Expression of purinergic receptors in non-melanoma skin cancers and their functional roles in A431 cells

Ion channel P2X7 receptor in the progression of cancer

P2X7 receptor (P2X7) is a non-selective and ATP-sensitive ligand-gated cation channel. Studies have confirmed that it is expressed in a variety of cells and correlates with their function, frequently in immune cells and tumor cells. We found increased expression of this receptor in many tumor cells, and it has a role in tumor survival and progression. In immune cells, upregulation of the receptor has a double effect on tumor suppression as well as tumor promotion. This review describes the structure of P2X7 and its role in the tumor microenvironment and presents possible mechanisms of P2X7 in tumor invasion and metastasis. Understanding the potential of P2X7 for tumor treatment, we also present several therapeutic agents targeting P2X7 and their mechanisms of action. In conclusion, the study of P2X7 is an important guideline for the use of clinical tumor therapy and may be able to provide a new idea for tumor treatment, but considering the complexity of the biological effects of P2X7, the drugs should be used with caution in clinical practice.

Anti-aging Strategies and Topical Delivery of Biopolymer-based Nanocarriers for Skin Cancer Treatment

Environmental factors like UV radiation and epigenetic changes are significant factors for skin cancer that trigger early aging. This review provides essential information on cancer development concerning aging, the receptors involved, and the therapeutic targets. Biopolymers like polysaccharide, polyphenols, proteins, and nucleic acid plays a vital role in the regulation of normal cell homeostasis. Therefore, it is pertinent to explore the role of biopolymers as antiaging formulations and the possibility of these formulations being used against cancer via topical administrations. As UV radiation is one of the predominant factors in causing skin cancer, the association of receptors between aging and cancer indicated that insulin receptor, melatonin receptor, toll-like receptor, SIRT 1 receptor, tumor-specific T cell receptor and mitochondria-based targeting could be used to direct therapeutics for suppression of cancer and prevent aging. Biopolymer-based nanoformulations have tremendously progressed by entrapment of drugs like curcumin and resveratrol which can prevent cancer and aging simultaneously. Certain protein signaling or calcium and ROS signaling pathways are different for cancer and aging. The involvement of mitochondrial DNA mutation along with telomere shortening with a change in cellular energetics leading to genomic instability in the aging process can also induce mitochondrial dysfunction and epigenetic alterations leading to skin cancer. Therefore, the use of biopolymers as a topical supplement during the aging process can result in the prevention of cancer.

Purine and purinergic receptors in health and disease

Purines and purinergic receptors are widely distributed throughout the human body. Purine molecules within cells play crucial roles in regulating energy metabolism and other cellular processes, while extracellular purines transmit signals through specific purinergic receptors. The ubiquitous purinergic signaling maintains normal neural excitability, digestion and absorption, respiratory movement, and other complex physiological activities, and participates in cell proliferation, differentiation, migration, and death. Pathological dysregulation of purinergic signaling can result in the development of various diseases, including neurodegeneration, inflammatory reactions, and malignant tumors. The dysregulation or dysfunction of purines and purinergic receptors has been demonstrated to be closely associated with tumor progression. Compared with other subtypes of purinergic receptors, the P2X7 receptor (P2X7R) exhibits distinct characteristics (i.e., a low affinity for ATP, dual functionality upon activation, the mediation of ion channels, and nonselective pores formation) and is considered a promising target for antitumor therapy, particularly in patients with poor response to immunotherapy This review summarizes the physiological and pathological significance of purinergic signaling and purinergic receptors, analyzes their complex relationship with tumors, and proposes potential antitumor immunotherapy strategies from tumor P2X7R inhibition, tumor P2X7R overactivation, and host P2X7R activation. This review provides a reference for clinical immunotherapy and mechanism investigation.

The Role of IL-18 in P2RX7-Mediated Antitumor Immunity

Cancer is the leading cause of death worldwide despite the variety of treatments that are currently used. This is due to an innate or acquired resistance to therapy that encourages the discovery of novel therapeutic strategies to overcome the resistance. This review will focus on the role of the purinergic receptor P2RX7 in the control of tumor growth, through its ability to modulate antitumor immunity by releasing IL-18. In particular, we describe how the ATP-induced receptor activities (cationic exchange, large pore opening and NLRP3 inflammasome activation) modulate immune cell functions. Furthermore, we recapitulate our current knowledge of the production of IL-18 downstream of P2RX7 activation and how IL-18 controls the fate of tumor growth. Finally, the potential of targeting the P2RX7/IL-18 pathway in combination with classical immunotherapies to fight cancer is discussed.

P2RX7 promotes osteosarcoma progression and glucose metabolism by enhancing c-Myc stabilization

BACKGROUND

Osteosarcoma is the most common malignant tumor in bone and its prognosis has reached a plateau in the past few decades. Recently, metabolic reprogramming has attracted increasing attention in the field of cancer research. In our previous study, P2RX7 has been identified as an oncogene in osteosarcoma. However, whether and how P2RX7 promotes osteosarcoma growth and metastasis through metabolic reprogramming remains unexplored.

METHODS

We used CRISPR/Cas9 genome editing technology to establish P2RX7 knockout cell lines. Transcriptomics and metabolomics were performed to explore metabolic reprogramming in osteosarcoma. RT-PCR, western blot and immunofluorescence analyses were used to determine gene expression related to glucose metabolism. Cell cycle and apoptosis were examined by flowcytometry. The capacity of glycolysis and oxidative phosphorylation were assessed by seahorse experiments. PET/CT was carried out to assess glucose uptake in vivo.

RESULTS

We demonstrated that P2RX7 significantly promotes glucose metabolism in osteosarcoma via upregulating the expression of genes related to glucose metabolism. Inhibition of glucose metabolism largely abolishes the ability of P2RX7 to promote osteosarcoma progression. Mechanistically, P2RX7 enhances c-Myc stabilization by facilitating nuclear retention and reducing ubiquitination-dependent degradation. Furthermore, P2RX7 promotes osteosarcoma growth and metastasis through metabolic reprogramming in a predominantly c-Myc-dependent manner.

CONCLUSIONS

P2RX7 plays a key role in metabolic reprogramming and osteosarcoma progression via increasing c-Myc stability. These findings provide new evidence that P2RX7 might be a potential diagnostic and/or therapeutic target for osteosarcoma. Novel therapeutic strategies targeting metabolic reprogramming appear to hold promise for a breakthrough in the treatment of osteosarcoma.

Purinergic signaling: Diverse effects and therapeutic potential in cancer

Regardless of improved biological insights and therapeutic advances, cancer is consuming multiple lives worldwide. Cancer is a complex disease with diverse cellular, metabolic, and physiological parameters as its hallmarks. This instigates a need to uncover the latest therapeutic targets to advance the treatment of cancer patients. Purines are building blocks of nucleic acids but also function as metabolic intermediates and messengers, as part of a signaling pathway known as purinergic signaling. Purinergic signaling comprises primarily adenosine triphosphate (ATP) and adenosine (ADO), their analogous membrane receptors, and a set of ectonucleotidases, and has both short- and long-term (trophic) effects. Cells release ATP and ADO to modulate cellular function in an autocrine or paracrine manner by activating membrane-localized purinergic receptors (purinoceptors, P1 and P2). P1 receptors are selective for ADO and have four recognized subtypes-A1, A2A, A2B, and A3. Purines and pyrimidines activate P2 receptors, and the P2X subtype is ligand-gated ion channel receptors. P2X has seven subtypes (P2X1-7) and forms homo- and heterotrimers. The P2Y subtype is a G protein-coupled receptor with eight subtypes (P2Y1/2/4/6/11/12/13/14). ATP, its derivatives, and purinoceptors are widely distributed in all cell types for cellular communication, and any imbalance compromises the homeostasis of the cell. Neurotransmission, neuromodulation, and secretion employ fast purinergic signaling, while trophic purinergic signaling regulates cell metabolism, proliferation, differentiation, survival, migration, invasion, and immune response during tumor progression. Thus, purinergic signaling is a prospective therapeutic target in cancer and therapy resistance.

Purinergic signaling in the male reproductive tract

Purinergic receptors are ubiquitously expressed throughout the body and they participate in the autocrine and paracrine regulation of cell function during normal physiological and pathophysiological conditions. Extracellular nucleotides activate several types of plasma membrane purinergic receptors that form three distinct families: P1 receptors are activated by adenosine, P2X receptors are activated by ATP, and P2Y receptors are activated by nucleotides including ATP, ADP, UTP, UDP, and UDP-glucose. These specific pharmacological fingerprints and the distinct intracellular signaling pathways they trigger govern a large variety of cellular responses in an organ-specific manner. As such, purinergic signaling regulates several physiological cell functions, including cell proliferation, differentiation and death, smooth muscle contraction, vasodilatation, and transepithelial transport of water, solute, and protons, as well as pathological pathways such as inflammation. While purinergic signaling was first discovered more than 90 years ago, we are just starting to understand how deleterious signals mediated through purinergic receptors may be involved in male infertility. A large fraction of male infertility remains unexplained illustrating our poor understanding of male reproductive health. Purinergic signaling plays a variety of physiological and pathophysiological roles in the male reproductive system, but our knowledge in this context remains limited. This review focuses on the distribution of purinergic receptors in the testis, epididymis, and vas deferens, and their role in the establishment and maintenance of male fertility.

Lung Adenocarcinoma Transcriptomic Analysis Predicts Adenylate Kinase Signatures Contributing to Tumor Progression and Negative Patient Prognosis

The ability to detect and respond to hypoxia within a developing tumor appears to be a common feature amongst most cancers. This hypoxic response has many molecular drivers, but none as widely studied as Hypoxia-Inducible Factor 1 (HIF-1). Recent evidence suggests that HIF-1 biology within lung adenocarcinoma (LUAD) may be associated with expression levels of adenylate kinases (AKs). Using LUAD patient transcriptome data, we sought to characterize AK gene signatures related to lung cancer hallmarks, such as hypoxia and metabolic reprogramming, to identify conserved biological themes across LUAD tumor progression. Transcriptomic analysis revealed perturbation of HIF-1 targets to correlate with altered expression of most AKs, with AK4 having the strongest correlation. Enrichment analysis of LUAD tumor AK4 gene signatures predicts signatures involved in pyrimidine, and by extension, nucleotide metabolism across all LUAD tumor stages. To further discriminate potential drivers of LUAD tumor progression within AK4 gene signatures, partial least squares discriminant analysis was used at LUAD stage-stage interfaces, identifying candidate genes that may promote LUAD tumor growth or regression. Collectively, these results characterize regulatory gene networks associated with the expression of all nine human AKs that may contribute to underlying metabolic perturbations within LUAD and reveal potential mechanistic insight into the complementary role of AK4 in LUAD tumor development.

Discovery of bilirubin as novel P2X7R antagonist with anti-tumor activity

As a unique ligand gated ion channel in the P2-receptor family, P2X7R is highly expressed in various tumors. The activated P2X7R facilitates tumor growth and metastasis. Hypoxia, inflammation and necrosis in the tumor microenvironment (TME) cause a large amount of adenosine triphosphate (ATP) accumulated in the TME. High concentration of ATP can abnormally activate P2X7R, which induces pore formation and further facilitates the Ca²⁺ ion influx and non-specific substance intake. Therefore, inhibition of P2X7R activation can be applied as a potential anti-tumor therapy strategy. However, there is currently no FDA approved drugs for this target for anti-tumor treatment. In this study, we identified bilirubin as novel P2X7R antagonist by using structure based virtual screening combined with cell based assays. Molecular docking studies indicated that bilirubin probably interacted with P2X7R by forming hydrogen-π interactions with residues V173, E174 and K311. The compound bilirubin inhibited the P2X7R gated EB intake by cancer cells. Meanwhile, bilirubin was capable to inhibit the cell proliferation and migration of P2X7R expressed HT29 cells. The phosphorylation of mTOR, STAT3 and GSK3β were significantly decreased when bilirubin was present. Finally, in vivo experiment exhibited the anti-tumor effect of bilirubin in the MC38 bearing mice model, but did not show tissue damage in different organs. In conclusion, bilirubin was identified as a novel P2X7R antagonist and it may have potential for anti-cancer treatment, although various functions of the molecule should be considered.

Expression Pattern of Purinergic Signaling Components in Colorectal Cancer Cells and Differential Cellular Outcomes Induced by Extracellular ATP and Adenosine

The purine nucleotide adenosine triphosphate (ATP) is known for its fundamental role in cellular bioenergetics. However, in the last decades, different works have described emerging functions for ATP, such as that of a danger signaling molecule acting in the extracellular space on both tumor and stromal compartments. Beside its role in immune cell signaling, several studies have shown that high concentrations of extracellular ATP can directly or indirectly act on cancer cells. Accordingly, it has been reported that purinergic receptors are widely expressed in tumor cells. However, their expression pattern is often associated with contradictory cellular outcomes. In this work, we first investigated gene expression profiles through "RNA-Sequencing" (RNA Seq) technology in four colorectal cancer (CRC) cell lines (HT29, LS513, LS174T, HCT116). Our results demonstrate that CRC cells mostly express the A2B, P2X4, P2Y1, P2Y2 and P2Y11 purinergic receptors. Among these, the P2Y1 and P2Y2 coding genes are markedly overexpressed in all CRC cells compared to the HCEC-1CT normal-like colonic cells. We then explored the cellular outcomes induced by extracellular ATP and adenosine. Our results show that in terms of cell death induction extracellular ATP is consistently more active than adenosine against CRC, while neither compound affected normal-like colonic cell survival. Intriguingly, while for the P2Y2 receptor pharmacological inhibition completely abolished the rise in cytoplasmic Ca²⁺ observed after ATP exposure in all CRC cell lines, Ca²⁺ mobilization only impacted the cellular outcome for HT29. In contrast, non-selective phosphodiesterase inhibition completely abolished the effects of extracellular ATP on CRC cells, suggesting that cAMP and/or cGMP levels might determine cellular outcome. Altogether, our study provides novel insights into the characterization of purinergic signaling in CRC.

EMP2 induces cytostasis and apoptosis via the TGFβ/SMAD/SP1 axis and recruitment of P2RX7 in urinary bladder urothelial carcinoma

PURPOSE

Urinary bladder urothelial carcinoma (UBUC) is a common malignant disease, and its high recurrence rates impose a heavy clinical burden. The objective of this study was to identify signaling pathways downstream of epithelial membrane protein 2 (EMP2), which induces cytostasis and apoptosis in UBUC.

METHODS

A series of in vitro and in vivo assays using different UBUC-derived cell lines and mouse xenograft models were performed, respectively. In addition, primary UBUC specimens were evaluated by immunohistochemistry.

RESULTS

Exogenous expression of EMP2 in J82 UBUC cells significantly decreased DNA replication and altered the expression levels of several TGFβ signaling-related proteins. EMP2 knockdown in BFTC905 UBUC cells resulted in opposite effects. EMP2-dysregulated cell cycle progression was found to be mediated by the TGFβ/TGFBR1/SP1 family member SMAD. EMP2 or purinergic receptor P2X7 (P2RX7) gene expression upregulation induced apoptosis via both intrinsic and extrinsic pathways. In 242 UBUC patient samples, P2RX7 protein levels were found to be significantly and positively correlated with EMP2 protein levels. Low P2RX7 levels conferred poor disease-specific and metastasis-free survival rates, and significantly decreased apoptotic cell rates. EMP2 was found to physically interact with P2RX7. In the presence of a P2RX7 agonist, BzATP, overexpression of both EMP2 and P2RX7 significantly increased apoptotic cell rates compared to overexpression of EMP2 or P2RX7 alone.

CONCLUSIONS

EMP2 induces cytostasis via the TGFβ/SMAD/SP1 axis and recruits P2RX7 to enhance apoptosis in UBUC. Our data provide new insights that may be employed for the design of UBUC targeting therapies.

m6A Modification: A Double-Edged Sword in Tumor Development

Modification of m6A, as the most abundant mRNA modification, plays diverse roles in various biological processes in eukaryotes. Emerging evidence has revealed that m6A modification is closely associated with the activation and inhibition of tumor pathways, and it is significantly linked to the prognosis of cancer patients. Aberrant reduction or elevated expression of m6A regulators and of m6A itself have been identified in numerous tumors. In this review, we give a description of the dynamic properties of m6A modification regulators, such as methyltransferases, demethylases, and m6A binding proteins, and indicate the value of the balance between these proteins in regulating the expression of diverse genes and the underlying effects on cancer development. Furthermore, we summarize the “dual-edged weapon” role of RNA methylation in tumor progression and discuss that RNA methylation can not only result in tumorigenesis but also lead to suppression of tumor formation. In addition, we summarize the latest research progress on small-molecule targeting of m6A regulators to inhibit or activate m6A. These studies indicate that restoring the balance of m6A modification via targeting specific imbalanced regulators may be a novel anti-cancer strategy.

Identification of novel P2X7R antagonists by using structure-based virtual screening and cell-based assays

In the tumor microenvironment, inflammation and necrosis cause the accumulations of ATP extracellularly, and high concentrations of ATP can activate P2X7 receptors (P2X7R), which leads to the influx of Na⁺ , K⁺ , or Ca²⁺ into cells and trigger the downstream signaling pathways. P2X7R is a relatively unique ligand-gated ion channel, which is over-expressed in most tumor cells. The activated P2X7R facilitates the tumor growth, invasion, and metastasis. Inhibition of the P2X7R activation can be applied as a potential anti-tumor therapy strategy. There are currently no anti-tumor agents against P2X7R, though several P2X7R antagonists for indications such as anti-inflammatory and anti-depression were reported. In this study, we combined homology modeling (HM), virtual screening, and EB intake assay to characterize the structural features of P2X7R and identify several novel antagonists, which were chemically different from any other known P2X7R antagonists. The identified antagonists could effectively prevent the pore opening of P2X7R with IC50 values ranging from 29.14 to 35.34 μM. HM model showed the area between ATP-binding pocket, and allosteric sides were hydrophobic and suitable for small molecule interaction. Molecular docking indicated a universal binding mode, of which residues R294 and K311 were used as hydrogen bond donors to participate in antagonist interactions. The binding mode can potentially be utilized for inhibitor optimization for increased affinity, and the identified antagonists can be further tested for anti-cancer activity or may serve as chemical agents to study P2X7R related functions.

P2Y receptors for extracellular nucleotides: Contributions to cancer progression and therapeutic implications

Purinergic receptors for extracellular nucleotides and nucleosides contribute to a vast array of cellular and tissue functions, including cell proliferation, intracellular and transmembrane ion flux, immunomodulation and thrombosis. In mammals, the purinergic receptor system is composed of G protein-coupled P1 receptors A₁, A_2A, A_2B and A₃ for extracellular adenosine, P2X1-7 receptors that are ATP-gated ion channels and G protein-coupled P2Y_{1,2,4,6,11,12,13 and 14} receptors for extracellular ATP, ADP, UTP, UDP and/or UDP-glucose. Recent studies have implicated specific P2Y receptor subtypes in numerous oncogenic processes, including cancer tumorigenesis, metastasis and chemotherapeutic drug resistance, where G protein-mediated signaling cascades modulate intracellular ion concentrations and activate downstream protein kinases, Src family kinases as well as numerous mitogen-activated protein kinases. We are honored to contribute to this special issue dedicated to the founder of the field of purinergic signaling, Dr. Geoffrey Burnstock, by reviewing the diverse roles of P2Y receptors in the initiation, progression and metastasis of specific cancers with an emphasis on pharmacological and genetic strategies employed to delineate cell-specific and P2Y receptor subtype-specific responses that have been investigated using in vitro and in vivo cancer models. We further highlight bioinformatic and empirical evidence on P2Y receptor expression in human clinical specimens and cover clinical perspectives where P2Y receptor-targeting interventions may have therapeutic relevance to cancer treatment.

P2X receptors in cancer growth and progression

It is increasingly appreciated that ion channels have a crucial role in tumors, either as promoters of cancer cell growth, or modulators of immune cell functions, or both. Among ion channels, P2X receptors have a special status because they are gated by ATP, a common and abundant component of the tumor microenvironment. Furthermore, one P2X receptor, i.e. P2X7, may also function as a conduit for ATP release, thus fuelling the increased extracellular ATP level in the tumor interstitium. These findings show that P2X receptors and extracellular ATP are indissoluble partners and key regulators of tumor growth, and suggest the exploitation of the extracellular ATP-P2X partnership to develop innovative therapeutic approaches to cancer.

Purinergic Signaling in Pancreas-From Physiology to Therapeutic Strategies in Pancreatic Cancer

The purinergic signaling has an important role in regulating pancreatic exocrine secretion. The exocrine pancreas is also a site of one of the most serious cancer forms, the pancreatic ductal adenocarcinoma (PDAC). Here, we explore how the network of purinergic and adenosine receptors, as well as ecto-nucleotidases regulate normal pancreatic cells and various cells within the pancreatic tumor microenvironment. In particular, we focus on the P2X7 receptor, P2Y2 and P2Y12 receptors, as well as A2 receptors and ecto-nucleotidases CD39 and CD73. Recent studies indicate that targeting one or more of these candidates could present new therapeutic approaches to treat pancreatic cancer. In pancreatic cancer, as much as possible of normal pancreatic function should be preserved, and therefore physiology of purinergic signaling in pancreas needs to be considered.

Extracellular ATP: A Feasible Target for Cancer Therapy

Adenosine triphosphate (ATP) is one of the main biochemical components of the tumor microenvironment (TME), where it can promote tumor progression or tumor suppression depending on its concentration and on the specific ecto-nucleotidases and receptors expressed by immune and cancer cells. ATP can be released from cells via both specific and nonspecific pathways. A non-regulated release occurs from dying and damaged cells, whereas active release involves exocytotic granules, plasma membrane-derived microvesicles, specific ATP-binding cassette (ABC) transporters and membrane channels (connexin hemichannels, pannexin 1 (PANX1), calcium homeostasis modulator 1 (CALHM1), volume-regulated anion channels (VRACs) and maxi-anion channels (MACs)). Extracellular ATP acts at P2 purinergic receptors, among which P2X7R is a key mediator of the final ATP-dependent biological effects. Over the years, P2 receptor- or ecto-nucleotidase-targeting for cancer therapy has been proposed and actively investigated, while comparatively fewer studies have explored the suitability of TME ATP as a target. In this review, we briefly summarize the available evidence suggesting that TME ATP has a central role in determining tumor fate and is, therefore, a suitable target for cancer therapy.

The P2X7 purinergic receptor: a potential therapeutic target for lung cancer

PURPOSE

Purinergic P2X7 receptor (P2X7R) is a gated ion channel for which adenosine triphosphate (ATP) is a ligand. Activated P2X7R is widely expressed in a variety of immune cells and tissues and is involved in a variety of physiological and pathological processes. Studies have confirmed that P2X7R is involved in the regulation of tumor cell growth, stimulating cell proliferation or inducing apoptosis. Recent studies have found that P2X7R is abnormally expressed in lung cancer and is closely related to the carcinogenesis and development of lung cancer. In this paper, we comprehensively describe the structure, function, and genetic polymorphisms of P2X7R. In particular, the role and therapeutic potential of P2X7R in lung cancer are discussed to provide new targets and new strategies for the treatment and prognosis of clinical lung cancer.

METHODS

The relevant literature on P2X7R and lung cancer from PubMed databases is reviewed in this article.

RESULTS

P2X7R regulates the function of lung cancer cells by activating multiple intracellular signaling pathways (such as the JNK, Rho, HMGB1 and EMT pathways), thereby affecting cell survival, growth, invasion, and metastasis and patient prognosis. Targeting P2X7R with inhibitors effectively suppresses the growth and metastasis of lung cancer cells.

CONCLUSION

In summary, P2X7R is expected to become a potential target for the treatment of lung cancer, and more clinical research is needed in the future to explore the effectiveness of P2X7R antagonists as treatments.

P2RX7B is a new theranostic marker for lung adenocarcinoma patients

Rationale: The characterization of new theranostic biomarkers is crucial to improving the clinical outcome of patients with advanced lung cancer. Here, we aimed at characterizing the P2RX7 receptor, a positive modulator of the anti-tumor immune response, in patients with lung adenocarcinoma.

Methods: The expression of P2RX7 and its splice variants was analyzed by RT-qPCR using areas of tumor and non-tumor lung adenocarcinoma (LUAD) tissues on both immune and non-immune cells. The biological activity of P2RX7 was studied by flow cytometry using fluorescent dyes. Bi-molecular fluorescence complementation and confocal microscopy were used to assess the oligomerization of P2RX7. Tumor immune infiltrates were characterized by immunohistochemistry.

Results: Fifty-three patients with LUAD were evaluated. P2RX7A, and 3 alternative splice variants were expressed in LUAD tissues and expression was down regulated in tumor versus adjacent non-tumor tissues. The protein retained biological activity only in immune cells. The P2RX7B splice variant was differentially upregulated in immune cells (P < 0.001) of the tumor and strong evidence of oligomerization of P2RX7A and B was observed in the HEK expression model, which correlated with a default in the activity of P2RX7. Finally, LUAD patients with a high level of P2RX7B had non-inflamed tumors (P = 0.001).

Conclusion: Our findings identified P2RX7B as a new theranostic tool to restore functional P2RX7 activity and open alternative therapeutic opportunities to improve LUAD patient outcome.

Purinergic Signaling in the Hallmarks of Cancer

Cancer is a complex expression of an altered state of cellular differentiation associated with severe clinical repercussions. The effort to characterize this pathological entity to understand its underlying mechanisms and visualize potential therapeutic strategies has been constant. In this context, some cellular (enhanced duplication, immunological evasion), metabolic (aerobic glycolysis, failure in DNA repair mechanisms) and physiological (circadian disruption) parameters have been considered as cancer hallmarks. The list of these hallmarks has been growing in recent years, since it has been demonstrated that various physiological systems misfunction in well-characterized ways upon the onset and establishment of the carcinogenic process. This is the case with the purinergic system, a signaling pathway formed by nucleotides/nucleosides (mainly adenosine triphosphate (ATP), adenosine (ADO) and uridine triphosphate (UTP)) with their corresponding membrane receptors and defined transduction mechanisms. The dynamic equilibrium between ATP and ADO, which is accomplished by the presence and regulation of a set of ectonucleotidases, defines the pro-carcinogenic or anti-cancerous final outline in tumors and cancer cell lines. So far, the purinergic system has been recognized as a potential therapeutic target in cancerous and tumoral ailments.

P2X7 in Cancer: From Molecular Mechanisms to Therapeutics

P2X7 is a transmembrane receptor expressed in multiple cell types including neurons, dendritic cells, macrophages, monocytes, B and T cells where it can drive a wide range of physiological responses from pain transduction to immune response. Upon activation by its main ligand, extracellular ATP, P2X7 can form a nonselective channel for cations to enter the cell. Prolonged activation of P2X7, via high levels of extracellular ATP over an extended time period can lead to the formation of a macropore, leading to depolarization of the plasma membrane and ultimately to cell death. Thus, dependent on its activation state, P2X7 can either drive cell survival and proliferation, or induce cell death. In cancer, P2X7 has been shown to have a broad range of functions, including playing key roles in the development and spread of tumor cells. It is therefore unsurprising that P2X7 has been reported to be upregulated in several malignancies. Critically, ATP is present at high extracellular concentrations in the tumor microenvironment (TME) compared to levels observed in normal tissues. These high levels of ATP should present a survival challenge for cancer cells, potentially leading to constitutive receptor activation, prolonged macropore formation and ultimately to cell death. Therefore, to deliver the proven advantages for P2X7 in driving tumor survival and metastatic potential, the P2X7 macropore must be tightly controlled while retaining other functions. Studies have shown that commonly expressed P2X7 splice variants, distinct SNPs and post-translational receptor modifications can impair the capacity of P2X7 to open the macropore. These receptor modifications and potentially others may ultimately protect cancer cells from the negative consequences associated with constitutive activation of P2X7. Significantly, the effects of both P2X7 agonists and antagonists in preclinical tumor models of cancer demonstrate the potential for agents modifying P2X7 function, to provide innovative cancer therapies. This review summarizes recent advances in understanding of the structure and functions of P2X7 and how these impact P2X7 roles in cancer progression. We also review potential therapeutic approaches directed against P2X7.

Germline Mutations in Familial Papillary Thyroid Cancer

Thyroid cancer, predominantly of papillary histology (PTC), is a common cancer mostly diagnosed sporadically. Hereditary PTC is encountered in ~ 5% of cases and may present at an earlier age, with greater risks of metastasis and recurrence, compared with sporadic cases. The molecular basis of hereditary PTC is unknown in most cases. In this study, the genetic basis of hereditary PTC in three Brazilian families was investigated. Whole exome sequencing (WES) was carried out for probands in each family, and validated, pathogenic/likely pathogenic sequence variants (P/LPSVs) were genotyped in additional family members to establish their putative pathogenic role. Overall, seven P/LPSVs in seven novel genes were detected: p.D283N*ANXA3, p.Y157S*NTN4, p.G172W*SERPINA1, p.G188S*FKBP10, p.R937C*PLEKHG5, p.L32Q*P2RX5, and p.Q76*SAPCD1. These results indicate that these novel genes are seemingly associated with hereditary PTC, but extension and validation in other PTC families are required.

P2Y2 purinergic receptor modulates virus yield, calcium homeostasis, and cell motility in human cytomegalovirus-infected cells

Human cytomegalovirus (HCMV) manipulates many aspects of host cell biology to create an intracellular milieu optimally supportive of its replication and spread. Our study reveals that levels of several components of the purinergic signaling system, including the P2Y2 and P2X5 receptors, are elevated in HCMV-infected fibroblasts. Knockdown and drug treatment experiments demonstrated that P2Y2 enhances the yield of virus, whereas P2X5 reduces HCMV production. The HCMV IE1 protein induces P2Y2 expression; and P2Y2-mediated signaling is important for efficient HCMV gene expression, DNA synthesis, and the production of infectious HCMV progeny. P2Y2 cooperates with the viral UL37x1 protein to regulate cystolic Ca2+ levels. P2Y2 also regulates PI3K/Akt signaling and infected cell motility. Thus, P2Y2 functions at multiple points within the viral replication cycle to support the efficient production of HCMV progeny, and it may facilitate in vivo viral spread through its role in cell migration.

The m6A-suppressed P2RX6 activation promotes renal cancer cells migration and invasion through ATP-induced Ca2+ influx modulating ERK1/2 phosphorylation and MMP9 signaling pathway

Background

Previous study demonstrated that extracellular ATP could promote cell migration and invasion in multiple human cancers. Till now, the pro-invasive mechanisms of ATP and P2RX6, a preferred receptor for ATP, are still poorly studied in RCC.

Methods

Bioinformatics analysis was performed to identify the differentially expressed genes during RCC different stages. Tissue microarray, IHC staining and survival analysis was respectively used to evaluate potential clinical function. In vitro and in vivo assays were performed to explore the P2RX6 biological effects in RCC progression.

Results

We found that ATP might increase RCC cells migration and invasion through P2RX6. Mechanism dissection revealed that ATP-P2RX6 might modulate the Ca²⁺-mediated p-ERK1/2/MMP9 signaling to increase the RCC cells migration and invasion. Furthermore, METTL14 implicated m⁶A modification in RCC and down-regulated P2RX6 protein translation. In addition, human clinical survey also indicated the positive correlation of this newly identified signaling in RCC progression and prognosis.

Conclusions

Our findings revealed that the newly identified ATP-P2RX6-Ca²⁺-p-ERK1/2-MMP9 signaling facilitates RCC cell invasion and metastasis. Targeting this novel signaling pathway with small molecules might help us to develop a new approach to better suppress RCC progression.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1223-y) contains supplementary material, which is available to authorized users.

The role of microglia and P2X7 receptors in gliomas

Gliomas are the most prevalent tumours of the central nervous system and present with high morbidity and mortality. The most common and most aggressive form of glioma is glioblastoma multiforme, of which patients have a median survival time of only 12 to 15 months. Current treatment options are limited and have a small impact on clinical outcome and prognosis. There is accumulating evidence that microglia, the immunocompetent cells of the central nervous system, and the purinergic P2X7 receptor (P2X7R) may contribute to tumour progression and pathology. Importantly, P2X7R on both tumour cells and infiltrating microglia is overexpressed in animal and human glioma cultures. Factors released by glioma cells and P2X7R activation recruit microglia into the largely immunosuppressive tumour microenvironment where they have been demonstrated to contribute to either tumour proliferation or tumour suppression. It is likely that P2X7R mediates a range of microglia effector functions in the glioma setting, potentially increasing tumour growth and proliferation. This review evaluates current evidence on the roles of microglia and P2X7R in glioma pathogenesis. Understanding the nature, mechanisms and outcomes of microglia and P2X7R activation in gliomas is necessary for the development of more therapies with increased efficacy and specificity.

Mechanosensitive ion channels push cancer progression

In many cases, the mechanical properties of a tumor are different from those of the host tissue. Mechanical cues regulate cancer development by affecting both tumor cells and their microenvironment, by altering cell migration, proliferation, extracellular matrix remodeling and metastatic spread. Cancer cells sense mechanical stimuli such as tissue stiffness, shear stress, tissue pressure of the extracellular space (outside-in mechanosensation). These mechanical cues are transduced into a cellular response (e. g. cell migration and proliferation; inside-in mechanotransduction) or to a response affecting the microenvironment (e. g. inducing a fibrosis or building up growth-induced pressure; inside-out mechanotransduction). These processes heavily rely on mechanosensitive membrane proteins, prominently ion channels. Mechanosensitive ion channels are involved in the Ca²⁺-signaling of the tumor and stroma cells, both directly, by mediating Ca²⁺ influx (e. g. Piezo and TRP channels), or indirectly, by maintaining the electrochemical gradient necessary for Ca²⁺ influx (e. g. K_2P, K_Ca channels). This review aims to discuss the diverse roles of mechanosenstive ion channels in cancer progression, especially those involved in Ca²⁺-signaling, by pinpointing their functional relevance in tumor pathophysiology.

Purinergic P2X7 Receptor: A Cation Channel Sensitive to Tumor Microenvironment

Objective:

Current review was conducted to check involvement of P2X7R use in cancer treatment.

Methods:

We review the most recent patents focused on the use of P2X7R in the treatment of cancer.

Results:

P2X7R is an intriguing purinergic receptor that plays different roles in tumor progression.

Conclusion:

Powerful strategies able to selectively interfere with its expression and function should reveal helpful in the development of new anti-cancer therapies.

P2Y2 Receptor Functions in Cancer: A Perspective in the Context of Colorectal Cancer

Purinergic signaling has recently emerged as a network of signaling molecules, enzymes and receptors that coordinates the action and behavior of cancerous cells. Extracellular adenosine 5' triphosphate activates a plethora of P2 nucleotide receptors that can putatively modulate cancer cell proliferation, survival and dissemination. In this context, the G protein-coupled P2Y₂ receptor was identified as one of the entities coordinating the cellular and molecular events that characterize cancerous cells. In this chapter, we will look at the contribution of the P2Y₂ receptor in cancer outcomes and use this information to demonstrate that the P2Y₂ receptor represents a drug target of interest in the setting of colorectal cancer, for which the role and function of this receptor is poorly defined. More particularly, we will review how the P2Y₂ receptor modulates cancer cell proliferation and survival, while promoting cell dissemination and formation of metastases. Finally, we will investigate how the P2Y₂ receptor can contribute to the detrimental development of drug resistance that is often observed in cancerous cells.

Activating P2X7 Receptors Increases Proliferation of Human Pancreatic Cancer Cells via ERK1/2 and JNK

OBJECTIVES

The aim of this study was to investigate the effects of the activated P2X7 receptors on the proliferation and growth of human pancreatic cancer cells.

METHODS

Proliferation was measured by incorporating bromodeoxyuridine into pancreatic cancer cells, MIA PaCa-2 and HPAC. Expression of P2 receptors and signal molecules was examined using quantitative reverse transcription/polymerase chain reaction and/or Western blot. Proliferative effects of the P2X7 receptors in vivo were examined using a xenotransplant model of pancreatic cancer cell lines.

RESULTS

Incubating pancreatic cancer cells with adenosine triphosphate (ATP) and 2'(3')-O-(4-Benzoylbenzoyl)ATP resulted in a dose-dependent increase of cell proliferation. The P2 receptor antagonist, KN-62, and small interfering RNA against P2X7 receptors, significantly decreased the proliferative effects of ATP. The ATP-induced proliferation was mediated by protein kinase C, extracellular signal-regulated protein kinases 1 and 2 (ERK1/2), and c-Jun N-terminal kinase (JNK); specifically, ATP increased the phosphorylation of ERK1/2 and JNK. The expression of inducible nitric oxide synthase was decreased by P2X7 receptor activation. In a xenotransplant model, applying ATP significantly increased the growth of induced tumors.

CONCLUSIONS

The P2X7 receptor activation by extracellular nucleotides increased proliferation and growth of human pancreatic cancer cells via ERK1/2 and JNK. This supports the pathophysiological role of P2X7 receptors in pancreatic disease and recovery.

Extracellular ATP induces apoptosis through P2X7R activation in acute myeloid leukemia cells but not in normal hematopoietic stem cells

Recent studies have shown that high ATP levels exhibit direct cytotoxic effects on several cancer cells types. Among the receptors engaged by ATP, P2X7R is the most consistently expressed by tumors. P2X7R is an ATP-gated ion channel that could drive the opening of a non-selective pore, triggering cell-death signal. We previously demonstrated that acute myeloid leukemia (AML) cells express high level of P2X7R. Here, we show that P2X7R activation with high dose ATP induces AML blast cells apoptosis. Moreover, P2X7R is also expressed on leukemic stem/progenitor cells (LSCs) which are sensitive to ATP-mediated cytotoxicity. Conversely, this cytotoxic effect was not observed on normal hematopoietic stem/progenitor cells (HSCs). Notably, the antileukemic activity of ATP was also observed in presence of bone marrow stromal cells and its addition to the culture medium enhanced cytosine arabinoside cytotoxicity despite stroma-induced chemoresistance. Xenotransplant experiments confirmed ATP antineoplastic activity in vivo.Overall, our results demonstrate that P2X7R stimulation by ATP induced a therapeutic response in AML at the LSC level while the normal stem cell compartment was not affected. These results provide evidence that ATP would be promising for developing innovative therapy for AML.

Hypermethylation downregulates P2X7 receptor expression in astrocytoma

The present study investigated the altered expression of p2X purinoceptor (P2X₇R) in astrocytoma. Reverse transcription-quantitative polymerase chain reaction and western blot analysis were used to determine the P2X₇R expression in glioblastoma (GBM) and surrounding normal brain tissue. DNA methylation levels of P2X₇R gene promoter in GBM were analyzed using a Sequenom MassARRAY^® System. Immunohistochemistry (IHC) was used to detect the expression of P2X₇R in astrocytoma at different malignancy grades, including diffuse astrocytoma, anaplastic astrocytoma and GBM. P2X₇R mRNA and protein were significantly decreased in GBM compared with normal brain tissues. IHC results showed a negative correlation between P2X₇R expression and tumor grade. The decreased P2X₇R expression was mostly attributed to hypermethylation of its promoter. Therefore, P2X₇R was found to perform an important role in tumorigenesis and progression of astrocytoma.

Multifaceted Effects of Extracellular Adenosine Triphosphate and Adenosine in the Tumor-Host Interaction and Therapeutic Perspectives

Cancer is still one of the world's most pressing health-care challenges, leading to a high number of deaths worldwide. Immunotherapy is a new developing therapy that boosts patient's immune system to fight cancer by modifying tumor-immune cells interaction in the tumor microenvironment (TME). Extracellular adenosine triphosphate (eATP) and adenosine (Ado) are signaling molecules released in the TME that act as modulators of both immune and tumor cell responses. Extracellular adenosine triphosphate and Ado activate purinergic type 2 (P2) and type 1 (P1) receptors, respectively, triggering the so-called purinergic signaling. The concentration of eATP and Ado within the TME is tightly controlled by several cell-surface ectonucleotidases, such as CD39 and CD73, the major ecto-enzymes expressed in cancer cells, immune cells, stromal cells, and vasculature, being CD73 also expressed on tumor-associated fibroblasts. Once accumulated in the TME, eATP boosts antitumor immune response, while Ado attenuates or suppresses immunity against the tumor. In addition, both molecules can mediate growth stimulation or inhibition of the tumor, depending on the specific receptor activated. Therefore, purinergic signaling is able to modulate both tumor and immune cells behavior and, consequently, the tumor-host interaction and disease progression. In this review, we discuss the role of purinergic signaling in the host-tumor interaction detailing the multifaceted effects of eATP and Ado in the inflammatory TME. Moreover, we present recent findings into the application of purinergic-targeting therapy as a potential novel option to boost antitumor immune responses in cancer.

Short- and long-term (trophic) purinergic signalling

There is long-term (trophic) purinergic signalling involving cell proliferation, differentiation, motility and death in the development and regeneration of most systems of the body, in addition to fast purinergic signalling in neurotransmission, neuromodulation and secretion. It is not always easy to distinguish between short- and long-term signalling. For example, adenosine triphosphate (ATP) can sometimes act as a short-term trigger for long-term trophic events that become evident days or even weeks after the original challenge. Examples of short-term purinergic signalling during sympathetic, parasympathetic and enteric neuromuscular transmission and in synaptic transmission in ganglia and in the central nervous system are described, as well as in neuromodulation and secretion. Long-term trophic signalling is described in the immune/defence system, stratified epithelia in visceral organs and skin, embryological development, bone formation and resorption and in cancer. It is likely that the increase in intracellular Ca(2+) in response to both P2X and P2Y purinoceptor activation participates in many short- and long-term physiological effects.This article is part of the themed issue 'Evolution brings Ca(2+) and ATP together to control life and death'.

Mesenchymal stem cells from tumor microenvironment favour breast cancer stem cell proliferation, cancerogenic and metastatic potential, via ionotropic purinergic signalling

Interaction between tumor cells and the microenvironment is key in initiation, progression, and invasiveness of cancer. In particular, mesenchymal stem cells (MSCs) are recruited to the sites of developing tumors, thus promoting metastasis formation. Although it is well known that MSCs migrate and integrate in the tumor microenvironment (TME), their fate and function inside the tumor is still not clear. In this study, we analyzed the role played by MSCs in breast cancer oncogenesis. Data indicate that interaction of breast cancer cells with MSCs results in an increased proliferation and metabolic activity of breast cancer cells, partially due to MSC-derived microvesicles that are shed in the TME. Moreover, we addressed the question of whether we could modulate such interaction by acting on P2X-mediated intercellular communication. By inhibiting P2X-mediated purinergic signaling, we succeeded in reducing both the cancerogenic as well as the metastatic potential of breast cancer cells co-cultured with MSCs, in 2D as well as in 3D in vitro models. Data obtained demonstrate for the first time that the trophic effect of MSCs on breast cancer cell growth is exerted via ionotropic purinergic signaling, thus suggesting the inhibition of the purinergic signaling system as a potential target for therapeutic intervention.

ATP-P2Y2-β-catenin axis promotes cell invasion in breast cancer cells

Extracellular adenosine 5'-triphosphate (ATP), secreted by living cancer cells or released by necrotic tumor cells, plays an important role in tumor invasion and metastasis. Our previous study demonstrated that ATP treatment in vitro could promote invasion in human prostate cancer cells via P2Y2, a preferred receptor for ATP, by enhancing EMT process. However, the pro-invasion mechanisms of ATP and P2Y2 are still poorly studied in breast cancer. In this study, we found that P2Y2 was highly expressed in breast cancer cells and associated with human breast cancer metastasis. ATP could promote the in vitro invasion of breast cancer cells and enhance the expression of β-catenin as well as its downstream target genes CD44, c-Myc and cyclin D1, while P2Y2 knockdown attenuated above ATP-driven events in vitro and in vivo. Furthermore, iCRT14, a β-catenin/TCF complex inhibitor, could also suppress ATP-driven migration and invasion in vitro. These results suggest that ATP promoted breast cancer cell invasion via P2Y2-β-catenin axis. Thus blockade of the ATP-P2Y2-β-catenin axis could suppress the invasive and metastatic potential of breast cancer cells and may serve as potential targets for therapeutic interventions of breast cancer.

A phase I clinical trial demonstrates that nfP2X7 -targeted antibodies provide a novel, safe and tolerable topical therapy for basal cell carcinoma

BACKGROUND

Expression of P2X₇ , an ATP-gated calcium channel, increases cancer cell proliferation and invasiveness. A variant of P2X₇ (termed nfP2X₇ ), in which a normally hidden epitope (E200) is exposed for antibody binding, is observed in a variety of different cancers.

OBJECTIVES

To investigate the safety, tolerability and pharmacokinetics and assess indicative efficacy of a novel antibody ointment as a therapeutic for basal cell carcinoma (BCC).

METHODS

An open-label, phase I clinical trial was undertaken at three dermatology clinics to evaluate the safety and tolerability of topical administration of an ointment containing 10% sheep polyclonal anti-nfP2X₇ antibodies (BIL010t) to primary BCC lesions twice daily for 28 days. Twenty-one patients with primary BCC lesions at least 0·5 cm² in area and less than 2·0 cm in diameter were enrolled. The primary end points were safety, tolerability and pharmacokinetics. Change in lesion size after treatment was determined and histology was performed on pretreatment and end-of-treatment (EOT) biopsies.

RESULTS

Compliance was very high, with treatment being well tolerated. The most common adverse events were treatment site erythema, pruritus, dryness and pain. There was no evidence of systemic penetration of the sheep antibody. Lesions were measured prior to and after 28 days of treatment, with 65% of patients showing a reduction in lesion area, 20% showing no change and 15% showing an increase. Histopathology of post-treatment excision of lesion sites showed eight patients with stable disease, nine with partial response and three with complete response.

CONCLUSIONS

Antibodies against nfP2X₇ (BIL010t) provide a novel, safe and well-tolerated treatment for BCC.

The purine receptor P2X7R regulates the release of pro-inflammatory cytokines in human craniopharyngioma

Craniopharyngiomas (CPs) are usually benign, non-metastasizing embryonic malformations originating from the sellar area. They are, however, locally invasive and generate adherent interfaces with the surrounding brain parenchyma. Previous studies have shown the tumor microenvironment is characterized by a local abundance of adenosine triphosphate (ATP), infiltration of leukocytes and elevated levels of pro-inflammatory cytokines that are thought to be responsible, at least in part, for the local invasion. Here, we examine whether ATP, via the P2X7R, participates in the regulation of cytokine expression in CPs. The expression of P2X7R and pro-inflammatory cytokines were measured at the RNA and protein levels both in tumor samples and in primary cultured tumor cells. Furthermore, cytokine modulation was measured after manipulating P2X7R in cultured tumor cells by siRNA-mediated knockdown, as well as pharmacologically by using selective agonists and antagonists. The following results were observed. A number of cytokines, in particular IL-6, IL-8 and MCP-1, were elevated in patient plasma, tumor tissue and cultured tumor cells. P2X7R was expressed in tumor tissue as well as in cultured tumor cells. RNA expression as measured in 48 resected tumors was positively correlated with the RNA levels of IL-6, IL-8 and MCP-1 in tumors. Furthermore, knockdown of P2X7R in primary tumor cultures reduced, and stimulation of P2XR7 by a specific agonist enhanced the expression of these cytokines. This latter stimulation involved a Ca²⁺-dependent mechanism and could be counteracted by the addition of an antagonist. In conclusion, the results suggest that P2X7R may promote IL-6, IL-8 and MCP-1 production and secretion and contribute to the invasion and adhesion of CPs to the surrounding tissue.

Potential role of P2X7R in esophageal squamous cell carcinoma proliferation

Esophageal cancer is an aggressive tumor and is the sixth leading cause of cancer death worldwide. ATP is well known to regulate cancer progression in a variety of models by different mechanisms, including P2X7R activation. This study aimed to evaluate the role of P2X7R in esophageal squamous cell carcinoma (ESCC) proliferation. Our results show that treatment with high ATP concentrations induced a decrease in cell number, cell viability, number of polyclonal colonies, and reduced migration of ESCC. The treatment with the selective P2X7R antagonist A740003 or siRNA for P2X7 reverted this effect in the KYSE450 cell line. In addition, results showed that P2X7R is highly expressed, at mRNA and protein levels, in KYSE450 lineage. Additionally, KYSE450, KYSE30, and OE21 cells express P2X3R, P2X4R, P2X5R, P2X6R, and P2X7R genes. P2X1R is expressed by KYSE30 and KYSE450, and only KYSE450 expresses the P2X2R gene. Furthermore, esophageal cancer cell line KYSE450 presented higher expression of E-NTPDases 1 and 2 and of Ecto-5'-NT/CD73 when compared to normal cells. This cell line also exhibits ATPase, ADPase, and AMPase activity, although in different levels, and the co-treatment of apyrase was able to revert the antiproliferative effects of ATP. Moreover, results showed high immunostaining for P2X7R in biopsies of patients with esophageal carcinoma, indicating the involvement of this receptor in the growth of this type of cancer. The results suggest that P2X7R may be a potential pharmacological target to treat ESCC and can lead us to further investigate the effect of this receptor in cancer cell progression.

Targeting of the P2X7 receptor in pancreatic cancer and stellate cells

The ATP‐gated receptor P2X7 (P2X7R) is involved in regulation of cell survival and has been of interest in cancer field. Pancreatic ductal adenocarcinoma (PDAC) is a deadly cancer and new markers and therapeutic targets are needed. PDAC is characterized by a complex tumour microenvironment, which includes cancer and pancreatic stellate cells (PSCs), and potentially high nucleotide/side turnover. Our aim was to determine P2X7R expression and function in human pancreatic cancer cells in vitro as well as to perform in vivo efficacy study applying P2X7R inhibitor in an orthotopic xenograft mouse model of PDAC. In the in vitro studies we show that human PDAC cells with luciferase gene (PancTu‐1 Luc cells) express high levels of P2X7R protein. Allosteric P2X7R antagonist AZ10606120 inhibited cell proliferation in basal conditions, indicating that P2X7R was tonically active. Extracellular ATP and BzATP, to which the P2X7R is more sensitive, further affected cell survival and confirmed complex functionality of P2X7R. PancTu‐1 Luc migration and invasion was reduced by AZ10606120, and it was stimulated by PSCs, but not by PSCs from P2X7^‐/‐ animals. PancTu‐1 Luc cells were orthotopically transplanted into nude mice and tumour growth was followed noninvasively by bioluminescence imaging. AZ10606120‐treated mice showed reduced bioluminescence compared to saline‐treated mice. Immunohistochemical analysis confirmed P2X7R expression in cancer and PSC cells, and in metaplastic/neoplastic acinar and duct structures. PSCs number/activity and collagen deposition was reduced in AZ10606120‐treated tumours.

What's new?

Pancreatic ductal adenocarcinoma (PDAC) is one the most difficult types of cancer to detect and treat, challenges that could be overcome through the discovery and development of novel markers and therapeutic strategies. Here, the P2X7 receptor, which regulates cell survival, is shown to also support cell proliferation, migration and invasion in human P2X7R‐expressing PDAC cells. Treatment of orthotopic PDAC tumor‐bearing mice with the P2X7R‐specific inhibitor, AZ10606120, resulted in decreased tumor bioluminescence and reductions in pancreatic stellate cells and collagen deposition. Targeting of P2X7R warrants further investigation as a promising therapeutic approach in pancreatic cancer.

Extracellular purines, purinergic receptors and tumor growth

Virtually, all tumor cells as well as all immune cells express plasma membrane receptors for extracellular nucleosides (adenosine) and nucleotides (ATP, ADP, UTP, UDP and sugar UDP). The tumor microenvironment is characterized by an unusually high concentration of ATP and adenosine. Adenosine is a major determinant of the immunosuppressive tumor milieu. Sequential hydrolysis of extracellular ATP catalyzed by CD39 and CD73 is the main pathway for the generation of adenosine in the tumor interstitium. Extracellular ATP and adenosine mold both host and tumor responses. Depending on the specific receptor activated, extracellular purines mediate immunosuppression or immunostimulation on the host side, and growth stimulation or cytotoxicity on the tumor side. Recent progress in this field is providing the key to decode this complex scenario and to lay the basis to harness the potential benefits for therapy. Preclinical data show that targeting the adenosine-generating pathway (that is, CD73) or adenosinergic receptors (that is, A2A) relieves immunosuppresion and potently inhibits tumor growth. On the other hand, growth of experimental tumors is strongly inhibited by targeting the P2X7 ATP-selective receptor of cancer and immune cells. This review summarizes the recent data on the role played by extracellular purines (purinergic signaling) in host-tumor interaction and highlights novel therapeutic options stemming from recent advances in this field.

P2 receptors in cancer progression and metastatic spreading

Tumor microenvironment is nucleoside and nucleotide rich. Adenosine is a key determinant of the highly immunosuppressive tumor interstitium. Extracellular ATP also affects anti-tumor immunity, albeit its effects on host-tumor interaction are incompletely understood. We give here an overview of recent literature covering the role of nucleotide-selective (P2) plasma membrane receptors in tumor growth and progression. P2 receptors are expressed on both host and cancer cells, where depending on the receptor subtype, the inflammatory infiltrate and the tumor cell type they may drive an anti-tumor response or promote tumor progression. It is anticipated that knowledge of the pharmacology, biochemistry and functional activity of the P2 receptors will allow a better understanding of host-tumor interaction and the development of innovative anti-cancer therapy.

Important roles of P2Y receptors in the inflammation and cancer of digestive system

Purinergic signaling is important for many biological processes in humans. Purinoceptors P2Y are widely distributed in human digestive system and different subtypes of P2Y receptors mediate different physiological functions from metabolism, proliferation, differentiation to apoptosis etc. The P2Y receptors are essential in many gastrointestinal functions and also involve in the occurrence of some digestive diseases. Since different subtypes of P2Y receptors are present on the same cell of digestive organs, varying subtypes of P2Y receptors may have opposite or synergetic functions on the same cell. Recently, growing lines of evidence strongly suggest the involvement of P2Y receptors in the pathogenesis of several digestive diseases. In this review, we will focus on their important roles in the development of digestive inflammation and cancer. We anticipate that as the special subtypes of P2Y receptors are studied in depth, specific modulators for them will have good potentials to become promising new drugs to treat human digestive diseases in the near future.

P2X7 receptor in skin biology and diseases

The P2X7 receptor is a trimeric ligand-gated cation channel present on immune and other cells. Activation of this receptor by its natural ligand extracellular adenosine triphosphate results in a variety of downstream responses, including the release of pro-inflammatory mediators and cell death. In normal skin, P2X7 is present on keratinocytes, Langerhans cells and fibroblasts, while the presence of this receptor on other cutaneous cells is mainly inferred from studies of equivalent cell types present in other tissues. Mast cells in normal skin however express negligible amounts of P2X7, which can be upregulated in cutaneous disease. This review discusses the potential significance of P2X7 in skin biology, and the role of this receptor in inflammatory skin disorders such as irritant and chronic dermatitis, psoriasis, graft-versus-host disease, as well is in wound healing, transplantation and skin cancer.

Molecular Structure and Regulation of P2X Receptors With a Special Emphasis on the Role of P2X2 in the Auditory System

The P2X purinergic receptors are cation-selective channels gated by extracellular adenosine 5'-triphosphate (ATP). These purinergic receptors are found in virtually all mammalian cell types and facilitate a number of important physiological processes. Within the past few years, the characterization of crystal structures of the zebrafish P2X4 receptor in its closed and open states has provided critical insights into the mechanisms of ligand binding and channel activation. Understanding of this gating mechanism has facilitated to design and interpret new modeling and structure-function experiments to better elucidate how different agonists and antagonists can affect the receptor with differing levels of potency. This review summarizes the current knowledge on the structure, activation, allosteric modulators, function, and location of the different P2X receptors. Moreover, an emphasis on the P2X2 receptors has been placed in respect to its role in the auditory system. In particular, the discovery of three missense mutations in P2X2 receptors could become important areas of study in the field of gene therapy to treat progressive and noise-induced hearing loss. J. Cell. Physiol. 231: 1656-1670, 2016. © 2015 Wiley Periodicals, Inc.

The P2X7 receptor regulates cell survival, migration and invasion of pancreatic ductal adenocarcinoma cells

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is presently one of the cancers with the worst survival rates and least effective treatments. Moreover, total deaths due to PDAC are predicted to increase in the next 15 years. Therefore, novel insights into basic mechanism of PDAC development and therapies are needed. PDAC is characterized by a complex microenvironment, in which cancer and stromal cells release different molecules, such as ATP. ATP can be transported and/or exocytosed from active cancer cells and released from dying cells in the necrotic core of the cancer. We hypothesized that one of the ATP receptors, the P2X7 receptor (P2X7R) could be an important player in PDAC behaviour.

METHODS

We determined the expression (real time PCR and Western blot) and localization (immunofluorescence) of P2X7R in human PDAC cell lines (AsPC-1, BxPC-3, Capan-1, MiaPaCa-2, Panc-1) and a "normal" human pancreatic duct epithelial cell line (HPDE). The function of P2X7R in proliferation (BrdU assay), migration (wound assay) and invasion (Boyden chamber with matrigel) was characterized. Furthermore, we studied P2X7R-dependent pore formation (YoPro-1 assay) and cell death (caspase and annexin V / propidium iodide assays).

RESULTS

We found higher expression of P2X7R protein in PDAC compared to HPDE cells. P2X7R had notable disparate effects on PDAC survival. Firstly, high concentrations of ATP or the specific P2X7R agonist, BzATP, had cytotoxic effects in all cell lines, and cell death was mediated by necrosis. Moreover, the P2X7R-pore antagonist, A438079, prevented ATP-induced pore formation and cell death. Second, in basal conditions and with low concentrations of ATP/BzATP, the P2X7R allosteric inhibitor AZ10606120 reduced proliferation in all PDAC cell lines. P2X7R also affected other key characteristics of cancer cell behavior. AZ10606120 reduced cell migration and invasion in PDAC cell lines compared to that of untreated/vehicle-treated control cells, and stimulation with sub-millimolar concentrations of ATP or BzATP substantially increased cell invasion.

CONCLUSIONS

PDAC cell lines overexpress P2X7R and the receptor plays crucial roles in cell survival, migration and invasion. Therefore, we propose that drugs targeting P2X7R could be exploited in therapy of pancreatic cancer.

ATP promotes cell survival via regulation of cytosolic [Ca2+] and Bcl-2/Bax ratio in lung cancer cells

Adenosine triphosphate (ATP) is a ubiquitous extracellular messenger elevated in the tumor microenvironment. ATP regulates cell functions by acting on purinergic receptors (P2X and P2Y) and activating a series of intracellular signaling pathways. We examined ATP-induced Ca(2+) signaling and its effects on antiapoptotic (Bcl-2) and proapoptotic (Bax) proteins in normal human airway epithelial cells and lung cancer cells. Lung cancer cells exhibited two phases (transient and plateau phases) of increase in cytosolic [Ca(2+)] ([Ca(2+)]cyt) caused by ATP, while only the transient phase was observed in normal cells. Removal of extracellular Ca(2+) eliminated the plateau phase increase of [Ca(2+)]cyt in lung cancer cells, indicating that the plateau phase of [Ca(2+)]cyt increase is due to Ca(2+) influx. The distribution of P2X (P2X1-7) and P2Y (P2Y1, P2Y2, P2Y4, P2Y6, P2Y11) receptors was different between lung cancer cells and normal cells. Proapoptotic P2X7 was nearly undetectable in lung cancer cells, which may explain why lung cancer cells showed decreased cytotoxicity when treated with high concentration of ATP. The Bcl-2/Bax ratio was increased in lung cancer cells following treatment with ATP; however, the antiapoptotic protein Bcl-2 demonstrated more sensitivity to ATP than proapoptotic protein Bax. Decreasing extracellular Ca(2+) or chelating intracellular Ca(2+) with BAPTA-AM significantly inhibited ATP-induced increase in Bcl-2/Bax ratio, indicating that a rise in [Ca(2+)]cyt through Ca(2+) influx is the critical mediator for ATP-mediated increase in Bcl-2/Bax ratio. Therefore, despite high ATP levels in the tumor microenvironment, which would induce cell apoptosis in normal cells, the decreased P2X7 and elevated Bcl-2/Bax ratio in lung cancer cells may enable tumor cells to survive. Increasing the Bcl-2/Bax ratio by exposure to high extracellular ATP may, therefore, be an important selective pressure promoting transformation and cancer progression.

Altered purinergic signaling in the tumor associated immunologic microenvironment in metastasized non-small-cell lung cancer

OBJECTIVES

Purines are well-known as intracellular sources for energy but they also act as extracellular signaling molecules. In the recent years, there has been a growing interest in the therapeutic potential of purinergic signaling for cancer treatment. This is the first study to analyze lung purine levels and purinergic receptors in non-small-cell lung cancer (NSCLC) patients.

MATERIALS AND METHODS

In this prospective clinical trial we enrolled 26 patients with NSCLC and 21 patients with chronic obstructive pulmonary disease (COPD) without signs of malignancy. The purine concentrations were analyzed in bronchoalveolar lavage fluid (BALF) using fluorescent/luminescent assays. Expression of purinergic receptors and ectonucleotidases were analyzed using real time quantitative polymerase chain reaction (RT-qPCR).

RESULTS

Patients with NSCLC have significantly lower ATP and ADP concentrations in BALF than patients with COPD (p=0.006 and p=0.009). Expression of the ectonucleotidase CD39 is significantly higher in BAL cells from cancer patients compared to COPD (p=0.001) as well as in metastasized tumors compared to non-metastasized tumors (p=0.009). Receptor-analysis revealed a higher expression of P2X4 (p=0.03), P2X7 (p=0.001) and P2Y1 (p=0.003) in BAL cells of tumors with distant metastasis.

CONCLUSION

Our data suggests a role for CD39 in lung cancer tumor microenvironment, influencing tumor invasiveness and metastasization. Potentially the increased degradation of ATP and ADP leads to a subversion of their anti-neoplastic effects. Furthermore P2Y1, P2X4 and P2X7 receptors are upregulated in BAL cells in metastatic disease. Our findings might facilitate the identification of new therapeutic targets for cancer immunotherapy.

P2X7 receptor predicts postoperative cancer-specific survival of patients with clear-cell renal cell carcinoma

The P2X7 receptor, an ATP-gated plasma membrane ion channel, is involved in inflammation, apoptosis and cell proliferation, and thereby plays a crucial role during oncogenic transformation in various malignancies. This study aims to evaluate the impact of P2X7 receptor expression on postoperative cancer-specific survival of patients with clear-cell renal cell carcinoma (ccRCC). A total of 273 patients with ccRCC undergoing nephrectomy at a single institution were retrospectively enrolled in this study, among which 86 patients died of this disease and six patients died of other causes. Clinicopathologic features and cancer-specific survival (CSS) were recorded. P2X7 expression was assessed by immunohistochemistry in clinical specimens. Kaplan–Meier method with log rank test was performed to compare survival curves. Cox regression models were used to evaluate the prognostic values of variables on CSS. Concordance index was calculated to assess prognostic accuracy of prognostic models. Median follow-up period was 90 months (range, 11–120 months). Intratumoral P2X7 expression was significantly lower than peritumoral tissues (P < 0.001). Moreover, high intratumoral P2X7 expression, which was significantly associated with shorten CSS (P < 0.001), high TNM stage (P = 0.038), Fuhrman grade (P = 0.035), SSIGN (stage, size, grade, and necrosis) score (P = 0.021) and University of California Integrated Staging System (UISS) score (P = 0.007), was indicated to be an independent prognostic factor for CSS (hazard ratio [HR], 1.693; P = 0.034). The prognostic accuracy of TNM stage, UISS and SSIGN scoring models was improved when intratumoral P2X7 expression was added. Intratumoral P2X7 expression is a potential independent adverse prognostic indicator for postoperative CSS of patients with ccRCC.

P2X7 receptors: role in bone cell formation and function

The role of the P2X7 receptor (P2X7R) is being explored with intensive interest in the context of normal bone physiology, bone-related diseases and, to an extent, bone cancer. In this review, we cover the current understanding of P2X7R regulation of bone cell formation, function and survival. We will discuss how the P2X7R drives lineage commitment of undifferentiated bone cell progenitors, the vital role of P2X7R activation in bone mineralisation and its relatively unexplored role in osteocyte function. We also review how P2X7R activation is imperative for osteoclast formation and its role in bone resorption via orchestrating osteoclast apoptosis. Variations in the gene for the P2X7R (P2RX7) have implications for P2X7R-mediated processes and we review the relevance of these genetic variations in bone physiology. Finally, we highlight how targeting P2X7R may have therapeutic potential in bone disease and cancer.