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

Hypoxia-regulated gene expression explains differences between melanoma cell line-derived xenografts and patient-derived xenografts

Cell line-derived xenografts (CDXs) are an integral part of drug efficacy testing during development of new pharmaceuticals against cancer but their accuracy in predicting clinical responses in patients have been debated. Patient-derived xenografts (PDXs) are thought to be more useful for predictive biomarker identification for targeted therapies, including in metastatic melanoma, due to their similarities to human disease. Here, tumor biopsies from fifteen patients and ten widely-used melanoma cell lines were transplanted into immunocompromised mice to generate PDXs and CDXs, respectively. Gene expression profiles generated from the tumors of these PDXs and CDXs clustered into distinct groups, despite similar mutational signatures. Hypoxia-induced gene signatures and overexpression of the hypoxia-regulated miRNA hsa-miR-210 characterized CDXs. Inhibition of hsa-miR-210 with decoys had little phenotypic effect in vitro but reduced sensitivity to MEK1/2 inhibition in vivo, suggesting down-regulation of this miRNA could result in development of resistance to MEK inhibitors.

Carbonic Anhydrase IX (CAIX), Cancer, and Radiation Responsiveness

Carbonic anhydrase IX has been under intensive investigation as a therapeutic target in cancer. Studies demonstrate that this enzyme has a key role in pH regulation in cancer cells, allowing these cells to adapt to the adverse conditions of the tumour microenviroment. Novel CAIX inhibitors have shown efficacy in both in vitro and in vivo pre-clinical cancer models, adversely affecting cell viability, tumour formation, migration, invasion, and metastatic growth when used alone. In co-treatments, CAIX inhibitors may enhance the effects of anti-angiogenic drugs or chemotherapy agents. Research suggests that these inhibitors may also increase the response of tumours to radiotherapy. Although many of the anti-tumour effects of CAIX inhibition may be dependent on its role in pH regulation, recent work has shown that CAIX interacts with several of the signalling pathways involved in the cellular response to radiation, suggesting that pH-independent mechanisms may also be an important basis of its role in tumour progression. Here, we discuss these pH-independent interactions in the context of the ability of CAIX to modulate the responsiveness of cancer to radiation.

"Seriously Sweet": Acesulfame K Exhibits Selective Inhibition Using Alternative Binding Modes in Carbonic Anhydrase Isoforms

Human carbonic anhydrase IX (CA IX) is upregulated in neoplastic tissues; as such, it is studied as a drug target for anticancer chemotherapy. Inhibition of CA IX has been shown to be therapeutically favorable in terms of reducing tumor growth. Previously, saccharin, a commonly used artificial sweetener, has been observed to selectively inhibit CA IX over other CA isoforms. In this study, X-ray crystallography showed acesulfame potassium (Ace K) binding directly to the catalytic zinc in CA IX (mimic) and through a bridging water in CA II. This modulation in binding is reflected in the binding constants, with Ace K inhibiting CA IX but not other CA isoforms. Hence, this study establishes the potential of Ace K (an FDA approved food additive) as a lead compound in the design and development of CA IX specific inhibitors.

Proteus mirabilis inhibits cancer growth and pulmonary metastasis in a mouse breast cancer model

A variety of bacteria have been used as agents and vectors for antineoplastic therapy. A series of mechanisms, including native bacterial toxicity, sensitization of the immune system and competition for nutrients, may contribute to antitumor effects. However, the antitumor effects of Proteus species have been minimally studied, and it is not clear if bacteria can alter tumor hypoxia as a component of their antineoplastic effect. In the present study, Proteus mirabilis bacteria were evaluated for the ability to proliferate and accumulate in murine tumors after intravenous injection. To further investigate the efficacy and safety of bacterial injection, mice bearing 4T1 tumors were treated with an intravenous dose of 5×107 CFU Proteus mirabilis bacteria via the tail vein weekly for three treatments. Histopathology, immunohistochemistry (IHC) and western analysis were then performed on excised tumors. The results suggested Proteus mirabilis localized preferentially to tumor tissues and remarkably suppressed the growth of primary breast cancer and pulmonary metastasis in murine 4T1 models. Results showed that the expression of NKp46 and CD11c was significantly increased after bacteria treatment. Furthermore, tumor expression of carbonic anhydrase IX (CA IX) and hypoxia inducible factor-1a (HIF-1a), surrogates for hypoxia, was significantly lower in the treated group than the control group mice as assessed by IHC and western analysis. These findings demonstrated that Proteus mirabilis may a promising bacterial strain for used against primary tumor growth and pulmonary metastasis, and the immune system and reduction of tumor hypoxia may contribute to the antineoplastic and antimetastatic effects observed.

Carbonic anhydrase IX inhibition affects viability of cancer cells adapted to extracellular acidosis

Among the players of the adaptive response of cancer cells able to promote a resistant and aggressive phenotype, carbonic anhydrase IX (CAIX) recently has emerged as one of the most relevant drug targets. Indeed, CAIX targeting has received a lot of interest, and selective inhibitors are currently under clinical trials. Hypoxia has been identified as the master inductor of CAIX, but, to date, very few is known about the influence that another important characteristic of tumor microenvironment, i.e., extracellular acidosis, exerts on CAIX expression and activity. In the last decades, acidic microenvironment has been associated with aggressive tumor phenotype endowed with epithelial-to-mesenchymal transition (EMT) profile, high invasive and migratory ability, apoptosis, and drug resistance. We demonstrated that melanoma, breast, and colorectal cancer cells transiently and chronically exposed to acidified medium (pH 6.7 ± 0.1) showed a significantly increased CAIX expression compared to those grown in standard conditions (pH 7.4 ± 0.1). Moreover, we observed that the CAIX inhibitor FC16-670A (also named SLC-0111, which just successfully ended phase I clinical trials) not only prevents such increased expression under acidosis but also promotes apoptotic and necrotic programs only in acidified cancer cells. Thus, CAIX could represent a selective target of acidic cancer cells and FC16-670A inhibitor as a useful tool to affect this aggressive subpopulation characterized by conventional therapy escape.

KEY MESSAGES

Cancer cells overexpress CAIX under transient and chronic extracellular acidosis. Acidosis-induced CAIX overexpression is NF-κB mediated and HIF-1α independent. FC16-670A prevents CAIX overexpression and induces acidified cancer cell death.

Exosomes expressing carbonic anhydrase 9 promote angiogenesis

Exosomes or microvesicles that are secreted from cells are considered to play important roles in tumor microenvironment. Carbonic anhydrase 9 (CA9), which is induced by hypoxia-inducible factor 1 (HIF1) in response to hypoxia, is overexpressed in many types of cancer including renal cell carcinoma (RCC). We examined the expression level of CA9 in several RCC cell lines and found that the basal level of CA9 was much higher in OSRC-2 cells than in Caki-1, KMRC-1 and 786-O cells. Consistent with the intracellular expression levels, CA9 was abundantly detected in exosomes isolated by ultracentrifugation from OSRC-2 cells. Density gradient centrifugation of OSRC-2 and 786-O exosomes confirmed the co-presence of CA9 with exosomal markers. Upon hypoxia and treatment with CoCl₂, a hypoxia mimic agent, the CA9 level in exosomes was increased for all cell lines. In order to examine the effects of CA9 exosomes on angiogenesis, we generated stably transfected HEK293 cells expressing CA9. Immunocytochemical staining demonstrated the uptake of CA9 exosomes by human umbilical vein endothelial cells (HUVEC). In vitro angiogenesis assays using HUVEC revealed that CA9 exosomes promoted migration and tube formation. Lastly, MMP2 expression was increased by treatment with CA9 exosomes in HUVEC. Taken together, our results suggest the possibility that CA9 exosomes released from hypoxic RCC may enhance angiogenesis in microenvironment, thereby contributing to cancer progression.

Overexpression of carbonic anhydrase IX induces cell motility by activating matrix metalloproteinase-9 in human oral squamous cell carcinoma cells

Oral cancer is a solid malignant tumor that is prone to occur following hypoxia. There are no clear studies showing a link between hypoxia and oral carcinogenesis. Carbonic anhydrase IX (CAIX), which is a hypoxia-induced transmembrane protein, is highly expressed in various types of human cancer. However, the effects of CAIX on the metastasis of human oral cancer cells and the underlying molecular mechanisms have not been clarified. In this study, we observed that CAIX overexpression increased the migratory and invasive abilities of SCC-9 and SAS cells. In addition, CAIX overexpression increased the mRNA and protein expression of matrix metalloproteinase-9 (MMP-9) and the phosphorylation of focal adhesion kinase (FAK), steroid receptor coactivator (Src), and extracellular signal-regulated kinase 1/2 signaling proteins. CAIX overexpression also increased the binding capacity of nuclear factor-κB (NF-κB), c-Jun, and c-Fos on the MMP-9 gene promoter. In addition, treatment with MMP-9 short hairpin RNA, an MMP inhibitor (GM6001), an FAK mutant, or an MEK inhibitor (U0126) inhibited CAIX-induced cell motility in SCC-9 cells. Moreover, data sets from The Cancer Genome Atlas demonstrated that CAIX expression was significantly associated with advanced progression and poor survival in oral cancer. In conclusion, it can be inferred that CAIX overexpression induces MMP-9 gene expression, which consequently induces the metastasis of oral cancer cells.

Depletion of carbonic anhydrase IX abrogates hypoxia-induced overexpression of stanniocalcin-1 in triple negative breast cancer cells

Carbonic anhydrase IX (CAIX) is a pH-regulating enzyme that plays a key role in maintaining an alkaline intracellular pH under hypoxic conditions. It is overexpressed in a variety of solid cancers, including breast cancer (BC), and has been implicated in the migration, invasion and stemness of breast cancer cells. Therefore, CAIX recently emerged as a novel therapeutic target for the treatment of BC. To gain an insight into the mechanism of action of CAIX inhibitors, we investigated the impact of CAIX knock-down on the transcriptional response to hypoxia in 2 BC cell lines - MCF7 and MDA-MB-231, by performing a global gene expression analysis. This showed that CAIX knock-down had a relatively minor effect on the global transcriptional response to hypoxia, however it blocked hypoxia-induced upregulation of stanniocalcin-1 (STC1), a secreted glycoprotein that has been shown to promote tumor progression and metastasis in BC. Kaplan-Meier survival analysis showed that high STC1 expression is significantly associated with poor survival in patients with basal-type breast cancer but not luminal A and HER2+ subtypes. Moreover, the association was particularly high in a subgroup of basal-type BC patients with TP53 mutations thus revealing a putative cooperation of STC1 with mutated TP53 in generating highly aggressive BC subgroup. Taken together, these findings show that CAIX inhibitors at least partially act through blocking STC1 induction in BC cells and reveal a subgroup of BC patients, who potentially would benefit most from the treatment with CAIX inhibitors.

Inhibition of Carbonic Anhydrase IX by Ureidosulfonamide Inhibitor U104 Reduces Prostate Cancer Cell Growth, But Does Not Modulate Daunorubicin or Cisplatin Cytotoxicity

Carbonic anhydrase (CA) IX has emerged as a promising target for cancer therapy. It is highly upregulated in hypoxic regions and mediates pH regulation critical for tumor cell survival as well as extracellular acidification of the tumor microenvironment, which promotes tumor aggressiveness via various mechanisms, such as augmenting metastatic potential. Therefore, the aim of this study was to analyze the complex interdependency between CA IX and the tumor microenvironment in prostate tumor cells with regard to potential therapeutic implications. CA IX was upregulated by hypoxia as well as acidosis in prostate cancer cells. This induction did not modulate intracellular pH but led to extracellular acidification. Pharmacological inhibition of CA IX activity by U104 (SLC-0111) resulted in a reduction in tumor cell growth and an increase in apoptotic cell death. Intracellular pH was reduced under normoxic and even more so under hypoxic conditions when CA IX level was high. However, although intracellular pH regulation was disturbed, targeting CA IX in combination with daunorubicin or cisplatin did not intensify apoptotic tumor cell death. Hence, targeting CA IX in prostate cancer cells can lead to intracellular pH dysregulation and, consequently, can reduce cellular growth and elevate apoptotic cell death. Attenuation of extracellular acidification by blocking CA IX might additionally impede tumor progression and metastasis. However, no beneficial effect was seen when targeting CA IX in combination with chemotherapeutic drugs.

Role of carbonic anhydrases in skin wound healing

Skin wound closure occurs when keratinocytes migrate from the edge of the wound and re-epithelialize the epidermis. Their migration takes place primarily before any vascularization is established, that is, under hypoxia, but relatively little is known regarding the factors that stimulate this migration. Hypoxia and an acidic environment are well-established stimuli for cancer cell migration. The carbonic anhydrases (CAs) contribute to tumor cell migration by generating an acidic environment through the conversion of carbon dioxide to bicarbonate and a proton. On this basis, we explored the possible role of CAs in tissue regeneration using mouse skin wound models. We show that the expression of mRNAs encoding CA isoforms IV and IX are increased (~25 × and 4 ×, respectively) during the wound hypoxic period (days 2-5) and that cells expressing CAs form a band-like structure beneath the migrating epidermis. RNA-Seq analysis suggested that the CA IV-specific signal in the wound is mainly derived from neutrophils. Due to the high level of induction of CA IV in the wound, we treated skin wounds locally with recombinant human CA IV enzyme. Recombinant CA IV significantly accelerated wound re-epithelialization. Thus, CA IV could contribute to wound healing by providing an acidic environment in which the migrating epidermis and neutrophils can survive and may offer novel opportunities to accelerate wound healing under compromised conditions.

Cell survival: Interplay between hypoxia and pre-mRNA splicing

RNA splicing takes place in the nucleus and occurs either co- or post-transcriptionally. Noncoding sequences (introns) in nuclear mRNA precursors (pre-mRNA) are removed by dedicated splicing machinery. The coding sequences (exons) are joined to generate the mature mRNA that is exported to the cytoplasm and translated into protein. Splicing events are tissue-specific. This process plays an important role in cellular differentiation and organism development. The splicing machinery heavily contributes to biological complexity and especially to the ability of cells to adapt to different developmental stages and altered cellular conditions. A striking change has been observed in alternative splicing pattern of genes and alterations in splicing factor expression under pathologic conditions especially in human cancers. Cancer cells are often confronted with a significant reduction in oxygen availability, which is a major reason for changeover of major cellular processes. Hypoxic regions have been identified within all solid tumors and their presence has been linked to malignant progression, metastasis, resistance to therapy, and poor clinical outcomes following treatment. Cellular responses to hypoxia are mediated by hypoxia inducible transcription factors (HIFs). This review focuses on currently available data how pre-mRNAs splicing contributes to cellular adaptation to hypoxic conditions, to genes which alternative splicing is regulated dependent on hypoxia and how regulation of alternative splicing under hypoxic conditions is achieved.

PSMA redirects cell survival signaling from the MAPK to the PI3K-AKT pathways to promote the progression of prostate cancer

Increased abundance of the prostate-specific membrane antigen (PSMA) on prostate epithelium is a hallmark of advanced metastatic prostate cancer (PCa) and correlates negatively with prognosis. However, direct evidence that PSMA functionally contributes to PCa progression remains elusive. We generated mice bearing PSMA-positive or PSMA-negative PCa by crossing PSMA-deficient mice with transgenic PCa (TRAMP) models, enabling direct assessment of PCa incidence and progression in the presence or absence of PSMA. Compared with PSMA-positive tumors, PSMA-negative tumors were smaller, lower-grade, and more apoptotic with fewer blood vessels, consistent with the recognized proangiogenic function of PSMA. Relative to PSMA-positive tumors, tumors lacking PSMA had less than half the abundance of type 1 insulin-like growth factor receptor (IGF-1R), less activity in the survival pathway mediated by PI3K-AKT signaling, and more activity in the proliferative pathway mediated by MAPK-ERK1/2 signaling. Biochemically, PSMA interacted with the scaffolding protein RACK1, disrupting signaling between the β₁ integrin and IGF-1R complex to the MAPK pathway, enabling activation of the AKT pathway instead. Manipulation of PSMA abundance in PCa cell lines recapitulated this signaling pathway switch. Analysis of published databases indicated that IGF-1R abundance, cell proliferation, and expression of transcripts for antiapoptotic markers positively correlated with PSMA abundance in patients, suggesting that this switch may be relevant to human PCa. Our findings suggest that increase in PSMA in prostate tumors contributes to progression by altering normal signal transduction pathways to drive PCa progression and that enhanced signaling through the IGF-1R/β₁ integrin axis may occur in other tumors.

Dissecting the Process of Activation of Cancer-promoting Zinc-requiring Ectoenzymes by Zinc Metalation Mediated by ZNT Transporters

Zinc-requiring ectoenzymes, including both secreted and membrane-bound enzymes, are considered to capture zinc in their active site for their activation in the early secretory pathway. This idea has been confirmed by our studies conducted using tissue-nonspecific alkaline phosphatase (TNAP), which is elaborately activated by means of a two-step mechanism by zinc transporter 5 (ZNT5)-ZNT6 heterodimers and ZNT7 homodimers, through protein stabilization followed by enzyme activation with zinc in the early secretory pathway. However, the molecular basis of the activation process in other zinc-requiring ectoenzymes remains largely unknown. In this study, we investigated this activation process by using three cancer-promoting zinc-requiring ectoenzymes, autotaxin (ATX), matrix metalloproteinase 9 (MMP9), and carbonic anhydrase IX (CAIX), and the chicken DT40 cell mutants that we generated; we specifically focused on clarifying whether the same or a similar activation mechanism operates in these ectoenzymes. ATX activation required ZNT5-ZNT6 heterodimers and ZNT7 homodimers in a manner similar to TNAP activation, although the protein stability of ATX was differently regulated from that of TNAP. MMP9 required ZNT5-ZNT6 heterodimers and ZNT7 homodimers for its activation as well as secretion; MMP9 was not secreted into the spent medium unless both zinc-transport complexes were present. Finally, CAIX activation by zinc was mediated not only by ZNT5-ZNT6 heterodimers and ZNT7 homodimers but also by ZNT4 homodimers; thus, these three zinc-transport complexes redundantly contribute to CAIX activation. Our results provide pivotal insights into the activation processes of zinc-requiring ectoenzymes, and furthermore, they offer novel insights for potential cancer therapy applications given the cancer-promoting potencies of ATX, MMP9, and CAIX.

Evaluation of carbonic anhydrase IX as a therapeutic target for inhibition of breast cancer invasion and metastasis using a series of in vitro breast cancer models

Triple negative, resistant or metastatic disease are major factors in breast cancer mortality, warranting novel approaches. Carbonic anhydrase IX (CAIX) is implicated in survival, migration and invasion of breast cancer cells and inhibition provides an innovative therapeutic strategy. The efficacy of 5 novel ureido-substituted sulfamate CAIX inhibitors were assessed in increasingly complex breast cancer models, including cell lines in normoxia and hypoxia, 3D spheroids and an ex-vivo explant model utilizing fresh biopsy tissue from different breast cancer subtypes. CAIX expression was evaluated in a tissue microarray (TMA) of 92 paired lymph node and primary breast cancers and 2 inhibitors were appraised in vivo using MDA-MB-231 xenografts. FC11409B, FC9398A, FC9403, FC9396A and S4 decreased cell proliferation and migration and inhibited 3D spheroid invasion. S4, FC9398A and FC9403A inhibited or prevented invasion into collagen. FC9403A significantly reversed established invasion whilst FC9398A and DTP348 reduced xenograft growth. TMA analysis showed increased CAIX expression in triple negative cancers. These data establish CAIX inhibition as a relevant therapeutic goal in breast cancer, targeting the migratory, invasive, and metastatic potential of this disease. The use of biopsy tissue suggests efficacy against breast cancer subtypes, and should provide a useful tool in drug testing against invasive cancers.

Lipocalin 2 prevents oral cancer metastasis through carbonic anhydrase IX inhibition and is associated with favourable prognosis

Lipocalin 2 (LCN2), a secreted glycoprotein, is up- or downregulated in different human cancers. At present, the functional role of LCN2 in the progression of oral squamous cell carcinoma (OSCC), which accounts for most head and neck cancers, remains poorly understood, particularly with respect to its involvement in invasion and metastasis. In this study, we observed that LCN2 expression decreased in patients with OSCC and lymph node metastasis compared with that in patients without metastasis. A higher LCN2 expression correlated with the survival of patients with OSCC. Furthermore, LCN2 overexpression in OSCC cells reduced in vitro migration and invasion and in vivo metastasis, whereas its silencing induced an increase in cell motility. Mechanistically, LCN2 inhibited the cell motility of OSCC cells through hypoxia-inducible factor (HIF)-1α-dependent transcriptional inhibition of the carbonic anhydrase IX (CAIX). CAIX overexpression relieved the migration inhibition imposed by LCN2 overexpression in OSCC cells. Moreover, a microRNA (miR) analysis revealed that LCN2 can suppress CAIX expression and cell migration through miR-4505 induction. Examination of tumour tissues from patients with OSCC and OSCC-transplanted mice revealed an inverse correlation between LCN2 and CAIX expression. Furthermore, patients with LCN2(strong)/CAIX(weak) revealed the lowest frequency of lymph node metastasis and the longest survival. Our findings suggest that LCN2 suppresses tumour metastasis by targeting the transcriptional and post-transcriptional regulation of CAIX in OSCC cells. LCN2 overexpression may be a novel OSCC treatment strategy and a useful biomarker for predicting OSCC progression.

The metabolic microenvironment of melanomas: Prognostic value of MCT1 and MCT4

BRAF mutations are known drivers of melanoma development and, recently, were also described as players in the Warburg effect, while this reprogramming of energy metabolism has been identified as a possible strategy for treating melanoma patients. Therefore, the aim of this work was to evaluate the expression and prognostic value of a panel of glycolytic metabolism-related proteins in a series of melanomas. The immunohistochemical expression of MCT1, MCT4, GLUT1, and CAIX was evaluated in 356 patients presenting melanoma and 20 patients presenting benign nevi. Samples included 20 benign nevi, 282 primary melanomas, 117 lymph node and 54 distant metastases samples. BRAF mutation was observed in 29/92 (31.5%) melanoma patients and 17/20 (85%) benign nevi samples. NRAS mutation was observed in 4/36 (11.1%) melanoma patients and 1/19 (5.3%) benign nevi samples. MCT4 and GLUT1 expression was significantly increased in metastatic samples, and MCT1, MCT4 and GLUT1 were significantly associated with poor prognostic variables. Importantly, MCT1 and MCT4 were associated with shorter overall survival. In conclusion, the present study brings new insights on metabolic aspects of melanoma, paving the way for the development of new-targeted therapies.

Prophylactic irradiation of para-aortic lymph nodes for patients with locally advanced cervical cancers with and without high CA9 expression (KROG 07-01): A randomized, open-label, multicenter, phase 2 trial

BACKGROUND AND PURPOSE

The efficacy of prophylactic extended-field irradiation (EFI) plus concomitant cisplatin in patients with locally advanced uterine cervical cancer (LAUCC) is unknown, nor is it known whether tumor carbonic anhydrase IX (CA9) expression level, a hypoxia marker, influences survival outcome.

MATERIAL AND METHODS

We recruited patients with UCC, FIGO stage IB1 with pelvic lymph node (LN) metastases to IVA with negative para-aortic LN on PET/CT. CA9 expression was examined and patients were randomized to either EFI or pelvic only radiotherapy (PRT) in each CA9 group. The primary outcomes were para-aortic recurrence-free survival (PARFS) and disease-free survival (DFS).

RESULTS

Between 2006 and 2011, 79 patients with CA9-positive and 37 with CA9-negative tumors were enrolled, respectively. The median follow-up period was 69.2months (range 6.8-102.1). For CA9-positive patients, 5-year PARFS was 100% and 81.7% for those receiving EFI and PRT (p=0.007), respectively. DFS was 78.6% for EFI and 71.3% for PRT patients (p=0.353). For CA9-negative patients, 5y PARFS was 100% and 94.1% for EFI and PRT (p=0.317), respectively. DFS was 100% for EFI and 70.7% for PRT (p=0.018).

CONCLUSION

EFI significantly reduced recurrences in PAN in patients with CA9-positive tumors, but survival outcome was not improved, due to high local recurrence and high distant metastases rates. This study indicates the necessity for new therapeutic strategies for LAUCC patients whose tumors show high CA9 expression.

In Vivo Loss of Function Screening Reveals Carbonic Anhydrase IX as a Key Modulator of Tumor Initiating Potential in Primary Pancreatic Tumors

Reprogramming of energy metabolism is one of the emerging hallmarks of cancer. Up-regulation of energy metabolism pathways fuels cell growth and division, a key characteristic of neoplastic disease, and can lead to dependency on specific metabolic pathways. Thus, targeting energy metabolism pathways might offer the opportunity for novel therapeutics. Here, we describe the application of a novel in vivo screening approach for the identification of genes involved in cancer metabolism using a patient-derived pancreatic xenograft model. Lentiviruses expressing short hairpin RNAs (shRNAs) targeting 12 different cell surface protein transporters were separately transduced into the primary pancreatic tumor cells. Transduced cells were pooled and implanted into mice. Tumors were harvested at different times, and the frequency of each shRNA was determined as a measure of which ones prevented tumor growth. Several targets including carbonic anhydrase IX (CAIX), monocarboxylate transporter 4, and anionic amino acid transporter light chain, xc- system (xCT) were identified in these studies and shown to be required for tumor initiation and growth. Interestingly, CAIX was overexpressed in the tumor initiating cell population. CAIX expression alone correlated with a highly tumorigenic subpopulation of cells. Furthermore, CAIX expression was essential for tumor initiation because shRNA knockdown eliminated the ability of cells to grow in vivo. To the best of our knowledge, this is the first parallel in vivo assessment of multiple novel oncology target genes using a patient-derived pancreatic tumor model.

Metabolic changes associated with tumor metastasis, part 1: tumor pH, glycolysis and the pentose phosphate pathway

Metabolic adaptations are intimately associated with changes in cell behavior. Cancers are characterized by a high metabolic plasticity resulting from mutations and the selection of metabolic phenotypes conferring growth and invasive advantages. While metabolic plasticity allows cancer cells to cope with various microenvironmental situations that can be encountered in a primary tumor, there is increasing evidence that metabolism is also a major driver of cancer metastasis. Rather than a general switch promoting metastasis as a whole, a succession of metabolic adaptations is more likely needed to promote different steps of the metastatic process. This review addresses the contribution of pH, glycolysis and the pentose phosphate pathway, and a companion paper summarizes current knowledge regarding the contribution of mitochondria, lipids and amino acid metabolism. Extracellular acidification, intracellular alkalinization, the glycolytic enzyme phosphoglucose isomerase acting as an autocrine cytokine, lactate and the pentose phosphate pathway are emerging as important factors controlling cancer metastasis.

Role of nuclear receptors in breast cancer stem cells

The recapitulation of primary tumour heterogenity and the existence of a minor sub-population of cancer cells, capable of initiating tumour growth in xenografts on serial passages, led to the hypothesis that cancer stem cells (CSCs) exist. CSCs are present in many tumours, among which is breast cancer. Breast CSCs (BCSCs) are likely to sustain the growth of the primary tumour mass, as well as to be responsible for disease relapse and metastatic spreading. Consequently, BCSCs represent the most significant target for new drugs in breast cancer therapy. Both the hypoxic condition in BCSCs biology and pro-inflammatory cytokine network has gained increasing importance in the recent past. Breast stromal cells are crucial components of the tumours milieu and are a major source of inflammatory mediators. Recently, the anti-inflammatory role of some nuclear receptors ligands has emerged in several diseases, including breast cancer. Therefore, the use of nuclear receptors ligands may be a valid strategy to inhibit BCSCs viability and consequently breast cancer growth and disease relapse.

Antimitotic drugs in the treatment of cancer

Cancer is a complex disease since it is adaptive in such a way that it can promote proliferation and invasion by means of an overactive cell cycle and in turn cellular division which is targeted by antimitotic drugs that are highly validated chemotherapy agents. However, antimitotic drug cytotoxicity to non-tumorigenic cells and multiple cancer resistance developed in response to drugs such as taxanes and vinca alkaloids are obstacles faced in both the clinical and basic research field to date. In this review, the classes of antimitotic compounds, their mechanisms of action and cancer cell resistance to chemotherapy and other limitations of current antimitotic compounds are highlighted, as well as the potential of novel 17-β estradiol analogs as cancer treatment.

Characteristics of carbonic anhydrase 9 expressing cells in human intestinal crypt base

Though recent studies have revealed that stem cells of many tissues are harbored in hypoxic microenvironment, little is known about the relationship between hypoxia and intestinal crypt base, where intestinal stem cells are supposed to exist. In this study, we focused on carbonic anhydrase IX (CA9), a hypoxia-inducible membrane-tethered protein, in normal intestinal crypt base, adenoma and early colorectal cancer. Using surgically resected human colorectal cancer specimen, we searched for the expression pattern and functional association of CA9 in human adult normal intestinal epithelia, adenoma and early colorectal cancer by immunofluorescent and immunohistochemical staining, flow cytometry, and quantitative real-time-polymerase chain reaction. We demonstrated that almost all crypt base slender cells in ileum and crypt base cells with eosinophilic structure in their basal cytoplasm in right and left colon were CA9+ with the ratio of 25 to 40%, and that adenoma and T1 colorectal cancer showed broad expression of CA9. Flow cytometrically sorted CA9+ population showed increased mRNA level of a Wnt signaling factor AXIN2. In conclusion, these observations indicate that CA9 expression in normal crypt base cells has association with intestinal epithelial stemness and CA9 may be involved in the carcinogenesis of colorectal cancer.

CA IX is upregulated in CoCl2-induced hypoxia and associated with cell invasive potential and a poor prognosis of breast cancer

Hypoxia, a common phenomenon during the development of malignant solid tumors including breast cancer, serves to propagate a cascade of molecular pathways triggered by hypoxia-inducible factor-1α (HIF-1α). Carbonic anhydrase IX (CA IX), one of the target genes of HIF-1α, has been reported to be involved in progression of malignant tumors. The objective of this study was to investigate the expression of HIF-1α and CA IX in hypoxia, involvement of CA IX in the regulation of migration and invasion/metastasis and its prognostic significance in breast cancer. We used cobalt chloride (CoCl2) as a hypoxia-mimetic agent and found that the expression of HIF-1α protein, CA IX mRNA and protein, is effectively upregulated, except for HIF-1α mRNA. Data showed that the elevated CA IX expression is closely related to in vitro cell migration and invasion, and the underlying mechanism of this process may be associated with epithelial-mesenchymal transition (EMT). The study of clinical tissue samples also demonstrated that CA IX is an independent prognostic marker that may serve as a useful clinical biomarker for predicting tumor progression and the invasion/metastasis of breast cancer. These results provide further insight into the role of CA IX in tumor progression and put forward further strong evidence as well as new consideration for CA IX target therapy.

Betulinyl Sulfamates as Anticancer Agents and Radiosensitizers in Human Breast Cancer Cells

Betulinic acid (BA), a natural compound of birch bark, is cytotoxic for many tumors. Recently, a betulinyl sulfamate was described that inhibits carbonic anhydrases (CA), such as CAIX, an attractive target for tumor-selective therapy strategies in hypoxic cancer cells. Data on combined CAIX inhibition with radiotherapy are rare. In the human breast cancer cell lines MDA-MB231 and MCF7, the effects of BA and betulinyl sulfamates on cellular and radiobiological behavior under normoxia and hypoxia were evaluated. The two most effective betulinyl sulfamates CAI 1 and CAI 3 demonstrated a 1.8–2.8-fold higher cytotoxicity than BA under normoxia in breast cancer cells, with IC₅₀ values between 11.1 and 18.1 µM. BA exhibits its strongest cytotoxicity with IC₅₀ values of 8.2 and 16.4 µM under hypoxia. All three substances show a dose-dependent increase in apoptosis, inhibition of migration, and inhibition of hypoxia-induced gene expression. In combination with irradiation, betulinyl sulfamates act as radiosensitizers, with DMF10 values of 1.47 (CAI 1) and 1.75 (CAI 3) under hypoxia in MDA-MB231 cells. BA showed additive effects in combination with irradiation. Taken together; our results suggest that BA and betulinyl sulfamates seem to be attractive substances to combine with radiotherapy; particularly for hypoxic breast cancer.

Roles of Carbonic Anhydrase IX in Development of Pancreatic Cancer

The aim of this study was to study the effects of carbonic anhydrase IX (CA IX) towards the invasion and metastasis of pancreatic cancer. The expressions of CA IX in 58 cases of pancreatic cancer and paired paracancerous normal tissues, obtained from 2005 to 2012 in the first Affiliated Hospital of China Medical University, were detected, as well as its expressions in different pancreatic cancer cell lines, aiming to detect the impacts of CA IX silencing towards the invasion and metastasis of pancreatic cancer cells. The CA IX expressions in 58 pancreatic cancer cases were higher than those in the paired paracancerous normal tissues (P < 0.01), and positively correlated with the tumor size and the UICC staging UICC (P < 0.05), the multivariate analysis showed that the high expression of CA IX was the independent risk factor towards the prognosis of pancreatic cancer (P < 0.05). The CA IX was highly expressed in AxPC-1 and Miapaca-2, and the interference effects were significant. CA IX silencing could significantly inhibit the invasion and metastasis of AxPC-1 and Miapaca. We support a pro-tumor role of CA IX in the development and progression of pancreatic cancer.

Huaier aqueous extract inhibits cervical cancer cell proliferation via JNK/p38 pathway

Although the anticancer effects of Huaier extract have been widely investigated, including anti-proliferate, anti-angiogenic and anti-metastatic activities, the mechanisms are not well understood. This study aimed to elucidate the inhibitory effect of Huaier extract on tumor growth in cervical cancer cells and its molecular mechanisms. Cell viability and motility were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, colony assays, migration, and invasive assays, respectively. The distribution of the cell cycle was analyzed by flow cytometry. Huaier inhibited cell viability of SiHa and C33A cells in a time- and dose-dependent manner; cell migration and invasiveness were also suppressed; Huaier was able to cause G2/M cell cycle arrest in C33A cells. The western blot results confirmed Huaier dose-dependently increased expression of phosphorylated c-Jun N-terminal kinase (JNK), p-38 and downregulated the expression of phosphorylated extracellular signal-regulated kinase (ERK) in a time- and dose-dependently manner. In vivo experiments showed that Huaier significantly suppressed the tumor volume of SiHa cell xenografts. These data suggest that Huaier may inhibit tumor proliferation in cervical cancer via the JNK/p38 signaling pathway.

Carbonic anhydrase IX overexpression regulates the migration and progression in oral squamous cell carcinoma

Carbonic anhydrase IX (CAIX) is reportedly overexpressed in several types of carcinomas and is generally considered a marker of malignancy. The current study investigated the association between membrane expression of CAIX and the clinicopathological characteristics in oral squamous cell carcinoma (OSCC) patients. The study used immunohistochemistry to examine CAIX expression in 271 OSCC specimens by tissue microarray (TMA) and assessed the effect of CAIX overexpression and knockdown on migration of oral cancer cells in vitro. We found that CAIX expression was associated with more advanced clinical stages (p = 0.030) and positive lymph node metastasis (p = 0.026). Importantly, CAIX expression was correlated with a poorer patient prognosis in a univariate survival analysis (p = 0.025). Moreover, CAIX suppression by small interfering RNA (siRNA) significantly reduced cellular migration in OECM-1 oral cancer cell. In conclusion, our study showed that the expression of CAIX in OSCC samples can predict the progression of OSCC and survival of OSCC patients in Taiwan.

Sulfonamide bearing pyrazolylpyrazolines as potent inhibitors of carbonic anhydrase isoforms I, II, IX and XII

A series of pyrazolylpyrazolines was designed, synthesized and evaluated for carbonic anhydrase (CA, EC 4.2.1.1) inhibitory activity against cytosolic human (h) isozymes hCA I and hCA II as well as transmembrane tumor associated isozymes, hCA IX and hCA XII. All the tested compounds exhibited an excellent CA activity profile against hCA I, hCA II and hCA XII when compared to the reference drug acetazolamide (AZA). Compounds 6d, 6f and 7a-7f have exhibited better inhibition profile against hCA XII (Ki = 0.47-5.1 nM) as compared with AZA (Ki = 5.7 nM) especially, compounds 6a, 7a, 7c and 7d which were nearly 10-fold better than reference drug. Against hCA II, all of the tested compounds were better than the standard drug especially compounds 6c, 6d, 7c and 7d (Ki = 1.1-1.7 nM) were many fold better inhibitors than AZA (Ki = 12.1 nM). In addition, they acted as selective CA inhibitors of isoform hCA XII over the physiological isoform hCA I.

Chemokine-Dependent pH Elevation at the Cell Front Sustains Polarity in Directionally Migrating Zebrafish Germ Cells

Directional cell migration requires cell polarization with respect to the distribution of the guidance cue. Cell polarization often includes asymmetric distribution of response components as well as elements of the motility machinery. Importantly, the function and regulation of most of these molecules are known to be pH dependent. Intracellular pH gradients were shown to occur in certain cells migrating in vitro, but the functional relevance of such gradients for cell migration and for the response to directional cues, particularly in the intact organism, is currently unknown. In this study, we find that primordial germ cells migrating in the context of the developing embryo respond to the graded distribution of the chemokine Cxcl12 by establishing elevated intracellular pH at the cell front. We provide insight into the mechanisms by which a polar pH distribution contributes to efficient cell migration. Specifically, we show that Carbonic Anhydrase 15b, an enzyme controlling the pH in many cell types, including metastatic cancer cells, is expressed in migrating germ cells and is crucial for establishing and maintaining an asymmetric pH distribution within them. Reducing the level of the protein and thereby erasing the pH elevation at the cell front resulted in abnormal cell migration and impaired arrival at the target. The basis for the disrupted migration is found in the stringent requirement for pH conditions in the cell for regulating contractility, for the polarization of Rac1 activity, and hence for the formation of actin-rich structures at the leading edge of the migrating cells.

The Expression of Carbonic Anhydrase (CA) IX/XII and Lymph Node Metastasis in Early Breast Cancer

Purpose

The aim of study was to test by immunohistochemical (IHC) staining whether carbonic anhydrase (CA) 9 and 12 have an effect on sentinel lymph node (SLN) metastasis in early breast cancer and to find clinicopathologic factors associated with SLN metastasis.

Materials and Methods

Between June 2003 and June 2011, medical records of 470 patients diagnosedwith breast cancer with pT1-2, pN0-2, and M0 were reviewed. Of these 470, 314 patients who underwent SLN biopsy±axillary dissection were subjects of this study. Using tissue microarray, IHC staining for CA9 and CA12 was performed. Clinicopathologic factors such as patient age, tumour size, lymphatic invasion, hormone receptor status, and the Ki-67 labeling index were analysed together.

Results

The mean age of all patients was 51.7 years. The mean number of harvested SLN was 3.62, and 212 patients (67.5%) had negative SLN. Lymphatic invasion, the Ki-67 labelling index of primary tumours, and CA9 staining of stromal cells, were independent risk factors for SLN metastasis in the multivariate analysis. In 33 patients (10.5%) without the three risk factors, no patient had SLN metastasis. In 80 patients without lymphatic invasion of primary tumours or CA9 staining of stromal cells, only four patients (5%) had positive SLN.

Conclusion

CA9 staining of stromal cells is an independent risk factor for SLN metastasis as well as lymphatic invasion and a low Ki-67 labelling index of primary tumours in patients with early breast cancer. IHC staining of primary tumours for CA12was not associatedwith SLN metastasis.

Histopathological determinants of tumor resistance: a special look to the immunohistochemical expression of carbonic anhydrase IX in human cancers

Intrinsic and acquired drug resistance of tumor cells still causes the failure of treatment regimens in advanced human cancers. It may be driven by intrinsic tumor cells features, or may also arise from micro environmental influences. Hypoxia is a microenvironment feature associated with the aggressiveness and metastasizing ability of human solid cancers. Hypoxic cancer cells overexpress Carbonic Anhydrase IX (CA IX). CA IX ensures a favorable tumor intracellular pH, while contributing to stromal acidosis, which facilitates tumor invasion and metastasis. The overexpression of CA IX is considered an epiphenomenon of the presence of hypoxic, aggressive tumor cells. Recently, a relationship between CA IX overexpression and the cancer stem cells (CSCs) population has been hypothesized. CSCs are strictly regulated by tumor hypoxia and drive a major non-mutational mechanism of cancer drug-resistance. We reviewed the current data concerning the role of CA IX overexpression in human malignancies, extending such information to the expression of the stem cells markers CD44 and nestin in solid cancers, to explore their relationship with the biological behavior of tumors. CA IX is heavily expressed in advanced tumors. A positive trend of correlation between CA IX overexpression, tumor stage/grade and poor outcome emerged. Moreover, stromal CA IX expression was associated with adverse events occurrence, maybe signaling the direct action of CA IX in directing the mesenchymal changes that favor tumor invasion; in addition, membranous/cytoplasmic co-overexpression of CA IX and stem cells markers were found in several aggressive tumors. This suggests that CA IX targeting could indirectly deplete CSCs and counteract resistance of solid cancers in the clinical setting.

The potential of liposomes with carbonic anhydrase IX to deliver anticancer ingredients to cancer cells in vivo

Drug delivery nanocarriers, especially targeted drug delivery by liposomes are emerging as a class of therapeutics for cancer. Early research results suggest that liposomal therapeutics enhanced efficacy, while simultaneously reducing side effects, owing to properties such as more targeted localization in tumors and active cellular uptake. Here, we highlight the features of immunoliposomes that distinguish them from previous anticancer therapies, and describe how these features provide the potential for therapeutic effects that are not achievable with other modalities. While a large number of studies has been published, the emphasis here is placed on the carbonic anhydrase IX (CA-IX) and the conjugated liposomes that are likely to open a new chapter on drug delivery system by using immunoliposomes to deliver anticancer ingredients to cancer cells in vivo.

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.

4-Functionalized 1,3-diarylpyrazoles bearing benzenesulfonamide moiety as selective potent inhibitors of the tumor associated carbonic anhydrase isoforms IX and XII

A library of 4-functionalized 1,3-diarylpyrazoles (3a-3h, 5a-5g and 6a-6g) was designed, synthesized and evaluated against four human carbonic anhydrase (CA, EC 4.2.1.1) isozymes representing two cytosolic isozymes hCA I and hCA II, and two transmembrane tumor associated ones, hCA IX and hCA XII. All the twenty two tested compounds exhibited excellent CA activity profile against the four CA isozymes when compared to the reference drug acetazolamide. Six of the tested compounds (3a-3b, 3f, 3h, 6a and 6b) displayed low nanomolar affinity (Ki < 5 nM) for hCA IX whereas seven compounds (3a-3b, 3d-3f, 3h and 6f) displayed Ki < 10 nM against hCA XII. In addition, they acted as selective CA inhibitors of isoforms IX and XII over the physiological isoforms I and II.

Physical status of human papillomavirus integration in cervical cancer is associated with treatment outcome of the patients treated with radiotherapy

Integration of human papillomavirus (HPV) DNA into the host genome is a critical aetiological event in the progression from normal cervix to intraepithelial neoplasm, and finally to invasive cervical cancer. However, there has been little work on how HPV integration status relates to treatment outcome for cervical carcinomas. In the current study, HPV E2 and E6 gene copy numbers were measured in 111 cervical cancer tissues using real-time QPCR. Integration patterns were divided into four groups: single copy-integrated with episomal components (group 1), single copy-integrated without episomal components (group 2), multicopy tandem repetition-integrated (group 3), and low HPV (group 4) groups. A relapse-predicting model was constructed using multivariable Cox proportional hazards model to classify patients into different risk groups for disease-free survival (DFS). The model was internally validated using bootstrap resampling. Oligonucleotide microarray analysis was performed to evaluate gene expression patterns in relation to the different integration groups. DFS rate was inferior in the order of the patients in group 4, group 2/3, and group 1. Multivariate analysis showed that histologic grade, clinical stage group, and integration pattern were significant prognostic factors for poor DFS. The current prognostic model accurately predicted the risk of relapse, with an area under the receiver operating characteristic curve (AUC) of 0.74 (bootstrap corrected, 0.71). In conclusion, these data suggest that HPV integration pattern is a potent prognostic factor for tailored treatment of cervical cancer.

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.

Comparative mode-of-action analysis following manual and automated phenotype detection in Xenopus laevis

Given the increasing utilization of phenotypic screens in drug discovery also the subsequent mechanism-of-action analysis gains increased attention.

Carbonic anhydrase IX (CAIX) as a mediator of hypoxia-induced stress response in cancer cells

The development of hypoxic microenvironments within many types of solid tumors imposes a significant stress on cancer cells to which they must respond appropriately in order to survive and grow. Tumor-specific, hypoxia-induced upregulation of Carbonic Anhydrase IX (CAIX) is a component of the complex response of cancer cells to the evolving low oxygen environment. Here, we discuss evidence from in vivo tumor models employing inhibition or enhancement of CAIX expression, using gene depletion or overexpression strategies, respectively, or inhibition of its catalytic activity, using CAIX-specific small molecules or antibodies, to demonstrate that CAIX is a functional mediator of tumor growth and metastasis. We also discuss the functional contribution of CAIX to several specific biological processes critical for cancer progression, including pH regulation and cell survival, adhesion, migration and invasion, the maintenance of cancer stem cell function, and the acquisition of chemo and radioresistant properties. The demonstration of CAIX as a functional mediator of cancer progression provides a biological rationale for its use as a cancer-specific, clinically relevant therapeutic target.

Primary breast cancer stem-like cells metastasise to bone, switch phenotype and acquire a bone tropism signature

BACKGROUND

Bone metastases represent a common and severe complication in breast cancer, and the involvement of cancer stem cells (CSCs) in the promotion of bone metastasis is currently under discussion. Here, we used a human-in-mice model to study bone metastasis formation due to primary breast CSCs-like colonisation.

METHODS

Primary CD44⁺CD24⁻ breast CSCs-like were transduced by a luciferase-lentiviral vector and injected through subcutaneous and intracardiac (IC) routes in non-obese/severe-combined immunodeficient (NOD/SCID) mice carrying subcutaneous human bone implants. The CSCs-like localisation was monitored by in vivo luciferase imaging. Bone metastatic CSCs-like were analysed through immunohistochemistry and flow cytometry, and gene expression analyses were performed by microarray techniques.

RESULTS

Breast CSCs-like colonised the human-implanted bone, resulting in bone remodelling. Bone metastatic lesions were histologically apparent by tumour cell expression of epithelial markers and vimentin. The bone-isolated CSCs-like were CD44⁻CD24⁺ and showed tumorigenic abilities after injection in secondary mice. CD44⁻CD24⁺ CSCs-like displayed a distinct bone tropism signature that was enriched in genes that discriminate bone metastases of breast cancer from metastases at other organs.

CONCLUSION

Breast CSCs-like promote bone metastasis and display a CSCs-like bone tropism signature. This signature has clinical prognostic relevance, because it efficiently discriminates osteotropic breast cancers from tumour metastases at other sites.

Acidic extracellular microenvironment and cancer

Acidic extracellular pH is a major feature of tumor tissue, extracellular acidification being primarily considered to be due to lactate secretion from anaerobic glycolysis. Clinicopathological evidence shows that transporters and pumps contribute to H⁺ secretion, such as the Na⁺/H⁺ exchanger, the H⁺-lactate co-transporter, monocarboxylate transporters, and the proton pump (H⁺-ATPase); these may also be associated with tumor metastasis. An acidic extracellular pH not only activates secreted lysosomal enzymes that have an optimal pH in the acidic range, but induces the expression of certain genes of pro-metastatic factors through an intracellular signaling cascade that is different from hypoxia. In addition to lactate, CO₂ from the pentose phosphate pathway is an alternative source of acidity, showing that hypoxia and extracellular acidity are, while being independent from each other, deeply associated with the cellular microenvironment. In this article, the importance of an acidic extracellular pH as a microenvironmental factor participating in tumor progression is reviewed.

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

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

New selective carbonic anhydrase IX inhibitors: synthesis and pharmacological evaluation of diarylpyrazole-benzenesulfonamides

Carbonic anhydrase (CA) IX expression is increased upon hypoxia and has been proposed as a therapeutic target since it has been associated with poor prognosis, tumor progression and pH regulation. We report the synthesis and the pharmacological evaluation of a new class of human carbonic anhydrase (hCA) inhibitors, 4-(5-aryl-2-hydroxymethyl-pyrazol-1-yl)-benzenesulfonamides. A molecular modeling study was conducted in order to simulate the binding mode of this new family of enzyme inhibitors within the active site of hCA IX. Pharmacological studies revealed high hCA IX inhibitory potency in the parameters nanomolar range. This study showed that the position of sulfonamide group in meta of the 1-phenylpyrazole increase a selectivity hCA IX versus hCA II of our compounds. An in vitro antiproliferative screening has been performed on the breast cancer MDA-MB-231 cell using doxorubicin as cytotoxic agent and in presence of selected CA IX inhibitor. The results shown that the cytotoxic efficiency of doxorubicin in an hypoxic environment, expressed in IC50 value, is restored at 20% level with 1μM CA IX inhibitor.

Function of carbonic anhydrase IX in glioblastoma multiforme

Carbonic anhydrase (CA) IX is over-expressed in glioblastoma; however, its functions in this context are unknown. Metabolically, glioblastomas are highly glycolytic, leading to a significant lactic acid load. Paradoxically, the intracellular pH is alkaline. We hypothesized that CAIX contributes to the extrusion of hydrogen ions into the extracellular space, thereby moderating intra- and extracellular pH and creating an environment conductive to enhanced invasion. We investigated the role of CAIX as a prognostic marker in patients with glioblastoma and its biological function in vitro. CAIX expression was analyzed in 59 patients with glioblastoma by immunohistochemistry. The expression levels were correlated to overall survival. In vitro, U251 and Ln 18 glioblastoma cells were incubated under hypoxia to induce CAIX expression, and RNA interference (RNAi) was used to examine the function of CAIX on cell attachment, invasion, intracellular energy transfer, and susceptibility to adjuvant treatment. High CAIX expression was identified as an independent factor for poor survival in patients with glioblastoma. In vitro, cell attachment and invasion were strongly reduced after knockdown of CAIX. Finally, the effects of radiation and chemotherapy were strongly augmented after CAIX interference and were accompanied by a higher rate of apoptotic cell death. CAIX is an independent prognostic factor for poor outcome in patients with glioblastoma. Cell attachment, invasion, and survival during adjuvant treatment are significantly influenced by high CAIX expression. These results indicate that inhibition of CAIX is a potential metabolic target for the treatment of patients with glioblastoma.

Recent developments in targeting carbonic anhydrase IX for cancer therapeutics

Carbonic anhydrase IX (CAIX) is a hypoxia-inducible enzyme that is overexpressed by cancer cells from many tumor types, and is a component of the pH regulatory system invoked by these cells to combat the deleterious effects of a high rate of glycolytic metabolism. CAIX functions to help produce and maintain an intracellular pH (pHi) favorable for tumor cell growth and survival, while at the same time participating in the generation of an increasingly acidic extracellular space, facilitating tumor cell invasiveness. Pharmacologic interference of CAIX catalytic activity using monoclonal antibodies or CAIX-specific small molecule inhibitors, consequently disrupting pH regulation by cancer cells, has been shown recently to impair primary tumor growth and metastasis. Many of these agents are in preclinical or clinical development and constitute a novel, targeted strategy for cancer therapy.