Growth effects of regulatory peptides and intracellular signaling routes in human pancreatic cancer cell lines

Life with the pancreas: A personal experience

This review article has primary objective to summarize pancreatic research which has been done in our laboratory since 1965, the first year of the author's registration in the Ph.D. program at the University of Sherbrooke (Canada). It covers the following major topics of pancreatic physiology: controls of pancreatic adaptation to diet, control of pancreatic enzyme secretion, control of pancreatic enzyme synthesis, control of pancreatic growth, intracellular events stimulated during pancreatic growth, pancreas regeneration after pancreatitis and pancreatectomy, the pancreatic cholecystokinin receptor types 1 and 2, growth control and cell signaling in pancreatic cancer cells and finally, cystic fibrosis.

Targeting phospholipase D in cancer, infection and neurodegenerative disorders

Phospholipase D (PLD) enzymes are one source of receptor-generated phosphatidic acid (PtdOH),which may subsequently be metabolized to diacylglycerol (DAG) and lysophosphatidic acid. There are other pathways that lead to PtdOH generation, but differences in pathways and in the acyl composition of the products seem to provide some specificity.

Both direct and indirect inhibitors of PLD activity have been identified despite a long-held suspicion that this pathway was undruggable. The identification of raloxifene and halopemide as direct inhibitors was followed by the systematic development of isoenzyme-preferring compounds that have been used to further differentiate the functions of PLD1 and PLD2.

PLD2 in host cells has been associated with viral entry processes and innate immune response pathways such that inhibition blocks efficient infection. This PLD2 pathway has been linked to autophagy via AKT kinases.

As a potential target in antiretroviral therapy, PLD1 works through the CAD enzyme (which contains carbamoyl aspartate synthase, aspartate transcarbamylase and dihydro-orotase domains) to modulate pyrimidine biosynthesis.

PLD activity and expression have been shown to be upregulated in several types of human cancers, in which PLD enzymes function downstream of a variety of known oncogenes. Inhibition of PtdOH production has a marked effect on tumorigenesis and malignant invasion.

PLD1, PLD2 and PLD3 have each been suggested to have a role in Alzheimer disease and other neurodegenerative conditions, but a mechanism has not yet emerged to explain the roles of these proteins in central nervous system pathophysiology.

Lipid second messengers such as phosphatidic acid (PtdOH) have a role in a wide range of pathological processes, and phospholipase D (PLD) enzymes are one of the major sources of signal-activated PtdOH generation. In this Review, Brown, Thomas and Lindsley discuss the development of PLD inhibitors, with a focus on isoform-specific inhibitors, and their potential applications in the treatment of cancer, neurodegeneration and infection.

Lipid second messengers have essential roles in cellular function and contribute to the molecular mechanisms that underlie inflammation, malignant transformation, invasiveness, neurodegenerative disorders, and infectious and other pathophysiological processes. The phospholipase D (PLD) isoenzymes PLD1 and PLD2 are one of the major sources of signal-activated phosphatidic acid (PtdOH) generation downstream of a variety of cell-surface receptors, including G protein-coupled receptors (GPCRs), receptor tyrosine kinases (RTKs) and integrins. Recent advances in the development of isoenzyme-selective PLD inhibitors and in molecular genetics have suggested that PLD isoenzymes in mammalian cells and pathogenic organisms may be valuable targets for the treatment of several human diseases. Isoenzyme-selective inhibitors have revealed complex inter-relationships between PtdOH biosynthetic pathways and the role of PtdOH in pathophysiology. PLD enzymes were once thought to be undruggable owing to the ubiquitous nature of PtdOH in cell signalling and concerns that inhibitors would be too toxic for use in humans. However, recent promising discoveries suggest that small-molecule isoenzyme-selective inhibitors may provide novel compounds for a unique approach to the treatment of cancers, neurodegenerative disorders and other afflictions of the central nervous system, and potentially serve as broad-spectrum antiviral and antimicrobial therapeutics.

Genetically engineered mouse models of pancreatic adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal types of human cancer for which there are no effective therapies. Deep sequencing of PDAC tumors has revealed the presence of a high number of mutations (>50) that affect at least a dozen key signaling pathways. This scenario highlights the urgent need to develop experimental models that faithfully reproduce the natural history of these human tumors in order to understand their biology and to design therapeutic approaches that might effectively interfere with their multiple mutated pathways. Over the last decade, several models, primarily based on the genetic activation of resident KRas oncogenes knocked-in within the endogenous KRas locus have been generated. These models faithfully reproduce the histological lesions that characterize human pancreatic tumors. Decoration of these models with additional mutations, primarily involving tumor suppressor loci known to be also mutated in human PDAC tumors, results in accelerated tumor progression and in the induction of invasive and metastatic malignancies. Mouse PDACs also display a desmoplastic stroma and inflammatory responses that closely resemble those observed in human patients. Interestingly, adult mice appear to be resistant to PDAC development unless the animals undergo pancreatic damage, mainly in the form of acute, chronic or even temporary pancreatitis. In this review, we describe the most representative models available to date and how their detailed characterization is allowing us to understand their cellular origin as well as the events involved in tumor progression. Moreover, their molecular dissection is starting to unveil novel therapeutic strategies that could be translated to the clinic in the very near future.

Effect of secretin on preadipocyte, differentiating and mature adipocyte functions. Int J Obes (Lond). 2013;37:366-374. [PMID: 22565418 DOI: 10.1038/ijo.2012.73]

OBJECTIVE

Several gastrointestinal peptides are now recognized to have target functions beyond the intestinal wall, including effects on adipocytes. Secretin (SEC), one of the first identified, has not been evaluated in this context.

METHODS

Using cultured 3T3-L1 preadipocytes, adipocytes and primary rat adipocytes we evaluated the effect of SEC on cell proliferation, mitochondrial activity, differentiation, triglyceride (TG) synthesis, lipolysis as well expression of the SEC receptor (SCTR) in rodent and human adipose tissues.

RESULTS

In preadipocytes, SEC significantly increased mitochondrial activity (115%; P<0.01), thymidine incorporation (149.7%; P<0.05) and C/EBPβ expression (123.4%; P<0.05). During standard differentiation, SCTR mRNA increased up to a maximum of ninefold (P<0.001). In human adipose tissue, SCTR correlated with body mass index and plasma insulin, and SCTR mRNA expression was also detected in rat adipose tissues. SEC supplementation during differentiation enhanced TG accumulation (+138%; P<0.01). In mature adipocytes, SEC increased fatty acid (FA) uptake (186%; P<0.01), adiponectin and monocyte chemotactic protein-1 secretion (+142% and +149%, respectively; P<0.05) and mRNA expression of PPARγ (+206%; P<0.01), FABP4 (+164%; P<0.001), DGAT-1 (+144%; P<0.01), adiponectin (+138%; P<0.001) and CD36 (+149%; P<0.05). In primary rat adipocytes, SEC also increased FA uptake (137%; P<0.05). Pretreatment with a SEC antagonist impaired SEC-induced FA uptake and cAMP accumulation. SEC treatment simultaneously stimulated lipolysis measured as glycerol release in 3T3-L1 adipocytes and rat adipose tissue.

CONCLUSION

The present results suggest that SEC is a potent modulator of adipocyte functions, demonstrating overall a role in enhanced substrate cycling.

Control of somatostatin (SS) secretion by CCK-1 and CCK-2 receptors' occupation in RIN-14B cells, a rat pancreatic islet cell line

OBJECTIVES

This study evaluated the role played by cholecystokinin (CCK) receptors' occupation in the control of somatostatin (SS) secretion in RIN-14B cells.

METHODS

The presence of the CCK receptors 1 and 2 was confirmed by immunofluorescence, and SS secretion was evaluated by enzyme-linked immunosorbent assay.

RESULTS

By immunofluorescence, 95% of the cell population was composed of SS cells bearing both CCK-R subtypes with 5% of beta cells (data not shown). Cerulein (Cae), a CCK-1R agonist, and pentagastrin, a CCK-2R agonist, dose-dependently increased SS release, 3-fold at 1 mumol/L Cae, 2.5-fold at 10 mumol/L pentagastrin, with occupation of both CCKRs confirmed by L-364,178 and L-365,260 inhibition of CCK receptors 1 and 2. The occupation of high-affinity CCK-1R by Cae was confirmed on SS release with JMV-180, a high-affinity CCK-1R agonist, and absence of SS release inhibition at high Cae concentration occupying the low-affinity CCK-1R. These cells release more than 60% of their SS content by constitutive secretion, confirmed by cycloheximide and brefeldin inhibiting SS synthesis and intracellular trafficking, respectively.

CONCLUSIONS

Both CCKR subtypes occupy RIN-14B cells and initiate SS secretion through constitutive secretion controlled at SS synthesis level. Somatostatin secretion via the CCK-1R occupation mobilizes its high-affinity sites.

Synthesis and in-vitro antitumour activity of new naphthyridine derivatives on human pancreatic cancer cells

Objectives

The aim of the study was to evaluate the antitumour effect in vitro of newly synthesized 7-substituted 2,3-dihydro-1,8-naphthyridines.

Methods

Characterization tools included cell viability assay, caspase 3/7 induction, DNA fragmentation, fibroblast growth factor type 1 receptor kinase inhibition, and in-vitro antiangiogenic analysis.

Key findings

Treatment of MIA PaCa-2 human pancreatic cancer cells with test compounds showed time- and concentration-dependent cytotoxicity with IC50 values in the micromolar range. Compounds with an aminoalkyl or a diaminoalkyl side chain at the 7-position exhibited remarkable cytotoxicity, whereas the presence of a methyl group or a cyclic amine in the same position led to a significant decrease in their biological activity. Cytotoxicity screening demonstrated that the most active was compound 11 (mean 50% inhibition of cell proliferation (IC50) 11 μM). This compound had an in-vitro antitumour efficacy superior to 5-fluorouracil (the lowest cell viability value after treatment (Emax) 0.2% and 19%, respectively) and proved to be less toxic than 5-fluorouracil against non-cancerous human oral epithelial cells. In addition, compound 11 induced apoptosis in MIA PaCa-2 cells and it was able to promote antiangiogenic effects in vitro. Finally, its cytotoxicity was enhanced in pancreatic cancer cells stimulated with fibroblast growth factor, while no substantial effect was observed on human bronchial smooth muscle cells stimulated with the same growth factor.

Conclusions

These findings suggest that 1,8-naphthyridine derivatives are a promising class of compounds in cancer research. In particular, the antitumour activity of compound 11 is worth further investigation.

Future strategies for targeted therapies and tailored patient management in pancreatic cancer

Pancreatic cancer represents the fourth leading cause of cancer-related mortality in the United States. The vast majority of patients are diagnosed at advanced stages of the disease, at which time gemcitabine-based chemotherapy is typically offered as the standard of care. However, as investigators have arrived at a greater understanding of pancreatic tumor biology, newer therapeutic agents that "target" specific pathways or molecules governing the growth, spread, and maintenance of tumor cells have gained considerable interest. Erlotinib, an orally bioavailable small molecule inhibitor of the epidermal growth factor receptor, is the first of these targeted compounds to be approved for use in combination with gemcitabine for patients with advanced pancreatic cancer. Other targeted agents, including monoclonal antibodies and small molecule inhibitors aimed at a variety of targets, also have been extensively evaluated, with limited success to date. A newer strategy worth pursuing involves tailoring an individual patient's therapy according to the molecular characteristics of both host and tumor, as has shown promise in other solid tumor types.

Novel therapeutic approaches in the treatment of advanced pancreatic carcinoma

Pancreatic cancer is still a malignant disease of grim prognosis despite all therapeutic efforts. Because clinical symptoms in the early stage are usually absent or aspecific, it is frequently discovered at advanced or metastatic stage, only around 15-20% of tumors are resectable. In the majority of patients only the chemotherapy offers a prolongation of life, but even the first-line chemotherapeutic agent, the gemcitabine has a modest survival benefit, and objective tumor response is rarely achieved. Combination of various cytostatics did not produce a significant improvement either. For that reason, continuous search for other agents is mandatory. Nowadays, in the era of molecular-targeted oncotherapeutic approaches, pancreatic cancer is also a subject such trials: epidermal growth factor receptor blockade, inhibition of angiogenesis, modulation of tumor response through the extracellular matrix, inhibition of cyclooxygenase-2, farnesyl transferase inhibitors, signal transduction inhibitors, ablation of the hormonal influence and some other aspects have all been studies, but to date, no breakthrough in the treatment of pancreatic carcinoma is proven. In several Phase II-III studies these compounds given alone displayed marginal effects, but when combined with the standard cytostatics, some beneficial effects were observed, however, some of them displayed a severe (sometimes fatal) toxicity. To date, the role of the molecular targeted therapy in pancreatic carcinoma is promising, but the results are not convincingly superior to the standard chemotherapeutic treatments. Pancreatic adenocarcinoma remains a great challenge for the oncologists, and continuous search for better molecules and/or combinations is inevitable.

Secretin receptors in the human liver: expression in biliary tract and cholangiocarcinoma, but not in hepatocytes or hepatocellular carcinoma

BACKGROUND/AIMS

Gut hormone receptors are over-expressed in human cancer and allow receptor-targeted tumor imaging and therapy. A novel promising receptor for these purposes is the secretin receptor. The secretin receptor expression was investigated in the human liver because the liver is a physiological secretin target and because novel diagnostic and treatment modalities are needed for liver cancer.

METHODS

Nineteen normal livers, 10 cirrhotic livers, 35 cholangiocarcinomas, and 45 hepatocellular carcinomas were investigated for secretin receptor expression by in vitro receptor autoradiography using (125)I-[Tyr(10)] rat secretin and, in selected cases, for secretin receptor mRNA by RT-PCR.

RESULTS

Secretin receptors were present in normal bile ducts and ductules, but not in hepatocytes. A significant receptor up-regulation was observed in ductular reaction in liver cirrhosis. Twenty-two (63%) cholangiocarcinomas were positive for secretin receptors, while hepatocellular carcinomas were negative. RT-PCR revealed wild-type receptor mRNA in the non-neoplastic liver, wild-type and spliced variant receptor mRNAs in cholangiocarcinomas found receptor positive in autoradiography experiments, and no receptor transcripts in autoradiographically negative cholangiocarcinomas.

CONCLUSIONS

The expression of secretin receptors in the biliary tract is the molecular basis of the secretin-induced bicarbonate-rich choleresis in man. The high receptor expression in cholangiocarcinomas may be used for in vivo secretin receptor-targeting of these tumors and for the differential diagnosis with hepatocellular carcinoma.

Pituitary Adenylate Cyclase-Activating Polypeptide Is a Potent Inhibitor of the Growth of Light Chain-Secreting Human Multiple Myeloma Cells

Multiple myeloma represents a malignant proliferation of plasma cells in the bone marrow, which often overproduces immunoglobulin light chains. We have shown previously that pituitary adenylate cyclase-activating polypeptide (PACAP) markedly suppresses the release of proinflammatory cytokines from light chain-stimulated human renal proximal tubule epithelial cells and prevents the resulting tubule cell injury. In this study, we have shown that PACAP suppresses the proliferation of human kappa and lambda light chain-secreting multiple myeloma-derived cells. The addition of PACAP suppressed light chain-producing myeloma cell-stimulated interleukin 6 (IL-6) secretion by the bone marrow stromal cells (BMSCs). A specific antagonist to either the human PACAP-specific receptor or the vasoactive intestinal peptide receptor attenuated the suppressive effect of PACAP on IL-6 production in the adhesion of human multiple myeloma cells to BMSCs. The secretion of IL-6 by BMSCs was completely inhibited by 10(-9) mol/L PACAP, which also attenuated the phosphorylation of both p42/44 and p38 mitogen-activated protein kinases (MAPK) as well as nuclear factor-kappaB (NF-kappaB) activation in response to the adhesion of multiple myeloma cells to BMSCs, whereas the inhibition of p42/44 MAPK signaling attenuated PACAP action. The signaling cascades involved in the inhibitory effect of PACAP on IL-6-mediated paracrine stimulation of light chain-secreting myeloma cell growth was mediated through the suppression of p38 MAPK as well as modulation of activation of transcription factor NF-kappaB. These findings suggest that PACAP may be a new antitumor agent that directly suppresses light chain-secreting myeloma cell growth and indirectly affects tumor cell growth by modifying the bone marrow milieu of the multiple myeloma.

Potential protective action of pituitary adenylate cyclase-activating polypeptide (PACAP38) on in vitro and in vivo models of myeloma kidney injury

The most common type of renal injury in multiple myeloma is chronic tubulointerstitial nephropathy associated with casts in tubule lumens, an entity referred to as “myeloma kidney” that often progresses to end-stage kidney diseases. Myeloma kidney is associated with a significant increase in all-cause mortality, yet no effective intervention, except a limited use of steroid, is available. Here, we report that pituitary adenylate cyclase-activating polypeptide with 38 residues (PACAP38) dramatically prevents injury of cultured renal proximal tubule cells caused by myeloma light chains through suppression of proinflammatory cytokines production, by inhibiting p38 MAPK and translocation of NFκB via both PAC1 and VPAC1 receptors. The suppressive effects of PACAP was as effective as dexamethasone in all of their cytokine assays and demonstrated both in vitro and in vivo. Furthermore, PACAP38 inhibits myeloma cell growth directly and may also indirectly by suppressing production of the growth factor, IL-6, from bone marrow stromal cells, that is stimulated by adhesion of myeloma cells. These findings render PACAP38 worth evaluation as a promising candidate for an effective and safe renoprotectant in myeloma kidney, and possibly other nephropathy, and also as a new antitumor agent in multiple myeloma.

Secretin receptors in normal and diseased human pancreas: marked reduction of receptor binding in ductal neoplasia

Receptors for gut hormones, which are often overexpressed in cancer, are clinically relevant for receptor-targeted tumor imaging and therapy. Because the receptors for the gut hormone secretin are poorly characterized, we assessed secretin receptor expression in the main secretin target, the human pancreas. We investigated 58 non-neoplastic pancreases and 55 pancreatic tumors for receptor localization and density by in vitro receptor autoradiography using [(125)I]Tyr(10) rat secretin and for secretin receptor mRNA by reverse transcriptase-polymerase chain reaction. Secretin receptors were highly expressed in non-neoplastic ducts and lobuli and also in lower amounts in ductal neoplasias, including ductal adenocarcinoma, intraductal papillary mucinous tumors, and pancreatic intraepithelial neoplasia. Reverse transcriptase-polymerase chain reaction revealed wild-type receptor mRNA in the non-neoplastic pancreas and both wild-type and spliced variant receptor transcripts in ductal adenocarcinomas. Serous cystic tumors were highly positive for secretin receptors, whereas mucinous cystic tumors were negative. This study is the first to describe the precise secretin receptor distribution in human non-neoplastic pancreas and various pancreatic tumors. High secretin receptor expression in the non-neoplastic ducts reflects the major role of secretin in bicarbonate secretion. Reduced secretin binding in pancreatic ductal tumors may relate to (alternatively spliced) secretin receptor isoforms. Thus, secretin receptors in pancreatic tumors may represent potential clinical targets.

LTB4 stimulates growth of human pancreatic cancer cells via MAPK and PI-3 kinase pathways

We have previously shown the importance of LTB4 in human pancreatic cancer. LTB4 receptor antagonists block growth and induce apoptosis in pancreatic cancer cells both in vitro and in vivo. Therefore, we investigated the effect of LTB4 on proliferation of human pancreatic cancer cells and the mechanisms involved. LTB4 stimulated DNA synthesis and proliferation of both PANC-1 and AsPC-1 human pancreatic cancer cells, as measured by thymidine incorporation and cell number. LTB4 stimulated rapid and transient activation of MEK and ERK1/2 kinases. The MEK inhibitors, PD98059 and U0126, blocked LTB4-stimulated ERK1/2 activation and cell proliferation. LTB4 also stimulated phosphorylation of p38 MAPK; however, the p38 MAPK inhibitor, SB203580, failed to block LTB4-stimulated growth. The activity of JNK/SAPK was not affected by LTB4 treatment. Phosphorylation of Akt was also induced by LTB4 and this effect was blocked by the PI-3 kinase inhibitor wortmannin, which also partially blocked LTB4-stimulated cell proliferation. In conclusion, LTB4 stimulates proliferation of human pancreatic cancer cells through MEK/ERK and PI-3 kinase/Akt pathways, while p38 MPAK and JNK/SAPK are not involved.

Gastrins, cholecystokinins and gastrointestinal cancer

The gastrointestinal peptide hormones gastrin and cholecystokinin (CCK) are well known for their ability to stimulate gastric acid secretion and pancreatic enzyme secretion, respectively. The suggestion that gastrin and CCK might also promote the development of cancers of the gastrointestinal tract has been controversial, but an increasing body of evidence now supports the view that the amidated and non-amidated forms of gastrin act as growth factors via different receptors in different regions of the gut. For example, animal experiments indicate that amidated gastrins are involved in cellular differentiation and repair in the gastric mucosa, and synergize with Helicobacter pylori infection in the development of gastric carcinoma. In contrast, non-amidated gastrins stimulate colonic mucosal growth, accelerate the early steps in colorectal carcinoma formation, and are elevated in the tumour and circulation of patients with colorectal cancer. Although human pancreatic carcinomas express CCK-1 and CCK-2 receptors, the role of gastrins and CCK in pancreatic carcinogenesis is yet to be established. Further investigation of the possible role of the CCK-2 receptor in gastric and pancreatic neoplasia, and of the hypothesis that gastrin precursors act as autocrine growth factors in colorectal carcinoma, is warranted. However, therapies aimed at the gastrins must be targeted to the relevant gastrin/gastrin receptor combination.

Microarray and suppression subtractive hybridization analyses of gene expression in pheochromocytoma cells reveal pleiotropic effects of pituitary adenylate cyclase-activating polypeptide on cell proliferation, survival, and adhesion

Pituitary adenylate cyclase-activating polypeptide (PACAP) exerts trophic effects on several neuronal, neuroendocrine, and endocrine cells. To gain insight into the pattern of the transcriptional modifications induced by PACAP during cell differentiation, we studied the effects of this neuropeptide on rat pheochromocytoma PC12 cells. We first analyzed the transcriptome of PC12 cells in comparison to that of terminally differentiated rat adrenomedullary chromaffin cells, using a high-density microarray, to identify genes associated with the proliferative phenotype that are possible targets of PACAP during differentiation of sympathoadrenal normal and tumoral cells. We then studied global gene expression in PC12 cells after 48 h of exposure to PACAP, using both cDNA microarray and suppression subtractive hybridization technologies. These complementary approaches resulted in the identification of 75 up-regulated and 70 down-regulated genes in PACAP-treated PC12 cells. Among the genes whose expression is modified in differentiated cells, a vast majority are involved in cell proliferation, survival, and adhesion/motility. Expression changes of most of these genes have been associated with progression of several neoplasms. A kinetic study of the effects of PACAP on some of the identified genes showed that the neuropeptide likely exerts early as well as late actions to achieve the gene expression program necessary for cell differentiation. In conclusion, the results of the present study underscore the pleiotropic role of PACAP in cell differentiation and provide important information on novel targets that could mediate the effects of this neuropeptide in normal and tumoral neuroendocrine cells.

Antiproliferative actions of growth hormone-releasing hormone antagonists on MiaPaCa-2 human pancreatic cancer cells involve cAMP independent pathways

We evaluated the effects of GHRH antagonists on the proliferation of MiaPaCa-2 human pancreatic cancer cells and cAMP signaling in vitro. GHRH antagonists inhibited the proliferation of MiaPaCa-2 cells in vitro in a dose-dependent way and caused a significant elevation in cAMP production. In a superfusion system, short-term exposure of the cells to GHRH antagonists evoked an acute, dose-dependent release of cAMP into the medium. Native GHRH, which stimulates cAMP efflux from pituitary at nanomolar doses, did not influence cAMP release from cultured or superfused MiaPaCa-2 cells even at 10-30 microM. VIP, PACAP, secretin and glucagon also did not influence cell proliferation or cAMP production. Adenylate cyclase activator forskolin (FSK) caused a greater cAMP response, but a smaller antiproliferative effect than GHRH antagonists. Combined treatment with FSK and GHRH antagonist JV-1-38 potentiated the cAMP-inducing effect of FSK, but did not produce a greater inhibition of cell proliferation than JV-1-38 alone. A selective accumulation of radiolabeled GHRH antagonist [(125)I]JV-1-42 in vivo in MiaPaCa-2 carcinoma xenografted into nude mice was also observed. In conclusion, second messengers other than cAMP participate in the signal transduction pathways of GHRH analogs mediated by tumoral GHRH receptors.

The case for gastrin-releasing peptide acting as a morphogen when it and its receptor are aberrantly expressed in cancer

Gastrin-releasing peptide (GRP) and its receptor (GRP-R) are frequently expressed by cancers of the gastrointestinal tract, breast, lung, and prostate. Most studies have found that GRP and its amphibian homologue bombesin act to increase tumor cell proliferation, leading to the hypothesis that this peptide hormone is a mitogen important for the growth of various cancers. Yet GRP/GRP-R co-expression in cancer promotes the development of a well-differentiated phenotype; while multiple studies suggest that the presence of these 2 proteins confer a survival advantage. Along with recent reports showing that GRP and its receptor critically regulate aspects of colon and lung organogenesis, we argue that these proteins do not function primarily as mitogens when aberrantly expressed in cancer. Rather, we postulate that GRP/GRP-R are onco-fetal antigens that function as morphogens, with their effect on tumor cell proliferation being a component property of their ability to regulate differentiation. Thus aberrant GRP/GRP-R expression in cancer recapitulates, albeit in a dysfunctional manner, their normal role in development.

MEK/ERK-mediated proliferation is negatively regulated by P38 map kinase in the human pancreatic cancer cell line, PANC-1

Pancreatic carcinoma is characterized by a poor prognosis and lack of response to conventional therapy. The regulatory mechanisms for the rapid proliferation of pancreatic cancer cells and the particular aggressiveness of this cancer are still not fully understood. In mammalian cells, three MAPK families including ERK, JNK, and P38 MAPK have been characterized. ERK is known to play an important role in regulating pancreatic cancer cell proliferation. However, the role of P38 kinase in pancreatic cancer cell proliferation and its relationship with ERK are unclear. Using the specific P38 inhibitor, SB203580 we found that blockade of P38 MAP kinase significantly enhanced proliferation of the pancreatic cancer cell line, PANC-1 cell, in a concentration-dependent manner. In parallel with the stimulation of proliferation, blockade of P38 MAP kinase markedly induced MEK and ERK1/2 phosphorylation, indicating an interaction between MEK/ERK and P38 MAP kinase signaling. Clearly, the interaction between these kinase pathways does not involve transcription and translation because MEK/ERK was activated immediately upon SB203580 treatment. Furthermore, inhibition of the MEK/ERK cascade using the MEK inhibitor, PD098059 abolished SB203580-induced PANC-1 cell proliferation. From these results, we conclude that a MEK/ERK and P38 MAP kinase interaction is important for pancreatic cancer cell proliferation. Breaking the balance between these two signaling pathways will modify pancreatic cancer cell proliferation.

Genistein inhibits nonoxidative ribose synthesis in MIA pancreatic adenocarcinoma cells: a new mechanism of controlling tumor growth

Genistein is a plant isoflavonoid bearing potent tumor growth-regulating characteristics. This effect of genistein has been attributed partially to its tyrosine kinase-regulating properties, resulting in cell-cycle arrest and limited angiogenesis. Genistein has been used in chemotherapy-resistant cases of advanced leukemia with promising results. Here we demonstrate that genistein primarily affects nucleic acid synthesis and glucose oxidation in tumor cells using the [1,2-(13)C2]glucose isotope as the single tracer and gas chromatography/mass spectrometry to follow various intracellular glucose metabolites. The ribose fraction of RNA demonstrated a rapid 4.6%, 16.4%, and 46.3% decrease in isotope uptake through the nonoxidative branch of the pentose cycle and a sharp 4.8%. 24.6%, and 48% decrease in 13CO2 release from glucose after 2, 20, and 200 micromol/L genistein treatment, respectively. Fatty acid synthesis and the 13C enrichment of acetyl units were not significantly affected by genistein treatment. De novo glycogen synthesis from media glucose was not detected in cultured MIA cells. It can be concluded from these studies that genistein controls tumor growth primarily through the regulation of glucose metabolism, specifically targeting glucose carbon incorporation into nucleic acid ribose through the nonoxidative steps of the pentose cycle, which represents a new paradigm for the antiproliferative action of a plant phytochemical.

Promotion of health by soy isoflavones: efficacy, benefit and safety concerns

Cardiovascular diseases, osteoporosis-related hip fractures, and various cancers of the colon, prostate, uterus, and breast are remarkably less prevalent in Asia than in other industrialized countries. It is believed that the large consumption of soy products in Asian countries is contributory to the reduction of these chronic disorders. Genistein is a major isoflavone found in most soy products and plays an important role in the promotion of human health. Extensive epidemiological, in vitro, and animal studies have been performed, and most studies indicate that genistein has beneficial effects on a multitude of human disorders, including cancers, cardiovascular diseases, osteoporosis, and postmenopausal symptoms. To date, there is an abundance of promising studies supporting genistein's potential uses, but further research is still needed to validate its preventative and therapeutic efficacy. In addition, the adverse effects of genistein have drawn public attention. More studies are required to assess the potential detrimental effect of genistein, and a benefit-risk ratio should be considered before future clinical studies are performed.