Lipoxygenase inhibition in prostate cancer

Inflammation factors and element supplementation in cancer

The aim of the study was to evaluate the effect of dietary supplementation with chosen minerals (Zn, Se, Fe) on expression of selected cytokines (IL-1, IL-6, TNFα) in spleen of rats and on their concentrations in rat serum under inflammatory and pathological conditions obtained by implantation of prostate cancer cells (LnCaP). Serum levels of metabolites of arachidonic, eicosapentaenoic and linoleic acids (hydroxyeicosatetraenoic, hydroxyeicosapentaenoic and hydroxyoctadecadienoic acids, respectively), as compounds involved in inflammation and cancer development, were also investigated. Male rats were randomised into dietary groups supplemented with Zn, Se or Fe. Prostate cancer cells were implanted to some rats in each group. The study demonstrated that minerals supplemented with the diet may exert various effects on an organism. Selenium, zinc and iron influence pro-inflammatory cytokine expression, what leads to stimulation of inflammation. They also affect synthesis of arachidonic and linoleic acid metabolites that exert pro-inflammatory action and enable cancer development and metastasis.

A new treatment for severe pulmonary arterial hypertension based on an old idea: inhibition of 5-lipoxygenase

It has been generally accepted that severe forms of pulmonary arterial hypertension are associated with inflammation. Plasma levels in patients with severe pulmonary arterial hypertension show elevated levels of interleukins and mediators of inflammation and histologically the diseased small pulmonary arterioles show infiltrates of inflammatory and immune cells. Here, we review the literature that connects pulmonary hypertension with the arachidonic acid/5-lipoxygenase-derived leukotriens. This mostly preclinical background data together with the availability of 5-lipoxygenase inhibitors and leukotriene receptor blockers provide the rationale for testing the hypothesis that 5-lipoxygenase products contribute to the pathobiology of severe pulmonary arterial hypertension in a subgroup of patients.

Redox circuitries driving Src regulation

SIGNIFICANCE

Here, we review recent advances with regard to the role of Src kinase in the regulation of cytoskeleton organization, cell adhesion, and motility, focusing on redox circuitries engaging this kinase for anchorage and motility, control of cell survival to anoikis, as well as metabolic deregulation, all features belonging to the new hallmarks of cancer.

RECENT ADVANCES

Several recent insights have reported that, alongside the well-known phosphorylation/dephosphorylation control, cysteine oxidation is a further mechanism of enzyme activation for both c-Src kinase and its oncogenic counterparts. Indeed, mounting evidence portrays redox regulation of Src kinase as a compulsory outcome in growth factors/cytokines signaling, integrin engagement, motility and invasiveness of tissues, receptor cross-talking at plasmamembrane, as well as during carcinogenesis and progression toward tumor malignancy or fibrotic disease. In addition, the kinase is an upstream regulator of NADPH oxidase-driven oxidants, a critical step for invadopodia formation and metastatic spread.

CRITICAL ISSUES

Not satisfactorily unraveled yet, the exact role of Src kinase in redox cancer biology needs to be implemented with studies that are aimed at clarifying (i) the exact hierarchy between oxidants sources, Src redox-dependent activation and the regulation of cell motility, and (ii) the actual susceptibility of invading cells to redox-based treatments, owing to the well-recognized ability of cancer cells to find new strategies to adapt to new environments.

FUTURE DIRECTIONS

Once these critical issues are addressed, redox circuitries involving Src kinase should potentially be used as both biomarkers and targets for personalized therapies in the fight against cancer or fibrotic diseases.

Targeting 20-HETE producing enzymes in cancer - rationale, pharmacology, and clinical potential

Studies demonstrate that lipid mediator 20-Hydroxyeicosatetraenoic acid (20-HETE) synthesis and signaling are associated with the growth of cancer cells in vitro and in vivo. Stable 20-HETE agonists promote the proliferation of cancer cells, whereas selective inhibitors of the 20-HETE-producing enzymes of the Cytochrome (CYP450)4A and CYP4F families can block the proliferation of glioblastoma, prostate, renal cell carcinoma, and breast cancer cell lines. A recent observation that the expression of CYP4A/4F genes was markedly elevated in thyroid, breast, colon, and ovarian cancer further highlights the significance of 20-HETE-producing enzymes in the progression of different types of human cancer. These findings provide the rationale for targeting 20-HETE-producing enzymes in human cancers and set the basis for the development of novel therapeutic strategies for anticancer treatment.

Regulation of inflammation in cancer by eicosanoids

Inflammation in the tumor microenvironment is now recognized as one of the hallmarks of cancer. Endogenously produced lipid autacoids, locally acting small molecule lipid mediators, play a central role in inflammation and tissue homeostasis, and have recently been implicated in cancer. A well-studied group of autacoid mediators that are the products of arachidonic acid metabolism include: the prostaglandins, leukotrienes, lipoxins and cytochrome P450 (CYP) derived bioactive products. These lipid mediators are collectively referred to as eicosanoids and are generated by distinct enzymatic systems initiated by cyclooxygenases (COX 1 and 2), lipoxygenases (5-LOX, 12-LOX, 15-LOXa, 15-LOXb), and cytochrome P450s, respectively. These pathways are the target of approved drugs for the treatment of inflammation, pain, asthma, allergies, and cardiovascular disorders. Beyond their potent anti-inflammatory and anti-cancer effects, non-steroidal anti-inflammatory drugs (NSAIDs) and COX-2 specific inhibitors have been evaluated in both preclinical tumor models and clinical trials. Eicosanoid biosynthesis and actions can also be directly influenced by nutrients in the diet, as evidenced by the emerging role of omega-3 fatty acids in cancer prevention and treatment. Most research dedicated to using eicosanoids to inhibit tumor-associated inflammation has focused on the COX and LOX pathways. Novel experimental approaches that demonstrate the anti-tumor effects of inhibiting cancer-associated inflammation currently include: eicosanoid receptor antagonism, overexpression of eicosanoid metabolizing enzymes, and the use of endogenous anti-inflammatory lipid mediators. Here we review the actions of eicosanoids on inflammation in the context of tumorigenesis. Eicosanoids may represent a missing link between inflammation and cancer and thus could serve as therapeutic target(s) for inhibiting tumor growth.

Dietary fatty acid quality affects AR and PPARgamma levels and prostate growth

BACKGROUND

Fatty acids are among the most important nutritional factors associated with the ethiopathogenesis of prostate cancer, therefore the main objective of this work was to evaluate the effect of quality of fatty acid on the rat ventral prostate growth, tissue organization, and expression of androgen receptor (AR) and peroxisome proliferation activator receptor gamma (PPARgamma).

METHODS

Wistar rats were distributed into five groups, which were fed isocaloric normolipidic diets containing soybean oil (7% Control), linseed (7% or 3.5% linseed plus 3.5% soybean oil) and rendered pork fat (7% or 3.5% lard plus 3.5% soybean oil) for 10 weeks after weaning.

RESULTS

At the end of treatment, the experiments demonstrated that lard and linseed oil caused opposite effects on prostatic growth. While the lard promoted an increase in prostatic weight associated to epithelial hyperplasia (confirmed by stereology); the linseed resulted in a significantly lighter organ. Immunohistochemistry and Western blotting demonstrated increased expression of AR and PPARgamma in groups fed with lard diet, while linseed oil promoted a decrease.

CONCLUSIONS

Prostatic growth is influenced by dietary fatty acids with concurrent variation in the expression of AR and PPARgamma. PPARgamma might represent the link between diet and prostate growth and AR expression and function. Since the levels of testosterone were altered it is also possible that prostatic changes are secondary to systemic effects of the diet.

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.

Roles of Eicosanoids in Prostate Cancer

Eicosanoids, the metabolites of arachidonic acid, have diverse functions in the regulation of cancer including prostate cancer. This review will provide an overview of the roles of eicosanoids and endocannabinoids and their potential as therapeutic targets for prostate cancer treatment.

Molecular modeling of the non-covalent binding of the dietary tomato carotenoids lycopene and lycophyll, and selected oxidative metabolites with 5-lipoxygenase

Numerous studies on human prostate cancer cell lines indicate a role for arachidonic acid (AA) and its oxidative metabolites in prostate cancer proliferation. The metabolism of AA by either the cyclooxygenase (COX) or the lipoxygenase (LOX) pathways generates eicosanoids involved in tumor promotion, progression, and metastasis. In particular, products of the 5-LOX pathway (including 5-HETE and 5-oxo-EET) have been implicated as potential 'survival factors' that may confer escape after androgen withdrawal therapy through fatty-acid (i.e., AA) drive. Potent natural dietary antioxidant compounds such as lycopene and lycophyll, with tissue tropism for human prostate, have been shown to be effective in ameliorating generalized oxidative stress at the DNA level. Suppressing the 5-LOX axis pharmacologically is also a promising avenue for intervention in human patients. The recently recognized direct interaction of the astaxanthin-based soft-drug Cardax to human 5-LOX with molecular modeling, and the downregulation of both 5-HETE and 5-oxo-EET in vivo in a murine peritonitis model, suggest that other important dietary carotenoids may share this enzyme regulatory feature. In the current study, the acyclic tomato carotene lycopene (in all-trans and 5-cis isomeric configurations) and its natural dihydroxy analog lycophyll (also present in tomato fruit) were subjected to molecular modeling calculations in order to investigate their predicted binding interaction(s) with human 5-LOX. Two bioactive oxidative metabolites of lycopene (4-methyl-8-oxo-2,4,6-nonatrienal and 2,7,11-trimethyl-tetradecahexaene-1,14-dial) were also investigated. A homology model of 5-LOX was constructed using 8-LOX and 15-LOX structures as templates. The model was validated by calculating the binding energy of Cardax to 5-LOX, which was demonstrated to be in good agreement with the published experimental data. Blind docking calculations were carried out in order to explore the possible binding sites of the carotenoids on 5-LOX, followed by focused docking to more accurately calculate the predicted energy of binding. Lycopene and lycophyll were predicted to bind with high affinity in the superficial cleft at the interface of the beta-barrel and the catalytic domain of 5-LOX (the 'cleavage site'). Carotenoid binding at this cleavage site provides the structural rationale by which polyenic compounds could modify the 5-LOX enzymatic function via an allosteric mechanism, or by radical scavenging in proximity to the active center. In addition, the two bioactive metabolites of lycopene were predicted to bind to the catalytic site with high affinity--therefore suggesting potential direct competitive inhibition of 5-LOX activity that should be shared by both lycopene and lycophyll after in vivo supplementation, particularly in the case of the dial metabolite.

Therapeutic options for 5-lipoxygenase inhibitors

5-Lipoxygenase (5-LO) catalyzes the conversion of arachidonic acid (AA) into leukotriene (LT) A(4) and 5-hydroperoxyeicosatetraenoic acid. LTA(4) can then be converted into LTB(4) by LTA(4) hydrolase or into LTC(4) by LTC(4) synthase and the LTC(4) synthase isoenzymes MGST2 and MGST3. LTB(4) is a potent chemoattractant for neutrophils, eosinophils and monocytes leading to adherence of phagocytes to vessel walls, neutrophil degranulation and release of superoxide anions. LTC(4) and its metabolite, LTD(4), are potent bronchoconstrictors that increase vascular permeability and stimulate mucus secretion from airways. Recent data also suggest that LT have an immunomodulatory role. Due to these properties, the increased biosynthesis of LT in asthma, and based upon clinical data obtained with CysLT(1) receptor antagonists in asthma patients, there is a consensus that CysLT play a prominent role in asthma. In this review, we summarize the knowledge on possible functions of the 5-LO pathway in various diseases like asthma, cancer and cardiovascular events and review the corresponding potential therapeutic roles of 5-LO inhibitors.

The effects of oral Cardax (disodium disuccinate astaxanthin) on multiple independent oxidative stress markers in a mouse peritoneal inflammation model: influence on 5-lipoxygenase in vitro and in vivo

Disodium disuccinate astaxanthin ('rac'-dAST; Cardax) is a water-dispersible C40 carotenoid derivative under development for oral and parenteral administration for cardioprotection of the at-risk ischemic cardiovascular patient. In experimental infarction models in animals (rats, rabbits, and dogs), significant myocardial salvage has been obtained, up to 100% at the appropriate dose in dogs. The documented mechanism of action in vitro includes direct scavenging of biologically produced superoxide anion; in vivo in rabbits, modulation of the complement activity of serum has also been shown. A direct correlation between administration of the test compound in animals and reductions of multiple, independent markers of oxidative stress in serum was recently obtained in a rat experimental infarction model. For the current study, it was hypothesized that oral Cardax administration would inhibit oxidative damage of multiple relevant biological targets in a representative, well-characterized murine peritoneal inflammation model. A previously developed mass spectrometry-based (LC/ESI/MS/MS) approach was used to interrogate multiple distinct pathways of oxidation in a black mouse (C57/BL6) model system. In vivo markers of oxidant stress from peritoneal lavage samples (supernatants) were evaluated in mice on day eight (8) after treatment with either Cardax or vehicle (lipophilic emulsion without drug) orally by gavage at 500 mg/kg once per day for seven (7) days at five (5) time points: (1) baseline prior to treatment (t=0); (2) 16 h following intraperitoneal (i.p.) injection with thioglycollate to elicit a neutrophilic infiltrate; (3) 4 h following i.p. injection of yeast cell wall (zymosan; t=16 h/4 h thioglycollate+zymosan); (4) 72 h following i.p. injection with thioglycollate to elicit monocyte/macrophage infiltration; and (5) 72 h/4 h thioglycollate+zymosan. A statistically significant sparing effect on the arachidonic acid (AA) and linoleic acid (LA) substrates was observed at time points two and five. When normalized to the concentration of the oxidative substrates, statistically significant reductions of 8-isoprostane-F(2alpha) (8-iso-F(2alpha)) at time point three (maximal neutrophil recruitment/activation), and 5-HETE, 5-oxo-EET, 11-HETE, 9-HODE, and PGF(2alpha) at time point five (maximal monocyte/macrophage recruitment/activation) were observed. Subsequently, the direct interaction of the optically inactive stereoisomer of Cardax (meso-dAST) with human 5-lipoxygenase (5-LOX) was evaluated in vitro with circular dichroism (CD) and electronic absorption (UV/Vis) spectroscopy, and subsequent molecular docking calculations were made using mammalian 15-LOX as a surrogate (for which XRC data has been reported). The results suggested that the meso-compound was capable of interaction with, and binding to, the solvent-exposed surface of the enzyme. These preliminary studies provide the foundation for more detailed evaluation of the therapeutic effects of this compound on the 5-LOX enzyme, important in chronic diseases such as atherosclerosis, asthma, and prostate cancer in humans.

Effects of selective COX-2 and 5-LOX inhibition on prostaglandin and leukotriene synthesis in ductal pancreatic cancer in Syrian hamster

Selective inhibition of eicosanoid synthesis seems to decrease carcinogenesis, however, the effect on liver metastasis in pancreatic cancer is still unknown. Ductal pancreatic adenocarcinoma was chemically induced by weekly injection of N-nitrosobis-2-oxopropylamine (BOP) in Syrian hamster. Animals received selective inhibition of cyclooxygenase-2 (Celebrex) and 5-lipoxygenase (Zyflo). In week 33, hamsters were sacrificed and incidence of pancreatic carcinomas as well as liver metastases were examined. Furthermore, size and number of liver metastases per animal were determined and concentration of PGF1alpha, PGE2 and leukotrienes was measured in hepatic and pancreatic tissue. Combined therapy (Celebrex+Zyflo) significantly decreased incidence, number and size of liver metastases. Furthermore extra- and intrametastatic concentration of PGE2 was reduced by this treatment in hepatic tissue. Single Cox-2-inhibition (Celebrex) decreased intrametastatic hepatic PGF1alpha and PGE2 concentration while PGF1alpha concentration was reduced in non-metastatic liver (nml). Moreover 5-LOX-inhibition (Zyflo) decreased intrametastatic PGE2 concentration as well as PGF1alpha and PGE2 in nml. In pancreatic carcinomas highest LT-concentration was found after combined treatment and this therapy group was the only one revealing a significantly higher amount of LTs in carcinomas compared to tumour-free tissue. Hepatic LT-concentration was significantly lower in the control groups than in nml of the tumour groups. Combination of Cox-2-inhibition and 5-Lox-inhibition might be a suitable adjuvant therapy to prevent liver metastasis in human ductal pancreatic adenocarcinoma.

Oxidative stress and cyclooxygenase activity in prostate carcinogenesis: targets for chemopreventive strategies

Over the last decade, epidemiological, experimental and clinical studies have implicated oxidative stress in the development and progression of prostate cancer. Oxidative stress may be linked to the effects of androgens, anti-oxidant systems and the pre-malignant condition, high-grade prostatic intraepithelial neoplasia. Cyclooxygenase-2 activity has been linked with prostate carcinogenesis. Evidence suggests that oxidative stress and cyclo-oxygenase-2 activity may be mechanistically linked. Agents such as anti-oxidants and cyclo-oxgenase-2 inhibitors may be of value in the chemoprevention of prostate cancer. The feasibility of intervention with such agents will depend on the development and validation of biomarkers for clinical trials, particularly markers of oxidative damage caused by reactive oxygen species (ROS). A greater understanding of the molecular events associated with oxidative stress will enhance the development of such biomarkers and should result in better strategies for the chemoprevention of prostate cancer.

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.

Multiple signal pathways are involved in the mitogenic effect of 5(S)-HETE in human pancreatic cancer

Pancreatic carcinoma is characterized by poor prognosis and lack of response to conventional therapy. The reasons for this are not fully understood. We have reported that inhibition of 5-lipoxygenase abolished proliferation and induced apoptosis in pancreatic cancer cells while the 5-lipoxygenase metabolite, 5(S)-hydroxyeicosatetraenoic acid [5(S)-HETE] stimulated pancreatic cancer cell proliferation. The current study was designed to investigate the underlying mechanisms for 5(S)-HETE-stimulated proliferation of pancreatic cells. Two human pancreatic cancer cell lines, PANC-1 and HPAF, were used. Cell proliferation was monitored by thymidine incorporation and cell counting. Phosphorylation of P42/44(MAPK) (mitogen activated protein kinase, ERK), MEK (MAPK/ERK kinase), P38 kinase, JNK/SAPK (c-Jun N-terminal kinase/ stress-activated protein kinase), AKT and tyrosine residues of intracellular proteins was measured by Western blot using their corresponding phospho-specific antibodies. The results showed that (1) 5(S)-HETE markedly stimulated pancreatic cancer cell proliferation in a time- and concentration-dependent manner; (2) 5(S)-HETE induced tyrosine phosphorylation of multiple intracellular proteins while the tyrosine kinase inhibitor, genestein, blocked 5(S)-HETE-stimulated cell proliferation; (3) 5(S)-HETE significantly stimulated both MEK and P42/44(MAPK) phosphorylation and the MEK inhibitors, PD098059 and U0126, inhibited 5(S)-HETE-stimulated proliferation in these two cell lines; (4) 5(S)-HETE also stimulated P38 kinase phosphorylation but the P38 inhibitor, SB203580, did not effect 5(S)-HETE-stimulated cell proliferation; (5) 5(S)-HETE markedly stimulated AKT phosphorylation while the phosphatidylinositide-3 (PI3)-kinase inhibitor, wortmannin, blocked 5(S)-HETE-stimulated cell proliferation; (6) phosphorylation of JNK/SAPK was not induced by 5(S)-HETE, and (7) the general protein kinase C (PKC) inhibitor, GF109203X, did not affect 5(S)-HETE-stimulated cancer cell proliferation. These findings suggest that intracellular tyrosine kinases, MEK/ERK and PI3 kinase/AKT pathways are involved in 5(S)-HETE-stimulated pancreatic cancer cell proliferation but P38 kinase, JNK/SAPK and PKC are not involved in this mitogenic effect.

Nuclear prostaglandin receptors: role in pregnancy and parturition?

The key regulatory role of prostanoids [prostaglandins (PGs) and thromboxanes (TXs)] in the maintenance of pregnancy and initiation of parturition has been established. However, our understanding of how these events are fine-tuned by the recruitment of specific signaling pathways remains unclear. Whereas, initial thoughts were that PGs were lipophilic and would easily cross cell membranes without specific receptors or transport processes, it has since been realized that PG signaling occurs via specific cell surface G-protein coupled receptors (GPCRs) coupled to classical adenylate cyclase or inositol phosphate signaling pathways. Furthermore, specific PG transporters have been identified and cloned adding a further level of complexity to the regulation of paracrine action of these potent bioactive molecules. It is now apparent that PGs also activate nuclear receptors, opening the possibility of novel intracrine signaling mechanisms. The existence of intracrine signaling pathways is further supported by accumulating evidence linking the perinuclear localization of PG synthesizing enzymes with intracellular PG synthesis. This review will focus on the evidence for a role of nuclear actions of PGs in the regulation of pregnancy and parturition.

New advances on prostate carcinogenesis and therapies: involvement of EGF-EGFR transduction system

The prostate cancers (PCs) are among the major causes of death because therapeutic treatments are not effective against advanced and metastatic forms of this cellular hyperproliferative disorder. In fact, although androgen-deprivation therapies permit to cure localized PC forms, the metastatic PC cells have acquired multiple functional features that confer to them resistance to ionizing radiations and anticarcinogenic drugs currently used in therapy. The present review describes last advances on molecular mechanisms that might be responsible for sustained growth and survival of PC cells. In particular, emphasis is on intracellular signaling cascades which are involved in the mitogenic and antiapoptotic effects of epidermal growth factor EGF-EGFR system. Of therapeutic interest, recent advances and prospects for development of new treatments against incurable forms of metastatic PC forms are also discussed.

Effects of Celebrex and Zyflo on BOP-induced pancreatic cancer in Syrian hamsters

BACKGROUND/AIMS

Selective inhibition of eicosanoid synthesis decreases inflammation, however, it is still unknown whether oxidative stress and carcinogenesis might be influenced in ductal pancreatic ductal cancer as well.

METHODS

120 male hamsters were randomized into 8 groups (n = 15). While control group 1-4 received 0.5 ml normal saline s.c. weekly for 16 weeks, groups 5-8 were injected 10 mg BOP/kg body weight to induce pancreatic cancer. After establishment of pancreatic cancer, groups 1 and 5 received no therapy, groups 2 and 6 were fed 7 mg Celebrex daily, groups 3 and 7 were given 28 mg Zyflo and groups 4 and 8 received Celebrex and Zyflo orally daily in weeks 17-32. In week 33, all animals were sacrificed, macroscopic size of pancreatic carcinomas was measured, incidence of pancreatic cancer was analyzed histopathologically and activities of antioxidative enzymes and concentration of products of lipid peroxidation in tumor-free and pancreatic intratumoral tissue were determined.

RESULTS

Incidence and size of macroscopic pancreatic carcinomas were decreased by single therapy with Zyflo as well as combined therapy (Zyflo + Celebrex). Activities of antioxidative enzymes were increased and the concentration of products of lipid peroxidation was decreased in tumor-free pancreas. On the other hand, lipid peroxidation was increased in pancreatic tumors.

CONCLUSION

Zyflo alone or in combination with Celebrex reduce tumor growth in pancreatic cancer and thus might be a new therapeutic option in advanced pancreatic cancer.

Cyclooxygenases and lipoxygenases as potential targets for treatment of pancreatic cancer

Pancreatic adenocarcinoma is characterized by poor prognosis, late diagnosis and lack of response to conventional therapies. The incidence of this disease shows no sign of declining in the Western world. Thus, new targets need to be identified for pancreatic cancer treatment. In particular, new chemotherapeutic agents would be extremely beneficial for control of unresectable cancer and metastatic lesions as well as for prevention of this deadly disease. Mounting evidence suggests that both lipoxygenases (LOXs) and cyclooxygenases (COXs), the key enzymes for arachidonic acid metabolism, have a profound influence on the development and progression of several human cancers. Recent evidence suggests that both COX and LOX pathways are important in pancreatic cancer. Results from immunocytochemical, RT-PCR, and Western blotting studies have shown that COX, specifically COX-2, is upregulated in human pancreatic cancer cell lines as well as human pancreatic cancer tissues compared with normal ductal cells and normal pancreas specimens. Agents that block COX enzymes significantly inhibit pancreatic cancer growth both in vitro and in vivo, in parallel with induction of apoptosis. Expression of both 5-LOX and 12-LOX is also seen in pancreatic cancer, although compared to the expression of COX this has not been extensively investigated. Chemical inhibitors or antisense oligonucleotides that block either 5-LOX or 12-LOX cause marked inhibition of pancreatic cancer cell proliferation. On the other hand, LOX metabolites stimulate growth of the tumor cells and reverse LOX-inhibitor-induced growth inhibition, suggesting the specific role of LOX in regulating pancreatic cancer cell proliferation. Although questions still need to be answered, such as the underlying mechanisms for COX and LOX-induced growth inhibition, both COX and LOX pathways are potential targets for pancreatic cancer treatment and chemoprevention. COX and LOX enzyme inhibitors are available and have been shown to be relatively safe in the treatment of other diseases.

5-Lipoxygenase and leukotriene B(4) receptor are expressed in human pancreatic cancers but not in pancreatic ducts in normal tissue

The 5-lipoxygenase (5-LOX) pathway is critical for pancreatic cancer cell growth and escape from apoptosis. Inhibition of 5-LOX blocks proliferation and induces apoptosis in human pancreatic cancer cells. However, the expression of 5-LOX and its downstream signaling pathway have not been investigated in human pancreatic adenocarcinoma. Reverse transcriptase-polymerase chain reaction revealed expression of 5-LOX mRNA in all pancreatic cancer cell lines tested including, PANC-1, AsPC-1, and MiaPaCa2 cells, but not in normal pancreatic ductal cells. The expression of 5-LOX protein in pancreatic cancer cell lines was demonstrated by Western blotting. Finally, 5-LOX up-regulation in human pancreatic cancer tissues was verified by intense positive staining in cancer cells by immunohistochemistry. Staining for the 5-LOX protein was particularly evident in the ductal components of the more differentiated tumors but not in ductal cells in normal pancreatic tissues from cadaver donors. Immunohistochemistry also revealed strong staining of cancer tissues with an antibody to the receptor of the downstream 5-LOX metabolite, leukotriene B(4). The current study demonstrated marked expression of 5-LOX and the leukotriene B(4) receptor in human pancreatic cancer tissues. These findings provide further evidence of up-regulation of this pathway in pancreatic cancer and that LOX inhibitors are likely to be valuable in the treatment of this dreadful disease.

Prostate cancer vs hyperplasia: relationships with prostatic and adipose tissue fatty acid composition

The objective of the present study was to study whether adipose tissue and prostatic tissue fatty acid composition differentiates between prostate cancer and benign hyperplasia patients. In addition, the present investigation aimed at exploring the extent to which prostatic tissue fatty acid composition differentiates between prostate-confined cancer and extraprostatic disease including possible metastasis. The subjects were 71 male patients from the island of Crete. Half the patients (n=35) had been diagnosed with benign hyperplasia of the prostate, half with prostatic malignancy (n=36). Patients were examined at the outpatient clinic of the urology unit, University Hospital, Medical School, University of Crete. Relative to benign hyperplasia patients, cancer patients had elevated adipose tissue saturated and reduced monounsaturated fatty acid levels. Cancer patients had reduced prostate tissue stearic to oleic acid ratios and stearic acid levels as opposed to hyperplasia patients. The most pronounced difference between cancer patients and hyperplasia patients was a 3-fold elevated prostatic palmitoleic acid in the former group. Relative to benign hyperplasia patients, cancer patients had reduced prostate tissue arachidonic and docosahexaenoic acid levels. Finally, there was a significantly reduced omega-3/omega-6 polyunsaturated fatty acid ratio in the prostate cancer patient as opposed to the benign hyperplasia group. The pronounced elevations in prostatic tissue palmitoleic acid in cancer patients highlight a possible role of this fatty acid in neoplastic processes. The decreased arachidonic acid levels in cancer patients possibly stem from enhanced metabolism of arachidonic acid via lipoxygenase and cyclooxygenase pathways, and the formation of derivatives such as 5-HETE, 15-HETE, 12(S)-HETE and PGE(2).

5-Lipoxygenase is required for proliferation of immature cerebellar granule neurons in vitro

Primary cultures of rat cerebellar granule neurons express 5-lipoxygenase, an enzyme from the inflammatory pathway of arachidonic acid. Outside the central nervous system (CNS) 5-lipoxygenase participates in cell proliferation. We hypothesized that 5-lipoxygenase is needed for proliferation of immature cerebellar granule neurons. Using cultures prepared from 7-day-old rat pups, we confirmed in vitro neurogenesis by immunocytolabeling with 2-bromo-5-deoxyuridine and beta-tubulin isotype III and quantified the rate of cell proliferation by assaying [3H]thymidine incorporation. We found that immature cerebellar granule neurons express large amounts of 5-lipoxygenase, and that treatment with a 5-lipoxygenase antisense, to reduce expression of this gene, decreased significantly (by 60%) the content of 5-lipoxygenase protein and effectively reduced cell proliferation. [3H]thymidine incorporation was significantly reduced by each of the three 5-lipoxygenase inhibitors we tested: AA-861 [2-(12-hydroxydodeca-5, 10-diynyl)-3,5,6-trimethyl-1,4-benzoquinone], MK-886 (C(27)H(33)ClNO(2)S.Na), and L-655,238 [alpha-penyl-3-(2-quinolinylmethoxy)-benzenemethanol]. Their anti-proliferative effect was reversible. We propose that neuronal expression of 5-lipoxygenase is crucial for neurogenesis in vitro, and possibly also in vivo.

5-HETE congeners as modulators of cell proliferation

The synthesis and assessment of the mitogenic properties of 5-HETE congeners are reported. These studies represent an effort to develop a structure-activity profile for ligands of the 5-HETE/5-oxoETE G-protein coupled receptor(s). Many of these agents possess mitogenic activity that equals or exceeds that of racemic 5-HETE family constituents in prostate cancer cell lines.

Potential use of lipoxygenase inhibitors for cancer chemoprevention

Increasing evidence suggests that lipoxygenase (LO)-catalysed metabolites have a profound influence on the development and progression of human cancers. Compared with normal tissues, significantly elevated levels of LO products have been found in breast tumours, colon cancers, lung, skin and prostate cancers, as well as in cells from patients with both acute and chronic leukaemias. LO-mediated products elicit diverse biological activities needed for neoplastic cell growth, influencing growth factor and transcription factor activation, oncogene induction, stimulation of tumour cell adhesion and regulation of apoptotic cell death. Agents that block LO catalytic activity may be effective in preventing cancer by interfering with signalling events needed for tumour growth. In the past ten years, pharmaceuticals agents that specifically inhibit the 5-LO metabolic pathway have been developed to treat inflammatory diseases such as asthma, arthritis and psoriasis. Some of these compounds possess anti-oxidant properties and may be effective in preventing cancer by blocking free radical-induced genetic damage or by preventing the metabolic activation of carcinogens. Other compounds may work by negatively modulating DNA synthesis. Pharmacological profiles of potential chemopreventive agents are compiled from enzyme assays, in vitro testing (e.g., cell proliferation inhibition in human cancer cells) and in vivo animal carcinogenesis models (e.g., N-methyl-N-nitrosourea-induced rat mammary cancer, benzo(a)pyrene-induced lung tumours in strain A/J mice and hormone-induced prostate tumours in rats). In this way, compounds are identified for chemoprevention trials in human subjects. Based on currently available data, it is expected that the prevention of lung and prostate cancer will be initially studied in human trials of LO inhibitors.