CD73 participates in cellular multiresistance program and protects against TRAIL-induced apoptosis

The Clinical Significance of CD73 in Cancer

The search for new and effective treatment targets for cancer immunotherapy is an ongoing challenge. Alongside the more established inhibitory immune checkpoints, a novel potential target is CD73. As one of the key enzymes in the purinergic signalling pathway CD73 is responsible for the generation of immune suppressive adenosine. The expression of CD73 is higher in tumours than in the corresponding healthy tissues and associated with a poor prognosis. CD73, mainly by the production of adenosine, is critical in the suppression of an adequate anti-tumour immune response, but also in promoting cancer cell proliferation, tumour growth, angiogenesis, and metastasis. The upregulation of CD73 and generation of adenosine by tumour or tumour-associated immune cells is a common resistance mechanism to many cancer treatments such as chemotherapy, radiotherapy, targeted therapy, and immunotherapy. Therefore, the inhibition of CD73 represents a new and promising approach to increase therapy efficacy. Several CD73 inhibitors have already been developed and successfully demonstrated anti-cancer activity in preclinical studies. Currently, clinical studies evaluate CD73 inhibitors in different therapy combinations and tumour entities. The initial results suggest that inhibiting CD73 could be an effective option to augment anti-cancer immunotherapeutic strategies. This review provides an overview of the rationale behind the CD73 inhibition in different treatment combinations and the role of CD73 as a prognostic marker.

CD73, a Promising Therapeutic Target of Diclofenac, Promotes Metastasis of Pancreatic Cancer through a Nucleotidase Independent Mechanism

CD73, a cell surface-bound nucleotidase, facilitates extracellular adenosine formation by hydrolyzing 5'-AMP to adenosine. Several studies have shown that CD73 plays an essential role in immune escape, cell proliferation and tumor angiogenesis, making it an attractive target for cancer therapies. However, there are limited clinical benefits associated with the mainstream enzymatic inhibitors of CD73, suggesting that the mechanism underlying the role of CD73 in tumor progression is more complex than anticipated, and further investigation is necessary. In this study, CD73 is found to overexpress in the cytoplasm of pancreatic ductal adenocarcinoma (PDAC) cells and promotes metastasis in a nucleotidase-independent manner, which cannot be restrained by the CD73 monoclonal antibodies or small-molecule enzymatic inhibitors. Furthermore, CD73 promotes the metastasis of PDAC by binding to the E3 ligase TRIM21, competing with the Snail for its binding site. Additionally, a CD73 transcriptional inhibitor, diclofenac, a non-steroidal anti-inflammatory drug, is more effective than the CD73 blocking antibody for the treatment of PDAC metastasis. Diclofenac also enhances the therapeutic efficacy of gemcitabine in the spontaneous KPC (LSL-Kras^G12D/+ , LSL-Trp53^R172H/+ , and Pdx-1-Cre) pancreatic cancer model. Therefore, diclofenac may be an effective anti-CD73 therapy, when used alone or in combination with gemcitabine-based chemotherapy regimen, for metastatic PDAC.

Targeting two distinct epitopes on human CD73 with a bispecific antibody improves anticancer activity

Background

Immunosuppressive extracellular adenosine is generated by the enzymatic activity of CD73. In preclinical models, antibodies (Abs) targeting different epitopes on CD73 exert anticancer activity through distinct mechanisms such as inhibition of enzymatic activity, engagement of Fc receptors, and spatial redistribution of CD73.

Methods

Using controlled Fab arm exchange, we generated biparatopic bispecific antibodies (bsAbs) from parental anti-CD73 Abs with distinct anticancer activities. The resulting anticancer activity was evaluated using in vitro and in vivo models.

Results

We demonstrate that different anticancer activities can be combined in a biparatopic bsAb. Remarkably, the bsAb significantly improved the enzyme inhibitory activity compared with the parental Abs, which led to neutralization of adenosine-mediated T-cell suppression as demonstrated by proliferation and interferon gamma (IFN-γ) production and prolonged survival of tumor-bearing mice. Additionally, the bsAb caused more efficient internalization of cell surface CD73 and stimulated potent Fc-mediated engagement of human immune effector cells in vitro and in vivo.

Conclusions

Our data collectively demonstrate that complementary anticancer mechanisms of action of distinct anti-CD73 Abs can be combined and enhanced in a biparatopic bsAb. The multiple mechanisms of action and superior activity compared with the monospecific parental Abs make the bsAb a promising candidate for therapeutic targeting of CD73 in cancer. This concept may greatly improve future Ab design.

A Novel Anti-CD73 Antibody That Selectively Inhibits Membrane CD73 Shows Antitumor Activity and Induces Tumor Immune Escape

CD73 catalyzes the conversion of ATP to adenosine, which is involved in various physiological and pathological processes, including tumor immune escape. Because CD73 expression and activity are particularly high on cancer cells and contribute to the immunosuppressive properties of the tumor environment, it is considered an attractive target molecule for specific cancer therapies. In line, several studies demonstrated that CD73 inhibition has a significant antitumor effect. However, complete blocking of CD73 activity can evoke autoimmune phenomena and adverse side effects. We developed a CD73-specific antibody, 22E6, that specifically inhibits the enzymatic activity of membrane-tethered CD73 present in high concentrations on cancer cells and cancer cell-derived extracellular vesicles but has no inhibitory effect on soluble CD73. Inhibition of CD73 on tumor cells with 22E6 resulted in multiple effects on tumor cells in vitro, including increased apoptosis and interference with chemoresistance. Intriguingly, in a xenograft mouse model of acute lymphocytic leukemia (ALL), 22E6 treatment resulted in an initial tumor growth delay in some animals, followed by a complete loss of CD73 expression on ALL cells in all 22E6 treated animals, indicating tumor immune escape. Taken together, 22E6 shows great potential for cancer therapy, favorably in combination with other drugs.

Adenosine and adenosine receptors in colorectal cancer

CD39 (nucleoside triphosphate diphosphohydrolase) and Ecto-5-nucleotidase (CD73) have been recognized as important factors mediating various pathological and physiological responses in the tumor microenvironment. Elevated expression of CD73 and CD39 is correlated with the over-production of adenosine in the tumor region. This increase is associated with an immunosuppressive state in the tumor site that enhances various tumor hallmarks such as metastasis, angiogenesis, and cell proliferation. Adenosine promotes these behaviors through interaction with four adenosine receptors, including A3R, A2BR, A2AR, and A1R. Signaling of these receptors reduces the function of immune effector cells and enhances the expansion and function of tumor-associated immune cells. Several studies have been shown the important role of adenosine/CD73/CD39/ARs axis in the immunopathogenesis of colorectal cancer. These findings imply that components of this axis can be considered as a worthy target for colorectal cancer immunotherapy. In this review, we summarized the role of CD73/CD39/adenosine/ARs in the immunopathogenesis of colorectal cancer.

Drug repurposing for targeting cyclic nucleotide transporters in acute leukemias - A missed opportunity

While current treatment regimens for acute leukemia can dramatically improve patient survival, there remains room for improvement. Due to its roles in cell differentiation, cell survival, and apoptotic signaling, modulation of the cyclic AMP (cAMP) pathway has provided a meaningful target in hematological malignancies. Several studies have demonstrated that gene expression profiles associated with increased pro-survival cAMP activity or downregulation of various pro-apoptotic factors associated with the cAMP pathway are apparent in acute leukemia patients. Previous work to increase leukemia cell intracellular cAMP focused on the use of cAMP analogs, stimulating cAMP production via transmembrane-associated adenylyl cyclases, or decreasing cAMP degradation by inhibiting phosphodiesterase activity. However, targeting cyclic nucleotide efflux by ATP-binding cassette (ABC) transporters represents an unexplored approach for modulation of intracellular cyclic nucleotide levels. Preliminary studies have shown that inhibition of cAMP efflux can stimulate leukemia cell differentiation, cell growth arrest, and apoptosis, indicating that targeting cAMP efflux may show promise for future therapeutic development. Furthermore, inhibition of cyclic nucleotide transporter activity may also contribute multiple anticancer benefits by reducing extracellular pro-survival signaling in malignant cells. Hence, several opportunities for drug repurposing may exist for targeting cyclic nucleotide transporters.

Upregulation of CD73 Confers Acquired Radioresistance and is Required for Maintaining Irradiation-selected Pancreatic Cancer Cells in a Mesenchymal State

The molecular mechanisms underlying exceptional radioresistance in pancreatic cancer remain elusive. In the present study, we established a stable radioresistant pancreatic cancer cell line MIA PaCa-2-R by exposing the parental MIA PaCa-2 cells to fractionated ionizing radiation (IR). Systematic proteomics and bioinformatics analysis of protein expression in MIA PaCa-2 and MIA PaCa-2-R cells revealed that several growth factor-/cytokine-mediated pathways, including the OSM/STAT3, PI3K/AKT, and MAPK/ERK pathways, were activated in the radioresistant cells, leading to inhibition of apoptosis and increased epithelial-mesenchymal plasticity. In addition, the radioresistant cells exhibited enhanced capabilities of DNA repair and antioxidant defense compared with the parental cells. We focused functional analysis on one of the most up-regulated proteins in the radioresistant cells, ecto-5'-nucleotidase (CD73), which is a cell surface protein that is overexpressed in different types of cancer. Ectopic overexpression of CD73 in the parental cells resulted in radioresistance and conferred resistance to IR-induced apoptosis. Knockdown of CD73 re-sensitized the radioresistant cells to IR and IR-induced apoptosis. The effect of CD73 on radioresistance and apoptosis is independent of the enzymatic activity of CD73. Further studies demonstrate that CD73 up-regulation promotes Ser-136 phosphorylation of the proapoptotic protein BAD and is required for maintaining the radioresistant cells in a mesenchymal state. Our findings suggest that expression alterations in the IR-selected pancreatic cancer cells result in hyperactivation of the growth factor/cytokine signaling that promotes epithelial-mesenchymal plasticity and enhancement of DNA repair. Our results also suggest that CD73, potentially a novel downstream factor of the enhanced growth factor/cytokine signaling, confers acquired radioresistance by inactivating proapoptotic protein BAD via phosphorylation of BAD at Ser-136 and by maintaining the radioresistant pancreatic cancer cells in a mesenchymal state.

Changes in the Surface Expression of Intercellular Adhesion Molecule 3, the Induction of Apoptosis, and the Inhibition of Cell-Cycle Progression of Human Multidrug-Resistant Jurkat/A4 Cells Exposed to a Random Positioning Machine

Experiments from flight- and ground-based model systems suggest that unexpected alterations of the human lymphoblastoid cell line Jurkat, as well as effects on cell growth, metabolism, and apoptosis, can occur in altered gravity conditions. Using a desktop random positioning machine (RPM), we investigated the effects of simulated microgravity on Jurkat cells and their multidrug-resistant subline, Jurkat/A4 cells. The viability of Jurkat/A4 cells decreased after simulated microgravity in contrast with the Jurkat cells. At the same time, the viability between the experimental Jurkat cells and control Jurkat cells was not significantly different. Of note, Jurkat cells appeared as less susceptible to apoptosis than their multidrug-resistant clone Jurkat/A4 cells, whereas cell-cycle analysis showed that the percentage of Jurkat/A4 cells in the S-phase was increased after 72 and 96 h of RPM-simulated microgravity relative to their static counterparts. The differences in Jurkat cells at all phases between static and simulated microgravity were not significant. The surface expression of the intercellular adhesion molecule 3 (ICAM-3)-also known as cluster of differentiation (CD)50-protein was changed for Jurkat/A4 cells following exposure to the RPM. Changes in cell morphology were observed in the Jurkat/A4 cells after 96 h of RPM-simulated microgravity. Thus, we concluded that Jurkat/A4 cells are more sensitive to RPM-simulated microgravity as compared with the parental Jurkat cell line. We also suggest that intercellular adhesion molecule 3 may be an important adhesion molecule involved in the induction of leukocyte apoptosis. The Jurkat/A4 cells with an acquired multidrug resistance phenotype could be a useful model for studying the effects of simulated microgravity and testing anticancer drugs.

CD73 Promotes Age-Dependent Accretion of Atherosclerosis

OBJECTIVE

CD73 is an ectonucleotidase which catalyzes the conversion of AMP (adenosine monophosphate) to adenosine. Adenosine has been shown to be anti-inflammatory and vasorelaxant. The impact of ectonucleotidases on age-dependent atherosclerosis remains unclear. Our aim was to investigate the role of CD73 in age-dependent accumulation of atherosclerosis. Approach and results: Mice doubly deficient in CD73 and ApoE (apolipoprotein E; (cd73^-/-/apoE^-/-) were generated, and the extent of aortic atherosclerotic plaque was compared with apoE^-/- controls at 12, 20, 32, and 52 weeks. By 12 weeks of age, cd73^-/-/apoE^-/- mice exhibited a significant increase in plaque (1.4±0.5% of the total vessel surface versus 0.4±0.1% in apoE^-/- controls, P<0.005). By 20 weeks of age, this difference disappeared (2.9±0.4% versus 3.3±0.7%). A significant reversal in phenotype emerged at 32 weeks (9.8±1.2% versus 18.3±1.4%; P<0.0001) and persisted at the 52 week timepoint (22.4±2.1% versus 37.0±2.1%; P<0.0001). The inflammatory response to aging was found to be comparable between cd73^-/-/apoE^-/- mice and apoE^-/- controls. A reduction in lipolysis in CD73 competent mice was observed, even with similar plasma lipid levels (cd73^-/-/apoE^-/- versus apoE^-/- at 12 weeks [16.2±0.7 versus 9.5±1.4 nmol glycerol/well], 32 weeks [24.1±1.5 versus 7.4±0.4 nmol/well], and 52 weeks [13.8±0.62 versus 12.7±2.0 nmol/well], P<0.001).

CONCLUSIONS

At early time points, CD73 exerts a subtle antiatherosclerotic influence, but with age, the pattern reverses, and the presence of CD73 promoted suppression of lipid catabolism.

Inhibition of the Adenosinergic Pathway in Cancer Rejuvenates Innate and Adaptive Immunity

The adenosine pathway plays a key role in modulating immune responses in physiological and pathological conditions. Physiologically, anti-inflammatory effects of adenosine balance pro-inflammatory adenosine 5'-triphosphate (ATP), protecting tissues from damage caused by activated immune cells. Pathologically, increased adenosine monophosphatase (AMPase) activity in tumors leads to increased adenosine production, generating a deeply immunosuppressed microenvironment and promoting cancer progression. Adenosine emerges as a promising target for cancer therapy. It mediates protumor activities by inducing tumor cell proliferation, angiogenesis, chemoresistance, and migration/invasion by tumor cells. It also inhibits the functions of immune cells, promoting the formation of a tumor-permissive immune microenvironment and favoriting tumor escape from the host immune system. Pharmacologic inhibitors, siRNA or antibodies specific for the components of the adenosine pathway, or antagonists of adenosine receptors have shown efficacy in pre-clinical studies in various in vitro and in vivo tumor models and are entering the clinical arena. Inhibition of the adenosine pathway alone or in combination with classic immunotherapies offers a potentially effective therapeutic strategy in cancer.

Luciferase-assisted detection of extracellular ATP and ATP metabolites during immunogenic death of cancer cells

The efficacy of cancer chemotherapy is enhanced by induction of sustainable anti-tumor immune responses. Such responses involve accumulation of immunogenic mediators, such as extracellular ATP and ATP metabolites, within the tumor microenvironment. Recent studies have identified nucleotide-permeable plasma membrane channels or pores that are activated as early downstream consequences of different regulated cell death pathways: pannexin-1 channels in apoptosis, MLKL pores in necroptosis, and gasdermin-family pores in pyroptosis. This chapter describes the use of highly quantitative and semi-high-throughput methods based on the ATP sensor luciferase to measure dynamic changes in extracellular ATP, ADP, and AMP in tissue/cell culture models of cancer cells during various modes of regulated cell death in response to chemotherapeutic drugs, death receptors, or metabolic perturbation.

The CD73/Ado System-A New Player in RT Induced Adverse Late Effects

Radiotherapy (RT) is a central component of standard treatment for many cancer patients. RT alone or in multimodal treatment strategies has a documented contribution to enhanced local control and overall survival of cancer patients, and cancer cure. Clinical RT aims at maximizing tumor control, while minimizing the risk for RT-induced adverse late effects. However, acute and late toxicities of IR in normal tissues are still important biological barriers to successful RT: While curative RT may not be tolerable, sub-optimal tolerable RT doses will lead to fatal outcomes by local recurrence or metastatic disease, even when accepting adverse normal tissue effects that decrease the quality of life of irradiated cancer patients. Technical improvements in treatment planning and the increasing use of particle therapy have allowed for a more accurate delivery of IR to the tumor volume and have thereby helped to improve the safety profile of RT for many solid tumors. With these technical and physical strategies reaching their natural limits, current research for improving the therapeutic gain of RT focuses on innovative biological concepts that either selectively limit the adverse effects of RT in normal tissues without protecting the tumor or specifically increase the radiosensitivity of the tumor tissue without enhancing the risk of normal tissue complications. The biology-based optimization of RT requires the identification of biological factors that are linked to differential radiosensitivity of normal or tumor tissues, and are amenable to therapeutic targeting. Extracellular adenosine is an endogenous mediator critical to the maintenance of homeostasis in various tissues. Adenosine is either released from stressed or injured cells or generated from extracellular adenine nucleotides by the concerted action of the ectoenzymes ectoapyrase (CD39) and 5′ ectonucleotidase (NT5E, CD73) that catabolize ATP to adenosine. Recent work revealed a role of the immunoregulatory CD73/adenosine system in radiation-induced fibrotic disease in normal tissues suggesting a potential use as novel therapeutic target for normal tissue protection. The present review summarizes relevant findings on the pathologic roles of CD73 and adenosine in radiation-induced fibrosis in different organs (lung, skin, gut, and kidney) that have been obtained in preclinical models and proposes a refined model of radiation-induced normal tissue toxicity including the disease-promoting effects of radiation-induced activation of CD73/adenosine signaling in the irradiated tissue environment. However, expression and activity of the CD73/adenosine system in the tumor environment has also been linked to increased tumor growth and tumor immune escape, at least in preclinical models. Therefore, we will discuss the use of pharmacologic inhibition of CD73/adenosine-signaling as a promising strategy for improving the therapeutic gain of RT by targeting both, malignant tumor growth and adverse late effects of RT with a focus on fibrotic disease. The consideration of the therapeutic window is particularly important in view of the increasing use of RT in combination with various molecularly targeted agents and immunotherapy to enhance the tumor radiation response, as such combinations may result in increased or novel toxicities, as well as the increasing number of cancer survivors.

Tumor-Selective Altered Glycosylation and Functional Attenuation of CD73 in Human Hepatocellular Carcinoma

CD73, a cell-surface N-linked glycoprotein that produces extracellular adenosine, is a novel target for cancer immunotherapy. Although anti-CD73 antibodies have entered clinical development, CD73 has both protumor and antitumor functions, depending on the target cell and tumor type. The aim of this study was to characterize CD73 regulation in human hepatocellular carcinoma (HCC). We examined CD73 expression, localization, and activity using molecular, biochemical, and cellular analyses on primary HCC surgical specimens, coupled with mechanistic studies in HCC cells. We analyzed CD73 glycan signatures and global alterations in transcripts encoding other N-linked glycoproteins by using mass spectrometry glycomics and RNA sequencing (RNAseq), respectively. CD73 was expressed on tumor hepatocytes where it exhibited abnormal N-linked glycosylation, independent of HCC etiology, tumor stage, or fibrosis presence. Aberrant glycosylation of tumor-associated CD73 resulted in a 3-fold decrease in 5'-nucleotidase activity (P < 0.0001). Biochemically, tumor-associated CD73 was deficient in hybrid and complex glycans specifically on residues N311 and N333 located in the C-terminal catalytic domain. Blocking N311/N333 glycosylation by site-directed mutagenesis produced CD73 with significantly decreased 5'-nucleotidase activity in vitro, similar to the primary tumors. Glycosylation-deficient CD73 partially colocalized with the Golgi structural protein GM130, which was strongly induced in HCC tumors. RNAseq analysis further revealed that N-linked glycoprotein-encoding genes represented the largest category of differentially expressed genes between HCC tumor and adjacent tissue. Conclusion: We provide the first detailed characterization of CD73 glycosylation in normal and tumor tissue, revealing a novel mechanism that leads to the functional suppression of CD73 in human HCC tumor cells. The present findings have translational implications for therapeutic candidate antibodies targeting cell-surface CD73 in solid tumors and small-molecule adenosine receptor agonists that are in clinical development for HCC.

Cell type- and tissue-specific functions of ecto-5'-nucleotidase (CD73)

Ecto-5'-nucleotidase [cluster of differentiation 73 (CD73)] is a ubiquitously expressed glycosylphosphatidylinositol-anchored glycoprotein that converts extracellular adenosine 5'-monophosphate to adenosine. Anti-CD73 inhibitory antibodies are currently undergoing clinical testing for cancer immunotherapy. However, many protective physiological functions of CD73 need to be taken into account for new targeted therapies. This review examines CD73 functions in multiple organ systems and cell types, with a particular focus on novel findings from the last 5 years. Missense loss-of-function mutations in the CD73-encoding gene NT5E cause the rare disease "arterial calcifications due to deficiency of CD73." Aside from direct human disease involvement, cellular and animal model studies have revealed key functions of CD73 in tissue homeostasis and pathology across multiple organ systems. In the context of the central nervous system, CD73 is antinociceptive and protects against inflammatory damage, while also contributing to age-dependent decline in cortical plasticity. CD73 preserves barrier function in multiple tissues, a role that is most evident in the respiratory system, where it inhibits endothelial permeability in an adenosine-dependent manner. CD73 has important cardioprotective functions during myocardial infarction and heart failure. Under ischemia-reperfusion injury conditions, rapid and sustained induction of CD73 confers protection in the liver and kidney. In some cases, the mechanism by which CD73 mediates tissue injury is less clear. For example, CD73 has a promoting role in liver fibrosis but is protective in lung fibrosis. Future studies that integrate CD73 regulation and function at the cellular level with physiological responses will improve its utility as a disease target.

Inhibition of the adenosinergic pathway: the indispensable part of oncological therapy in the future

In recent years, immunotherapy has produced many unexpected breakthroughs in oncological therapy; however, it still has many deficiencies. For example, the number of patients who are unresponsive to anti-programmed death-ligand 1 (PD-L1), anti-cytotoxic T-like antigen-4 (CTLA4), and anti-programmed death-1 (PD1) therapies cannot be ignored, and the search for an undiscovered immunosuppressive pathway is imminent. Five decades ago, researchers found that activation of the adenosinergic pathway was negatively correlated with prognosis in many cancers. This review describes the entire process of the adenosinergic pathway in the tumor microenvironment and the mechanism of immunosuppression, which promotes tumor metastasis and drug resistance. Additionally, the review explores factors that regulate this pathway, including signaling factors secreted by the tumor microenvironment and certain anti-tumor drugs. Additionally, the combination of adenosinergic pathway inhibitors with chemotherapy, checkpoint blockade therapy, and immune cell-based therapy is summarized. Finally, certain issues regarding treatment via inhibition of this pathway and the use of targeted nanoparticles to reduce adverse reactions in patients are put forward in this review. Graphical Abstract The inhibitors of adenosinergic pathway loaded nanoparticles enter tumor tissue through EPR effect, and inhibit adenosinergic pathway to enhance or restore the effect of immune checkpoint blockade therapy, chemotherapies and immune cell-based therapy. Note: EPR means enhanced penetration and retention, × means blockade.

Targeting the Adenosinergic Axis in Chronic Lymphocytic Leukemia: A Way to Disrupt the Tumor Niche?

Targeting adenosine triphosphate (ATP) metabolism and adenosinergic signaling in cancer is gaining momentum, as increasing evidence is showing their relevance in tumor immunology and biology. Chronic lymphocytic leukemia (CLL) results from the expansion of a population of mature B cells that progressively occupies the bone marrow (BM), the blood, and peripheral lymphoid organs. Notwithstanding significant progress in the treatment of these patients, the cure remains an unmet clinical need, suggesting that novel drugs or drug combinations are needed. A unique feature of CLL is its reliance on micro-environmental signals for proliferation and cell survival. We and others have shown that the lymphoid niche, an area of intense interactions between leukemic and bystander non-tumor cells, is a typically hypoxic environment. Here adenosine is generated by leukemic cells, as well as by cells of myeloid origin, acting through autocrine and paracrine mechanisms, ultimately affecting tumor growth, limiting drug responses, and skewing the immune cells towards a tolerant phenotype. Hence, understanding the mechanisms through which this complex network of enzymes, receptors, and metabolites functions in CLL, will pave the way to the use of pharmacological agents targeting the system, which, in combination with drugs targeting leukemic cells, may get us one step closer to curing these patients.

CD73 Regulates Stemness and Epithelial-Mesenchymal Transition in Ovarian Cancer-Initiating Cells

Cancer-initiating cells (CICs) have been implicated in tumor development and aggressiveness. In ovarian carcinoma (OC), CICs drive tumor formation, dissemination, and recurrence, as well as drug resistance, thus accounting for the high death-to-incidence ratio of this neoplasm. However, the molecular mechanisms that underlie such a pathogenic role of ovarian CICs (OCICs) remain elusive. Here, we have capitalized on primary cells either from OC or from its tissues of origin to obtain the transcriptomic profile associated with OCICs. Among the genes differentially expressed in OCICs, we focused on CD73, which encodes the membrane-associated 5′-ectonucleotidase. The genetic inactivation of CD73 in OC cells revealed that this molecule is causally involved in sphere formation and tumor initiation, thus emerging as a driver of OCIC function. Furthermore, functional inhibition of CD73 via either a chemical compound or a neutralizing antibody reduced sphere formation and tumorigenesis, highlighting the druggability of CD73 in the context of OCIC-directed therapies. The biological function of CD73 in OCICs required its enzymatic activity and involved adenosine signaling. Mechanistically, CD73 promotes the expression of stemness and epithelial-mesenchymal transition-associated genes, implying a regulation of OCIC function at the transcriptional level. CD73, therefore, is involved in OCIC biology and may represent a therapeutic target for innovative treatments aimed at OC eradication.

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CD73 is enriched in ovarian cancer-initiating cells (OCICs)

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CD73 orchestrates OCIC stemness and EMT

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OC initiation and growth require CD73 activity

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OCIC-associated CD73 is a therapeutic target useful for OC eradication

Eviction from the sanctuary: Development of targeted therapy against cell adhesion molecules in acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is a malignant hematological disease afflicting hematopoiesis in the bone marrow. While 80%-90% of patients diagnosed with ALL will achieve complete remission at some point during treatment, ALL is associated with high relapse rate, with a 5-year overall survival rate of 68%. The initial remission failure and the high rate of relapse can be attributed to intrinsic chemoprotective mechanisms that allow persistence of ALL cells despite therapy. These mechanisms are mediated, at least in part, through the engagement of cell adhesion molecules (CAMs) within the bone marrow microenvironment. This review assembles CAMs implicated in protection of leukemic cells from chemotherapy. Such studies are limited in ALL. Therefore, CAMs that are associated with poor outcomes or are overexpressed in ALL and have been shown to be involved in chemoprotection in other hematological cancers are also included. It is likely that these molecules play parallel roles in ALL because the CAMs identified to be a factor in ALL chemoresistance also work similarly in other hematological malignancies. We review the signaling mechanisms activated by the engagement of CAMs that provide protection from chemotherapy. Development of targeted therapies against CAMs could improve outcome and raise the overall cure rate in ALL.

Up-regulated Ectonucleotidases in Fas-Associated Death Domain Protein- and Receptor-Interacting Protein Kinase 1-Deficient Jurkat Leukemia Cells Counteract Extracellular ATP/AMP Accumulation via Pannexin-1 Channels during Chemotherapeutic Drug-Induced Apoptosis

Pannexin-1 (Panx1) channels mediate the efflux of ATP and AMP from cancer cells in response to induction of extrinsic apoptosis by death receptors or intrinsic apoptosis by chemotherapeutic agents. We previously described the accumulation of extracellular ATP /AMP during chemotherapy-induced apoptosis in Jurkat human leukemia cells. In this study, we compared how different signaling pathways determine extracellular nucleotide pools in control Jurkat cells versus Jurkat lines that lack the Fas-associated death domain (FADD) or receptor-interacting protein kinase 1 (RIP1) cell death regulatory proteins. Tumor necrosis factor-α induced extrinsic apoptosis in control Jurkat cells and necroptosis in FADD-deficient cells; treatment of both lines with chemotherapeutic drugs elicited similar intrinsic apoptosis. Robust extracellular ATP/AMP accumulation was observed in the FADD-deficient cells during necroptosis, but not during apoptotic activation of Panx1 channels. Accumulation of extracellular ATP/AMP was similarly absent in RIP1-deficient Jurkat cells during apoptotic responses to chemotherapeutic agents. Apoptotic activation triggered equivalent proteolytic gating of Panx1 channels in all three Jurkat cell lines. The differences in extracellular ATP/AMP accumulation correlated with cell-line-specific expression of ectonucleotidases that metabolized the released ATP/AMP. CD73 mRNA, and αβ-methylene-ADP-inhibitable ecto-AMPase activity were elevated in the FADD-deficient cells. In contrast, the RIP1-deficient cells were defined by increased expression of tartrate-sensitive prostatic acid phosphatase as a broadly acting ectonucleotidase. Thus, extracellular nucleotide accumulation during regulated tumor cell death involves interplay between ATP/AMP efflux pathways and different cell-autonomous ectonucleotidases. Differential expression of particular ectonucleotidases in tumor cell variants will determine whether chemotherapy-induced activation of Panx1 channels drives accumulation of immunostimulatory ATP versus immunosuppressive adenosine within the tumor microenvironment.

Adenosine signaling mediates hypoxic responses in the chronic lymphocytic leukemia microenvironment

The chronic lymphocytic leukemia (CLL) niche is a closed environment where leukemic cells derive growth and survival signals through their interaction with macrophages and T lymphocytes. Here, we show that the CLL lymph node niche is characterized by overexpression and activation of HIF-1α, which increases adenosine generation and signaling, affecting tumor and host cellular responses. Hypoxia in CLL lymphocytes modifies central metabolic pathways, protects against drug-driven apoptosis, and induces interleukin 10 (IL-10) production. In myeloid cells, it forces monocyte differentiation to macrophages expressing IRF4, IDO, CD163, and CD206, hallmarks of the M2 phenotype, which promotes tumor progression. It also induces IL-6 production and enhances nurturing properties. Low oxygen levels decrease T-cell proliferation, promote glycolysis, and cause the appearance of a population of PD-1⁺ and IL-10-secreting T cells. Blockade of the A2A adenosine receptor counteracts these effects on all cell populations, making leukemic cells more susceptible to pharmacological agents while restoring immune competence and T-cell proliferation. Together, these results indicate that adenosine signaling through the A2A receptor mediates part of the effects of hypoxia. They also suggest that therapeutic strategies to inhibit the adenosinergic axis may be useful adjuncts to chemotherapy or tyrosine kinase inhibitors in the treatment of CLL patients.

Antiproliferative and proapoptotic effects of a pyrrole containing arylthioindole in human Jurkat leukemia cell line and multidrug-resistant Jurkat/A4 cells

Recently, a series of novel arylthioindole compounds, potent inhibitors of tubulin polymerization and cancer cell growth, were synthesized. In the present study the effects of 2-(1H-pyrrol-3-yl)-3-((3,4,5-trimethoxyphenyl)thio)-1H-indole (ATI5 compound) on cell proliferation, cell cycle progression, and induction of apoptosis in human T-cell acute leukemia Jurkat cells and their multidrug resistant Jurkat/A4 subline were investigated. Treatment of the Jurkat cells with the ATI5 compound for 48 hrs resulted in a strong G2/M cell cycle arrest and p53-independent apoptotic cell death accompanied by the induction of the active form of caspase-3 and poly(ADP-ribose) polymerase-1 (PARP-1) cleavage. ATI5 treatment also caused non-cell death related mitotic arrest in multidrug resistant Jurkat/A4 cells after 48 hrs of treatment suggesting promising opportunities for the further design of pyrrole-containing ATI compounds as anticancer agents. Cell death resistance of Jurkat/A4 cells to ATI5 compound was associated with alterations in the expression of pro-survival and anti-apoptotic protein-coding and microRNA genes. More importantly, findings showing that ATI5 treatment induced p53-independent apoptosis are of great importance from a therapeutic point of view since p53 mutations are common genetic alterations in human neoplasms.

Targeting CD73 in the tumor microenvironment with MEDI9447

MEDI9447 is a human monoclonal antibody that is specific for the ectoenzyme CD73 and currently undergoing Phase I clinical trials. Here we show that MEDI9447 is a potent inhibitor of CD73 ectonucleotidase activity, with wide ranging immune regulatory consequences. MEDI9447 results in relief from adenosine monophosphate (AMP)-mediated lymphocyte suppression in vitro and inhibition of mouse syngeneic tumor growth in vivo. In contrast with other cancer immunotherapy agents such as checkpoint inhibitors or T-cell agonists, MEDI9447 drives changes in both myeloid and lymphoid infiltrating leukocyte populations within the tumor microenvironment of mouse models. Changes include significant alterations in a number of tumor micro-environmental subpopulations including increases in CD8⁺ effector cells and activated macrophages. Furthermore, these changes correlate directly with responder and non-responder subpopulations within animal studies using syngeneic tumors. Combination data showing additive activity between MEDI9447 and anti-PD-1 antibodies using human cells in vitro and mouse tumor models further demonstrate the potential value of relieving adenosine-mediated immunosuppression. Based on these data, a Phase I study to test the safety, tolerability, and clinical activity of MEDI9447 in cancer patients was initiated (NCT02503774).

Extracellular Adenosine Production by ecto-5'-Nucleotidase (CD73) Enhances Radiation-Induced Lung Fibrosis

Radiation-induced pulmonary fibrosis is a severe side effect of thoracic irradiation, but its pathogenesis remains poorly understood and no effective treatment is available. In this study, we investigated the role of the extracellular adenosine as generated by the ecto-5'-nucleotidase CD73 in fibrosis development after thoracic irradiation. Exposure of wild-type C57BL/6 mice to a single dose (15 Gray) of whole thorax irradiation triggered a progressive increase in CD73 activity in the lung between 3 and 30 weeks postirradiation. In parallel, adenosine levels in bronchoalveolar lavage fluid (BALF) were increased by approximately 3-fold. Histologic evidence of lung fibrosis was observed by 25 weeks after irradiation. Conversely, CD73-deficient mice failed to accumulate adenosine in BALF and exhibited significantly less radiation-induced lung fibrosis (P < 0.010). Furthermore, treatment of wild-type mice with pegylated adenosine deaminase or CD73 antibodies also significantly reduced radiation-induced lung fibrosis. Taken together, our findings demonstrate that CD73 potentiates radiation-induced lung fibrosis, suggesting that existing pharmacologic strategies for modulating adenosine may be effective in limiting lung toxicities associated with the treatment of thoracic malignancies. Cancer Res; 76(10); 3045-56. ©2016 AACR.

Ecto-5'-nucleotidase expression is associated with the progression of renal cell carcinoma

Renal cell carcinoma (RCC) is a common tissue tumor that occurs across all age groups and has become one of the types of cancer with the fastest increasing incidence. Due to the resistance of RCC chemo- and radiotherapy, surgery is the only currently effective treatment. Therefore, specific markers for the diagnosis and prognosis of RCC are expected to result in novel methods of treatment. Ecto-5'-nucleotidase, also termed cluster of differentiation (CD)73, is a protein that is activated in several types of aggressive cancer and may promote cancer progression. CD73 was examined in the present study to determine the association between the protein and RCC. The expression levels of CD73 in 159 RCC tissue sections and 30 paratumorous normal renal tissue samples obtained from 235 patients that underwent nephrectomy were examined by immunohistochemical staining. By contrast, the expression level of P-glycoprotein (P-gp), a potential prognostic factor in RCC, was also examined in 85 RCC and 13 normal tissue samples. Intense CD73 expression was identified in 75 out of 159 RCC cell membranes compared with normal renal tissues. In contrast, there was high P-gp expression in the blood vessels of 42 out of 85 RCC tissues and there was no significant difference between the P-gp expression identified in RCC cells (34 out of 85) and the cell membrane of normal renal cells (2 out of 13). The expression level of CD73 in RCC cells was significantly associated with tumor type, tumor node metastasis (TNM) stage, and tumor grade. However, the expression of P-gp in RCC cells was only associated with the TNM stage and tumor grade. Using a multivariable Cox regression analysis, it was found that the median survival rate of RCC patients with intense CD73 expression in RCC cells was 62.06±5.35 months, which was drastically shorter compared with rare CD73 expression (103.72±3.67 months). In conclusion, the expression level of CD73 is significantly associated with RCC tumor progression and may serve as a favorable marker for the diagnosis and prognosis of RCC, in addition to being a therapeutic target for the treatment of RCC.

Alternative splicing of human NT5E in cirrhosis and hepatocellular carcinoma produces a negative regulator of ecto-5'-nucleotidase (CD73)

Alternative splicing of human NT5E generates CD73S, an endoplasmic reticulum–associated and dimerization-deficient glycoprotein that lacks enzymatic activity. CD73S functions as a negative regulator of canonical CD73 by promoting its proteasomal degradation, which may have significance in chronic liver disease and liver cancer.

Ecto-5′-nucleotidase (CD73), encoded by NT5E, is the major enzymatic source of extracellular adenosine. CD73 controls numerous pathophysiological responses and is a potential disease target, but its regulation is poorly understood. We examined NT5E regulation by alternative splicing. Genomic database analysis of human transcripts led us to identify NT5E-2, a novel splice variant that was expressed at low abundance in normal human tissues but was significantly up-regulated in cirrhosis and hepatocellular carcinoma (HCC). NT5E-2 encodes a shorter CD73 isoform we named CD73S. The presence of CD73S protein, which lacks 50 amino acids, was detected in HCC using an isoform-specific antibody. A noncanonical mouse mRNA, similar to human CD73S, was observed, but the corresponding protein was undetectable. The two human isoforms exhibited functional differences, such that ectopic expression of canonical CD73 (CD73L) in human HepG2 cells was associated with decreased expression of the proliferation marker Ki67, whereas CD73S expression did not have an effect on Ki67 expression. CD73S was glycosylated, catalytically inactive, unable to dimerize, and complexed intracellularly with the endoplasmic reticulum chaperone calnexin. Furthermore, CD73S complexed with CD73L and promoted proteasome-dependent CD73L degradation. The findings reveal species-specific CD73 regulation, with potential significance to cancer, fibrosis, and other diseases characterized by changes in CD73 expression and function.

HIV "elite controllers" are characterized by a high frequency of memory CD8+ CD73+ T cells involved in the antigen-specific CD8+ T-cell response

Human immunodeficiency virus type 1 (HIV-1) infection is characterized by chronic immune activation and suppressed T-lymphocyte functions. Here we report that CD73, both a coactivator molecule of T cells and an immunosuppressive ecto-enzyme through adenosine production, is only weakly expressed by CD8+ T cells of HIV-infected patients and only partially restored after successful antiviral treatment. CD73 expression on CD8+ T cells correlates inversely with cell activation both ex vivo and in vitro. However, CD8+ T cells from HIV controllers (HICs), which spontaneously control HIV replication, express CD73 strongly, despite residual immune activation. Finally, we demonstrate that CD73 is involved in the HIV-specific CD8+ T-cell expansion. Thus, we show that CD73 is central to the functionality of HIV-specific CD8+ T cells and that the preservation of HIV-specific CD73+ CD8+ T cells is a characteristic of HICs. These observations reveal a novel mechanism involved in the control of viral replication.

Potential prognostic biomarker CD73 regulates epidermal growth factor receptor expression in human breast cancer

CD73, an ecto-enzyme overexpressed in breast-cancer cells, catalyzes the dephosphorylation of adenosine monophosphates into adenosine. Anti-CD73 slows breast cancer growth and its spread both in vivo and in vitro. In this study, we investigated the relation of CD73 to epidermal growth factor receptor (EGFR) expression using tissue array and breast cancer cell lines. We found that CD73 expression correlated positively to EGFR expression in vivo (n = 80, r = 0.425, P < 0.01) and in vitro. EGFR expression can be decreased by suppressing CD73 with an inhibitor or small shRNA, and this effect was reversed by adenosine and NECA (adenosine A2 receptor agonist), which suggested that adenosine is involved in EGFR expression regulated by CD73 (P < 0.01). We also showed that CD73 regulates EGFR phosphorylation by Src (P < 0.01). By transcription factor (TF) assay, CD73 was found to regulate some associated TFs activity such as PPARγ, which mediates EGFR expression, although whether PPARγ mediates the effect of CD73 on EGFR expression needs further study. The Kaplan-Meier recurrence-free survival curves for CD73 were also plotted in www.kmplot.com. The curves show that CD73 expression separates the cases into significantly different prognostic groups among the estrogen receptor-negative cancers (P < 0.01). Our results suggest that CD73 may be a potential prognostic biomarker associated with coexpression of EGFR in human breast cancer.

Graft-versus-host disease is enhanced by selective CD73 blockade in mice

CD73 functions as an ecto-5′-nucleotidase to produce extracellular adenosine that has anti-inflammatory and immunosuppressive activity. We here demonstrate that CD73 helps control graft-versus-host disease (GVHD) in mouse models. Survival of wild-type (WT) recipients of either allogeneic donor naïve CD73 knock-out (KO) or WT T cells was similar suggesting that donor naïve T cell CD73 did not contribute to GVHD. By contrast, donor CD73 KO CD4⁺CD25⁺ regulatory T cells (Treg) had significantly impaired ability to mitigate GVHD mortality compared to WT Treg, suggesting that CD73 on Treg is critical for GVHD protection. However, compared to donor CD73, recipient CD73 is more effective in limiting GVHD. Pharmacological blockade of A2A receptor exacerbated GVHD in WT recipients, but not in CD73 KO recipients, suggesting that A2 receptor signaling is primarily implicated in CD73-mediated GVHD protection. Moreover, pharmacological blockade of CD73 enzymatic activity induced stronger alloreactive T cell activity, worsened GVHD and enhanced the graft-versus-leukemia (GVL) effect. These findings suggest that both donor and recipient CD73 protects against GVHD but also limits GVL effects. Thus, either enhancing or blocking CD73 activity has great potential clinical application in allogeneic bone marrow transplants.

Cellular function and molecular structure of ecto-nucleotidases

Ecto-nucleotidases play a pivotal role in purinergic signal transmission. They hydrolyze extracellular nucleotides and thus can control their availability at purinergic P2 receptors. They generate extracellular nucleosides for cellular reuptake and salvage via nucleoside transporters of the plasma membrane. The extracellular adenosine formed acts as an agonist of purinergic P1 receptors. They also can produce and hydrolyze extracellular inorganic pyrophosphate that is of major relevance in the control of bone mineralization. This review discusses and compares four major groups of ecto-nucleotidases: the ecto-nucleoside triphosphate diphosphohydrolases, ecto-5'-nucleotidase, ecto-nucleotide pyrophosphatase/phosphodiesterases, and alkaline phosphatases. Only recently and based on crystal structures, detailed information regarding the spatial structures and catalytic mechanisms has become available for members of these four ecto-nucleotidase families. This permits detailed predictions of their catalytic mechanisms and a comparison between the individual enzyme groups. The review focuses on the principal biochemical, cell biological, catalytic, and structural properties of the enzymes and provides brief reference to tissue distribution, and physiological and pathophysiological functions.

NT5E CpG island methylation is a favourable breast cancer biomarker

BACKGROUND

Relapse risk assessment and individual treatment recommendations remain suboptimal for breast cancer patients. In the light of existing preclinical and clinical data, we studied NT5E (5'-nucleotidase, ecto) expression and NT5E CpG island methylation in breast cancer.

METHODS

We used RT-PCR, qPCR, methylation-specific PCR and pyrosequencing to analyse NT5E in breast carcinoma cell lines and primary and breast carcinomas.

RESULTS

NT5E CpG island methylation was inversely associated with NT5E expression in breast carcinoma cell lines. In clinical series, patients whose primary tumours had NT5E CpG island methylation were less likely to develop metastasis (P=0.003, OR=0.34, 95% CI: 0.17-0.69). In 3/4 paired samples, NT5E was methylated in primary tumours and demethylated in CNS metastases. Patients progressing to non-visceral as compared with visceral metastases were more likely to have NT5E CpG island methylation in primary tumours (P=0.01, OR=11.8). Patients with tumours lacking detectable methylation had shorter disease-free survival (DFS) (P=0.001, HR=2.7) and overall survival (OS) (P=0.001, HR=3). The favourable prognostic value of NT5E methylation was confirmed in oestrogen receptor negative (P=0.011, HR=3.27, 95% CI: 1.31-8.12) and in triple negative cases (P=0.004; HR=6.2, 95% CI: 1.9-20). Moreover, we observed a more favourable outcome to adjuvant chemotherapy in patients whose tumours were positive for NT5E CpG island methylation: DFS (P=0.0016, HR=5.1, 95% CI: 1.8-14.37) and OS (P=0.0005, HR=7.4, 95% CI: 2.416-23.08).

CONCLUSION

NT5E CpG island methylation is a promising breast cancer biomarker.

CD73-generated extracellular adenosine in chronic lymphocytic leukemia creates local conditions counteracting drug-induced cell death

Extracellular adenosine (ADO), generated from ATP or ADP through the concerted action of the ectoenzymes CD39 and CD73, elicits autocrine and paracrine effects mediated by type 1 purinergic receptors. We have tested whether the expression of CD39 and CD73 by chronic lymphocytic leukemia (CLL) cells activates an adenosinergic axis affecting growth and survival. By immunohistochemistry, CD39 is widely expressed in CLL lymph nodes, whereas CD73 is restricted to proliferation centers. CD73 expression is highest on Ki-67(+) CLL cells, adjacent to T lymphocytes, and is further localized to perivascular areas. CD39(+)/CD73(+) CLL cells generate ADO from ADP in a time- and concentration-dependent manner. In peripheral blood, CD73 expression occurs in 97/299 (32%) CLL patients and pairs with CD38 and ZAP-70 expression. CD73-generated extracellular ADO activates type 1 purinergic A2A receptors that are constitutively expressed by CLL cells and that are further elevated in proliferating neoplastic cells. Activation of the ADO receptors increases cytoplasmic cAMP levels, inhibiting chemotaxis and limiting spontaneous drug-induced apoptosis of CLL cells. These data are consistent with the existence of an autocrine adenosinergic loop, and support engraftment of leukemic cells in growth-favorable niches, while simultaneously protecting from the action of chemotherapeutic agents.

Inactivation of CD73 promotes atherogenesis in apolipoprotein E-deficient mice

AIMS

CD73 (ecto-5'-nucleotidase) is expressed by a broad range of immune cells and attenuates inflammation in several acute disease models. This study therefore explored the role of CD73-derived adenosine in a model of chronic vascular inflammation such as atherogenesis.

METHODS AND RESULTS

CD73(-/-) mice were backcrossed into the apolipoprotein E (ApoE(-/-)) background. In CD73(-/-)/ApoE(-/-) double mutants, atherosclerotic lesion formation was increased by ∼50% compared with ApoE(-/-). However, the cellular composition and extracellular matrix of the plaques did not differ. Surprisingly, we found significant activity and expression of CD73 in the plaque of ApoE(-/-) mice which increased over time. CD73 co-localized with macrophages, Tregs, and cells of mesenchymal origin. Genome-wide microarray analysis of the aorta lacking CD73 revealed upregulation of endothelin-1 (Edn1) mRNA together with changes of genes in lipid metabolism and the Wnt and nuclear factor kappa B pathways. Measurement of plasma levels verified the upregulation of Edn1 in CD73(-/-) and double mutants. Plasma triglycerides (TG) were also found to be significantly elevated in the CD73(-/-)/ApoE(-/-) mice compared with ApoE(-/-) controls.

CONCLUSION

Lack of CD73 promotes atherogenesis most likely by de-inhibition of resident macrophages and T cells. Elevated Edn1 and TG levels may have contributed. This establishes CD73-derived adenosine as a direct or indirect regulator of atherogenesis.

Colony-stimulating factor 2 inhibits induction of apoptosis in the bovine preimplantation embryo

PROBLEM

Addition of colony-stimulating factor 2 (CSF2) to culture medium increases post-transfer survival of bovine embryos. Here we provide evidence that one mechanism by which CSF2 affects the embryo is through inhibition of apoptosis.

METHOD OF STUDY

In the first experiment, genes and pathways whose expression were regulated by CSF2 were identified by microarray analysis. Embryos were treated with 10 ng/ml CSF2 or vehicle at Day 5 after insemination; morulae were selected for microarray analysis at Day 6. In a second experiment, antiapoptotic effects of CSF2 were determined. Embryos were treated with CSF2 or vehicle at Day 5. On Day 6 (24 h after treatment), morulae were cultured for 15 h at either 42°C (a temperature that induces apoptosis) or 38.5°C (cow body temperature).

RESULTS

In the first experiment, a total of 214 genes were differentially regulated and 160 of these could be annotated (67 upregulated genes and 93 downregulated genes). Differentially expressed genes could be placed in 13 biological process ontologies in four functional groups (development and differentiation process, cell communication, apoptosis and cell adhesion). Antiapoptotic effects of CSF2 were confirmed in the second experiment because the magnitude of the increase in TUNEL positive cells caused by heat shock was reduced by CSF2.

CONCLUSION

CSF2 blocks apoptosis in bovine embryos through actions associated with regulation of genes controlling apoptosis.

RNAi-mediated CD73 suppression induces apoptosis and cell-cycle arrest in human breast cancer cells

Ecto-5'-nucleotidase (CD73), a cell surface protein that hydrolyzes extracellular AMP into adenosine and phosphate, is overexpressed in many solid tumors. In this study, we tested the hypothesis that increased CD73 may promote tumor progression by examining the effect of CD73 suppression via RNA interference and CD73 overexpression on tumor growth in vivo and in vitro. Using digitized whole-body images, plate clone forming assay and TUNEL assay in frozen tissue sections, we found that the cell growth rate was significantly lower in vivo and in vitro after CD73 suppression and late apoptosis was much higher in xenograft tumors developed from the CD73-siRNA transfected MB-MDA-231 clone (P1). By flow cytometry, the P1 cell cycle was arrested in the G0/G1 phase. Moreover, Bcl-2 was downregulated, while Bax and caspase-3 were upregulated with CD73 suppression. CD73 inhibitor α,β-methylene adenosine-5'-disphosphate (APCP) functioned similarly with RNAi-mediated CD73 suppression. In addition, in transfected MCF-7 cells, we found that CD73 overexpression increased cell viability and promoted cell cycle progression, depending on its enzyme activity. More intriguingly, CD73 overexpression in MCF-7 breast cancer cells produces a tumorigenic phenotype. We conclude that CD73 plays an important role in breast cancer growth by affecting cell cycle progression and apoptosis.

Development of potent and selective inhibitors of ecto-5'-nucleotidase based on an anthraquinone scaffold

ecto-5'-Nucleotidase (eN, CD73) plays a major role in controlling extracellular adenosine levels. eN inhibitors have potential as novel drugs, for example, for the treatment of cancer. In the present study, we synthesized and investigated a series of 55 anthraquinone derivatives as potential inhibitors of eN, 11 of which are novel compounds and another 11 of which had previously been described but have now been synthesized by an improved method. We identified several potent inhibitors of rat eN. The most potent compounds were 1-amino-4-[4-fluoro-2-carboxyphenylamino]-9,10-dioxo-9,10-dihydroanthracene-2-sulfonate (45, PSB-0952, K(i) = 260 nM) and 1-amino-4-[2-anthracenylamino]-9,10-dioxo-9,10-dihydroanthracene-2-sulfonate (52, PSB-0963, 150 nM), with 52 being the most potent eN inhibitor described to date. Selected compounds were further characterized and found to exhibit a competitive mechanism of inhibition. Investigations of ecto-nucleoside triphosphate diphosphohydrolases (NTPDases) and the P2Y receptor subtypes P2Y(2), P2Y(4), P2Y(6), and P2Y(12) showed that compound 45 exhibited the highest degree of selectivity (>150-fold).

CD73 represses pro-inflammatory responses in human endothelial cells

BACKGROUND

CD73 is a 5'-ectonucleotidase that produces extracellular adenosine, which then acts on G protein-coupled purigenic receptors to induce cellular responses. CD73 has been reported to regulate expression of pro-inflammatory molecules in mouse endothelium. Our aim is to determine the function of CD73 in human endothelial cells.

METHODS

We used RNAi to deplete CD73 levels in human umbilical cord endothelial cells (HUVECs).

RESULTS

CD73 depletion resulted in a strong reduction in adenosine production, indicating that CD73 is the major source of extracellular adenosine in HUVECs. We find that CD73 depletion induces a similar response to pro-inflammatory stimuli such as the cytokine TNF-alpha. In CD73-depleted cells, surface levels of the leukocyte adhesion molecules ICAM-1, VCAM-1 and E-selectin increase. This correlates with increased translocation of the transcription factor NF-kB to the nucleus, which is known to regulate ICAM-1, VCAM-1 and E-selectin expression in response to TNF-alpha. Adhesion of monocytic cells to endothelial cells is enhanced. In addition, CD73-depleted cells become elongated, have higher levels of stress fibres and increased endothelial permeability, resembling known responses to TNF-alpha.

CONCLUSIONS

These results indicate that CD73 normally suppresses pro-inflammatory responses in human endothelial cells.

Anti-CD73 antibody therapy inhibits breast tumor growth and metastasis

Extracellular adenosine is a potent immunosuppressor that accumulates during tumor growth. We performed proof-of-concept studies investigating the therapeutic potential and mechanism of action of monoclonal antibody (mAb)-based therapy against CD73, an ecto-enzyme overexpressed on breast-cancer cells that catalyzes the dephosphorylation of adenosine monophosphates into adenosine. We showed that anti-CD73 mAb therapy significantly delayed primary 4T1.2 and E0771 tumor growth in immune-competent mice and significantly inhibited the development of spontaneous 4T1.2 lung metastases. Notably, anti-CD73 mAb therapy was essentially dependent on the induction of adaptive anti-tumor immune responses. Knockdown of CD73 in 4T1.2 tumor cells confirmed the tumor-promoting effects of CD73. In addition to its immunosuppressive effect, CD73 enhanced tumor-cell chemotaxis, suggesting a role for CD73-derived adenosine in tumor metastasis. Accordingly, administration of adenosine-5'-N-ethylcarboxamide to tumor-bearing mice significantly enhanced spontaneous 4T1.2 lung metastasis. Using selective adenosine-receptor antagonists, we showed that activation of A2B adenosine receptors promoted 4T1.2 tumor-cell chemotaxis in vitro and metastasis in vivo. In conclusion, our study identified tumor-derived CD73 as a mechanism of tumor immune escape and tumor metastasis, and it also established the proof of concept that targeted therapy against CD73 can trigger adaptive anti-tumor immunity and inhibit metastasis of breast cancer.

Gene expression classifiers for relapse-free survival and minimal residual disease improve risk classification and outcome prediction in pediatric B-precursor acute lymphoblastic leukemia

To determine whether gene expression profiling could improve outcome prediction in children with acute lymphoblastic leukemia (ALL) at high risk for relapse, we profiled pretreatment leukemic cells in 207 uniformly treated children with high-risk B-precursor ALL. A 38-gene expression classifier predictive of relapse-free survival (RFS) could distinguish 2 groups with differing relapse risks: low (4-year RFS, 81%, n = 109) versus high (4-year RFS, 50%, n = 98; P < .001). In multivariate analysis, the gene expression classifier (P = .001) and flow cytometric measures of minimal residual disease (MRD; P = .001) each provided independent prognostic information. Together, they could be used to classify children with high-risk ALL into low- (87% RFS), intermediate- (62% RFS), or high- (29% RFS) risk groups (P < .001). A 21-gene expression classifier predictive of end-induction MRD effectively substituted for flow MRD, yielding a combined classifier that could distinguish these 3 risk groups at diagnosis (P < .001). These classifiers were further validated on an independent high-risk ALL cohort (P = .006) and retainedindependent prognostic significance (P < .001) in the presence of other recently described poor prognostic factors (IKAROS/IKZF1 deletions, JAK mutations, and kinase expression signatures). Thus, gene expression classifiers improve ALL risk classification and allow prospective identification of children who respond or fail current treatment regimens. These trials were registered at http://clinicaltrials.gov under NCT00005603.