Buckminster Farrow

Inflammation and the development of pancreatic cancer.

OBJECTIVE Pancreatic cancer has an extremely poor prognosis and the cellular mechanisms contributing to pancreatic cancer are relatively unknown. The goals of this review are to present the epidemiological and experimental data that supports inflammation as a key mediator of pancreatic cancer development, to explain how inflammatory pathways may create an environment that supports tumor formation, and to discuss how the use of novel agents directed at these pathways may be used for the treatment of pancreatic malignancy. SUMMARY BACKGROUND DATA Inflammation has been identified as a significant factor in the development of other solid tumor malignancies. Both hereditary and sporadic forms of chronic pancreatitis are associated with an increased risk of developing pancreatic cancer. The combined increase in genomic damage and cellular proliferation, both of which are seen with inflammation, strongly favors malignant transformation of pancreatic cells. Cytokines, reactive oxygen species, and mediators of the inflammatory pathway (e.g., NF-kappaB and COX-2) have been shown to increase cell cycling, cause loss of tumor suppressor function, and stimulate oncogene expression; all of which may lead to pancreatic malignancy. Anti-cytokine vaccines, inhibitors of pro-inflammatory NF-kappaB and COX-2 pathways, thiazolidinediones, and anti-oxidants are potentially useful for the prevention or treatment of pancreatic cancer. Redirection of experimental interests toward pancreatic inflammation and mechanisms of carcinogenesis may identify other novel anti-inflammatory agents or other ways to screen for or prevent pancreatic cancer. CONCLUSION Pancreatic inflammation, mediated by cytokines, reactive oxygen species, and upregulated pro-inflammatory pathways, may play a key role in the early development of pancreatic malignancy.

Inflammatory mechanisms contributing to pancreatic cancer development.

Objective:Pancreatic cancer is the most deadly of all gastrointestinal (GI) malignancies, yet relatively little is known regarding mechanisms of tumor development including the role of inflammation. Summary Background Data:Chronic pancreatitis (CP) increases the risk of developing cancer by 10- to 20-fold; mediators of the chronic inflammatory process and the surrounding fibrotic stroma likely support a transformation to malignancy, yet the exact mechanisms remain undefined. The purpose of our present study was to determine potential inflammatory components in epithelial and stromal cells that may contribute to both CP and pancreatic cancers. Methods:Specimens of normal pancreas, CP, and pancreatic cancer were examined using laser-capture microdissection (LCM), gene array, and immunohistochemistry. Results:Gene array analysis from LCM-dissected tissues demonstrated: (i) increased expression of interleukin-8 (IL-8), an activator of the inflammatory factor nuclear factor-κB (NF-κB), and (ii) decreased expression of IκB (an inhibitor of NF-κB) in CP ductal cells compared with normal ducts. Compared with CP, cancers demonstrated: (i) increased expression of tumor related genes including S100A4, cyclin E1, and epidermal growth factor (EGF) receptor, and (ii) expression of matrix metalloproteinase 2, a pro-invasive factor for tumor cells, which was not present in the CP stroma. Increased staining of both the p50 NF-κB subunit and IKK&agr; kinase (a protein that allows activation of NF-κB) was noted in CP and cancers. Conclusions:Our results demonstrate that similar inflammatory components and downstream effectors are present in CP and pancreatic cancers. Importantly, these findings suggest that a common pathway for pancreatic cancer development may be through a chronic inflammatory process including stroma formation. These findings may lead to novel strategies for pancreatic cancer prophylaxis based on inhibition of inflammatory mediators.

Activation of PPARγ increases PTEN expression in pancreatic cancer cells

The PI3K pathway contributes to the invasive properties and apoptosis resistance that epitomize pancreatic cancers. PPARγ is a ligand-activated transcription factor with anti-inflammatory and anti-tumor effects; the mechanisms of tumor suppression are unknown. The purpose of this study was to examine whether activation of PPARγ can increase the expression of the tumor suppressor PTEN and inhibit PI3K activity. AsPC-1 human pancreatic cancer cells, transfected with a PPRE-luciferase construct, demonstrated increased luminescence following treatment with PPARγ ligands, indicating the presence of functional PPARγ protein. The selective PPARγ ligand rosiglitazone increased PTEN expression in AsPC-1 cells; concurrent treatment with GW9662, which inhibits PPARγ activation, prevented the increase in PTEN protein levels. Levels of phosphorylated Akt decreased as PTEN levels increased, indicating inhibition of PI3K activity. Taken together, our results suggest that activation of PPARγ may represent a novel approach for the treatment of pancreatic cancer by increasing PTEN levels and inhibiting PI3K activity.

Mitochondrial DNA damage and altered membrane potential (ΔΨ) in pancreatic acinar cells induced by reactive oxygen species

Background: Reactive oxygen species (ROS) have been implicated in the induction of acute pancreatitis. Mitochondria possess a distinct genome (mtDNA) that is more susceptible to ROS-induced damage than nuclear DNA (nDNA). The purpose of our study was to determine the effect of ROS on mitochondrial function and membrane potential (ΔΨmt), to identify signal transduction mechanisms activated by ROS, and to quantify damage to mtDNA in an in vitro pancreatitis model. Methods: Pancreatic acinar cells, AR4-2J, were treated with saline solution (control) or hydrogen peroxide (H2O2), a representative ROS. Mitochondrial function was assessed with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay; to determine ΔΨmt, rhodamine-123 uptake was measured. Intracellular calcium levels and c-Jun N-terminal kinase activity was determined; gel mobility shift assays were performed to assess induction of the transcription factor NF-κB. To quantitate DNA damage, a novel polymerase chain reaction–based procedure was performed. Results: Mitochondrial function and ΔΨmt were significantly decreased with oxidative damage. H2O2 treatment resulted in increased intracellular calcium levels, activation of c-Jun N-terminal kinase, and induction of NF-κB DNA binding. Treatment of AR4-2J cells with H2O2 resulted in selective mtDNA damage; nDNA was not affected. Conclusions: Our data demonstrate that pancreatic mtDNA is more susceptible to oxidative damage than nDNA; this damage is associated with decreases in mitochondrial function and ΔΨmt and activation of downstream signal transduction pathways. Mitochondrial damage mediated by ROS may play a central role in pancreatic cell injury associated with acute pancreatitis. (Surgery 1999:126:148-55.)

Activation of conventional PKC isoforms increases expression of the pro-apoptotic protein bad and trail receptors

AbstractBackground. Pancreatic cancer is a leading cause of cancer death worldwide; current treatment options have been ineffective in prolonging survival. Agents that target specific signaling pathways (e.g., protein kinase C [PKC]) may regulate apoptotic gene expression rendering resistant cancers sensitive to the effects of other chemotherapeutic drugs. The purpose of our study was to assess the effect of PKC stimulation on apoptotic gene expression in pancreatic cancer cells. Methods. The human pancreatic cancer cell line, PANC-1, was treated with PKC-stimulating agents, phorbol 12-myristate 13-acetate (PMA) or bryostatin-1, and analyzed for expression of apoptosis-related genes. Results. Both PMA and bryostatin-1 induced expression of the pro-apoptotic gene Bad in a dosedependent fashion. The expression of Bad was blocked by the PKC inhibitors GF109203x, Gö6983, and Ro-31-8220, suggesting a role for the conventional isoforms of PKC. In addition, treatment with the MEK inhibitors PD98059 or UO126 reduced PMA-mediated induction of Bad gene expression. PMA also increased the expression of TRAIL receptors DR4 and DR5; this expression was inhibited by the PKC inhibitors GF109203x, Gö6983, and Ro-31-8220 and the MEK inhibitor UO126, suggesting a role for conventional PKC isoforms and MEK in the regulation of TRAIL receptor expression. Conclusions. PKC stimulation in PANC-1 cells increases expression of the pro-apoptotic gene Bad and the TRAIL receptors, DR4 and DR5, through both conventional PKC- and MEK-dependent pathways. Agents that stimulate PKC may sensitize pancreatic cancer cells to apoptosis and provide a potential adjuvant therapy for the treatment of chemoresistant pancreatic cancers.