Mechanisms of free-radical induction in relation to fenretinide-induced apoptosis of neuroblastoma

The mechanisms of fenretinide-induced cell death of neuroblastoma cells are complex, involving signaling pathways mediated by free radicals or reactive oxygen species (ROS). The aim of this study was to identify mechanisms generating ROS and apoptosis of neuroblastoma cells in response to fenretinide. Fenretinide-induced ROS or apoptosis of SH-SY5Y or HTLA 230 neuroblastoma cells were not blocked by Nitro l-argenine methyl ester (l-NAME), an inhibitor of nitric oxide synthase. Flavoprotein-dependent superoxide-producing enzymes such as NADPH oxidase were also not involved in fenretinide-induced apoptosis or ROS generation. Similarly, ketoconazole, a cytochrome P450 inhibitor, and inhibitors of cyclooxygenase (COX) were also ineffective. In contrast, inhibition of phospholipase A(2) or lipoxygenases (LOX) blocked the induction of ROS and apoptosis in response to fenretinide. Using specific inhibitors of LOX, blocking 12-LOX but not 5- or 15-LOX inhibited both fenretinide-induced ROS and apoptosis. The effects of eicosatriynoic acid, a specific 12-LOX inhibitor, were reversed by the addition of the 12-LOX products, 12 (S)-hydroperoxyeicosatetraenoic acid and 12 (S)-hydroxyeicosatetraenoic acid. The targeting of 12-LOX in neuroblastoma cells may thus be a novel pathway for the development of drugs inducing apoptosis of neuroblastoma with improved tumor specificity.     

COX-2/12-LOX dual pathway, a novel strategy for treatment of multiple myeloma?

Cyclooxygenase (COX) and lipoxygenase (LOX) metabolic enzymes are the two main pathways for arachidonic acid (AA) metabolism. Emerging reports now indicate alterations of arachidonic acid metabolism with carcinogenesis and many COX and LOX inhibitors are being investigated as potential anticancer drugs. COX-2 is frequently expressed in many tumors, such as multiple myeloma (MM), a disorder in which malignant plasma cells accumulate, generally derived from one clone in the bone marrow, and is an independent predictor of poor outcome. 12-LOX, an important member of LOX, is proved to be expressed in MM cells. We hypothesize that COX-2 and 12-LOX represent an integrated system, COX-2/12-LOX dual pathway, which much more efficiently enhances the intracellular levels of unesterified arachidonate and regulates cell proliferative, apoptosis and pro-angiogenic potential of MM. The COX-2/12-LOX dual pathway may act as a novel potential strategy for treatment of tumors co-expressing COX-2 and 12-LOX, and the agents that can simultaneously inhibit the two enzymes of COX-2 and 12-LOX may present a novel and promising therapeutic approach to these tumors.     

Putative role of neuronal 5-lipoxygenase in an aging brain.

Aging is associated with increased incidence and/or severity of neurodegenerative pathologies. Oxygen-mediated events are being considered as possible mechanisms responsible for the increasing neuronal vulnerability. Lipoxygenases are enzymes that, as cyclooxygenases (COX), can insert oxygen into the molecule of arachidonic acid and thereby synthesize inflammatory eicosanoids: leukotrienes [due to 5-lipoxygenase (5-LOX) activity] and prostaglandins (via COX activity). It appears that 5-LOX is expressed in central nervous system neurons and may participate in neurodegeneration. 5-LOX-triggered cell death may be initiated by the enzymatic activity of 5-LOX but could also occur via the nonenzymatic actions of the 5-LOX protein; new data point to the possibility that 5-LOX protein exerts actions such as interaction with tyrosine kinase receptors, cytoskeletal proteins, and the nucleus. The expression of neuronal 5-LOX is susceptible to hormonal regulation, presumably due to the presence of hormone-responsive elements in the structure of the 5-LOX gene promoter. The expression of the 5-LOX gene and the activity of the 5-LOX pathway are increased in elderly subjects. One possible mechanism of such 5-LOX up-regulation implies the contribution of aging-associated hormonal changes: relative melatonin deficiency and/or hyperglucocorticoidemia. Thus, the 5-LOX pathway could become a promising target of neuroprotective therapies for the aging brain.     

Identification of 12-lipoxygenase interaction with cellular proteins by yeast two-hybrid screening

The platelet isoform of 12-lipoxygenase (12-LOX) is expressed in a variety of human tumors. 12-LOX metabolizes arachidonic acid to 12(S)-hydroxyeicosateraenoic acid (12(S)-HETE), which induces a number of cellular responses associated with tumor progression and metastasis. Little is known about 12-LOX regulation and no direct regulators of 12-LOX activity have been identified. To identify potential regulators of 12-LOX, we isolated cDNAs encoding 12-LOX interacting proteins using the yeast two-hybrid system. We screened a yeast two-hybrid interaction library from human epidermoid carcinoma A431 cells and identified four cellular proteins that interact specifically with 12-LOX. We identified type II keratin 5, lamin A, the cytoplasmic domain of integrin beta4 subunit and a phosphoprotein C8FW as 12-LOX interacting proteins. Here, we demonstrated that keratin 5, a 58 kD protein required for formation of 8 nm intermediate filaments, binds to 12-LOX in human tumor cells and may contribute to the regulated trafficking of 12-LOX. We also showed that lamin A binds 12-LOX in human tumor cells. These proteins provide the first candidate regulators of 12-LOX.     

Eicosanoids mediate Manduca sexta cellular response to the fungal pathogen Beauveria bassiana: a role for the lipoxygenase pathway

Many studies have documented the involvement of eicosanoids in insect cellular immune responses to bacteria. The use of the fungal pathogen Beauveria bassiana as a nodulation elicitor, with inhibition of phospholipase A(2) by dexamethasone, extends the principle to fungi. This study also provides the first evidence of involvement of the lipoxygenase (LOX) pathway rather than the cyclooxygenase (COX) pathway in synthesis of the nodulation mediating eicosanoid(s). The LOX product, 5(S)-hydroperoxyeicosa-6E,8Z,11Z,14Z-tetraenoic acid (5-HPETE), substantially reversed nodulation inhibition caused by dexamethasone and the LOX inhibitors, caffeic acid and esculetin. The COX product, prostaglandin H(2) (PGH(2)), did not reverse the nodulation inhibition by dexamethasone or the COX inhibitor, ibuprofen. None of the inhibitors tested had a significant effect on the phagocytosis of B. bassiana blastospores in vitro. Hemocyte phenoloxidase activity was reduced by dexamethasone, esculetin, and the COX inhibitor, indomethacin. The rescue candidates 5-HPETE and PGH(2) did not reverse the inhibition.     

Lipoxygenase inhibition induced apoptosis, morphological changes, and carbonic anhydrase expression in human pancreatic cancer cells

Epidemiologic and animal studies have linked pancreatic cancer growth with fat intake, especially unsaturated fats. Arachidonic acid release from membrane phospholipids is essential for tumor cell proliferation. Lipoxygenases (LOX) constitute one pathway for arachidonate metabolism. We previously reported that 5-LOX and 12-LOX are upregulated in human pancreatic cancer cells and that blockade of these enzymes abolishes pancreatic cancer cell growth. The present study was aimed at evaluating the effect of LOX inhibition on differentiation and apoptosis in pancreatic cancer cells in parallel with growth inhibition. Four human pancreatic cancer cell lines, PANC-1, MiaPaca2, Capan2, and HPAF, were used. Apoptosis was evaluated by three separate methods, including DNA propidium iodide staining, DNA fragmentation, and the TUNEL assay. Morphological changes and carbonic anhydrase activity were used to determine the effect of LOX inhibitors on differentiation. The general LOX inhibitor NDGA, the 5-LOX inhibitor Rev5901, and the 12-LOX inhibitor baicalein all induced apoptosis in all four pancreatic cancer cell lines, as confirmed by all three methods, suggesting that both the 5-LOX and 12-LOX pathways are important for survival of these cells. Furthermore, NDGA, Rev5901, or baicalein resulted in marked cellular morphological changes in parallel with increased intracellular carbonic anhydrase activity, indicating that LOX blockade induced a more differentiated phenotype in human pancreatic cancer cells. Together with our previous findings, this study suggests that perturbations of LOX activity affect pancreatic cancer cell proliferation and survival. Blockade of LOX enzymes may be valuable for the treatment of human pancreatic cancer.     

Cyclooxygenase (COX) and 5-lipoxygenase (5-LOX) selectivity of COX inhibitors

In vitro evaluations of the selectivity of COX inhibitors are based on a great variety of experimental protocols. As a result, data available on cyclooxygenase (COX)-1/COX-2/5- lipoxygenase (LOX) selectivity of COX inhibitors lack consistency. We, therefore, performed a systematic analysis of the COX-1/COX-2/5-LOX selectivity of 14 compounds with selective COX inhibitory activity (Coxibs). The compounds belonged to different structural classes and were analyzed employing the well-recognized whole-blood assay. 5-LOX activity was also tested on isolated human polymorphonuclear leukocytes. Among COX inhibitors, celecoxib and ML-3000 (licofelone) inhibited 5-LOX in human neutrophils at micromolar ranges. Surprisingly, ML-3000 had no effect on 5-LOX product synthesis in whole-blood assay. In addition, we could show that inhibition of COX pathways did not increase the transformation of arachidonic acid by the 5-LOX pathway.     

Hepoxilin A(3) protects β-cells from apoptosis in contrast to its precursor, 12-hydroperoxyeicosatetraenoic acid

Pancreatic β-cells have a deficit of scavenging enzymes such as catalase (Cat) and glutathione peroxidase (GPx) and therefore are susceptible to oxidative stress and apoptosis. Our previous work showed that, in the absence of cytosolic GPx in insulinoma RINm5F cells, an intrinsic activity of 12 lipoxygenase (12(S)-LOX) converts 12S-hydroperoxyeicosatetraenoic acid (12(S)-HpETE) to the bioactive epoxide hepoxilin A(3) (HXA(3)). The aim of the present study was to investigate the effect of HXA(3) on apoptosis as compared to its precursor 12(S)-HpETE and shed light upon the underlying pathways. In contrast to 12(S)-HpETE, which induced apoptosis via the extrinsic pathway, we found HXA(3) not only to prevent it but also to promote cell proliferation. In particular, HXA(3) suppressed the pro-apoptotic BAX and upregulated the anti-apoptotic Bcl-2. Moreover, HXA(3) induced the anti-apoptotic 12(S)-LOX by recruiting heat shock protein 90 (HSP90), another anti-apoptotic protein. Finally, a co-chaperone protein of HSP90, protein phosphatase 5 (PP5), was upregulated by HXA(3), which counteracted oxidative stress-induced apoptosis by dephosphorylating and thus inactivating apoptosis signal-regulating kinase 1 (ASK1). Taken together, these findings suggest that HXA(3) protects insulinoma cells from oxidative stress and, via multiple signaling pathways, prevents them from undergoing apoptosis.     

Up-regulation of 12(S)-lipoxygenase induces a migratory phenotype in colorectal cancer cells

12(S)-Lipoxygenase (LOX) and its product 12(S)-hydroxyeicosatetraenic (HETE) acid have been implicated in angiogenesis and tumour invasion in several tumour types while their role in colorectal cancer progression has not yet been studied. We have analysed 12(S)-LOX expression in colorectal tumours and found gene expression up-regulated in colorectal cancer specimens for which the pathology report described involvement of inflammation. Using cell line models exposed to 12(S)-HETE or over-expressing 12(S)-LOX malignant cell growth as well as tumour cell migration was found to be stimulated. Specifically, Caco2 and SW480 cells over-expressing 12(S)-LOX formed fewer colonies from sparse cultures, but migrated better in filter-migration assays. SW480 LOX cells also had higher anchorage-independent growth capacity and a higher tendency to metastasise in vivo. Knock-down or inhibition of 12(S)-LOX inhibited cell migration and anchorage-independent growth in both 12(S)-LOX transfectants and SW620 cells that express high endogenous levels of 12(S)-LOX. On the cell surface E-cadherin and integrin-β1 expression were down-regulated in a 12(S)-LOX-dependent manner disturbing cell-cell interactions. The results demonstrate that 12(S)-LOX expression in inflammatory areas of colorectal tumours has the capacity to induce an invasive phenotype in colorectal cancer cells and could be targeted for therapy.     

5-LOX in Alzheimer’s Disease: Potential Serum Marker and In Vitro Evidences for Rescue of Neurotoxicity by Its Inhibitor YWCS

The inflammatory process plays a key role in neurodegenerative disorder. The inflammatory molecule, 5-lipooxygenase (5-LOX), protein is involved in the pathologic phenotype of Alzheimer’s disease (AD) which includes Aβ amyloid deposition and tau hyperphosphorylation. This study determined the level of 5-LOX in serum of AD patients, mild cognitive impairment (MCI) patients, and the normal elderly, and the rescue effect by YWCS, a peptide inhibitor of 5-LOX on neurotoxicity by Aβ amyloid_25–35 (Aβ_25–35) in neuroblastoma cells. The concentration of serum 5-LOX was estimated by surface plasmon resonance and western blot. The neuroprotective effect of 5-LOX peptide inhibitor YWCS in Aβ_25–35-induced neurotoxicity was analyzed by MTT assay and western blotting. We found significant upregulated serum 5-LOX in AD patients and also in MCI patients compared to the normal control group. The peptide inhibitor of 5-LOX, YWCS, prevented the neurotoxic effect of Aβ_25–35 by reducing the expression of γ-secretase as well as p-Tau₁₈₁ in SH-SY5Y cells. However, YWCS was nontoxic towards normal HEK cells. The differential expression of serum 5-LOX among the study groups suggests it can be one of potential serum protein marker and a therapeutic regimen for AD and MCI. The negative correlation with neuropsychological parameters, i.e., MoCA and HMSE, increases its importance and makes it useful during the clinical setup which is very needful in developing countries. Peptide YWCS can serve as a new platform as a 5-LOX inhibitor which can prevent neurotoxicity developed in AD.     

Synthesis and biological evaluation of acyclic triaryl (Z)-olefins possessing a 3,5-di-tert-butyl-4-hydroxyphenyl pharmacophore: dual inhibitors of cyclooxygenases and lipoxygenases

A new class of regioisomeric acyclic triaryl (Z)-olefins possessing a 3,5-di-tert-butyl-4-hydroxyphenyl (DTBHP) 5-lipoxygenase (5-LOX) pharmacophore that is vicinal to a para-methanesulfonylphenyl cyclooxygenase-2 (COX-2) pharmacophore were designed for evaluation as selective COX-2 and/or 5-LOX inhibitors. The target compounds were synthesized via a highly stereoselective McMurry olefination cross-coupling reaction. This key synthetic step afforded a (Z):(E) olefinic mixture with a predominance for the (Z)-olefin stereoisomer. Structure-activity studies for the (Z)-1-(3,5-di-tert-butyl-4-hydroxyphenyl)-2-(4-methanesulfonylphenyl)-1-phenylalk-1-ene regioisomers showed that COX-1 inhibition decreased, COX-2 inhibition increased, and the COX-2 selectivity index (SI) increased as the chain length of the alkyl substituent attached to the olefinic double bond was increased (Et-->n-butyl-->n-heptyl). In this group of compounds, inhibition of both 5-LOX and 15-LOX was dependent upon the length of the alkyl substituent with the hex-1-ene compound 9c having a n-butyl substituent exhibiting potent inhibition of both 5-LOX (IC50=0.3 microM) and 15-LOX (IC50=0.8 microM) relative to the inactive (IC50>10 microM) Et and n-heptyl analogs. Compound 9c is of particular interest since it also exhibits a dual inhibitory activity against the COX (COX-1 IC50=3.0 microM, and COX-2 IC50=0.36 microM, COX-2 SI=8.3) isozymes. A comparison of the relative inhibitory activities of the two groups of regioisomers investigated shows that the regioisomers in which the alkyl substituent is attached to the same olefinic carbon atom (C-2) as the para-methanesulfonylphenyl moiety generally exhibit a greater potency with respect to COX-2 inhibition. The 4-hydroxy substituent in the 3,5-di-tert-butyl-4-hydroxyphenyl moiety is essential for COX and LOX inhibition since 3,5-di-tert-butyl-4-acetoxyphenyl derivatives were inactive inhibitors. These structure-activity data indicate acyclic triaryl (Z)-olefins constitute a suitable template for the design of dual COX-2/LOX inhibitors.     

Deletion of microsomal prostaglandin E synthase-1 protects neuronal cells from cytotoxic effects of β-amyloid peptide fragment 31-35

Epidemiological studies have suggested that the long-term use of nonsteroidal anti-inflammatory drugs that inhibit cyclooxygenase (COX) activity moderates the onset or progression of Alzheimer's disease (AD). Thus it has been suggested that prostaglandin E(2) (PGE(2)), a major end-product of COX, may play a pathogenic role in AD, but the involvement of PGE synthase (PGES), a terminal enzyme downstream from COX, has not been fully elucidated. To examine the involvement in AD pathology of microsomal PGES-1 (mPGES-1), a PGES enzyme, we here prepared primary cerebral neuronal cells from the cerebri of wild-type and mPGES-1-deficient mice and then treated them with β-amyloid (Aβ) fragment 31-35 (Aβ(31-35)), which represents the shortest sequence of native Aβ peptide required for neurotoxicity. Treatment of wild-type neuronal cells with Aβ(31-35) induced mPGES-1 gene expression and PGE(2) production, followed by significant apoptotic cell death, but apoptosis was not induced in mPGES-1-deficient cells. Furthermore, the combined treatment of Aβ(31-35) and PGE(2) induced apoptosis in mPGES-1-deficient neuronal cells. These results indicated that mPGES-1 is induced during Aβ-mediated neuronal cell death and is involved in Aβ-induced neurotoxicity associated with AD pathology.     

Involvement of arachidonic acid metabolism and EGF receptor in neurotensin-induced prostate cancer PC3 cell growth

Dietary fats, which increase the risk of prostate cancer, stimulate release of intestinal neurotensin (NT), a growth-promoting peptide that enhances the formation of arachidonic acid metabolites in animal blood. This led us to use PC3 cells to examine the involvement of lipoxygenase (LOX) and cyclooxygenase (COX) in the growth effects of NT, including activation of EGF receptor (EGFR) and downstream kinases (ERK, AKT), and stimulation of DNA synthesis. NT and EGF enhanced [3H]-AA release, which was diminished by inhibitors of PLA2 (quinacrine), EGFR (AG1478) and MEK (U0126). NT and EGF phosphorylated EGFR, ERK and AKT, and stimulated DNA synthesis. These effects were diminished by PLA2 inhibitor (quinacrine), general LOX inhibitors (NDGA, ETYA), 5-LOX inhibitors (Rev 5901, AA861), 12-LOX inhibitor (baicalein) and FLAP inhibitor (MK886), while COX inhibitor (indomethacin) was without effect. Cells treated with NT and EGF showed an increase in 5-HETE levels by HPLC. PKC inhibitor (bisindolylmaleimide) blocked the stimulatory effects of NT, EGF and 5-HETE on DNA synthesis. We propose that 5-LOX activity is required for NT to stimulate growth via EGFR and its downstream kinases. The mechanism may involve an effect of 5-HETE on PKC, which is known to facilitate MEK-ERK activation. NT may enhance 5-HETE formation by Ca2+-mediated and ERK-mediated activation of DAG lipase and cPLA2. NT also upregulates cPLA2 and 5-LOX protein expression. Thus, the growth effects of NT and EGF involve a feed-forward system that requires cooperative interactions of the 5-LOX, ERK and AKT pathways.     

Hypertonic stress activates glycogen synthase kinase 3beta-mediated apoptosis of renal medullary interstitial cells, suppressing an NFkappaB-driven cyclooxygenase-2-dependent survival pathway

The survival of renal medullary interstitial cells (RMICs) requires their adaptation to rapid shifts in ambient tonicity normally occurring in the renal medulla. Previous studies determined that cyclooxygenase-2 (COX 2) activation is critical for this adaptation. The present studies find that these adaptive mechanisms are dampened by the simultaneous activation of an apoptotic pathway linked to a glycogen synthase kinase 3beta (GSK 3beta). Inhibition of GSK 3 by LiCl or specific small molecule GSK inhibitors increased RMIC survival following hypertonic stress, and transduction of RMICs with a constitutively active GSK 3beta (AdGSK 3betaA9) significantly increased apoptosis, consistent with a proapoptotic role of GSK 3beta. Following GSK 3beta inhibition, increased survival was accompanied by increased COX 2 expression and COX 2 reporter activity. In contrast, GSK 3beta overexpression reduced COX 2 reporter activity. Importantly, enhanced RMIC survival produced by GSK 3beta inhibition was completely dependent on COX 2 because it was abolished by a COX 2-specific inhibitor, SC58236. The signaling pathway by which GSK 3beta suppresses COX 2 expression was then explored. GSK 3beta inhibition increased both NFkappaB and beta-catenin activity associated with decreased IkappaB and increased beta-catenin levels. The increase in COX 2 following GSK 3beta inhibition was entirely blocked by NFkappaB inhibition using mutant IkappaB adenovirus. However, adenoviral overexpression of beta-catenin did not increase COX 2 levels. These findings suggest that GSK 3beta negatively regulates COX 2 expression and that GSK 3beta inhibitors protect RMICs from hypertonic stress via induction of NFkappaB-COX 2-dependent pathway.     

Expression of 5-oxoETE receptor in prostate cancer cells: critical role in survival

Previously, we reported that metabolism of arachidonic acid through the 5-lipoxygenase (5-LOX) pathway plays an important role in the survival and growth of human prostate cancer cells. Inhibition of 5-LOX by pharmacological inhibitors triggers apoptosis in prostate cancer cells within hours of treatment, which is prevented by the metabolites of arachidonate 5-lipoxygenase, 5(S)-hydroxyeicosatetraenoic acid (5(S)-HETE), and its dehydrogenated derivative, 5-oxoeicosatetraenoic acid (5-oxoETE). These findings suggested that 5-lipoxygenase metabolites are critical survival factors of prostate cancer cells. However, molecular mechanisms by which 5(S)-HETE and its derivative 5-oxoETE exert their effects on prostate cancer cell survival are yet to be understood. Here, we report that human prostate cancer cells differentially express a G-protein-coupled 5-oxoETE receptor (5-oxoER) in them. Blocking expression of 5-oxoER by short-interfering RNA (siRNA) significantly reduced the viability of prostate cancer cells, suggesting that 5-oxoER is critical for prostate cancer cell survival, and that the 5-LOX metabolite, 5-oxoETE, controls survival of prostate cancer cells through its own G-protein-coupled receptor, 5-oxoER.     

Reactive oxygen intermediate-dependent NF-kappaB activation by interleukin-1beta requires 5-lipoxygenase or NADPH oxidase activity

We previously reported that the role of reactive oxygen intermediates (ROIs) in NF-kappaB activation by proinflammatory cytokines was cell specific. However, the sources for ROIs in various cell types are yet to be determined and might include 5-lipoxygenase (5-LOX) and NADPH oxidase. 5-LOX and 5-LOX activating protein (FLAP) are coexpressed in lymphoid cells but not in monocytic or epithelial cells. Stimulation of lymphoid cells with interleukin-1beta (IL-1beta) led to ROI production and NF-kappaB activation, which could both be blocked by antioxidants or FLAP inhibitors, confirming that 5-LOX was the source of ROIs and was required for NF-kappaB activation in these cells. IL-1beta stimulation of epithelial cells did not generate any ROIs and NF-kappaB induction was not influenced by 5-LOX inhibitors. However, reintroduction of a functional 5-LOX system in these cells allowed ROI production and 5-LOX-dependent NF-kappaB activation. In monocytic cells, IL-1beta treatment led to a production of ROIs which is independent of the 5-LOX enzyme but requires the NADPH oxidase activity. This pathway involves the Rac1 and Cdc42 GTPases, two enzymes which are not required for NF-kappaB activation by IL-1beta in epithelial cells. In conclusion, three different cell-specific pathways lead to NF-kappaB activation by IL-1beta: a pathway dependent on ROI production by 5-LOX in lymphoid cells, an ROI- and 5-LOX-independent pathway in epithelial cells, and a pathway requiring ROI production by NADPH oxidase in monocytic cells.     

Suppression of 5-lipoxygenase gene is involved in triptolide-induced apoptosis in pancreatic tumor cell lines

Pancreatic adenocarcinoma is characterized by a poor prognosis and lack of response to conventional therapy. The purpose of this study was to investigate the effects of triptolide (TL) on proliferation and apoptosis of pancreatic cancer cells in vitro. We found that TL induced prominent growth inhibition and apoptosis in human pancreatic cell lines. In addition, TL treatment significantly down-regulated 5-lipoxygenase (5-LOX) expression, as well as downstream leukotriene B4 (LTB4) production, in these cell lines. Furthermore, overexpression of 5-LOX in SW1990 cell lines or exogenous LTB4 made them more resistant to TL-induced apoptosis, which was correlated with increased Bcl-2 expression. Taken together, these findings suggest that inhibition of the 5-LOX pathway of arachidonic acid metabolism is associated with the anti-proliferation activity of TL. We also provide evidence that TL has clinical therapeutic value for patients with pancreatic cancer.     

The mechanisms of lipoxygenase inhibitor-induced apoptosis in human breast cancer cells

Previous experimental studies have shown that high dietary fat intake is associated with mammary carcinogenesis. In the current study, the effect of 5-LOX or 12-LOX inhibitors on human breast cancer cell proliferation and apoptosis, as well as the possible mechanisms were investigated. The LOX inhibitors, NDGA, Rev-5901, and baicalein all inhibited proliferation and induced apoptosis in MCF-7 (ER+) and MDA-MB-231 (ER-) breast cancer cell in vitro. In contrast, the LOX products, 5-HETE and 12-HETE had mitogenic effects, stimulating the proliferation of both cell lines. These inhibitors also induced cytochrome c release, caspase-9 activation, as well as downstream caspase-3, caspase-7 activation, and PARP cleavage. LOX inhibitor treatment also reduced the levels of anti-apoptotic proteins Bcl-2 and Mcl-1 and increased the levels of the pro-apoptotic protein bax. In conclusion, blockade of both 5-LOX and 12-LOX pathways induces apoptosis in breast cancer cells through the cytochrome c release and caspase-9 activation, with changes in the levels of Bcl-2 family proteins.