Growth and metastasis of B16-F10 melanoma cells is not critically dependent on host CD73 expression in mice

Intracellular Delivery of Functional Proteins with DNA-Protein Nanogels-Lipids Complex

Using functional proteins for therapeutic purposes due to their high selectivity and/or catalytic properties can enable the control of various cellular processes; however, the transport of active proteins inside living cells remains a major challenge. In contrast, intracellular delivery of nucleic acids has become a routine method for a number of applications in gene therapy, genome editing, or immunization. Here we report a functionalizable platform constituting of DNA-protein nanogel carriers cross-linked through streptavidin-biotin or streptactin-biotin interactions and demonstrate its applicability for intracellular delivery of active proteins. We show that the nanogels can be loaded with proteins bearing either biotin, streptavidin, or strep-tag, and the resulting functionalized nanogels can be delivered into living cells after complexation with cationic lipid vectors. We use this approach for delivery of alkaline phosphatase enzyme, which is shown to keep its catalytic activity after internalization by mouse melanoma B16 cells, as demonstrated by the DDAO-phosphate assay. The resulting functionalized nanogels have dimensions on the order of 100 nm, contain around 100 enzyme molecules, and are shown to be transfectable at low lipid concentrations (charge ratio R± = 0.75). This ensures the low toxicity of our system, which in combination with high local enzyme concentration (∼100 μM) underlines potential interest of this nanoplatform for biomedical applications.

CD73 contributes to the pathogenesis of fusion-negative rhabdomyosarcoma through the purinergic signaling pathway

Rhabdomyosarcoma (RMS) is the most common type of soft tissue sarcoma in children and adolescents. Fusion-negative RMS (FN-RMS) accounts for more than 80% of all RMS cases. The long-term event-free survival rate for patients with high-grade FN-RMS is below 30%, highlighting the need for improved therapeutic strategies. CD73 is a 5' ectonucleotidase that hydrolyzes AMP to adenosine and regulates the purinergic signaling pathway. We found that CD73 is elevated in FN-RMS tumors that express high levels of TWIST2. While high expression of CD73 contributes to the pathogenesis of multiple cancers, its role in FN-RMS has not been investigated. We found that CD73 knockdown decreased FN-RMS cell growth while up-regulating the myogenic differentiation program. Moreover, mutation of the catalytic residues of CD73 rendered the protein enzymatically inactive and abolished its ability to stimulate FN-RMS growth. Overexpression of wildtype CD73, but not the catalytically inactive mutant, in CD73 knockdown FN-RMS cells restored their growth capacity. Likewise, treatment with an adenosine receptor A2A-B agonist partially rescued FN-RMS cell proliferation and bypassed the CD73 knockdown defective growth phenotype. These results demonstrate that the catalytic activity of CD73 contributes to the pathogenic growth of FN-RMS through the activation of the purinergic signaling pathway. Therefore, targeting CD73 and the purinergic signaling pathway represents a potential therapeutic approach for FN-RMS patients.

The Endogenous Dual Retinoid Receptor Agonist Alitretinoin Exhibits Immunoregulatory Functions on Antigen-Presenting Cells

Retinoids are a frequently used class of drugs in the treatment of inflammatory as well as malignant skin diseases. Retinoids have differential affinity for the retinoic acid receptor (RAR) and/or the retinoid X receptor (RXR). The endogenous dual RAR and RXR agonist alitretinoin (9-cis retinoic acid) demonstrated remarkable efficacy in the treatment of chronic hand eczema (CHE) patients; however, detailed information on the mechanisms of action remains elusive. Here, we used CHE as a model disease to unravel immunomodulatory pathways following retinoid receptor signaling. Transcriptome analyses of skin specimens from alitretinoin-responder CHE patients identified 231 significantly regulated genes. Bioinformatic analyses indicated keratinocytes as well as antigen presenting cells as cellular targets of alitretinoin. In keratinocytes, alitretinoin interfered with inflammation-associated barrier gene dysregulation as well as antimicrobial peptide induction while markedly inducing hyaluronan synthases without affecting hyaluronidase expression. In monocyte-derived dendritic cells, alitretinoin induced distinct morphological and phenotypic characteristics with low co-stimulatory molecule expression (CD80 and CD86), the increased secretion of IL-10 and the upregulation of the ecto-5'-nucleotidase CD73 mimicking immunomodulatory or tolerogenic dendritic cells. Indeed, alitretinoin-treated dendritic cells demonstrated a significantly reduced capacity to activate T cells in mixed leukocyte reactions. In a direct comparison, alitretinoin-mediated effects were significantly stronger than those observed for the RAR agonist acitretin. Moreover, longitudinal monitoring of alitretinoin-responder CHE patients could confirm in vitro findings. Taken together, we demonstrate that the dual RAR and RXR agonist alitretinoin targets epidermal dysregulation and demonstrates strong immunomodulatory effects on antigen presenting cell functions.

Influence of Various Light Regimes on Morphofunctional Condition of Transplantable Melanoma B16

A study of the morphofunctional condition of mice with transplantable melanoma B16 under the influence of a normal daylight regime, constant lighting and constant darkness was conducted. It was shown that exposure to constant lighting leads to intensification of the proliferation of melanoma cells, more significant growth and spread of the tumor, the development of more pronounced secondary changes, the presence of perivascular growth and an increase in perineural invasion. At the same time, keeping of animals in constant darkness significantly reduced the intensity of the proliferative process in the tumor and lead to tumor regression in the absence of signs of lympho-, intravascular and intraneural invasion. Intergroup differences in tumor cell status were confirmed by the results of micromorphometric studies. It was also shown that the expression of clock genes was suppressed by an exposure to constant light, while an influence of constant darkness, on contrary, led to its intensification.

Characteristic of Ultrastructure of Mice B16 Melanoma Cells under the Influence of Different Lighting Regimes

Circadian rhythms of physiological processes, constantly being in a state of dynamic equilibrium and plastically associated with changes in environmental conditions, are the basis of homeostasis of an organism of human and other mammals. Violation of circadian rhythms due to significant disturbances in parameters of main environmental effectors (desynchronosis) leads to the development of pathological conditions and a more severe course of preexisting pathologies. We conducted the study of the ultrastructure of cells of mice transplantable malignant melanoma B16 under the condition of normal (fixed) lighting regime and under the influence of constant lighting. Results of the study show that melanoma B16 under fixed light regime represents a characteristic picture of this tumor-predominantly intact tissue with safe junctions of large, functionally active cells with highly irregular nuclei, developed organelles and a relatively low content of melanin. The picture of the B16 melanoma tissue structure and the ultrastructure of its cells under the action of constant lighting stand in marked contrast to the group with fixed light: under these conditions the tumor exhibits accelerated growth, a significant number of cells in the state of apoptosis and necrosis, ultrastructural signs of degradation of the structure and functions, and signs of embryonization of cells with the background of adaptation to oxygen deficiency.

Targeting CD73 with AB680 (Quemliclustat), a Novel and Potent Small-Molecule CD73 Inhibitor, Restores Immune Functionality and Facilitates Antitumor Immunity

T cells play a critical role in the control of cancer. The development of immune checkpoint blockers (ICB) aimed at enhancing antitumor T-cell responses has revolutionized cancer treatment. However, durable clinical benefit is observed in only a subset of patients, prompting research efforts to focus on strategies that target multiple inhibitory signals within the tumor microenvironment (TME) to limit tumor evasion and improve patient outcomes. Adenosine has emerged as a potent immune suppressant within the TME, and CD73 is the major enzyme responsible for its extracellular production. CD73 can be co-opted within the TME to impair T-cell-mediated antitumor immunity and promote tumor growth. To target this pathway and block the formation of adenosine, we designed a novel, selective, and potent class of small-molecule inhibitors of CD73, including AB680 (quemliclustat), which is currently being tested in patients with cancer. AB680 effectively restored T-cell proliferation, cytokine secretion, and cytotoxicity that were dampened by the formation of immunosuppressive adenosine by CD73. Furthermore, in an allogeneic mixed lymphocyte reaction where CD73-derived adenosine had a dominant suppressive effect in the presence of PD-1 blockade, AB680 restored T-cell activation and function. Finally, in a preclinical mouse model of melanoma, AB680 inhibited CD73 in the TME and increased the antitumor activity of PD-1 blockade. Collectively, these data provide a rationale for the inhibition of CD73 with AB680 in combination with ICB, such as anti-PD-1, to improve cancer patient outcomes.

Melanization as unfavorable factor in amelanotic melanoma cell biology

The biology of three amelanotic melanoma cell lines (Ab, B16F10, and A375) of different species origin was analyzed during in vitro induced melanization in these cells. Melanin production was induced by DMEM medium characterized by a high level of L-tyrosine (a basic amino acid for melanogenesis). The biodiversity of amelanotic melanoma cells was confirmed by their different responses to melanogenesis induction; Ab hamster melanomas underwent intensive melanization, mouse B16F10 darkened slightly, while human A375 cells did not show any change in melanin content. Highly melanized Ab cells entered a cell death pathway, while slight melanization did not influence cell biology in a significant way. The rapid and high melanization of Ab cells induced apoptosis documented by phosphatidylserine externalization, caspase activation, and mitochondrial energetic state decrease. Melanoma cell type, culture medium, and time of incubation should be taken into consideration during amelanotic melanoma cell culture in vitro. L-tyrosine, as a concentration-dependent factor presented in the culture media, could stimulate some amelanotic melanoma cell lines (Ab, B16F10) to melanin production. The presence of melanin should be considered in the examination of antimelanoma compounds in vitro, because induction of melanin may interfere or be helpful in the treatment of amelanotic melanoma.

Metabolic Interplay between the Immune System and Melanoma Cells: Therapeutic Implications

Malignant melanoma represents the most fatal skin cancer due to its aggressive biological behavior and high metastatic potential. Treatment strategies for advanced disease have dramatically changed over the last years due to the introduction of BRAF/MEK inhibitors and immunotherapy. However, many patients either display primary (i.e., innate) or eventually develop secondary (i.e., acquired) resistance to systemic treatments. Treatment resistance depends on multiple mechanisms driven by a set of rewiring processes, which involve cancer metabolism, epigenetic, gene expression, and interactions within the tumor microenvironment. Prognostic and predictive biomarkers are needed to guide patients’ selection and treatment decisions. Indeed, there are no recognized clinical or biological characteristics that identify which patients will benefit more from available treatments, but several biomarkers have been studied with promising preliminary results. In this review, we will summarize novel tumor metabolic pathways and tumor-host metabolic crosstalk mechanisms leading to melanoma progression and drug resistance, with an overview on their translational potential as novel therapeutic targets.

The progression of metastatic melanoma augments a pro-oxidative milieu locally but not systemically

Malignant melanoma is the most dangerous form of skin cancer. Despite new therapies for melanoma treatment, effective therapy is mainly limited by excessive metastasis. Currently, the factors determining metastasis development are not elucidated, but oxidative stress was suggested to be involved. To this end, we analyzed oxidative stress parameters during the metastatic development using the syngeneic B16F10 melanoma model. An increase in blood plasma lipid peroxidation occurred at the earliest stage of the disease, with a progressive decrease in oxidative damage and an increase in antioxidant defense. Vice versa, increased lipid peroxidation and 3-nitrotyrosine, and decreased antioxidant parameters were observed in the metastatic nodules throughout the disease. This was concomitant with a progressive increase in vascular endothelial growth factor and proliferating cell nuclear antigen. We conclude that the oxidative stress in the bloodstream decreases during the metastatic process and that nitrosative stress increases during the proliferation and growth of metastatic nodules in the tumor microenvironment. These results will help to better understand the role of oxidative stress during melanoma metastasis.

Varied functions of immune checkpoints during cancer metastasis

Immune checkpoints comprise diverse receptors and ligands including costimulatory and inhibitory molecules, which play monumental roles in regulating the immune system. Immune checkpoints retain key potentials in maintaining the immune system homeostasis and hindering the malignancy development and autoimmunity. The expression of inhibitory immune checkpoints delineates an increase in a plethora of metastatic tumors and the inhibition of these immune checkpoints can be followed by promising results. On the other hand, the stimulation of costimulatory immune checkpoints can restrain the metastasis originating from diverse tumors. From the review above, key findings emerged regarding potential functions of inhibitory and costimulatory immune checkpoints targeting the metastatic cascade and point towards novel potential Achilles’ heels of cancer that might be exploited therapeutically in the future.

BIRC2 Expression Impairs Anti-Cancer Immunity and Immunotherapy Efficacy

Immune checkpoint blockade (ICB) has led to therapeutic responses in some cancer patients for whom no effective treatment previously existed. ICB acts on T lymphocytes and other immune cells that are inactivated due to checkpoint signals that inhibit their infiltration and function within tumors. But for more than 80% of patients, immunotherapy has not been effective. Here, we demonstrate a cancer-cell-intrinsic mechanism of immune evasion and resistance to ICB mediated by baculoviral IAP repeat-containing 2 (BIRC2). Knockdown of BIRC2 expression in mouse melanoma or breast cancer cells increases expression of the chemokine CXCL9 and impairs tumor growth by increasing the number of intratumoral activated CD8⁺ T cells and natural killer cells. Administration of anti-CXCL9 neutralizing antibody inhibits the recruitment of CD8⁺ T cells and natural killer cells to BIRC2-deficient tumors. Most importantly, BIRC2 deficiency dramatically increases the sensitivity of mouse melanoma and breast tumors to anti-CTLA4 and/or anti-PD1 ICB.

Characterization of the N6-etheno-bridge method to assess extracellular metabolism of adenine nucleotides: detection of a possible role for purine nucleoside phosphorylase in adenosine metabolism

The goal of this study was to determine the validity of using N6-etheno-bridged adenine nucleotides to evaluate ecto-nucleotidase activity. We observed that the metabolism of N6-etheno-ATP versus ATP was quantitatively similar when incubated with recombinant CD39, ENTPD2, ENTPD3, or ENPP-1, and the quantitative metabolism of N6-etheno-AMP versus AMP was similar when incubated with recombinant CD73. This suggests that ecto-nucleotidases process N6-etheno-bridged adenine nucleotides similarly to endogenous adenine nucleotides. Four cell types rapidly (t1/2, 0.21 to 0.66 h) metabolized N6-etheno-ATP. Applied N6-etheno-ATP was recovered in the medium as N6-etheno-ADP, N6-etheno-AMP, N6-etheno-adenosine, and surprisingly N6-etheno-adenine; intracellular N6-etheno compounds were undetectable. This suggests minimal cellular uptake, intracellular metabolism, or deamination of these compounds. N6-etheno-ATP, N6-etheno-ADP, N6-etheno-AMP, N6-etheno-adenosine, and N6-etheno-adenine had little affinity for recombinant A1, A2A, or A2B receptors, for a subset of P2X receptors (3H-α,β-methylene-ATP binding to rat bladder membranes), or for a subset of P2Y receptors (35S-ATP-αS binding to rat brain membranes), suggesting minimal pharmacological activity. N6-etheno-adenosine was partially converted to N6-etheno-adenine in four different cell types; this was blocked by purine nucleoside phosphorylase (PNPase) inhibition. Intravenous N6-etheno-ATP was quickly metabolized, with N6-etheno-adenine being the main product in naïve rats, but not in rats pretreated with a PNPase inhibitor. PNPase inhibition reduced the urinary excretion of endogenous adenine and attenuated the conversion of exogenous adenosine to adenine in the renal cortex. The N6-etheno-bridge method is a valid technique to assess extracellular metabolism of adenine nucleotides by ecto-nucleotidases. Also, rats express an enzyme with PNPase-like activity that metabolizes N6-etheno-adenosine to N6-etheno-adenine.

Morphological Characteristic of Melanoma B16 Progression in C57BL/6 Mice with High and Low Resistance to Hypoxia

The features of B16 melanoma progression in male C57BL/6 mice with initially high and low resistance to hypoxia were studied. To assess the resistance to hypoxia, the mice were placed in a low-pressure chamber at a simulated altitude of 10,000 m. One month after testing, B16 melanoma was inoculated to high- and low-resistant animals. In 19 days after melanoma transplantation, the severity of melanoma progression was assessed by morphological and immunofluorescent methods. The expression of vegf-a and hif-1a in the liver of melanomabearing and control mice was evaluated by real-time PCR. Tumor growth progression was more pronounced in low-resistant mice, which was seen from high weight of the primary tumor node, relative necrosis area, proliferation rates (mitotic index and number of Ki-67+ cells), and expression of vegf-a gene in the liver. In high-resistant to hypoxia animals, the number of caspase-3+ cells dying by apoptosis was higher. The data on more rapid melanoma progression in mice with low resistance to hypoxia should be considered during the search of new prognostic markers and methods for therapy of malignant neoplasms.

CD73 (Cluster of Differentiation 73) and the Differences Between Mice and Humans

As vascular disease is complex and the various manifestations are influenced by differences in vascular bed architecture, exposure to shear and mechanical forces, cell types involved, and inflammatory responses, in vivo models are necessary to recapitulate the complex physiology and dynamic cellular interactions during pathogenesis. Murine knockout models are commonly used tools for investigators to study the role of a specific gene or pathway in multifaceted disease traits. Although valuable, these models are not perfect, and this is particularly true in regard to CD73 (cluster of differentiation 73), the extracellular enzyme that generates adenosine from AMP. At baseline, CD73-deficient mice do not present with an overt phenotype, whereas CD73-deficient humans present with the complex phenotype of vascular calcification, arteriomegaly and tortuosity, and calcification in small joints. In this review, we highlight the differences between the mouse and human systems and discuss the potential to leverage findings in mice to inform us on the human conditions.

Development of a MEL Cell-Derived Allograft Mouse Model for Cancer Research

Murine erythroleukemia (MEL) cells are often employed as a model to dissect mechanisms of erythropoiesis and erythroleukemia in vitro. Here, an allograft model using MEL cells resulting in splenomegaly was established to develop a diagnostic model for isolation/quantification of metastatic cells, anti-cancer drug screening, and evaluation of the tumorigenic or metastatic potentials of molecules in vivo. In this animal model, circulating MEL cells from the blood stream were successfully isolated and quantified with an additional in vitro cultivation step. In terms of the molecular-pathological analysis, we were able to successfully evaluate the functional discrimination between methyl-CpG-binding domain 2 (Mbd2) and p66α in erythroid differentiation, and tumorigenic potential in spleen and blood stream of allograft model mice. In addition, we found that the number of circulating MEL cells in anti-cancer drug-treated mice was dose-dependently decreased. Our data demonstrate that the newly established allograft model is useful to dissect erythroleukemia pathologies and non-invasively provides valuable means for isolation of metastatic cells, screening of anti-cancer drugs, and evaluation of the tumorigenic potentials.

The metabolic milieu in melanoma: Role of immune suppression by CD73/adenosine

The mechanisms leading to immune escape of melanoma have been largely investigated in relation to its tumour immunogenicity and features of inflamed microenvironment that promote the immune suppression during the disease progression. These findings have recently led to advantages in terms of immunotherapy-based approaches as rationale for overcoming the immune escape. However, besides immune checkpoints, other mechanisms including the adenosine produced by ectonucleotidases CD39 and CD73 contribute to the melanoma progression due to the immunosuppression induced by the tumour milieu. On the other hand, CD73 has recently emerged as both promising therapeutic target and unfavourable prognostic biomarker. Here, we review the major mechanisms of immune escape activated by the CD39/CD73/adenosine pathway in melanoma and focus potential therapeutic strategies based on the control of CD39/CD73 downstream adenosine receptor signalling. These evidences provide the basis for translational strategies of immune combination, while CD73 would serve as potential prognostic biomarker in metastatic melanoma.

Metabolic adaptation of cancer and immune cells mediated by hypoxia-inducible factors

Cancer cells are characterized by high metabolic demand. The substrates in demand include oxygen, glucose, glutamine and lipids. Oxygen serves as a key substrate in cellular metabolism and bioenergetics. Hypoxia or low oxygen abundance is a common feature of the tumor microenvironment that occurs due to an imbalance in supply and demand. Many of the metabolic responses to hypoxia in both cancer cells and stromal cells are orchestrated by hypoxia-inducible factors (HIFs). In this review we summarize our current understanding of how HIFs modulate the metabolism of hypoxic cancer cells and immune cells, and how altered metabolism plays a role in cancer progression.

Controlling the Immune Suppressor: Transcription Factors and MicroRNAs Regulating CD73/NT5E

The NT5E (CD73) molecule represents an ecto-5′-nucleotidase expressed on the cell surface of various cell types. Hydrolyzing extracellular adenosine monophosphate into adenosine and inorganic phosphate, NT5E performs numerous homeostatic functions in healthy organs and tissues. Importantly, NT5E can act as inhibitory immune checkpoint molecule, since free adenosine generated by NT5E inhibits cellular immune responses, thereby promoting immune escape of tumor cells. MicroRNAs (miRNAs) are small non-coding RNA molecules regulating gene expression on posttranscriptional level through binding to mRNAs, resulting in translational repression or degradation of the targeted mRNA molecule. In tumor cells, miRNA expression patterns are often altered which in turn might affect NT5E surface expression and eventually influence the efficacy of antitumor immune responses. This review describes the diverse roles of NT5E, summarizes current knowledge about transcription factors controlling NT5E expression, and highlights the significance of miRNAs involved in the posttranscriptional regulation of NT5E expression.

VEGF/PKD-1 signaling mediates arteriogenic gene expression and angiogenic responses in reversible human microvascular endothelial cells with extended lifespan

Microvascular ECs (MVECs) are an ideal model in angiogenesis research. The aim of this study was to determine vascular endothelial growth factor (VEGF)/protein kinase D1 (PKD-1) signaling in expression of arteriogenic genes in human MVECs. To achieve this aim, we transduced specific SV40 large T antigen and telomerase into primary human dermal MVECs (HMVEC-D) to establish reversible HMVECs with extended lifespan (HMVECi-D). HMVECi-D was then exposed to VEGF/VEGF-inducer GS4012 or transduced with constitutively active protein kinase PKD-1 (PKD-CA). Quantitative RT-PCR was performed to detect arteriogenic gene expression. Furthermore, the angiogenic capacity in response to VEGF pathway was evaluated by Matrigel tube-formation and proliferation assays. We observed that VEGF/PKD-1 signaling axis significantly stimulated the expression of arteriogenic genes and promoted EC proliferation, along with downregulation of CD36 expression. Intriguingly, overexpression of PKD-CA also resulted in formation of tip cell morphology, accompanied by increased mRNA of delta-like ligand 4 (DLL4). In conclusion, we have successfully established and characterized HMVECi-D, and showed that VEGF/PKD-1 signaling axis increases angiogenic and arteriogenic gene expression. These studies suggest that the axis may regulate arteriolar differentiation through changing MVEC gene expression.

Switching off CD73: a way to boost the activity of conventional and targeted antineoplastic therapies

Over the past few years, several preclinical studies have highlighted the value of CD73 (ecto-5'-nucleotidase) as a potential therapeutic target for cancer therapy. Indeed, the pharmacological blockade of CD73, via monoclonal antibodies or small molecules, has promise in counteracting cancer development, growth and spread. Synergistic combinations of anti-CD73 drugs with conventional cancer treatments (i.e., chemotherapy, radiation therapy, immunotherapy, targeted therapy) have increased therapeutic potential. In this review, we discuss the potential synergistic effects of CD73 blockers and conventional antineoplastic therapies in the treatment of cancer.

Tiamulin inhibits breast cancer growth and pulmonary metastasis by decreasing the activity of CD73

BACKGROUND

Metastasis is the leading cause of death in breast cancer patients. CD73, also known as ecto-5'-nucleotidase, plays a critical role in cancer development including metastasis. The existing researches indicate that overexpression of CD73 promotes growth and metastasis of breast cancer. Therefore, CD73 inhibitor can offer a promising treatment for breast cancer. Here, we determined whether tiamulin, which was found to inhibit CD73, was able to suppress breast cancer development and explored the related mechanisms.

METHODS

We firstly measured the effect of tiamulin hydrogen fumarate (THF) on CD73 using high performance liquid chromatography (HPLC). Then, we investigated cell proliferation, migration and invasion in MDA-MB-231 human breast cancer cell line and 4 T1 mouse breast cancer cell line treated with THF by migration assay, invasion assay and activity assay. Besides, we examined the effect of THF on syngeneic mammary tumors of mice by immunohistochemistry.

RESULTS

Our data demonstrated that THF inhibited CD73 by decreasing the activity instead of the expression of CD73. In vitro, THF inhibited the proliferation, migration and invasion of MDA-MB-231 and 4 T1 cells by suppressing CD73 activity. In vivo, animal experiments showed that THF treatment resulted in significant reduction in syngeneic tumor growth, microvascular density and lung metastasis rate.

CONCLUSIONS

Our results indicate that THF inhibits growth and metastasis of breast cancer by blocking the activity of CD73, which may offer a promising treatment for breast cancer therapy.

Melanoma growth and lymph node metastasis is independent of host CD169 expression

Metastasis to the lymph node is a frequent and early event in tumour dissemination. Tumour soluble factors, including extracellular vesicles, condition host organs for metastatic tumour spread, thereby facilitating tumour cell migration and survival. In the peripheral lymphatics, extracellular vesicles are captured via their sialic acids by lymph node macrophages expressing the CD169 (sialoadhesin) molecule, thereby suppressing the immune response. We hypothesised that the CD169 molecule could modulate primary tumour growth and invasion into the regional lymph node by altering the immune response to tumour extracellular vesicles, or by directly interacting with invading tumour cells. No significant difference was noted in primary tumour growth between wild-type and CD169^-/- mice, and protection against tumour challenge with tumour extracellular vesicle immunisation was similar between the strains. Subcutaneous implantation of B16 (F1 or F10) into the ventral-carpal aspect of forelimb resulted in melanoma infiltration into the axillary and brachial lymph nodes. CD169^-/- mice displayed a lower level of metastatic lymph node lesions, however this failed to reach statistical significance. Although CD169 participates in the immune response to tumour antigen and appears to be a positive prognostic marker for human cancers, its role in modulating melanoma growth and metastasis is less clear.

Purinergic regulation of the immune system

Cellular stress or apoptosis triggers the release of ATP, ADP and other nucleotides into the extracellular space. Extracellular nucleotides function as autocrine and paracrine signalling molecules by activating cell-surface P2 purinergic receptors that elicit pro-inflammatory immune responses. Over time, extracellular nucleotides are metabolized to adenosine, leading to reduced P2 signalling and increased signalling through anti-inflammatory adenosine (P1 purinergic) receptors. Here, we review how local purinergic signalling changes over time during tissue responses to injury or disease, and we discuss the potential of targeting purinergic signalling pathways for the immunotherapeutic treatment of ischaemia, organ transplantation, autoimmunity or cancer.

Specific Activation of A3, A2A and A1 Adenosine Receptors in CD73-Knockout Mice Affects B16F10 Melanoma Growth, Neovascularization, Angiogenesis and Macrophage Infiltration

CD73 (ecto-5'-nucleotidase), a cell surface enzyme hydrolyzing AMP to adenosine, was lately demonstrated to play a direct role in tumor progression including regulation of tumor vascularization. It was also shown to stimulate tumor macrophage infiltration. Interstitial adenosine, accumulating in solid tumors due to CD73 enzymatic activity, is recognized as a main mediator regulating the production of pro- and anti-angiogenic factors, but the engagement of specific adenosine receptors in tumor progression in vivo is still poorly researched. We have analyzed the role of high affinity adenosine receptors A₁, A_2A, and A₃ in B16F10 melanoma progression using specific agonists (CCPA, CGS-21680 and IB-MECA, respectively). We limited endogenous extracellular adenosine background using CD73 knockout mice treated with CD73 chemical inhibitor, AOPCP (adenosine α,β-methylene 5’-diphosphate). Activation of any adenosine receptor significantly inhibited B16F10 melanoma growth but only at its early stage. At 14th day of growth, the decrease in tumor neovascularization and MAPK pathway activation induced by CD73 depletion was reversed by all agonists. Activation of A₁AR primarily increased angiogenic activation measured by expression of VEGF-R2 on tumor blood vessels. However, mainly A₃AR activation increased both the microvessel density and expression of pro-angiogenic factors. All agonists induced significant increase in macrophage tumor infiltration, with IB-MECA being most effective. This effect was accompanied by substantial changes in cytokines regulating macrophage polarization between pro-inflammatory and pro-angiogenic phenotype. Our results demonstrate an evidence that each of the analyzed receptors has a specific role in the stimulation of tumor angiogenesis and confirm significantly more multifaceted role of adenosine in its regulation than was already observed. They also reveal previously unexplored consequences to extracellular adenosine signaling depletion in recently proposed anti-CD73 cancer therapy.

The role of extracellular-5'-nucleotidase/CD73 in glioma peritumoural brain edema

During pathological conditions, extracellular-5'-nucleotidase/CD73 can protect neurons by reducing the permeability of the blood brain barrier. In recent years, it has been demonstrated that CD73 can negatively contribute to the growth of gliomas; however, the function of CD73 in glioma blood vessels is not clear. We analysed the expression of CD73 in 72 glioma patients using immunohistochemistry and correspondingly compared the results with the Edema index (EI). We established an in vitro model of the blood-tumour barrier and analysed the expression of CD73 in vascular endothelial cells. Lastly, CD73 expression was inhibited in endothelial cells, and the effects of this inhibition on tight junction structure and transendothelial resistance were observed. Compared to normal brains, the expression of CD73 in blood vessels of glioma patients was significantly decreased, and the amount was lower in the centre of the tumour than the periphery. The proportion of CD73-positive blood vessels had a positive correlation with the EI. The expression of CD73 in the in vitro endothelial cell blood-tumour barrier model was decreased. Lastly, inhibiting CD73 was found to decrease the expression of tight junction related proteins in endothelial cells and to decrease the value of transendothelial electric resistance. The expression of CD73 in glioma blood vessels was significantly decreased, which may play a multi-functional role in decreasing the expression of tight junction related proteins of brain microvascular endothelial cells and may also increase blood-tumour barrier permeability and accelerate the formation of PTBE.

Anti-CD73 in cancer immunotherapy: awakening new opportunities

In recent years, cancer immunotherapy made significant advances due to a better understanding of the principles underlying tumor biology and immunology. In this context, CD73 is a key molecule, since via degradation of adenosine monophosphate into adenosine, endorses the generation of an immunosuppressed and pro-angiogenic niche within the tumor microenvironment that promotes the onset and progression of cancer. Targeting CD73 results in favorable antitumor effects in pre-clinical models and combined treatments of CD73 blockade with other immune-modulating agents (i.e. anti-CTLA-4 mAb or anti-PD1 mAb) is particularly attractive. Although there is still a long way to go, anti-CD73 therapy, through the development of CD73 monoclonal antibodies, can potentially constitute a new biologic therapy for cancer patients. In this review, we discuss the link between CD73 and the onset, development and spread of tumors, highlighting the potential value of this molecule as a target and as a novel biomarker in the context of personalized cancer therapy.

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.