Carbonic anhydrase in human pancreas: hypotheses for the pathophysiological roles of CA isozymes

Clinical and Pre-Clinical Evidence of Carbonic Anhydrase IX in Pancreatic Cancer and Its High Expression in Pre-Cancerous Lesions

Hypoxia is a common phenomenon that occurs in most solid tumors. Regardless of tumor origin, the evolution of a hypoxia-adapted phenotype is critical for invasive cancer development. Pancreatic ductal adenocarcinoma is also characterized by hypoxia, desmoplasia, and the presence of necrosis, predicting poor outcome. Carbonic anhydrase IX (CAIX) is one of the most strict hypoxia regulated genes which plays a key role in the adaptation of cancer cells to hypoxia and acidosis. Here, we summarize clinical data showing that CAIX expression is associated with tumor necrosis, vascularization, expression of Frizzled-1, mucins, or proteins involved in glycolysis, and inevitably, poor prognosis of pancreatic cancer patients. We also describe the transcriptional regulation of CAIX in relation to signaling pathways activated in pancreatic cancers. A large part deals with the preclinical evidence supporting the relevance of CAIX in processes leading to the aggressive behavior of pancreatic tumors. Furthermore, we focus on CAIX occurrence in pre-cancerous lesions, and for the first time, we describe CAIX expression within intraductal papillary mucinous neoplasia. Our review concludes with a detailed account of clinical trials implicating that treatment consisting of conventionally used therapies combined with CAIX targeting could result in an improved anti-cancer response in pancreatic cancer patients.

The Physiology and Pathophysiology of Pancreatic Ductal Secretion: The Background for Clinicians

The human exocrine pancreas consists of 2 main cell types: acinar and ductal cells. These exocrine cells interact closely to contribute to the secretion of pancreatic juice. The most important ion in terms of the pancreatic ductal secretion is HCO3. In fact, duct cells produce an alkaline fluid that may contain up to 140 mM NaHCO3, which is essential for normal digestion. This article provides an overview of the basics of pancreatic ductal physiology and pathophysiology. In the first part of the article, we discuss the ductal electrolyte and fluid transporters and their regulation. The central role of cystic fibrosis transmembrane conductance regulator (CFTR) is highlighted, which is much more than just a Cl channel. We also review the role of pancreatic ducts in severe debilitating diseases such as cystic fibrosis (caused by various genetic defects of cftr), pancreatitis, and diabetes mellitus. Stimulation of ductal secretion in cystic fibrosis and pancreatitis may have beneficial effects in their treatment.

Acid-base transport in pancreatic cancer: molecular mechanisms and clinical potential

Solid tumors are characterized by a microenvironment that is highly acidic, while intracellular pH (pHi) is normal or even elevated. This is the result of elevated metabolic rates in the highly proliferative cancer cells, in conjunction with often greatly increased rates of net cellular acid extrusion. Studies in various cancers have suggested that while the acid extrusion mechanisms employed are generally the same as those in healthy cells, the specific transporters upregulated vary with the cancer type. The main such transporters include Na(+)/H(+) exchangers, various HCO3(-) transporters, H(+) pumps, and lactate-H(+) cotransporters. The mechanisms leading to their dysregulation in cancer are incompletely understood but include changes in transporter expression levels, trafficking and membrane localization, and posttranslational modifications. In turn, accumulating evidence has revealed that in addition to supporting their elevated metabolic rate, their increased acid efflux capacity endows the cancer cells with increased capacity for invasiveness, proliferation, and chemotherapy resistance. The pancreatic duct exhibits an enormous capacity for acid-base transport, rendering pHi dysregulation a potentially very important topic in pancreatic ductal adenocarcinoma (PDAC). PDAC - accounting for about 90% of all pancreatic cancers - has one of the highest cancer mortality rates known, and new diagnostic and treatment options are highly needed. However, very little is known about whether pH regulation is altered in PDAC and, if so, the possible role of this in cancer development. Here, we review current models for pancreatic acid-base transport and pH homeostasis and summarize current views on acid-base dysregulation in cancer, focusing where possible on the few studies to date in PDAC. Finally, we present new data-mining analyses of acid-base transporter expression changes in PDAC and discuss essential directions for future work.

Down regulation of CAII is associated with tumor differentiation and poor prognosis in patients with pancreatic cancer

BACKGROUND AND OBJECTIVES

Altered expression of carbonic anhydrase (CA)I and II associated with human carcinogenesis. But there was no definite study investigating their expression for clinical significance in pancreatic cancer and effect of the CA inhibitor acetazolamide (AZ) on regulation biological behavior of pancreatic cancer cells.

METHODS

Immunohistochemistry, immunofluorescence, immunoblot, and qRT-PCR were used to detect CAI, II, and p53 expression. Tumor cell viability, apoptosis, and invasion assays were used to investigate the effect of AZ on pancreatic cancer cells.

RESULTS

Expression of CAI and p53 was increased in pancreatic cancer than that in paired non-cancerous tissues (P = 0.021; P = 0.007), whereas CAII was down-regulated in pancreatic cancer (P = 0.001). CAI overexpression was associated with tumor differentiation and negatively with vascular invasion (P = 0.015 and P = 0.018, respectively), while overexpression of CAII was associated with tumor differentiation (P = 0.017) and a better prognosis of pancreatic cancer patients (P = 0.017), and was an independent prognostic indicator (P = 0.011). p53 overexpression was related with lymph node metastasis (P = 0.032) and TNM stage (P = 0.016). Treatment with AZ inhibited tumor cell validity, invasion, and induced apoptosis in some of six pancreatic cancer cells.

CONCLUSION

This study suggests the clinical significance of CAI, CAII and p53 expression in pancreatic cancer and provides evidence for AZ as a potential target for controlling pancreatic cancer.

Commensal Flora, is it an Unwelcomed Companion as a Triggering Factor of Autoimmune Pancreatitis?

The etiopathogenesis of many autoimmune disorders has not been identified. The aim of this paper is to focus on the involvement of bacterial exposure, as an environmental factor, in the pathogenesis of autoimmune pancreatitis (AIP), which is broadly categorized as autoimmune disorders involving pancreatic lesions. Avirulent and/or commensal bacteria, which may have an important role(s) as initiating/progressing factors in the pathogenesis of autoimmune disorder AIP, will be emphasized.

Molecular mechanism of pancreatic and salivary gland fluid and HCO3 secretion

Fluid and HCO(3)(-) secretion is a vital function of all epithelia and is required for the survival of the tissue. Aberrant fluid and HCO(3)(-) secretion is associated with many epithelial diseases, such as cystic fibrosis, pancreatitis, Sjögren's syndrome, and other epithelial inflammatory and autoimmune diseases. Significant progress has been made over the last 20 years in our understanding of epithelial fluid and HCO(3)(-) secretion, in particular by secretory glands. Fluid and HCO(3)(-) secretion by secretory glands is a two-step process. Acinar cells secrete isotonic fluid in which the major salt is NaCl. Subsequently, the duct modifies the volume and electrolyte composition of the fluid to absorb the Cl(-) and secrete HCO(3)(-). The relative volume secreted by acinar and duct cells and modification of electrolyte composition of the secreted fluids varies among secretory glands to meet their physiological functions. In the pancreas, acinar cells secrete a small amount of NaCl-rich fluid, while the duct absorbs the Cl(-) and secretes HCO(3)(-) and the bulk of the fluid in the pancreatic juice. Fluid secretion appears to be driven by active HCO(3)(-) secretion. In the salivary glands, acinar cells secrete the bulk of the fluid in the saliva that is driven by active Cl(-) secretion and contains high concentrations of Na(+) and Cl(-). The salivary glands duct absorbs both the Na(+) and Cl(-) and secretes K(+) and HCO(3)(-). In this review, we focus on the molecular mechanism of fluid and HCO(3)(-) secretion by the pancreas and salivary glands, to highlight the similarities of the fundamental mechanisms of acinar and duct cell functions, and to point out the differences to meet gland-specific secretions.

Acute recurrent pancreatitis: An autoimmune disease?

In this review article, we will briefly describe the main characteristics of autoimmune pancreatitis and then we will concentrate on our aim, namely, evaluating the clinical characteristics of patients having recurrence of pain from the disease. In fact, the open question is to evaluate the possible presence of autoimmune pancreatitis in patients with an undefined etiology of acute pancreatitis and for this reason we carried out a search in the literature in order to explore this issue. In cases of recurrent attacks of pain in patients with “diopathic”pancreatitis, we need to keep in mind the possibility that our patients may have autoimmune pancreatitis. Even though the frequency of this disease seems to be quite low, we believe that in the future, by increasing our knowledge on the subject, we will be able to diagnose an ever-increasing number of patients having acute recurrence of pain from autoimmune pancreatitis.

Hypoxia and angiogenesis in pancreatic cancer

BACKGROUND

Pancreatic cancer remains one of the most lethal of all solid tumours of the gastrointestinal tract. It is characterized by late diagnosis, aggressive local invasion, early metastasis and resistance to chemoradiotherapy. Increasing knowledge regarding the molecular events behind the growth and invasion of pancreatic cancer may lead to new targets for intervention.

METHODS

A search of Pubmed and Medline databases was undertaken using the keywords pancreatic cancer, gastrointestinal cancer, hypoxia, angiogenesis and anti-angiogenesis therapy.

RESULTS

Hypoxia is the driving force behind angiogenesis in pancreatic cancers. Research into angiogenesis has shown many different sites that can be targeted by agents such as tyrosine kinase inhibitors.

CONCLUSION

Anti-angiogenic therapy could be an important adjunct to conventional chemotherapy treatment of gastrointestinal neoplasia.

Evidence by signal peptide trap technology for the expression of carbonic anhydrase 6 in rat incisor enamel organs

During screening of a rat incisor enamel organ cDNA library by signal peptide trap technology, we identified a DNA fragment matching a predicted translation sequence for rat carbonic anhydrase 6 (CA6). This result was unexpected because CA6, to date, has been associated primarily with secretions from glandular tissues. To further characterize this observation, reverse transcription-polymerase chain reaction (RT-PCR) amplifications were carried out on total RNA extracted from freeze-dried secretory and maturation-stage rat incisor enamel organs. A cDNA fragment of the expected size was detected in control samples from rat salivary glands as well as within maturation-stage enamel organ samples. This CA6 RT-PCR fragment was further cloned and sequenced and found to match the nucleotide sequence 770-1079 from clone XM_216584 of GenBank. Northern blot analyses with the rat CA6 cDNA fragment confirmed its expression relative to maturation-stage enamel organ samples. It is at present unclear whether the CA6 expressed by enamel organ cells is secreted into the enamel layer or into the intercellular spaces of the enamel organ itself to assist in neutralizing excess protons arising from the growth of apatite crystals during the maturation stage of amelogenesis.

SLC4 base (HCO3 -, CO3 2-) transporters: classification, function, structure, genetic diseases, and knockout models

In prokaryotic and eukaryotic organisms, biochemical and physiological processes are sensitive to changes in H(+) activity. For these processes to function optimally, a variety of proteins have evolved that transport H(+)/base equivalents across cell and organelle membranes, thereby maintaining the pH of various intracellular and extracellular compartments within specific limits. The SLC4 family of base (HCO(3)(-), CO(3)(2(-))) transport proteins plays an essential role in mediating Na(+)- and/or Cl(-)-dependent base transport in various tissues and cell types in mammals. In addition to pH regulation, specific members of this family also contribute to vectorial transepithelial base transport in several organ systems including the kidney, pancreas, and eye. The importance of these transporters in mammalian cell biology is highlighted by the phenotypic abnormalities resulting from spontaneous SLC4 mutations in humans and targeted deletions in murine knockout models. This review focuses on recent advances in our understanding of the molecular organization and functional properties of SLC4 transporters and their role in disease.

Characterization of H+ and HCO3- transporters in CFPAC-1 human pancreatic duct cells

AIM: To characterize H⁺ and HCO₃^- transporters in polarized CFPAC-1 human pancreatic duct cells, which were derived from a cystic fibrosis patient with the ΔF508 CFTR mutation.

METHODS: CFPAC-1 cells were seeded at high density onto permeable supports and grown to confluence. The cells were loaded with the pH-sensitive fluorescent dye BCECF, and mounted into a perfusion chamber, which allowed the simultaneous perfusion of the basolateral and apical membranes. Transmembrane base flux was calculated from the changes in intracellular pH and the buffering capacity of the cells.

RESULTS: Our results showed differential permeability to HCO₃^-/CO₂ at the apical and basolateral membranes of CFPAC-1 cells. Na⁺/HCO₃^- co-transporters (NBCs) and Cl^-/HCO₃^- exchangers (AEs) were present on the basolateral membrane, and Na⁺/H⁺ exchangers (NHEs) on both the apical and basolateral membranes of the cells. Basolateral HCO₃^- uptake was sensitive to variations of extracellular K⁺ concentration, the membrane permeable carbonic anhydrase (CA) inhibitors acetazolamide (100 µmol/L) and ethoxyzolamide (100 µmol/L), and was partially inhibited by H₂-DIDS (600 µmol/L). The membrane-impermeable CA inhibitor 1-N-(4-sulfamoylphenylethyl)-2,4,6-trimethylpyridine perchlorate did not have any effect on HCO₃^- uptake. The basolateral AE had a much higher activity than that in the apical membrane, whereas there was no such difference with the NHE under resting conditions. Also, 10 µmol/L forskolin did not significantly influence Cl^-/HCO₃^- exchange on the apical and basolateral membranes. The administration of 250 µmol/L H₂-DIDS significantly inhibited the basolateral AE. Amiloride (300 µmol/L) completely inhibited NHEs on both membranes of the cells. RT-PCR revealed the expression of pNBC1, AE2, and NHE1 mRNA.

CONCLUSION: These data suggest that apart from the lack of CFTR and apical Cl^-/HCO₃^- exchanger activity, CFPAC-1 cells express similar H⁺ and HCO₃^- transporters to those observed in native animal tissue.

Notch 2-positive progenitors with the intrinsic ability to give rise to pancreatic ductal cells

Pancreatic adenocarcinomas display foci of duct-like structures that are positive for markers of pancreatic ductal cells. The development of these tumors is promoted by conditions leading to acinar-to-ductal metaplasia, a process by which acinar cells are replaced by ductal cells. Acinar-to-ductal metaplasia has recently been shown to proceed through intermediary cells expressing Nestin. To create an in vitro system to study pancreatic adenocarcinomas, we had used an hTERT cDNA to immortalize primary cells of the human pancreas. In this report, we show that the immortalized cells, termed hTERT-HPNE cells, have the ability to differentiate to pancreatic ductal cells. Exposing hTERT-HPNE cells to sodium butyrate and 5-aza-2'-deoxycytidine lead to the formation of pancreatic ductal cells marked by the expression of MDR-1, carbonic anhydrase II, and the cytokeratins 7, 8, and 19. hTERT-HPNE cells were found to have properties of the intermediary cells formed during acinar-to-ductal metaplasia, which included their undifferentiated phenotype, expression of Nestin, evidence of active Notch signaling, and ability to differentiate to pancreatic ductal cells. These results provide further evidence for the presence in the adult pancreas of a precursor of ductal cells. hTERT-HPNE cells should provide a useful model to study acinar-to-ductal metaplasia and the role played by this process in pancreatic cancer development.

Mechanisms of bicarbonate secretion in the pancreatic duct

In many species the pancreatic duct epithelium secretes HCO3- ions at a concentration of around 140 mM by a mechanism that is only partially understood. We know that HCO3- uptake at the basolateral membrane is achieved by Na+-HCO3- cotransport and also by a H+-ATPase and Na+/H+ exchanger operating together with carbonic anhydrase. At the apical membrane, the secretion of moderate concentrations of HCO3- can be explained by the parallel activity of a Cl-/HCO3- exchanger and a Cl- conductance, either the cystic fibrosis transmembrane conductance regulator (CFTR) or a Ca2+-activated Cl- channel (CaCC). However, the sustained secretion of HCO3- into a HCO- -rich luminal fluid cannot be explained by conventional Cl-/HCO3- exchange. HCO3- efflux across the apical membrane is an electrogenic process that is facilitated by the depletion of intracellular Cl-, but it remains to be seen whether it is mediated predominantly by CFTR or by an electrogenic SLC26 anion exchanger.

Casodex treatment induces hypoxia-related gene expression in the LNCaP prostate cancer progression model

Background

The changes in gene expression profile as prostate cancer progresses from an androgen-dependent disease to an androgen-independent disease are still largely unknown.

Methods

We examined the gene expression profile in the LNCaP prostate cancer progression model during chronic treatment with Casodex using cDNA microarrays consisting of 2305 randomly chosen genes.

Results

Our studies revealed a representative collection of genes whose expression was differentially regulated in LNCaP cells upon treatment with Casodex. A set of 15 genes were shown to be highly expressed in Casodex-treated LNCaP cells compared to the reference sample. This set of highly expressed genes represents a signature collection unique to prostate cancer since their expression was significantly greater than that of the collective pool of ten cancer cell lines of the reference sample. The highly expressed signature collection included the hypoxia-related genes membrane metallo-endopeptidase (MME), cyclin G2, and Bcl2/adenovirus E1B 19 kDa (BNIP3). Given the roles of these genes in angiogenesis, cell cycle regulation, and apoptosis, we further analyzed their expression and concluded that these genes may be involved in the molecular changes that lead to androgen-independence in prostate cancer.

Conclusion

Our data indicate that one of the mechanisms of Casodex action in prostate cancer cells is induction of hypoxic gene expression.

Mineral acquisition rates in developing enamel on maxillary and mandibular incisors of rats and mice: implications to extracellular acid loading as apatite crystals mature

The formation rates of mineral in developing enamel were determined by microweighing of incisors of mice and rats. Computations indicated that a large excess of hydrogen ions would result from creating apatite at the calculated rates. Enamel organ cells (ameloblasts), therefore, likely excrete bicarbonate ions to prevent pH in fluid bathing enamel from becoming too acidic.

INTRODUCTION

Protons (H+) are generated whenever calcium and phosphate ions combine directly from aqueous solutions to form hydroxyapatite. Enamel is susceptible to potential acid loading during development because the amount of fluid bathing this tissue is small and its buffering capacity is low. The epithelial cells covering this tissue are also believed to form permeability barriers at times during the maturation stage when crystals grow at their fastest rates. The goal of this study was to measure the bulk weight of mineral present in rodent enamel at specific times in development and estimate the amount of acid potentially formed as the apatite crystals mature.

MATERIALS AND METHODS

Upper and lower jaws of mice and rats were freeze-dried, and the enamel layers on the incisors were partitioned into a series of 0.5 mm (mouse) or 1.0 mm (rat) strips along the length of each tooth. The strips were weighed on a microbalance, ashed at 575 degrees C for 18-24 h to remove organic material, and reweighed to determine the actual mineral weight for each strip.

RESULTS AND CONCLUSIONS

The data indicated that, despite differences in gross sizes and shapes of maxillary and mandibular incisors in rats and mice, the overall pattern and rates of mineral acquisition were remarkably similar. This included sharply increasing rates of mineral acquisition between the secretory and maturation stages, with peak levels approaching 40 microg/mm tooth length. Computer modeling indicated that quantities of H+ ions potentially generated as apatite crystals grew during the maturation stage greatly exceeded local buffering capacity of enamel fluid and matrix proteins. In other systems, bicarbonate ions are excreted to neutralize highly acidic materials generated extracellularly. Data from this study indicate that ameloblasts, and perhaps cells in other apatite-based hard tissues, use similar bicarbonate release mechanisms to control excess acid arising from mineral formation.

Expression of carbonic anhydrase IX in human pancreatic cancer

BACKGROUND

Carbonic anhydrase IX has been linked to cancer development and progression.

AIM

To analyse carbonic anhydrase IX expression and anhydrase inhibition in pancreatic cancer and to correlate these findings with p53 expression and microvessel density.

MATERIALS AND METHODS

Seventy-seven pancreatic cancers were examined (43 males, 34 females; mean age, 64 years). The anti-carbonic anhydrase IX M75 antibody was used for immunohistochemistry and Western blot analysis. Microvessels were visualized using the anti-CD34 antibody, and p53 expression in cancer cells was assessed with a specific anti-p53 antibody. Quantitative polymerase chain reaction was performed in order to assess carbonic anhydrase IX mRNA levels in the pancreas. Furthermore, pancreatic cancer cell lines were treated with acetazolamide, a carbonic anhydrase inhibitor.

RESULTS

In the normal pancreas, carbonic anhydrase IX immunoreactivity was observed at the basolateral membrane of ductal cells in 24 cases (31%). Carbonic anhydrase IX expression was found at the membrane and in the cytoplasm of pancreatic cancer cells in 16 pancreatic cancers (21%). Carbonic anhydrase IX expression was independent of the localization, stage, size, metastases and differentiation of the tumour. p53 expression was significantly more frequent in poorly differentiated cancers (P=0.0323); however, p53 expression and microvessel density were independent of carbonic anhydrase IX expression. Overall, carbonic anhydrase IX expression was not altered in pancreatic cancers vs. adjacent normal pancreatic tissue as assessed by Western blot and quantitative polymerase chain reaction analysis. However, incubation of pancreatic cancer cell lines with acetazolamide led to a significant inhibition of cell proliferation in AsPC-1 and PANC-1 pancreatic cancer cells.

CONCLUSION

Carbonic anhydrase IX expression is observed in both ductal epithelial and cancer cells of the pancreas. Although the expression of carbonic anhydrase IX in pancreatic cancer is not associated with angiogenesis or advanced disease, it may well be a target for carbo-anhydrase inhibitors in a subset of pancreatic cancers.

Structural determinants and significance of regulation of electrogenic Na(+)-HCO(3)(-) cotransporter stoichiometry

Na(+)-HCO(3)(-) cotransporters play an important role in intracellular pH regulation and transepithelial HCO(3)(-) transport in various tissues. Of the characterized members of the HCO(3)(-) transporter superfamily, NBC1 and NBC4 proteins are known to be electrogenic. An important functional property of electrogenic Na(+)-HCO(3)(-) cotransporters is their HCO(3)(-):Na(+) coupling ratio, which sets the transporter reversal potential and determines the direction of Na(+)-HCO(3)(-) flux. Recent studies have shown that the HCO(3)(-):Na(+) transport stoichiometry of NBC1 proteins is either 2:1 or 3:1 depending on the cell type in which the transporters are expressed, indicating that the HCO(3)(-):Na(+) coupling ratio can be regulated. Mutational analysis has been very helpful in revealing the molecular mechanisms and signaling pathways that modulate the coupling ratio. These studies have demonstrated that PKA-dependent phosphorylation of the COOH terminus of NBC1 proteins alters the transport stoichiometry. This cAMP-dependent signaling pathway provides HCO(3)(-) -transporting epithelia with an efficient mechanism for modulating the direction of Na(+)-HCO(3)(-) flux through the cotransporter.

Bile duct involvement in a case of autoimmune pancreatitis successfully treated with an oral steroid

In the case reported here, the characteristic features of AIP were evaluated by ultrasonography, computed tomography and endoscopic retrograde cholangiopancreatography, initially in the intrahepatic- and extrahepatic bile ducts, and later in the pancreas. In addition, histological examination revealed lymphocytic sclerosis around the intralobular bile ducts, as is reported in AIP, without chronic nonsuppurative destructive cholangitis or onion-skin-like appearance. Immunohistochemistry identified the infiltrating lymphocytes as T cells. Although hypergammaglobulinemia was observed with elevation of hepatobiliary and pancreatic enzymes, no other serological or physiological abnormalities suggestive of other systemic autoimmune diseases were detected. These findings progressed over a three-month period and were dramatically resolved within one month by steroid therapy. These observations support a novel clinical entity characterized by the presence of bile duct lesions similar to the pancreatic involvement seen in AIP that is distinct pathophysiologically, histologically, and therapeutically from the so-called autoimmune cholangitis or primary sclerosing cholangitis.

Immunohistochemical localization of pyruvate carboxylase and carbamyl-phosphate synthetase I in normal and neoplastic human pancreatic tissues

INTRODUCTION

It has been suggested that pyruvate carboxylase (PC) and carbamyl-phosphate synthetase I (CPS I) might be colocalized with carbonic anhydrase V (CA V), which is generally considered to provide HCO3- ions for PC and CPS I.

AIM

To examine the immunohistochemical staining of endogenous biotin; of three mitochondrial biotin-binding enzymes (namely, PC, CPS I, and propionyl CoA-carboxylase); and of cytosolic acetyl CoA-carboxylase in pancreatic tissues.

METHODOLOGY

Immunohistochemical analysis was performed on 23 samples of normal pancreas and 63 samples of neoplastic pancreatic tissues.

RESULTS

It was found that the distribution of PC, CPS I, and endogenous biotin was not related to that of CA V but was similar to that of CA II in normal centroacinar cells, intercalated duct cells, and intralobular duct cells. In addition, PC was detected unexpectedly in delta-cells of islets.

CONCLUSION

It seems likely that CA II plays a major role in the secretion of NaHCO3 into the pancreatic juice. Hence, it is possible that PC and CPS I in the centroacinar cells, intercalated duct cells, and intralobular duct cells are strongly activated and might use HCO3- ions provided by CA II and not by CA V. Among the pancreatic neoplasms examined, ductal adenocarcinomas exhibited significantly elevated immunoreactivity specific for the four biotin-binding enzymes.

Autocrine stimulation of human pancreatic duct-like development by soluble isoforms of epimorphin in vitro

Epimorphin was recently described as a mesenchymal factor modulating morphogenesis of murine mammary ducts, skin, liver, and lung in vitro. In this study epimorphin was analyzed in a human, pancreatic adenocarcinoma cell line (A818-6) which develops single layer epithelial hollow spheres resembling normal pancreatic ductal structures in vitro. Soluble 34- and 31-kD isoforms of epimorphin were found in the culture supernatant of A818-6 cells. In lysates of A818-6 cells we detected the 34-and 31-kD isoforms and the dimers, and in lysates of fibroblasts the 150-kD tetramers of epimorphin additionally. A neutralizing monoclonal antibody against epimorphin (MC-1) efficiently blocked the development of hollow sphere structures from A818-6 cells. Coculture of A818-6 cells with fibroblasts stimulated the development of hollow sphere structures in general and increased differentiation in 5-6-d-old hollow spheres. A818-6 hollow sphere development in the presence of fibroblasts was also blocked by MC-1. In this novel system for human duct-like differentiation of pancreatic epithelial cells, we provide evidence for an autocrine and paracrine function of epimorphin as a major mediator for morphogenesis.

Expression of the hypoxia-inducible and tumor-associated carbonic anhydrases in ductal carcinoma in situ of the breast

Carbonic anhydrases (CA) influence intra- and extracellular pH and ion transport in varied biological processes. We recently identified CA9 and CA12 as hypoxia-inducible genes. In this study we examined the expression of these tumor-associated CAs by immunohistochemistry in relation to necrosis and early breast tumor progression in 68 cases of ductal carcinoma in situ (DCIS) (39 pure DCIS and 29 DCIS associated with invasive carcinoma). CA IX expression was rare in normal epithelium and benign lesions, but was present focally in DCIS (50% of cases) and in associated invasive carcinomas (29%). In comparison, CA XII was frequently expressed in normal breast tissues (89%), in DCIS (84%), and in invasive breast lesions (71%). In DCIS, CA IX was associated with necrosis (P: = 0.0053) and high grade (P: = 0.012). In contrast, CA XII was associated with the absence of necrosis (P: = 0.036) and low grade (P: = 0.012). Despite this, augmented CA XII expression was occasionally observed adjacent to necrosis within high-grade lesions. Neither CA IX nor CA XII expression was associated with regional or overall proliferation as determined by MIB1 staining. Assessment of mammographic calcification showed that CA XII expression was associated with the absence of calcification (n = 43, P: = 0.0083). Our results demonstrate that induction of CA IX and CA XII occurs in regions adjacent to necrosis in DCIS. Furthermore, these data suggest that proliferation status does not influence expression of either CA in breast tissues, that hypoxia may be a dominant factor in the regulation of CA IX, and that factors related to differentiation, as determined by tumor grade, dominate the regulation of CA XII. The existence of differential regulation and associations with an aggressive phenotype may be important in the development of selective inhibitors of CAs, because the latter have recently been shown to prevent tumor invasion.

Carbonic anhydrase inhibitors: sulfonamides as antitumor agents?

Novel sulfonamide inhibitors of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1) were prepared by reaction of aromatic or heterocyclic sulfonamides containing amino, imino, or hydrazino moieties with N,N-dialkyldithiocarbamates in the presence of oxidizing agents (sodium hypochlorite or iodine). The N,N-dialkylthiocarbamylsulfenamido-sulfonamides synthesized in this way behaved as strong inhibitors of human CA I and CA II (hCA I and hCA II) and bovine CA IV (bCA IV). For the most active compounds, inhibition constants ranged from 10(-8) to 10(-9) M (for isozymes II and IV). Three of the derivatives belonging to this new class of CA inhibitors were also tested as inhibitors of tumor cell growth in vitro. These sulfonamides showed potent inhibition of growth against several leukemia, non-small cell lung, ovarian, melanoma, colon, CNS, renal, prostate and breast cancer cell lines. With several cell lines. GI50 values of 10-75 nM were observed. The mechanism of antitumor action with the new sulfonamides reported here remains obscure, but may involve inhibition of CA isozymes which predominate in tumor cell membranes (CA IX and CA XII), perhaps causing acidification of the intercellular milieu, or inhibition of intracellular isozymes which provide bicarbonate for the synthesis of nucleotides and other essential cell components (CA II and CA V). Optimization of these derivatives from the SAR point of view, might lead to the development of effective novel types of anticancer agents.

Carbonic anhydrase and matrix metalloproteinase inhibitors: sulfonylated amino acid hydroxamates with MMP inhibitory properties act as efficient inhibitors of CA isozymes I, II, and IV, and N-hydroxysulfonamides inhibit both these zinc enzymes

The 14 different carbonic anhydrase (CA, EC 4.2.1.1) isozymes as well as the 23 different matrix metalloproteinases (MMPs) isolated up to now in higher vertebrates play important physiological functions in these organisms. Unsubstituted sulfonamides act as high-affinity inhibitors for the first type of these enzymes, whereas hydroxamates strongly inhibit the latter ones. Since the active site geometry around the zinc ion in these two types of metalloenzymes is rather similar, we tested whether sulfonylated amino acid hydroxamates of the type RSO(2)NX-AA-CONHOH (X = H, benzyl, substituted benzyl; AA = amino acid moiety, such as Gly, Ala, Val, Leu) with well-known inhibitory properties against MMPs and Clostridium histolyticum collagenase (ChC, another zinc enzyme related to the MMPs) might also act as CA inhibitors. We also investigated whether N-hydroxysulfonamides of the type RSO(2)NHOH (which are effective CA inhibitors) inhibit MMPs and ChC. Here we report several potent sulfonylated amino acid hydroxamate CA inhibitors (with inhibition constants in the range of 5-40 nM, against the human isozymes hCA I and hCA II, and 10-50 nM, against the bovine isozyme bCA IV), as well as preliminary SAR for this new class of non-sulfonamide CA inhibitors. Some N-hydroxysulfonamides also showed inhibitory properties (in the micromolar range) against MMP-1, MMP-2, MMP-8, MMP-9, and ChC. Thus, the SO(2)NHOH group is a new zinc-binding function for the design of MMP inhibitors. Both CA as well as MMPs are involved, among others, in carcinogenesis and tumor invasion processes. On the basis of these findings, we suggest that the mechanism of antitumor action with some hydroxamate inhibitors might also involve inhibition of some CA isozymes (such as CA IX, CA XII, and CA XIV) present only in tumor cell membranes, in addition to collagenases/gelatinases of the MMP type. Our data also suggest that it should be possible to develop dual enzyme inhibitors that would strongly inhibit both these metalloenzymes, CAs and MMPs, based on the nature of the R, AA, and X moieties in the above formula. Compact X (such as H) and AA (such as Gly) moieties favor CA over MMP inhibition, whereas bulkier X (benzyl, substituted benzyl, etc.) and AA (such as Val, Leu) moieties and substituted-aryl R groups are advantageous for obtaining potent MMP and ChC inhibitors, which show lower affinity for CA.

Loss of TGF-beta signaling contributes to autoimmune pancreatitis

Recent observations suggest that immune response is involved in the development of pancreatitis. However, the exact pathogenesis underlying this immune-mediated response is still under debate. TGF-beta has been known to be an important regulating factor in maintaining immune homeostasis. To determine the role of TGF-beta in the initiation or progression of pancreatitis, TGF-beta signaling was inactivated in mouse pancreata by overexpressing a dominant-negative mutant form of TGF-beta type II receptor in the pancreas, under control of the pS2 mouse trefoil peptide promoter. Transgenic mice showed marked increases in MHC class II molecules and matrix metalloproteinase expression in pancreatic acinar cells. These mice also showed increased susceptibility to cerulein-induced pancreatitis. This pancreatitis was characterized by severe pancreatic edema, inflammatory cell infiltration, T- and B-cell hyperactivation, IgG-type autoantibodies against pancreatic acinar cells, and IgM-type autoantibodies against pancreatic ductal epithelial cells. Therefore, TGF-beta signaling seems to be essential either in maintaining the normal immune homeostasis and suppressing autoimmunity or in preserving the integrity of pancreatic acinar cells.

Chloride-bicarbonate exchangers in the human fetal pancreas

Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene that encodes a small conductance cAMP-activated chloride ion channel. In the CF pancreatic duct, mutations in CFTR cause a reduction in bicarbonate secretion. This is thought to result from CFTR operating in parallel with a chloride-bicarbonate (Cl(-)/HCO(-)(3)) exchanger, located in the apical membrane of pancreatic duct cells. The molecular basis of this Cl(-)/HCO(-)(3) exchanger has not been identified. A combination of screening cDNA libraries, RNase protection, and 5' RACE analysis was used to identify Cl(-)/HCO(-)(3) exchangers in human fetal pancreas. An AE2 Cl(-)/HCO(-)(3) exchanger was shown to be expressed in human fetal pancreas from the midtrimester of gestation, at a time when CF-associated pathology commences. In addition, an AE1 Cl(-)/HCO(3) was identified in fetal pancreas but was absent from the adult pancreas and cultured ductal epithelial cells from fetal and adult pancreas.