Molecular mechanisms of carbonic anhydrase IX-mediated pH regulation under hypoxia

Targeting CA9 restricts pancreatic cancer progression through pH regulation and ROS production

PURPOSE

Lactate is a key metabolite produced by glycolytic metabolism, yet it also serves as an energy source for cancer cells. Lactate accumulation in the tumor microenvironment (TME) has been demonstrated to correlate with immunosuppressive TME and tumor progression. As a highly glycolytic tumor, it is crucial to decipher the underlying mechanism in pancreatic ductal adenocarcinoma (PDAC).

METHODS

Bioinformation analysis was used to identify lactate mediated carbonic anhydrase IX (CA9) upregulation. CCK-8, colony formation and mouse xenograft assay were utilized to study the effect of CA9 in PDAC. ECAR, OCR and pHi measurement confirmed the impacts of CA9 in Warburg phenotype. Using confocal microscopy, flow cytometry, qRT-PCR, co-IP, we validated the signaling pathways in PDAC to regulate reactive oxygen species (ROS) production.

RESULTS

We confirmed that CA9 is highly expressed in PDAC and positively regulated by lactate levels. CA9 can enhance the proliferative and migratory capabilities of PDAC cells. Pharmacologic inhibition or knockdown of CA9 significantly reduce pHi, increase the intracellular lactate and reverse the Warburg phenotype. The intracellular lactate accumulation caused by CA9 knockdown upregulates ROS and mitochondrial dysfunction. Furthermore, it was discovered that the competitive binding of CA9 with FUS inhibits the facilitation of FUS on NOX4 pre-mRNA splicing.

CONCLUSION

Collectively, our data illustrate that CA9 has a direct regulatory role in pHi homeostasis and ROS production, providing a potential therapeutic target for PDAC treatment.

Selective Tumor Hypoxia Targeting Using M75 Antibody Conjugated Photothermally Active MoOx Nanoparticles

Photothermal therapy (PTT) mediated at the nanoscale has a unique advantage over currently used cancer treatments, by being spatially highly specific and minimally invasive. Although PTT combats traditional tumor treatment approaches, its clinical implementation has not yet been successful. The reasons for its disadvantage include an insufficient treatment efficiency or low tumor accumulation. Here, we present a promising new PTT platform combining a recently emerged two-dimensional (2D) inorganic nanomaterial, MoOx, and a tumor hypoxia targeting element, the monoclonal antibody M75. M75 specifically binds to carbonic anhydrase IX (CAIX), a hypoxia marker associated with many solid tumors with a poor prognosis. The as-prepared nanoconjugates showed highly specific binding to cancer cells expressing CAIX while being able to produce significant photothermal yield after irradiation with near-IR wavelengths. Small aminophosphonic acid linkers were recognized to be more effective over the combination of poly(ethylene glycol) chain and biotin-avidin-biotin bridge in constructing a PTT platform with high tumor-binding efficacy. The in vitro cellular uptake of nanoconjugates was visualized by high-resolution fluorescence microscopy and label-free live cell confocal Raman microscopy. The key to effective cancer treatment may be the synergistic employment of active targeting and noninvasive, tumor-selective therapeutic approaches, such as nanoscale-mediated PTT. The use of active targeting can streamline nanoparticle delivery increasing photothermal yield and therapeutic success.

Repurposing of World-Approved Drugs for Potential Inhibition against Human Carbonic Anhydrase I: A Computational Study

Human carbonic anhydrases (hCAs) have enzymatic activities for reversible hydration of CO2 and are acknowledged as promising targets for the treatment of various diseases. Using molecular docking and molecular dynamics simulation approaches, we hit three compounds of methyl 4-chloranyl-2-(phenylsulfonyl)-5-sulfamoyl-benzoate (84Z for short), cyclothiazide, and 2,3,5,6-tetrafluoro-4-piperidin-1-ylbenzenesulfonamide (3UG for short) from the existing hCA I inhibitors and word-approved drugs. As a Zn2+-dependent metallo-enzyme, the influence of Zn2+ ion models on the stability of metal-binding sites during MD simulations was addressed as well. MM-PBSA analysis predicted a strong binding affinity of -18, -16, and -14 kcal/mol, respectively, for these compounds, and identified key protein residues for binding. The sulfonamide moiety bound to the Zn2+ ion appeared as an essential component of hCA I inhibitors. Vina software predicted a relatively large (unreasonable) Zn2+-sulfonamide distance, although the relative binding strength was reproduced with good accuracy. The selected compounds displayed potent inhibition against other hCA isoforms of II, XIII, and XIV. This work is valuable for molecular modeling of hCAs and further design of potent inhibitors.

The relationship between carbonic anhydrase IX (CAIX) and patient survival in breast cancer: systematic review and meta-analysis

PURPOSE

Hypoxia is a characteristic of many solid tumours and an adverse prognostic factor for cancer therapy. Hypoxia results in upregulation of carbonic anhydrase IX (CAIX) expression, a pH-regulating enzyme. Many human tissue studies have examined the prognostic value of CAIX expression in breast cancer but have yielded inconsistent results. Therefore, a systematic review and meta-analysis was undertaken to assess the prognostic value of CAIX expression for breast cancer patients.

METHODS

The electronic databases were systematically searched to identify relevant papers. The clinical outcomes included disease-free survival (DFS), recurrence-free survival (RFS) and overall survival (OS) in breast cancer patients. Review Manager version 5.4 was employed to analysis data from 23 eligible studies (containing 8390 patients).

RESULTS

High CAIX expression was associated with poorer RFS [HR = 1.42, 95% CI (1.32-1.51), p < 0.00001], DFS [HR = 1.64, 95% CI (1.34-2.00), p < 0.00001], and OS [HR = 1.48, 95% CI (1.22-1.80), p < 0.0001]. Heterogeneity was observed across the studies. There was an effect of the CAIX antibody employed, scoring methods, and tumour localisation on CAIX expression.

CONCLUSION

CAIX overexpression was significantly associated with poorer RFS, DFS, and OS in breast cancer patients. However, further work in high quantity tissue cohorts is required to define the optimal methodological approach.

Carbonic anhydrase IX: A tumor acidification switch in heterogeneity and chemokine regulation

The primary physiological process of respiration produces carbon dioxide (CO₂) that reacts with water molecules which subsequently liberates bicarbonate (HCO-₃) and protons. Carbonic anhydrases (CAs) are the primary catalyst involved in this conversion. More than 16 isoforms of human CAs show organ or subcellular specific activity. Dysregulation of each CA is associated with multiple pathologies. Out of these members, the overexpression of membrane-bound carbonic anhydrase IX (CAIX) is associated explicitly with hypoxic tumors or various solid cancers. CAIX helps tumors deal with higher CO₂ by sequestering it with bicarbonate ions and helping cancer cells to grow in a comparatively hypoxic or acidic environment, thus acting as a pH adaptation switch. CAIX-mediated adaptations in cancer cells include angiogenesis, metabolic alterations, tumor heterogeneity, drug resistance, and regulation of cancer-specific chemokines. This review comprehensively collects and describe the cancer-specific expression mechanism and role of CAIX in cancer growth, progression, heterogeneity, and its structural insight to develop future combinatorial targeted cancer therapies.

Hypoxia-regulated carbonic anhydrase IX (CAIX) protein is an independent prognostic indicator in triple negative breast cancer

Background

The effect of extracellular microenvironment (hypoxia and pH) has been regarded as a key hallmark in cancer progression. The study aims to investigate the effects of carbonic anhydrase IX (CAIX), a key hypoxia-inducible marker, in triple-negative breast cancer (TNBC) in correlation with clinicopathological parameters and predicting survival outcomes.

Methods

A total of 323 TNBC cases diagnosed at the Department of Anatomical Pathology, Singapore General Hospital from 2003 to 2013 were used. Immunohistochemical staining (IHC) was performed using CAIX antibody and digital mRNA quantification was performed using NanoString assays. CAIX membranous expression was correlated with clinicopathological parameters using Chi-squared test or Fisher’s exact tests. Disease-free survival (DFS) and overall-survival (OS) were estimated using Kaplan–Meier analysis and compared between groups with the log-rank test.

Results

Forty percent of TNBCs were observed to express CAIX protein and demonstrated significant association with larger tumour size (P = 0.002), higher histological grade (P < 0.001), and significantly worse disease-free survival (DFS) and overall survival (OS) (after adjustment: HR = 2.99, 95% CI = 1.78–5.02, P < 0.001 and HR = 2.56, 95% CI = 1.41–4.65, P = 0.002, respectively). Gene ontology enrichment analysis revealed six significantly enriched cellular functions (secretion, cellular component disassembly, regulation of protein complex assembly, glycolytic process, cellular macromolecular complex assembly, positive regulation of cellular component biogenesis) associated with genes differentially expressed (CAIX, SETX, WAS, HK2, DDIT4, TUBA4α, ARL1). Three genes (WAS, SETX and DDIT4) were related to DNA repair, indicating that DNA stability may be influenced by hypoxia in TNBC.

Conclusions

Our results demonstrate that CAIX appears to be a significant hypoxia-inducible molecular marker and increased CAIX protein levels are independently associated with poor survival in TNBC. Identification of CAIX-linked seven gene-signature and its relationship with enriched cellular functions further support the implication and influence of hypoxia-mediated CAIX expression in TNBC tumour microenvironment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13058-022-01532-0.

Hypoxia Marker Carbonic Anhydrase IX Is Present in Abdominal Aortic Aneurysm Tissue and Plasma

Abdominal aortic aneurysms (AAA) are a significant cause of premature deaths worldwide. Since there is no specific treatment for reducing AAA progression, it is crucial to understand the pathogenesis leading to aneurysm wall weakening/remodeling and identify new proteins involved in this process which could subsequently serve as novel therapeutic targets. In this study, we analyzed the presence of the hypoxia-related proteins carbonic anhydrase IX (CA IX), hypoxia-inducible factor 1α (HIF-1α), and AKT as the key molecule in the phosphoinositide-3-kinase pathway in the AAA wall. Additionally, we used a blood-based assay to examine soluble CA IX (s-CA IX) levels in the plasma of AAA patients. Using western blotting, we detected CA IX protein in 12 out of 15 AAA tissue samples. Immunohistochemistry staining proved CA IX expression in the media of the aneurysmal wall. Evaluation of phosphorylated (p-AKT) and total AKT showed elevated levels of both forms in AAA compared to normal aorta. Using ELISA, we determined the concentration of s-CA IX >20 pg/mL in 13 out of 15 AAA patients. Results obtained from in silico analysis of CA9 and aneurysm-associated genes suggest a role for CA IX in aneurysmal wall remodeling. Our results prove the presence of hypoxia-related CA IX in AAA tissues and indicate a possible role of CA IX in hypoxia-associated cardiovascular diseases.

Carbonic anhydrase IX and hypoxia-inducible factor 1 attenuate cardiac dysfunction after myocardial infarction

Myocardial infarction (MI) is one of the leading causes of death worldwide. Prognosis and mortality rate are directly related to infarct size and post-infarction pathological heart remodeling, which can lead to heart failure. Hypoxic MI-affected areas increase the expression of hypoxia-inducible factor (HIF-1), inducing infarct size reduction and improving cardiac function. Hypoxia translocates HIF-1 to the nucleus, activating carbonic anhydrase IX (CAIX) transcription. CAIX regulates myocardial intracellular pH, critical for heart performance. Our objective was to investigate CAIX participation and relation with sodium bicarbonate transporters 1 (NBC1) and HIF-1 in cardiac remodeling after MI. We analyzed this pathway in an "in vivo" rat coronary artery ligation model and isolated cardiomyocytes maintained under hypoxia. Immunohistochemical studies revealed an increase in HIF-1 levels after 2 h of infarction. Similar results were observed in 2-h infarcted cardiac tissue (immunoblotting) and in hypoxic cardiomyocytes with a nuclear distribution (confocal microscopy). Immunohistochemical studies showed an increase CAIX in the infarcted area at 2 h, mainly distributed throughout the cell and localized in the plasma membrane at 24 h. Similar results were observed in 2 h in infarcted cardiac tissue (immunoblotting) and in hypoxic cardiomyocytes (confocal microscopy). NBC1 expression increased in cardiac tissue after 2 h of infarction (immunoblotting). CAIX and NBC1 interaction increases in cardiac tissue subjected to MI for 2h when CAIX is present (immunoprecipitation). These results suggest that CAIX interacts with NBC1 in our infarct model as a mechanism to prevent acidic damage in hypoxic tissue, making it a promising therapeutic target.

Anticancer Effect of Biodegradable Magnesium on Hepatobiliary Carcinoma: An In Vitro and In Vivo Study

Biliary-stent implantation has become an effective treatment for patients with malignant obstructive jaundice caused by hepatobiliary carcinoma. Stent restenosis due to tumor ingrowth is a common problem. In this study, we assessed a biodegradable form of magnesium (Mg) for its anticancer effect on hepatobiliary carcinoma, compared to the conventional stent material of titanium (Ti). The results showed that a Mg extract inhibited proliferation and induced apoptosis in human cholangiocarcinoma cells, while a Mg plate inhibited cell adhesion and destroyed the cytoskeleton in the process of biodegradation. In animal experiments with H22 tumor-bearing mice, Mg wires implanted in tumors exhibited an inhibitory effect on their growth compared with Ti wires. Fifteen days after implantation of metal wires, the mean tumor volume and weight in the Mg group were significantly smaller than in the Ti group. We observed the dynamic-degradation process of Mg wires in tumors and generation of H₂ gas via soft X-ray photography and scanning electron microscopy. Histopathological analyses showed that apoptosis of tumor cells around Mg wires significantly increased, expression of carbonic anhydrase 9 significantly decreased, and the upstream protein hypoxia-inducible factor 1-alpha also decreased to some extent. Taken together, these results indicated that biodegradable Mg had antitumor properties both in vitro and in vivo, suggesting its potential application as a novel material for biodegradable biliary stents.

Novel insights on saccharin- and acesulfame-based carbonic anhydrase inhibitors: design, synthesis, modelling investigations and biological activity evaluation

A large library of saccharin and acesulfame derivatives has been synthesised and evaluated against four isoforms of human carbonic anhydrase, the two off-targets hCA I/II and the tumour related isoforms hCA IX/XII. Different strategies of scaffold modification have been attempted on both saccharin as well as acesulfame core leading to the obtainment of 60 compounds. Some of them exhibited inhibitory activity in the nanomolar range, albeit some of the performed changes led to either micromolar activity or to its absence, against hCA IX/XII. Molecular modelling studies focused the attention on the binding mode of these compounds to the enzyme. The proposed inhibition mechanism is the anchoring to zinc-bound water molecule. Docking studies along with molecular dynamics also underlined the importance of the compounds flexibility (e.g. achieved through the insertion of methylene group) which favoured potent and selective hCA inhibition.

CA9 Silencing Promotes Mitochondrial Biogenesis, Increases Putrescine Toxicity and Decreases Cell Motility to Suppress ccRCC Progression

Carbonic anhydrase IX (CA9), a pH-regulating transmembrane protein, is highly expressed in solid tumors, and particularly in clear cell renal cell carcinoma (ccRCC). The catalytic mechanisms of CA9 are well defined, but its roles in mediating cell migration/invasion and survival in ccRCC remain to be determined. Here, we confirmed that the mRNA expression of CA9 in ccRCC was significantly higher than that in para-carcinoma tissues from analysis of the datasets in The Cancer Genome Atlas. CA9 knockdown upregulated oxidative phosphorylation-associated proteins and increased mitochondrial biogenesis, resulting in the reversal of the Warburg phenotype and the inhibition of cell growth. Our study revealed that CA9 knockdown upregulated mitochondrial arginase 2 (ARG2), leading to the accumulation of putrescine, which suppressed ccRCC proliferation. Surfaceomics analysis revealed that CA9 knockdown downregulated proteins associated with extracellular matrix (ECM)-receptor interaction and cell adhesion, resulting in decreased cell migration. CA9 silencing also downregulated amino acid transporters, leading to reduced cellular amino acids. Collectively, our data show that CA9 knockdown suppresses proliferation via metabolic reprogramming and reduced cell migration, reaffirming that CA9 is a potential therapeutic target for ccRCC treatment.

Progress in the development of human carbonic anhydrase inhibitors and their pharmacological applications: Where are we today?

Carbonic anhydrases (CAs, EC 4.2.1.1) are widely distributed metalloenzymes in both prokaryotes and eukaryotes. They efficiently catalyze the reversible hydration of carbon dioxide to bicarbonate and H⁺  ions and play a crucial role in regulating many physiological processes. CAs are well-studied drug target for various disorders such as glaucoma, epilepsy, sleep apnea, and high altitude sickness. In the past decades, a large category of diverse families of CA inhibitors (CAIs) have been developed and many of them showed effective inhibition toward specific isoforms, and effectiveness in pathological conditions in preclinical and clinical settings. The discovery of isoform-selective CAIs in the last decade led to diminished side effects associated with off-target isoforms inhibition. The many new classes of such compounds will be discussed in the review, together with strategies for their development. Pharmacological advances of the newly emerged CAIs in diseases not usually associated with CA inhibition (neuropathic pain, arthritis, cerebral ischemia, and cancer) will also be discussed.

Impairment of carbonic anhydrase IX ectodomain cleavage reinforces tumorigenic and metastatic phenotype of cancer cells

BACKGROUND

Carbonic anhydrase IX (CA IX) is a hypoxia-induced enzyme regulating tumour pH and facilitating cell migration/invasion. It is primarily expressed as a transmembrane cell-surface protein, but its ectodomain can be shed by ADAM17 to extracellular space. This study aims to elucidate the impact of CA IX shedding on cancer cells.

METHODS

We generated a non-shed CA IX mutant by deletion of amino acids 393-402 from the stalk region and studied its phenotypic effects compared to full-length, shedding-competent CA IX using a range of assays based on immunodetection, confocal microscopy, in vitro real-time cell monitoring and in vivo tumour cell inoculation using xenografted NMRI and C57BL/6J female mice.

RESULTS

We demonstrated that the impairment of shedding does not alter the ability of CA IX to bind ADAM17, internalise, form oligomers and regulate pH, but induces cancer-promoting changes in extracellular proteome. Moreover, it affects intrinsic properties of cells expressing the non-shed variant, in terms of their increased ability to migrate, generate primary tumours and form metastatic lesions in lungs.

CONCLUSIONS

Our results show that the ectodomain shedding controls pro-tumorigenic and pro-metastatic roles of the cell-associated CA IX and suggest that this phenomenon should be considered when developing CA IX-targeted therapeutic strategies.

Sulfonamido carboranes as highly selective inhibitors of cancer-specific carbonic anhydrase IX

Carbonic anhydrase IX (CA IX) is a transmembrane enzyme overexpressed in hypoxic tumors, where it plays an important role in tumor progression. Specific CA IX inhibitors potentially could serve as anti-cancer drugs. We designed a series of sulfonamide inhibitors containing carborane clusters based on prior structural knowledge of carborane binding into the enzyme active site. Two types of carborane clusters, 12-vertex dicarba-closo-dodecaborane and 11-vertex 7,8-dicarba-nido-undecaborate (dicarbollide), were connected to a sulfonamide moiety via aliphatic linkers of varying lengths (1-4 carbon atoms; n = 1-4). In vitro testing of CA inhibitory potencies revealed that the optimal linker length for selective inhibition of CA IX was n = 3. A 1-sulfamidopropyl-1,2-dicarba-closo-dodecaborane (3) emerged as the strongest CA IX inhibitor from this series, with a K_i value of 0.5 nM and roughly 1230-fold selectivity towards CA IX over CA II. X-ray studies of 3 yielded structural insights into their binding modes within the CA IX active site. Compound 3 exhibited moderate cytotoxicity against cancer cell lines and primary cell lines in 2D cultures. Cytotoxicity towards multicellular spheroids was also observed. Moreover, 3 significantly lowered the amount of CA IX on the cell surface both in 2D cultures and spheroids and facilitated penetration of doxorubicin. Although 3 had only a moderate effect on tumor size in mice, we observed favorable ADME properties and pharmacokinetics in mice, and preferential presence in brain over serum.

Liver Cancer Cell Lines Treated with Doxorubicin under Normoxia and Hypoxia: Cell Viability and Oncologic Protein Profile

Hepatocellular carcinoma is often treated with a combination of doxorubicin and embolization, exposing it to high concentrations and hypoxia. Separation of the possible synergistic effect of this combination in vivo is difficult. Here, treatment with doxorubicin, under hypoxia or normoxia in different liver cancer cell lines, was evaluated. Liver cancer cells HepG2, Huh7, and SNU449 were exposed to doxorubicin, hypoxia, or doxorubicin + hypoxia with different duration. Treatment response was evaluated with cell viability, apoptosis, oxidative stress, and summarized with IC₅₀. The protein profile of a 92-biomarker panel was analyzed on cells treated with 0 or 0.1 µM doxorubicin during 6 or 72 h, under normoxia or hypoxia. Hypoxia decreased viability of HepG2 and SNU499. HepG2 was least and SNU449 most tolerant to doxorubicin treatment. Cytotoxicity of doxorubicin increased over time in HepG2 and Huh7. The combination of doxorubicin + hypoxia affected the cells differently. Normalized protein expression was lower for HepG2 than Huh7 and SNU449. Hierarchical clustering separated HepG2 from Huh7 and SNU449. These three commonly used cell lines have critically different responses to chemotherapy and hypoxia, which was reflected in their different protein expression profile. These different responses suggest that tumors can respond differently to the combination of local chemotherapy and embolization.

Prostate cancer cells and exosomes in acidic condition show increased carbonic anhydrase IX expression and activity

Acidity and hypoxia are crucial phenotypes of tumour microenvironment both contributing to the selection of malignant cells under a micro evolutionistic pressure. During the tumour progression, nanovesicles, called exosomes and the metalloenzyme carbonic anhydrase IX (CA IX) affect the tumour growth and proliferation. Exosomes are released into the tumour microenvironment and spilt all over the body, while CA IX is a tumour-associated protein overexpressed in many different solid tumours. In the present study, to better understand the relationships between exosomes and CA IX, it has been used an in vitro cellular model of cells cultured in different pH conditions. The results showed that the acidic microenvironment induced upregulation of both expression and activity of CA IX in cancer cells and their exosomes, together with increasing the number of released exosomes. These data strongly support the importance of CA IX as a cancer biomarker and as a valuable target of new anticancer therapies.

Working with Hypoxia

A hypoxic environment can be defined as a region of the body or the whole body that is deprived of oxygen. Hypoxia is a feature of many diseases, such as cardiovascular disease, tissue trauma, stroke, and solid cancers. A loss of oxygen supply usually results in cell death; however, when cells gradually become hypoxic, they may survive and continue to thrive as described for conditions that promote metastatic growth. The role of hypoxia in these pathogenic pathways is therefore of great interest, and understanding the effect of hypoxia in regulating these mechanisms is fundamentally important. This chapter gives an extensive overview of these mechanisms. Moreover, given the challenges posed by tumor hypoxia we describe the current methods to simulate and detect hypoxic conditions followed by a discussion on current and experimental therapies that target hypoxic cells.

Exposure of Breast and Lung Cancer Cells to a Novel Estrone Analog Prior to Radiation Enhances Bcl-2-Mediated Cell Death

Following exposure of cells to gamma-radiation, a cascade of intracellular consequences may be observed in a semitemporal manner. This includes deoxyribonucleic acid (DNA) damage and reactive oxygen species (ROS) accumulation initially, with consequent signaling for DNA repair and facilitative regulation of the cell cycle. Failure to rectify the damage or ROS levels leads to induction of senescence or apoptosis. 2-Ethyl-3-O-sulfamoyl-estra-1,3,5(10),15-tetraen-17-ol (ESE-15-ol), a 2-methoxyestradiole analog designed in silico for superior pharmacokinetics, was investigated for its potential to enhance apoptotic signaling and decrease the long-term survival of cells exposed to radiation. Sequential early intracellular effects within radiation-treated MCF-7 breast- and A549 lung cancer cells pre-exposed to low-dose ESE-15-ol were investigated using various flow cytometric protocols, spectrophotometry, and microscopy. Long-term cellular survival and proliferation was examined using clonogenic studies, which demonstrated a significant decrease in the presensitized cells. Combination-treated cells exhibited increased superoxide formation, and decreased Bcl-2 expression and -phosphorylation. Induction of apoptosis and elevation of the sub-G₁ phase was evident in the pre-exposed MCF-7 cells, although only minimally in the A549 cells at 48-h. These results indicate that low-dose ESE-15-ol may increase tumor response to radiation. Future studies will investigate the effect of ESE-15-ol pre-exposure on radiation-induced DNA damage and repair mechanisms.

Nitroimidazole-based inhibitors DTP338 and DTP348 are safe for zebrafish embryos and efficiently inhibit the activity of human CA IX in Xenopus oocytes

Carbonic anhydrase (CA) IX is a hypoxia inducible enzyme that is highly expressed in solid tumours. Therefore, it has been considered as an anticancer target using specific chemical inhibitors. The nitroimidazoles DTP338 and DTP348 have been shown to inhibit CA IX in nanomolar range in vitro and reduce extracellular acidification in hypoxia, and impair tumour growth. We screened these compounds for toxicity using zebrafish embryos and measured their in vivo effects on human CA IX in Xenopus oocytes. In the toxicity screening, the LD₅₀ for both compounds was 3.5 mM. Neither compound showed apparent toxicity below 300 µM concentration. Above this concentration, both compounds altered the movement of zebrafish larvae. The IC₅₀ was 0.14 ± 0.02 µM for DTP338 and 19.26 ± 1.97 µM for DTP348, suggesting that these compounds efficiently inhibit CA IX in vivo. Our results suggest that these compounds can be developed as drugs for cancer therapy.

Methods for the evaluation of biomarkers in patients with kidney and liver diseases: multicentre research programme including ELUCIDATE RCT

Background

Protein biomarkers with associations with the activity and outcomes of diseases are being identified by modern proteomic technologies. They may be simple, accessible, cheap and safe tests that can inform diagnosis, prognosis, treatment selection, monitoring of disease activity and therapy and may substitute for complex, invasive and expensive tests. However, their potential is not yet being realised.

Design and methods

The study consisted of three workstreams to create a framework for research: workstream 1, methodology – to define current practice and explore methodology innovations for biomarkers for monitoring disease; workstream 2, clinical translation – to create a framework of research practice, high-quality samples and related clinical data to evaluate the validity and clinical utility of protein biomarkers; and workstream 3, the ELF to Uncover Cirrhosis as an Indication for Diagnosis and Action for Treatable Event (ELUCIDATE) randomised controlled trial (RCT) – an exemplar RCT of an established test, the ADVIA Centaur® Enhanced Liver Fibrosis (ELF) test (Siemens Healthcare Diagnostics Ltd, Camberley, UK) [consisting of a panel of three markers – (1) serum hyaluronic acid, (2) amino-terminal propeptide of type III procollagen and (3) tissue inhibitor of metalloproteinase 1], for liver cirrhosis to determine its impact on diagnostic timing and the management of cirrhosis and the process of care and improving outcomes.

Results

The methodology workstream evaluated the quality of recommendations for using prostate-specific antigen to monitor patients, systematically reviewed RCTs of monitoring strategies and reviewed the monitoring biomarker literature and how monitoring can have an impact on outcomes. Simulation studies were conducted to evaluate monitoring and improve the merits of health care. The monitoring biomarker literature is modest and robust conclusions are infrequent. We recommend improvements in research practice. Patients strongly endorsed the need for robust and conclusive research in this area. The clinical translation workstream focused on analytical and clinical validity. Cohorts were established for renal cell carcinoma (RCC) and renal transplantation (RT), with samples and patient data from multiple centres, as a rapid-access resource to evaluate the validity of biomarkers. Candidate biomarkers for RCC and RT were identified from the literature and their quality was evaluated and selected biomarkers were prioritised. The duration of follow-up was a limitation but biomarkers were identified that may be taken forward for clinical utility. In the third workstream, the ELUCIDATE trial registered 1303 patients and randomised 878 patients out of a target of 1000. The trial started late and recruited slowly initially but ultimately recruited with good statistical power to answer the key questions. ELF monitoring altered the patient process of care and may show benefits from the early introduction of interventions with further follow-up. The ELUCIDATE trial was an ‘exemplar’ trial that has demonstrated the challenges of evaluating biomarker strategies in ‘end-to-end’ RCTs and will inform future study designs.

Conclusions

The limitations in the programme were principally that, during the collection and curation of the cohorts of patients with RCC and RT, the pace of discovery of new biomarkers in commercial and non-commercial research was slower than anticipated and so conclusive evaluations using the cohorts are few; however, access to the cohorts will be sustained for future new biomarkers. The ELUCIDATE trial was slow to start and recruit to, with a late surge of recruitment, and so final conclusions about the impact of the ELF test on long-term outcomes await further follow-up. The findings from the three workstreams were used to synthesise a strategy and framework for future biomarker evaluations incorporating innovations in study design, health economics and health informatics.

Trial registration

Current Controlled Trials ISRCTN74815110, UKCRN ID 9954 and UKCRN ID 11930.

Funding

This project was funded by the NIHR Programme Grants for Applied Research programme and will be published in full inProgramme Grants for Applied Research; Vol. 6, No. 3. See the NIHR Journals Library website for further project information.

An update on anticancer drug development and delivery targeting carbonic anhydrase IX

The expression of carbonic anhydrase (CA) IX is up-regulated in many types of solid tumors in humans under hypoxic and acidic microenvironment. Inhibition of CA IX enzymatic activity with selective inhibitors, antibodies or labeled probes has been shown to reverse the acidic environment of solid tumors and reduce the tumor growth establishing the significant role of CA IX in tumorigenesis. Thus, the development of potent antitumor drugs targeting CA IX with minimal toxic effects is important for the target-specific tumor therapy. Recently, several promising antitumor agents against CA IX have been developed to treat certain types of cancers in combination with radiation and chemotherapy. Here we review the inhibition of CA IX by small molecule compounds and monoclonal antibodies. The methods of enzymatic assays, biophysical methods, animal models including zebrafish and Xenopus oocytes, and techniques of diagnostic imaging to detect hypoxic tumors using CA IX-targeted conjugates are discussed with the aim to overview the recent progress related to novel therapeutic agents that target CA IX in hypoxic tumors.

Impact of tumoral carbonic anhydrase IX and Ki-67 expression on survival in oral squamous cell carcinoma patients

Oral squamous cell carcinoma (OSCC) is the most commonly diagnosed type of head and neck cancer, accounting for ~300,000 new cases worldwide annually. Carbonic anhydrase IX (CAIX) and Ki-67 have been associated with reduced disease-specific survival (DSS) in patients with OSCC. We previously proposed a combined CAIX and Ki-67 signature of 'functional hypoxia' and sought to replicate this association in a larger independent cohort of patients with OSCC at the Fred Hutchinson Cancer Research Center (FHCRC) in Seattle. The study population included patients with incident primary OSCC treated at the University of Washington Medical Center and the Harborview Medical Center in Seattle between December 2003 and February 2012. Archived tumor blocks were obtained with tissue samples from 189 patients, and triplicate 0.6 mm cores were assembled into tissue microarrays (TMAs). Fluorescence immunohistochemistry and AQUAnalysis® were used to quantify the expression of tumoral CAIX (tCAIX) and stromal CAIX (sCAIX) and tumoral Ki-67 for each TMA core. Hazard ratios for DSS were calculated using Cox proportional hazards analysis. High tCAIX and sCAIX expression levels were associated with reduced DSS (aHR=1.003, 95% CI:1.00-1.01 and aHR=1.010, 95% CI:1.001-1.019, per AQUA score unit, respectively). Ki-67 expression was not associated with survival (aHR=1.01, 95% CI:0.99-1.02) in the FHCRC cohort. DSS for patients with high sCAIX and low Ki-67 did not differ from that of other patient groups. Elevated tCAIX was associated with reduced DSS as a continuous and as a dichotomized (75%) variable. sCAIX was associated with DSS as a continuous variable but not when dichotomized (75%). However, the previously proposed 'functional hypoxia' signature was not replicated in the current FHCRC study. The failure to replicate our prior observation of poorer survival in patients with combined high sCAIX and low tumoral Ki-67 was likely due to the absence of an association between tumoral Ki-67 and DSS in this cohort. However, the association between DSS and tCAIX and sCAIX supports a role for CAIX in OSCC clinical outcomes.

Hypoxia induces cancer-associated cAMP/PKA signalling through HIF-mediated transcriptional control of adenylyl cyclases VI and VII

Hypoxia is a phenomenon often arising in solid tumours, linked to aggressive malignancy, bad prognosis and resistance to therapy. Hypoxia-inducible factor-1 has been identified as a key mediator of cell and tissue adaptation to hypoxic conditions through transcriptional activation of many genes involved in glucose metabolism and other cancer-related processes, such as angiogenesis, cell survival and cell invasion. Cyclic adenosine 3′5′-monophosphate is one of the most ancient and evolutionarily conserved signalling molecules and the cAMP/PKA signalling pathway plays an important role in cellular adaptation to hypoxia. We have investigated possible new mechanisms behind hypoxic activation of the cAMP/PKA pathway. For the first time, we have shown that hypoxia induces transcriptional up-regulation of the system of adenylyl cyclases, enzymes responsible for cAMP production, in a panel of carcinoma cell lines of various origin. Our data prove functional relevance of the hypoxic increase of adenylyl cyclases VI and VII at least partially mediated by HIF-1 transcription factor. We have identified adenylyl cyclase VI and VII isoforms as mediators of cellular response to hypoxia, which led to the elevation of cAMP levels and enhanced PKA activity, with an impact on cell migration and pH regulation.

Expression of carbonic anhydrase IX is associated with poor prognosis through regulation of the epithelial‑mesenchymal transition in hepatocellular carcinoma

Carbonic anhydrase 9 (CA9) is a plasma membrane-associated isoenzyme that catalyzes pH regulation under hypoxic conditions. CA9 is transcriptionally regulated by hypoxia-inducible factor 1. Recent studies reported that hypoxia also promoted the epithelial-mesenchymal transition (EMT) in various cancers. In the present study, we evaluated the relationship between CA9 expression and EMT in vitro with two hepatoma cell lines. We also examined the clinical significance of CA9 expression in 117 consecutive patients that underwent hepatectomies for hepatocellular carcinoma (HCC). We evaluated CA9 expression and EMT induction under hypoxia with quantitative RT-PCR, western blot analysis and immunofluorescence staining, in HuH7 and HepG2 cells. We knocked down CA9 expression with small interfering RNA to evaluate the relationship between CA9 and EMT. We found that hypoxia induced CA9 expression in HCC cells and promoted EMT, evidenced by a loss of E-cadherin and an increase in N-cadherin. Twist, a transcriptional regulator of EMT, was also upregulated with hypoxia. The CA9 deficiency attenuated hypoxia-induced changes in E-cadherin and N-cadherin. Immunohistochemical evaluations of patient samples showed that CA9 was expressed in 50.4% of patients (59/117). However, patients with and without CA9 expression were not significantly different in clinicopathological factors. Nevertheless, a multivariate analysis showed that CA9 expression was an independent factor for both recurrence and prognosis among patients that underwent curative surgery for HCC. In conclusion, this study revealed that CA9 expression was a pivotal predictive factor for poor prognosis after radical surgery for HCC. Moreover, the CA9 regulation of the expression of EMT-related molecules represented a mechanism that enhanced malignant potential.

3'UTR polymorphisms of carbonic anhydrase IX determine the miR-34a targeting efficiency and prognosis of hepatocellular carcinoma

Carbonic anhydrase IX (CA9) expression level has been considered as a poor prognostic factor in hepatocellular carcinoma (HCC) patients. However, the judging criteria of CA9 level is hard to define for potential clinical applications. Unlike CA9 expression level, CA9 polymorphism is poorly documented in HCC. Here, we found that people carry A allele at CA9 rs1048638, a 3′UTR SNP, has higher risk of HCC. rs1048638-CA correlates with advanced stages, larger tumor sizes, more vascular invasion, and shorter survival of HCC patients. A allele at CA9 rs1048638 impairs miR-34a, a tumor suppressor miRNA in HCC, binding to CA9 3′UTR and desensitizes CA9 mRNA to miR-34a-dependent RNA degradation. CA9 expression levels were also correlated with miR-34a levels and rs1048638 genotypes in HCC patients. rs1048638 influences HCC risk and progression through effects on miR-34a-targeted CA9 expression in HCC. In conclusion, genetic variations of the CA9 3′UTR play important roles in regulating CA9 expression and cancer progression, which is a novel determinant and target for HCC metastasis and prognosis.

Dual-tail approach to discovery of novel carbonic anhydrase IX inhibitors by simultaneously matching the hydrophobic and hydrophilic halves of the active site

Dual-tail approach was employed to design novel Carbonic Anhydrase (CA) IX inhibitors by simultaneously matching the hydrophobic and hydrophilic halves of the active site, which also contains a zinc ion as part of the catalytic center. The classic sulfanilamide moiety was used as the zinc binding group. An amino glucosamine fragment was chosen as the hydrophilic part and a cinnamamide fragment as the hydrophobic part in order to draw favorable interactions with the corresponding halves of the active site. In comparison with sulfanilamide which is largely devoid of the hydrophilic and hydrophobic interactions with the two halves of the active site, the compounds so designed and synthesized in this study showed 1000-fold improvement in binding affinity. Most of the compounds inhibited the CA effectively with IC₅₀ values in the range of 7-152 nM. Compound 14e (IC₅₀: 7 nM) was more effective than the reference drug acetazolamide (IC₅₀: 30 nM). The results proved that the dual-tail approach to simultaneously matching the hydrophobic and hydrophilic halves of the active site by linking hydrophobic and hydrophilic fragments was useful for designing novel CA inhibitors. The effectiveness of those compounds was elucidated by both the experimental data and molecular docking simulations. This work laid a solid foundation for further development of novel CA IX inhibitors for cancer treatment.

Hypoxia regulates global membrane protein endocytosis through caveolin-1 in cancer cells

Hypoxia promotes tumour aggressiveness and resistance of cancers to oncological treatment. The identification of cancer cell internalizing antigens for drug targeting to the hypoxic tumour niche remains a challenge of high clinical relevance. Here we show that hypoxia down-regulates the surface proteome at the global level and, more specifically, membrane proteome internalization. We find that hypoxic down-regulation of constitutive endocytosis is HIF-independent, and involves caveolin-1-mediated inhibition of dynamin-dependent, membrane raft endocytosis. Caveolin-1 overexpression inhibits protein internalization, suggesting a general negative regulatory role of caveolin-1 in endocytosis. In contrast to this global inhibitory effect, we identify several proteins that can override caveolin-1 negative regulation, exhibiting increased internalization at hypoxia. We demonstrate antibody-mediated cytotoxin delivery and killing specifically of hypoxic cells through one of these proteins, carbonic anhydrase IX. Our data reveal that caveolin-1 modulates cell-surface proteome turnover at hypoxia with potential implications for specific targeting of the hypoxic tumour microenvironment.

Hypoxia promotes tumour aggressiveness and resistance of cancers to oncological treatment. Here, the authors show that caveolin-1 can down-regulate global membrane protein endocytosis in hypoxic cells with potential implications for targeting the hypoxic 3microenvironment of aggressive tumours.

Gene expression and enzyme activities of carbonic anhydrase and glutaminase in rat kidneys induced by chronic systemic hypoxia

Background: Hypoxia can cause acidosis. Kidney plays an essential role in maintaining acid-base balance, which involves the activities of carbonic anhydrase (CA) and glutaminase (GLS). This study is aimed to determine the expression and activities of the CA9 and GLS1 enzymes in relation to hypoxia inducible factor-1α (HIF-1α), a transcription factor protein which is a marker of hypoxia.Methods: This study was an in vivo experimental study with coupled paralel design. used 25 male Sprague-Dawley rats weighing 150-200 g. Rats were divided into 5 groups: the control group (normoxic condition) and 4 treatment groups. The latter were kept in a hypoxic chamber (10% O2: 90% N2) for 1, 3, 5 and 7 days. All rats were euthanized after treatment, kidneys excised, tissues homogenized and investigated for gene expression of CA9, GLS1 and HIF-1α. On protein level, total enzymatic activities of CA and GLS and protein of HIF-1α were also investigated. Data were analyzed statistically using ANOVA for significance, and as its alternative, used Mann-Whitney and Kruskal-Wallis test.Results: Results showed that HIF-1α mRNA increased during hypoxia, but not HIF-1α protein. It seemed that acidosis occurs in kidney tissue, indicated by increased CA9 and GLS1 mRNA expression and specific activity of total CA and GLS1. Expression of CA9 and GLS1 mRNA both showed strong positive correlation with HIF-1α mRNA, but not with HIF-1α protein.Conclusion: It is suggested that during chronic systemic hypoxia, gene expression of CA9 and GLS1 and their enzyme activities were increased as a response to acidosis and related with the expression of HIF-1α mRNA.

Carnosine inhibits carbonic anhydrase IX-mediated extracellular acidosis and suppresses growth of HeLa tumor xenografts

BACKGROUND

Carbonic anhydrase IX (CA IX) is a transmembrane enzyme that is present in many types of solid tumors. Expression of CA IX is driven predominantly by the hypoxia-inducible factor (HIF) pathway and helps to maintain intracellular pH homeostasis under hypoxic conditions, resulting in acidification of the tumor microenvironment. Carnosine (β-alanyl-L-histidine) is an anti-tumorigenic agent that inhibits the proliferation of cancer cells. In this study, we investigated the role of CA IX in carnosine-mediated antitumor activity and whether the underlying mechanism involves transcriptional and translational modulation of HIF-1α and CA IX and/or altered CA IX function.

METHODS

The effect of carnosine was studied using two-dimensional cell monolayers of several cell lines with endogenous CA IX expression as well as Madin Darby canine kidney transfectants, three-dimensional HeLa spheroids, and an in vivo model of HeLa xenografts in nude mice. mRNA and protein expression and protein localization were analyzed by real-time PCR, western blot analysis, and immunofluorescence staining, respectively. Cell viability was measured by a flow cytometric assay. Expression of HIF-1α and CA IX in tumors was assessed by immunohistochemical staining. Real-time measurement of pH was performed using a sensor dish reader. Binding of CA IX to specific antibodies and metabolon partners was investigated by competitive ELISA and proximity ligation assays, respectively.

RESULTS

Carnosine increased the expression levels of HIF-1α and HIF targets and increased the extracellular pH, suggesting an inhibitory effect on CA IX-mediated acidosis. Moreover, carnosine significantly inhibited the growth of three-dimensional spheroids and tumor xenografts compared with untreated controls. Competitive ELISA showed that carnosine disrupted binding between CA IX and antibodies specific for its catalytic domain. This finding was supported by reduced formation of the functional metabolon of CA IX and anion exchanger 2 in the presence of carnosine.

CONCLUSIONS

Our results indicate that interaction of carnosine with CA IX leads to conformational changes of CA IX and impaired formation of its metabolon, which in turn disrupts CA IX function. These findings suggest that carnosine could be a promising anticancer drug through its ability to attenuate the activity of CA IX.

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.

The effects of CA IX catalysis products within tumor microenvironment

Solid tumors are composed of both cancer cells and various types of accessory cells, mainly fibroblasts, that collectively compose the so called tumor-microenvironment. Cancer-associated fibroblasts have been described to actively participate in cancer progression by establishing a cytokine-mediated as well as metabolic crosstalk with cancer cells. In the present paper we show that activated human fibroblasts are able to boost tumor cells proliferation and that this effect is greatly dependent on stromal carbonic anhydrase IX (CA IX) activity. In fact fibroblasts show a strong upregulation of CA IX expression upon activation by cancer cells, while CA IX products, protons and bicarbonate, exert differential effects on cancer cells proliferation. While acidification of extracellular pH, a typical condition of rapidly growing solid tumors, is detrimental for tumor cells proliferation, bicarbonate, through its organication, supplies cancer cells with intermediates useful to sustain their high proliferation rate. Here we propose a new kind of fibroblasts/tumor cells crosstalk within tumor microenvironment, mediated by stromal CA IX products, aimed to favor cancer cells growth, opening new perspectives on CA IX role in tumor microenvironment.

The prognostic impact of a combined carbonic anhydrase IX and Ki67 signature in oral squamous cell carcinoma

Background:

Tumour hypoxia is associated with impaired apoptosis, resistance to therapy and poor prognosis. We previously reported that high stromal expression of the endogenous marker of hypoxia, carbonic anhydrase IX (CAIX), is associated with significantly reduced survival in oral squamous cell carcinoma (OSCC). In addition to hypoxia, CAIX expression is regulated by proliferation-associated signalling. We hypothesised that incorporating Ki67, a proliferation marker, into our existing CAIX-based stratification of OSCC would identify patients with the least favourable prognosis.

Methods:

Surgically resected tumours from 60 OSCC patients were analysed for CAIX, Ki67 and BAX expression using fluorescence immunohistochemistry and automated quantitative analysis (AQUA).

Results:

In patients expressing high stromal CAIX (sCAIX), stratification by tumour Ki67 expression revealed significantly distinct survival outcomes (P=0.005). In our OSCC cohort, below-median Ki67 and top-quartile sCAIX expression (Ki67^losCAIX^hi) were associated with significantly worse disease-specific survival in univariate (HR 7.2 (2.5–20.4), P=0.001) and multivariate (HR 4.2 (1.4–12.8), P=0.011) analyses. Hypoxia is associated with decreased BAX expression; the Ki67^losCAIX^hi group was more strongly associated with low BAX expression than high sCAIX alone.

Conclusion:

These data suggest that combined analysis of tumour Ki67 and sCAIX expression may provide a more clinically relevant assessment of tumour hypoxia in OSCC.

Molecular crosstalk between apoptosis and autophagy induced by a novel 2-methoxyestradiol analogue in cervical adenocarcinoma cells

Background

2-Methoxyestradiol has been shown to induce both autophagy and apoptosis in various carcinogenic cell lines. Although a promising anti-cancer agent, it has poor bioavailability and rapid in vivo metabolism which decreases its efficiency. In order to improve 2-methoxyestradiol’s anti-proliferative properties, a novel 2-methoxyestradiol analogue, 2-ethyl-3-O-sulphamoyl-estra-1,3,5 (10)16-tetraene (ESE-16), was previously in silico-designed in our laboratory. This study investigated ESE-16 for its anti-proliferative potential on a cervical adenocarcinoma cell (HeLa) cell line. Additionally, the possible intracellular crosstalk mechanisms between the two types of cell death were investigated.

Methods and results

HeLa cells exposed to 0.5 μM ESE-16 for 24 hours showed morphological evidence of both apoptotic and autophagic death pathways as assessed by polarization-optical transmitted light differential interference contrast microscopy, fluorescent microscopy and transmission electron microscopy. Flow cytometric cyclin B1 quantification revealed induction of programmed cell death after halting cell cycle progression in metaphase. Confocal microscopy demonstrated that ESE-16 caused microtubule fragmentation. Flow cytometric analysis of cell cycle progression and phosphatidylserine flip determination confirmed induction of apoptosis. Moreover, an increase in aggresome formation and microtubule-associated protein light chain, LC3, was demonstrated indicative of autophagy. Both caspase 8 and 3 were upregulated in a spectrophotometric analysis, indicating the involvement of the extrinsic pathway of apoptotic induction.

Conclusions

We conclude that the novel in silico-designed compound, ESE-16, exerts its anti-proliferative effect on the tumorigenic human epithelial cervical (HeLa) cells by sequentially targeting microtubule integrity, resulting in a metaphase block, causing induction of both autophagic and apoptotic cell death via a crosstalk mechanism that involves the extrinsic pathway. Future investigations will expand on signal transduction pathways involved in both apoptosis and autophagy for assessment of ESE-16 effects on microtubule dynamic instability parameters.

Signaling pathways of ESE-16, an antimitotic and anticarbonic anhydrase estradiol analog, in breast cancer cells

The aim of this study was to characterize the in vitro action of 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10)16-tetraene (ESE-16) on non-tumorigenic MCF-12A, tumorigenic MCF-7 and metastatic MDA-MB-231 breast cancer cells. ESE-16 is able to inhibit the activity of a carbonic anhydrase II and a mimic of carbonic anhydrase IX in the nanomolar range. Gene and protein expression studies using various techniques including gene and antibody microarrays and various flow cytometry assays yielded valuable information about the mechanism of action of ESE-16. The JNK pathway was identified as an important pathway mediating the effects of ESE-16 while the p38 stress-induced pathway is more important in MDA-MB-231 cells exposed to ESE-16. Lysosomal rupture and iron metabolism was identified as important mediators of mitochondrial membrane depolarization. Abrogation of Bcl-2 phosphorylation status as a result of ESE-16 also plays a role in inducing mitochondrial membrane depolarization. The study provides a basis for future research projects to develop the newly synthesized compound into a clinically usable anticancer agent either alone or in combination with other agents.

Keywords: Antimitotic, anticarbonic anhydrase IX, apoptosis, autophagy, cell cycle arrest, Bcl-2, JNK, p38, mitochondrial membrane depolarization, flow cytometry, gene expression and protein microarray, anticancer.

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.

In vitro evaluation of ESE-15-ol, an estradiol analogue with nanomolar antimitotic and carbonic anhydrase inhibitory activity

Antimitotic compounds are still one of the most widely used chemotherapeutic anticancer drugs in the clinic today. Given their effectiveness against cancer it is beneficial to continue enhancing these drugs. One way is to improve the bioavailability and efficacy by synthesizing derivatives that reversibly bind to carbonic anhydrase II (CAII) in red blood cells followed by a slow release into the blood circulation system. In the present study we describe the in vitro biological activity of a reduced derivative of 2-ethyl-3-O-sulphamoyl-estradiol (2EE), 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10),15-tetraen-17-ol (ESE-15-ol). ESE-15-ol is capable of inhibiting carbonic anhydrase activity in the nanomolar range and is selective towards a mimic of carbonic anhydrase IX when compared to the CAII isoform. Docking studies using Autodock Vina suggest that the dehydration of the D-ring plays a role towards the selectivity of ESE-15-ol to CAIX and that the binding mode of ESE-15-ol is substantially different when compared to 2EE. ESE-15-ol is able to reduce cell growth to 50% after 48 h at 50–75 nM in MCF-7, MDA-MB-231, and MCF-12A cells. The compound is the least potent against the non-tumorigenic MCF-12A cells. In vitro mechanistic studies demonstrate that the newly synthesized compound induces mitochondrial membrane depolarization, abrogates the phosphorylation status of Bcl-2 and affects gene expression of genes associated with cell death and mitosis.

In vivo imaging and quantification of carbonic anhydrase IX expression as an endogenous biomarker of tumor hypoxia

Carbonic anhydrase IX (CA IX) is a transmembrane protein that has been shown to be greatly upregulated under conditions of hypoxia in many tumor cell lines. Tumor hypoxia is associated with impaired efficacy of cancer therapies making CA IX a valuable target for preclinical and diagnostic imaging. We have developed a quantitative in vivo optical imaging method for detection of CA IX as a marker of tumor hypoxia based on a near-infrared (NIR) fluorescent derivative of the CA IX inhibitor acetazolamide (AZ). The agent (HS680) showed single digit nanomolar inhibition of CA IX as well as selectivity over other CA isoforms and demonstrated up to 25-fold upregulation of fluorescent CA IX signal in hypoxic versus normoxic cells, which could be blocked by 60%-70% with unlabeled AZ. CA IX negative cell lines (HCT-116 and MDA-MB-231), as well as a non-binding control agent on CA IX positive cells, showed low fluorescent signal under both conditions. In vivo FMT imaging showed tumor accumulation and excellent tumor definition from 6-24 hours. In vivo selectivity was confirmed by pretreatment of the mice with unlabeled AZ resulting in >65% signal inhibition. HS680 tumor signal was further upregulated >2X in tumors by maintaining tumor-bearing mice in a low oxygen (8%) atmosphere. Importantly, intravenously injected HS680 signal was co-localized specifically with both CA IX antibody and pimonidazole (Pimo), and was located away from non-hypoxic regions indicated by a Hoechst stain. Thus, we have established a spatial correlation of fluorescence signal obtained by non-invasive, tomographic imaging of HS680 with regions of hypoxia and CA IX expression. These results illustrate the potential of HS680 and combined with FMT imaging to non-invasively quantify CA IX expression as a hypoxia biomarker, crucial to the study of the underlying biology of hypoxic tumors and the development and monitoring of novel anti-cancer therapies.

Polypharmacology of sulfonamides: pazopanib, a multitargeted receptor tyrosine kinase inhibitor in clinical use, potently inhibits several mammalian carbonic anhydrases

Pazopanib, a new, multi-targeted tyrosine kinase inhibitor (TKI) used clinically for the treatment of several types of tumors, incorporates a primary sulfonamide moiety normally associated with the inhibition of the metallo enzyme carbonic anhydrase (CA, EC 4.2.1.1). Here we show that pazopanib and related sulfonamides such as indisulam, acetazolamide or ureido-substituted peptidomimetic benzenesulfonamides are low nanomolar inhibitors of many of the fifteen human isoforms hCA I-XIV. These data indicate that in addition to the TK inhibitory action, pazopanib may exert antitumor/antimetastatic effects also due to the potent inhibition of the tumor-associated, hypoxia-inducible enzymes CA IX and XII.

Phosphorylation of carbonic anhydrase IX controls its ability to mediate extracellular acidification in hypoxic tumors

In the hypoxic regions of a tumor, carbonic anhydrase IX (CA IX) is an important transmembrane component of the pH regulatory machinery that participates in bicarbonate transport. Because tumor pH has implications for growth, invasion, and therapy, determining the basis for the contributions of CA IX to the hypoxic tumor microenvironment could lead to new fundamental and practical insights. Here, we report that Thr443 phosphorylation at the intracellular domain of CA IX by protein kinase A (PKA) is critical for its activation in hypoxic cells, with the fullest activity of CA IX also requiring dephosphorylation of Ser448. PKA is activated by cAMP, which is elevated by hypoxia, and we found that attenuating PKA in cells disrupted CA IX-mediated extracellular acidification. Moreover, following hypoxia induction, CA IX colocalized with the sodium-bicarbonate cotransporter and other PKA substrates in the leading edge membranes of migrating tumor cells, in support of the concept that bicarbonate metabolism is spatially regulated at cell surface sites with high local ion transport and pH control. Using chimeric CA IX proteins containing heterologous catalytic domains derived from related CA enzymes, we showed that CA IX activity was modulated chiefly by the intracellular domain where Thr443 is located. Our findings indicate that CA IX is a pivotal mediator of the hypoxia-cAMP-PKA axis, which regulates pH in the hypoxic tumor microenvironment.