cytotoxic effects. TH588, one of the first-in-class MTH1 inhibitors, kills cancer cells by an off-target effect. However, a low concentration of TH588 may effectively inhibit MTH1 activity without inhibiting cell proliferation. Phenethyl isothiocyanate (PEITC) is a dietary anticarcinogenic compound and an inducer of ROS. In the present study, it has been demonstrated that combined treatment with PEITC and TH588 effectively inhibited the growth of pancreatic cancer MIAPaCa-2 and Panc-1 cells. The antioxidant N-acetylcysteine negated this synergistic growth inhibition. PEITC and TH588 cooperatively induced the formation of 8-oxo-deoxyguanine in nuclei and pH2AX foci, a marker of DNA damage. However, the combined effects are not associated with MTH1 mRNA expression in several cancer cell lines, suggesting that the possibility of an off-target effect of TH588 cannot be eliminated. These results suggest that the combination of PEITC and TH588 has potential as a novel therapeutic strategy against pancreatic cancer.

Combined treatment with cotylenin A and phenethyl isothiocyanate induces strong antitumor activity mainly through the induction of ferroptotic cell death in human pancreatic cancer cells

The treatment of pancreatic cancer, one of the most aggressive gastrointestinal tract malignancies, with current chemotherapeutic drugs has had limited success due to its chemoresistance and poor prognosis. Therefore, the development of new drugs or effective combination therapies is urgently needed. Cotylenin A (CN-A) (a plant growth regulator) is a potent inducer of differentiation in myeloid leukemia cells and exhibits potent antitumor activities in several cancer cell lines. In the present study, we demonstrated that CN-A and phenethyl isothiocyanate (PEITC), an inducer of reactive oxygen species (ROS) and a dietary anticarcinogenic compound, synergistically inhibited the proliferation of MIAPaCa-2, PANC-1 and gemcitabine-resistant PANC-1 cells. A combined treatment with CN-A and PEITC also effectively inhibited the anchorage-independent growth of these cancer cells. The combined treatment with CN-A and PEITC strongly induced cell death within 1 day at concentrations at which CN-A or PEITC alone did not affect cell viability. A combined treatment with synthetic CN-A derivatives (ISIR-005 and ISIR-042) or fusicoccin J (CN-A-related natural product) and PEITC did not have synergistic effects on cell death. The combined treatment with CN-A and PEITC synergistically induced the generation of ROS. Antioxidants (N-acetylcysteine and trolox), ferroptosis inhibitors (ferrostatin-1 and liproxstatin), and the lysosomal iron chelator deferoxamine canceled the synergistic cell death. Apoptosis inhibitors (Z-VAD-FMK and Q-VD-OPH) and the necrosis inhibitor necrostatin-1s did not inhibit synergistic cell death. Autophagy inhibitors (3-metyladenine and chloroquine) partially prevented cell death. These results show that synergistic cell death induced by the combined treatment with CN-A and PEITC is mainly due to the induction of ferroptosis. Therefore, the combination of CN-A and PEITC has potential as a novel therapeutic strategy against pancreatic cancer.

Vitamin K2 and cotylenin A synergistically induce monocytic differentiation and growth arrest along with the suppression of c-MYC expression and induction of cyclin G2 expression in human leukemia HL-60 cells

Although all-trans retinoic acid (ATRA) is a standard and effective drug used for differentiation therapy in acute promyelocytic leukemia, ATRA-resistant leukemia cells ultimately emerge during this treatment. Therefore, the development of new drugs or effective combination therapy is urgently needed. We demonstrate that the combined treatment of vitamin K2 and cotylenin A synergistically induced monocytic differentiation in HL-60 cells. This combined treatment also synergistically induced NBT-reducing activity and non-specific esterase-positive cells as well as morphological changes to monocyte/macrophage-like cells. Vitamin K2 and cotylenin A cooperatively inhibited the proliferation of HL-60 cells in short-term and long-term cultures. This treatment also induced growth arrest at the G1 phase. Although 5 µg/ml cotylenin A or 5 µM vitamin K2 alone reduced c-MYC gene expression in HL-60 cells to approximately 45% or 80% that of control cells, respectively, the combined treatment almost completely suppressed c-MYC gene expression. We also demonstrated that the combined treatment of vitamin K2 and cotylenin A synergistically induced the expression of cyclin G2, which had a positive effect on the promotion and maintenance of cell cycle arrest. These results suggest that the combination of vitamin K2 and cotylenin A has therapeutic value in the treatment of acute myeloid leukemia.

Extracellular NM23-H1 protein inhibits the survival of primary cultured normal human peripheral blood mononuclear cells and activates the cytokine production

An elevated serum level of NM23-H1 protein is found in acute myelogenous leukemia (AML) and predicts a poor treatment outcome for AML patients. To investigate the potential pathological link between the elevated serum level of this protein and poor prognosis, we examined the extracellular effects of recombinant NM23-H1 protein on the in vitro survival of primary cultured normal peripheral blood mononuclear cells (PBMNC) at concentrations equivalent to the levels found in the serum of AML patients. Extracellular NM23-H1 protein inhibited the in vitro survival of PBMNC and promoted the production of various cytokines, such as GM-CSF and IL-1beta, which in fact promoted the growth of primary cultured AML cells. These findings indicate a novel biological action of extracellular NM23-H1 and its association with poor prognosis of patients with elevated serum levels of NM23-H1 protein. These results suggest an important role of extracellular NM23-H1 in the malignant progression of leukemia and a potential therapeutic target for these malignancies.

Cotylenin A, a new differentiation inducer, and rapamycin cooperatively inhibit growth of cancer cells through induction of cyclin G2

Cotylenin A, a plant growth regulator, and rapamycin, an inhibitor of mammalian target of rapamycin (mTOR), are potent inducers of differentiation of myeloid leukemia cells. Recently, we found that cotylenin A and rapamycin effectively inhibited the proliferation of several human breast cancer cell lines including MCF-7. Herein, we demonstrate that cotylenin A and rapamycin rapidly and markedly induced the cyclin G2 gene expression in several cancer cells including MCF-7 cells. The growth arrest of the MCF-7 cells at the G1 phase, induced by the treatment with cotylenin A and rapamycin or the culture in low serum medium, markedly induced the cyclin G2 gene expression. Anticancer drugs including doxorubicin, etoposide and 5-fluorouracil also induced cyclin G2 expression during induction of growth arrest of the MCF-7 cell at the G1 phase or G2/M phase. Ectopically inducible cyclin G2 expression potently inhibited the proliferation of MCF-7 cells. Furthermore, cyclin G2 knockdown induced by cyclin G2 small interfering RNA markedly reduced the potency of cotylenin A plus rapamycin to induce growth inhibition. Taken together, our results suggest that cotylenin A and rapamycin induce inhibition of cancer cell growth through the induction of cyclin G2.

Protein factors that regulate the growth and differentiation of mouse myeloid leukaemia cells

We have purified and characterized several protein factors that regulate the growth and differentiation of mouse myeloid leukaemia M1 cells. The differentiation factor (D-factor) from conditioned medium (CM) of Ehrlich ascites tumour cells is a glycoprotein of Mr 40,000-50,000. Its amino acid sequence was found to be almost identical to that of leukaemia inhibitory factor (LIF) from Krebs II ascites cells. The differentiation inhibitory factor (I-factor) from the CM of variant M1 cell clones which were resistant to several differentiation inducers is a basic protein of apparent Mr 68,000. The growth inhibitory factor (GI-factor) that specifically inhibits the partially differentiated and still growing monocytic leukaemia M1 cells was isolated from the CM of a clone of M1 cells resistant to the differentiation inducers. This GI-factor is a basic protein with an Mr of 25,000. Regulation by these protein factors together with other known cytokines of growth and differentiation of M1 cells is reported.

Cotylenin A-induced differentiation is independent of the transforming growth factor-beta signaling system in human myeloid leukemia HL-60 cells

Cotylenin A, which has been isolated as a plant growth regulator, potently induces the differentiation of human myeloid leukemia cells. Treatment of HL-60 cells with a combination of transforming growth factor (TGF)-beta and 1alpha, 25-dihydroxyvitamin D(3) (VD3) resulted in increased differentiation compared to separate treatments, but TGF-beta did not affect the cotylenin A-induced differentiation of HL-60 cells. It is possible that the signal transduction pathway used by cotylenin A for inducing the differentiation of leukemia cells is the same as that used by TGF-beta. However, cotylenin A did not affect the expression of TGF superfamily or Smad genes in HL-60 cells. Treatment with neutralizing anti-TGF-beta antibody or an inhibitor of TGF-beta signaling did not inhibit cotylenin A-induced differentiation, although VD3-induced differentiation was significantly suppressed by these treatments. The subcellular distribution of Smad3 was also unaffected by cotylenin A. These results suggest that the cotylenin A-induced differentiation of leukemia cells is independent of the TGF-beta signaling system, although TGF-beta acts as an autocrine mediator of the growth arrest and differentiation of leukemia cells induced by VD3 and other inducers.

Clinical significance of serum NM23-H1 protein in neuroblastoma

We have previously reported that NM23 genes are overexpressed in various hematological malignancies and that serum NM23-H1 protein levels are useful for predicting patient outcomes. In this study we assessed the clinical implications of serum NM23-H1 protein on neuroblastoma. We examined serum NM23-H1 protein levels in 217 patients with neuroblastoma, including 131 found by mass-screening and 86 found clinically by an enzyme-linked immunosorbent assay, and determined the association between levels of this protein, and known prognostic factors or the clinical outcome. The serum NM23-H1 protein level was higher in neuroblastoma patients than in control children (P < 0.0001). Patients with MYCN amplification had higher serum NM23-H1 levels than those with a single copy of MYCN. Overall survival was assessed in the 86 patients found clinically, and was found to be worse in patients with higher serum MN23-H1 levels (> or = 250 ng/mL) than in those with lower levels (< 250 ng/mL; P = 0.034). The higher level of NM23-H1 was correlated with a worse outcome in patients with a single MYCN copy, or in those younger than 12 months of age. Serum NM23-H1 protein levels may contribute to predictions of clinical outcome in patients with neuroblastoma.

Effects of combined treatment with rapamycin and cotylenin A, a novel differentiation-inducing agent, on human breast carcinoma MCF-7 cells and xenografts

INTRODUCTION

Rapamycin, an inhibitor of the serine/threonine kinase target of rapamycin, induces G1 arrest and/or apoptosis. Although rapamycin and its analogues are attractive candidates for cancer therapy, their sensitivities with respect to growth inhibition differ markedly among various cancer cells. Using human breast carcinoma cell line MCF-7 as an experimental model system, we examined the growth-inhibitory effects of combinations of various agents and rapamycin to find the agent that most potently enhances the growth-inhibitory effect of rapamycin.

METHOD

We evaluated the growth-inhibitory effect of rapamycin plus various agents, including cotylenin A (a novel inducer of differentiation of myeloid leukaemia cells) to MCF-7 cells, using either MTT assay or trypan blue dye exclusion test. The cell cycle was analyzed using propidium iodide-stained nuclei. Expressions of several genes in MCF-7 cells with rapamycin plus cotylenin A were studied using cDNA microarray analysis and RT-PCR. The in vitro results of MCF-7 cells treated with rapamycin plus cotylenin A were further confirmed in vivo in a mouse xenograft model.

RESULTS

We found that the sensitivity of rapamycin to MCF-7 cells was markedly affected by cotylenin A. This treatment induced growth arrest of the cells at the G1 phase, rather than apoptosis, and induced senescence-associated beta-galactosidase activity. We examined the gene expression profiles associated with exposure to rapamycin and cotylenin A using cDNA microarrays. We found that expressions of cyclin G2, transforming growth factor-beta-induced 68 kDa protein, BCL2-interacting killer, and growth factor receptor-bound 7 were markedly induced in MCF-7 cells treated with rapamycin plus cotylenin A. Furthermore, combined treatment with rapamycin and cotylenin A significantly inhibited the growth of MCF-7 cells as xenografts, without apparent adverse effects.

CONCLUSION

Rapamycin and cotylenin A cooperatively induced growth arrest in breast carcinoma MCF-7 cells in vitro, and treatment with rapamycin and cotylenin A combined more strongly inhibited the growth of MCF-7 cells as xenografts in vivo than treatment with rapamycin or cotylenin A alone, suggesting that this combination may have therapeutic value in treating breast cancer. We also identified several genes that were markedly modulated in MCF-7 cells treated with rapamycin plus cotylenin A.

Immediate up-regulation of the calcium-binding protein S100P and its involvement in the cytokinin-induced differentiation of human myeloid leukemia cells

Cytokinins are important purine derivatives that act as redifferentiation-inducing hormones to control many processes in plants. Cytokinins such as isopentenyladenine (IPA) and kinetin are very effective at inducing the granulocytic differentiation of human myeloid leukemia HL-60 cells. We examined the gene expression profiles associated with exposure to IPA using cDNA microarrays and compared the results with those obtained with other inducers of differentiation, such as all-trans retinoic acid (ATRA), 1 alpha,25-dihydroxyvitamin D3 (VD3) and cotylenin A (CN-A). Many genes were up-regulated, and only a small fraction were down-regulated, upon exposure to the inducers. IPA and CN-A, but not ATRA or VD3, immediately induced the expression of mRNA for the calcium-binding protein S100P. The up-regulation of S100P was confirmed at the protein expression level. We also examined the expression of other S100 proteins, including S100A8, S100A9 and S100A12, and found that IPA preferentially up-regulated S100P at the early stages of differentiation. IPA-induced differentiation of HL-60 cells was suppressed by treatment with antisense oligonucleotides against S100P, suggesting that S100P plays an important role in cell differentiation.

Antitumor effect of cotylenin A plus interferon-alpha: possible therapeutic agents against ovary carcinoma

OBJECTIVE

Recently, we found that cotylenin A and IFNalpha synergistically inhibited growth both in vitro and in vivo, and induced apoptosis in human cancer cells. For the clinical application of this combined treatment, suitable cancer targets should be selected.

METHODS

We examined the combined effects of these compounds on various types of cancer cells by a human cancer cell line panel assay, and on cancer cells that had been freshly isolated from patients in three-dimensional cultures embedded in collagen gel.

RESULTS

In the analysis of 39 cancer cell lines, ovarian cancer cells were highly sensitive to combined treatment with cotylenin A and IFNalpha in inhibiting cell growth. This treatment was also effective toward ovarian cancer cells that were refractory to CDDP, and significantly inhibited the growth of ovarian cancer cells as xenografts without apparent adverse effects. Ovarian cancer cells from the patients were also sensitive to the combined treatment in primary cultures.

CONCLUSION

Combined treatment with cotylenin A and IFNalpha may have therapeutic value in treating ovarian cancer.

Induction of CCAAT/enhancer binding protein-delta by cytokinins, but not by retinoic acid, during granulocytic differentiation of human myeloid leukaemia cells

Cytokinins, purine derivatives that act as hormones to control many processes in plants, are very effective at inducing the granulocytic differentiation of human myeloid leukaemia cells. Isopentenyladenine (IPA), a potent cytokinin, significantly induced the expression of CCAAT/enhancer-binding protein (C/EBP)delta, but not C/EBP alpha protein, whereas all-trans retinoic acid, a well-known inducer of granulocytic differentiation, induced C/EBP alpha but not C/EBP delta protein. Antisense oligonucleotide for C/EBP delta, but not C/EBP alpha or C/EBP beta, effectively suppressed IPA-induced differentiation, suggesting that the expression of C/EBP delta protein is necessary for cytokinin-induced differentiation. Although C/EBP alpha is known to be crucial for granulocytic differentiation, the function of C/EBP delta has not been well documented in the regulation of haematopoiesis. The role of C/EBP delta in the granulocytic differentiation of myeloid leukaemia cells is discussed.

MmTRA1b/phospholipid scramblase 1 gene expression is a new prognostic factor for acute myelogenous leukemia

We previously found that expression of the Mm-1 cell-derived transplantability-associated gene 1b (MmTRA1b)/phospholipid scramblase 1 gene was markedly induced during the granulocytic differentiation of human myeloid leukemia cells. To evaluate the role of MmTRA1b expression in human myeloid leukemia, we investigated the relative levels of MmTRA1b transcripts in 81 patients with acute myelogenous leukemia (AML) by the reverse transcriptase polymerase chain reaction. The expression of MmTRA1b in AML-M1, -M5a and -M5b was significantly lower than that in normal bone marrow cells. The levels of MmTRA1b expression in AML-M2 and -M4 varied among patients. Higher MmTRA1b mRNA levels were associated with significantly longer overall survival in AML, especially in AML-M4 patients, independent of chromosomal aberrations such as t(8;21) and inv(16). The present results suggest that the MmTRA1b mRNA level is a new prognostic factor for AML, especially the AML-M4 subtype.

Induction of apoptosis by combined treatment with differentiation-inducing agents and interferon-alpha in human lung cancer cells

BACKGROUND

Differentiation-inducing agents for myeloid leukemic cells, such as dimethyl sulfoxide (DMSO), Na-butyrate and hexamethylene-bis-acetamide (HMBA), barely induce irreversible differentiation or growth inhibition in solid tumors when used alone. However, we previously reported that combined treatment with differentiation-inducing agents and interferon (IFN)-alpha effectively suppressed the growth of human lung cancer cell lines in vitro and in vivo. We show here that combined treatment-induced cell death is caused by apoptosis.

MATERIALS AND METHODS

Induction of apoptosis was examined by expression of several apoptotic markers.

RESULTS

Combined treatment-induced cell death is caused by apoptosis, which is characterized by the induction of apoptotic morphological changes and the activation of caspase-3-like protease. The expression of Apo2.7, an early apoptotic change, is also induced by this combined treatment, and is suppressed by the addition of Z-Asp-CH2-DCB, a pan caspase inhibitor. The signal transduction pathway of IFN-alpha is rapidly observed in lung cancer cells, although it does not induce significant growth inhibition when used alone. We analyzed the effect of IFN-alpha on the apoptotic pathway and found that IFN-alpha but not DMSO induces the expression of caspase-4. The combination of IFN-alpha and DMSO did not cause further increase in the expression of caspase-4. In many cases of the induction of apoptosis, cytochrome c is released from mitochondria, which induces the formation of large caspase-activating complexes. Caspase-3-like-activities induced by the combination of DMSO or Na-butyrate with IFN-alpha were analyzed by gel filtration and detected equally in fractions with molecular weights of 200-300 kDa, suggesting that caspase-3 is activated in large complexes in lung cancer cells. However, Na-butyrate and HMBA, when used alone, induced the release of cytochrome c and enhanced the loss of mitochondrial membrane potential, whereas DMSO had no effect.

CONCLUSION

These results suggest that the combination of differentiation-inducing agents with IFN-alpha effectively induces apoptosis in lung cancer cells whereas the mechanism of such induction varies depending on the differentiation-inducing agent used.

Physiological and pathological relevance of extracellular NM23/NDP kinases

The NM23 gene is overexpressed in many hematological malignancies and other neoplasms. Some tumor cell lines that overexpress NM23 secrete this protein into extracellular environment. In this study, we found that the serum concentration of NM23-H1 protein was significantly higher in patients with various hematological malignancies. The serum level of NM23-H1 protein was clinically useful as a prognostic factor in malignant lymphoma and acute myelogeneous leukemia (AML). The level of NM23-H1 protein in all of the normal serum samples examined was lower than 10 ng/mL, while those in the tumors varied from about 0 to 1000 ng/mL. Exogenously added NM23-H1 protein did not affect the growth or survival of various leukemia and lymphoma cell lines. However, NM23-H1 protein inhibited the survival of adherent normal peripheral blood mononuclear cells (PBMNC) at 100-1000 ng/mL, and slightly stimulated the survival of nonadherent PBMNC. These results suggest that the effect of NM23-H1 protein on normal PBMNC may be associated with a poor prognosis in hematological malignancies.

Expression of cell surface NM23 proteins of human leukemia cell lines of various cellular lineage and differentiation stages

Cell surface expression of NM23 protein is only observed on tumor cell lines, but not on normal cells. To examine what types of tumor cell line express the cell surface NM23 protein, we measured the cell surface NM23-H1 and NM23-H2 proteins of leukemia line cells on various cellular lineage and differentiation stages. The NM23-H1 was expressed on myeloid leukemia lines but not lymphoid lines, while NM23-H2 was only expressed on erythroleukemia lines. The complement-dependent cytolysis confirmed the expression of these proteins on the surface. Surface NM23-H1 and NM23-H2 proteins were decreased during in vitro erythroid and granulocyte differentiation. These results show that the surface expression of NM23 proteins is related to cellular lineage and differentiation stage of leukemia line cells.

Role of MmTRA1b/phospholipid scramblase1 gene expression in the induction of differentiation of human myeloid leukemia cells into granulocytes

OBJECTIVE

We previously cloned a human normal counterpart (MmTRA1b/phospholipid scramblase 1) of the mouse leukemogenesis-associated gene MmTRA1a. MmTRA1b gene expression was increased during differentiation of human monoblastic leukemia U937 cells using some differentiation inducers but not 1alpha,25-dihydroxyvitamin D(3) (a typical monocytic differentiation inducer). To further elucidate the role of human MmTRA1b gene expression in the differentiation of myelogenous leukemia cells, we measured MmTRA1b gene expression in several myeloid leukemia cell lines and primary leukemia cells.

MATERIALS AND METHODS

The expression of MmTRA1b mRNA was determined by semiquantitative reverse transcriptase polymerase chain reaction.

RESULTS

Expression of the MmTRA1b gene was markedly induced during granulocytic differentiation of promyelocytic leukemia NB4 and HT93 cells induced by all-trans retinoic acid (ATRA). The level of MmTRA1b mRNA was significantly increased during differentiation toward granulocytes, but not monocytes/macrophages, in bipotential myeloid leukemia HL-60 cells. The level of MmTRA1 mRNA was not increased during erythroid differentiation induced by hemin in erythroid leukemia K562 and HEL cells or during megakaryocytic differentiation induced by 12-O-tetradecanoylphorbol-13-acetate in K562 cells. Expression of the MmTRA1b gene also was not induced when apoptosis of NB4 cells was induced by antileukemic drugs. ATRA-induced differentiation of antisense MmTRA1b-transfected NB4 cells was significantly suppressed. On the other hand, ATRA induced the differentiation of MmTRA1b-transfected NB4 cells more efficiently than that of mock-transfected cells. MmTRA1b mRNA also was clearly induced in ATRA-treated primary acute promyelocytic leukemia cells during granulocytic differentiation.

CONCLUSION

MmTRA1b mRNA was specifically induced during granulocytic differentiation of acute promyelocytic leukemia cells and was associated with induction of their differentiation.

Induction of differentiation of human myeloid leukemia cells by immunosuppressant macrolides (rapamycin and FK506) and calcium/calmodulin-dependent kinase inhibitors

OBJECTIVE

Potent immunosuppressants, such as rapamycin, FK506, and ascomycin, are known to regulate the phosphorylation of proteins. The purpose of this study was to investigate the effects of these immunosuppressants on differentiation of several human myeloid leukemic cell lines.

MATERIALS AND METHODS

Human myeloid leukemic cell lines were cultured with each immunosuppressant, and several differentiation markers were assayed.

RESULTS

Rapamycin effectively induced granulocytic differentiation of human myeloid leukemic HL-60 and ML-1 cells. In addition to morphologic differentiation, it also induced nitroblue tetrazolium reduction, lysozyme activity, and expression of CD11b in HL-60 cells. The commitment to differentiation was observed after treatment with rapamycin for 1 day, indicating that the effect of rapamycin was irreversible. FK506 and ascomycin induced differentiation of HL-60 cells, but at higher concentrations than rapamycin. A calcium/calmodulin-dependent kinase (CaMK) was copurified with FKBP52 immunophilin, a binding protein of immunosuppressants. We also found that the CaMK inhibitors KN62 and KN93 induced differentiation of HL-60 cells. Rapamycin and CaMK inhibitors induced differentiation of human myeloid leukemia ML-1 and K562, but not of other cell lines such as NB4, U937, or HEL.

CONCLUSION

Immunosuppressants and CaMK inhibitors induced differentiation of HL-60, ML-1, and K562 cells.

Induction of differentiation of human myeloid leukemia cells by novel synthetic neurotrophic pyrimidine derivatives

OBJECTIVE

Some pyrimidine analogues have been found to induce differentiation of several human myeloid leukemia cells. Newly synthesized heterocyclic pyrimidine derivatives promote neurite outgrowth and survival in neuronal cell lines. In this study, the growth-inhibiting and differentiation-inducing effects of these pyrimidine derivatives on human myeloid leukemia cells were examined.

MATERIALS AND METHODS

Several myeloid leukemia cells were cultured with novel heterocyclic pyrimidine derivatives. Cell differentiation was determined by nitroblue tetrazolium-reducing activity, morphologic changes, expression of CD11b, lysozyme activity, and hemoglobin production.

RESULTS

MS-430 (2-piperidino-5,6-dihydro-7-methyl-6-oxo (7H) pyrrolo [2,3-d] pyrimidine maleate) effectively induced HL-60 cells into mature granulocytes. MS-430 activated the mitogen-activated protein kinase (MAPK) of the cells before causing granulocytic differentiation. MAPK activation was necessary for MS-430-induced differentiation, because PD98059, an inhibitor of MAPK kinase, suppressed the differentiation induced by MS-430. MS-430 also induced monocytic differentiation of THP-1, P39/Tsu, and P31/Fuj leukemia cells, but did not affect erythroid differentiation of K562 or HEL cells.

CONCLUSIONS

MS-430 potently induces differentiation of some myelomonocytic leukemia cells. This novel synthesized pyrimidine compound shows promise as a therapeutic agent for treatment of leukemia and as a neurotrophic drug.

Antileukemic efficacy of 2-deoxycoformycin in monocytic leukemia cells

2'-Deoxycoformycin (dCF) as a single agent has been reported to be less effective against myeloid than against lymphoid malignancies in clinical trials. However, previous studies have shown that in the presence of 2'-deoxyadenosine (dAd), human monocytoid leukemia cell lines are much more sensitive to dCF with regard to the inhibition of cell proliferation. Thus, dCF might be useful for treating monocytoid leukemia with the aid of dAd analogs. The antiproliferative effects of dCF in combination with dAd or its derivatives were examined on normal and malignant blood and bone marrow cells. In the presence of 10 micromol/L dAd, the concentration of dCF required to inhibit the viability of primary monocytoid leukemia cells was much lower than that required to inhibit normal or non-monocytoid leukemic cells. Among the dAd analogs, 9-beta-D-arabinofuranosyladenine (AraA) was also effective in combination with dCF. Athymic nude mice were inoculated with human monocytoid leukemia U937 cells and treated with dCF or a dAd analog or both. Although dCF alone slightly but significantly prolonged the survival of mice inoculated with U937 cells, combined treatment with dCF and AraA markedly prolonged their survival. These data suggest that the combination of dCF and AraA may be useful for the clinical treatment of acute monocytic leukemia. (Blood. 2000;96:1512-1516)

Anticancer derivative of butyric acid (Pivalyloxymethyl butyrate) specifically potentiates the cytotoxicity of doxorubicin and daunorubicin through the suppression of microsomal glycosidic activity

Pivalyloxymethyl butyrate (AN9) is an anticancer derivative of butyric acid. In this study, doxorubicin (DXR) and AN9 synergistically inhibited the growth of lymphoma and lung carcinoma cells, whereas there was no synergy between AN9 and antimetabolites. AN9 did not affect the intracellular uptake of DXR. Among anthracyclines and their derivatives, the synergistic effect was prominent in compounds with a daunosamine moiety, suggesting that AN9 may affect the catabolism of these compounds. The degradation of DXR in the extract from AN9-treated cells was much less than that in extract from untreated cells. AN9 did not directly inhibit the enzyme activity but rather suppressed expression of the enzyme. With respect to the expression of drug resistance-related genes, there was no significant difference between untreated and AN9-treated cells. However, AN9 significantly down-regulated the levels NADPH-cytochrome P450 reductase and DT-diaphorase mRNA in the presence of DXR but not the level of xanthine oxidase mRNA. The enhancement of the sensitivity to anthracyclines was closely associated with the suppression of the mRNA expression.

Expression of estrogen receptor alpha and beta in the mouse cornea

PURPOSE

To test the possibility that estrogen has a direct effect on corneal cells, the possible occurrence of estrogen receptor alpha (ERalpha) and beta (ERbeta) in the cornea of mice was examined.

METHODS

To test for the occurrence of ER proteins in the cornea of mice, an immunocytochemical method was used. To test for the occurrence of ER mRNAs in the cornea of mice, reverse transcription-polymerase chain reaction (RT-PCR) was used.

RESULTS

Immunocytochemical examination revealed that both ERalpha and ERbeta exist in the cell nuclei of corneal epithelial, stromal, and endothelial cells of both male and female mice. RT-PCR revealed that RNAs of ERs occur in the cornea of both male and female mice.

CONCLUSIONS

Because ERalpha and ERbeta occur in corneal cells of mice, estrogen may exert biological functions in corneal cells through direct interaction with these ERs.

Expression of androgen receptor in mouse eye tissues

PURPOSE

To test the possibility that androgen directly affects the corneal cells, the possible occurrence of androgen receptor (AR) in the cornea and other eye tissues of mice was examined.

METHODS

To examine the occurrence of AR protein in the mouse eye tissues, an immunocytochemical method was used. To examine the occurrence of AR mRNA in the cornea and lens, reverse transcription-polymerase chain reaction (RT-PCR) was used.

RESULTS

Immunocytochemical examination revealed that antigenicity for AR antibody exists in cell nuclei of cornea, lens, iris, and ciliary body of both male and female mice. RT-PCR revealed that mRNA of AR occurs in the cornea and lens of both male and female mice.

CONCLUSIONS

It is concluded that AR occurs in cells of cornea, lens, iris, and ciliary body of the mouse eye. Androgen may affect cells in these tissues directly through interaction with AR.

Prognostic implications of the differentiation inhibitory factor nm23-H1 protein in the plasma of aggressive non-Hodgkin's lymphoma

The outcome of patients with non-Hodgkin's lymphoma has been improved by current approaches to treatment. Nevertheless, many patients either do not have a complete remission or ultimately relapse. To identify such patients, it is important to be able to predict the outcome. We previously found that the differentiation inhibitory factor/nm23 was correlated with the prognosis of acute myeloid leukemia. To examine the prognostic effect of nm23 on non-Hodgkin's lymphoma, we established an enzyme-linked immunosorbent assay procedure to determine nm23-H1 protein levels in plasma and assessed the association of this protein level with the response to chemotherapy, overall survival, and progression-free survival in patients with aggressive non-Hodgkin's lymphoma. The plasma concentration of nm23-H1 was significantly higher in patients with malignant lymphoma than in normal controls, especially in aggressive non-Hodgkin's lymphoma. The complete remission rate in patients with higher nm23-H1 levels was significantly worse than that in patients with lower nm23-H1 levels. Overall survival and progression-free survival were also lower in patients with higher nm23-H1 levels than in those with lower levels. The 3-year survival rates in patients with low and high nm23-H1 levels were 79.5% and 6. 7% (P =.0001). A multivariate analysis of prognostic factors showed that the plasma nm23-H1 level was independently associated with the survival and progression-free survival. An elevated plasma nm23-H1 concentration predicts a poor outcome of advanced non-Hodgkin's lymphoma. Therefore, nm23-H1 in plasma may be useful for identifying a distinct group of patients at very high risk.

Role of CD14 expression in the differentiation-apoptosis switch in human monocytic leukemia cells treated with 1alpha,25-dihydroxyvitamin D3 or dexamethasone in the presence of transforming growth factor beta1

Transforming growth factor beta (TGF-beta) enhanced the growth-inhibitory activities of dexamethasone (Dex) and 1alpha,25-dihydroxyvitamin D3 (VD3) on human monocytoid leukemia U937 cells. TGF-beta and VD3 synergistically increased the expression of differentiation-associated markers such as the CD11b and CD14 antigens, whereas TGF-beta and Dex did not. On the other hand, TGF-beta and Dex synergistically increased the number of Apo2.7-positive cells, which represents the early stage of apoptosis, whereas TGF-beta and VD3 did not, suggesting that TGF-beta enhanced apoptosis with Dex and enhanced monocytic differentiation with VD3. In the presence of TGF-beta, the retinoblastoma susceptibility gene product, pRb, was synergistically dephosphorylated by Dex as well as VD3. TGF similarly enhanced the expression of the p21Waf1 gene in U937 cells treated with Dex and VD3. TGF-beta dose-dependently increased the expression of Bcl-2 and Bad and decreased the expression of Bcl-X(L) in U937 cells. Dex enhanced the down-regulation of Bcl-X(L) expression in TGF-beta-treated cells, whereas VD3 blocked this down-regulation of Bcl-X(L). However, the down-regulation of Bcl-X(L) by treatment with the antisense oligomer did not affect the apoptosis or differentiation of U937 cells. The apoptosis of CD14-positive cells was suppressed in the VD3 plus TGF-beta-treated cultures. These results suggest that the expression of CD14 is involved in the survival of differentiated cells.

Differentiation inhibitory factor Nm23 as a prognostic factor for acute myeloid leukemia

The differentiation inhibitory factor nm23 inhibits the differentiation of murine and human myeloid leukemia cells. The inhibition of differentiation may be associated with the aggressive behavior of leukemia. To clarify the role of nm23 in human myeloid leukemia, we investigated the relative levels of nm23-H1, nm23-H2 and c-myc transcripts in bone marrow and blood samples from 110 patients with acute myeloid leukemia (AML) using the reverse transcriptase polymerase chain reaction. The expression levels of nm23-H1 and nm23-H2 in these AML samples were significantly higher than in normal blood cells, and a higher level of nm23-H1 expression was correlated with poor prognosis for AML patients. Analysis of the correlation between nm23 expression and clinical parameters demonstrated that increased nm23-H1 mRNA levels were associated with resistance to initial chemotherapy and reduced overall survival. Multivariate analysis of putative prognostic factors revealed that elevated nm23-H1 mRNA levels significantly influenced the prognosis of patients with AML, particularly in AML-M5.

Identity of human normal counterpart (MmTRA1b) of mouse leukemogenesis-associated gene (MmTRA1a) product as plasma membrane phospholipid scramblase and chromosome mapping of the human MmTRA1b/phospholipid scramblase gene

We recently cloned a new leukemogenesis-associated gene MmTRA1a (Mm-1 cell derived transplantability-associated gene 1a, former name "TRA1") from a mouse leukemogenic and monocytic Mm-P cell cDNA library and also cloned its normal counterpart MmTRA1b (former name "NOR1") from a normal mouse kidney cDNA library. The mouse MmTRA1a is a truncated form of mouse MmTRA1b. Here we report the cloning of a cDNA (human MmTRA1b) homologous to the mouse MmTRA1b from a human monocytic U937 cell cDNA library. The human MmTRA1b cDNA predicts a peptide containing 318 amino acids with a calculated molecular weight of 35,047 Da. The predicted human MmTRA1b protein sequence shared 78% amino acid identity with the mouse counterpart (328 amino acids). Both the human homologue and mouse MmTRA1b protein but not MmTRA1a protein possess a proline-rich domain at the N-terminal end. The human MmTRA1b gene was mapped to chromosome 3q23. Expression of the human homologue was increased during differentiation of U937 cells induced by most typical differentiation inducers. Moreover, predicted amino acid sequence analysis of human MmTRA1b cDNA revealed perfect identity with the human plasma membrane phospholipid scramblase that is required for transbilayer movement of membrane phospholipids. These results provide new information on the possible roles of MmTRA1b/phospholipid scramblase and the truncated MmTRA1a in the leukemogenesis and differentiation of monocytic leukemia cells.

TRA1, a novel mRNA highly expressed in leukemogenic mouse monocytic sublines but not in nonleukemogenic sublines

Mouse monocytic Mm-A, Mm-P, Mm-S1, and Mm-S2 cells are sublines of mouse monocytic and immortalized Mm-1 cells derived from spontaneously differentiated, mouse myeloblastic M1 cells. Although these subline cells retain their monocytic characteristics in vitro, Mm-A and Mm-P cells are highly leukemogenic to syngeneic SL mice and athymic nude mice, whereas Mm-S1 and Mm-S2 cells are not or are only slightly leukemogenic. To better understand the molecular mechanisms of these levels of leukemogenicity, we investigated putative leukemogenesis-associated genes or oncogenes involved in the maintenance of growth, especially in vivo, by means of differential mRNA display. We isolated a fragment clone (15T01) from Mm-P cells. The mRNA probed with 15T01 was expressed at high levels in leukemogenic Mm-P and Mm-A cells but not in nonleukemogenic Mm-S1 and Mm-S2 cells. The gene corresponding to 15T01, named TRA1, was isolated from an Mm-P cDNA library. The longest open reading frame of the TRA1 clone predicts a peptide containing 204 amino acids with a calculated molecular weight of 23,049 D. The predicted TRA1 protein is cysteine-rich and contains multiple cysteine doublets. A putative normal counterpart gene, named NOR1, was also isolated from a normal mouse kidney cDNA library and sequenced. NOR1 cDNA predicts a peptide containing 234 amino acids. The sequence of 201 amino acids from the C-terminal NOR1 was completely identical to that of TRA1, whereas the remaining N-terminal amino acids (33 amino acids) were longer than that (3 amino acids) of TRA1 and the N-terminus of NOR1 protein contained proline-rich sequence. A similarity search against current nucleotide and protein sequence databases indicated that the NOR1/TRA1 gene(s) is conserved in a wide range of eukaryotes, because apparently homologous genes were identified in Caenorhabditis elegans and Saccharomyces cerevisiae genomes. Northern blotting using TRA1-specific and NOR1-specific probes indicated that TRA1 mRNA is exclusively expressed in leukemogenic but not in nonleukemogenic Mm sublines and normal tissues and also indicated that NOR1 mRNA is expressed in normal tissues, especially in kidney, lung, liver, and bone marrow cells but not in any Mm sublines. After leukemogenic Mm-P cells were induced to differentiate into normal macrophages by sodium butyrate, the normal counterpart, NOR1, was expressed, whereas the TRA1 level decreased. Furthermore, transfection of TRA1 converted nonleukemogenic Mm-S1 cells into leukemogenic cells. These results indicate that the TRA1 gene is associated at least in part with the leukemogenesis of monocytic Mm sublines.

An anti-cancer derivative of butyric acid (pivalyloxmethyl buterate) and daunorubicin cooperatively prolong survival of mice inoculated with monocytic leukaemia cells

A derivative of butyric acid, pivalyloxymethyl butyrate (AN-9), inhibited the proliferation and induced apoptosis of mouse monocytic leukaemia Mm-A cells, although sodium butyrate, but not AN-9, induced differentiation of the cells. AN-9 and DNA-specific antineoplastic agents synergistically inhibited the growth of Mm-A cells, and the simultaneous treatment was required to evoke the maximum growth-inhibitory effect. On the other hand, there was no synergy between butyrate and the drugs, or AN-9 and anti-metabolic agents in inhibiting the growth of the cells, suggesting that the synergistic effect is specific to AN-9 and DNA-reacting agents. AN-9 as a single agent prolonged the survival of mice inoculated with Mm-A cells in a dose-dependent manner. Moreover, administration of AN-9 plus daunorubicin (DNR) markedly prolonged their survival. These results suggest that combination with AN-9 and DNR entails an obvious therapeutic potential.

Differentiation inhibitory factor nm23 as a new prognostic factor in acute monocytic leukemia

Differentiation inhibitory factor (nm23 protein) inhibited the induction of differentiation of mouse myeloid leukemia M1 and WEHI-3BD+ and human erythroleukemia HEL, KU812, and K562 cells. Block of differentiation may be associated with the aggressive behavior of leukemia. To examine the role of nm23 in human myeloid leukemia, we investigated the relative levels of nm23-H1, nm23-H2, and c-myc transcripts in 42 patients with acute myelogenous leukemia (AML), and in 5 with chronic myelogenous leukemia at chronic phase by reverse transcriptase polymerase chain reaction. The expression of nm23-H1 and -H2 but not of c-myc in AML was significantly higher than that in normal blood cells. Among AMLs, acute monocytic leukemia (presentation with AML-M5 morphology) was especially associated with elevated nm23-H1 and -H2 mRNA levels. On the other hand, the elevated levels of c-myc expression in AML-M5 were less evident. An analysis of correlation between nm23 expression and clinicopathological parameters showed that resistance to initial chemotherapy is associated with increased nm23-H1 mRNA levels and that a high initial white blood cell count is associated with increased nm23-H2 mRNA levels. Elevated nm23-H1 mRNA levels were associated with significantly reduced the overall survival of AML, especially of AML-M5 patients. The present results indicate that nm23-H1 and -H2 are overexpressed in AML and especially nm23-H1 gene expression predicts the prognosis of AML, especially of AML-M5.

Reversible differentiation of human monoblastic leukemia U937 cells by ML-9, an inhibitor of myosin light chain kinase

Human monoblastic leukemia U937 cells are induced to differentiate into monocytes and macrophages by various agents. We have shown that 1-(5-chloronaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML-9), an inhibitor of myosin light chain kinase, induces differentiation of monocytoid leukemia cell lines U937 and THP-1 but not of myeloblastic leukemic ML-1 cell or erythroleukemia K562 cells. In the present study, we further analyzed the effect of ML-9 in comparison with that of 1 alpha, 25-dihydroxyvitamin D3 (VD3) a typical inducer of monocytic differentiation. ML-9 induced nitroblue tetrazolium (NBT)-reducing activity of U937 cell more rapidly than VD3: This differentiation marker was induced significantly after incubation with ML-9 and VD3 for 4 hours and 1 day, respectively. ML-9 also induced alpha-naphthyl acetate esterase (ANAE) activity, another monocytic differentiation marker, more rapidly than VD3. The maximum levels of these markers induced by ML-9 were comparable to those induced by VD3, but after removal of ML-9 from the medium by washing the cells, the expressions of theses markers decreased within 4 hours and reached basal levels in 1 day, indicating that ML-9's induction of expression of differentiation-associated phenotypes was reversible. The growth inhibition of U937 cells by ML-9 was also reversible. Similar effects were observed in another line of human monoblastic cells, THP-1. ML-9 had little or no effect on the morphology of U937 cells but increased the expression of monocyte-macrophage lineage-associated surface antigen, CD14, to some extent. Irreversible terminal differentiation induced by VD3 is associated with down regulation of the expression of c-myc and upregulation of the expression of c-fos and c-jun, but ML-9 did not affect the expression of these oncogenes appreciably. ML-9-induced differentiation was also reversible when the cells were cultured with cultured with ML-9 plus an anti-cancer drug such as 1-beta-D-arabino-furanosylcytosine or daunomycin. it became irreversible, however, upon simultaneous treatment with dexamethasone and transforming growth factor-beta 1 (TGF-beta 1), which did not induce differentiation of U937 cells but caused growth arrest of the cells in the G0/G1 phase of the cell cycle. These results suggest that ML-9 should be useful for studying the mechanisms of monocytic differentiation.

Transforming growth factor beta and dexamethasone cooperatively enhance c-jun gene expression and inhibit the growth of human monocytoid leukemia cells

Glucocorticoids inhibit the proliferation of lymphoid leukemia cells, whereas most myeloid leukemia cells are resistant to glucocorticoids. However, this study showed that glucocorticoids significantly and preferentially inhibited growth of monocytoid leukemia cells in combination with a low concentration of transforming growth factor beta (TGF beta). Combined 1 alpha,25-dihydroxyvitamin D3 and TGF beta markedly induced monocytic differentiation of U937 cells, whereas dexamethasone (Dex) and TGF beta essentially did not, although both combinations similarly inhibited the growth of U937 cells. The growth inhibition was accompanied by a block in the cell cycle progression from G1 to S phase (G1 arrest). Expression of glucocorticoid receptors was not affected by TGF beta, although they are induced during the monocytic differentiation of myelogenous leukemia cells and have increased sensitivity to glucocorticoids. The expression of TGF beta receptors also was not enhanced by Dex. TGF beta significantly stimulated glucocorticoid responsive element-mediated transcription activity. Combined Dex and TGF beta stimulated the expression of c-jun and c-fos early responsive genes in U937 cells, although Dex or TGF beta alone did not. The combination synergistically induced expression of c-jun gene, reaching a maximum level at 24 h. On the other hand, expression of c-fos gene was induced by TGF beta alone and increased additively in combination with Dex. Treatment with antisense oligonucleotide complementary to the first exon of c-jun mRNA reduced the growth-inhibitory effect of Dex and TGF beta in a dose-dependent manner. However, exposure of U937 cells to the sense oligomer of c-jun mRNA or an antisense oligomer of c-fos mRNA did not affect the growth inhibition. These results suggested that the preferential expression of c-jun and stimulation of glucocorticoid responsive element-mediated transactivation are closely associated with the growth arrest of U937 cells incubated with Dex and TGF beta.

Inhibitory action of nm23 proteins on induction of erythroid differentiation of human leukemia cells

We recently identified a differentiation inhibitory factor (I-factor) in mouse myeloid leukemia M1 cells as a murine homolog of the human nm23-H2 gene product. nm23 genes encode proteins that participate in tumor metastasis regulation and in various fundamental cellular processes, although their mechanisms of action are still unknown. Although all nm23 proteins contain nucleoside diphosphate (NDP) kinase activity, it has not been established that the enzyme activity mediated the various functions of nm23 proteins. In the present experiment, we examined the effect of nm23 proteins on various differentiation induction systems of human leukemic cells including HL-60, U937, HEL/S, KU812F, K562, and HEL cells. Native human erythrocyte NDP kinase protein inhibited the induction of erythroid differentiation of HEL, KU812 and K562 cells, but not the induction of monocytic or granulocytic differentiation of HL-60, U937 and HEL/S cells. The erythroid differentiation of HEL cells was inhibited by recombinant human nm23-H1, -H2, mouse nm23-M1, and -M2 proteins. Moreover, both the mutant nm23-H2His protein and truncated nm23-H2 protein containing N-terminal (1-60) peptide, which do not have NDP kinase activity, also inhibited erythroid differentiation of HEL cells. These results suggest that (1) the differentiation inhibitory activity of I-factor/nm23 protein is not restricted to monocytic differentiation of M1 cells, (2) the inhibitory activity is exhibited without species specificity, and (3) the differentiation inhibitory activity of the nm23/NDP kinase protein is independent of its enzyme activity and requires the presence of N-terminal peptides.

A new function of Nm23/NDP kinase as a differentiation inhibitory factor, which does not require it's kinase activity

We recently identified a differentiation inhibiting factor (I-factor) in mouse myeloid leukemia M1 cells as a murine homolog of nm23-H2/nucleoside diphosphate kinase (NDPK)-B gene product. We examined the I-factor activities of several authentic nm23/NDPK proteins, i.e. recombinant rat NDPK alpha and beta, recombinant mouse nm23-M1 and -M2, and recombinant human nm23-H1 and -H2 containing a mutant nm23-H2His protein lacing NDPK activity. Almost all these nm23/NDPK proteins showed I-factor activity. Moreover, to understand the active domain exhibiting I-factor activity of nm23-H2 protein lacking NDPK activity, we have investigated the I-factor activities of some truncated nm23-H2 proteins. The truncated nm23-H2 protein containing N-terminal peptide 1-60 retained the I-factor activity. These results provide the first evidence for a function of nm23/NDPK as a differentiation inhibiting factor in leukemic cells, that is independent of its NDPK activity and dependent on the presence of N-terminal peptide.

Inhibition by interleukin 4 of leukemia inhibitory factor-, interleukin 6-, and dexamethasone-induced differentiation of mouse myeloid leukemia cells: role of c-myc and junB proto-oncogenes

Interleukin 4 (IL-4) inhibited the differentiation of mouse myeloid leukemia M1 cells induced by leukemia inhibitory factor (LIF), interleukin 6, or dexamethasone and conversely enhanced the induction of M1 cell differentiation by 1 alpha,25-dihydroxyvitamin D3. IL-4 blocked LIF-induced differentiation of M1 cells when it was added to the culture medium within 10 h after LIF, but IL-4 did not block differentiation when it was added 12 h after LIF. These results indicate that IL-4 inhibited a critical intermediate step in myeloid leukemia cell differentiation. LIF markedly stimulated the expression of junB mRNA within 2 h but suppressed the expression of c-myb and c-myc after 2- and 12-h treatment, respectively. IL-4 did not significantly affect LIF-induced junB expression or suppression of c-myb expression. However, it interfered significantly with the LIF-induced suppression of c-myc gene expression. Similar results were obtained when interleukin 6 was used to induce differentiation of M1 cells. Dexamethasone and 1 alpha,25-dihydroxyvitamin D3 did not induce junB gene expression but suppressed the expression of c-myb and c-myc. IL-4 also interfered with dexamethasone-induced suppression of c-myc gene expression. On the other hand, IL-4 enhanced 1 alpha,25-dihydroxyvitamin D3-induced down-regulation of c-myc gene expression, consistent with its enhancement of differentiation. These results indicate that the change in c-myc expression induced by IL-4 in M1 cells is closely associated with the effect of IL-4 on the induction of differentiation of M1 cells.

Genistein exhibits preferential cytotoxicity to a leukemogenic variant but induces differentiation of a non-leukemogenic variant of the mouse monocytic leukemia Mm cell line

Mouse leukemia Mm-A and Mm-S2 cells are subclones of mouse monocytic leukemia Mm cells, Mm-A cells having much higher leukemogenicity than Mm-S2 cells. The growth-inhibitory effects of several protein kinase inhibitors on leukemogenic Mm-A and non-leukemogenic Mm-S2 cells were examined. Most inhibitors of protein serine/threonine kinases inhibited the growth of Mm-A and Mm-S2 cells similarly, but some protein tyrosine kinase inhibitors exhibited differential inhibitory effects on Mm-A and Mm-S2 cells. Genistein inhibited growth of Mm-A cells more effectively than that of Mm-S2 cells, but another inhibitor of tyrosine kinase, herbimycin A, preferentially inhibited growth of non-leukemogenic Mm-S2 cells. Genistein induced or enhanced several differentiation markers of Mm-S2 cells, such as cell spreading, immunophagocytosis, nitroblue tetrazolium (NBT) reduction and lysozyme activity in a dose-dependent manner, but herbimycin A did not. Genistein was cytotoxic to Mm-A cells rather than inducing cell differentiation. Genistein has effects on several other cellular events as well as inhibition of tyrosine kinases. However, it effectively inhibited protein tyrosine phosphorylation in Mm-A cells and its decrease of tyrosine phosphorylation was closely associated with its inhibition of cell growth. Thus, a genistein-sensitive tyrosine kinase(s) may play an important role in the growth and/or survival of leukemogenic Mm-A cells.

Interleukin 4 potentiates the antiproliferative effect of 1 alpha, 25-dihydroxyvitamin D3 on mouse monocytic leukemia cells but antagonizes the antiproliferative effects of interferon alpha, beta and interleukin 6

Mouse monocytic leukemia Mm cells are a line of spontaneously differentiated cells obtained from mouse myeloblastic leukemia M1 cells. The effect of interleukin 4(IL-4) on the proliferation of Mm cells in the presence or absence of growth inhibitory substances was investigated. In semi-solid agar culture, IL-4 markedly inhibited colony formation by Mm cells, reducing the number of colonies to 50% of that in control cultures at concentration of 3 U/ml. In contrast, IL-4 did not inhibit colony formation by the parent M1 cells. In liquid culture, IL-4 alone inhibited the proliferation of Mm cells only slightly. However, a combination of IL-4 and 1 alpha,25-dihydroxyvitamin D3 (VD3), which alone did not inhibit growth significantly, markedly inhibited the growth of Mm cells. This combination also increased the lysozyme activity of Mm cells significantly. On the other hand, IL-4 suppressed the antiproliferative effects of interferon alpha, beta and IL-6, which are growth inhibitory cytokines for these Mm cells. These results indicate that IL-4 can modulate the growth of monocytic leukemia Mm cells and that its modulatory effects depend on growth inhibitory substances.

Control of growth and differentiation of Philadelphia chromosome-positive leukemia cells by tyrosine kinase inhibitors

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.

Synthesis of active metabolite(s) from 1 alpha-hydroxyvitamin D3 by human monocytic leukemia cells

Synthesis of the biologically active metabolite(s) from 1 alpha-hydroxyvitamin D3 (1 alpha(OH)D3) was examined in various types of human leukemia cell lines. Untreated monocytoid leukemia cells (U937 and HEL/S) metabolized 1 alpha (OH)D3 to the active metabolite(s), possibly 1 alpha, 24- and/or 1 alpha, 25-dihydroxyvitamin D3, and these cells were efficiently induced to differentiate by treatment with 1 alpha (OH)D3. However, the other types of leukemia cells did not efficiently metabolize it and were not induced to differentiate by 1 alpha (OH)D3. The possible therapeutic advantage of 1 alpha (OH)D3 in the treatment of monocytic leukemia is discussed.

Herbimycin A, an inhibitor of tyrosine kinase, prolongs survival of mice inoculated with myeloid leukemia C1 cells with high expression of v-abl tyrosine kinase

Herbimycin A, a benzoquinonoid ansamycin antibiotic, reduces intracellular phosphorylation by some tyrosine kinases, including v-abl. The mouse megakaryoblastic cell line C1 expresses v-abl protein at high levels. Herbimycin A at about 20 ng/ml caused 50% inhibition of growth of C1 cells but at 100 ng/ml scarcely affected the growth of another mouse leukemia cell line, M1 cells, or of normal bone marrow cells. Injection of 10(6) C1 cells into nude mice resulted in death of all the mice within 30 days. Administration of herbimycin A significantly enhanced the survival of mice inoculated with C1 cells but scarcely affected the survival of mice inoculated with M1 cells. These results suggest that herbimycin A and/or related compounds may be useful for treatment of some types of leukemia in which tyrosine kinase activity is implicated as a determinant of the oncogenic state.

Identity of a differentiation inhibiting factor for mouse myeloid leukemia cells with NM23/nucleoside diphosphate kinase

Mouse myeloid leukemic line M1 cells can be induced to differentiate into the monocyte/macrophage pathway by various inducers. The induction of differentiation of M1 cells can be inhibited by protein inhibitors termed differentiation inhibiting factors (I-factors) in a cell lysate and conditioned medium of differentiation resistant M1 cells. Production of the I-factor activity in resistant M1 cells is well associated with development of resistance of M1 cells to differentiation inducers. We have now purified one of the I-factors from conditioned medium of differentiation resistant M1 cells. The purified I-factor has a relative molecular mass of approximately 16000-17000 Da (16K I-factor). The amino acid sequence of all fragments of the 16K I-factor we have found are identical with Nm23/nucleoside diphosphate kinase (EC2.7.4.6) protein involved in tumor metastasis. The findings indicate that the I-factor, a candidate suppressor protein for differentiation of leukemic cells, is Nm23/nucleoside diphosphate kinase protein.

Characterization of growth inhibitory factors for mouse monocytic leukemia cells

Growth inhibitory (GI) factors for mouse monocytic leukemia cells were previously found in conditioned medium (CM) of a clone of mouse myeloblastic leukemia Ml cells (R1-GI factor) and in CM of mouse lung tissue (L-GI factor). In the present study, the effects of these GI factors on the growth of variant cell lines (Mm-A, Mm-P and Mm-S2) of mouse monocytic line Mm-1 cells were examined. Mm-A are highly leukemogenic to syngeneic SL mice, Mm-P cells are moderately leukemogenic, while Mm-S2 cells have little or no leukemogenicity. The R1-GI factor markedly suppressed the growth of Mm-A cells, whereas it inhibited the growth of Mm-P and Mm-S2 cells only moderately. Recombinant mouse interferon beta (IFN beta) had similar target specificities to those of the R1-GI factor on these variant cells. Moreover, anti-mouse IFN beta antibody completely neutralized the GI activity of the R1-GI factor on Mm-A cells. These results show that the R1-GI factor and mouse IFN beta are very similar and probably identical proteins. The L-GI factor had different target specificities from the R1-GI factor: it showed strongest GI activity on Mm-P cells, moderate GI activity on Mm-S2 cells and weak GI activity on Mm-A cells. Recombinant human interleukin 6 (IL-6) had similar target specificities to the L-GI factor on these Mm-1 variant cells. Furthermore, the L-GI factor could support the proliferation of IL-6-dependent MH60.BSF2 cells. Anti-mouse IL-6 antiserum neutralized the GI activity of the L-GI factor on Mm-P cells. Thus the L-GI factor and mouse IL-6 seem to be closely related and possibly to be identical proteins.

Effects of herbimycin A derivatives on growth and differentiation of K562 human leukemic cells

Herbimycin A, a specific tyrosine kinase inhibitor, induced erythroid differentiation of human myelogenous leukemia K562 cells with a high level of bcr/abl tyrosine kinase. Several derivatives of herbimycin A were synthesized and their effects on cell proliferation and differentiation of K562 cells were examined. Of the compounds tested, 19-allylaminoherbimycin A was the most effective in inducing differentiation of K562 cells. However, the parent compound was the most potent growth inhibitor, suggesting that chemical modification of herbimycin A reduces the growth-inhibiting activity. The sensitivities of K562 cells to herbimycin derivatives were different from those of a rat kidney cell line infected with Rous sarcoma virus (v-src), suggesting that bcr/abl kinase may differ in sensitivity from other tyrosine kinases. These results indicate that a specific inhibitor of bcr/abl kinase could be an effective antitumor agent against chronic myelogenous leukemia.