Ectodomain shedding of the hypoxia-induced carbonic anhydrase IX is a metalloprotease-dependent process regulated by TACE/ADAM17

Hypoxia-induced carbonic anhydrase IX as a target for cancer therapy: from biology to clinical use

The tumor microenvironment includes a complicated network of physiological gradients contributing to plasticity of tumor cells and heterogeneity of tumor tissue. Hypoxia is a key component generating intratumoral oxygen gradients, which affect the cellular expression program and lead to therapy resistance and increased metastatic propensity of weakly oxygenated cell subpopulations. One of the adaptive responses of tumor cells to hypoxia involves the increased expression and functional activation of carbonic anhydrase IX (CA IX), a cancer-related cell surface enzyme catalyzing the reversible conversion of carbon dioxide to bicarbonate ion and proton. Via its catalytic activity, CA IX participates in regulation of intracellular and extracellular pH perturbations that result from hypoxia-induced changes in cellular metabolism producing excess of acid. Through the ability to regulate pH, CA IX also facilitates cell migration and invasion. In addition, CA IX has non-catalytic function in cell adhesion and spreading. Thus, CA IX endows tumor cells with survival advantages in hypoxia/acidosis and confers an increased ability to migrate, invade and metastasize. Accordingly, CA IX is expressed in a broad range of tumors, where it is associated with prognosis and therapy outcome. Its expression pattern and functional implications in tumor biology make CA IX a promising therapeutic target, which can be hit either by immunotherapy with monoclonal antibodies or with compounds inhibiting its enzyme activity. The first strategy has already reached the clinical trials, whereas the second one is still in preclinical testing. Both strategies indicate that CA IX can become a clinically useful anticancer target, but urge further efforts toward better selection of patients for immunotherapy and deeper understanding of tumor types, clinical situations and synthetic lethality interactions with other treatment approaches.

Carbonic anhydrase IX: regulation and role in cancer

Tumor microenvironment substantially influences the process of tumorigenesis. In many solid tumors, imbalance between the demand of rapidly proliferating cancer cells and the capabilities of the vascular system generates areas with insufficient oxygen supply. In response to tumor hypoxia, cancer cells modulate their gene expression pattern to match the requirements of the altered microenvironment. One of the most significant adaptations to this milieu is the shift towards anaerobic glycolysis to keep up the energy demands. This oncogenic metabolism is often maintained also in aerobic cells. Lactic acid, its metabolic end-product, accumulates hand-in-hand with carbon dioxide, leading to acidification of the extracellular environment. Carbonic anhydrase IX (CA IX) is the most widely expressed gene in response to hypoxia. Its crucial role in intracellular pH maintenance represents the means by which cancer cells adapt to the toxic conditions of the extracellular milieu. Furthermore, the activity of CA IX stimulates the migratory pathways of cancer cells and is connected with the increase of the aggressive/invasive phenotype of tumors. CA IX expression in many types of tumors indicates its relevance as a general marker of tumor hypoxia. Moreover, its expression is closely related to prognosis of the clinical outcome in several tumor types. All above mentioned facts support the strong position of CA IX as a potential drug therapy target. Here, we summarize the state-of-the-art knowledge on its regulation and role in cancer development.

Carbonic anhydrase IX, a hypoxia-induced catalytic component of the pH regulating machinery in tumors

Acidic tissue microenvironment contributes to tumor progression via multiple effects including the activation of angiogenic factors and proteases, reduced cell-cell adhesion, increased migration and invasion, etc. In addition, intratumoral acidosis can influence the uptake of anticancer drugs and modulate the response of tumors to conventional therapy. Acidification of the tumor microenvironment often develops due to hypoxia-triggered oncogenic metabolism, which leads to the extensive production of lactate, protons, and carbon dioxide. In order to avoid intracellular accumulation of the acidic metabolic products, which is incompatible with the survival and proliferation, tumor cells activate molecular machinery that regulates pH by driving transmembrane inside-out and outside-in ion fluxes. Carbonic anhydrase IX (CA IX) is a hypoxia-induced catalytic component of the bicarbonate import arm of this machinery. Through its catalytic activity, CA IX directly participates in many acidosis-induced features of tumor phenotype as demonstrated by manipulating its expression and/or by in vitro mutagenesis. CA IX can function as a survival factor protecting tumor cells from hypoxia and acidosis, as a pro-migratory factor facilitating cell movement and invasion, as a signaling molecule transducing extracellular signals to intracellular pathways (including major signaling and metabolic cascades) and converting intracellular signals to extracellular effects on adhesion, proteolysis, and other processes. These functional implications of CA IX in cancer are supported by numerous clinical studies demonstrating the association of CA IX with various clinical correlates and markers of aggressive tumor behavior. Although our understanding of the many faces of CA IX is still incomplete, existing knowledge supports the view that CA IX is a biologically and clinically relevant molecule, exploitable in anticancer strategies aimed at targeting adaptive responses to hypoxia and/or acidosis.

Carbonic anhydrase IX as an imaging and therapeutic target for tumors and metastases

Carbonic anhydrase IX (CAIX) which is a zinc containing metalloprotein, efficiently catalyzes the reversible hydration of carbon dioxide. It is constitutively up-regulated in several cancer types and has an important role in tumor progression, acidification and metastasis. High expression of CAIX generally correlates with poor prognosis and is related to a decrease in the disease-free interval following successful therapy. Therefore, it is considered as a prognostic indicator in oncology.In this review, we describe CAIX regulation and its role in tumor hypoxia, acidification and metastasis. In addition, the molecular imaging of CAIX and its potential for use in cancer detection, diagnosis, staging, and for use in following therapy response is discussed. Both antibodies and small molecular weight compounds have been used for targeted imaging of CAIX expression. The use of CAIX expression as an attractive and promising candidate marker for systemic anticancer therapy is also discussed.

Carbonic anhydrase expression in kidney and renal cancer: implications for diagnosis and treatment

Four different carbonic anhydrases are expressed in the human nephron, the functional unit of the kidney. These are specifically expressed in different nephron segments, emphasizing the critical role carbonic anhydrases play in maintaining the homeostasis of this crucial organ.Whereas the localization of carbonic anhydrases in the kidney has been long established, interest in carbonic anhydrases has increased dramatically for renal cancer, in particular for the clear cell variant of renal cell carcinoma (ccRCC) because carbonic anhydrase IX is specifically expressed in ccRCC. Therefore carbonic anhydrase IX is being studied as potential diagnostic and therapeutic target, despite carbonic anhydrase IX expression in non-renal tissues.

Carbonic anhydrase IX from cancer-associated fibroblasts drives epithelial-mesenchymal transition in prostate carcinoma cells

Extracellular acidification, a mandatory feature of several malignancies, has been mainly correlated with metabolic reprogramming of tumor cells toward Warburg metabolism, as well as to the expression of carbonic anydrases or proton pumps by malignant tumor cells. We report herein that for aggressive prostate carcinoma, acknowledged to be reprogrammed toward an anabolic phenotype and to upload lactate to drive proliferation, extracellular acidification is mainly mediated by stromal cells engaged in a molecular cross-talk circuitry with cancer cells. Indeed, cancer-associated fibroblasts, upon their activation by cancer delivered soluble factors, rapidly express carbonic anhydrase IX (CA IX). While expression of CAIX in cancer cells has already been correlated with poor prognosis in various human tumors, the novelty of our findings is the upregulation of CAIX in stromal cells upon activation. The de novo expression of CA IX, which is not addicted to hypoxic conditions, is driven by redox-based stabilization of hypoxia-inducible factor-1. Extracellular acidification due to carbonic anhydrase IX is mandatory to elicit activation of stromal fibroblasts delivered metalloprotease-2 and -9, driving in cancer cells the epithelial-mesenchymal transition epigenetic program, a key event associated with increased motility, survival and stemness. Both genetic silencing and pharmacological inhibition of CA IX (with sulfonamide/sulfamides potent inhibitors) or metalloprotease-9 are sufficient to impede epithelial-mesenchymal transition and invasiveness of prostate cancer cells induced by contact with cancer-associated fibroblasts. We also confirmed in vivo the upstream hierarchical role of stromal CA IX to drive successful metastatic spread of prostate carcinoma cells. These data include stromal cells, as cancer-associated fibroblasts as ideal targets for carbonic anhydrase IX-directed anticancer therapies.

Carbonic anhydrase IX: a hypoxia-controlled "catalyst" of cell migration

Cell migration can be principally viewed as a chain of well-orchestrated morphological events that lead to dynamic reshaping of the cell body. However, behind the scene of such a "morphological theater" there are very complex, interrelated molecular and physiological processes that drive the cell movement. Among them, ion transport and pH regulation play a key role, with carbonic anhydrase IX (CA IX) emerging as one of the important "molecular actors." CA IX is a highly active cell surface enzyme expressed in a broad range of solid tumors in response to hypoxia and explored as a clinically useful biomarker of hypoxia and as a therapeutic target. Its biological role is to protect tumor cells from hypoxia and acidosis in the tumor microenvironment. The study published recently by our group showed that CA IX actively contributes to cell migration and invasion. For the first time, we demonstrated CA IX accumulation in lamellipodia of migrating cells and its direct in situ interaction with bicarbonate transporters. Our findings indicate that tumor cells need CA IX not only as a pro-survival factor in hypoxia and acidosis, but also as a pro-migratory component of the cellular apparatus driving epithelial-mesenchymal transition.

Carbonic anhydrase IX is a clinically significant tissue and serum biomarker associated with renal cell carcinoma

Carbonic anhydrase IX (CA IX) is regarded as one of the most prominent markers of tumor hypoxia with potential to serve as a diagnostic biomarker, prognostic indicator as well as tumor therapeutic target. The aim of the present study was to perform an in-depth analysis of CA IX expression in blood and tissue samples and to evaluate the significance of CA IX status for different renal cell carcinomas (RCCs). The expression of CA IX was determined in blood and tissue samples from 74 kidney cancer patients using reverse transcription polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA), Western blotting (WB) and immunohistochemistry (IHC). The CA IX status was correlated with RCC type and tumor stage. IHC and WB provided evidence for a significantly higher expression of CA IX in clear cell RCC (CCRCC) specimens compared to other RCCs. RT-PCR assay revealed that 32.42% of all RCC patients possess CA9-positive cells in peripheral blood and three-quarters of CA9-positive patients were diagnosed with CCRCC. When the patients were subdivided according to tumor stage, decreased positivity was observed with higher tumor stage (50% in T1 vs. 17% in T3). Serum CA IX levels determined by ELISA were significantly higher in CCRCC patients than in non-CCRCC. A significant association between s-CA IX and CCRCC tumor stage was also determined (T1-87.51 vs. T3-341.98 pg/ml, p=0.046). We demonstrated that the CA IX expression profiles in blood and tissue samples from 74 kidney cancer patients are closely correlated with their histological subtypes. This is the first study reporting CA IX expression in blood and tissue samples from kidney cancer patients determined by four different methods.

ADAM17 promotes glioma cell malignant phenotype

A disintegrin and metalloproteinase-17 (ADAM17) is involved in proteolytic ectodomain shedding of several membrane-bound growth factors and cytokines. The expression and activity of ADAM17 increase under some pathological conditions such as stroke and cancer. ADAM17 promotes neural progenitor cell migration and contributes to neurogenesis after stroke and breast cancer growth and invasion. In the present study, we sought to elucidate whether ADAM17 contributes to glioma progression. To this end, we examined the role of ADAM17 in the proliferation, invasion, and tube formation of U87 human glioma cells in vitro and tumor growth in vivo. Stable transfection of the U87 cell line with either a plasmid for over-expression of human ADAM17, or a siRNA to ADAM17 was employed in this study to establish high- or low-ADAM17 expression in glioma cells, respectively. For study of mechanism, the ADAM17 inhibitor TAPI-2 and the PI3K-AKT inhibitor LY294002 were used to counteract high-ADAM17 expression and the activated PI3K-AKT pathway, respectively. Proliferation of glioma cells were tested by thiazolyl blue tetrazolium bromide (MTT) assay, bromodeoxyuridine incorporation assay, growth curve, and sulforhodamine B assay. Matrigel invasion assays were used to assess the ability of U87 cells to penetrate the extracellular matrix (ECM). A Matrigel tube formation assay was performed to test capillary tube formation ability. EGFR-PI3K-Akt pathway activation in U87 cells under different ADAM17 expression levels were tested by Western blot. Our data show that ADAM17 promotes the U87 malignant phenotype by increased proliferation, invasion, angiogenesis, and in vivo tumor growth. Tumor growth in nude mice was significantly inhibited by ADAM17 inhibitor and A17-shRNA in vivo transfection. TGF-α, VEGF secretion, and VEGF expression was increased by ADAM17 and counteracted by ADAM17 siRNA, TAPI-2, and LY294002 in U87 cells. ADAM17 activated, whereas ADAM17 siRNA, TAPI-2, and LY294002 deactivated the EGFR-PI3K-AKT signal pathway, which correlated with U87 cell malignant phenotype changes. This study suggests ADAM17 contributes to glioma progression through activation of the EGFR-PI3K-AKT signal pathway.

Carbonic anhydrase IX (CA9) modulates tumor-associated cell migration and invasion

Expression of carbonic anhydrase IX (CA9) was shown to be strongly involved in high incidences of metastasis and poor prognosis in various human tumors. In this study, we investigated the possible role for CA9 in tumor metastases in vitro, using a gene transfection tool in the human cervical carcinoma cell line C33A. Gene expression profiling of CA9-transfected cells (C33A/CA9) and vector-transfected cells (C33A/Mock) was investigated by DNA microarray. The biological functions of differentially expressed genes between the C33A/CA9 and C33A/Mock cells included cell growth, regulation of cell-cell and cell-extracellular matrix adhesion and cytoskeletal organization. Immunofluorescent stain and Matrigel culture showed cytoskeletal remodeling, disassembled focal adhesion, weakened cell-cell adhesion and increased motility in C33A/CA9 cells. These invasive and metastatic phenotypes were associated with Rho-GTPase-related epithelial-mesenchymal transition. Inhibition of the Rho/Rho kinase pathway by a ROCK inhibitor (Y27632) and si-Rho (short interference RNA against RhoA) showed that Rho-GTPase signaling was involved in cellular morphologic and migratory changes. The effect of CA9 on Rho-GTPase signaling was also confirmed by silencing CA9 expression. Our results suggest that CA9 overexpression induces weakening of cell adhesions and augmented cell motility by aberrant Rho-GTPase signal transduction. Our study shows an underlying mechanism of CA9-related enhanced metastatic potential of tumor cells.

Measuring carbonic anhydrase IX as a hypoxia biomarker: differences in concentrations in serum and plasma using a commercial enzyme-linked immunosorbent assay due to influences of metal ions

BACKGROUND

There is increasing interest in measuring the soluble forms of carbonic anhydrase IX (CA IX) in blood as a marker of hypoxia for prognostic purposes or for predictive use in therapeutic trials in various cancers. Following our initial observations of marked differences in the measured concentrations of CA IX in EDTA plasma versus serum, we sought to investigate these further in order to determine their effects on results in published studies and to ensure accurate measurement in future studies.

METHODS

Serum and EDTA plasma samples from healthy controls and patients with renal cancer were used in the validation of two commercially available enzyme-linked immunosorbent assays (ELISAs) for CA IX with examination of recovery, parallelism and specificity and comparison of paired plasma and serum.

RESULTS

Successful validation of one of the ELISAs was not achieved with particular problems with parallelism and marked differences in measured CA IX concentrations between EDTA plasma and serum. This appeared to be due to a metal ion-dependent epitope on CA IX recognized by the detection antibody in this assay. The other commercially available ELISA examined was successfully validated and showed no difference in CA IX between EDTA plasma and serum.

CONCLUSIONS

These results have important consequences for published studies using this assay where the conclusions drawn from the measurements made may be invalid. This study highlights the need for stringent validation of commercially available assays, including examination of various sample types, before use in research studies.

Carbonic anhydrase 9 in clear cell renal cell carcinoma: a marker for diagnosis, prognosis and treatment

Carbonic anhydrase 9 (CA9) is a transmembrane member of the carbonic anhydrase family. It catalyses the reversible hydration of carbon dioxide into bicarbonate and a proton, thus enabling tumour cells to maintain a neutral pH despite an acidic microenvironment. CA9 is not expressed in healthy renal tissue but is expressed in most clear cell renal cell carcinomas (CCRCC) through HIF-1α accumulation driven by hypoxia and inactivation of the VHL gene. CA9 expression can be detected in the tumour by immunohistochemistry (IHC), in blood and tissue by ELISA assay and RT-PCR. It has a 100% diagnostic specificity in solid renal tumours, while ELISA assays on aspiration fluids may help in atypical cysts. Blood-based assays, ELISA for CA9 antigen and RT-PCR for CA9 mRNA are promising for the prognosis and follow-up of localised CCRCC. In metastatic disease, high CA9 expression by IHC was reported to be a powerful prognostic marker with better survival and sensitivity to IL-2, but this is still debated. Almost no data are currently available on the association of CA9 expression and outcome to targeted drugs. The prognostic value of CA9 in CCRCC could be explained by the frequent VHL gene inactivation driving an early activation of the HIF pathway. The poorer prognosis associated with low CA9 expressing tumours could be due to the simultaneous overexpression of EGFR contributing to the activation of AkT and mTOR pathways. Targeting CA9 by inhibitors, radioimmunotherapy, monoclonal antibodies or vaccination is promising and offers new avenues for clinical research.

High levels of carbonic anhydrase IX in tumour tissue and plasma are biomarkers of poor prognostic in patients with non-small cell lung cancer

Background:

Carbonic anhydrase IX (CAIX) is an enzyme upregulated by hypoxia during tumour development and progression. This study was conducted to assess if the expression of CAIX in tumour tissue and/or plasma can be a prognostic factor in patients with non-small cell lung cancer (NSCLC).

Methods:

Tissue microarrays containing 555 NSCLC tissue samples were generated for quantification of CAIX expression. The plasma level of CAIX was determined by ELISA in 209 of these NSCLC patients and in 58 healthy individuals. The CAIX tissue immunostaining and plasma levels were correlated with clinicopathological factors and patient outcome.

Results:

CAIX tissue overexpression correlated with shorter overall survival (OS) (P=0.05) and disease-specific survival (DSS) of patients (P=0.002). The CAIX plasma level was significantly higher in patients with NSCLC than in healthy individuals (P<0.001). A high level of CAIX in the plasma of patients was associated with shorter OS (P<0.001) and DSS (P<0.001), mostly in early stage I+II NSCLC. Multivariate Cox analyses revealed that high CAIX tissue expression (P=0.002) was a factor of poor prognosis in patients with resectable NSCLC. In addition, a high CAIX plasma level was an independent variable predicting poor OS (P<0.001) in patients with NSCLC.

Conclusion:

High expression of CAIX in tumour tissue is a predictor of worse survival, and a high CAIX plasma level is an independent prognostic biomarker in patients with NSCLC, in particular in early-stage I+II carcinomas.

Metalloproteinase-dependent shedding of low-density lipoprotein receptor-related protein-1 ectodomain decreases endocytic clearance of endometrial matrix metalloproteinase-2 and -9 at menstruation

Cyclic elimination of the endometrium functional layer through menstrual bleeding results from intense tissue breakdown by proteolytic enzymes, mainly members of the matrix metalloproteinase (MMP) family. In contrast to menstrual-restricted MMPs, e.g. interstitial collagenase (MMP-1), gelatinases A (MMP-2) and B (MMP-9) mRNAs are abundant throughout the cycle without detectable tissue degradation at proliferative and secretory phases, implying a tight posttranslational control of both gelatinases. This paper addresses the role of low-density lipoprotein receptor-related protein (LRP)-1 in the endocytic clearance of endometrial gelatinases. LRP-1 mRNA and protein were studied using RT-PCR, Western blotting, and immunolabeling. Posttranslational control of LRP-1 was analyzed in explant culture. The receptor-associated protein (RAP), used as LRP antagonist, strongly increased (pro)gelatinase accumulation in medium conditioned by endometrial explants, suggesting a role for LRP-1 in their clearance. Although LRP-1 mRNA remained constant throughout the cycle, the protein ectodomain vanished at menses. LRP-1 immunolabeling selectively disappeared in areas of extracellular matrix breakdown in menstrual samples. It also disappeared from explants cultured without estrogen and progesterone (EP) due to ectodomain shedding in the medium. The shedding was inhibited by metalloproteinase inhibitors, including a disintegrin and metalloproteinase (ADAM) inhibitor, and by tissue inhibitors of MMPs (TIMP)-3 and -2, but barely by TIMP-1, pointing to ADAM-12 as the putative sheddase. In good agreement, ADAM-12 mRNA expression was repressed by EP. In conclusion, the efficient LRP-1-mediated clearance of gelatinase activity in nonbleeding endometrium is abrogated upon EP withdrawal, due to shedding of LRP-1 ectodomain by a metalloproteinase, presumably ADAM-12, itself regulated by EP.

ADAM17 promotes breast cancer cell malignant phenotype through EGFR-PI3K-AKT activation

A disintegrin and metalloproteinase-17 (ADAM17) is involved in proteolytic ectodomain shedding of several membrane-bound growth factors and cytokines. The expression and activity of ADAM17 increase under some pathological conditions such as stroke and glioma. ADAM17 promotes neural progenitor cell migration and contributes to stroke-induced neurogenesis after stroke and brain tumor growth and invasion. In the present study, we sought to elucidate whether ADAM17 contributes to breast cancer progression and its mechanisms. To this end, we examined the role of ADAM17 in the proliferation, invasion and tube formation of MDA-MB-231 breast cancer cells in vitro. Stable transfection of the MDA-MB-231 cell line with either a plasmid for overexpression of human ADAM17, or a siRNA to ADAM17 was employed in this study to establish high or low ADAM17 expression in breast cancer cells, respectively. For study of mechanism, the ADAM17 inhibitor TAPI-2 and the PI3K-AKT inhibitor LY294002 were used to counteract high ADAM17 expression or the activated PI3K-AKT pathway. Proliferation of MDA-MB-231 breast cancer cells were tested by MTT, Bromodeoxyuridine incorporation assay, growth curve and sulforhodamine B assay. Matrigel invasion assays were used to assess the ability of MDA-MB-231 cells to penetrate the Extra Cellular Matrix. A Matrigel tube formation assay was performed to test capillary tube formation ability. EGFR-PI3K-Akt pathway activation in MDA-MB-231 cells under different ADAM17 expression levels were tested by western blot and ELISA. Our data show that ADAM17 promotes the MDA-MB-231 malignant phenotype by increased proliferation, invasion and angiogenesis. TGFalpha, VEGF secretion and VEGF expression was increasing by ADAM17 and counteracted by ADAM17 siRNA, TAPI-2 and LY294002 in MDA-MB-231 cells. ADAM17 activated, whereas ADAM17 siRNA, TAPI-2 and LY294002 deactivated the EGFR-PI3K-AKT signal pathway, which correlated with MDA-MB-231 cell malignant phenotype changes. This study suggests ADAM17 contributes to breast cancer progression through activation of the EGFR-PI3K-AKT signal pathway.

Carbonic anhydrase IX has chaperone-like functions and is an immunoadjuvant

Carbonic anhydrase IX (CA9) is a hypoxia-regulated, transmembrane protein associated with neoplastic growth in a large spectrum of human tumors. CA9 is expressed in nearly all clear-cell renal tumors; levels of CA9 expression predict prognosis and response to interleukin-2 therapy. These observations may be explained by a novel chaperone-like function of CA9, which allows it to serve as an immunoadjuvant and stimulate an adaptive immune response against tumor antigens. Classic heat shock proteins (HSP) such as HSP110 and HSP70 are up-regulated in response to cellular stress and function to protect intracellular proteins from aggregation. Similarly, CA9 formed complexes with client proteins and inhibited heat-induced aggregation and enabled refolding of denatured client protein. HSP released from injured cells activate an immune response. CA9 bound dendritic cells in a receptor-specific manner. Bound CA9 was internalized by dendritic cells and processed primarily through the proteosomal pathway. In a murine melanoma model, a complex of CA9 and gp100 generated a gp100-specific antitumor response. A soluble form of CA9 shed from tumor cells had the same chaperone-like functions, providing renal tumors and hypoxic cells with a mechanism for stimulating an immune response against extracellular antigens. Interleukin-2 treatment of patient renal tumors in short-term culture increased CA9 shedding, suggesting a strategy for augmenting the immunogenicity of renal tumors. CA9 has chaperone-like functions and CA9 shed from tumors may play a direct role in stimulating an adaptive immune response.

Sensitization of cerebral tissue in nude mice with photodynamic therapy induces ADAM17/TACE and promotes glioma cell invasion

In the present study, we tested the hypothesis that a mild cerebral tissue injury promotes subsequent glioma invasion via activation of the ADAM17-EGFR-PI3K-Akt pathway. Mild injury was induced by photodynamic therapy (PDT), which employs tissue-penetrating laser light exposure following systemic administration of a tumor-localizing photosensitizer. Athymic nude mice were treated with sublethal PDT (80 J/cm2 with 2 mg/kg Photofrin). Hypoxic stress and ADAM17-EGFR-PI3K-Akt were measured using Western blot and immunostaining. Additional groups with/without pro-sublethal PDT were subsequently implanted with U87 glioma tumor cell. Tumor invasion and ADAM17-EGFR-PI3K-Akt pathway in tumor area were measured. After a sublethal dose of PDT, HIF-1alpha expression was increased by a factor of three in PDT-treated normal brain tissue compared to contralateral control brain tissue. PDT-treated brain tissue exhibited a significant increase in ADAM17, p-EGFR, p-Akt expression compared to non-treated tissue. ADAM17 positive area significantly increased from 1.78% to 10.89%. The percentage of p-EGFR and p-Akt positive cells significantly increased from 9.50% and 14.50% to 21.31% and 32.29%, respectively, PDT treatment significantly increased subsequent implanted U87 glioma cell invasion by 3.68-fold and increased ADAM17, EGFR, p-EGFR, Akt, p-Akt expression by 178%, 43.9%, 152.7%, 89.6%,and 164.2%, respectively, compared to control group. Our data showed that a sublethal sensitization of cerebral tissue with PDT significantly increased U87 cell invasion in nude mice, and that glioma cell invasion is highly correlated with activation of the ADAM17-EGFR-PI3K-Akt pathway (r=0.928, 0.775, 0.870, 0.872, and 0.883, respectively), most likely via HIF-1alpha.

Drug insight: tumor necrosis factor-converting enzyme as a pharmaceutical target for rheumatoid arthritis

The success of agents that inhibit tumor necrosis factor (TNF), such as infliximab, adalimumab and etanercept, has led to a desire for orally available small molecules that have a better safety profile and are less costly to produce than current agents. One target for anti-TNF therapy that is currently under investigation is TNF-converting enzyme, which promotes the release of soluble TNF from its membrane-bound precursor. Inhibitors of this enzyme with drug-like properties have been made and tested in the clinic. These inhibitors include TMI-005 and BMS-561392, both of which have entered into phase II clinical trials. This article summarizes preclinical and clinical findings regarding the use of inhibitors of TNF-converting enzyme for the treatment of rheumatoid arthritis.

Regulation of tumor pH and the role of carbonic anhydrase 9

The high metabolic rate required for tumor growth often leads to hypoxia in poorly-perfused regions. Hypoxia activates a complex gene expression program, mediated by hypoxia inducible factor 1 (HIF1alpha). One of the consequences of HIF1alpha activation is up-regulation of glycolysis and hence the production of lactic acid. In addition to the lactic acid-output, intracellular titration of acid with bicarbonate and the engagement of the pentose phosphate shunt release CO(2) from cells. Expression of the enzyme carbonic anhydrase 9 on the tumor cell surface catalyses the extracellular trapping of acid by hydrating cell-generated CO(2) into [see text] and H(+). These mechanisms contribute towards an acidic extracellular milieu favoring tumor growth, invasion and development. The lactic acid released by tumor cells is further metabolized by the tumor stroma. Low extracellular pH may adversely affect the intracellular milieu, possibly triggering apoptosis. Therefore, primary and secondary active transporters operate in the tumor cell membrane to protect the cytosol from acidosis. We review mechanisms regulating tumor intracellular and extracellular pH, with a focus on carbonic anhydrase 9. We also review recent evidence that may suggest a role for CA9 in coordinating pH(i) among cells of large, unvascularized cell-clusters.

Inhibition of ADAM17 reduces hypoxia-induced brain tumor cell invasiveness

The membrane-anchored metalloproteinase tumor necrosis factor-alpha-converting enzyme (TACE/a disintegrin and metalloproteinase [ADAM] 17) is key in proteolytic ectodomain shedding of several membrane-bound growth factors, cytokines and receptors. The expression and activity of ADAM17 increases under some pathological conditions including stroke, and promotes neural progenitor cell migration and contributes to stroke-induced neurogenesis. Hypoxia initiates cellular invasive processes that occur under both physiological and pathological conditions such as invasion and metastasis of some tumors. In the present study, we sought to elucidate whether ADAM17 contributes to brain tumor invasion. To this end, we examined the role of ADAM17 in the invasiveness of two different brain tumor cell lines, 9L rat gliosarcoma and U87 human glioma, under normoxic and hypoxic conditions. Additionally, we tested the effects of ADAM17 suppression on in vitro tumor cell invasion by means of ADAM17 proteolytic inhibitors and specific small interfering RNA. We found that tumor cells upregulated ADAM17 expression under hypoxia, and that ADAM17 activity correlated with increased tumor cell invasion. Conversely, suppression of ADAM17 proteolysis decreased invasiveness induced by hypoxia in 9L and U87 cells. Furthermore, the contribution of ADAM17 to tumor invasion was independent of matrix metalloproteinase (MMP)-2 and MMP-9 activity. ADAM17 was also found to activate the epidermal growth factor/phosphoinositide-3 kinase/serine/threonine kinase signal transduction pathway. Our data suggest that hypoxia-induced ADAM17 contributes to glioma cell invasiveness through activation of the EGFR signal pathway.

Role of carbonic anhydrases in the progression of renal cell carcinoma subtypes: proposal of a unified hypothesis

Renal cell carcinoma (RCC) has the highest rate of occurrence within the US when compared with other countries. Recent advances in the basic research and molecular diagnostics of this malignancy have revealed that RCC is not a single disease, but it is a mixture of several types of malignancies with unique molecular mechanisms and pathological attributes. RCC is now divided into clear cell carcinoma (80% of all kidney cancers), papillary type 1 and papillary type 2 neoplasms (10-15% of all RCC patients) and RCC with chromophobic and oncocytic features, called the Birt-Hogg-Dube (BHD) subtype, in roughly 5% of all patients. Apart from these, neoplasms such as the tuberous sclerosis (TSC) syndrome may occur with a mixed pathological features with a renal presentation. In this review, molecular evidence, both direct and indirect, published so far on all these RCC subtypes have been analyzed to find out whether there is any common thread that could run through these disparate malignancies that happen to occur in a single organ, i.e., the kidney. We believe that the role played by the expression and certain non-traditional activities of the cabonic anhydrase (CA) family members, along with the differing levels of hypoxia induced within these tumors may be the most common denominators. Evidence is presented focusing on how the CA family members could participate in the genesis and progression of each and every one of these RCC subtypes and how their function could be influenced by hypoxia, activities of receptor type protein tyrosine kinases and certain other pre-disposing factors. These rationalizations point towards a unified hypothesis that may help explain the occurrence of all these RCC subtypes in a molecular manner. We hope that these analyses would a) stimulate further studies aimed toward a better understanding of the role played by carbonic anhydrases in RCC subtypes and b) would pave way to a better and rationally designed therapies to interfere with their function to benefit patients with RCC and possibly other cancers.

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.

The role of carbonic anhydrases in renal physiology

Carbonic anhydrase (CA) catalyzes the reversible hydration of CO(2). CA is expressed in most segments of the kidney. CAII and CAIV predominate in human and rabbit kidneys; in rodent kidneys, CAXII, and CAXIV are also present. CAIX is expressed by renal cell carcinoma (RCC). Most of these isoforms, except for rodent CAIV, have high turnover rates. CAII is a cytoplasmic enzyme, whereas the others are membrane-associated; CAIV is anchored by glycosylphosphatidylinositol linkage. Membrane polarity is apical for CAXIV, basolateral for CAXII, and apical and basolateral for CAIV. Luminal membrane CAs facilitate the dehydration of carbonic acid (H(2)CO(3)) that is formed when secreted protons combine with filtered bicarbonate. Basolateral CA enhances the efflux of bicarbonate via dehydration of H(2)CO(3). CAII and CAIV can associate with bicarbonate transporters (e.g., AE1, kNBC1, NBC3, and SCL26A6), and proton antiporter, NHE1 in a membrane protein complex called a transport metabolon. CAXII and CAXIV may also be associated with transporters in normal kidney and CAIX in RCCs. The multiplicity of CAs implicates their importance in acid-base and other solute transport along the nephron. For example, CAII on the cytoplasmic face and CAIV on the extracellular surface provide the 'push' and 'pull' for bicarbonate transport by supplying and dissipating substrate respectively.

Recent advances in MMP inhibitor design

The search for an MMP inhibitor with anticancer efficacy is a nearly three-decade endeavor. This inhibitor is yet to be found. The reasons for this failure include shortcomings in the chemistry of these compounds (including broad MMP sub-type selectivity, metabolic lability, and toxicity) as well as the emerging, and arguably extraordinary, complexity of MMP cell (and cancer) biology. Together these suggest that the successful anticancer inhibitor must possess MMP selectivity against the MMP subtype whose involvement is critical, yet highly temporally (with respect to metastatic progression) and mechanistically (with respect to matrix degradation) regulated. This review summarizes the progression of chemical structure and mechanistic thinking toward these objectives, with emphasis on the disappointment, the perseverance, and the resilient optimism that such an inhibitor is there to be discovered.