Transcriptional regulation of the MN/CA 9 gene coding for the tumor-associated carbonic anhydrase IX. Identification and characterization of a proximal silencer element

Betulin Sulfonamides as Carbonic Anhydrase Inhibitors and Anticancer Agents in Breast Cancer Cells

Hypoxia-regulated protein carbonic anhydrase IX (CA IX) is up-regulated in different tumor entities and correlated with poor prognosis in breast cancer patients. Due to the radio- and chemotherapy resistance of solid hypoxic tumors, derivatives of betulinic acid (BA), a natural compound with anticancer properties, seem to be promising to benefit these cancer patients. We synthesized new betulin sulfonamides and determined their cytotoxicity in different breast cancer cell lines. Additionally, we investigated their effects on clonogenic survival, cell death, extracellular pH, HIF-1α, CA IX and CA XII protein levels and radiosensitivity. Our study revealed that cytotoxicity increased after treatment with the betulin sulfonamides compared to BA or their precursors, especially in triple-negative breast cancer (TNBC) cells. CA IX activity as well as CA IX and CA XII protein levels were reduced by the betulin sulfonamides. We observed elevated inhibitory efficiency against protumorigenic processes such as proliferation and clonogenic survival and the promotion of cell death and radiosensitivity compared to the precursor derivatives. In particular, TNBC cells showed benefit from the addition of sulfonamides onto BA and revealed that betulin sulfonamides are promising compounds to treat more aggressive breast cancers, or are at the same level against less aggressive breast cancer cells.

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.

Carbonic Anhydrase IX-Mouse versus Human

In contrast to human carbonic anhydrase IX (hCA IX) that has been extensively studied with respect to its molecular and functional properties as well as regulation and expression, the mouse ortholog has been investigated primarily in relation to tissue distribution and characterization of CA IX-deficient mice. Thus, no data describing transcriptional regulation and functional properties of the mouse CA IX (mCA IX) have been published so far, despite its evident potential as a biomarker/target in pre-clinical animal models of tumor hypoxia. Here, we investigated for the first time, the transcriptional regulation of the Car9 gene with a detailed description of its promoter. Moreover, we performed a functional analysis of the mCA IX protein focused on pH regulation, cell-cell adhesion, and migration. Finally, we revealed an absence of a soluble extracellular form of mCA IX and provided the first experimental evidence of mCA IX presence in exosomes. In conclusion, though the protein characteristics of hCA IX and mCA IX are highly similar, and the transcription of both genes is predominantly governed by hypoxia, some attributes of transcriptional regulation are specific for either human or mouse and as such, could result in different tissue expression and data interpretation.

Lactate stimulates CA IX expression in normoxic cancer cells

Besides hypoxia, other factors and molecules such as lactate, succinate, and reactive oxygen species activate transcription factor hypoxia-inducible factor-1 (HIF-1) even in normoxia. One of the main target gene products of HIF-1 is carbonic anhydrase IX (CA IX). CA IX is overexpressed in many tumors and serves as prognostic factor for hypoxic, aggressive and malignant cancers. CA IX is also induced in normoxia in high cell density. In this study, we observed that lactate induces CA IX expression in normoxic cancer cells in vitro and in vivo. We further evidenced that participation of both HIF-1 and specificity protein 1 (SP1) transcription factors is crucial for lactate-driven normoxic induction of the CA9 gene. By inducing CA IX, lactate can facilitate the maintenance of cancer cell aggressive behavior in normoxia.

Dexamethasone downregulates expression of carbonic anhydrase IX via HIF-1α and NF-κB-dependent mechanisms

Dexamethasone is a synthetic glucocorticoid frequently used to suppress side-effects of anticancer chemotherapy. In the present study, we showed that dexamethasone treatment leads to concentration-dependent downregulation of cancer-associated marker, carbonic anhydrase IX (CA IX), at the level of promoter activity, mRNA and protein expression in 2D and 3D cancer cell models. The effect of dexamethasone on CA IX expression under hypoxic conditions is predominantly mediated by impaired transcriptional activity and decreased protein level of the main hypoxic transcription factor HIF-1α. In addition, CA9 downregulation can be caused by protein-protein interactions between activated glucocorticoid receptors, major effectors of glucocorticoid action, and transcription factors that trigger CA9 transcription (e.g. AP-1). Moreover, we identified a potential NF-κB binding site in the CA9 promoter and propose the involvement of NF-κB in the dexamethasone-mediated inhibition of CA9 transcription. As high level of CA IX is often linked to aggressive tumor behavior, poor prognosis and chemo- and radiotherapy resistance, uncovering its reduction after dexa-methasone treatment and implication of additional regulatory mechanisms can be relevant for the CA IX-related clinical applications.

Drug delivery system targeting advanced hepatocellular carcinoma: Current and future

Hepatocellular carcinoma (HCC) has a fairly high morbidity and is notoriously difficult to treat due to long latent period before detection, multidrug resistance and severe drug-related adverse effects from chemotherapy. Targeted drug delivery systems (DDS) that can selectively deliver therapeutic drugs into tumor sites have demonstrated a great potential in cancer treatment, which could be utilized to resolve the limitations of conventional chemotherapy. Numerous preclinical studies of DDS have been published, but targeted DDS for HCC has yet to be made for practical clinical use. Since rational targeted DDS design should take cancer-specific properties into consideration, we have reviewed the biological and physicochemical properties of HCC extensively to provide a comprehensive understanding on HCC, and recent DDS studies on HCC, aiming to find some potential targeted DDSs for HCC treatment and a meaningful platform for further development of HCC treatments.

FROM THE CLINICAL EDITOR

Hepatocellular carcinoma has a high incidence worldwide and is known to be multidrug resistant. Thus, intensive research is being carried out to find better chemotherapeutic agents as well as new drug delivery systems. In this article, the authors reviewed in depth the current challenges facing new drug designs and also outlined novel targeted drug delivery systems (DDS) in the fight against HCC.

Sulforaphane reduces molecular response to hypoxia in ovarian tumor cells independently of their resistance to chemotherapy

One of the recently emerging anticancer strategies is the use of natural dietary compounds, such as sulforaphane, a cancer-chemopreventive isothiocyanate found in broccoli. Based on the growing evidence, sulforaphane acts through molecular mechanisms that interfere with multiple oncogenic pathways in diverse tumor cell types. Herein, we investigated the anticancer effects of bioavailable concentrations of sulforaphane in ovarian carcinoma cell line A2780 and its two derivatives, adriamycin-resistant A2780/ADR and cisplatin-resistant A2780/CP cell lines. Since tumor microenvironment is characterized by reduced oxygenation that induces aggressive tumor phenotype (such as increased invasiveness and resistance to chemotherapy), we evaluated the effects of sulforaphane in ovarian cancer cells exposed to hypoxia (2% O₂). Using the cell-based reporter assay, we identified several oncogenic pathways modulated by sulforaphane in hypoxia by activating anticancer responses (p53, ARE, IRF-1, Pax-6 and XRE) and suppressing responses supporting tumor progression (AP-1 and HIF-1). We further showed that sulforaphane decreases the level of HIF-1α protein without affecting its transcription and stability. It can also diminish transcription and protein level of the HIF-1 target, CA IX, which protects tumor cells from hypoxia-induced pH imbalance and facilitates their migration/invasion. Accordingly, sulforaphane treatment leads to diminished pH regulation and reduced migration of ovarian carcinoma cells. These effects occur in all three ovarian cell lines suggesting that sulforaphane can overcome the chemoresistance of cancer cells. This offers a path potentially exploitable in sensitizing resistant cancer cells to therapy, and opens a window for the combined treatments of sulforaphane either with conventional chemotherapy, natural compounds, or with other small molecules.

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.

Expression pattern of carbonic anhydrase IX in Medullary thyroid carcinoma supports a role for RET-mediated activation of the HIF pathway

Medullary thyroid carcinoma is a relatively rare tumor with poor prognosis and therapy response. Its phenotype is determined by both genetic alterations (activating RET oncoprotein) and physiological stresses, namely hypoxia [activating hypoxia-inducible factor (HIF)]. Here, we investigated the cooperation between these two mechanisms. The idea emerged from the immunohistochemical analysis of carbonic anhydrases (CA) IX and XII expression in thyroid cancer. Although CAXII was present in all types of thyroid carcinomas, CAIX, a direct HIF target implicated in tumor progression, was associated with aggressive medullary and anaplastic carcinomas, and its expression pattern in medullary thyroid carcinomas suggested contribution of both hypoxic and oncogenic signaling. Therefore, we analyzed the CA9 promoter activity in transfected tumor cells expressing RET and/or the HIF-α subunit. We showed that overexpression of both wild-type and mutant RET can increase the CA9 promoter activity induced by HIF-1 (but not HIF-2) in hypoxia. Similar results were obtained with another HIF-1-regulated promoter derived from the lactate dehydrogenase A gene. Moreover, inhibition of the major kinase pathways, which transmit signals from RET and regulate HIF-1, abrogated their cooperative effect on the CA9 promoter. Thus, we brought the first experimental evidence for the crosstalk between RET and HIF-1 that can explain the increased expression of CAIX in medullary thyroid carcinoma and provide a rationale for therapy simultaneously targeting both pathways.

Interaction of HIF-1α and Notch3 Is Required for the Expression of Carbonic Anhydrase 9 in Breast Carcinoma Cells

Expression of carbonic anhydrase 9 (CA9) is associated with poor prognosis and increased tumor aggressiveness and does not always correlate with HIF-1α expression. Presently, we analyzed the regulation of CA9 expression during hypoxia by HIF-1α, Notch3, and the von Hippel-Lindau (VHL) in breast carcinoma cells. Both HIF-1α and Notch3 were absolutely required for the expression of CA9 mRNA, protein, and reporter. Reciprocal co-immunoprecipitation of HIF-1α, Notch3 intracellular domain (NICD3), and pVHL demonstrated their association. The presence of common consensus prolyl hydroxylation and pVHL binding motifs (L(XY)LAP);LLPLAP(2191) suggested an oxygen-dependent regulation for NICD3. However, unlike the HIF-1α protein, NICD3 protein levels were not modulated with hypoxia or hypoxia-mimetic agents. Surprisingly, mutations of the common prolyl hydroxylation and pVHL binding domain lead to the loss of CA9 mRNA, protein, and reporter activity. Chromatin immunoprecipitation assay demonstrated the association of NICD3, HIF-1α, and pVHL at the CA9 promoter. Further, the NICD3 mutant defective in prolyl hydroxylation and subsequent pVHL binding caused a reduction in cell proliferation of breast carcinoma cells. We show here for the first time that the interaction of HIF-1α with NICD3 is important for the regulation of CA9 expression. These findings suggest that although CA9 is a hypoxia-responsive gene, its expression is modulated by the interaction of HIF-1α, Notch3, and VHL proteins. Targeting the expression of CA9 by targeting upstream regulators could be useful in cancer/stem cell therapy.

Carbonic anhydrase IX: a promising diagnostic and prognostic biomarker in breast carcinoma

We examined the expression of carbonic anhydrase IX (CA IX) by immunohistochemical staining using monoclonal antibody M75 (Institute of Virology, Slovak Academy of Sciences, Bratislava) in a group of 38 fibroadenomas and 55 carcinomas of the breast. In each case, the intensity of staining, percentage of labeled cells and subcellular localization of CA IX were assessed. CA IX was detected in 11/38 fibroadenomas (28.9%). Weak cytoplasmic positivity was dominant in these positive cases. Immunohistochemical analysis of 55 carcinomas showed CA IX expression in 34 cases (61.8%). Membrane staining alone was observed in 27/55 carcinomas (49.1%), while cytoplasmic positivity was found in 4/55 cases (7.3%). Combined membrane and cytoplasmic immunostaining of CA IX was detected in 3/55 carcinomas (5.4%). The intensity of immunoreactivity varied from weak to strong. Under 50% of reactive cells were found in 9/38 fibroadenomas (23.6%) and in 29/55 carcinomas (52.7%). More than 50% of reactive cells were found in 2/38 fibroadenomas (5.3%) and in 5/55 carcinomas (9.1%). Statistical analysis confirmed significant differences in the subcellular localization, intensity of immunoreactivity and percentage of labeled cells in fibroadenomas and carcinomas (p<0.05). Our results confirmed the hypothesis that expression of CA IX may represent a valuable tumor biomarker as well as a promising diagnostic and prognostic parameter in breast cancer.

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.

Involvement of histone deacetylation in MORC2-mediated down-regulation of carbonic anhydrase IX

Carbonic anhydrase IX (CAIX) plays an important role in the growth and survival of tumor cells. MORC2 is a member of the MORC protein family. The MORC proteins contain a CW-type zinc finger domain and are predicted to have the function of regulating transcription, but no MORC2 target genes have been identified. Here we performed a DNA microarray hybridization and found CAIX mRNA to be down-regulated 8-fold when MORC2 was overexpressed. This result was further confirmed by northern and western blot analysis. Our results also showed that the protected region 4 (PR4) was important for the repression function of MORC2. Moreover, MORC2 decreased the acetylation level of histone H3 at the CAIX promoter. Meanwhile, trichostatin A (TSA) had an increasing effect on CAIX promoter activity. Among the six HDACs tested, histone deacetylase 4 (HDAC4) had a much more prominent effect on CAIX repression. ChIP and ChIP Re-IP assays showed that MORC2 and HDAC4 were assembled on the same region of the CAIX promoter. Importantly, we further confirmed that both proteins are simultaneously present in the PR4-binding complex. These results may contribute to understanding the molecular mechanisms of CAIX regulation.

Tumour hypoxia induces a metabolic shift causing acidosis: a common feature in cancer

Maintenance of cellular pH homeostasis is fundamental to life. A number of key intracellular pH (pHi) regulating systems including the Na⁺/H⁺ exchangers, the proton pump, the monocarboxylate transporters, the HCO₃⁻ transporters and exchangers and the membrane-associated and cytosolic carbonic anhydrases cooperate in maintaining a pHi that is permissive for cell survival. A common feature of tumours is acidosis caused by hypoxia (low oxygen tension). In addition to oncogene activation and transformation, hypoxia is responsible for inducing acidosis through a shift in cellular metabolism that generates a high acid load in the tumour microenvironment. However, hypoxia and oncogene activation also allow cells to adapt to the potentially toxic effects of an excess in acidosis. Hypoxia does so by inducing the activity of a transcription factor the hypoxia-inducible factor (HIF), and particularly HIF-1, that in turn enhances the expression of a number of pHi-regulating systems that cope with acidosis. In this review, we will focus on the characterization and function of some of the hypoxia-inducible pH-regulating systems and their induction by hypoxic stress. It is essential to understand the fundamentals of pH regulation to meet the challenge consisting in targeting tumour metabolism and acidosis as an anti-tumour approach. We will summarize strategies that take advantage of intracellular and extracellular pH regulation to target the primary tumour and metastatic growth, and to turn around resistance to chemotherapy and radiotherapy.

Hypoxia-induced expression of carbonic anhydrase 9 is dependent on the unfolded protein response

Adaptation to tumor hypoxia is mediated in large part by changes in protein expression. These are driven by multiple pathways, including activation of the hypoxia inducible factor-1 (HIF-1) transcription factor and the PKR-like endoplasmic reticulum kinase PERK, a component of the unfolded protein response. Through gene expression profiling we discovered that induction of the HIF-1 target gene CA9 was defective in mouse embryo fibroblasts derived from mice harboring an eIF2alpha S51A knock-in mutation. This finding was confirmed in two isogenic human cell lines with an engineered defect in eIF2alpha phosphorylation. We show that impaired CA9 expression was not due to changes in HIF activity or CA9 mRNA stability. Using chromatin immunoprecipitation we show that the eIF2alpha-dependent translationally regulated gene ATF4 binds directly to the CA9 promoter and is associated with loss of the transcriptional repressive histone 3 lysine 27 tri-methylation mark. Loss or overexpression of ATF4 confirmed its role in CA9 induction during hypoxia. Our data indicate that expression of CA9 is regulated through both the HIF-1 and unfolded protein response hypoxia response pathways in vitro and in vivo.

TGF-beta upregulates tumor-associated carbonic anhydrase IX gene expression in Hep3B cells

Carbonic anhydrase IX (CAIX) is a membrane-associated carbonic anhydrase (CA) that is overexpressed in a variety of tumor types and associated with increased metastasis, giving a poor prognosis. Transcriptional regulation of transmembrane protein CAIX is complex. We describe further characterization of the 1.2kb hCA9 promoter, and the effect of TGF-beta on the transcriptional activity and expression of hCAIX in Hep3B cells. Transcriptional activity of different promoter regions of hCA9 promoter showed the presence of negative regulatory region between -300bp and -500bp of hCAIX promoter. The -116/+38 region was enough for basal transcriptional activity in Hep3B cells. TGF-beta upregulates all promoter regions of hCA9 with the highest beig for -466/+38 that has a negatively regulated region. The transcriptional activation of hCA9 promoter by TGF-beta is consistent with hCAIX mRNA levels revealed by RT-PCR and hCAIX protein expression levels by flow cytometry in Hep3B cells.

Role of aryl hydrocarbon receptor in modulation of the expression of the hypoxia marker carbonic anhydrase IX

Tumour-associated expression of CA IX (carbonic anhydrase IX) is to a major extent regulated by HIF-1 (hypoxia-inducible factor-1) which is important for transcriptional activation and consists of the oxygen-regulated subunit HIF-1alpha and the partner factor ARNT [AhR (aryl hydrocarbon receptor) nuclear translocator]. We have previously observed that HIF-1alpha competes with the AhR for interaction with ARNT under conditions when both conditionally regulated factors are activated. We have therefore investigated whether TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin)-induced activation of the AhR pathway might interfere with CA IX expression. The results from the present study suggest that TCDD treatment reduces hypoxic induction of both CA IX mRNA and protein expression. Moreover, the transcriptional activity of the CA9 promoter was significantly reduced by expression of CAAhR (constitutively active AhR), which activates transcription in a ligand-independent manner. Finally, we found that ARNT is critical for both hypoxic induction and the TCDD-mediated inhibition of CA9 expression.

Transcriptional control of the tumor- and hypoxia-marker carbonic anhydrase 9: A one transcription factor (HIF-1) show?

Transcriptional activation by hypoxia is mediated by the hypoxia-inducible factor (HIF) via binding to the hypoxia-responsive element (HRE). Hypoxia in solid tumors associates with poorer outcome of the disease and reliable cellular markers of tumor hypoxia would represent a valuable diagnostic marker and a potential therapeutic target. In this category, carbonic anhydrase IX (CAIX) is one of the most promising candidates. Here, we summarize the knowledge about transcriptional regulation of CA9. The HRE is the central regulatory element in the CA9 promoter, whereas other elements are limited to lesser roles of amplification of signals received at the HRE. The analysis of known mechanisms of activation of CA9 reveals the prominent role of the HIF-1 pathway. Experimental paradigms with uncoupled HIF-1alpha stability and transcriptional activity (pericellular hypoxia, proteasomal inhibitor) provide evidence that CA9 expression monitors transcriptional activity of HIF-1, rather than the abundance of HIF-1alpha. Furthermore, these paradigms could provide a corollary to some of the apparently discordant cases (CAIX+, HIF-1alpha-) or (CAIX-, HIF-1alpha+) observed in vivo. In conclusion, the existing data support the notion that CA9, due to the unique structure of its promoter, is one of the most sensitive endogenous sensors of HIF-1 activity.

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.

Proteasomal inhibition attenuates transcriptional activity of hypoxia-inducible factor 1 (HIF-1) via specific effect on the HIF-1alpha C-terminal activation domain

The ubiquitin-proteasome pathway (UPP) is involved in regulation of multiple cellular processes. Hypoxia-inducible factor 1 alpha (HIF-1 alpha) is a prototypic target of the UPP and, as such, is stabilized under conditions of proteasomal inhibition. Using carbonic anhydrase IX (CAIX) and vascular endothelial growth factor (VEGF) expression as paradigmatic markers of HIF-1 activity, we found that proteasomal inhibitors (PI) abrogated hypoxia-induced CAIX expression in all cell lines tested and VEGF expression in two out of three. Mapping of the inhibitory effect identified the C-terminal activation domain (CAD) of HIF-1 alpha as the primary target of PI. PI specifically inhibited the HIF-1 alpha CAD despite activating the HIF-1 alpha coactivator p300 and another p300 cysteine/histidine-rich domain 1-dependent transcription factor, STAT-2. Coimmunoprecipitation and glutathione S-transferase pull downs indicated that PI does not disrupt interactions between HIF-1 alpha and p300. Mutational analysis failed to confirm involvement of sites of known or putative posttranslational modifications in regulation of HIF-1 alpha CAD function by PI. Our data provide evidence for the counterintuitive hypothesis that inhibition of HIF-1 function could be responsible for at least some of the antitumor effects of proteasomal inhibition. Further studies of the mechanism of the PI-induced attenuation of HIF-1alpha will provide important, potentially novel insight into regulation of HIF-1 activity and possibly identify new targets for HIF-directed therapy.

Eukaryotic expression vectors and immunoconjugates for cancer therapy

This review considers ways to address specificity to therapeutic targeted anticancer agents. These include transcriptional activation of tissue- and tumor-specific promoters in eukaryotic expression vectors and use of antitumor-directed immunoconjugates. The review deals with analysis of strategies used for selection of targeted promoters and examples of antibody fusion proteins exhibiting antitumor activity. A new direction in antitumor treatment pooling together methods of gene therapy and antibody therapy has appeared. This direction is based on the development of vectors encoding secreted forms of immunoconjugates. After vector introduction into a cell, the latter is capable of synthesizing and secreting antibody fusion protein composed of a therapeutic anticancer agent and antibody specifically targeted to cancer cells.

The role of extracellular signal-regulated protein kinase in transcriptional regulation of the hypoxia marker carbonic anhydrase IX

In the present study, we investigated the role of the extracellular signal-regulated protein kinase (ERK) in regulation of the hypoxia marker, carbonic anhydrase IX (CAIX). U0126, a specific inhibitor of MEK1/2, downregulated CAIX expression induced by true hypoxia and cell density. CA9 promoter activity was similarly affected. Mapping of the U0126 effect revealed that both critical elements within the CA9 promoter, the hypoxia response element and the juxtaposed SP1-binding PR1, were inhibited. This confirmed that ERK signaling modulates CA9 promoter activity via its effects on hypoxia inducible factor-1 (HIF-1) and SP1. Further analysis of the U0126 effect on HIF-1-dependent transcription in MCF-7 cells identified p300, a transcriptional co-activator of HIF-1, as the target of ERK. Constitutively increased ERK activity in isogenic fibrosarcoma cell lines did not cause increased cell density-dependent CAIX expression/CA9 promoter activity. In HeLa cells, an inverse correlation between cell density-induced CAIX expression and ERK activation was observed: sparse cultures did not express CAIX and displayed high ERK activation, whereas CAIX expression in dense cultures was associated with low ERK activation. Collectively, our data do not support any quantitative relationship between ERK activation and CAIX expression. Thus, although ERK signaling is required for optimal CAIX expression, our data are consistent with a model in which constitutive basal ERK activity plays an auxiliary role in CA9 promoter transactivation by modulating activity of the transcription factor SP1 and the transcriptional co-activator p300.

Quantitative analysis of carbonic anhydrase IX mRNA in human non-small cell lung cancer

Hypoxia is associated with malignant progression and poor outcome in human cancers. The effects of hypoxia are mediated by a series of genomic changes that enable tumor cells to survive or escape their oxygen deficient environment. Recent studies indicated that carbonic anhydrase IX (CA IX) is an intrinsic marker of hypoxia. In the present study we investigated with quantitative RT-PCR the expression of CA IX mRNA in 93 non-small cell lung carcinomas (NSCLC) and in their paired not affected tissues. CA IX mRNA was expressed in 100% NSCLC and in 76% of paired not affected tissues, even if tumoral CA IX expression was found constantly higher (p < 0.02) than that found in normal tissues. The increase of CA IX mRNA expression in cancer tissues was significantly correlated to the increase of corresponding protein, as determined with conventional immunoblotting (p = 0.027). In addition the expression of CA IX mRNA in NSCLC samples was significantly correlated to VEGF (p = 0.002) and MMP-9 (p = 0.002) mRNAs. Whereas CA IX mRNA expression was not associated to any clinical-pathological parameters in our patients, global survival analysis of cancer-related death revealed that high expression of CA IX mRNA predicted unfavorable outcome (p = 0.001) and shorter disease free survival interval (p = 0.004). A multivariate analysis showed that CA IX expression was the strongest prognostic parameter (p = 0.000) in comparison to other conventional predictive markers. In addition, differences emerged on the basis of clinical-pathological parameters: in fact separate Kaplan-Meyer analyses of patients indicated that whereas high levels of CA IX mRNA expression were not predictive of worse prognosis in early NSCLC (G1, T1, Stage 1 and pN- patients), this parameter appeared highly significant in advanced NSCLC (G2-G3, T2-T3, Stage 2-3 and pN+ patients). Finally we demonstrated that CA IX expression was not able to discriminate different survival probability in adenocarcinomas, whereas the same parameter was highly predictive in squamous (p = 0.03) and adenosquamous cell carcinomas (p = 0.001).

MAPK pathway contributes to density- and hypoxia-induced expression of the tumor-associated carbonic anhydrase IX

Transcription of the CA9 gene coding for a tumor-associated carbonic anhydrase IX (CA IX) isoform is regulated by hypoxia via the hypoxia-inducible factor 1 (HIF-1) and by high cell density via the phosphatidylinositol-3-kinase (PI3K) pathway. We examined the role of the mitogen-activated protein kinase (MAPK) pathway in the control of CA9 gene expression. Inhibition of MAPK signaling by U0126 in HeLa cells led to reduced activity of the PR1-HRE-luc CA9 promoter construct and decreased CA IX protein levels in dense culture as well as in hypoxia. Similar reduction was obtained by expression of a dominant-negative ERK1 mutant and was also observed in U0126-treated HIF-1alpha-deficient Ka13 cells. Simultaneous treatment with the MAPK and PI3K inhibitors U0126 and LY 294002 had stronger effect than individual inhibition of these pathways. Taken together, our results suggest that besides the PI3K pathway, the MAPK cascade is involved in the regulation of CA9 gene expression under both hypoxia and high cell density.

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.

Strict regulation of CAIX(G250/MN) by HIF-1alpha in clear cell renal cell carcinoma

Renal cell carcinoma of the clear cell type (ccRCC) is associated with loss of functional von Hippel-Lindau (VHL) protein and high, homogeneous expression of the G250MN protein, an isoenzyme of the carbonic anhydrase family. High expression of G250MN is found in all ccRCCs, but not in most normal tissues, including normal human kidney. We specifically studied the mechanism of transcriptional regulation of the CAIXG250 gene in RCC. Previous studies identified Sp1 and hypoxia-inducible factor (HIF) as main regulatory transcription factors of G250MN in various non-RCC backgrounds. However, G250MN regulation in RCC has not been studied and may be differently regulated in view of the HIF accumulation under normoxic conditions due to VHL mutations. Transient transfection of different G250MN promoter constructs revealed strong promoter activity in G250MN -positive RCC cell lines, but no activity in G250MN -negative cell lines. DNase-I footprint and band-shift analysis demonstrated that Sp1 and HIF-1alpha proteins in nuclear extracts of RCC cells bind to the CAIX promoter and mutations in the most proximal Sp1 binding element or HIF binding element completely abolished CAIX promoter activity, indicating their critical importance for the activation of G250 expression in RCC. A close correlation between HIF-1alpha expression and G250MN expression was observed. In contrast, no relationship between HIF-2alpha expression and G250MN was seen. The participation of cofactor CBP/p300 in the regulation of G250 transcription was shown. In conclusion, HIF-1alpha and Sp1, in combination with CBP/p300, are crucial elements for G250MN expression in ccRCC, and CAIXG250 can be regarded as a unique HIF-1alpha target gene in ccRCC.

DNA damage is a prerequisite for p53-mediated proteasomal degradation of HIF-1alpha in hypoxic cells and downregulation of the hypoxia marker carbonic anhydrase IX

We investigated the relationship between the tumor suppressor p53 and the hypoxia-inducible factor-1 (HIF-1)-dependent expression of the hypoxia marker, carbonic anhydrase IX (CAIX). MCF-7 (wt p53) and Saos-2 (p53-null) cells displayed similar induction of CAIX expression and CA9 promoter activity under hypoxic conditions. Activation of p53 by the DNA damaging agent mitomycin C (MC) was accompanied by a potent repression of CAIX expression and the CA9 promoter in MCF-7 but not in Saos-2 cells. The activated p53 mediated increased proteasomal degradation of HIF-1alpha protein, resulting in considerably lower steady-state levels of HIF-1alpha protein in hypoxic MCF-7 cells but not in Saos-2 cells. Overexpression of HIF-1alpha relieved the MC-induced repression in MCF-7 cells, confirming regulation at the HIF-1alpha level. Similarly, CA9 promoter activity was downregulated by MC in HCT 116 p53(+/+) but not the isogenic p53(-/-) cells. Activated p53 decreased HIF-1alpha protein levels by accelerated proteasome-dependent degradation without affecting significantly HIF-1alpha transcription. In summary, our results demonstrate that the presence of wtp53 under hypoxic conditions has an insignificant effect on the stabilization of HIF-1alpha protein and HIF-1-dependent expression of CAIX. However, upon activation by DNA damage, wt p53 mediates an accelerated degradation of HIF-1alpha protein, resulting in reduced activation of CA9 transcription and, correspondingly, decreased levels of CAIX protein. A model outlining the quantitative relationship between p53, HIF-1alpha, and CAIX is presented.

Interferons Can Upregulate the Expression of the Tumor Associated Antigen G250-MN/CA IX, a Potential Target for (Radio)Immunotherapy of Renal Cell Carcinoma

BACKGROUND

Interleukin-2 (IL-2) and interferon-alpha (IFN-alpha) can induce therapeutic responses in a minority (5-25%) of patients with metastatic renal cell carcinoma (RCC). G250-MN/CA IX, a tumor-associated antigen expressed on the majority of clear cell RCCs, is a potential (radio)immunotherapeutic target for G250-antibody based (radio)immunotherapy. We investigated the effect of the biological response modifiers (BRMs) IL-2, IFN-alpha, and IFN-gamma on the expression of the G250 antigen on RCC cells.

METHODS

In vitro, the expression of the G250 antigen was measured by flow cytometry (FCM) after culturing RCC cells in the presence of various concentrations of the BRMs. Additionally, the number of G250 epitopes per cell was determined quantitatively by Scatchard analysis.

RESULTS

Upregulation of G250 expression was observed on RCC cells cultured in the presence of IFN-alpha or IFN-gamma, whereas the addition of IL-2 had no effect. For both IFNs a clear dose-response relation between G250 antigen expression and IFN dose was observed, with IFN-gamma being the more potent agent. G250 expression could be upregulated four-fold. Interestingly, the effect of combining IFN-alpha and IFN-gamma revealed a more pronounced upregulation of G250 expression than either one of the IFNs alone.

CONCLUSIONS

On the basis of in vitro experiments, G250 expression can be upregulated by IFN-alpha and IFN-gamma. In vivo studies are warranted to investigate whether due to IFN treatment increased G250 expression occurs, and whether increased G250 expression can enhance the therapeutic efficacy of G250-antibody based (radio)immunotherapy.

131 I-cG250 monoclonal antibody immunoscintigraphy versus [18 F]FDG-PET imaging in patients with metastatic renal cell carcinoma: a comparative study

The aims of this study were to establish the percentage of metastatic renal cell carcinoma (RCC) lesions detected by radioimmunoscintigraphy (RIS) with the chimeric monoclonal antibody 131I-cG250 versus positron emission tomography (PET) with 18F-labelled deoxyglucose ([18F]FDG), and to evaluate the use of these radionuclide imaging modalities compared with routinely used imaging techniques. Twenty patients with metastatic RCC disease were examined with [18F]FDG-PET and 131I-cG250 RIS within 1 week. Total body gamma camera images were obtained up to 120h after injection of 232MBq 131I-cG250. Total body PET scanning was performed 45-60 min after intravenous injection of 370MBq [18F]FDG. Nuclear medicine techniques were compared to routine imaging procedures. Routine imaging modalities revealed a total of 79 metastases. [18F]FDG-PET and 131I-cG250 RIS detected 33 previously unknown metastases, of which 32 were [18F]FDG positive and seven were 131I-cG250 positive. Of the 112 tumour lesions that were documented, [18F]FDG-PET detected 69% (77 out of 112), whereas 131I-cG250 RIS detected only 30% (34 out of 112). In conclusion, [18F]FDG-PET is superior to 131I-cG250 RIS in detecting metastases in patients with metastatic RCC, and therefore seems a promising tool for (re)staging patients with RCC. The usefulness of RIS with a diagnostic dose of 131I-cG250 seems to be restricted to selecting patients for radioimmunotherapy with 131I-cG250.

Characterization of the MN/CA 9 promoter proximal region: a role for specificity protein (SP) and activator protein 1 (AP1) factors

MN/CA IX (MN) is a tumour-associated isoenzyme of the carbonic anhydrase family. Previous deletion analysis of the MN promoter established that protected regions (PRs) 1 and 2 are crucial for its transcriptional activity. Computer-assisted searching indicated putative binding sites for activator protein (AP) 2 and specificity protein (SP) 1 transcription factors, plus a CACCC box in PR1 and an AP1 site in PR2. PR1 produced four complexes in electrophoretic mobility-shift assay (EMSA) with HeLa nuclear extracts. Of these, three were completely competed with the SP1 and transforming growth factor-beta retinoblastoma control-element CACCC box (RCE) probes, whereas the AP2 probe competed against the same three complexes partially. Supershift EMSA identified SP1 in the complex 1 and SP3 in the complexes 2 and 4. Point mutations in the SP1 site abrogated the PR1 function, while mutations affecting the overlapping CACCC box/AP2 site in PR1 had minor effect on MN promoter activity. Block-replaced MN promoter mutants that had a consensus binding site (SP1 or AP2) or the RCE in place of PR1 demonstrated the stringent selectivity of the PR1 position as only the SP1 mutant reconstituted the MN promoter activity. The consensus SP1 probe generated the same SP1 and SP3 complexes as PR1 in EMSA; therefore we conclude that SP activity is both necessary and sufficient in the PR1 position. The critical role of AP1 in the PR2 position was confirmed by supershift of the PR2 complex with c-Fos antibody and markedly decreased activity of the construct with a mutated AP1 site. Detailed deletion analysis proved that PR1+PR2 account for 90% of the MN promoter activity, while neither PR1 nor PR2 on their own are sufficient for transactivation. Thus, synergistic co-operation between SP and AP1 factors bound to the adjacent PR1 and PR2, respectively, is necessary for MN transcriptional activity. The PR1+PR2 module also stimulated transcription from a heterologous promoter. The modulation of AP1 activity with PMA stimulated MN expression and activated the MN promoter, whereas inhibition of protein kinase C activity had no effect on MN expression in HeLa cells.

Hypomethylation of the MN/CA9 promoter and upregulated MN/CA9 expression in human renal cell carcinoma

MN/CA9 is a cancer-related gene, frequently activated in human renal cell carcinomas (RCCs). To reveal the activation mechanism, we investigated the relationship between methylation status of the MN/CA9 promoter region and gene expression using 13 human RCCs, and examined the effect of in vitro CpG methylation on the MN/CA9 promoter activity using a human RCC cell line (SK-RC-44), expressing MN/CA9. MN/CA9 expression was evaluated by RT-PCR and observed in 10 of 13 RCCs (77%). A total of 9 out of 10 MN/CA9 -positive RCCs (90%) contained clear cell components. Methylation status of 6 CpGs in the MN/CA9 promoter region was decided by using the bisulfite genomic sequencing protocol. Out of 13 RCCs 9 (69%) showed partial hypomethylation of the CpG at -74 bp, while the other 4 RCCs and 3 normal kidney tissue samples showed complete methylation. Hypomethylation of the CpG at -74 bp was strongly correlated with MN/CA9 expression. Luciferase assay revealed that the MN/CA9 promoter activity was strongly suppressed by methylation of the CpG at -74 bp. These findings suggest that hypomethylation of the CpG at -74 bp in the MN/CA9 promoter region might play an important role in this gene activation of human RCC.

Block-replacement mutagenesis for functional dissection of multiple transcription factor complexes

We propose a simple method for investigation of roles of individual transcription factors in complexes of multiple factors bound to the same cis element. By block-replacement mutagenesis, the whole cis element is replaced with a new one containing a binding site for a single factor. From the reporter activity of the mutant promoter construct, the importance of the individual factor in transcriptional activation is deduced. This approach allowed us to functionally identify SP1 as the most important PR1 binding transcription factor in the MN promoter.

Isolation and characterization of the promoter of the human prostate cancer-specific DD3 gene

Recently, we have described a novel gene, DD3, which is one of the most prostate cancer-specific genes described to date (Bussemakers, M. J. G., van Bokhoven, A., Verhaegh, G. W., Smit, F. P., Karthaus, H. F. M., Schalken, J. A., Debruyne, F. M. J., Ru, N., and Isaacs, W. B. (1999) Cancer Res. 59, 5975-5979). The prostate cancer-specific expression of DD3 indicates that the DD3 gene promoter is a promising tool for the treatment of prostate cancer. To identify the promoter elements that are responsible for the prostate cancer-specific expression of DD3, we have isolated and characterized the DD3 promoter. Sequence analysis of the DD3 5'-flanking region was performed and several promoter-human growth hormone reporter constructs were prepared, which were transiently transfected in the DD3-positive cell line LNCaP and several DD3-negative cell lines. Using a 500-base pair DD3 promoter construct, we could detect promoter activity in LNCaP cells, which was not affected by increasing the size of the constructs. Truncated constructs, however, showed an increased transcriptional activity, suggesting the presence of a silencer that negatively regulates the expression of DD3. DNase-I footprint analysis, using nuclear extracts from LNCaP cells, revealed the presence of three DNase-I-protected areas within the DD3 proximal promoter. We show that the high mobility group I(Y) protein binds to one of the DNase-I-protected areas and recruits another, yet unidentified, protein to the DD3 promoter in LNCaP cells.

P53 tumour suppressor modulates transcription of the TATA-less gene coding for the tumour-associated carbonic anhydrase MN/CA IX in MaTu cells

MN/CA IX (MN) exhibits a strong association with tumours. Co-transfection experiments revealed that in MaTu cells the activity of the (-173;+31) MN promoter construct was repressed by the wild type p53 in a dose-responsive manner and stimulated by the (143(Val-->Ala)) mutant. Upregulation of endogenous p53 by mitomycin C treatment in MaTu cells also had a profound effect on MN expression as well as the activity of MN promoter in a reporter construct. p53 can thus modulate MN expression and at least in a subset of tumours the changed p53 status might be responsible for MN positivity. Co-transfections with internally deleted MN promoter constructs demonstrated that the wild type p53 exerts its repression activity on the level of the basal transcriptional machinery and not on a particular cis element within the MN promoter.