Omega-3 fatty acid (omega-3 FA) consumption has long been associated with a lower incidence of colon, breast and prostate cancers in many human populations. Human trials have demonstrated omega-3 FA to have profound anti-inflammatory effects in those with cancer. In vitro and small animal studies have yielded a strong body of evidence establishing omega-3 FA as having anti-inflammatory, anti-apoptotic, anti-proliferative and anti-angiogenic effects. This review explores the evidence and the mechanisms by which omega-3 FA may act as angiogenesis inhibitors and identifies opportunities for original research trialling omega-3 FAs as anti-cancer agents in humans. The conclusions drawn from this review suggest that omega-3 FAs in particular eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) found principally in oily fish have potent anti-angiogenic effects inhibiting production of many important angiogenic mediators namely; Vascular Endothelial Growth Factor (VEGF), Platelet-Derived Growth Factor (PDGF), Platelet-Derived Endothelial Cell Growth Factor (PDECGF), cyclo-oxygenase 2 (COX-2), prostaglandin-E2 (PGE2), nitric oxide, Nuclear Factor Kappa Beta (NFKB), matrix metalloproteinases and beta-catenin.

OBJECTIVE

Epidemiologic studies suggest that fish oil, rich in n-3 polyunsaturated fatty acids (PUFA), possesses antitumor activity, whereas n-6 PUFAs may stimulate the development of cancers. The aim of this study was to evaluate the effects of n-6 and n-3 PUFAs on the growth of pancreatic cancer.

METHODS

The n-6 PUFA arachidonic acid (AA) stimulated the growth of cyclooxygenase (COX) 2 positive human pancreatic cancer (PaCa) cells, which was mediated by COX-2 generated prostaglandin E2 (PGE2) binding to EP2 and EP4 receptors. In contrast, the n-3 PUFA eicosapentaenoic acid decreased the growth of COX-2-positive and COX-2-negative PaCa cells. The COX-2-dependent mechanism of eicosapentaenoic acid was mediated by binding of PGE3 to EP2 and EP4 receptors. Dietary intake of n-3 PUFAs decreased the growth of pancreatic cancers in a xenograft model, which was accompanied by a decrease of PGE2 and an increase of PGE3 in the tumors.

CONCLUSIONS

Our studies provide evidence that n-3 PUFAs possess antitumor activities, whereas n-6 PUFAs stimulate pancreatic tumor growth. The opposite effects of n-3 and n-6 PUFAs are mediated by the formation of different prostaglandin species. n-3 PUFAs may prove beneficial as monotherapy or combination therapy with standard chemotherapeutic agents in pancreatic cancer patients.

We investigated the ability of fatty acids to induce growth inhibition and apoptosis in the human PaCa-44 pancreatic cancer cell line and the mechanism(s) underlying apoptosis. Butyric acid, alpha-linoleic acid, and docosahexaenoic acid (DHA) were supplemented at 200 microM concentration in the medium of cell cultures. Our results showed that all fatty acids inhibited cell growth, whereas only DHA induced cell apoptosis. An oxidative process was implicated in apoptosis induced by DHA because butylated hydroxytoluene and vitamin E prevented lipid peroxidation and reversed apoptosis. Intracellular and extracellular glutathione [reduced glutathione (GSH) and oxidized glutathione (GSSG)] concentrations were measured following DHA treatment in the presence or in the absence of GSH extrusion inhibitors such as cystathionine or methionine. DHA induced intracellular GSH depletion without affecting intracellular GSSG concentration and increased extracellular GSH and GSSG levels. Intracellular GSH depletion and extracellular GSH increase were both reversed by cystathionine. Inhibition of active GSH extrusion from the cell by cystathionine or methionine completely reversed lipid peroxidation and apoptosis. These data document the antiproliferative and apoptotic activities of DHA. The date provide evidence that intracellular GSH depletion represents an active extrusion process rather than a consequence of an oxidative stress, suggesting a causative role of GSH depletion in DHA-induced apoptosis.

BACKGROUND

Pancreatic cancer-gemcitabine (GEM) chemoresistance has been demonstrated to be associated with enhanced NF-kB activation and antiapoptotic protein synthesis. The well-known capacity of omega-3 fatty acids (n-3 FAs) to inhibit NF-kB activation and promote cellular apoptosis has the potential to restore or facilitate gemcitabine chemosensitivity.

METHODS

Four pancreatic cancer cell lines (MIA PaCa-2, BxPC-3, PANC-1, and L3.6), each with distinct basal NF-kB and differing GEM sensitivity profiles, were administered: 100 uM of (1) n-3FA, (2) n-6FA, (3) GEM, (4) n-3FA + GEM, or (5) n-6FA + GEM for 24 and 48 hours. Proliferation was assessed using the WST-1 assay. To define the mechanism(s) of altered proliferation, electron mobility shift assay for NF-kB activity, western blots of phoshoStat3, phosphoIkappaB, and poly(ADP-ribose) polymerase (PARP) cleavage were performed in the MIA PaCa-2 cell line.

RESULTS

All cell lines demonstrated a time/dose-dependent inhibition of proliferation in response to n-3FA. For MIA PaCa-2 cells, n-3FA and n-3FA + GEM treatment resulted in reduction of I-kB phosphorylation and NF-kB activation when compared with n-6FA control. n-3FA and combination treatment also significantly decreased Stat3 phosphorylation, whereas GEM alone had no effect. n-3FAs and n-3FA + GEM groups demonstrated increased PARP cleavage, mirroring NF-kB activity and Stat3 phosphorylation.

CONCLUSIONS

n-3 FA treatment is specifically associated with inhibition of proliferation in these four pancreatic cell lines irrespective of varied gemcitabine resistance. An experimental paradigm to screen for potential contributory mechanism(s) in altered pancreatic cancer cellular proliferation was defined, and using this approach the co-administration of n-3 FA with GEM inhibited GEM-induced NF-kB activation and restored apoptosis in the MIA PaCa-2 cell-line.

OBJECTIVE

Clinical studies have shown that administration of eicosapentaenoic acid (EPA) to patients who have unresectable pancreatic cancer induces marked attenuation of cachexia. However, the exact mechanisms of the beneficial effect of EPA on pancreatic cancer are unknown. This examined the effect of EPA on proliferation of human pancreatic cancer cell lines and sought to clarify its mechanisms.

METHODS

The effects of EPA on proliferation of three human pancreatic cancer cell lines (SW1990, AsPC-1, and PANC-1) were assessed. Induction of apoptosis and expressions of apoptosis-related proteins were measured. The effect of EPA on cyclo-oxygenase-2 expression in these cell lines was determined.

RESULTS

EPA inhibited proliferation of all three human pancreatic cancer cell lines in a dose-dependent fashion. Simultaneously, EPA treatment induced apoptosis and this was associated with caspase-3 activation. EPA treatment was also associated with a decrease in intracellular levels of cyclo-oxygenase-2 protein.

CONCLUSIONS

We have demonstrated that EPA inhibits human pancreatic cancer cell growth due at least in part to the induction of apoptotic cell death. Such apoptosis is associated with activation of caspase-3 and suppression of cyclo-oxygenase-2 expression. Greater understanding of the molecular events associated with the biological activity of EPA should enhance the therapeutic potential of administration of EPA to patients who have pancreatic cancer.

BACKGROUND

Laboratory and epidemiological studies have indicated that 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] and dietary omega 3 (omega3)-polyunsaturated fatty acids (PUFAs) are capable of inhibiting the proliferation of various cancer cells.

METHODS

Human hepatoblastoma cells (HepG2) were treated with 1alpha,25(OH)2D3 and fish oil alone and in combination. Cell proliferation was measured either by the uptake of [3H]-thymidine into DNA or by counting the cell numbers using a hemocytometer.

RESULTS

The HepG2 cell proliferation was inhibited by 1alpha,25(OH)2D3 and fish oil in a dose-dependent manner. The lowest effective concentration of 1alpha,25(OH)2D3 was 10(-7) M and 10(-8) M using the [3H]-thymidine incorporation method and the cell counting method, respectively. Fish oil also caused a significant inhibition in HepG2 cell proliferation at 25 microg/mL. When HepG2 cells were treated with 1alpha,25(OH)2D3 in combination with fish oil, it was found that fish oil increased the antiproliferative effect of 1alpha,25(OH)2D3 on HepG2 cell growth compared to treatment with 1alpha,25(OH)2D3 alone.

CONCLUSIONS

1alpha,25(OH)2D3 could be used to treat hepatocellular carcinoma (HCC). However, the major side-effect of hypercalcemia limits its use. An enhanced 1alpha,25(OH)2D3-induced inhibition of HepG2 cell proliferation in the presence of PUFAs in the form of fish oil suggests that a lower concentration of 1alpha,25(OH)2D3 could be used to treat hepatocellular carcinoma in the presence of PUFAs to decrease the risk of hypercalcemia caused by high concentrations of 1alpha,25(OH)2D3.

Oxidative stress is regarded as a major pathogenic factor in acute pancreatitis. Inflammation and apoptosis linked to oxidative stress has been implicated in cerulein-induced pancreatitis as an experimental model of acute pancreatitis. Recently, we found that reactive oxygen species mediate inflammatory cytokine expression and apoptosis of pancreatic acinar cells stimulated with cerulein. Omega-3 fatty acids show antioxidant action in various cells and tissues. In the present study, we investigated whether omega-3 fatty acids inhibit cytokine expression in cerulein-stimulated pancreatic acinar cells and whether omega-3 fatty acids suppress apoptotic cell death in pancreatic acinar cells exposed to hydrogen peroxide. We found that omega-3 fatty acids, such as docosahexaenoic acid (DHA) and alpha-linolenic acid (ALA), suppressed the expression of inflammatory cytokines (IL-1beta, IL-6) and inhibited the activation of transcription factor activator protein-1 in cerulein-stimulated pancreatic acinar cells. DHA and ALA inhibited DNA fragmentation, inhibited the decrease in cell viability, and inhibited the expression of apoptotic genes (p53, Bax, apoptosis-inducing factor) induced by hydrogen peroxide in pancreatic acinar cells. In conclusion, omega-3 fatty acids may be beneficial for preventing oxidative stress-induced pancreatic inflammation and apoptosis by inhibiting inflammatory cytokine and apoptotic gene expression of pancreatic acinar cells.

Patients with pancreatic cancer often experience a loss of weight and appetite, known as the anorexia-cachexia syndrome, which is associated with decreased quality of life and reduced survival. Research into the biological mechanisms of cachexia has demonstrated that an array of inflammatory mediators and tumor-derived factors cause appetite suppression, skeletal muscle proteolysis, and lipolysis,producing an overall hypercatabolic state that contributes to loss of fat and lean body mass. Omega-3 polyunsaturated fatty acids (n-3 PUFAs) have been shown to modulate levels of proinflammatory cytokines, hepatic acute phase proteins, eicosanoids, and tumor-derived factors in animal models of cancer and may reverse some aspects of the process of cachexia. Results of clinical trials of n-3 PUFAs in the form of fish oils have been mixed, but should encourage further investigation into dietary fish oil supplementation, including the most effective route of administration and the proper dosage to promote optimal weight maintenance and to limit side effects. Concerns about standardization and quality control should also be considered. With the current available evidence, a recommendation for the use of omega 3 polyunsaturated fatty acids in pancreatic cancer cachexia is premature.