The effects of CA IX catalysis products within tumor microenvironment

Multi- and polypharmacology of carbonic anhydrase inhibitors

Eight genetically distinct families of the enzyme carbonic anhydrase (CA, EC 4.2.1.1) have been described in organisms overall in the phylogenetic tree. They catalyze the hydration of CO2 to bicarbonate and protons and are involved in pH regulation, chemosensing, and metabolism. The 15 α-CA isoforms present in humans are pharmacological drug targets known for decades, their inhibitors being used as diuretics, antiglaucoma, antiepileptic, or antiobesity drugs, as well as for the management of acute mountain sickness, idiopathic intracranial hypertension, and recently, as antitumor theragnostic agents. Other potential applications include the use of CA inhibitors (CAIs) in inflammatory conditions, cerebral ischemia, neuropathic pain, or Alzheimer/Parkinson disease management. CAs from pathogenic bacteria, fungi, protozoans, and nematodes have started to be considered as drug targets in recent years, with notable advances being registered. CAIs have a complex multipharmacology probably unique to this enzyme, which has been exploited intensely but may lead to other relevant applications in the future due to the emergence of drug design approaches that afforded highly isoform-selective compounds for most α-CAs known to date. They belong to a multitude of chemical classes (sulfonamides and isosteres, [iso]coumarins and related compounds, mono- and dithiocarbamates, selenols, ninhydrines, boronic acids, benzoxaboroles, etc). The polypharmacology of CAIs will also be discussed because drugs originally discovered for the treatment of non-CA related conditions (topiramate, zonisamide, celecoxib, pazopanib, thiazide, and high-ceiling diuretics) show effective inhibition against many CAs, which led to their repurposing for diverse pharmacological applications. SIGNIFICANCE STATEMENT: CAIs have multiple pharmacologic applications, such as diuretics, antiglaucoma, antiepileptic, antiobesity, antiacute mountain sickness, anti-idiopathic intracranial hypertension, and antitumor drugs. Their use in inflammatory conditions, cerebral ischemia, neuropathic pain, or neurodegenerations has started to be investigated recently. Parasite carbonic anhydrases are also drug targets for anti-infectives with novel mechanisms of action that can bypass drug resistance to commonly used agents. Drugs discovered for the management of other conditions that effectively inhibit these enzymes exert interesting polypharmacologic effects.

Carbonic anhydrase IX: An atypical target for innovative therapies in cancer

Carbonic anhydrases (CAs), are metallo-enzymes implicated in several pathophysiological processes where tissue pH regulation is required. CA IX is a tumor-associated CA isoform induced by hypoxia and involved in the adaptation of tumor cells to acidosis. Indeed, several tumor-driving pathways can induce CA IX expression, and this in turn has been associated to cancer cells invasion and metastatic features as well as to induction of stem-like features, drug resistance and recurrence. After its functional and structural characterization CA IX targeting approaches have been developed to inhibit its activity in neoplastic tissues, and to date this field has seen an incredible acceleration in terms of therapeutic options and biological readouts. Small molecules inhibitors, hybrid/dual targeting drugs, targeting antibodies and adoptive (CAR-T based) cell therapy have been developed at preclinical level, whereas a sulfonamide CA IX inhibitor and an antibody entered Phase Ib/II clinical trials for the treatment and imaging of different solid tumors. Here recent advances on CA IX biology and pharmacology in cancer, and its therapeutic targeting will be discussed.

Carbonic anhydrase versatility: from pH regulation to CO2 sensing and metabolism

While the carbonic anhydrase (CA, EC 4.2.1.1) superfamily of enzymes has been described primarily as involved only in pH regulation for decades, it also has many other important functions. CO2, bicarbonate, and protons, the physiological substrates of CA, are indeed the main buffering system in organisms belonging to all life kingdoms; however, in the last period, relevant progress has been made in the direction of elucidating the involvement of the eight genetically distinct CA families in chemical sensing, metabolism, and several other crucial physiological processes. Interference with CA activity, both by inhibiting and activating these enzymes, has thus led to novel applications for CA inhibitors and activators in the field of innovative biomedicine and environment and health. In this perspective article, I will discuss the recent advances which have allowed for a deeper understanding of the biochemistry of these versatile enzymes and various applications of their modulators of activity.

Metabolic reprogramming of donor T cells enhances graft-versus-leukemia effects in mice and humans

Acute myeloid leukemia (AML) relapse after allogeneic hematopoietic cell transplantation (allo-HCT) has a dismal prognosis. We found that T cells of patients relapsing with AML after allo-HCT exhibited reduced glycolysis and interferon-γ production. Functional studies in multiple mouse models of leukemia showed that leukemia-derived lactic acid (LA) interfered with T cell glycolysis and proliferation. Mechanistically, LA reduced intracellular pH in T cells, led to lower transcription of glycolysis-related enzymes, and decreased activity of essential metabolic pathways. Metabolic reprogramming by sodium bicarbonate (NaBi) reversed the LA-induced low intracellular pH, restored metabolite concentrations, led to incorporation of LA into the tricarboxylic acid cycle as an additional energy source, and enhanced graft-versus-leukemia activity of murine and human T cells. NaBi treatment of post-allo-HCT patients with relapsed AML improved metabolic fitness and interferon-γ production in T cells. Overall, we show that metabolic reprogramming of donor T cells is a pharmacological strategy for patients with relapsed AML after allo-HCT.

MicroRNA-Mediated Metabolic Shaping of the Tumor Microenvironment

The metabolism of cancer cells is generally very different from what is found in normal counterparts. However, in a tumor mass, the continuous crosstalk and competition for nutrients and oxygen among different cells lead to metabolic alterations, not only in cancer cells, but also in the different stromal and immune cells of the tumor microenvironment (TME), which are highly relevant for tumor progression. MicroRNAs (miRs) are small non-coding RNAs that silence their mRNA targets post-transcriptionally and are involved in numerous physiological cell functions as well as in the adaptation to stress situations. Importantly, miRs can also be released via extracellular vesicles (EVs) and, consequently, take part in the bidirectional communication between tumor and surrounding cells under stress conditions. Certain miRs are abundantly expressed in stromal and immune cells where they can regulate various metabolic pathways by directly suppressing enzymes or transporters as well as by controlling important regulators (such as transcription factors) of metabolic processes. In this review, we discuss how miRs can induce metabolic reprogramming in stromal (fibroblasts and adipocytes) and immune (macrophages and T cells) cells and, in turn, how the biology of the different cells present in the TME is able to change. Finally, we debate the rebound of miR-dependent metabolic alterations on tumor progression and their implications for cancer management.

Nutritional Exchanges Within Tumor Microenvironment: Impact for Cancer Aggressiveness

Neoplastic tissues are composed not only by tumor cells but also by several non-transformed stromal cells, such as cancer-associated fibroblasts, endothelial and immune cells, that actively participate to tumor progression. Starting from the very beginning of carcinogenesis, tumor cells, through the release of paracrine soluble factors and vesicles, i.e., exosomes, modify the behavior of the neighboring cells, so that they can give efficient support for cancer cell proliferation and spreading. A mandatory role in tumor progression has been recently acknowledged to metabolic deregulation. Beside undergoing a metabolic reprogramming coherent to their high proliferation rate, tumor cells also rewire the metabolic assets of their stromal cells, educating them to serve as nutrient donors. Hence, an alteration in the composition and in the flow rate of many nutrients within tumor microenvironment has been associated with malignancy progression. This review is focused on metabolic remodeling of the different cell populations within tumor microenvironment, dealing with reciprocal re-education through the symbiotic sharing of metabolites, behaving both as nutrients and as transcriptional regulators, describing their impact on tumor growth and metastasis.

Metabolic Remodeling as a Way of Adapting to Tumor Microenvironment (TME), a Job of Several Holders

The microenvironment depends and generates dependence on all the cells and structures that share the same niche, the biotope. The contemporaneous view of the tumor microenvironment (TME) agrees with this idea. The cells that make up the tumor, whether malignant or not, behave similarly to classes of elements within a living community. These elements inhabit, modify and benefit from all the facilities the microenvironment has to offer and that will contribute to the survival and growth of the tumor and the progression of the disease.The metabolic adaptation to microenvironment is a crucial process conducting to an established tumor able to grow locally, invade and metastasized. The metastatic cancer cells are reasonable more plastic than non-metastatic cancer cells, because the previous ones must survive in the microenvironment where the primary tumor develops and in addition, they must prosper in the microenvironment in the metastasized organ.The metabolic remodeling requires not only the adjustment of metabolic pathways per se but also the readjustment of signaling pathways that will receive and obey to the extracellular instructions, commanding the metabolic adaptation. Many diverse players are pivotal in cancer metabolic fitness from the initial signaling stimuli, going through the activation or repression of genes, until the phenotype display. The new phenotype will permit the import and consumption of organic compounds, useful for energy and biomass production, and the export of metabolic products that are useless or must be secreted for a further recycling or controlled uptake. In the metabolic network, three subsets of players are pivotal: (1) the organic compounds; (2) the transmembrane transporters, and (3) the enzymes.This chapter will present the "Pharaonic" intent of diagraming the interplay between these three elements in an attempt of simplifying and, at the same time, of showing the complex sight of cancer metabolism, addressing the orchestrating role of microenvironment and highlighting the influence of non-cancerous cells.

Prostate Cancer Energetics and Biosynthesis

Cancers must alter their metabolism to satisfy the increased demand for energy and to produce building blocks that are required to create a rapidly growing tumor. Further, for cancer cells to thrive, they must also adapt to an often changing tumor microenvironment, which can present new metabolic challenges (ex. hypoxia) that are unfavorable for most other cells. As such, altered metabolism is now considered an emerging hallmark of cancer. Like many other malignancies, the metabolism of prostate cancer is considerably different compared to matched benign tissue. However, prostate cancers exhibit distinct metabolic characteristics that set them apart from many other tumor types. In this chapter, we will describe the known alterations in prostate cancer metabolism that occur during initial tumorigenesis and throughout disease progression. In addition, we will highlight upstream regulators that control these metabolic changes. Finally, we will discuss how this new knowledge is being leveraged to improve patient care through the development of novel biomarkers and metabolically targeted therapies.

Carbonic Anhydrases and Metabolism

Although the role of carbonic anhydrases (CAs, EC 4.2.1.1) in metabolism is well-established, pharmacological applications of this phenomenon started to be considered only recently. In organisms all over the phylogenetic tree, the seven CA genetic families known to date are involved in biosynthetic processes and pH modulation, which may influence metabolism in multiple ways, with both processes being amenable to pharmacologic intervention. CA inhibitors possess antiobesity action directly by inhibiting lipogenesis, whereas the hypoxic tumor metabolism is highly controlled by the transmembrane isoforms CA IX and XII, which contribute to the acidic extracellular environment of tumors and supply bicarbonate for their high proliferation rates. Many of the articles from this special issue deal with the role of cancer CAs in tumor metabolism and how these phenomena can be used for designing innovative antitumor therapies/imaging agents. The metabolic roles of CAs in bacteria and algae are also discussed.

The microenvironment induces collective migration in SDHB-silenced mouse pheochromocytoma spheroids

Pheochromocytomas (Pheos) and paragangliomas (PGLs) are neuroendocrine tumors. Approximately 30-40% of Pheos/PGLs are due to germline mutations in one of the susceptibility genes, including those encoding the succinate dehydrogenase subunits A-D (SDHA-D). Up to 2/3 of patients affected by SDHB mutated Pheo/PGL develop metastatic disease with no successful cure at present. Here, for the first time, we evaluated the effects of SDHB silencing in a three dimension (3D) culture using spheroids of a mouse Pheo cell line silenced or not (wild type/wt/control) for the SDHB subunit. We investigated the role of the microenvironment on spheroid growth and migration/invasion by co-culturing SDHB-silenced or wt spheroids with primary cancer-activated fibroblasts (CAFs). When spheroids were co-cultured with fibroblasts, SDHB-silenced cells showed a significant increase in matrigel invasion as demonstrated by the computation of the migratory areas (P < 0.001). Moreover, cells detaching from the SDHB-silenced spheroids moved collectively, unlike the cells of wt spheroids that moved individually. Additionally, SDHB-silenced spheroids developed long filamentous formations along which clusters of cells migrated far away from the spheroid, whereas these structures were not present in wt spheroids. We found that lactate, largely secreted by CAFs, plays a specific role in promoting migration only of SDHB-silenced cells. In this study, we demonstrated that SDHB silencing per se increases tumor cell migration/invasion and that microenvironment, as represented by CAFs, plays a pivotal role in enhancing collective migration/invasion in Pheo SDHB-silenced tumor cells, suggesting their role in increasing the tumor metastasizing potential.

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.

Infliximab Modulates Cisplatin-Induced Hepatotoxicity in Rats

BACKGROUND

Cisplatin (Cis) is one of the most commonly used antineoplastic drugs. It is used as chemotherapy for many solid organ malignancies such as brain, neck, male and female urogenital, vesical and pulmonary cancers. Infliximab blocks tumor necrosis factor alpha (TNF-α). Several studies have reported that infliximab ameliorates cell damage by reducing cytokine levels.

AIMS

We aimed to investigate whether infliximab has a preventive effect against cisplatin-induced hepatotoxicity and whether it has a synergistic effect when combined with Cis.

STUDY DESIGN

Animal experimentation.

METHODS

Male Wistar albino rats were divided in three groups as follows: Cis group, infliximab + Cis (CIN) group and the control group. Each group comprised 10 animals. Animals in the Cis group received an intraperitoneal single-dose injection of Cis (7 mg/kg). In the CIN group, a single dose of infliximab (7 mg/kg) was administered 72 h prior to the Cis injection. After 72 h, a single dose of Cis (7 mg/kg) was administered. All rats were sacrificed five days after Cis injection.

RESULTS

TNF-α levels in the Cis group were significantly higher (345.5±40.0 pg/mg protein) than those of the control (278.7±62.1 pg/mg protein, p=0.003) and CIN groups (239.0±64.2 pg/mg protein, p=0.013). The Cis group was found to have high carbonic anhydrase (CA)-II and low carbamoyl phosphate synthetase-1 (CPS-1) levels. Aspartate transaminase (AST) and alanine transaminase (ALT) levels were lower in the CIN group as compared to the Cis group. Total histological damage was greater in the Cis group as compared to the control and CIN groups.

CONCLUSION

Cis may lead to liver damage by increasing cytokine levels. It may increase oxidative stress-induced tissue damage by increasing carbonic anhydrase II (CA-II) enzyme levels and decreasing CPS-1 enzyme levels. Infliximab decreases Cis-induced hepatic damage by blocking TNF-α and it may also protect against liver damage by regulating CPS-1 and CA-II enzyme levels.

Metabolic plasticity in heterogeneous pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDA) is one of the most lethal malignant neoplasms. The recognized hallmarks of PDA are regarded to be downstream events of metabolic reprogramming. Because PDA is a heterogeneous disease that is influenced by genetic polymorphisms and changes in the microenvironment, metabolic plasticity is a novel feature of PDA. As intrinsic factors for metabolic plasticity, K-ras activation and mutations in other tumor suppressor genes induce abnormal mitochondrial metabolism and enhance glycolysis, with alterations in glutamine and lipid metabolism. As extrinsic factors, the acidic and oxygen/nutrient-deprived microenvironment also induces cancer cells to reprogram their metabolic pathway and hijack stromal cells (mainly cancer-associated fibroblasts and immunocytes) to communicate, thereby adapting to metabolic stress. Therefore, a better understanding of the metabolic features of PDA will contribute to the development of novel diagnostic and therapeutic strategies.

Infliximab Modulates Cisplatin-Induced Hepatotoxicity in Rats

BACKGROUND

Cisplatin (Cis) is one of the most commonly used antineoplastic drugs. It is used as chemotherapy for many solid organ malignancies such as brain, neck, male and female urogenital, vesical and pulmonary cancers. Infliximab blocks tumor necrosis factor alpha (TNF-α). Several studies have reported that infliximab ameliorates cell damage by reducing cytokine levels.

AIMS

We aimed to investigate whether infliximab has a preventive effect against cisplatin-induced hepatotoxicity and whether it has a synergistic effect when combined with Cis.

STUDY DESIGN

Animal experimentation.

METHODS

Male Wistar albino rats were divided in three groups as follows: Cis group, infliximab + Cis (CIN) group and the control group. Each group comprised 10 animals. Animals in the Cis group received an intraperitoneal single-dose injection of Cis (7 mg/kg). In the CIN group, a single dose of infliximab (7 mg/kg) was administered 72 h prior to the Cis injection. After 72 h, a single dose of Cis (7 mg/kg) was administered. All rats were sacrificed five days after Cis injection.

RESULTS

TNF-α levels in the Cis group were significantly higher (345.5±40.0 pg/mg protein) than those of the control (278.7±62.1 pg/mg protein, p=0.003) and CIN groups (239.0±64.2 pg/mg protein, p=0.013). The Cis group was found to have high carbonic anhydrase (CA)-II and low carbamoyl phosphate synthetase-1 (CPS-1) levels. Aspartate transaminase (AST) and alanine transaminase (ALT) levels were lower in the CIN group as compared to the Cis group. Total histological damage was greater in the Cis group as compared to the control and CIN groups.

CONCLUSION

Cis may lead to liver damage by increasing cytokine levels. It may increase oxidative stress-induced tissue damage by increasing carbonic anhydrase II (CA-II) enzyme levels and decreasing CPS-1 enzyme levels. Infliximab decreases Cis-induced hepatic damage by blocking TNF-α and it may also protect against liver damage by regulating CPS-1 and CA-II enzyme levels.

Melanoma Cells Block PEDF Production in Fibroblasts to Induce the Tumor-Promoting Phenotype of Cancer-Associated Fibroblasts

Loss of pigment epithelium-derived factor (PEDF, SERPINF1) in cancer cells is associated with poor prognosis and metastasis, but the contribution of stromal PEDF to cancer evolution is poorly understood. Therefore, we investigated the role of fibroblast-derived PEDF in melanoma progression. We demonstrate that normal dermal fibroblasts expressing high PEDF levels attenuated melanoma growth and angiogenesis in vivo, whereas PEDF-depleted fibroblasts exerted tumor-promoting effects. Accordingly, mice with global PEDF knockout were more susceptible to melanoma metastasis. We also demonstrate that normal fibroblasts in close contact with PEDF-null melanoma cells lost PEDF expression and tumor-suppressive properties. Further mechanistic investigations underlying the crosstalk between tumor and stromal cells revealed that melanoma cells produced PDGF-BB and TGFβ, which blocked PEDF production in fibroblasts. Notably, cancer-associated fibroblasts (CAF) isolated from patient-derived tumors expressed markedly low levels of PEDF. Treatment of patient CAF and TGFβ-treated normal fibroblasts with exogenous PEDF decreased the expression of CAF markers and restored PEDF expression. Finally, expression profiling of PEDF-depleted fibroblasts revealed induction of IL8, SERPINB2, hyaluronan synthase-2, and other genes associated with tumor promotion and metastasis. Collectively, our results demonstrate that PEDF maintains tumor-suppressive functions in fibroblasts to prevent CAF conversion and illustrate the mechanisms by which melanoma cells silence stromal PEDF to promote malignancy. Cancer Res; 76(8); 2265-76. ©2016 AACR.

Metabolic exchanges within tumor microenvironment

Tumor progression toward malignancy often requires a metabolic rewiring of cancer cells to meet changes in metabolic demand to forefront nutrient and oxygen withdrawal, together with strong anabolic requests to match high proliferation rate. Tumor microenvironment highly contributes to metabolic rewiring of cancer cells, fostering complete nutrient exploitation, favoring OXPHOS of lipids and glutamine at the expense of glycolysis and enhancing exchanges via extracellular microvesicles or exosomes of proteins, lipids and small RNAs among tumor and stromal cells. Noteworthy, the same molecular drivers of metabolic reprogramming within tumor and stroma are also able to elicit motility, survival and self-renewal on cancer cells, thereby sustaining successful escaping strategies to circumvent the hostile hypoxic, acidic and inflammatory environment. This review highlights the emerging role of nutrients and vesicle-mediated exchanges among tumor and stromal cells, defining their molecular pathways and offering new perspectives to develop treatments targeting this complex metabolic rewiring.

Cancer associated fibroblasts transfer lipids and proteins to cancer cells through cargo vesicles supporting tumor growth

Fibroblasts are the most abundant cells in connective tissue and, with fibrillar extracellular matrix, form the structural scaffolding of organs. In solid tumors, interaction with cancer cells induces fibroblasts transdifferentiation into an activated form, which become a fundamental part of the tumor stroma. Within tumor microenvironment stromal and cancer cells engage a crosstalk that is mediated by soluble factors, cellcell contacts and extracellular vesicles trafficlking. Here we report that fibroblasts have the ability to transfer a remarkable amount of proteins and lipids to neighboring cells, in an ectosome-dependent fashion, identifying a novel and native property of these cells. Cancer-associated fibroblasts show an enhanced production and delivering of ectc:Jsomes to cancer cells compared to normal fibroblasts. As a consequence of this phenomenon, tumor cells increase their proliferation rate, indicating that ectosome-mediated trafficking could be a relevant mechanism mediating the trophic function of activated connective tissue on tumor cells.

Role of microenvironment on neuroblastoma SK-N-AS SDHB-silenced cell metabolism and function

In solid tumors, neoplastic cells grow in contact with the so-called tumor microenvironment. The interaction between tumor cells and the microenvironment causes reciprocal metabolic reprogramming and favorable conditions for tumor growth and metastatic spread. To obtain an experimental model resembling the in vivo conditions of the succinate dehydrogenase B subunit (SDHB)-mutated paragangliomas (PGLs), we evaluated the effects of SDHB silencing on metabolism and proliferation in the human neuroblastoma cell line (SK-N-AS), cultured alone or in association with human fibroblasts. Silencing caused a 70% decrease in protein expression, an almost complete loss of the complex specific enzymatic activity, and a significant increase in HIF1α and HIF2α expression; it thus resembled the in vivo tumor cell phenotype. When compared with WT SK-N-AS cells, SDHB-silenced cells showed an altered metabolism characterized by an unexpected significant decrease in glucose uptake and an increase in lactate uptake. Moreover, silenced cells exhibited a significant increase in cell proliferation and metalloproteinase activity. When co-cultured with human fibroblasts, control cells displayed a significant decrease in glucose uptake and a significant increase in cell proliferation as compared with their mono-cultured counterparts. These effects were even more evident in co-cultured silenced cells, with a 70% decrease in glucose uptake and a 92% increase in cell proliferation as compared to their mono-cultured counterparts. The present data indicate for the first time, to our knowledge, that SDHB impairment causes metabolic and functional derangement of neural-crest-derived tumor cells and that the microenvironment, here represented by fibroblasts, strongly affects their tumor metabolism and growth capacity.

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.

Tumor microenvironment and metabolism in prostate cancer

Prostate cancer is no longer viewed mostly as a disease of abnormally proliferating epithelial cells, but rather as a disease affecting the complex interactions between the cells of the prostate epithelial compartment and the surrounding stromal compartment in which they live. Indeed, the microenvironment in which tumor cells evolve towards an aggressive phenotype is highly heterogeneous, as it is composed of different cell populations such as endothelial cells, fibroblasts, macrophages, and lymphocytes, either resident or trans-differentiated by bone marrow-derived mesenchymal stem cells recruited at the tumor site. Cancer-associated fibroblasts, the most abundant population within this microenvironment, exert a mandatory role in prostate cancer progression as they metabolically sustain cancer cell survival and growth, recruit inflammatory and immune cells, and promote cancer cells stemness and epithelial mesenchymal transition, thereby favoring metastatic dissemination of aggressive cancers. The interruption of this two-compartment crosstalk, together with the idea that stromal cells are mostly vulnerable, being drug-sensitive, could lead to the development of anticancer therapies that target tumor stromal elements.