Selective inhibitors of 5-lipoxygenase reduce CML blast cell proliferation and induce limited differentiation and apoptosis

LPS induces ALOX5 promoter activation and 5-lipoxygenase expression in human monocytic cells

5-lipoxygenase (5-LO), coded by the ALOX5 gene, is expressed in leukocytes and catalyzes the formation of leukotrienes, pro-inflammatory lipid mediators. Leukotrienes are central to immune responses, but are also involved in inflammatory disorders and 5-LO expression is associated with leukemia stem cell survival. It is therefore important to understand mechanisms that control 5-LO expression. This study investigated the control of 5-LO expression and leukotriene biosynthesis following the maturation of human monocytic cells. MonoMac-1 (MM1) and THP-1 cells were incubated for up to 72 h with or without LPS and TGF-β. LPS, but not TGF-β, increased CD14 expression in both MM1 and THP-1 cells. Incubation with LPS (100 ng/ml) and TGF-β (1 ng/ml) synergistically increased the capacity of MM1 cells to produce 5-LO products from undetectable levels to 40±5 pmol/10⁶ cells. 5-LO product biosynthesis in THP-1 cells increased 25-fold. A synergistic effect of LPS and TGF-β was measured with increases in 5-LO mRNA of 54- and 13-fold in MM1 and THP-1 cells, respectively. 5-LO protein expression increased significantly in both MM1 and THP-1 cells. ALOX5 promoter activity was significantly elevated >2-fold in both cell lines following LPS treatment, but TGF-β was without effect. The main 5-LO products were cysteinyl-leukotrienes, however LPS and TGF-β did not impact on the capacity of the cells to metabolize leukotriene A₄. Overall, this study demonstrates that receptor-mediated stimulation of MM1 and THP-1 cells by LPS is associated with increased 5-LO expression. This represents a new mechanism by which leukotriene biosynthesis can be modulated by pathological agents.

An insight into the role of arachidonic acid derived lipid mediators in virus associated pathogenesis and malignancies

Several studies shed light on the size and diversity of the lipidome, along with its role in physiological and pathological processes in human health. Besides that, lipids also function as important signaling mediators. This review focuses on discussing the role of arachidonic acid (AA) derived lipids as mediators in diseases with special emphasis on viral infections. Structurally, arachidonic acid derived lipids, also referred to as lipid mediators, can be classified into three specific classes: Class 1-eicosanoids derived from arachidonic acid metabolism; Class 2-lysophospholipids consisting of either a glycerol or a sphingosine backbone; Class 3-AA and ω-3 polyunsaturated fatty acid (PUFA) derivatives. Class 1 and 2 lipids are commonly referred to as pro-inflammatory molecules, which are found upregulated in diseases like cancer and viral infection. Class 3 lipids are anti-inflammatory molecules, which could be potentially used in treatment of diseases associated with inflammation. The function of each class has been elucidated as unique and contributory to an overall cellular homeostasis. Current work in this field is promising and will surely usher in a new era of lipid understanding and control not only at the molecular level, but also in terms of holistic patient care.

Survival regulation of leukemia stem cells

Leukemia stem cells (LSCs) are a subpopulation cells at the apex of hierarchies in leukemia cells and responsible for disease continuous propagation. In this article, we discuss some cellular and molecular components, which are critical for LSC survival. These components include intrinsic signaling pathways and extrinsic microenvironments. The intrinsic signaling pathways to be discussed include Wnt/β-catenin signaling, Hox genes, Hh pathway, Alox5, and some miRNAs, which have been shown to play important roles in regulating LSC survival and proliferation. The extrinsic components to be discussed include selectins, CXCL12/CXCR4, and CD44, which involve in LSC homing, survival, and proliferation by affecting bone marrow microenvironment. Potential strategies for eradicating LSCs will also discuss.

Alternative approaches to eradicating the malignant clone in chronic myeloid leukemia: tyrosine-kinase inhibitor combinations and beyond

In patients with chronic myeloid leukemia (CML) in chronic phase who have achieved complete molecular remission on imatinib therapy, clinical trials from France and Australia have demonstrated that the majority experience prompt molecular relapse of their leukemia upon discontinuation of the drug, showing that long-term monotherapy with tyrosine kinase inhibitors is not curative in the majority of patients with CML. This has focused attention on strategies to eradicate residual disease in CML that is presumed to arise from malignant Ph+ stem cells, which should result in permanent cure and long-term leukemia-free survival. Here, we review the evidence that targeting CML stem cells will be of clinical benefit and discuss pharmacological and immunological approaches to accomplish this goal. Where possible, we link preclinical studies of CML stem cell biology to emerging results from clinical trials of agents that may target these cells.

Acetyl-11-keto-β-boswellic acid (AKBA); targeting oral cavity pathogens

BACKGROUND

Boswellic acids mixture of triterpenic acids obtained from the oleo gum resin of Boswellia serrata and known for its effectiveness in the treatment of chronic inflammatory disease including peritumor edema. Boswellic acids have been extensively studied for a number of activities including anti inflammatory, antitumor, immunomodulatory, and inflammatory bowel diseases. The present study describes the antimicrobial activities of boswellic acid molecules against oral cavity pathogens. Acetyl-11-keto-β-boswellic acid (AKBA), which exhibited the most potent antibacterial activity, was further evaluated in time kill studies, mutation prevention frequency, postantibiotic effect (PAE) and biofilm susceptibility assay against oral cavity pathogens.

FINDINGS

AKBA exhibited an inhibitory effect on all the oral cavity pathogens tested (MIC of 2-4 μg/ml). It exhibited concentration dependent killing of Streptococcus mutans ATCC 25175 up to 8 × MIC and also prevented the emergence of mutants of S.mutans ATCC 25175 at 8× MIC. AKBA demonstrated postantibiotic effect (PAE) of 5.7 ± 0.1 h at 2 × MIC. Furthermore, AKBA inhibited the formation of biofilms generated by S.mutans and Actinomyces viscosus and also reduced the preformed biofilms by these bacteria.

CONCLUSIONS

AKBA can be useful compound for the development of antibacterial agent against oral pathogens and it has great potential for use in mouthwash for preventing and treating oral infections.

Chronic myeloid leukemia stem cells and developing therapies

Chronic myeloid leukemia therapy has remarkably improved with the use of frontline BCR-ABL kinase inhibitors such that newly diagnosed patients have minimal disease manifestations or progression. Effective control of disease may also set the stage for eventual 'cure' of this leukemia. However, the existence of Philadelphia chromosome-positive leukemic cells that are unaffected by BCR-ABL inhibition represents a major barrier that may delay or prevent curative therapy with the current approaches. The most commonly reported mechanism of resistance to tyrosine kinase inhibitor-based therapies involves BCR-ABL gene mutations and amplification, but these changes may not be solely responsible for disease relapse when inhibitor-based therapies are curtailed. Therefore new targets may need to be defined before significant advancement in curative therapies is possible. Emerging evidence suggests that persistence of chronic myeloid leukemia stem cells or acquisition of stem cell-like characteristics prevents complete elimination of chronic myeloid leukemia by tyrosine kinase inhibition alone. This review focuses on several recently emerging concepts regarding the existence and characteristics of chronic myeloid leukemia stem cells. Definitions based on human primary cells and animal model studies are highlighted as are the potential signaling pathways associated with disease repopulating cells. Finally, several recently defined therapeutic targets and active compounds that have emerged from stem cell studies are described. Our goal is to provide an unbiased report on the current state of discovery within the chronic myeloid leukemia stem cell field and to orient the reader to emerging therapeutic targets and strategies that may lead to elimination of this leukemia.

Antistaphylococcal and biofilm inhibitory activities of acetyl-11-keto-β-boswellic acid from Boswellia serrata

Background

Boswellic acids are pentacyclic triterpenes, which are produced in plants belonging to the genus Boswellia. Boswellic acids appear in the resin exudates of the plant and it makes up 25-35% of the resin. β-boswellic acid, 11-keto-β-boswellic acid and acetyl-11-keto-β-boswellic acid have been implicated in apoptosis of cancer cells, particularly that of brain tumors and cells affected by leukemia or colon cancer. These molecules are also associated with potent antimicrobial activities. The present study describes the antimicrobial activities of boswellic acid molecules against 112 pathogenic bacterial isolates including ATCC strains. Acetyl-11-keto-β-boswellic acid (AKBA), which exhibited the most potent antibacterial activity, was further evaluated in time kill studies, postantibiotic effect (PAE) and biofilm susceptibility assay. The mechanism of action of AKBA was investigated by propidium iodide uptake, leakage of 260 and 280 nm absorbing material assays.

Results

AKBA was found to be the most active compound showing an MIC range of 2-8 μg/ml against the entire gram positive bacterial pathogens tested. It exhibited concentration dependent killing of Staphylococcus aureus ATCC 29213 up to 8 × MIC and also demonstrated postantibiotic effect (PAE) of 4.8 h at 2 × MIC. Furthermore, AKBA inhibited the formation of biofilms generated by S. aureus and Staphylococcus epidermidis and also reduced the preformed biofilms by these bacteria. Increased uptake of propidium iodide and leakage of 260 and 280 nm absorbing material by AKBA treated cells of S aureus indicating that the antibacterial mode of action of AKBA probably occurred via disruption of microbial membrane structure.

Conclusions

This study supported the potential use of AKBA in treating S. aureus infections. AKBA can be further exploited to evolve potential lead compounds in the discovery of new anti-Gram-positive and anti-biofilm agents.

Critical molecular pathways in cancer stem cells of chronic myeloid leukemia

Inhibition of BCR-ABL with kinase inhibitors in the treatment of Philadelphia-positive (Ph(+)) chronic myeloid leukemia (CML) is highly effective in controlling but not curing the disease. This is largely due to the inability of these kinase inhibitors to kill leukemia stem cells (LSCs) responsible for disease relapse. This stem cell resistance is not associated with the BCR-ABL kinase domain mutations resistant to kinase inhibitors. Development of curative therapies for CML requires the identification of crucial molecular pathways responsible for the survival and self-renewal of LSCs. In this review, we will discuss our current understanding of these crucial molecular pathways in LSCs and the available therapeutic strategies for targeting these stem cells in CML.

Loss of the Alox5 gene impairs leukemia stem cells and prevents chronic myeloid leukemia

Targeting of cancer stem cells is believed to be essential for curative therapy of cancers, but supporting evidence is limited. Few selective target genes in cancer stem cells have been identified. Here we identify the arachidonate 5-lipoxygenase (5-LO) gene (Alox5) as a critical regulator for leukemia stem cells (LSCs) in BCR-ABL-induced chronic myeloid leukemia (CML). In the absence of Alox5, BCR-ABL failed to induce CML in mice. This Alox5 deficiency caused impairment of the function of LSCs but not normal hematopoietic stem cells (HSCs) through affecting differentiation, cell division, and survival of long-term LSCs (LT-LSCs), consequently causing a depletion of LSCs and a failure of CML development. Treatment of CML mice with a 5-LO inhibitor also impaired the function of LSCs similarly by affecting LT-LSCs, and prolonged survival. These results demonstrate that a specific target gene can be found in cancer stem cells and its inhibition can completely inhibit the function of these stem cells.

Monocytic differentiation of leukemic HL-60 cells induced by co-treatment with TNF-alpha and MK886 requires activation of pro-apoptotic machinery

The block of hematopoietic differentiation program in acute myeloid leukemia cells can be overcome by differentiating agent like retinoic acid, but it has several side effects. A study of other differentiation signaling pathways is therefore useful to predict potential targets of anti-leukemic therapy. We demonstrated previously that the co-treatment of HL-60 cells with Tumor necrosis factor-alpha (TNF-alpha) (1 ng/mL) and inhibitor of 5-lipoxygenase MK886 (5 microm) potentiated both monocytic differentiation and apoptosis. In this study, we detected enhanced activation of three main types of mitogen-activated protein kinases (MAPKs) (p38, c-Jun amino-terminal kinase [JNK], extracellular signal-regulated kinase [ERK]), so we assessed their role in differentiation using appropriate pharmacologic inhibitors. The inhibition of pro-apoptotic MAPKs (p38 and JNK) suppressed the effect of MK886 + TNF-alpha co-treatment. On the other hand, down-regulation of pro-survival ERK pathway led to increased differentiation. Those effects were accompanied by increased activation of caspases in cells treated by MK886 + TNF-alpha. Pan-caspase inhibitor ZVAD-fmk significantly decreased both number of apoptotic and differentiated cells. The same effect was observed after inhibition of caspase 9, but not caspase 3 and 8. To conclude, we evidenced that the activation of apoptotic processes and pathways supporting apoptosis (p38 and JNK MAPKs) is required for the monocytic differentiation of HL-60 cells.

Neutrophil gelatinase-associated lipocalin as a survival factor

NGAL (human neutrophil gelatinase-associated lipocalin) and its mouse analogue 24p3 are members of the lipocalin family of small secreted proteins. These proteins are up-regulated in a number of pathological conditions, including cancers, and may function as transporters of essential factors. Although previous publications have suggested that 24p3 has pro-apoptotic functions, other data are more suggestive of a survival function. The current study was designed to determine whether NGAL is pro- or anti-apoptotic. Apoptosis induced in human adenocarcinoma A549 cells by the 5-lipoxygenase-activating-protein inhibitor MK886, or several celecoxib-derived PDK1 (phosphoinositide-dependent kinase 1) inhibitors that are devoid of cyclo-oxygenase-2 inhibitory activity, was accompanied by a dose- and time-dependent increase of NGAL mRNA levels, as was reported previously with 24p3. A similar induction of NGAL mRNA was observed in human breast cancer MCF7 cells treated with MK886, indicating this was not a cell-specific effect. Treatment of A549 cells with up to 150 mug/10(6) cells of purified recombinant NGAL protein had no effect on viability, whereas antisera against the full-length NGAL protein induced apoptosis in these cells. The stable overexpression of NGAL in A549 cells had no effect on proliferation or viability. However, the cell death induced by a PDK1 inhibitor was reduced by 50% in NGAL-overexpressing cells. Decreasing NGAL mRNA and protein expression with siRNA (small interfering RNA) in A549 cells increased the toxicity of a PDK1 inhibitor by approx. 45%. These data indicate that, although the induction of NGAL correlates with apoptosis, this induction represents a survival response. Because NGAL is a secreted protein, it may play an extracellular role in cell defence against toxicants and/or facilitate the survival of the remaining cells.

Abnormal LTC4 synthase RNA degradation in neutrophils from CML patients

Neutrophils from patients with chronic myeloid leukaemia (CML) have an aberrant expression of leukotriene (LT)C4 synthase. In order to learn more about the regulation of this abnormality, LTC4 synthase mRNA expression was determined by reverse transcription polymerase chain reaction. A digoxigenin (DIG)-labelled LTC4 synthase RNA was synthesized and incubated in cytosolic extracts from CML neutrophils, normal neutrophils and eosinophils. LTC4 synthase mRNA was detected in total but not cytoplasmic RNA from normal neutrophils. In contrast, LTC4 synthase mRNA was found in the cytoplasm of CML neutrophils and in normal eosinophils, which also express the enzyme. The DIG-labelled LTC4 synthase RNA was, as opposed to normal neutrophils, degraded in cytosolic extracts from CML neutrophils. The degradation was time dependent and cell concentration dependent. Degradation was also seen in eosinophils, indicating that degradation of LTC4 synthase RNA was correlated to the expression of the protein. This study showed that the difference in expression of LTC4 synthase in normal and CML neutrophils was not because of a total lack of LTC4 synthase mRNA in normal neutrophils. However normal neutrophils lack, in contrast to CML neutrophils, LTC4 synthase mRNA in the cytoplasm. This discrepancy is not caused by a stabilized LTC4 synthase RNA in the cytosol of CML neutrophils. Instead an abnormal degradation of LTC4 synthase RNA was found in the cytosol of CML neutrophils.

Nutritional and botanical modulation of the inflammatory cascade--eicosanoids, cyclooxygenases, and lipoxygenases--as an adjunct in cancer therapy

Emerging on the horizon in cancer therapy is an expansion of the scope of treatment beyond cytotoxic approaches to include molecular management of cancer physiopathology. The goal in these integrative approaches, which extends beyond eradicating the affected cells, is to control the cancer phenotype. One key new approach appears to be modulation of the inflammatory cascade, as research is expanding that links cancer initiation, promotion, progression, angiogenesis, and metastasis to inflammatory events. This article presents a literature review of the emerging relationship between neoplasia and inflammatory eicosanoids (PGE2 and related prostaglandins), with a focus on how inhibition of their synthesizing oxidases, particularly cyclooxygenase (COX), offers anticancer actions in vitro and in vivo. Although a majority of this research emphasizes the pharmaceutical applications of nonsteroidal anti-inflammatory drugs and selective COX-2 inhibitors, these agents fail to address alternate pathways available for the synthesis of proinflammatory eicosanoids. Evidence is presented that suggests the inhibition of lipoxygenase and its by-products-LTB4, 5-HETE, and 12-HETE-represents an overlooked but crucial component in complementary cancer therapies. Based on the hypothesis that natural agents capable of modulating both lipoxygenase and COX may advance the efficacy of cancer therapy, an overview and discussion is presented of dietary modifications and selected nutritional and botanical agents (notably, omega-3 fatty acids, antioxidants, boswellia, bromelain, curcumin, and quercetin) that favorably influence eicosanoid production.

Caspase-dependent and -independent panc-1 cell death due to actinomycin D and MK 886 are additive but increase clonogenic survival

In human panc-1 pancreatic cancer cells, actinomycin D (act D) induces a type 1 (apoptotic, extrinsic, death domain, receptor-dependent, and caspase-positive) form of programmed cell death (PCD) and MK 886, a 5-lipoxygenase inhibitor serving among other functions as a surrogate for increasing oxidative stress, a type 2 form, defined as an intrinsic, mitochondria-dependent, autophagic form of cellular suicide. Using both agents simultaneously should allow for examination of their interaction in cells able to express either form of PCD. Activation of both forms might result in synergistic, additive, null, or inhibitory effects on the reduction in proliferation, PCD, and clonogenicity of surviving cells. Co-culture of panc-1 cells with act D and MK 886, which both inhibit their proliferation, had an additive effect on increasing the development of these forms of PCD, as determined by morphology, a nucleosome assay, and flow cytometry. Initially, laddering on agarose detected with propidium iodide, present in act D, and act D plus MK 886-treated cells was partially obscured by randomly degraded DNA. With the use of the more sensitive SYBR green dye and reduced exposure of detached cells to 37 degrees C, a limited laddering of DNA from MK 886-treated cells was also detected. Caspase activity was present in act-D-cultured cells but was absent in cells cultured with MK 886. Combined culture reduced caspase activity in act D-treated cells, consistent with interference from type 2 of type 1 PCD. Removal after 48 hr of act D or MK 886 allowed regrowth of residual cells, the latter agent to a greater extent than the former. In combination, the number of clones was increased compared with act D alone. These features distinguish two forms of PCD. In therapeutic settings in which the modes of cell death have not been identified, unintentional activation of several cellular suicide pathways with "crosstalk" between them occurs. Their intentional simultaneous activation and responses, as modulated by the history of cells in or out of cycle, could reduce the intended therapeutic outcome with survival of additional clonogenic cells due to various forms of mutual interference.

Inverse relationship between myeloid maturation and leukotriene C4 synthase expression in normal and leukemic myelopoiesis-consistent overexpression of the enzyme in myeloid cells from patients with chronic myeloid leukemia

OBJECTIVE

Leukotriene (LT) C(4) synthase (LTC(4)S) is the key enzyme in the biosynthesis of LTC(4), which has been reported to stimulate the growth of human myeloid progenitor cells and is specifically overproduced in chronic myeloid leukemia (CML). The aim of this study was to clarify the expression of LTC(4)S during normal and leukemic myelopoiesis and to investigate the correlation between abnormal LTC(4)S expression in CML myeloid cells and the activity of the disease-specific tyrosine kinase p210 BCR-ABL.

MATERIALS AND METHODS

Immature and mature myeloid cell subpopulations were isolated with magnetic cell sorting from healthy volunteer bone marrow (n = 11) and CML patient peripheral blood (n = 8), respectively. The cells were subjected to analysis of LTC(4)S protein expression and activity. Expression of LTC(4)S was investigated in CD16(+) neutrophils from CML patients before and after 1 month of medication with imatinib mesylate (STI571), which is a specific inhibitor of p210 BCR-ABL.

RESULTS

Among normal cells, the highest enzyme activity was observed in the most immature, CD34(+) progenitor cell-enriched and CD15(+) myelocyte-enriched fractions. Subsequently, LTC(4)S activity decreased with increasing maturity, with only negligible amounts of LTC(4) produced in CD16(+) neutrophils. LTC(4)S was expressed at the protein level in the immature myeloid cell fractions but not in CD16(+) cells. In CML cells, LTC(4)S activity and expression were consistently elevated. Thus, the CML CD34(+) and CD15(+) cell fractions, as well as the CD11b(+) myelocyte/metamyelocyte-enriched fractions, produced 6 to 10 times as much LTC(4) as the corresponding normal cells. Again, enzyme expression was highest in the most immature cells, although evident LTC(4)S expression and activity remained in CML CD16(+) neutrophils. Interestingly, treatment of five CML patients with imatinib mesylate down-regulated the abnormal neutrophil LTC(4)S expression and activity.

CONCLUSIONS

Expression of LTC(4)S in immature myelopoid cells is in line with a role for this enzyme in myelopoiesis. In addition, consistent overexpression of LTC(4)S in CML and the correlation to p210 BCR-ABL activity suggests that LTC(4)S may be involved in leukemic pathogenesis.

Changes in the proteome associated with the action of Bcr-Abl tyrosine kinase are not related to transcriptional regulation

Chronic myeloid leukemia (CML) is a hematopoietic stem cell disease, the hallmark of which is the Bcr-Abl protein tyrosine kinase (PTK). Without intervention the disease progresses from a benign chronic phase to a rapidly fatal blast crisis. To identify the molecular mechanisms underlying disease progression we used two-dimensional gel electrophoresis on a model we have previously described using the expression of a conditional mutant of Bcr-Abl PTK in a multipotent stem cell line, FDCP-Mix. Long term exposure of FDCP-Mix cells to Bcr-Abl mimics disease progression in CML. Four major differences were observed as a consequence of long term exposure to the Bcr-Abl PTK compared with cells exposed short term. The proteins were identified using matrix-assisted laser desorption ionization-time of flight mass spectrometry-generated peptide mass fingerprint data and liquid chromatography-tandem mass spectrometry-generated sequence information. Leukotriene A4 hydrolase, an enzyme known to be deregulated in CML, was found to be up-regulated. Annexin VI, vacuolar ATP synthase catalytic subunit A, and mortalin were found to be down-regulated. Poly(A) PCR cDNA analysis showed there was no correlation between the protein expression changes and mRNA levels. Western blot analysis also indicated no change in the levels of mortalin or leukotriene A4 hydrolase, indicating that post-translational events may modify protein content of the specific spots. Leukotriene B4 levels (product of leukotriene A4 hydrolase) were, however, reduced in cells exposed long term to Bcr-Abl activity. This study demonstrates the potential of proteomic analysis to define novel effects of oncogenes.

Mitochondria are direct targets of the lipoxygenase inhibitor MK886. A strategy for cell killing by combined treatment with MK886 and cyclooxygenase inhibitors

We have investigated the mitochondrial and cellular effects of the lipoxygenase inhibitor MK886. Low concentrations (1 microM) of MK886 selectively sensitized the permeability transition pore (PTP) to opening, whereas higher concentrations of MK886 (10 microM) caused depolarization through combination of an ionophoretic effect with inhibition of respiration. MK886 killed prostate cancer PC3 cells only at the higher, toxic concentration (10 microM), whereas the lower concentration (1 microM) had no major effect on cell survival. However, 1 microM MK886 alone demonstrably induced PTP-dependent mitochondrial dysfunction; and it caused cell death through the mitochondrial pathway when it was used in combination with the cyclooxygenase inhibitor, indomethacin, which had no effects per se. Treatment with 1 microM MK886 plus indomethacin sensitized cells to killing by exogenous arachidonic acid, which induces PTP opening and cytochrome c release (Scorrano, L., Penzo, D., Petronilli, V., Pagano, F., and Bernardi, P. (2001) J. Biol. Chem. 276, 12035-12040). Combination of MK886 and cyclooxygenase inhibitors may represent a viable therapeutic strategy to force cell death through the mitochondrial pathway. This approach should be specifically useful to kill cells possessing a high flux of arachidonic acid and its metabolites like prostate and colon cancer cells.

The effect of cysteinyl leukotrienes on growth of eosinophil progenitors from peripheral blood and bone marrow of atopic subjects

BACKGROUND

The accumulation of eosinophils into the peripheral blood and airways of asthmatic subjects is, in part, dependent on cysteinyl leukotrienes (cysLTs). However, the effect of cysLTs on peripheral blood and bone marrow eosinophil pro-genitor cells in allergic subjects is not known.

OBJECTIVE

The purpose of this study was to evaluate the effects of leukotriene (LT) D(4) and LTE(4) and the cysLT(1) receptor antagonist montelukast on peripheral blood and bone marrow eosinophil-basophil progenitor growth and development in atopic subjects.

METHODS

Semisolid methylcellulose cultures for peripheral blood and bone marrow eosinophil-basophil colonies were counted after incubation with or without addition of LTD(4), LTE(4), and montelukast in the presence of suboptimal concentrations of GM-CSF, IL-3, and IL-5.

RESULTS

Peripheral blood eosinophil-basophil colony-forming unit cultures grown in the presence of GM-CSF and bone marrow eosinophil-basophil colony-forming units grown in the presence of IL-5 were significantly increased by the addition of LTD(4) (0.1 micromol/L). This increase was suppressed by montelukast (1 micromol/L).

CONCLUSION

This study has demonstrated that the cysLT LTD(4) can stimulate proliferation of eosinophil hematopoietic progenitor cells in the presence of eosinophilopoietic cytokines. The suppressive effect by montelukast demonstrates that this is a cysLT(1) receptor-mediated effect.

Fatty acid oxidation and signaling in apoptosis

It is well established that fatty acid metabolites of cyclooxygenase, lipoxygenase (LOX), and cytochrome P450 are implicated in essential aspects of cellular signaling including the induction of programmed cell death. Here we review the roles of enzymatic and non-enzymatic products of polyunsaturated fatty acids in controlling cell growth and apoptosis. Also, the spontaneous oxidation of polyunsaturated fatty acids yields reactive aldehydes and other products of lipid peroxidation that are potentially toxic to cells and may also signal apoptosis. Significant conflicting data in terms of the role of LOX enzymes are highlighted, prompting a re-evaluation of the relationship between LOX and prostate cancer cell survival. We include new data showing that LNCaP, PC3, and Du145 cells express much lower levels of 5-LOX mRNA and protein compared with normal prostate epithelial cells (NHP2) and primary prostate carcinoma cells (TP1). Although the 5-LOX activating protein inhibitor MK886 killed these cells, another 5-LOX inhibitor AA861 hardly showed any effect. These observations suggest that 5-LOX is unlikely to be a prostate cancer cell survival factor, implying that the mechanisms by which LOX inhibitors induce apoptosis are more complex than expected. This review also suggests several mechanisms involving peroxisome proliferator activated receptor activation, BCL proteins, thiol regulation, and mitochondrial and kinase signaling by which cell death may be produced in response to changes in non-esterified and non-protein bound fatty acid levels. Overall, this review provides a context within which the effects of fatty acids and fatty acid oxidation products on signal transduction pathways, particularly those involved in apoptosis, can be considered in terms of their overall importance relative to the much better studied protein or peptide signaling factors.

5-Lipoxygenase and human pulmonary artery endothelial cell proliferation

Increased 5-lipoxygenase (5LO) expression in pulmonary artery endothelial cells (PAECs) has been observed in primary pulmonary hypertension, a disorder associated with pulmonary vascular remodeling and aberrant endothelial cell proliferation. To examine whether 5LO plays a role in endothelial cell proliferation, we analyzed the effect of 5LO inhibitors on cultured human PAECs. Analysis of [(3)H]thymidine incorporation showed that 5LO and 5LO-activating protein inhibitors AA-861, nordihydroguaiaretic acid (NDGA), and MK-886 all inhibited PAEC growth in a dose-dependent manner, with maximal inhibition of >90% and IC(50) values of 3.9, 1.8, and 0.48 microM, respectively. The effect of AA-861 and NDGA correlated with their effect on 5LO activity in PAECs. Concentrations of these inhibitors at or below their IC(90) values did not cause significant cell death as determined by lactate dehydrogenase release, but decreased cell doubling, as measured by cell counting at 24 h after serum replenishment. Analysis of DNA content suggested that the inhibitors led to an accumulation of PAECs at the G(0)/G(1) phase. Antisense oligonucleotides to 5LO mRNA delivered at a transfection efficiency of approximately 60% inhibited cell growth by 40 +/- 26% compared with that of a sequence-unrelated oligonucleotide. Indomethacin had no effect on PAEC growth over a range of concentrations (0.3-5 microM). These data show that 5LO inhibitors impaired the proliferative response of the cultured PAECs, suggesting that this enzyme may contribute to PAEC growth under certain pathological conditions.

Inhibition of peroxisome-proliferator-activated receptor (PPAR)alpha by MK886

Although MK886 was originally identified as an inhibitor of 5-lipoxygenase activating protein (FLAP), recent data demonstrate that this activity does not underlie its ability to induce apoptosis [Datta, Biswal and Kehrer (1999) Biochem. J. 340, 371--375]. Since FLAP is a fatty-acid binding protein, it is conceivable that MK886 may affect other such proteins. A family of nuclear receptors that are activated by fatty acids and their metabolites, the peroxisome-proliferator-activated receptors (PPARs), have been implicated in apoptosis and may represent a target for MK886. The ability of MK886 to inhibit PPAR-alpha, -beta and -gamma activity was assessed using reporter assay systems (peroxisome-proliferator response element--luciferase). Using a transient transfection system in monkey kidney fibroblast CV-1 cells, mouse keratinocyte 308 cells and human lung adenocarcinoma A549 cells, 10--20 microM MK886 inhibited Wy14,643 activation of PPAR alpha by approximately 80%. Similar inhibition of PPAR alpha by MK886 was observed with a stable transfection reporter system in CV-1 cells. Only minimal inhibitory effects were seen on PPAR beta and PPAR gamma. MK886 inhibited PPAR alpha by a non-competitive mechanism as shown by its effects on the binding of arachidonic acid to PPAR alpha protein, and a dose-response study using a transient transfection reporter assay in COS-1 cells. An assay assessing PPAR ligand-receptor interactions showed that MK886 prevents the conformational change necessary for active-complex formation. The expression of keratin-1, a protein encoded by a PPAR alpha-responsive gene, was reduced by MK886 in a culture of mouse primary keratinocytes, suggesting that PPAR inhibition has functional consequences in normal cells. Although Jurkat cells express all PPAR isoforms, various PPAR alpha and PPAR gamma agonists were unable to prevent MK886-induced apoptosis. This is consistent with MK886 functioning as a non-competitive inhibitor of PPAR alpha, but may also indicate that PPAR alpha is not directly involved in MK886-induced apoptosis. Although numerous PPAR activators have been identified, the results show that MK886 can inhibit PPAR alpha, making it the first compound identified to have such an effect.

Association between bcl-x(L) and 5-lipoxygenase activating protein (FLAP) levels in IL-3-dependent FL5.12 cells

The expression of 5-lipoxygenase activating protein (FLAP) in murine hematopoietic FL5.12 cells that are transfected to overexpress bcl-x(L) is less than in control cells. In addition, the withdrawal of IL-3 from the bcl-x(L) overexpressing cells, but not control cells, leads to the rapid loss of FLAP even though these cells, in contrast to control cells, do not undergo apoptosis (Datta et al., J. Biol. Chem. 273, 28163-28169 [1998]). The mechanism(s) underlying these observations is not known. Basal FLAP mRNA levels were actually 2.8-fold higher in bcl-x(L) than control cells indicating that this difference does not have a transcription basis. In addition, an examination of FLAP mRNA levels in response to withdrawal of IL-3 revealed a 2-3-fold increase after 4 and 8 h relative to time-matched samples in both control and bcl-x(L) overexpressing cells. This further indicates that the decrease in FLAP levels in bcl-x(L) overexpressing cells is not related to transcription and suggests an attempt at compensation perhaps in response to increased FLAP degradation/turnover. A proteolytic mechanism was explored by examining the effect of the general caspase inhibitor Boc-D-FMK, and the non-caspase protease inhibitors phenylmethylsulfonyl fluoride (PMSF), pepstatin and leupeptin, on the loss of FLAP in bcl-x(L) overexpressing cells subsequent to IL-3 withdrawal. All inhibitors provided some protection from the loss of FLAP, with PMSF being the most effective, actually increasing FLAP levels above those seen in untreated cells. Given the absence of apoptosis in bcl-x(L) cells, it appears that protease activation is an effect that can accompany a variety of cellular perturbations. The functional consequences of a loss of FLAP in growth-factor deprived cells overexpressing bcl-x(L) is not known. However, these data continue to suggest some link between bcl-x(L) and FLAP.

Current prospects for controlling cancer growth with non-cytotoxic agents--nutrients, phytochemicals, herbal extracts, and available drugs

In animal or cell culture studies, the growth and spread of cancer can be slowed by many nutrients, food factors, herbal extracts, and well-tolerated, available drugs that are still rarely used in the clinical management of cancer, in part because they seem unlikely to constitute definitive therapies in themselves. However, it is reasonable to expect that mechanistically complementary combinations of these measures could have a worthwhile impact on survival times and, when used as adjuvants, could improve the cure rates achievable with standard therapies. The therapeutic options available in this regard include measures that: down-regulate serum free IGF-I; suppress the synthesis of mevalonic acid and/or certain derivatives thereof; modulate arachidonate metabolism by inhibiting 5-lipoxygenase, 12-lipoxygenase, or COX-2; antagonize the activation of AP-1 transcription factors; promote the activation of PPAR-gamma transcription factors; and that suppress angiogenesis by additional mechanisms. Many of these measures appear suitable for use in cancer prevention.

Induction of apoptosis in HL-60 cells by eicosapentaenoic acid (EPA) is associated with downregulation of bcl-2 expression

Dietary polyunsaturated fatty acids (PUFAs) have been reported as a potential group of natural products which modulate tumor cell growth. In present study, eicosapentaenoic acid (EPA) was found to inhibit proliferation of human leukemic HL-60 and K-562 cells in vitro. EPA arrested cell cycle progression at G0/G1 phase, and induced necrosis in both HL-60 and K-562 cells. However, EPA induced apoptosis only in HL-60 but not K-562 cells. Also, bcl-2 protein expression was downregulated in much greater extent than that of bax showing that depression of bcl-2 might be an important step during the EPA-induced apoptosis in HL-60 cells.

Induction of type 1 programmed cell death in U937 cells by the antioxidant, butylated hydroxy-toluene or the free radical spin trap, NTBN

Oxidative stress can initiate programmed cell death and contributes to the patho-physiology of a number of diseases. Low micromolar to millimolar concentrations of various antioxidants or free radical scavengers promote cell growth and reduce cellular suicide induced by several functionally distinct agents, including some known to produce oxidative stress. Severe anoxia or inhibitors of oxidative phosphorylation also initiate programmed cell death. These results seem paradoxical. In order to compare the response of U937 monoblastoid cells to higher concentrations of an antioxidant or a free radical-spin trap, cells were cultured with 20-80 microM concentrations of butylated hydroxy-toluene or with 5 to 60 mM concentrations of the free radical spin trap, N-tertiary butyl phenyl-nitrone. At these concentrations, both agents inhibited cellular proliferation and induced oligosomic DNA, detected by its 'laddering' after electrophoresis on agarose, confirmed by TUNEL (BHT) or flow cytometric (NTBN) evidence of hypodiploid DNA and ultrastructural evidence of a type 1 programmed cell death. The ability of hydroxy-toluenes to oxidize DNA and promote carcinogenesis and whether free radical spin traps could augment or interfere with the response of malignantly transformed cells to chemotherapy or ionizing radiation provide the raison d'etre of these studies.

Lichen metabolites. 2. Antiproliferative and cytotoxic activity of gyrophoric, usnic, and diffractaic acid on human keratinocyte growth

The sensitivity of the human keratinocyte cell line HaCaT to several lichen metabolites isolated from Parmelia nepalensis and Parmelia tinctorum was evaluated. The tridepside gyrophoric acid (6), the dibenzofuran derivative (+)-usnic acid (1), and the didepside diffractaic acid (5) were potent antiproliferative agents and inhibited cell growth, with IC50 values of 1.7, 2.1, and 2.6 microM, respectively. Methyl beta-orcinolcarboxylate (2), ethyl hematommate (3), the didepside atranorin (4), and (+)-protolichesterinic acid (7) did not influence keratinocyte growth at concentrations of 5 microM. Keratinocytes were further tested for their susceptibility to the action of the potent antiproliferative agents on plasma membrane integrity. The release of lactate dehydrogenase activity into the culture medium was unchanged as compared to controls, documenting that the activity of gyrophoric acid (6), (+)-usnic acid (1), and diffractaic acid (5) was due to cytostatic rather than cytotoxic effects.

Perturbations in the control of cellular arachidonic acid levels block cell growth and induce apoptosis in HL-60 cells

Our previous studies demonstrated that inhibitors of arachidonate-phospholipid remodeling [i.e. the enzyme CoA-independent transacylase (CoA-IT)] decrease cell proliferation and induce apoptosis in neoplastic cells. The goal of the current study was to elucidate the molecular events associated with arachidonate-phospholipid remodeling that influence cell proliferation and survival. Initial experiments revealed the essential nature of cellular arachidonate to the signaling process by demonstrating that HL-60 cells depleted of arachidonate were more resistant to apoptosis induced by CoA-IT inhibition. In cells treated with CoA-IT inhibitors a marked increase in free arachidonic acid and AA-containing triglycerides were measured. TG enrichment was likely due to acylation of arachidonic acid into diglycerides and triglycerides via de novo glycerolipid biosynthesis. To determine the potential of free fatty acids to affect cell proliferation, HL-60 cells were incubated with varying concentrations of free fatty acids; exogenously provided 20-carbon polyunsaturated fatty acids caused a dose-dependent inhibition of cell proliferation, whereas oleic acid was without effect. Blocking 5-lipoxygenase or cyclooxygenases had no effect on the inhibition of cell proliferation induced by arachidonic acid or CoA-IT inhibitors. An increase in cell-associated ceramides (mainly in the 16:0-ceramide fraction) was measured in cells exposed to free arachidonic acid or to CoA-IT inhibitors. This study, in conjunction with other recent studies, suggests that perturbations in the control of cellular arachidonic acid levels affect cell proliferation and survival.

Do lipoxygenases modulate normal or aberrant lympho-hematopoiesis?

Whether 5- (and the 12- or 15-) lipoxygenases participate in normal or malignantly transformed hematopoietic cell proliferation and differentiation, or contribute to programmed or necrotic cell death has been difficult to decide. Recent evidence concerning these questions is reviewed and some reasons for these difficulties are considered.

Boswellic acid acetate induces differentiation and apoptosis in leukemia cell lines

Boswellic acid acetate (BC-4), a compound isolated from the herb Boswellia carterii Birdw., can induce differentiation and apoptosis of leukemia cells. Based on cell morphology and NBT reduction, BC-4 induced monocytic differentiation of myeloid leukemia HL-60, U937 and ML-1 cells at a dose under 12.5 microg/ml (24.2 microM). BC-4 was a potent inducer, with 90% of the cells showing morphologic changes and 80-90% of the cells showing NBT reduction. Specific and non-specific esterase were also increased by BC-4. Based on benzidine staining assay, BC-4 failed to induce erythroid leukemia DS-19 and K562 cells differentiation. In contrast to its selective differentiation effect, BC-4 strongly inhibited growth of all cell lines tested. The growth inhibition effect was dose- and time-dependent. In HL-60 cells, 20 microg/ml (38.8 microM) of BC-4 decreased viable cell number by 60% at 24 h, whereas at 3 days there was virtually no viable cells. Morphologic and DNA fragmentation analysis proved that BC-4 induced cell apoptosis. The dual apoptotic and differentiation effects of BC-4 suggest that it may be a powerful agent in the treatment of leukemia.

5-Lipoxygenase inhibitors reduce PC-3 cell proliferation and initiate nonnecrotic cell death

BACKGROUND

Products of the arachidonic acid-metabolizing enzyme, 5-lipoxygenase, stimulate the growth of several cell types. Selective inhibitors of the enzyme, including SC41661A and MK886, reduce PC-3 prostate cell proliferation. With continued culture, cells die, but the mode of death, necrotic or nonnecrotic, has not been established.

METHODS

Flow cytometry, laddering after agarose electrophoresis of DNA from inhibitor-treated cells, and light and electron microscopy were employed to examine the type of death in PC-3 prostate cells cultured with either 5-lipoxygenase inhibitor.

RESULTS

The inhibitors induced nonnecrotic, programmed cell death. SC41661A-treated cells exhibited "foamy," vacuolated cytoplasm and mitochondria with disrupted cristae and limiting membranes, while some cells contained numerous polysomes and extended hypertrophic Golgi and secretory cisternal networks. A proportion of the treated cells detached and the nuclei of these cells were characteristic of type 1 "apoptotic" programmed cell death. MK886, a 5-lipoxygenase-inhibitor with a different mechanism of action, induced nonnecrotic changes largely confined to the cytoplasm, most consistent with type 2 "autophagic" programmed cell death. In preliminary studies of mechanism, we demonstrated that PC-3 cells express mRNA for 5-lipoxygenase and for 5-lipoxygenase-activating protein. The less active inhibitor, SC45662 neither reduced proliferation nor induced DNA laddering. The antioxidant, N-acetyl-l-cysteine but not butylated hydroxy toluene or alpha tocopherol, partially reduced the inhibition of proliferation from SC41661A.

CONCLUSIONS

SC41661A and MK886 inhibit PC-3 cell proliferation and induce a form of type 1 or type 2 programmed cell death, respectively. PC-3 cells contain messenger RNA for 5-lipoxygenase and 5-lipoxygenase-activating proteins. Drug-induced changes included altered redox potential, inferred from the increased survival due to the antioxidant and glutathione precursor, N-acetyl-l-cysteine. PC-3 cells are an appropriate model for studying the mechanism responsible for 5-lipoxygenase inhibitor-induced cellular suicide.

Anti-proliferative effects of lichen-derived inhibitors of 5-lipoxygenase on malignant cell-lines and mitogen-stimulated lymphocytes

Several lichen species have been used traditionally as medicinal plants. It has previously been shown that two low-molecular-weight lichen metabolites, lobaric acid isolated from Stereocaulon alpinum Laur. and protolichesterinic acid isolated from Cetraria islandica L. (Ach.), have in-vitro inhibitory effects on arachidonate 5-lipoxygenase. We have studied the effects of these compounds on cultured cells from man, including three malignant cell-lines (T-47D and ZR-75-1 from breast carcinomas and K-562 from erythro-leukaemia), as well as normal skin fibroblasts and peripheral blood lymphocytes. Both test substances caused a significant reduction in DNA synthesis, as measured by thymidine uptake, in all three malignant cell-lines; the dose inducing 50% of maximum inhibition (ED50) was between 1.1 and 24.6 microg mL(-1) for protolichesterinic acid and between 14.5 and 44.7 microg mL(-1) for lobaric acid. The breast-cancer cell-lines were more sensitive than K-562. The proliferative response of mitogen-stimulated lymphocytes was inhibited with a mean ED50 of 8.4 microg mL(-1) and 24.5 microg mL(-1) for protolichesterinic acid and lobaric acid, respectively. These concentrations are of the same order of magnitude as the IC50 values in the 5-lipoxygenase assay. Significant cell death (assessed by the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-( 4-sulfophenyl)-2H-tetrazolium) assay and trypan blue exclusion) occurred in the three malignant cell-lines at protolichesterinic acid and lobaric acid concentrations above 20 and 30 microg mL(-1), respectively. In K-562 morphological changes consistent with apoptosis were detected. Up to 38% cell death was observed at 20 microg mL(-1) for protolichesterinic acid and 15 microg mL(-1) for lobaric acid in mitogen-stimulated lymphocytes but unstimulated lymphocytes were clearly less sensitive. In contrast, the DNA synthesis, proliferation and survival of normal skin fibroblasts were not affected at doses up to 20 microg mL(-1) for protolichesterinic acid and 30 microg mL(-1) for lobaric acid. We conclude that the anti-proliferative and cytotoxic effects observed might be related to the 5-lipoxygenase inhibitory activity of protolichesterinic acid and lobaric acid. These results open up the opportunity for future studies of these lichen metabolites with regard to their anti-tumour and anti-inflammatory properties.

Melatonin suppression of PC12 cell growth and death

Melatonin has previously been reported to influence cell differentiation and growth in a number of cell culture systems in vitro. In this paper, we describe the effects of high pharmacological and low physiological concentrations of melatonin on cell growth in rat pheochromocytoma cells (PC12 cells). Melatonin produced a biphasic response with respect to cell growth in PC12 cells. At low concentrations (1-10 nM) melatonin suppressed PC12 cell growth whereas at higher concentration (10 microM) it prevented cell death. Cultures treated with high concentrations of melatonin displayed an increase in cell number and a decreased release of lactic acid dehydrogenase (LDH) into the culture media, indicating that melatonin was enhancing cell survival as opposed to stimulating cell proliferation. Inhibition of cell death by high concentrations of melatonin was both time and concentration-dependent and did not require the continued presence of melatonin throughout the entire time of incubation. These studies suggest melatonin is preventing either apoptosis or programmed cell death. In contrast, concentrations of melatonin (1-10 nM) at or near the binding affinity for the nuclear receptor, RZRbeta, suppressed PC12 cell growth. At these concentrations, melatonin failed to inhibit forskolin-induced cAMP formation and process outgrowth as well as prevent forskolin suppression of cell growth. These data indicate that PC12 cells probably lack functionally active cell surface receptors for melatonin and suggest the interaction of melatonin with the nuclear receptor may be responsible for suppression of PC12 cell growth.

A 5-lipoxygenase inhibitor at micromolar concentration raises intracellular calcium in U937 cells prior to their physiologic cell death

Micromolar MK886, a selective inhibitor of 5-lipoxygenase at nanomolar concentration, induces physiologic cell death in U937 and chronic myelogenous leukemia blast cells. When U937 cells were challenged with 10 microM MK886, an acute, biphasic and sustained rise in intracellular Ca2+ occurred, as determined with Fura-2. The initial increase was followed by a transient decline and a larger rise due to an influx of external Ca2+. The first increase and part of the subsequent rise also developed in Ca(2+)-free medium, identifying their origin from intracellular stores. The intracellular Ca2+ concentration of U937 cells that remained after culture for 24 or 48 h with 5 or 10 microM MK886 was not reliably altered from the control values of 130 +/- 8.3 nM. Under similar conditions MK886 did not increase cytosol Ca2+ of a human prostate (PC3) cell line examined in suspension. The increase in intracellular Ca2+ in response to MK886 in calcium-containing medium was confirmed with an ACAS laser spectrometer. U937 cytosol pH was measured with the fluorescent probe BCECF, but not persistent acute or chronic change was induced by MK886. The rapid and sustained rise in Ca2+ induced by MK886 is an early event in U937 cells which subsequently undergo physiologic cell death characterized in many by apoptosis.

Inhibition of ICE-family cysteine proteases rescues murine lymphocytes from lipoxygenase inhibitor-induced apoptosis

Two lipophilic derivatives of caffeic acid which inhibit lipoxygenase, caffeic acid phenethyl ester (CAPE) and N,N'-dicyclohexyl-O-(3,4-dihydroxycinnamoyl)-isourea (DCHCU), reduced the proliferative response of murine splenocytes to concanavalin A in vitro. Both CAPE and DCHCU induced apoptosis in murine thymocyte cultures as verified by flow cytometry and by visualisation of DNA with acridine orange staining. CAPE-induced apoptosis was inhibited by z-VAD-fmk, an inhibitor of the interleukin-1beta-converting enzyme family of cysteine proteases. We suggest that the lipoxygenase pathway of arachidonic acid metabolism plays a role in regulating lymphocyte responses such as proliferation and apoptosis.