5-Lipoxygenase, a Marker for Early Pancreatic Intraepithelial Neoplastic Lesions

Lipoxygenases at the Intersection of Infection and Carcinogenesis

The persisting presence of opportunistic pathogens like Pseudomonas aeruginosa poses a significant threat to many immunocompromised cancer patients with pulmonary infections. This review highlights the complexity of interactions in the host's defensive eicosanoid signaling network and its hijacking by pathogenic bacteria to their own advantage. Human lipoxygenases (ALOXs) and their mouse counterparts are integral elements of the innate immune system, mostly operating in the pro-inflammatory mode. Taking into account the indispensable role of inflammation in carcinogenesis, lipoxygenases have counteracting roles in this process. In addition to describing the structure-function of lipoxygenases in this review, we discuss their roles in such critical processes as cancer cell signaling, metastases, death of cancer and immune cells through ferroptosis, as well as the roles of ALOXs in carcinogenesis promoted by pathogenic infections. Finally, we discuss perspectives of novel oncotherapeutic approaches to harness lipoxygenase signaling in tumors.

Formyl Peptide Receptor 2-Dependent cPLA2 and 5-LOX Activation Requires a Functional NADPH Oxidase

Phospholipases (PL) A2 catalyzes the hydrolysis of membrane phospholipids and mostly generates arachidonic acid (AA). The enzyme 5-lipoxygenase (5-LOX) can metabolize AA to obtain inflammatory leukotrienes, whose biosynthesis highly depends on cPLA2 and 5-LOX activities. Formyl Peptide Receptor 2 (FPR2) belongs to a subfamily of class A GPCRs and is considered the most versatile FPRs isoform. Signaling triggered by FPR2 includes the activation of several downstream kinases and NADPH oxidase (NOX)-dependent ROS generation. In a metabolomic analysis we observed a significant increase in AA concentration in FPR2-stimulated lung cancer cell line CaLu-6. We analyzed cPLA2 phosphorylation and observed a time-dependent increase in cPLA2 Ser505 phosphorylation in FPR2-stimulated cells, which was prevented by the MEK inhibitor (PD098059) and the p38MAPK inhibitor (SB203580) and by blocking NOX function. Similarly, we demonstrated that phosphorylation of 5-LOX at Ser271 and Ser663 residues requires FPR2-dependent p38MAPK and ERKs activation. Moreover, we showed that 5-LOX Ser271 phosphorylation depends on a functional NOX expression. Our overall data demonstrate for the first time that FPR2-induced ERK- and p38MAPK-dependent phosphorylation/activation of cPLA2 and 5-LOX requires a functional NADPH oxidase. These findings represent an important step towards future novel therapeutic possibilities aimed at resolving the inflammatory processes underlying many human diseases.

The ALOX5 inhibitor Zileuton regulates tumor-associated macrophage M2 polarization by JAK/STAT and inhibits pancreatic cancer invasion and metastasis

5-lipoxygenase (encoded by ALOX5) plays an important role in immune regulation. Zileuton is currently the only approved ALOX5 inhibitor. However, the mechanisms of ALOX5 and Zileuton in progression of pancreatic cancer remain unclear. Therefore, we investigated the effects of Zileuton on tumor-associated macrophage M2 polarization and pancreatic cancer invasion and metastasis, both in vivo and in vitro. In bulk RNA sequencing (RNA-seq) and single-cell RNA sequencing (scRNA-seq) analyses, we found a significant association between elevated levels of ALOX5 and poor survival, adverse stages, M2 macrophage infiltration, and the activation of JAK/STAT pathways in macrophages. In clinical samples, immunofluorescence, quantitative real-time PCR and immunohistochemical results verified the high expression of ALOX5 in pancreatic cancer, primarily in macrophages. We constructed PANC-1 human pancreatic cancer cells and macrophages overexpressing ALOX5 using lentivirus. In PANC-1 pancreatic cancer cells, low-dose Zileuton inhibited PANC-1 cell invasion and migration by blocking ALOX5. In macrophages, ALOX5 induced the M2-like phenotype through the JAK/STAT pathway and promoted the chemotaxis of macrophages towards PANC-1 cells, while Zileuton can inhibit these effects. We constructed the nude mouse model of in situ transplantation tumor of pancreatic cancer. After treatment with Zileuton, the mice showed increased survival rates and reduced liver metastasis. These findings indicate that ALOX5 regulates tumor-associated macrophage M2 polarization via the JAK/STAT pathway and promotes invasion and metastasis in pancreatic cancer. Zileuton can inhibit these effects by inhibiting ALOX5. These results provide a theoretical basis for the potential use of Zileuton in the treatment of pancreatic cancer.

Carborane-Based Analog of Rev-5901 Attenuates Growth of Colon Carcinoma In Vivo

Lipoxygenases convert polyunsaturated fatty acids into biologically active metabolites such as inflammatory mediators—prostaglandins and leukotrienes. The inhibition of lipoxygenases is increasingly employed in the treatment of cancer. We evaluated the anticancer potential of two novel 5-lipoxygenase inhibitors, named CarbZDNaph and CarbZDChin, which are analogues of the commercially available inhibitor Rev-5901. The in vitro segment of this study was conducted on a mouse colorectal carcinoma cell line—CT26CL25. For an in vivo model, we induced tumors in BALB/c mice by the implantation of CT26CL25 cells, and we treated the animals with potential inhibitors. A 48 h treatment resulted in diminished cell viability. Calculated IC₅₀ values (half-maximal inhibitory concentrations) were 25 μM, 15 μM and 30 μM for CarbZDNaph, CarbZDChin and Rev-5901, respectively. The detailed analysis of mechanism revealed an induction of caspase-dependent apoptosis and autophagy. In the presence of chloroquine, an autophagy inhibitor, we observed an increased mortality of cells, implying a cytoprotective role of autophagy. Our in vivo experiment reports tumor growth attenuation in animals treated with CarbZDChin. Compounds CarbZDNaph and Rev-5901 lacked an in vivo efficacy. The results presented in this study display a strong effect of compound CarbZDChin on malignant cell growth. Having in mind the important role of inflammation in cancer development, these results have a significant impact and are worthy of further evaluation.

MicroRNA-146a promotes proliferation, migration, and invasion of HepG2 via regulating FLAP

Abnormal expression of 5-Lipoxygenase Activating Protein (FLAP) has been detected in many tumor cells. MicroRNAs (miRNAs) negatively regulate gene expression post-transcriptionally by binding to the 3'–untranslated region (3'–UTR) of the target mRNA sequences and have been shown to be involved in various types of cancers. Herein, we aimed to demonstrate the expression of miR-146a and FLAP in human HCC tissues and liver cancer cell lines. We demonstrated that miR-146a expression is overexpressed, while FLAP protein and mRNA are suppressed in hepatocellular carcinoma tissues and HepG2 cells compared to para-carcinoma tissues and HL–7702 cells. Dual luciferase reporter gene assay showed that miR-146a-5p can directly target FLAP mRNA. Knockdown of miR-146a also resulted in increased FLAP expression of cancer cells. Additionally, miR-146a silencing or restoration of FLAP led to a reduction of HepG2 cell proliferation, cell cycle progression, migration, and invasion. This study showed that miR-146a has a stimulatory role in HepG2 cells and promotes HepG2 cell migration and invasion by targeting FLAP mRNA. Thus, miR-146a may be a tumor promoter and a potential therapeutic target for the treatment of HCC patients.

Untangling the web of 5-lipoxygenase-derived products from a molecular and structural perspective: The battle between pro- and anti-inflammatory lipid mediators

Arachidonic acid (AA) is the precursor to leukotrienes (LT), potent mediators of the inflammatory response. In the 35 + years since cysteinyl-LTs were reported to mediate antigen-induced constriction of bronchi in tissue from asthma patients, numerous cellular responses evoked by the LTs, such as chemoattraction and G protein-coupled receptor (GPCR) activation, have been elucidated and revealed a potential for 5-lipoxygenase (5-LOX) as a promising drug target that goes beyond asthma. We describe herein early work identifying 5-LOX as the key enzyme that initiates LT biosynthesis and the discovery of its membrane-embedded helper protein required to execute the two-step reaction that transforms AA to the progenitor leukotriene A4 (LTA4). 5-LOX must traffic to the nuclear membrane to interact with its partner and undergo a conformational change so that AA can enter the active site. Additionally, the enzyme must retain the hydroperoxy-reaction intermediate for its final transformation to LTA4. Each of these steps provide a unique target for inhibition. Next, we describe the recent structures of GPCRs that recognize metabolites of the 5-LOX pathway and thus provide target alternatives. We also highlight the role of 5-LOX in the biosynthesis of anti-inflammatory lipid mediators (LM), the so-called specialized pro-resolving mediators (SPM). The involvement of 5-LOX in the biosynthesis of LM with opposing functions undoubtedly complicates the continuing search for 5-LOX inhibitors as therapeutic leads. Finally, we address the recent discovery of how some allosteric 5-LOX inhibitors promote oxygenation at the 12/15 carbon on AA to generate mediators that resolve, rather than promote, inflammation.

Computer-Aided Drug Design Applied to Secondary Metabolites as Anticancer Agents

Computer-Aided Drug Design (CADD) techniques have garnered a great deal of attention in academia and industry because of their great versatility, low costs, possibilities of cost reduction in in vitro screening and in the development of synthetic steps; these techniques are compared with highthroughput screening, in particular for candidate drugs. The secondary metabolism of plants and other organisms provide substantial amounts of new chemical structures, many of which have numerous biological and pharmacological properties for virtually every existing disease, including cancer. In oncology, compounds such as vimblastine, vincristine, taxol, podophyllotoxin, captothecin and cytarabine are examples of how important natural products enhance the cancer-fighting therapeutic arsenal. In this context, this review presents an update of Ligand-Based Drug Design and Structure-Based Drug Design techniques applied to flavonoids, alkaloids and coumarins in the search of new compounds or fragments that can be used in oncology. A systematical search using various databases was performed. The search was limited to articles published in the last 10 years. The great diversity of chemical structures (coumarin, flavonoids and alkaloids) with cancer properties, associated with infinite synthetic possibilities for obtaining analogous compounds, creates a huge chemical environment with potential to be explored, and creates a major difficulty, for screening studies to select compounds with more promising activity for a selected target. CADD techniques appear to be the least expensive and most efficient alternatives to perform virtual screening studies, aiming to selected compounds with better activity profiles and better "drugability".

Lipoxygenase Inhibitors as Cancer Chemopreventives: Discovery, Recent Developments and Future Perspectives

BACKGROUND

Leukotrienes (LTs) constitute a bioactive group of Polyunsaturated Fatty Acid (PUFA) metabolites molded by the enzymatic activity of lipoxygenase (LO) and have a pivotal role in inflammation and allergy. Evidence is accumulating both by in vitro cell culture experiments and animal tumor model studies in support of the direct involvement of aberrant metabolism of arachidonic acid (ACD) in the development of several types of human cancers such as lung, prostate, pancreatic and colorectal malignancies. Several independent experimental data suggest a correlation between tumoral cells viability and LO gene expression, especially, 5-lipoxygenase (5-LO). Overexpressed 5-LO cells live longer, proliferate faster, invade more effectively through extracellular matrix destruction and activate the anti-apoptotic signaling mechanisms more intensively compared to the normal counterparts. Thus, some groups of lipoxygenase inhibitors may be effective as promising chemopreventive agents.

METHODS

A structured search of bibliographic databases for peer-reviewed research literature regarding the role of LO in the pathogenesis of cancer was performed. The characteristics of screened papers were summarized and the latest advances focused on the discovery of new LO inhibitors as anticancer agents were discussed.

RESULTS

More than 180 papers were included and summarized in this review; the majority was about the newly designed and synthesized 5-LO inhibitors as anti-inflammatory and anticancer agents. The enzyme's structure, 5-LO pathway, 5-LO inhibitors structure-activity relationships as well as the correlation between these drugs and a number of most prevalent human cancers were described. In most cases, it has been emphasized that dual cyclooxygenase-2/5-lipoxygenase (COX-2/5-LO) or dual 5-lipoxygenase/microsomal prostaglandin E synthase-1 (5-LO/mPGES-1) inhibitors possess considerable inhibitory activities against their target enzymes as well as potent antiproliferative effects. Several papers disclosing 5-lipoxygenase activating protein (FLAP) antagonists as a new group of 5-LO activity regulators are also subject to this review. Also, the potential of 12-lipoxygenase (12- LO) and 15-lipoxygenase (15-LO) inhibitors as chemopreventive agents was outlined to expand the scope of new anticancer agents discovery. Some peptides and peptidomimetics with anti-LT activities were described as well. In addition, the cytotoxic effects of lipoxygenase inhibitors and their adverse effects were discussed and some novel series of natural-product-derived inhibitors of LO was also discussed in this review.

CONCLUSION

This review gives insights into the novel lipoxygenase inhibitors with anticancer activity as well as the different molecular pharmacological strategies to inhibit the enzyme effectively. The findings confirm that certain groups of LO inhibitors could act as promising chemopreventive agents.

Selective inhibition of stemness through EGFR/FOXA2/SOX9 axis reduces pancreatic cancer metastasis

Pancreatic cancer (PC) is difficult to defeat due to mechanism (s) driving metastasis and drug resistance. Cancer stemness is a major challenging phenomenon associated with PC metastasis and limiting therapy efficacy. In this study, we evaluated the pre-clinical and clinical significance of eradicating pancreatic cancer stem cells (PCSC) and its components using a pan-EGFR inhibitor afatinib in combination with gemcitabine. Afatinib in combination with gemcitabine, significantly reduced Kras^G12D/+; Pdx-1 Cre (KC) (P<0.01) and Kras^G12D/+; p53^R172H/+; Pdx-1 Cre (KPC) (P<0.05) derived mouse tumoroids and KPC-derived murine syngeneic cell line growth compared to gemcitabine/afatinib alone treatment. The drug combination also reduced PC xenograft tumor burden (P<0.05) and the incidence of metastasis by affecting key stemness markers, as confirmed by co-localization studies. Moreover, the drug combination significantly decreases the growth of various PC patient-derived organoids (P<0.001). We found that SOX9 is significantly overexpressed in high-grade PC tumors (P<0.05) and in chemotherapy-treated patients compared to chemo-naïve patients (P<0.05). These results were further validated using publicly available datasets. Moreover, afatinib alone or in combination with gemcitabine decreased stemness and tumorspheres by reducing phosphorylation of EGFR family proteins, ERK, FAK, and CSC markers. Mechanistically, afatinib treatment decreased CSC markers by downregulating SOX9 via FOXA2. Indeed, EGFR and FOXA2 depletion reduced SOX9 expression in PCSCs. Taken together, pan EGFR inhibition by afatinib impedes PCSCs growth and metastasis via the EGFR/ERK/FOXA2/SOX9 axis. This novel mechanism of panEGFR inhibitor and its ability to eradicate CSC may serve as a tailor-made approach to enhance chemotherapeutic benefits in other cancer types.

A cheminformatic study on chemical space characterization and diversity analysis of 5-LOX inhibitors

The process of blocking 5-lipoxygenase (5-LOX) catalyzed leukotriene biosynthesis has been recognized for the past few decades as a promising therapeutic strategy for acute inflammatory, allergic, and respiratory diseases. Due to the toxicity effect of FDA approved 5-LOX inhibitor zileuton, novel 5-LOX inhibitors have been sought by the scientific community. As a result, a significant and relevant amount of information on the structure-activity of 5-LOX inhibitors has been released and stored in public databases. In this study, we aimed at the comprehensive cheminformatic characterization of the diversity and complexity of the chemical space of 5-LOX inhibitors and its activating protein FLAP inhibitors by comparing it with the Approved drug space and virtual LOX library. The visual representation of the property space indicates some compounds in the 5-LOX inhibitors space broaden the traditional medicinal space. The structural diversity of the databases is computed using complementary approaches, including Physicochemical Property (PCP) descriptors, molecular fingerprints, and molecular scaffold. With the apparent exception of approved drugs, the 5-LOX dataset shows more diversity compared to FLAP and LOX virtual library set. This study was able to identify the underlying patterns in the chemical and pharmacological properties space that were decisive for the drug discovery and development of 5-LOX inhibitors.

Lipoxygenase-5 Expression in Canine Urinary Bladder: Normal Urothelium, Cystitis and Transitional Cell Carcinoma

Transitional cell carcinoma (TCC) is the most common canine urinary tract tumour and mimics human invasive TCC. Human TCCs overexpress lipoxygenase (LOX)-5 and the use of target inhibitors has proven effective in inhibiting neoplastic growth. In this study, we investigated the immunohistochemical expression of LOX-5 in normal canine urinary bladder, cystitis and TCC. The comparative expression of LOX-5, cyclo-oxygenase (COX)-1 and COX-2 among the three tissue groups was also examined. Biopsy samples from cases of cystitis and TCC were reviewed from 2012 to 2016; samples of histologically normal bladder were used as controls. Dogs were excluded if they had received glucocorticoids, non-steroidal anti-inflammatory drugs (NSAIDs) and/or chemotherapy prior to tissue collection. LOX-5 was expressed in 95% of TCCs, 23% of cases of cystitis and 10% of controls. LOX-5 and COX-2 immunohistochemistry scores were significantly (P <0.01) higher in TCCs versus cystitis and normal bladders. Results of this study support the rationale for further investigation of the use of NSAIDs with dual anti COX-2 and LOX-5 effect for the treatment of canine TCC.

QSAR classification-based virtual screening followed by molecular docking studies for identification of potential inhibitors of 5-lipoxygenase

Developments of novel inhibitors to prevent the function of 5-lipoxygenase (5-LOX) proteins that are responsible for a variety of inflammatory and allergic disease are a major challenge in the scientific community. In this study, robust QSAR classification models for predicting 5-LOX activity were developed using machine learning algorithms. The Support Vector Machines (SVM), Logistic Regression, k-Nearest Neighbour (NN) and Decision Trees were adopted to improve the prediction ability of the classification models. The most informative molecular descriptors that contribute to the prediction of 5-LOX activity are screened from e-Dragon, Ochem, PowerMV and Combined databases using Filter-based feature selection methods such as Correlation Feature Selection (CFS) and Information Gain (IG). Performances of the models were measured by 5-fold cross-validation and external test sets prediction. Evaluation of performance of feature selection revealed that the CFS method outperforms the IG method for all descriptor databases except for PowerMV database. The best ensemble classification model was obtained with the IG filtered 'PowerMV' descriptor database using kNN (k = 5) algorithm which displayed an overall accuracy of 76.6% for the training set and 77.9% for the test set. Finally, we employed this model as a virtual screening tool for identifying potential 5-LOX inhibitors from the e-Drug3D drug database and found 43 potential hit candidates. This top screened hits containing one known 5-LOX inhibitors zileuton as well as novel scaffolds. These compounds further screened by applying molecular docking simulation and identified four potential hits such as Belinostat, Masoprocol, Mefloquine and Sitagliptin having a comparable binding affinity to zileuton.

Frondanol, a Nutraceutical Extract from Cucumaria frondosa, Attenuates Colonic Inflammation in a DSS-Induced Colitis Model in Mice

Frondanol is a nutraceutical lipid extract of the intestine of the edible Atlantic sea cucumber, Cucumaria frondosa, with potent anti-inflammatory effects. In the current study, we investigated Frondanol as a putative anti-inflammatory compound in an experimental model of colonic inflammation. C57BL/6J male black mice (C57BL/6J) were given 3% dextran sodium sulfate (DSS) in drinking water for 7 days to induce colitis. The colitis group received oral Frondanol (100 mg/kg body weight/per day by gavage) and were compared with a control group and the DSS group. Disease activity index (DAI) and colon histology were scored for macroscopic and microscopic changes. Colonic tissue length, myeloperoxidase (MPO) concentration, neutrophil and macrophage marker mRNA, pro-inflammatory cytokine proteins, and their respective mRNAs were measured using ELISA and real-time RT-PCR. The tissue content of leukotriene B4 (LTB4) was also measured using ELISA. Frondanol significantly decreased the DAI and reduced the inflammation-associated changes in colon length as well as macroscopic and microscopic architecture of the colon. Changes in tissue MPO concentrations, neutrophil and macrophage mRNA expression (F4/80 and MIP-2), and pro-inflammatory cytokine content (IL-1β, IL-6 and TNF-α) both at the protein and mRNA level were significantly reduced by Frondanol. The increase in content of the pro-inflammatory mediator leukotriene B4 (LTB4) induced by DSS was also significantly inhibited by Frondanol. It was thus found that Frondanol supplementation attenuates colon inflammation through its potent anti-inflammatory activity.

Regulation of cell signaling pathways by dietary agents for cancer prevention and treatment

Although it is widely accepted that better food habits do play important role in cancer prevention and treatment, how dietary agents mediate their effects remains poorly understood. More than thousand different polyphenols have been identified from dietary plants. In this review, we discuss the underlying mechanism by which dietary agents can modulate a variety of cell-signaling pathways linked to cancer, including transcription factors, nuclear factor κB (NF-κB), signal transducer and activator of transcription 3 (STAT3), activator protein-1 (AP-1), β-catenin/Wnt, peroxisome proliferator activator receptor- gamma (PPAR-γ), Sonic Hedgehog, and nuclear factor erythroid 2 (Nrf2); growth factors receptors (EGFR, VEGFR, IGF1-R); protein Kinases (Ras/Raf, mTOR, PI3K, Bcr-abl and AMPK); and pro-inflammatory mediators (TNF-α, interleukins, COX-2, 5-LOX). In addition, modulation of proteasome and epigenetic changes by the dietary agents also play a major role in their ability to control cancer. Both in vitro and animal based studies support the role of dietary agents in cancer. The efficacy of dietary agents by clinical trials has also been reported. Importantly, natural agents are already in clinical trials against different kinds of cancer. Overall both in vitro and in vivo studies performed with dietary agents strongly support their role in cancer prevention. Thus, the famous quote "Let food be thy medicine and medicine be thy food" made by Hippocrates 25 centuries ago still holds good.

Cross-Talk between Cancer Cells and the Tumour Microenvironment: The Role of the 5-Lipoxygenase Pathway

5-lipoxygenase is an enzyme responsible for the synthesis of a range of bioactive lipids signalling molecules known collectively as eicosanoids. 5-lipoxygenase metabolites such as 5-hydroxyeicosatetraenoic acid (5-HETE) and a number of leukotrienes are mostly derived from arachidonic acid and have been shown to be lipid mediators of inflammation in different pathological states including cancer. Upregulated 5-lipoxygenase expression and metabolite production is found in a number of cancer types and has been shown to be associated with increased tumorigenesis. 5-lipoxygenase activity is present in a number of diverse cell types of the immune system and connective tissue. In this review, we discuss potential routes through which cancer cells may utilise the 5-lipoxygenase pathway to interact with the tumour microenvironment during the development and progression of a tumour. Furthermore, immune-derived 5-lipoxygenase signalling can drive both pro- and anti-tumour effects depending on the immune cell subtype and an overview of evidence for these opposing effects is presented.

[Inflammation and Cancer Development in Pancreatic and Biliary Tract Cancer]

Chronic inflammation has been known to be a risk for many kinds of cancers, including pancreatic and biliary tract cancer. Recently, inflammatory process has emerged as a key mediator of cancer development and progression. Many efforts with experimental results have been given to identify the underlying mechanisms that contribute to inflammation-induced tumorigenesis. Diverse inflammatory pathways have been investigated and inhibitors for inflammation-related signaling pathways have been developed for cancer treatment. This review will summarize recent outcomes about this distinctive process in pancreatic and biliary tract cancer. Taking this evidence into consideration, modulation of inflammatory process will provide useful options for pancreatic and biliary tract cancer treatment.

Molecular Targeted Intervention for Pancreatic Cancer

Pancreatic cancer (PC) remains one of the worst cancers, with almost uniform lethality. PC risk is associated with westernized diet, tobacco, alcohol, obesity, chronic pancreatitis, and family history of pancreatic cancer. New targeted agents and the use of various therapeutic combinations have yet to provide adequate treatments for patients with advanced cancer. To design better preventive and/or treatment strategies against PC, knowledge of PC pathogenesis at the molecular level is vital. With the advent of genetically modified animals, significant advances have been made in understanding the molecular biology and pathogenesis of PC. Currently, several clinical trials and preclinical evaluations are underway to investigate novel agents that target signaling defects in PC. An important consideration in evaluating novel drugs is determining whether an agent can reach the target in concentrations effective to treat the disease. Recently, we have reported evidence for chemoprevention of PC. Here, we provide a comprehensive review of current updates on molecularly targeted interventions, as well as dietary, phytochemical, immunoregulatory, and microenvironment-based approaches for the development of novel therapeutic and preventive regimens. Special attention is given to prevention and treatment in preclinical genetically engineered mouse studies and human clinical studies.

Anti-proliferative and pro-apoptotic effects of lichen-derived compound protolichesterinic acid are not mediated by its lipoxygenase-inhibitory activity

Lipoxygenases (LOXs) and their products are involved in several biological functions and have been associated with carcinogenesis. Protolichesterinic acid (PA), a lichen metabolite, inhibits 5- and 12-LOX and has anti-proliferative effects on various cancer cell lines. Here, PA was shown to inhibit proliferation of multiple myeloma cells, RPMI 8226 and U266, and pancreatic cancer cells AsPC-1. Apoptosis was induced only in multiple myeloma cells. Cell-cycle associated changes in expression and sub-cellular localization of 5- and 12-LOX were not affected by PA but increased cytoplasmic localisation was found to accompany morphological changes at later stages. Assessment by mass spectrometry showed that PA entered the pancreatic cancer cells. However, effects on LOX metabolites were only evident after treatment with concentrations exceeding those having anti-proliferative effects and no effects were measurable in the myeloma cells. We conclude that the anti-proliferative and pro-apoptotic effects of PA are not mediated directly through inhibition of LOX activity.

Involvement of eicosanoids in the pathogenesis of pancreatic cancer: The roles of cyclooxygenase-2 and 5-lipoxygenase

The interplay between inflammation and cancer progression is a growing area of research. A combination of clinical, epidemiological, and basic science investigations indicate that there is a relationship between inflammatory changes in the pancreas and neoplastic progression. Diets high in ω-6 polyunsaturated fatty acids provide increased substrate for arachidonic acid metabolism by cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) to form eicosanoids. These eicosanoids directly contribute to pancreatic cancer cell proliferation. Both COX-2 and 5-LOX are upregulated in multiple cancer types, including pancreatic cancer. In vitro studies using pancreatic cancer cell lines have demonstrated upregulation of COX-2 and 5-LOX at both the mRNA and protein levels. When COX-2 and 5-LOX are blocked via a variety of mechanisms, cancer cell proliferation is abrogated both in vitro and in vivo. The mechanism of COX-2 has been shown to include effects on apoptosis as well as angiogenesis. 5-LOX has been implicated in apoptosis. The use of COX-2 and 5-LOX inhibitors in clinical studies in patients with pancreatic cancer has been limited. Patient enrollment has been restricted to those with advanced disease which makes evaluation of these drugs as chemopreventive agents difficult. COX-2 and 5-LOX expression have been shown to be present during the early neoplastic changes of pancreatic cancer, well before progression to invasive disease. This indicates that the ideal role for these interventions is early in the disease process as preventive agents, perhaps in patients with chronic pancreatitis or hereditary pancreatitis.

Inflammation, Cancer and Oxidative Lipoxygenase Activity are Intimately Linked

Cancer and inflammation are intimately linked due to specific oxidative processes in the tumor microenvironment. Lipoxygenases are a versatile class of oxidative enzymes involved in arachidonic acid metabolism. An increasing number of arachidonic acid metabolites is being discovered and apart from their classically recognized pro-inflammatory effects, anti-inflammatory effects are also being described in recent years. Interestingly, these lipid mediators are involved in activation of pro-inflammatory signal transduction pathways such as the nuclear factor κB (NF-κB) pathway, which illustrates the intimate link between lipid signaling and transcription factor activation. The identification of the role of arachidonic acid metabolites in several inflammatory diseases led to a significant drug discovery effort around arachidonic acid metabolizing enzymes. However, to date success in this area has been limited. This might be attributed to the lack of selectivity of the developed inhibitors and to a lack of detailed understanding of the functional roles of arachidonic acid metabolites in inflammatory responses and cancer. This calls for a more detailed investigation of the activity of arachidonic acid metabolizing enzymes and development of more selective inhibitors.

The role of inflammation in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease with an extremely poor prognosis. Inflammatory processes have emerged as key mediators of pancreatic cancer development and progression. In genetically engineered mouse models, induction of pancreatitis accelerates PDAC development, and patients with chronic pancreatitis are known to have a higher risk of developing pancreatic cancer. In recent years, much effort has been given to identify the underlying mechanisms that contribute to inflammation-induced tumorigenesis. Many inflammatory pathways have been identified and inhibitors have been developed in order to prevent cancer development and progression. In this chapter, we discuss the role of inflammatory pathways in the initiation and progression of pancreatic cancer as well as the role of inhibitors used in treatment and prevention of pancreatic cancer.

Targeted chiral analysis of bioactive arachidonic Acid metabolites using liquid-chromatography-mass spectrometry

A complex structurally diverse series of eicosanoids arises from the metabolism of arachidonic acid. The metabolic profile is further complicated by the enantioselectivity of eicosanoid formation and the variety of regioisomers that arise. In order to investigate the metabolism of arachidonic acid in vitro or in vivo, targeted methods are advantageous in order to distinguish between the complex isomeric mixtures that can arise by different metabolic pathways. Over the last several years this targeted approach has become more popular, although there are still relatively few examples where chiral targeted approaches have been employed to directly analyze complex enantiomeric mixtures. To efficiently conduct targeted eicosanoid analyses, LC separations are coupled with collision induced dissociation (CID) and tandem mass spectrometry (MS/MS). Product ion profiles are often diagnostic for particular regioisomers. The highest sensitivity that can be achieved involves the use of selected reaction monitoring/mass spectrometry (SRM/MS); whereas the highest specificity is obtained with an SRM transitions between an intense parent ion, which contains the intact molecule (M) and a structurally significant product ion. This review article provides an overview of arachidonic acid metabolism and targeted chiral methods that have been utilized for the analysis of the structurally diverse eicosanoids that arise.

Inflammation and cancer

There is evidence supporting the hypothesis that inflammation participates in providing conditions that lead to cancer. An unresolved inflammation due to any failure in the precise control of the immune response can continue to perturb the cellular microenvironment, thereby leading to alterations in cancer-related genes and posttranslational modification in crucial cellular proteins involved in the cell cycle, DNA repair and apoptosis. In addition, there are data indicating that inflammatory cells and immunomodulatory mediators present in the tumor microenvironment influence tumor progression and metastasis. Historically, tumor-infiltrating leukocytes have been considered to be manifestations of an intrinsic defence mechanism against developing tumors. However, increasing evidence indicates that leukocyte infiltration can promote tumor phenotypes, such as angiogenesis, growth and invasion. This may be due to inflammatory cells that probably can influence cancer promotion by secreting cytokines, growth factors, chemokines and proteases, which stimulate proliferation and invasiveness of cancer cells. Consequently, events and molecules implicated in this cross talk between the tumor microenvironment and inflammatory process may emerge as attractive targets in anticancer therapeutic interventions with significant clinical impact.

Multifaceted link between cancer and inflammation

Increasing evidence from epidemiological, preclinical and clinical studies suggests that dysregulated inflammatory response plays a pivotal role in a multitude of chronic ailments including cancer. The molecular mechanism(s) by which chronic inflammation drives cancer initiation and promotion include increased production of pro-inflammatory mediators, such as cytokines, chemokines, reactive oxygen intermediates, increased expression of oncogenes, COX-2 (cyclo-oxygenase-2), 5-LOX (5-lipoxygenase) and MMPs (matrix metalloproteinases), and pro-inflammatory transcription factors such as NF-κB (nuclear factor κB), STAT3 (signal transducer and activator of transcription 3), AP-1 (activator protein 1) and HIF-1α (hypoxia-inducible factor 1α) that mediate tumour cell proliferation, transformation, metastasis, survival, invasion, angiogenesis, chemoresistance and radioresistance. These inflammation-associated molecules are activated by a number of environmental and lifestyle-related factors including infectious agents, tobacco, stress, diet, obesity and alcohol, which together are thought to drive as much as 90% of all cancers. The present review will focus primarily on the role of various inflammatory intermediates responsible for tumour initiation and progression, and discuss in detail the critical link between inflammation and cancer.

Prevalence of 5-lipoxygenase expression in canine osteosarcoma and the effects of a dual 5-lipoxygenase/cyclooxygenase inhibitor on osteosarcoma cells in vitro and in vivo

Canine osteosarcoma is an insidious disease with few effective treatment modalities; therefore, use of pharmacologic intervention to improve mortality or morbidity is constantly sought. The use of cyclooxygenase enzyme inhibitors has been an area of interest with limited efficacy based on retrospective examination of tumor expression and in vivo cell proliferation models. Recently, examination of dual cyclooxygenase and 5-lipoxygenase inhibitors in human and canine oncology suggests that 5-lipoxygenase inhibitors may be an effective approach in vitro and during tumor induction in rodent models. Therefore, the authors decided to examine 5-lipoxygenase expression in primary canine osteosarcoma samples and have shown that approximately 65% of osteosarcomas label positive for cytoplasmic 5-lipoxygenase. Further examination of a cell culture and xenograft model shows similar 5-lipoxygenase expression. Surprisingly, a canine 5-lipoxygenase inhibitor (tepoxalin) significantly reduced cell proliferation at physiologic doses in vitro and diminished xenograft tumor growth in nude mice, suggesting that further investigation is needed. Traditionally, 5-lipoxygense leads to production of lipid mediators, such as leukotriene B(4) and 5-oxo-eicosatetraenoic acid, which, when added back to the media of tepoxalin-treated cells, did not recover cell proliferation. The lack of nuclear staining in primary and xenografted tumors and the lack of response to eicoasanoids suggest that lipid mediator production is not the primary means by which tepoxalin acts to alter proliferation. Regardless of the mechanisms involved in retarding cell proliferation, future investigation is warranted.

Cancer cell signaling pathways targeted by spice-derived nutraceuticals

Extensive research within the last half a century has revealed that cancer is caused by dysregulation of as many as 500 different gene products. Most natural products target multiple gene products and thus are ideally suited for prevention and treatment of various chronic diseases, including cancer. Dietary agents such as spices have been used extensively in the Eastern world for a variety of ailments for millennia, and five centuries ago they took a golden journey to the Western world. Various spice-derived nutraceuticals, including 1'-acetoxychavicol acetate, anethole, capsaicin, cardamonin, curcumin, dibenzoylmethane, diosgenin, eugenol, gambogic acid, gingerol, thymoquinone, ursolic acid, xanthohumol, and zerumbone derived from galangal, anise, red chili, black cardamom, turmeric, licorice, fenugreek, clove, kokum, ginger, black cumin, rosemary, hop, and pinecone ginger, respectively, are the focus of this review. The modulation of various transcription factors, growth factors, protein kinases, and inflammatory mediators by these spice-derived nutraceuticals are described. The anticancer potential through the modulation of various targets is also the subject of this review. Although they have always been used to improve taste and color and as a preservative, they are now also used for prevention and treatment of a wide variety of chronic inflammatory diseases, including cancer.

Enhancing antitumor effects in pancreatic cancer cells by combined use of COX-2 and 5-LOX inhibitors

Cyclooxygenase (COX)-2 and lipoxygenase (LOX)-5 are involved in carcinogenesis of pancreatic cancer. COX-2 inhibitor celecoxib displays inhibitory effects in pancreatic cancer cell growth. Recently, it has been reported that COX-2 inhibitor may not be able to suppress pancreatic tumor growth in vivo and its application is further limited by untoward side effects. The present study provides evidence that combined use of celecoxib and 5-LOX inhibitor MK886 markedly suppresses pancreatic tumor cell growth in vitro. Compared to the single inhibitor treatment, dual treatment with celecoxib and MK886 exerted additive antitumor effects in pancreatic tumor cells. We found that MK886 reversed celecoxib-induced increases in 5-LOX gene expression and Erk1/2 activation in pancreatic tumor cells. Moreover, Dual treatment of pancreatic tumor cells with celecoxib and MK886 inhibited the levels of LBT4 receptor BLT1 and vascular endothelial growth factor. Our results imply that combined use of celecoxib and MK886 might be an effective way to treat clinical patients with pancreatic cancer.

Dual inhibition of 5-LOX and COX-2 suppresses esophageal squamous cell carcinoma

COX-2 and 5-LOX are up-regulated in ESCC. This study aims to determine the efficacy of COX-2 inhibitor, 5-LOX inhibitor and their combination on ESCC. Nimesulide can suppress cell growth and promote apoptosis, accompanied with a decrease of PGE(2) production. AA861 has the similar effect with a down-regulation of LTB(4). In animal experiment, the tumor volumes in drug-treated groups were significantly smaller with the lowest rates of Ki-67 positive cells. In conclusion, either COX-2 inhibitor or 5-LOX inhibitor can suppress ESCC. Dual inhibition of COX-2 and 5-LOX pathway may present a superior anticancer efficacy to either inhibition of COX-2 or 5-LOX alone.

Experimental animal models of pancreatic carcinogenesis for prevention studies and their relevance to human disease

Pancreatic cancer is difficult to cure, so its prevention is very important. For this purpose, animal model studies are necessary to develop effective methods. Injection of N-nitrosobis(2-oxopropyl)amine (BOP) into Syrian golden hamsters is known to induce pancreatic ductal adenocarcinomas, the histology of which is similar to human tumors. Moreover, K-ras activation by point mutations and p16 inactivation by aberrant methylation of 5' CpG islands or by homozygous deletions have been frequently observed in common in both the hamster and humans. Thus, this chemical carcinogenesis model has an advantage of histopathological and genetic similarity to human pancreatic cancer, and it is useful to study promotive and suppressive factors. Syrian golden hamsters are in a hyperlipidemic state even under normal dietary conditions, and a ligand of peroxizome proliferator-activated receptor gamma was found to improve the hyperlipidemia and suppress pancreatic carcinogenesis. Chronic inflammation is a known important risk factor, and selective inhibitors of inducible nitric oxide synthase and cyclooxygenase-2 also have protective effects against pancreatic cancer development. Anti-inflammatory and anti-hyperlipidemic agents can thus be considered candidate chemopreventive agents deserving more attention.

Mast cell 5-lipoxygenase activity promotes intestinal polyposis in APCDelta468 mice

Arachidonic acid metabolism has been implicated in colon carcinogenesis, but the role of hematopoietic 5-lipoxygenase (5LO) that may impact tumor immunity in development of colon cancer has not been explored. Here we show that tissue-specific deletion of the 5LO gene in hematopoietic cells profoundly attenuates polyp development in the APC(Δ468) murine model of colon polyposis. In vitro analyses indicated that mast cells in particular utilized 5LO to limit proliferation of intestinal epithelial cells and to mobilize myeloid-derived suppressor cells (MDSCs). Mice lacking hemapoietic expression of 5LO exhibited reduced recruitment of MDSCs to the spleen, mesenteric lymph nodes, and primary tumor site. 5LO deficiency also reduced the activity in MDSCs of arginase-1, which is thought to be critical for MDSC function. Together, our results establish a pro-tumorigenic role of hematopoietic 5LO in the immune microenvironment and suggest 5LO inhibition as an avenue for future investigation in treatment of colorectal polyposis and cancer.

5-Lipoxygenase inhibitors induce potent anti-proliferative and cytotoxic effects in human tumour cells independently of suppression of 5-lipoxygenase activity

BACKGROUND AND PURPOSE

Certain 5-lipoxygenase (5-LO) inhibitors exhibit anti-carcinogenic activities against 5-LO overexpressing tumour types and cultured tumour cells. It has been proposed therefore that 5-LO products significantly contribute to tumour cell proliferation. To date, the relationship between the inhibitory mechanisms of 5-LO inhibitors, which vary widely, and tumour cell viability has not been evaluated. This study addresses the anti-proliferative and cytotoxic potency of a number of 5-LO inhibitors with different inhibitory mechanisms in 5-LO-positive and 5-LO-negative tumour cells.

EXPERIMENTAL APPROACH

Cell viability was measured by the WST-1 assay; cell proliferation was assessed using the bromodeoxyuridine (BrdU) incorporation assay. Cell death was analysed by annexin V staining, Western blot analysis of PARP (poly ADP-ribose polymerase) cleavage and a cytotoxicity assay. 5-LO product formation was quantified by a 5-LO activity assay.

KEY RESULTS

The common 5-LO inhibitors AA-861, Rev-5901 and MK-886 induced cytotoxic and anti-proliferative effects in 5-LO-positive Capan-2 pancreatic cancer cells; BWA4C and CJ-13,610 only caused anti-proliferative effects, while zileuton failed to impair cell viability. Moreover, the concentrations of the 5-LO inhibitors required to induce anti-proliferation and cytotoxicity highly exceeded those for suppression of 5-LO. Supplementation with mitogenic 5-LO products failed to protect Capan-2 cells from the effects of 5-LO inhibitors. Finally, the cytotoxic and anti-proliferative 5-LO inhibitors also potently reduced the viability of 5-LO-deficient tumour cell lines (HeLa, Panc-1 and U937).

CONCLUSIONS AND IMPLICATIONS

Certain 5-LO inhibitors cause cytotoxic and anti-proliferative effects independently of suppression of 5-LO activity. Thus, the role of 5-LO overexpression in tumour cell viability remains unclear and requires further elucidation.

Deploying mouse models of pancreatic cancer for chemoprevention studies

With the advent of mouse models that recapitulate the cellular and molecular pathology of pancreatic neoplasia and cancer, it is now feasible to recruit and deploy these models for the evaluation of various chemopreventive and/or anticancer regimens. The highly lethal nature of pancreatic ductal adenocarcinoma (PDAC) makes multiple areas of research a priority, including assessment of compounds that prevent or suppress the development of early lesions that can transform into PDAC. Currently, there are over a dozen models available, which range from homogeneous preneoplastic lesions with remarkable similarity to human pancreatic intraepithelial neoplasms to models with a more heterogeneous population of lesions including cystic papillary and mucinous lesions. The molecular features of these models may also vary in a manner comparable with the differences observed in lesion morphology, and so, navigating the route of model selection is not trivial. Yet, arming the community of cancer investigators with a repertoire of models and the guidance to select relevant models that fit their research themes promises to produce findings that will have clinical relevance.

Inflammation and cancer: how friendly is the relationship for cancer patients?

Evidence has emerged in the last two decades that at the molecular level most chronic diseases, including cancer, are caused by a dysregulated inflammatory response. The identification of transcription factors such as NF-kappaB, AP-1 and STAT3 and their gene products such as tumor necrosis factor, interleukin-1, interleukin-6, chemokines, cyclooxygenase-2, 5 lipooxygenase, matrix metalloproteases, and vascular endothelial growth factor, adhesion molecules and others have provided the molecular basis for the role of inflammation in cancer. These inflammatory pathways are activated by tobacco, stress, dietary agents, obesity, alcohol, infectious agents, irradiation, and environmental stimuli, which together account for as much as 95% of all cancers. These pathways have been implicated in transformation, survival, proliferation, invasion, angiogenesis, metastasis, chemoresistance, and radioresistance of cancer, so much so that survival and proliferation of most types of cancer stem cells themselves appear to be dependent on the activation of these inflammatory pathways. Most of this evidence, however, is from preclinical studies. Whether these pathways have any role in prevention, progression, diagnosis, prognosis, recurrence or treatment of cancer in patients, is the topic of discussion of this review. We present evidence that inhibitors of inflammatory biomarkers may have a role in both prevention and treatment of cancer.

Prevention and treatment of pancreatic cancer by curcumin in combination with omega-3 fatty acids

Pancreatic cancer BxPC-3 cells were exposed to curcumin, docosahexaenoic acid (DHA), or combinations of both and analyzed for proliferation and apoptosis. Pancreatic tumor xenografts were established by injecting BxPC-3 cells into each flank of nude mice. After the tumors reached a size of approximately 190-200 mm(3), animals were fed diets with or without 2,000 ppm curcumin in 18% corn oil or 15% fish oil + 3% corn oil for 6 more wk before assessing the tumor volume and expression of inducible nitric oxide synthase (iNOS), cyclooxygeanse-2 (COX-2), 5-lipoxinase (5-LOX), and p21. A synergistic effect was observed on induction of apoptosis (approximately sixfold) and inhibition of cell proliferation (approximately 70%) when cells were treated with curcumin (5 microM) together with the DHA (25 microM). Mice fed fish oil and curcumin showed a significantly reduced tumor volume, 25% (P < 0.04) and 43% (P < 0.005), respectively, and importantly, a combination of curcumin and fish oil diet showed > 72% (P < 0.0001) tumor volume reduction. Expression and activity of iNOS, COX-2, and 5-LOX are downregulated, and p21 is upregulated in tumor xenograft fed curcumin combined with fish oil diet when compared to individual diets. The preceding results evidence for the first time that curcumin combined with omega-3 fatty acids provide synergistic pancreatic tumor inhibitory properties.

The Role of PPARgamma Receptors and Leukotriene B(4) Receptors in Mediating the Effects of LY293111 in Pancreatic Cancer

Pancreatic cancer is a devastating disease in which current therapies are inadequate. Separate lines of research have identified the 5-lipoxygenase/leukotriene B(4) receptor pathway and the PPARgamma pathway as potential targets for prevention or treatment of this disease. LY293111 was originally designed as a potent leukotriene B(4) receptor antagonist for treatment of inflammatory conditions. LY293111 was also known to have inhibitory effects on 5-lipoxygenase, which is upstream of the production of leukotrienes. LY293111 was shown to have potent anticancer effects in pancreatic cancer and several other solid malignancies, where it caused cell cycle arrest and marked apoptosis. Subsequently, it came to light that LY293111 exhibited PPARgamma agonist activity in addition to its effects on the 5-lipoxygenase pathway. This raises the question of which of the two targets is of greatest importance with regard to the anticancer effects of this agent. The evidence to date is not conclusive, but suggests that the effects of LY293111 may be mediated by both LTB(4) receptors and PPARgamma.

5-lipoxygenase and 5-lipoxygenase-activating protein gene polymorphisms, dietary linoleic acid, and risk for breast cancer

The n-6 polyunsaturated fatty acid 5-lipoxygenase pathway has been shown to play a role in the carcinogenesis of breast cancer. We conducted a population-based case-control study among Latina, African-American, and White women from the San Francisco Bay area to examine the association of the 5-lipoxygenase gene (ALOX5) and 5-lipoxygenase-activating protein gene (ALOX5AP) with breast cancer risk. Three ALOX5AP polymorphisms [poly(A) microsatellite, -4900 A>G (rs4076128), and -3472 A>G (rs4073259)] and three ALOX5 polymorphisms [Sp1-binding site (-GGGCGG-) variable number of tandem repeat polymorphism, -1279 G>T (rs6593482), and 760 G>A (rs2228065)] were genotyped in 802 cases and 888 controls. We did not find significant main effects of ALOX5 and ALOX5AP genotypes on breast cancer risk that were consistent across race or ethnicity; however, there was a significant interaction between the ALOX5AP -4900 A>G polymorphism and dietary linoleic acid intake (P=0.03). Among women consuming a diet high in linoleic acid (top quartile of intake, >17.4 g/d), carrying the AA genotype was associated with higher breast cancer risk (age- and race-adjusted odds ratio, 1.8; 95% confidence interval, 1.2-2.9) compared with carrying genotypes AG or GG. Among women consuming <or=17.4 g/d of linoleic acid, ALOX5AP -4900 genotype was not associated with breast cancer risk (age- and race-adjusted odds ratio, 0.9; 95% confidence interval, 0.7-1.2). These results support a role for n-6 polyunsaturated fatty acids in breast carcinogenesis and suggest that epidemiologic studies on dietary fat and breast cancer should take into account genetic predisposition related to n-6 polyunsaturated fatty acid metabolism.

Triptolide suppresses 5-lipoxygenase metabolic pathway and induces apoptosis in pancreatic tumor cell lines

AIM: To investigate the effects and the mechanism of triptolide (TL) on proliferation and apoptosis of pancreatic cancer in vitro.

METHODS: Pancreatic tumor cell lines PANC-1, ASPC-1 and SW1990 were treated with different concentrations of TL for 24 h and then, cell death was determined by Typan Blue Staining. Annexin V/PI double staining was performed to evaluate TL-induced apoptosis using flow cytometry. The expression of 5-lipoxygenase (5-LOX) and concentration of its downstream product LTB₄ were determined by real time PCR, Western blot and ELISA. 5-LOX cDNA stable transfected SW1990 cells were established successfully. After treatment with TL, it was examined for overexpression of 5-LOX on TL-induced apoptosis.

RESULTS: TL induced prominent growth inhibition and apoptosis in human pancreatic cancer cell lines. After treatment at 50 μg/L, the cell viability was 70.5% ± 6.8%, 61.2% ± 5.6% and 52.8% ± 5.3% of PANC-1, ASPC-1 and SW1990, respectively, which were significantly decreased compared with control group (P < 0.05). The apoptosis at 12 h evaluated by AnnexinV positive cells increased in TL-treated group compared with control group (24.2 ± 3.23 vs 9.5 ± 2.18, P < 0.05). TL significantly down-regulated 5-LOX expression in these cell lines and decreased LTB₄ concentration in supernatant (P < 0.01, compared with control group). Furthermore, overexpression of 5-LOX in SW1990 cells made them more resistant to TL induced apoptosis, significantly inhibited the TL mediated cell death and apoptosis (P < 0.01 or 0.05, compared with control group).

CONCLUSION: Inhibition of 5-LOX pathway of arachidonic acid metabolism is associated with TL's anti-proliferation and pro-apoptotic activity. It also provides evidence that TL has clinic therapeutic value for patients with pancreatic cancer.

Expression of enzymes and receptors of the leukotriene pathway in human neuroblastoma promotes tumor survival and provides a target for therapy

The metabolism of arachidonic acid by the cyclooxygenase (COX) or lipoxygenase (LO) pathways generates eicosanoids that have been implicated in the pathogenesis of a variety of human diseases, including cancer. In this study, we examined the expression and significance of components within the 5-LO pathway in human neuroblastoma, an embryonal tumor of the sympathetic nervous system. High expression of 5-LO, 5-LO-activating protein (FLAP), leukotriene A(4) hydrolase, leukotriene C(4) synthase, and leukotriene receptors was detected in a majority of primary neuroblastoma tumors and all cell lines investigated. Expression of 5-LO and FLAP was evident in tumor cells but not in nonmalignant adrenal medulla where neuroblastomas typically arise. Moreover, neuroblastoma cells produce leukotrienes, and stimulation of neuroblastoma cells with leukotrienes increased neuroblastoma cell viability. Inhibitors of 5-LO (AA-861), FLAP (MK-886), or the leukotriene receptor antagonist montelukast inhibited neuroblastoma cell growth by induction of G(1)-cell cycle arrest and apoptosis. Similarly, specific 5-LO and leukotriene receptor silencing by small interfering RNA decreased neuroblastoma cell growth. These findings provide new insights into the pathobiology of neuroblastoma, and the use of leukotriene pathway inhibitors as a novel adjuvant therapy for children with neuroblastoma warrants further consideration.

Lycopene in cancer prevention and treatment

Dietary intake of lycopene is inversely associated with the risk of many cancers. Preclinical studies show that lycopene has potent in vitro and in vivo antitumor effects, suggesting potential preventive and therapeutic roles for the compound. However, clinical trials with lycopene have only recently been started, and available clinical data preclude firm conclusions with regard to its use in cancer prevention and treatment. Further mechanistic studies and randomized controlled clinical intervention trials with lycopene involving cancer patients are warranted.

Molecular markers and targets for colorectal cancer prevention

Colorectal cancer is the third most prevalent cancer in the world. If detected at an early stage, treatment often might lead to cure. As prevention is better than cure, epidemiological studies reveal that having a healthy diet often protects from promoting/ developing cancer. An important consideration in evaluating new drugs and devices is determining whether a product can effectively treat a targeted disease. There are quite a number of biomarkers making their way into clinical trials and few are awaiting the preclinical efficacy and safety results to enter into clinical trials. Researchers are facing challenges in modifying trial design and defining the right control population, validating biomarker assays from the biological and analytical perspective and using biomarker data as a guideline for decision making. In spite of following all guidelines, the results are disappointing from many of the large clinical trials. To avoid these disappointments, selection of biomarkers and its target drug needs to be evaluated in appropriate animal models for its toxicities and efficacies. The focus of this review is on the few of the potential molecular targets and their biomarkers in colorectal cancers. Strengths and limitations of biomarkers/surrogate endpoints are also discussed. Various pathways involved in tumor cells and the specific agents to target the altered molecular biomarker in biomolecular pathway are elucidated. Importance of emerging new platforms siRNAs and miRNAs technology for colorectal cancer therapeutics is reviewed.