Identification of sulfonic acids as efficient ecto-5′-nucleotidase inhibitors

Ectonucleotidase inhibitors: targeting signaling pathways for therapeutic advancement-an in-depth review

Ectonucleotidase inhibitors are a family of pharmacological drugs that, by selectively targeting ectonucleotidases, are essential in altering purinergic signaling pathways. The hydrolysis of extracellular nucleotides and nucleosides is carried out by these enzymes, which include ectonucleoside triphosphate diphosphohydrolases (NTPDases) and ecto-5'-nucleotidase (CD73). Ectonucleotidase inhibitors can prevent the conversion of ATP and ADP into adenosine by blocking these enzymes and reduce extracellular adenosine. These molecules are essential for purinergic signaling, which is associated with a variability of physiological and pathological processes. By modifying extracellular nucleotide metabolism and improving purinergic signaling regulation, ectonucleotide pyrophosphatase/phosphodiesterase (ENPP) inhibitors have the potential to improve cancer treatment, inflammatory management, and immune response modulation. Purinergic signaling is affected by CD73 inhibitors because they prevent AMP from being converted to adenosine. These inhibitors are useful in cancer therapy and immunotherapy because they may improve chemotherapy effectiveness and alter immune responses. Purinergic signaling is controlled by NTPDase inhibitors, which specifically target enzymes involved in extracellular nucleotide breakdown. These inhibitors show promise in reducing immunological responses, thrombosis, and inflammation, perhaps assisting in the treatment of cardiovascular and autoimmune illnesses. Alkaline phosphatase (ALP) inhibitors alter the function of enzymes involved in dephosphorylation reactions, which has an impact on a variety of biological processes. By altering the body's phosphate levels, these inhibitors may be used to treat diseases including hyperphosphatemia and certain bone problems. This article provides a guide for researchers and clinicians looking to leverage the remedial capability of ectonucleotidase inhibitors in a variety of illness scenarios by illuminating their processes, advantages, and difficulties.

Small molecular CD73 inhibitors: Recent progress and future perspectives

The occurrence and development of the tumor are very complex biological processes. In recent years, a large number of research data shows that CD73 is closely related to tumor growth and metastasis. It has been confirmed that the cascade hydrolysis of extracellular ATP to adenosine is one of the most important immunosuppressive regulatory pathways in the tumor microenvironment. The metabolite adenosine can mediate immunosuppression by activating adenosine receptor (such as A2A) on effector Immune cells and enable tumor cells to achieve immune escape. Therefore, attenuating or completely removing adenosine-mediated immunosuppression in the tumor microenvironment by inhibiting CD73 is a promising approach in the treatment of solid tumors. This paper focuses on the research progress of CD73 enzyme and CD73 small molecule inhibitors, and is expected to provide some insights into the development of small-molecule antitumor drugs targeting CD73.

Molecular Dynamics Simulations of the Human Ecto-5'-Nucleotidase (h-ecto-5'-NT, CD73): Insights into Protein Flexibility and Binding Site Dynamics

Human ecto-5'-nucleotidase (h-ecto-5'-NT, CD73) is a homodimeric Zn2+-binding metallophosphoesterase that hydrolyzes adenosine 5'-monophosphate (5'-AMP) to adenosine and phosphate. h-Ecto-5'-NT is a key enzyme in purinergic signaling pathways and has been recognized as a promising biological target for several diseases, including cancer and inflammatory, infectious, and autoimmune diseases. Despite its importance as a biological target, little is known about h-ecto-5'-NT dynamics, which poses a considerable challenge to the design of inhibitors of this target enzyme. Here, to explore h-ecto-5'-NT flexibility, all-atom unbiased molecular dynamics (MD) simulations were performed. Remarkable differences in the dynamics of the open (catalytically inactive) and closed (catalytically active) conformations of the apo-h-ecto-5'-NT were observed during the simulations, and the nucleotide analogue inhibitor AMPCP was shown to stabilize the protein structure in the closed conformation. Our results suggest that the large and complex domain motion that enables the h-ecto-5'-NT open/closed conformational switch is slow, and therefore, it could not be completely captured within the time scale of our simulations. Nonetheless, we were able to explore the faster dynamics of the h-ecto-5'-NT substrate binding site, which is mainly located at the C-terminal domain and well conserved among the protein's open and closed conformations. Using the TRAPP ("Transient Pockets in Proteins") approach, we identified transient subpockets close to the substrate binding site. Finally, conformational states of the substrate binding site with higher druggability scores than the crystal structure were identified. In summary, our study provides valuable insights into h-ecto-5'-NT structural flexibility, which can guide the structure-based design of novel h-ecto-5'-NT inhibitors.

Advances in CD73 inhibitors for immunotherapy: Antibodies, synthetic small molecule compounds, and natural compounds

Tumors, a disease with a high mortality rate worldwide, have become a serious threat to human health. Exonucleotide-5'-nucleotidase (CD73) is an emerging target for tumor therapy. Its inhibition can significantly reduce adenosine levels in the tumor microenvironment. It has a better therapeutic effect on adenosine-induced immunosuppression. In the immune response, extracellular ATP exerts immune efficacy by activating T cells. However, dead tumor cells release excess ATP, overexpress CD39 and CD73 on the cell membrane and catabolize this ATP to adenosine. This leads to further immunosuppression. There are a number of inhibitors of CD73 currently under investigation. These include antibodies, synthetic small molecule inhibitors and a number of natural compounds with prominent roles in the anti-tumor field. However, only a small proportion of the CD73 inhibitors studied to date have successfully reached the clinical stage. Therefore, effective and safe inhibition of CD73 in oncology therapy still holds great therapeutic potential. This review summarizes the currently reported CD73 inhibitors, describes their inhibitory effects and pharmacological mechanisms, and provides a brief review of them. It aims to provide more information for further research and development of CD73 inhibitors.

Targeting ecto-5'-nucleotidase: A comprehensive review into small molecule inhibitors and expression modulators

The purinergic signaling has drawn attention from academia and more recently from pharmaceutical industries as a potential therapeutic route for cancer treatment, since ATP may act as chemotactic agent and possess in vitro antineoplastic activity. On the other way, adenosine, produced in extracellular medium by ecto-5'-NT, acts as immunosuppressor and is related to neoangiogenesis, vasculogenesis and evasion to the immune system. Consequently, inhibitors of ecto-5'-NT may prevent tumor progression, reducing adenosine concentrations, preventing escape from the host's immune system and slowing cancer's growth. This review aims to highlight important biochemical and structural features of ecto-5'NT, highlight its expression profile in normal and cancer cell lines detailing compounds which may act as expression regulators and to review the several classes of ecto-5'NT inhibitors developed in the past 12 years, in order to build a general structure-activity relationship model to guide further compound design.

Identification of Phelligridin-Based Compounds as Novel Human CD73 Inhibitors

As an emerging immune checkpoint, CD73 has received more attention in the past decade. Inhibition of CD73 enzymatic activity can enhance antitumor immunity. Several CD73 inhibitors have been identified by in vitro assays in recent years, but they remain premature for clinical application, indicating that more novel CD73 inhibitors should be studied. Herein, we aimed to identify novel CD73 inhibitors that hopefully are suitable drug candidates by using computer-aided drug discovery and enzymatic-based assays. Five-hundred molecules with high binding affinity were retrieved from the Chemdiv-Plus database by using a structure-based virtual screening approach. Then, we analyzed the drug properties of these molecules and obtained 68 small molecules based on the oral noncentral nervous system (CNS) drug profile. The inhibition rates of these molecules against CD73 enzymatic activities were determined at a concentration of 100 μM, and 20 molecules had an inhibition rate greater than 20%, eight of which were dose-dependent, with IC50 values of 6.72-172.1 μM. Among the screening hits, phelligridin-based compounds had the best experimental inhibition values. Modeling studies indicate that the phelligridin group is sandwiched by the rings of F417 and F500 residues. The identified inhibitors have a molecular weight of approximately 500 Dal and are predicted to form primarily hydrogen bonds with CD73 in addition to hydrophobic stacking interactions. In conclusion, novel inhibitors with satisfactory drug properties may serve as lead compounds for the development of CD73-targeting drugs, and the binding modes may provide insight for phelligridin-based drug design.

Discovery of natural product ellagic acid as a potent CD73 and CD39 dual inhibitor

The ATP-adenosine pathway has been recently identified as an attractive immune-oncology target and several drug candidates have been entered clinic trials. Inspired by the report of the first small-molecule CD73inhibitor AB680, we describe the discovery of natural product ellagic acid as a dual CD73 and CD39 inhibitor with an IC₅₀ value of 1.85 ± 0.21 μM and 0.50 ± 0.22 μM, respectively. The result of cytotoxicity assays indicated that ellagic acid is a valuable lead compound with low cytotoxicity effect for immune therapy.

CD73 and cN-II regulate the cellular response to chemotherapeutic and hypoxic stress in lung adenocarcinoma cells

BACKGROUND

Cytosolic 5'-nucleotidase II (cN-II) and ecto-5'-nucleotidase (CD73) are enzymes involved in the nucleotide metabolism by dephosphorylating nucleoside monophosphates. Both enzymes are involved in cancer by modifying anticancer drug activity, cancer cell biology and immune modulation.

METHODS

We have modified lung cancer cells (NCI-H292) to become deficient for either or both enzymes using the CRISPR/Cas9 technique, and studied the implication of the two enzymes in the cellular response to different stress condition i.e. chemotherapeutic agents, hypoxia and nucleotide stress.

RESULTS

Our results show that there is no significant role of these enzymes in cell proliferation under hypoxic stress. Similarly, cN-II and CD73 are not involved in wound healing ability under CoCl₂-mediated HIF-1α stabilization. Furthermore, our results show that CD73-deficiency is associated with increased apoptosis in response to 1600 μM adenosine, decreased sensitivity to mitomycin and enhanced sensitivity to vincristine. cN-II deficiency increased in vivo tumor growth and sensitivity to vincristine and mitomycin C.

CONCLUSIONS

Our study gives new insights into the biological roles of cN-II and CD73 under stress conditions in this particular cancer cell line. Further experiments will help deciphering the molecular mechanisms underlying the observed differences.

Synthesis, Characterization, and In Silico Studies of Novel Spirooxindole Derivatives as Ecto-5'-Nucleotidase Inhibitors

Ecto-5'-nucleotidase (ecto-5'-NT, CD73) inhibitors are promising drug candidates for cancer therapy. Traditional efforts used to inhibit the ecto-5'-nucleotidase have involved antibody therapy or development of small molecule inhibitors that can mimic the acidic and ionizable structure of adenosine 5'-monophosphate (AMP). Herein, we report an efficient, environment friendly route for the synthesis of non-nucleotide based small molecules, i.e., substituted spirooxindole derivatives 9a-9l and investigated their inhibitory potential on human and rat recombinant ecto-5'-nucleotidase isozymes. These attempts have resulted in the identification of compound 9f (IC₅₀ = 0.15 ± 0.02 μM) inhibitor on h-ecto-5'-NT which showed 280-fold higher inhibition and compound 9h (IC₅₀ ± 0.19 ± 0.03 μM) on r-ecto-5'-NT with 406-fold enhanced inhibition than reference standard sulfamic acid. Moreover, in silico studies were carried out to assess binding interactions of potent compounds within enzyme active sites and demonstrated excellent correlation with the experimental findings.

Fluorescent Probes for Ecto-5'-nucleotidase (CD73)

Ecto-5'-nucleotidase (CD73) catalyzes the hydrolysis of AMP to anti-inflammatory, immunosuppressive adenosine. It is expressed on vascular endothelial, epithelial, and also numerous cancer cells where it strongly contributes to an immunosuppressive microenvironment. In the present study we designed and synthesized fluorescent-labeled CD73 inhibitors with low nanomolar affinity and high selectivity based on N ⁶ -benzyl-α,β-methylene-ADP (PSB-12379) as a lead structure. Fluorescein was attached to the benzyl residue via different linkers resulting in PSB-19416 (14b, K _i 12.6 nM) and PSB-18332 (14a, K _i 2.98 nM) as fluorescent high-affinity probes for CD73. These compounds are anticipated to become useful tools for biological studies, drug screening, and diagnostic applications.

Targeting Metabolism of Extracellular Nucleotides via Inhibition of Ectonucleotidases CD73 and CD39

In the tumor microenvironment, unusually high concentrations of extracellular adenosine promote tumor proliferation through various immunosuppressive mechanisms. Blocking adenosine production by inhibiting nucleotide-metabolizing enzymes, such as ectonucleotidases CD73 and CD39, represents a promising therapeutic strategy that may synergize with other immuno-oncology mechanisms and chemotherapies. Emerging small-molecule ectonucleotidase inhibitors have recently entered clinical trials. This Perspective will outline challenges, strategies, and recent advancements in targeting this class with small-molecule inhibitors, including AB680, the first small-molecule CD73 inhibitor to enter clinical development. Specific case studies, including structure-based drug design and lead optimization, will be outlined. Preclinical data on these molecules and their ability to enhance antitumor immunity will be discussed.

Orally Bioavailable Small-Molecule CD73 Inhibitor (OP-5244) Reverses Immunosuppression through Blockade of Adenosine Production

The adenosinergic pathway represents an attractive new therapeutic approach in cancer immunotherapy. In this pathway, ecto-5-nucleotidase CD73 has the unique function of regulating production of immunosuppressive adenosine (ADO) through the hydrolysis of AMP. CD73 is overexpressed in many cancers, resulting in elevated levels of ADO that correspond to poor patient prognosis. Therefore, reducing the level of ADO via inhibition of CD73 is a potential strategy for treating cancers. Based on the binding mode of adenosine 5'-(α,β-methylene)diphosphate (AOPCP) with human CD73, we designed a series of novel monophosphonate small-molecule CD73 inhibitors. Among them, OP-5244 (35) proved to be a highly potent and orally bioavailable CD73 inhibitor. In preclinical studies, 35 completely inhibited ADO production in both human cancer cells and CD8⁺ T cells. Furthermore, 35 lowered the ratio of ADO/AMP significantly and reversed immunosuppression in mouse models, indicating its potential as an in vivo tool compound for further development.

Sulfonylhydrazones: Design, synthesis and investigation of ectonucleotidase (ALP & e5'NT) inhibition activities

Medicinal importance of the sulfonylhydrazones is well-evident owing to their binding ability with zinc containing metalloenzymes. In the present study, we have synthesized different series of sulfonylhydrazones by using facile synthetic methods in good to excellent yield. All the successfully prepared sulfonylhydrazones were screened for ectonucleotidase (ALP & e5'NT) inhibitory activity. Among the chromen-2-one scaffold based sulfonylhydrazones, the compounds 7 was found to be most potent inhibitor for h-TNAP (human tissue non-specific alkaline phosphatase) and h-IAP (human intestinal alkaline phosphatase) with IC₅₀ values of 1.02 ± 0.13 and 0.32 ± 0.0 3 µM respectively, compared with levamisole (IC₅₀ = 25.2 ± 1.90 µM for h-TNAP) and l-phenylalanine (IC₅₀ = 100 ± 3.00 µM for h-IAP) as standards. Further, the chromen-2-one based molecule 5a showed excellent activity against h-ecto 5'-NT (human ecto-5'-nucleotidase) with IC₅₀ value of 0.29 ± 0.004 µM compared to standard, sulfamic acid (IC₅₀ = 42.1 ± 7.8 µM). However, among the series of phenyl ring based sulfonylhydrazones, compound 9d was found to be most potent against h-TNAP and h-IAP with IC₅₀ values of 0.85 ± 0.08 and 0.52 ± 0.03 µM, respectively. Moreover, in silico studies were also carried to demonstrate their putative binding with the target enzymes. The potent compounds 5a, 7, and 9d against different ectonucleotidases (h-ecto 5'-NT, h-TNAP, h-IAP) could potentially serve as lead for the development of new therapeutic agents.

2-Substituted α,β-Methylene-ADP Derivatives: Potent Competitive Ecto-5'-nucleotidase (CD73) Inhibitors with Variable Binding Modes

CD73 inhibitors are promising drugs for the (immuno)therapy of cancer. Here, we present the synthesis, structure-activity relationships, and cocrystal structures of novel derivatives of the competitive CD73 inhibitor α,β-methylene-ADP (AOPCP) substituted in the 2-position. Small polar or lipophilic residues increased potency, 2-iodo- and 2-chloro-adenosine-5'-O-[(phosphonomethyl)phosphonic acid] (15, 16) being the most potent inhibitors with K_i values toward human CD73 of 3-6 nM. Subject to the size and nature of the 2-substituent, variable binding modes were observed by X-ray crystallography. Depending on the binding mode, large species differences were found, e.g., 2-piperazinyl-AOPCP (21) was >12-fold less potent against rat CD73 compared to human CD73. This study shows that high CD73 inhibitory potency can be achieved by simply introducing a small substituent into the 2-position of AOPCP without the necessity of additional bulky N⁶-substituents. Moreover, it provides valuable insights into the binding modes of competitive CD73 inhibitors, representing an excellent basis for drug development.

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.

Be Aware of Aggregators in the Search for Potential Human ecto-5'-Nucleotidase Inhibitors

Promiscuous inhibition due to aggregate formation has been recognized as a major concern in drug discovery campaigns. Here, we report some aggregators identified in a virtual screening (VS) protocol to search for inhibitors of human ecto-5′-nucleotidase (ecto-5′-NT/CD73), a promising target for several diseases and pathophysiological events, including cancer, inflammation and autoimmune diseases. Four compounds (A, B, C and D), selected from the ZINC-11 database, showed IC₅₀ values in the micromolar range, being at the same time computationally predicted as potential aggregators. To confirm if they inhibit human ecto-5′-NT via promiscuous mechanism, forming aggregates, enzymatic assays were done in the presence of 0.01% (v/v) Triton X-100 and an increase in the enzyme concentration by 10-fold. Under both experimental conditions, these four compounds showed a significant decrease in their inhibitory activities. To corroborate these findings, turbidimetric assays were performed, confirming that they form aggregate species. Additionally, aggregation kinetic studies were done by dynamic light scattering (DLS) for compound C. None of the identified aggregators has been previously reported in the literature. For the first time, aggregation and promiscuous inhibition issues were systematically studied and evaluated for compounds selected by VS as potential inhibitors for human ecto-5′-NT. Together, our results reinforce the importance of accounting for potential false-positive hits acting by aggregation in drug discovery campaigns to avoid misleading assay results.

Comprehensive evaluation of NT5E/CD73 expression and its prognostic significance in distinct types of cancers

Background

CD73 is one of the critical component in the formation of immunosuppressive microenvironment in cancers. We aimed to provide an overview of the current status of CD73 expression and its relationship with clinicopathlogical features and prognosis in different cancers.

Methods

PubMed, Web of Science, EMBASE and Cochrane library were searched to identify the relevant studies. CD73 expression level in distinct cancers and its relationship with clinicopathlogical characteristics and prognosis were investigated using online database. Meta-analyses were conducted using RevMan v5.0 and STATA v12.0.

Results

Fourteen publications with 2951 cases were included. The incidence of high CD73 expression was 0.50 (95% CI: 0.36–0.63). Data from Oncomine validated that median CD73 expression level in tumor tissues was markedly higher than that in normal tissues in most kinds of cancers except cecum adenocarcinoma and ovarian cancer (P < 0.05). High CD73 expression was significantly correlated with shorter overall survival (OS) in various cancers (high risk [HR] = 1.48; P < 0.05). Subgroup analysis using online database demonstrated that high CD73 expression was significantly correlated with poor OS in breast (HR = 1.23; P < 0.05) and ovarian cancer (HR = 1.14; P < 0.05), but favorable OS in lung (HR = 0.80; P < 0.05) and gastric cancer (HR = 0.71; P < 0.05). High CD73 expression was dramatically associated with lymph node metastases (OR = 2.61; P = 0.05).

Conclusion

High CD73 expression was significantly associated with lymph node metastases and a promising prognostic factor in different types of cancers.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4073-7) contains supplementary material, which is available to authorized users.

Identification of allosteric inhibitors of the ecto-5'-nucleotidase (CD73) targeting the dimer interface

The ecto-5'-nucleotidase CD73 plays an important role in the production of immune-suppressive adenosine in tumor micro-environment, and has become a validated drug target in oncology. Indeed, the anticancer immune response involves extracellular ATP to block cell proliferation through T-cell activation. However, in the tumor micro-environment, two extracellular membrane-bound enzymes (CD39 and CD73) are overexpressed and hydrolyze efficiently ATP into AMP then further into immune-suppressive adenosine. To circumvent the impact of CD73-generated adenosine, we applied an original bioinformatics approach to identify new allosteric inhibitors targeting the dimerization interface of CD73, which should impair the large dynamic motions required for its enzymatic function. Several hit compounds issued from virtual screening campaigns showed a potent inhibition of recombinant CD73 with inhibition constants in the low micromolar range and exhibited a non-competitive inhibition mode. The structure-activity relationships studies indicated that several amino acid residues (D366, H456, K471, Y484 and E543 for polar interactions and G453-454, I455, H456, L475, V542 and G544 for hydrophobic contacts) located at the dimerization interface are involved in the tight binding of hit compounds and likely contributed for their inhibitory activity. Overall, the gathered information will guide the upcoming lead optimization phase that may lead to potent and selective CD73 inhibitors, able to restore the anticancer immune response.

Small molecule immuno-oncology therapeutic agents

Treatment of cancer by activation of an antitumor immune response is now a widely practiced and well-accepted approach to therapy. However, despite dramatic responses in some patients, the high proportion of unresponsive patients points to a considerable unmet medical need. Although antibody therapies have led the way, small molecule immuno-oncology agents are close behind. This perspective provides an overview of some of the many small molecule approaches being explored. It encompasses small molecule modulators of validated targets such as programed cell death 1 (PD-1) as well as novel approaches still to be proven clinically.

4-Aminopyridine based amide derivatives as dual inhibitors of tissue non-specific alkaline phosphatase and ecto-5'-nucleotidase with potential anticancer activity

Ecto-nucleotidase members i.e., ecto-5'-nucleotidase and alkaline phosphatase, hydrolyze extracellular nucleotides and play an important role in purinergic signaling. Their overexpression are implicated in a variety of pathological states, including immunological diseases, bone mineralization, vascular calcification and cancer, and thus they represent an emerging drug targets. In order to design potent and selective inhibitors, new derivatives of 4-aminopyridine have been synthesized (10a-10m) and their structures were established on the basis of spectral data. The effect of nature and position of substituent was interestingly observed and justified on the basis of their detailed structure activity relationships (SARs) against both families of ecto-nucleotidase. Compound 10a displayed significant inhibition (IC₅₀ ± SEM = 0.25 ± 0.05 µM) that was found ≈168 fold more potent as compared to previously reported inhibitor suramin (IC₅₀ ± SEM = 42.1 ± 7.8 µM). This compound exhibited 6 times more selectivity towards h-TNAP over h-e5'NT. The anticancer potential and mechanism were also established using cell viability assay, flow cytometric analysis and nuclear staining. Molecular docking studies were also carried out to gain insight into the binding interaction of potent compounds within the respective enzyme pockets and herring-sperm DNA.

Isonicotinohydrazones as inhibitors of alkaline phosphatase and ecto-5'-nucleotidase

A series of isonicotinohydrazide derivatives was synthesized and tested against recombinant human and rat ecto-5'-nucleotidases (h-e5'NT and r-e5'NT) and alkaline phosphatase isozymes including both bovine tissue-non-specific alkaline phosphatase (b-TNAP) and tissue-specific calf intestinal alkaline phosphatase (c-IAP). These enzymes are implicated in vascular calcifications, hypophosphatasia, solid tumors, and cancers, such as colon, lung, breast, pancreas, and ovary. All tested compounds were active against both enzymes. The most potent inhibitor of h-e5'NT was derivative (E)-N'-(1-(3-(4-fluorophenyl)-5-phenyl-4,5-dihydro-1H-pyrazol-1-yl)ethylidene)isonicotinohydrazide (3j), whereas derivative (E)-N'-(4-hydroxy-3-methoxybenzylidene)isonicotinohydrazide (3g) exhibited significant inhibitory activity against r-e5'NT. In addition, the derivative (E)-N'-(4'-chlorobenzylidene)isonicotinohydrazide (3a) was most potent inhibitor against calf intestinal alkaline phosphatase and the derivative (E)-N'-(4-hydroxy-3-methoxybenzylidene)isonicotinohydrazide (3g) was found to be most potent inhibitor of bovine tissue-non-specific alkaline phosphatase. Furthermore, putative binding modes of potent compounds against e5'NT (human and rat e5'NT) and AP (including b-TNAP and c-IAP) were determined computationally.

Inhibition of CD73 AMP hydrolysis by a therapeutic antibody with a dual, non-competitive mechanism of action

CD73 (ecto-5′-nucleotidase) has recently been established as a promising immuno-oncology target. Given its role in activating purinergic signaling pathways to elicit immune suppression, antagonizing CD73 (i.e., releasing the brake) offers a complimentary pathway to inducing anti-tumor immune responses. Here, we describe the mechanistic activity of a new clinical therapeutic, MEDI9447, a human monoclonal antibody that non-competitively inhibits CD73 activity. Epitope mapping, structural, and mechanistic studies revealed that MEDI9447 antagonizes CD73 through dual mechanisms of inter-CD73 dimer crosslinking and/or steric blocking that prevent CD73 from adopting a catalytically active conformation. To our knowledge, this is the first report of an antibody that inhibits an enzyme's function through 2 distinct modes of action. These results provide a finely mapped epitope that can be targeted for selective, potent, and non-competitive inhibition of CD73, as well as establish a strategy for inhibiting enzymes that function in both membrane-bound and soluble states.

CD73-adenosine: a next-generation target in immuno-oncology

Cancer immunotherapy has entered in a new era with the development of first-generation immune checkpoint inhibitors targeting the PD1/PD-L1 and CTLA-4 pathways. In this context, considerable research effort is being deployed to find the next generation of cancer immunotherapeutics. The CD73-adenosine axis constitutes one of the most promising pathways in immuno-oncology. We and others have demonstrated the immunosuppressive role of CD73-adenosine in cancer and established proof-of-concept that the targeted blockade of CD73 or adenosine receptors could effectively promote anti-tumor immunity and enhance the activity of first-generation immune checkpoint blockers. With Phase I clinical trials now underway evaluating anti-CD73 or anti-A2A therapies in cancer patients, we here discuss the fundamental, preclinical and clinical findings related to the role of the CD73-adenosinergic pathway in tumor immunity.

Targeting CD73 and downstream adenosine receptor signaling in triple-negative breast cancer

INTRODUCTION

Despite significant improvements in diagnosis and therapy over the past 20 years, breast cancer remains a worldwide public health issue. In particular, triple negative breast cancer (TNBC), a subset of very aggressive breast tumors, is associated with a poor prognosis and has very few efficient therapeutic options. The ectonucleotidase CD73 has recently emerged as a promising new target for TNBC in preclinical models. Pharmacological targeting of CD73 and downstream adenosine A2A/A2B receptor signaling is currently an active field of research that could lead to the development of new cancer therapeutics, including options against TNBC.

AREAS COVERED

This article reviews the basic structural and molecular features of CD73 and its role in the development of cancer, with a particular focus on CD73's role in the biology of TNBC.

EXPERT OPINION

It was recently demonstrated that CD73 expression in TNBC is associated with worse clinical outcomes and increased resistance to anthracycline chemotherapy. Targeted blockade of the CD73/A2A axis has been shown to impair various aspects of tumorigenesis and displays synergism with other anti-cancer treatments in preclinical studies. Hence, we strongly argue for the development of CD73 inhibitors and for the repositioning of A2A antagonists in cancer.