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

Dysregulation in CD39/CD73 Axis May Trigger the Upsurge of the Immune Suppressive Agent Adenosine in OSA Patients

INTRODUCTION

Although higher incidence of cancer represents a major burden for obstructive sleep apnea (OSA) patients, the molecular pathways driving this association are not completely understood. Interestingly, adenosinergic signaling has emerged as a powerful immune checkpoint driving tumor development and progression.

METHODS

Here, we explored the expression of the adenosinergic ecto-enzymes CD39 and CD73 in T-lymphocytes of OSA patients without any evidence of cancer, as well as their soluble forms in plasma (sCD39 and sCD73), along with adenosine. In addition, we explored the role of intermittent hypoxia (IH) in this context by in vitro models.

RESULTS

Our results showed that CD39 is upregulated while CD73 is downregulated in OSA T-cells' membrane. Moreover, our findings suggest that IH, through HIF-1, mediates the upregulation of both CD39 and CD73; and that CD73 downregulation could be mediated by a higher release of sCD73 by OSA T-lymphocytes. Importantly, we found that both sCD39 and sCD73 are upregulated in OSA plasma, suggesting T-lymphocytes as a potential source for plasmatic sCD73. Finally, our data propose the alterations in CD39/CD73 axis could underlie the upsurge of adenosine levels in the plasma of OSA patients.

CONCLUSION

Our study reveals a hypoxia-mediated alteration of the CD39/CD73 axis in OSA patients, which could trigger ADO upregulation, thus potentially contributing to the immune suppressive environment and ultimately facilitating tumor development and progression. Therefore, our data highlights the need for new longitudinal studies evaluating CD39 and/or CD73 as potential cancer-risk prognostic biomarkers in OSA patients.

Effect of adenosine treatment on ionizing radiation toxicity in zebrafish early life stages

The danger of ionizing radiation exposure to human health is a concern. Since its wide use in medicine and industry, the development of radioprotectors has been very significant. Adenosine exerts anti-inflammatory actions and promotes tissue protection and repair, by activating the P1 receptors (A1, A2A, A2B, and A3). Zebrafish (Danio rerio) is an appropriate tool in the fields of toxicology and pharmacology, including the evaluation of radiobiological outcomes and in the search for radioprotector agents. This study aims to evaluate the effect of adenosine in the toxicity induced by radiation in zebrafish. Embryos were treated with 1, 10, or 100 µM adenosine, 30 min before the exposure to 15 Gy of gamma radiation. Adenosine potentiated the effects of radiation in heart rate, body length, and pericardial edema. We evaluated oxidative stress, tissue remodeling and inflammatory. It was seen that 100 µM adenosine reversed the inflammation induced by radiation, and that A2A2 and A2B receptors are involved in these anti-inflammatory effects. Our results indicate that P1R activation could be a promising pharmacological strategy for radioprotection.

Small molecule inhibitors for cancer immunotherapy and associated biomarkers - the current status

Following the success of cancer immunotherapy using large molecules against immune checkpoint inhibitors, the concept of using small molecules to interfere with intracellular negative regulators of anti-tumor immune responses has emerged in recent years. The main targets for small molecule drugs currently include enzymes of negative feedback loops in signaling pathways of immune cells and proteins that promote immunosuppressive signals within the tumor microenvironment. In the adaptive immune system, negative regulators of T cell receptor signaling (MAP4K1, DGKα/ζ, CBL-B, PTPN2, PTPN22, SHP1), co-receptor signaling (CBL-B) and cytokine signaling (PTPN2) have been preclinically validated as promising targets and initial clinical trials with small molecule inhibitors are underway. To enhance innate anti-tumor immune responses, inhibitory immunomodulation of cGAS/STING has been in the focus, and inhibitors of ENPP1 and TREX1 have reached the clinic. In addition, immunosuppressive signals via adenosine can be counteracted by CD39 and CD73 inhibition, while suppression via intratumoral immunosuppressive prostaglandin E can be targeted by EP2/EP4 antagonists. Here, we present the status of the most promising small molecule drug candidates for cancer immunotherapy, all residing relatively early in development, and the potential of relevant biomarkers.

CD39/CD73/A2AR pathway and cancer immunotherapy

Cancer development is closely associated with immunosuppressive tumor microenvironment (TME) that attenuates antitumor immune responses and promotes tumor cell immunologic escape. The sequential conversion of extracellular ATP into adenosine by two important cell-surface ectonucleosidases CD39 and CD73 play critical roles in reshaping an immunosuppressive TME. The accumulated extracellular adenosine mediates its regulatory functions by binding to one of four adenosine receptors (A1R, A2AR, A2BR and A3R). The A2AR elicits its profound immunosuppressive function via regulating cAMP signaling. The increasing evidence suggests that CD39, CD73 and A2AR could be used as novel therapeutic targets for manipulating the antitumor immunity. In recent years, monoclonal antibodies or small molecule inhibitors targeting the CD39/CD73/A2AR pathway have been investigated in clinical trials as single agents or in combination with anti-PD-1/PD-L1 therapies. In this review, we provide an updated summary about the pathophysiological function of the adenosinergic pathway in cancer development, metastasis and drug resistance. The targeting of one or more components of the adenosinergic pathway for cancer therapy and circumvention of immunotherapy resistance are also discussed. Emerging biomarkers that may be used to guide the selection of CD39/CD73/A2AR-targeting treatment strategies for individual cancer patients is also deliberated.

Targeting purinergic pathway to enhance radiotherapy-induced immunogenic cancer cell death

Emerging evidence has demonstrated that radiotherapy (RT) can not only cause direct damage to cancer cells but also lead to immunogenic cell death (ICD), which involves the activation of host antitumor immune response in tumor immune microenvironment (TIME). RT-induced ICD comprises the release of damage-associated molecular patterns (DAMPs) from dying cancer cells that result in the activation of tumor-specific immunity to elicit long-term antitumor efficacy in both original and abscopal tumor sites. Adenosine triphosphate (ATP), as an important DAMP released by irradiated cancer cells and an essential factor within purinergic pathway, can be further hydrolyzed to adenosine (ADO) by two key ectonucleotidases, CD39 and CD73, to further modulate the antitumor immunity in TIME through purinergic signaling via the interaction to its specific receptors such as adenosine 2A receptor (A2AR) and A2BR widely expressed on the surface of the components in TIME, including cancer cells and many immune effector cells. In this review, we first introduced key components in purinergic pathway including ATP, ADO, their receptors, and essential ectonucleotidases. Then we reviewed the regulation of ATP and ADO levels and their main mechanisms by which they promote tumor growth and broadly suppress antitumor immunity through inhibiting the pro-inflammatory response of dendritic cells, cytotoxic T lymphocytes, and natural killer cells, while improving the anti-inflammatory response of regulatory T cells, macrophages, and myeloid-derived suppressor cells in TIME, especially after irradiation. Finally, we presented an overview of dozens of promising therapeutics including pharmacological antagonists and specific antibodies targeting ADO receptors and ectonucleotidases CD39 or CD73 investigated in the clinic for cancer treatment, especially focusing on the preclinical studies and clinical trials being explored for blocking the purinergic signaling to enhance RT as a combination antitumor therapeutic strategy, which has a robust potential to be translated to the clinic in the future.

Transcriptional Dynamics of DNA Damage Responsive Genes in Circulating Leukocytes during Radiotherapy

Simple Summary

In this study, the transcriptional response of a panel of radiation responsive genes was monitored over time in blood samples after radiation exposure in vivo. For this aim, cancer patients treated by radiotherapy were recruited after consent forms were obtained. Following the first fraction of radiotherapy, 2 mL blood samples were collected at different time points during the first 24h hours (before the second fraction was delivered) and at mid and end of treatment. Amongst the 9 genes studied, the gene FDXR stood out as the most sensitive and responsive to the low dose of radiation received from the localised radiation treatment by the circulating white blood cells. The activation of FDXR was found to depend on the volume of the body exposed with a peak of expression around 8–9 hours after irradiation was delivered. Finally results obtained ex vivo confirmed the results obtained in vivo.

Abstract

External beam radiation therapy leads to cellular activation of the DNA damage response (DDR). DNA double-strand breaks (DSBs) activate the ATM/CHEK2/p53 pathway, inducing the transcription of stress genes. The dynamic nature of this transcriptional response has not been directly observed in vivo in humans. In this study we monitored the messenger RNA transcript abundances of nine DNA damage-responsive genes (CDKN1A, GADD45, CCNG1, FDXR, DDB2, MDM2, PHPT1, SESN1, and PUMA), eight of them regulated by p53 in circulating blood leukocytes at different time points (2, 6–8, 16–18, and 24 h) in cancer patients (lung, neck, brain, and pelvis) undergoing radiotherapy. We discovered that, although the calculated mean physical dose to the blood was very low (0.038–0.169 Gy), an upregulation of Ferredoxin reductase (FDXR) gene transcription was detectable 2 h after exposure and was dose dependent from the lowest irradiated percentage of the body (3.5% whole brain) to the highest, (up to 19.4%, pelvic zone) reaching a peak at 6–8 h. The radiation response of the other genes was not strong enough after such low doses to provide meaningful information. Following multiple fractions, the expression level increased further and was still significantly up-regulated by the end of the treatment. Moreover, we compared FDXR transcriptional responses to ionizing radiation (IR) in vivo with healthy donors’ blood cells exposed ex vivo and found a good correlation in the kinetics of expression from the 8-hours time-point onward, suggesting that a molecular transcriptional regulation mechanism yet to be identified is involved. To conclude, we provided the first in vivo human report of IR-induced gene transcription temporal response of a panel of p53-dependant genes. FDXR was demonstrated to be the most responsive gene, able to reliably inform on the low doses following partial body irradiation of the patients, and providing an expression pattern corresponding to the % of body exposed. An extended study would provide individual biological dosimetry information and may reveal inter-individual variability to predict radiotherapy-associated adverse health outcomes.

Inversed Ratio of CD39/CD73 Expression on γδ T Cells in HIV Versus Healthy Controls Correlates With Immune Activation and Disease Progression

Background

γδ T cells are unconventional T cells that have been demonstrated to be crucial for the pathogenesis and potentially for the cure of HIV-1 infection. The ectonucleotidase CD39 is part of the purinergic pathway that regulates immune responses by degradation of pro-inflammatory ATP in concert with CD73. Few studies on the expression of the ectoenzymes CD73 and CD39 on human γδ T cells in HIV have been performed to date.

Methods

PBMC of n=86 HIV-1-infected patients were compared to PBMC of n=26 healthy individuals using 16-color flow cytometry determining the surface expression of CD39 and CD73 on Vδ1 and Vδ2 T cells in association with differentiation (CD45RA, CD28, CD27), activation and exhaustion (TIGIT, PD-1, CD38, and HLA-DR), and assessing the intracellular production of pro- and anti-inflammatory cytokines (IL-2, TGF-ß, TNF-α, Granzyme B, IL-10, IFN-γ) after in vitro stimulation with PMA/ionomycin.

Results

CD39 and CD73 expression on γδ T cells were inversed in HIV infection which correlated with HIV disease progression and immune activation. CD39, but not CD73 expression on γδ T cells of ART-treated patients returned to levels comparable with those of healthy individuals. Only a small subset (<1%) of γδ T cells co-expressed CD39 and CD73 in healthy or HIV-infected individuals. There were significantly more exhausted and terminally differentiated CD39+ Vδ1 T cells regardless of the disease status. Functionally, IL-10 was only detectable in CD39+ γδ T cells after in vitro stimulation in all groups studied. Viremic HIV-infected patients showed the highest levels of IL-10 production. The highest percentage of IL-10+ cells was found in the small CD39/CD73 co-expressing γδ T-cell population, both in healthy and HIV-infected individuals. Also, CD39+ Vδ2 T cells produced IL-10 more frequently than their CD39+ Vδ1 counterparts in all individuals regardless of the HIV status.

Conclusions

Our results point towards a potential immunomodulatory role of CD39+ and CD73+ γδ T cells in the pathogenesis of chronic HIV infection that needs further investigation.

Structure-Activity Relationship of 3-Methylcytidine-5'-α,β-methylenediphosphates as CD73 Inhibitors

We recently reported N4-substituted 3-methylcytidine-5'-α,β-methylenediphosphates as CD73 inhibitors, potentially useful in cancer immunotherapy. We now expand the structure-activity relationship of pyrimidine nucleotides as human CD73 inhibitors. 4-Chloro (MRS4598 16; Ki = 0.673 nM) and 4-iodo (MRS4620 18; Ki = 0.436 nM) substitution of the N4-benzyloxy group decreased Ki by ∼20-fold. Primary alkylamine derivatives coupled through a p-amido group with a varying methylene chain length (24 and 25) were functionalized congeners, for subsequent conjugation to carrier or reporter moieties. X-ray structures of hCD73 with two inhibitors indicated a ribose ring conformational adaptation, and the benzyloxyimino group (E configuration) binds to the same region (between the C-terminal and N-terminal domains) as N4-benzyl groups in adenine inhibitors. Molecular dynamics identified stabilizing interactions and predicted conformational diversity. Thus, by N4-benzyloxy substitution, we have greatly enhanced the inhibitory potency and added functionality enabling molecular probes. Their potential as anticancer drugs was confirmed by blocking CD73 activity in tumor tissues in situ.

Stimuli-Responsive Delivery Strategies for Controllable Gene Editing in Tumor Therapeutics

CRISPR system has attracted significant interest due to its great potential in tumour therapy. Developing effective, precise and safe delivery vectors is a prerequisite for CRISPR applications. Some disease-related biological...

Abscopal Effect and Drug-Induced Xenogenization: A Strategic Alliance in Cancer Treatment?

The current state of cancer treatment is still far from being satisfactory considering the strong impairment of patients' quality of life and the high lethality of malignant diseases. Therefore, it is critical for innovative approaches to be tested in the near future. In view of the crucial role that is played by tumor immunity, the present review provides essential information on the immune-mediated effects potentially generated by the interplay between ionizing radiation and cytotoxic antitumor agents when interacting with target malignant cells. Therefore, the radiation-dependent abscopal effect (i.e., a biological effect of ionizing radiation that occurs outside the irradiated field), the influence of cancer chemotherapy on the antigenic pattern of target neoplastic cells, and the immunogenic cell death (ICD) caused by anticancer agents are the main topics of this presentation. It is widely accepted that tumor immunity plays a fundamental role in generating an abscopal effect and that anticancer drugs can profoundly influence not only the host immune responses, but also the immunogenic pattern of malignant cells. Remarkably, several anticancer drugs impact both the abscopal effect and ICD. In addition, certain classes of anticancer agents are able to amplify already expressed tumor-associated antigens (TAA). More importantly, other drugs, especially triazenes, induce the appearance of new tumor neoantigens (TNA), a phenomenon that we termed drug-induced xenogenization (DIX). The adoption of the abscopal effect is proposed as a potential therapeutic modality when properly applied concomitantly with drug-induced increase in tumor cell immunogenicity and ICD. Although little to no preclinical or clinical studies are presently available on this subject, we discuss this issue in terms of potential mechanisms and therapeutic benefits. Upcoming investigations are aimed at evaluating how chemical anticancer drugs, radiation, and immunotherapies are interacting and cooperate in evoking the abscopal effect, tumor xenogenization and ICD, paving the way for new and possibly successful approaches in cancer therapy.

CD73, Tumor Plasticity and Immune Evasion in Solid Cancers

Simple Summary

Tumors are ecosystems composed of cancer cells and non-tumor stroma together in a hypoxic environment often described as wounds that do not heal. Accumulating data suggest that solid tumors hijack cellular plasticity possibly to evade detection by the immune system. CD73-mediated generation of the purine nucleoside adenosine, is an important biochemical constituent of the immunosuppressive tumor microenvironment. In this review, the association between CD73 expression and features associated with cellular plasticity involving stemness, epithelial-to-mesenchymal transition and metastasis together with immune infiltration is summarized for a wide range of solid tumor types. Our analyses demonstrate that CD73 correlates with signatures associated with cellular plasticity in solid tumors. In addition, there are strong associations between CD73 expression and type of infiltrating lymphocytes. Collectively, the observations suggest a biomarker-based stratification to identify CD73-adenosinergic rich tumors may help identify patients with solid cancers who will respond to a combinatorial strategy that includes targeting CD73.

Abstract

Regulatory networks controlling cellular plasticity, important during early development, can re-emerge after tissue injury and premalignant transformation. One such regulatory molecule is the cell surface ectoenzyme ecto-5′-nucleotidase that hydrolyzes the conversion of extracellular adenosine monophosphate to adenosine (eADO). Ecto-5′-nucleotidase (NT5E) or cluster of differentiation 73 (CD73), is an enzyme that is encoded by NT5E in humans. In normal tissue, CD73-mediated generation of eADO has important pleiotropic functions ranging from the promotion of cell growth and survival, to potent immunosuppression mediated through purinergic G protein-coupled adenosine receptors. Importantly, tumors also utilize several mechanisms mediated by CD73 to resist therapeutics and in particular, evade the host immune system, leading to undesired resistance to targeted therapy and immunotherapy. Tumor cell CD73 upregulation is associated with worse clinical outcomes in a variety of cancers. Emerging evidence indicates a link between tumor cell stemness with a limited host anti-tumor immune response. In this review, we provide an overview of a growing body of evidence supporting the pro-tumorigenic role of CD73 and adenosine signaling. We also discuss data that support a link between CD73 expression and tumor plasticity, contributing to dissemination as well as treatment resistance. Collectively, targeting CD73 may represent a novel treatment approach for solid cancers.

Radiation-induced lung toxicity - cellular and molecular mechanisms of pathogenesis, management, and literature review

Lung, breast, and esophageal cancer represent three common malignancies with high incidence and mortality worldwide. The management of these tumors critically relies on radiotherapy as a major part of multi-modality care, and treatment-related toxicities, such as radiation-induced pneumonitis and/or lung fibrosis, are important dose limiting factors with direct impact on patient outcomes and quality of life. In this review, we summarize the current understanding of radiation-induced pneumonitis and pulmonary fibrosis, present predictive factors as well as recent diagnostic and therapeutic advances. Novel candidates for molecularly targeted approaches to prevent and/or treat radiation-induced pneumonitis and pulmonary fibrosis are discussed.

Cardiovascular Damage Associated With Chest Irradiation

The improvement of anticancer-therapies results in a greater amount of long-term survivors after radiotherapy. Therefore, the understanding of cardiotoxicity after irradiation is of increasing importance. Cardiovascular adverse events after chest irradiation have been acknowledged for a long time but remain difficult to diagnose. Long-term cardiovascular adverse events may become evident years or decades after radiotherapy and the spectrum of potential cardiovascular side effects is large. Recent experimental and clinical data indicate that cardiovascular symptoms may be caused especially by heart failure with preserved ejection fraction, which remains incompletely understood in patients after radiation therapy. Heart radiation dose and co-existing cardiovascular risk factors represent some of the most important contributors for incidence and severity of radiation-induced cardiovascular side effects. In this review, we aim to elucidate the underlying patho-mechanisms and to characterize the development of radiation-induced cardiovascular damage. Additionally, approaches for clinical management and treatment options are presented.

Addendum: de Leve, S.; et al. The CD73/Ado System—A New Player in RT Induced Adverse Late Effects. Cancers 2019, 11, 1578

The authors would like to make an addendum to their published paper [...]