Transmembrane carbonic anhydrase, MN/CA IX, is a potential biomarker for biliary tumours

Regulation of Ion Homeostasis for Enhanced Tumor Radio-Immunotherapy

Intra/extracellular ion content affects the growth and metastasis of tumor cells, as well as the efficacy of various antitumor therapies. Herein, a carbonic anhydrase inhibitor (CAI) is loaded onto pH-responsive calcium carbonate (CaCO3 ) nanoparticles and then modify theses nanoparticles with liposomes to obtain biocompatible CaCO3 /CAI@Lipsome (CCL) for enhance tumor radio-immunotherapy. CCL can specially decompose in tumor microenvironment, releasing calcium ion (Ca2+ ) and CAI, as well as increasing the pH value of extracellular fluid. CAI restrains the flow of hydrogen ion (H+ ) inside and outside the tumor cells, resulting in the reversal of tumor acidic microenvironment and the increase of intracellular H+ , both of which can improve the sensitivity of tumor to radiotherapy. Afterward, the increased intracellular H+ together with radiotherapy-causes reactive oxygen species promotes calcium influx, leading to cellular calcium overload. Moreover, the CCL-tailored content of H+ and Ca2+ strengthens radiotherapy-induced immunogenic cell death and dendritic cell maturation, amplifying systemic anti-tumor adaptive immunity. Meanwhile, macrophages in the CCL-treated tumors are polarized from pro-tumor M2 to anti-tumor M1 under X-ray exposure, owing to the neutralization of tumor acidic microenvironment and enhances Ca2+ content. Therefore, multi-directional regulation of the intra/extra tumor cell pH/calcium by simple nano-preparation would provide a powerful way to improve the efficacy of radio-immunotherapy.

Pathology of Combined Hepatocellular Carcinoma-Cholangiocarcinoma: An Update

Combined hepatocellular carcinoma-cholangiocarcinoma (cHCC-CCA) is a rare primary liver cancer that is composed of both hepatocellular and cholangiocellular differentiated cells. It is slightly more common in men and among Asian and Pacific islanders. Overall, risk factors are similar to classic risk factors of hepatocellular carcinoma (HCC). The classification has significantly evolved over time. The last WHO classification (2019) mainly emphasized diagnosis on morphological basis with routine stainings, discarded previously recognized classifications with carcinomas with stem cell features, introduced intermediate cell carcinoma as a specific subtype and considered cholangiolocarcinoma as a subtype of cholangiocellular carcinoma. Immunohistochemical markers may be applied for further specification but have limited value for diagnosis. Recent discoveries in molecular pathway regulation may pioneer new therapeutic approaches for this poor prognostic and challenging diagnosis.

Hepatobiliary acid-base homeostasis: Insights from analogous secretory epithelia

Many epithelia secrete bicarbonate-rich fluid to generate flow, alter viscosity, control pH and potentially protect luminal and intracellular structures from chemical stress. Bicarbonate is a key component of human bile and impaired biliary bicarbonate secretion is associated with liver damage. Major efforts have been undertaken to gain insight into acid-base homeostasis in cholangiocytes and more can be learned from analogous secretory epithelia. Extrahepatic examples include salivary and pancreatic duct cells, duodenocytes, airway and renal epithelial cells. The cellular machinery involved in acid-base homeostasis includes carbonic anhydrase enzymes, transporters of the solute carrier family, and intra- and extracellular pH sensors. This pH-regulatory system is orchestrated by protein-protein interactions, the establishment of an electrochemical gradient across the plasma membrane and bicarbonate sensing of the intra- and extracellular compartment. In this review, we discuss conserved principles identified in analogous secretory epithelia in the light of current knowledge on cholangiocyte physiology. We present a framework for cholangiocellular acid-base homeostasis supported by expression analysis of publicly available single-cell RNA sequencing datasets from human cholangiocytes, which provide insights into the molecular basis of pH homeostasis and dysregulation in the biliary system.

Cancer Drug Development of Carbonic Anhydrase Inhibitors beyond the Active Site

Carbonic anhydrases (CAs) catalyze the reversible hydration of carbon dioxide to produce bicarbonate and a proton. Multiple CA isoforms are implicated in a range of diseases, including cancer. In solid tumors, continuously dividing cells create hypoxic conditions that eventually lead to an acidic microenvironment. Hypoxic tumor cells have different mechanisms in place to regulate and adjust the surrounding microenvironment for survival. These mechanisms include expression of CA isoform IX (CA IX) and XII (CA XII). These enzymes help maintain a physiological intracellular pH while simultaneously contributing to an acidic extracellular pH, leading to tumor cell survival. Expression of CA IX and CA XII has also been shown to promote tumor cell invasion and metastasis. This review discusses the characteristics of CA IX and CA XII, their mechanism of action, and validates their prospective use as anticancer targets. We discuss the current status of small inhibitors that target these isoforms, both classical and non-classical, and their future design in order to obtain isoform-specificity for CA IX and CA XII. Biologics, such as monoclonal antibodies, monoclonal-radionuclide conjugated chimeric antibodies, and antibody-small molecule conjugates are also discussed.

Dual farnesoid X receptor/TGR5 agonist INT-767 reduces liver injury in the Mdr2-/- (Abcb4-/-) mouse cholangiopathy model by promoting biliary HCO⁻₃ output

Chronic cholangiopathies have limited therapeutic options and represent an important indication for liver transplantation. The nuclear farnesoid X receptor (FXR) and the membrane G protein-coupled receptor, TGR5, regulate bile acid (BA) homeostasis and inflammation. Therefore, we hypothesized that activation of FXR and/or TGR5 could ameliorate liver injury in Mdr2(-/-) (Abcb4(-/-)) mice, a model of chronic cholangiopathy. Hepatic inflammation, fibrosis, as well as bile secretion and key genes of BA homeostasis were addressed in Mdr2(-/-) mice fed either a chow diet or a diet supplemented with the FXR agonist, INT-747, the TGR5 agonist, INT-777, or the dual FXR/TGR5 agonist, INT-767 (0.03% w/w). Only the dual FXR/TGR5 agonist, INT-767, significantly improved serum liver enzymes, hepatic inflammation, and biliary fibrosis in Mdr2(-/-) mice, whereas INT-747 and INT-777 had no hepatoprotective effects. In line with this, INT-767 significantly induced bile flow and biliary HCO 3- output, as well as gene expression of carbonic anhydrase 14, an important enzyme able to enhance HCO 3- transport, in an Fxr-dependent manner. In addition, INT-767 dramatically reduced bile acid synthesis via the induction of ileal Fgf15 and hepatic Shp gene expression, thus resulting in significantly reduced biliary bile acid output in Mdr2(-/-) mice.

CONCLUSION

This study shows that FXR activation improves liver injury in a mouse model of chronic cholangiopathy by reduction of biliary BA output and promotion of HCO 3--rich bile secretion.

Inhibition of hypoxia-inducible carbonic anhydrase-IX enhances hexokinase II inhibitor-induced hepatocellular carcinoma cell apoptosis

AIM

The hypoxic condition within large or infiltrative hypovascular tumors produces intracellular acidification, which could activate many signaling pathways and augment cancer cell growth and invasion. Carbonic anhydrase-IX (CA-IX) is an enzyme lowering pH. This study is to examine whether hypoxia induces CA-IX in hepatocellular carcinoma (HCC) cells, and to evaluate its clinical implication in HCC patients.

METHODS

Human HCC cell lines (Huh-7 and HepG2 cells) were used, and cell growth was assessed using MTS assay. CA-IX expression and apoptotic/kinase signaling were evaluated using immunoblotting. The cells were transfected with CA-IX-specific siRNA, or treated with its inhibitor 4-(2-aminoethyl) benzenesulfonamide (CAI#1), and/or the hexokinase II inhibitor, 3-bromopyruvate (3-BP). A clinic pathological analysis of 69 patients who underwent an HCC resection was performed using a tissue array.

RESULTS

Incubation of HCC cells under hypoxia (1% O₂, 5% CO₂, 94% N₂) for 36 h significantly increased CA-IX expression level. CAI#1 (400 μmol/L) or CA-IX siRNA (100 μmol/L) did not influence HCC cell growth and induce apoptosis. However, CAI#1 or CA-IX siRNA at these concentrations enhanced the apoptosis induced by 3-BP (100 μmol/L). This enhancement was attributed to increased ER stress and JNK activation, as compared with 3-BP alone. Furthermore, a clinic pathological analysis of 69 HCC patients revealed that tumor CA-IX intensity was inversely related to E-cadherin intensity.

CONCLUSION

Inhibition of hypoxia-induced CA-IX enhances hexokinase II inhibitor-induced HCC apoptosis. Furthermore, CA-IX expression profiles may have prognostic implications in HCC patients. Thus, the inhibition of CA-IX, in combination with a hexokinase II inhibitor, may be therapeutically useful in patients with HCCs that are aggressively growing in a hypoxic environment.

Molecular targeting of carbonic anhydrase IX in mice with hypoxic HT29 colorectal tumor xenografts

BACKGROUND

Carbonic anhydrase IX (CAIX) is a membrane spanning protein involved in the enzymatic regulation of tumor acid-base balance. CAIX has been shown to be elevated in a number of hypoxic tumor types. The purpose of this study was to determine the efficiency of intact and IgG fragments of cG250 to target CAIX in vivo in a hypoxic tumor model.

METHODOLOGY/PRINCIPAL FINDINGS

Conventional biodistribution studies were performed with (111)In-DO3A-cG250, (111)In-DO3A-F(ab')(2)-cG250 and (111)In-DO3A-Fab-cG250. Additional ex vivo analysis of the tumor was performed with markers for tumor hypoxia, blood perfusion and endogenous CAIX expression. All four data sets were digitally correlated to determine the optimal agent for determining hypoxia in a HT29 colon cancer xenograft. The HT29 human colorectal tumor xenografts show strong CAIX expression in hypoxic areas of poor blood perfusion. The intact IgG had an initial high focal uptake at the periphery of these hypoxic regions and penetration into the areas of highest CAIX expression over the 7-day study period. The lower molecular weight antibody fragments had a faster uptake into areas of high CAIX expression, but had a much lower absolute uptake at the optimal imaging times.

CONCLUSIONS/SIGNIFICANCE

For the clinical detection of hypoxia induced CAIX using cG250 antibody based agents, imaging with the intact IgG at 7 days post injection would allow for the most sensitive and accurate detection of CAIX.

Role of the HBx oncoprotein in carbonic anhydrase 9 induction

Carbonic anhydrase 9 (CA9), as one of the most hypoxia-responsive genes, has been associated almost exclusively with hypoxic tumors. Its principal role is in pH regulation which helps tumor cells overcome intracellular acidosis and survive extended periods of time with low oxygen. Hypoxia-inducible factor 1 (HIF-1) is the main transcriptional activator of CA9. Hepatitis B virus X protein (HBx) has been shown to increase the transcriptional activity of HIF-1. HBx is often expressed from the gene integrated in the hepatocytes infected persistently and contributes significantly to alterations in host gene expression that can lead to the development of hepatocellular carcinoma (HCC) associated with Hepatitis B virus (HBV). The aim of this study was to determine the effect of HBx on expression of CA9. Transient transfection of HBx led to an increase in the expression of CA9 as assessed by RT-PCR and Western blotting. HBx was able to increase CA9 promoter activity significantly in several cell lines. The effect was mediated via HIF-1 and a functional HRE element located -10/-3 bp upstream of the CA9 transcription initiation site. These data suggest that CA9 may be involved in the development of HCC by contributing to the survival of hepatocytes infected with HBV in liver tissue with fibrosis.

Cellular turnover and expression of hypoxic-inducible factor in acute acalculous and calculous cholecystitis

INTRODUCTION

Epithelial corrective and destructive mechanisms have not been studied in inflammatory gallbladder disease.

METHODS

Epithelial apoptosis, cell proliferation and expression of hypoxia-inducible factor (HIF)-1alpha were compared in gallbladders from patients with acute acalculous cholecystitis (AAC; n = 30) and acute calculous cholecystitis (ACC; n = 21), and from patients undergoing surgery for other reasons (normal gallbladders; n = 9), which were removed during open cholecystectomy. The immunohistochemical stains included antibodies to Ki-67 (proliferation), M30 (apoptosis) and HIF-1alpha. Proliferation and apoptosis were expressed as percentages of positive cells. HIF-1alpha expression was expressed as absent, weak, or strong.

RESULTS

Apoptosis (median [25th to 75th percentile]) was significantly increased in AAC (1.31% [0.75% to 1.8%], P < 0.001) and ACC (1.10% [0.63% to 1.64%], P = 0.001), compared with control samples (0.20% [0.07% to 0.45%]. The proliferation rate was significantly increased in AAC (8.0% [4.0% to 17.0%], P < 0.001) and ACC (14% [7.5% to 26.5%], P = 0.001) compared with control samples (1.0% [1.0% to 3.0%]). Strong HIF-1alpha staining was observed in 57% of AAC, in 100% of ACC and in 44% of control specimens (P < 0.001). Intense HIF-1alpha expression was associated with increased cell proliferation (P = 0.002).

CONCLUSION

Cell proliferation and apoptosis were increased in AAC and ACC, as compared with normal gallbladders. Expression of HIF-1alpha was lower in AAC than in ACC.

Carbonic anhydrase IX in oligodendroglial brain tumors

BACKGROUND

Carbonic anhydrase IX is a hypoxia-induced enzyme that has many biologically important functions, including its role in cell adhesion and invasion.

METHODS

This study was set out to investigate the role of CA IX in a series of 86 oligodendroglial brain tumors (71 primary and 15 recurrent; 48 pure oligodendrogliomas and 40 mixed oligoastrocytomas).

RESULTS

80% of the tumors showed CA IX expression by immunohistochemistry. Tumors with moderate or strong CA IX expression had decreased level of cell proliferation compared to weak or no CA IX expression (median 2.9 vs. 5.8, p = 0.015). CA IX correlated with two antioxidative enzymes, manganese superoxide dismutase (MnSOD) and regulatory gammaglutamylcysteine synthetase (GLCL-R): CA IX expression was significantly higher in MnSOD-positive tumors (p = 0.008) and decreased in GLCL-R-positive tumors (p = 0.044). In Cox multivariate analysis CA IX expression, patient age and histological component (pure oligodendroglioma vs. mixed oligoastrocytoma) showed independent prognostic values (p = 0.009, p = 0.003 and p = 0.022, respectively), CA IX positivity predicting poorer outcome.

CONCLUSION

CA IX was proved to be an independent prognostic indicator in oligodendroglial brain tumors, and it also correlates reversely with cell proliferation. It may have a role in the biology of oligodendrogliomas, and most interestingly, as it is mainly expressed in tumor tissue, CA IX could serve as a target molecule for anticancer treatments.

Targeting of biliary cancer with radiolabeled chimeric monoclonal antibody CG250

OBJECTIVE

Carbonic anhydrase 9 recognized by chimeric monoclonal antibody cG250 is overexpressed on biliary cancers. The aim of this study was to determine the targeting of radiolabeled cG250 in patients with biliary cancer to explore a potential role of radioimmunotherapy.

METHODS

Three (3) patients received a diagnostic dose 111In-cG250, and images were acquired 2 hours and 5 days after injection. Immediately after the last imaging session, 131I-cG250 was administered and images were acquired after 2 hours and 5 days. Visual and quantitative analyses was performed and tumor- to-background, tumor-to-normal liver-uptake ratios, and tumor uptake were calculated.

RESULTS

Administration of 111In-cG250 in patients with biliary cancer did not reveal enhanced uptake in the cancer lesions on whole-body scans. The scans obtained after the 131I-cG250 administration showed slightly enhanced tumor uptake in 1 patient with cholangiocarcinoma stage II. In 2 patients with gallbladder carcinoma stage IV, neither 111In-cG250 nor 131I-cG250 showed targeting of known tumor lesions. Immunohistochemical analysis demonstrated CAIX expression in all 3 cases. There were no adverse events related to radiolabeled cG250 administration.

CONCLUSIONS

111In- or 131I-labeled cG250 is not suitable for biliary cancer targeting. Therefore, there is no basis to develop radioimmunotherapy based on radiolabeled cG250 in biliary cancer.

Tumor-associated carbonic anhydrases and their clinical significance

Carbonic anhydrases (CAs) are physiologically important enzymes that catalyze a reversible conversion of carbon dioxide to bicarbonate and participate in ion transport and pH control. Two human isoenzymes, CA IX and CA XII, are overexpressed in cancer and contribute to tumor physiology. Particularly CA IX is confined to only few normal tissues but is ectopically induced in many tumor types mainly due to its strong transcriptional activation by hypoxia accomplished via HIF-1 transcription factor. Therefore, CA IX can serve as a surrogate marker of hypoxia and a prognostic indicator. CA IX appears implicated in cell adhesion and in balance of pH disturbances caused by tumor metabolism. Both tumor-related expression pattern and functional involvement in tumor progression make it a suitable target for anticancer treatment. Here we summarize a current knowledge on CA IX and CA XII, and discuss possibilities of their exploitation for cancer detection, diagnostics, and therapy.

Expression of transmembrane carbonic anhydrases IX and XII in ovarian tumours

AIMS

Carbonic anhydrase (CA) isozymes IX and XII have been suggested to play a role in oncogenic processes. The aim of the present study was to investigate CA IX and XII expression in patients with ovarian tumours.

METHODS AND RESULTS

A series of ovarian tumours was immunostained for CA IX and XII and the results were correlated with histopathological and clinical parameters. Most cases of borderline mucinous cystadenomas, mucinous cystadenocarcinomas and serous cystadenocarcinomas were moderately or strongly positive for CA IX. In malignant tumours, the staining was most prominent in hypoxic regions. Expression of CA XII was detected in all tumour categories, although the mean staining intensity was weaker than for CA IX in all groups except for clear cell carcinomas.

CONCLUSIONS

The wide expression of CA IX and XII in ovarian tumours suggests that these isozymes could represent potential targets in ovarian cancer therapy. The expression pattern of CA IX suggests that it could also serve as a useful histopathological marker protein for hypoxia in malignant ovarian tumours.

Gene expression profiles of hepatic cell-type specific marker genes in progression of liver fibrosis

AIM: To determine the gene expression profile data for the whole liver during development of dimethylni-trosamine (DMN)-induced hepatic fibrosis.

METHODS: Marker genes were identified for different types of hepatic cells, including hepatic stellate cells (HSCs), Kupffer cells (including other inflammatory cells), and hepatocytes, using independent temporal DNA microarray data obtained from isolated hepatic cells.

RESULTS: The cell-type analysis of gene expression gave several key results and led to formation of three hypotheses: (1) changes in the expression of HSC-specific marker genes during fibrosis were similar to gene expression data in in vitro cultured HSCs, suggesting a major role of the self-activating characteristics of HSCs in formation of fibrosis; (2) expression of mast cell-specific marker genes reached a peak during liver fibrosis, suggesting a possible role of mast cells in formation of fibrosis; and (3) abnormal expression of hepatocyte-specific marker genes was found across several metabolic pathways during fibrosis, including sulfur-containing amino acid metabolism, fatty acid metabolism, and drug metabolism, suggesting a mechanistic relationship between these abnormalities and symptoms of liver fibrosis.

CONCLUSION: Analysis of marker genes for specific hepatic cell types can identify the key aspects of fibrogenesis. Sequential activation of inflammatory cells and the self-supporting properties of HSCs play an important role in development of fibrosis.

Targeting tumor-associated carbonic anhydrase IX in cancer therapy

Carbonic anhydrase isoform IX (CA IX) is highly overexpressed in many types of cancer. Its expression, which is regulated by the HIF-1 transcription factor, is strongly induced by hypoxia and correlates with a poor response to classical chemo- and radiotherapies. CA IX contributes to acidification of the tumor environment by efficiently catalyzing the hydration of carbon dioxide to bicarbonate and protons, thereby leading to acquisition of metastatic phenotypes and chemoresistance to weakly basic anticancer drugs. Inhibition of this enzymatic activity by specific inhibitors, such as the sulfonamide indisulam, reverts these processes, establishing a clear-cut role for CA IX in tumorigenesis. Thus, selective CA IX inhibitors could prove useful for elucidating the role of CA IX in hypoxic cancers, for controlling the pH imbalance in tumor cells and for developing diagnostic or therapeutic applications for tumor management. Indeed, fluorescent inhibitors and membrane-impermeant sulfonamides have recently been used as proof-of-concept tools, demonstrating that CA IX is an interesting target for anticancer drug development.

Gene expression property of high-density three-dimensional tissue of HepG2 cells formed in radial-flow bioreactor

In our previous study, we examined three-dimensional culture using 5-ml radial-flow bioreactor (RFB) and showed that genes encoding cell cycle related proteins were suppressed in a stable phase. In this study, we analyzed the gene expression profiles of RFB-cultivated HepG2 cells and found that vascular endothelial growth factor (VEGF) production was strongly induced in the stable phase compared with the growth phase or static two-dimensional culture. When human umbilical vein endothelial cells (HUVECs) were grown under the conditioned medium of the stable phase, it was found that the formation of new blood vessels was induced in the angiogenesis model. DNA microarray analysis showed that the expression levels of both genes related to cell cycle arrest and which are known as tumor markers have increased in the stable phase. This result suggests that HepG2 cells in the stable phase maintain an active tumor phenotype. In addition, the expression of genes induced in the hypoxic condition was also induced in the stable phase. When the culture was carried out under a higher dissolved oxygen (DO) concentration, VEGF production did not decrease significantly and the new blood-vessel-forming ability of the conditioned medium was not suppressed. This suggests that the induction of VEGF production in a stable phase is not affected by DO during the tested level. These results suggest that the RFB cell culture system may be used to assess tumor progression mechanism under three-dimensional condition in vitro.

Cyclooxygenase-2 (COX-2)-independent anticarcinogenic effects of selective COX-2 inhibitors

Nonsteroidal antiinflammatory drugs (NSAIDs) appear to reduce the risk of developing cancer. One mechanism through which NSAIDs act to reduce carcinogenesis is to inhibit the activity of cyclooxygenase-2 (COX-2), an enzyme that is overexpressed in various cancer tissues. Overexpression of COX-2 increases cell proliferation and inhibits apoptosis. However, selective COX-2 inhibitors can also act through COX-independent mechanisms. In this review, we describe the COX-2-independent molecular targets of these COX-2 inhibitors and discuss how these targets may be involved in the anticarcinogenic activities of these selective COX-2 inhibitors. We also compare the concentrations of these inhibitors used in in vitro and in vivo experiments and discuss the implications of the in vitro studies for clinical management of cancer with these drugs.

Expression of carbonic anhydrases IX and XII during mouse embryonic development

BACKGROUND

Of the thirteen active carbonic anhydrase (CA) isozymes, CA IX and XII have been linked to carcinogenesis. It has been suggested that these membrane-bound CAs participate in cancer cell invasion, which is facilitated by an acidic tumor cell environment. Since active cell migration is a characteristic feature of embryonic development, we set out to explore whether these isozymes are expressed in mouse embryos of different ages. The studies were focused on organogenesis stage.

RESULTS

Immunohistochemistry demonstrated that both CA IX and XII are present in several tissues of the developing mouse embryo during organogenesis. Staining for CA IX revealed a relatively wide distribution pattern with moderate signals in the brain, lung, pancreas and liver and weak signals in the kidney and stomach. The expression pattern of CA XII in the embryonic tissues was also relatively broad, although the intensity of immunostaining was weak in most tissues. The CA XII-positive tissues included the brain, where the most prominent staining was seen in the choroid plexus, and the stomach, pancreas, liver and kidney.

CONCLUSION

Membrane-bound CA isozymes IX and XII are expressed in various tissues during mouse organogenesis. These enzymes may regulate ion and pH homeostasis within the developing embryo.

Expression of carbonic anhydrase IX (CA IX), a hypoxia-related protein, rather than vascular-endothelial growth factor (VEGF), a pro-angiogenic factor, correlates with an extremely poor prognosis in esophageal and gastric adenocarcinomas

OBJECTIVE

To evaluate the expression of carbonic anhydrase IX (CA IX) and vascular-endothelial growth factor (VEGF) in esophageal and gastric adenocarcinomas and in turn with the histologic subtype.

SUMMARY BACKGROUND DATA

Tumor hypoxia is an important factor in therapy resistance. A low oxygen concentration in tumors stimulates a.o. the expression of CA IX, a marker of hypoxia, and VEGF, a pro-angiogenic factor.

METHODS

We evaluated the immunohistochemical expression of CA IX and VEGF on paraffin-embedded material of 154 resection specimens: 39 esophageal, 73 cardiac, and 42 distal gastric adenocarcinomas (UICC classification). The adenocarcinomas were subtyped according to the Lauren classification (intestinal- and diffuse-type).

STATISTICAL ANALYSIS

chi test, Kaplan-Meier survival analysis, log-rank test, and Cox proportional hazards model.

RESULTS

CA IX and VEGF expression were independent of the localization of the tumor. However, intestinal-type adenocarcinomas showed a significantly higher expression of CA IX as well as VEGF than diffuse-type tumors. VEGF expression was associated with a high microvessel density. Although survival analysis showed that CA IX expression (P = 0.008) as well as the coexpression of CA IX and VEGF (P = 0.008) correlate with a poor outcome, only CA IX expression is an independent prognostic factor for overall survival and metastasis-free survival.

CONCLUSION

The difference in expression of CA IX and VEGF between intestinal- and diffuse-type adenocarcinomas may possibly explain the different clinical behavior of these tumors. CA IX expression, rather than VEGF positivity in tumors, enables the identification of a subpopulation, characterized by a more aggressive behavior and a poorer prognosis.

The role of carbonic anhydrase IX overexpression in kidney cancer

Carbonic anhydrase IX (CA IX) is a membrane isoenzyme, the overexpression of which is associated with clear cell carcinoma of the kidney. Its overexpression is restricted mainly to cancer, as it is absent in corresponding normal tissues making it a potential cancer biomarker. Several recent studies have shown that CA IX, apart from its classical enzyme activity of reversibly hydrating carbon dioxide extracellularly to facilitate the net extrusion of protons from inside to outside the cell, it can also be a key player in the modulation of cell adhesion processes and participate in the regulation of cell proliferation in response to hypoxic environment to ultimately contribute to tumour progression. Here, we have shown that the sole tyrosine moiety of CA IX present in its intracellular domain can be phosphorylated in an epidermal growth factor dependent manner, suggesting that it can feed into the growth factor receptor dependent signalling pathways. Our studies suggest that the tyrosine phosphorylated CA IX can interact with the regulatory subunit of PI-3-Kinase, contributing to Akt activation. These studies have revealed a positive feed back loop that can form the basis of a vicious cycle that could contribute to the progression of clear cell renal carcinoma and poor prognosis. These studies show that CA IX signalling may be a part of both the hypoxia driven and hypoxia independent pathways that occur in the cancer cell. Finally, our studies emphasize the need for a more refined strategy using signal transduction therapeutics to inhibit the cell surface carbonic anhydrases for the management of this malignancy.

Gastric pit cell hyperplasia and glandular atrophy in carbonic anhydrase IX knockout mice: studies on two strains C57/BL6 and BALB/C

Carbonic anhydrase (CA) isoenzyme IX is a hypoxia-inducible enzyme, which is expressed in the human and rodent gastrointestinal tract and overexpressed in several different tumors. Functionally, it has probably an effect on proliferation and differentiation of gastrointestinal epithelial cells. It may also participate in gastric morphogenesis, since a recent study has shown gastric pit cell hyperplasia and glandular atrophy in CA IX-knockout mice. However, it is not known whether CA IX produces morphological changes in the gastric mucosa, which can turn into a dysplasia or malignancy in the presence of some carcinogenic factors. High-salt diet is considered such a factor which has been shown to modulate Helicobacter pylori-associated carcinogenesis. We produced two strains of CA IX-knockout mice, C57/BL6 and BALB/c, and the mice ate either standard or high-salt feed for 20 weeks. Stomach samples were collected from 40 Car 9(-/-) knockout mice and 37 wildtype littermates, and the tissue sections were examined for histology. CA IX-deficiency caused gastric pit cell hyperplasia and glandular atrophy in both BALB/c and C57/BL6 strains. Excess dietary salt had no significant effect on the severity of pit cell hyperplasia. No dysplasia was found in any of the groups. In C57/BL6 mice, CA IX-deficiency was associated with gastric submucosal inflammation. The results indicate that CA IX-deficiency provides a useful model to study the mechanisms of gastric morphogenesis and epithelial integrity. Further studies are needed to see whether CA IX has a role in the regulation of immune response. The findings suggest that although CA IX-deficiency is not a tumor-promoting factor per se, it induces glandular atrophy in the body mucosa, a lesion which is considered to be a preneoplastic alteration in the stomach.

Expression of a novel carbonic anhydrase, CA XIII, in normal and neoplastic colorectal mucosa

Background

Carbonic anhydrase (CA) isozymes may have an important role in cancer development. Some isozymes control pH homeostasis in tumors that appears to modulate the behaviour of cancer cells. CA XIII is the newest member of the CA gene family. It is a cytosolic isozyme which is expressed in a number of normal tissues. The present study was designed to investigate CA XIII expression in prospectively collected colorectal tumor samples.

Methods

Both neoplastic and normal tissue specimens were obtained from the same patients. The analyses were performed using CA XIII-specific antibodies and an immunohistochemical staining method. For comparison, the tissue sections were immunostained for other cytosolic isozymes, CA I and II.

Results

The results indicated that the expression of CA XIII is down-regulated in tumor cells compared to the normal tissue. The lowest signal was detected in carcinoma samples. This pattern of expression was quite parallel for CA I and II.

Conclusion

The down-regulation of cytosolic CA I, II and XIII in colorectal cancer may result from reduced levels of a common transcription factor or loss of closely linked CA1, CA2 and CA13 alleles on chromosome 8. Their possible role as tumor suppressors should be further evaluated.

Carbonic anhydrases in normal gastrointestinal tract and gastrointestinal tumours

Carbonic anhydrases (CAs) catalyse the hydration of CO₂ to bicarbonate at physiological pH. This chemical interconversion is crucial since HCO₃^- is the substrate for several biosynthetic reactions. This review is focused on the distribution and role of CA isoenzymes in both normal and pathological gastrointestinal (GI) tract tissues. It has been known for many years that CAs are widely present in the GI tract and play important roles in several physiological functions such as production of saliva, gastric acid, bile, and pancreatic juice as well as in absorption of salt and water in intestine. New information suggests that these enzymes participate in several processes that were not envisioned earlier. Especially, the recent reports on plasma membrane-bound isoenzymes IX and XII have raised considerable interest since they were reported to participate in cancer invasion and spread. They are induced by tumour hypoxia and may also play a role in von Hippel-Lindau (VHL)-mediated carcinogenesis.

Carbonic anhydrase isozymes IX and XII in gastric tumors

AIM: To systematically study the expression of carbonic anhydrase (CA) isozymes IX and XII in gastric tumors.

METHODS: We analyzed a representative series of specimens from non-neoplastic gastric mucosa and from various dysplastic and neoplastic gastric lesions for the expression of CA IX and XII. Immunohistochemical staining was performed using isozyme-specific antibodies and biotin-streptavidin complex method.

RESULTS: CA IX was highly expressed in the normal gastric mucosa and remained positive in many gastric tumors. In adenomas, CA IX expression significantly decreased towards the high grade dysplasia. However, the expression resumed back to the normal level in well differentiated adenocarcinomas, while it again declined in carcinomas with less differentiation. In comparison, CA XII showed no or weak immunoreaction in the normal gastric mucosa and was slightly increased in tumors.

CONCLUSION: These results demonstrate that CA IX expression is sustained in several types of gastric tumors. The variations observed in the CA IX levels support the concept that gastric adenomas and carcinomas are distinct entities and do not represent progressive steps of a single pathway.