The Inhibition of CD39 and CD73 Cell Surface Ectonucleotidases by Small Molecular Inhibitors Enhances the Mobilization of Bone Marrow Residing Stem Cells by Decreasing the Extracellular Level of Adenosine

Hematopoiesis Revolves Around the Primordial Evolutional Rhythm of Purinergic Signaling and Innate Immunity - A Journey to the Developmental Roots

A cell's most significant existential task is to survive by ensuring proper metabolism, avoiding harmful stimuli, and adapting to changing environments. It explains why early evolutionary primordial signals and pathways remained active and regulate cell and tissue integrity. This requires energy supply and a balanced redox state. To meet these requirements, the universal intracellular energy transporter purine nucleotide-adenosine triphosphate (ATP) became an important signaling molecule and precursor of purinergic signaling after being released into extracellular space. Similarly, ancient proteins involved in intracellular metabolism gave rise to the third protein component (C3) of the complement cascade (ComC), a soluble arm of innate immunity. These pathways induce cytosol reactive oxygen (ROS) and reactive nitrogen species (RNS) that regulate the redox state of the cells. While low levels of ROS and RNS promote cell growth and differentiation, supra-physiological concentrations can lead to cell damage by pyroptosis. This balance explains the impact of purinergic signaling and innate immunity on cell metabolism, organogenesis, and tissue development. Subsequently, along with evolution, new regulatory cues emerge in the form of growth factors, cytokines, chemokines, and bioactive lipids. However, their expression is still modulated by both primordial signaling pathways. This review will focus on the data that purinergic signaling and innate immunity carry on their ancient developmental task in hematopoiesis and specification of hematopoietic stem/progenitor cells (HSPCs). Moreover, recent evidence shows both these regulatory pathways operate in a paracrine manner and inside HSPCs at the autocrine level.

Pineal Gland Hormone Melatonin Inhibits Migration of Hematopoietic Stem/Progenitor Cells (HSPCs) by Downregulating Nlrp3 Inflammasome and Upregulating Heme Oxygenase-1 (HO-1) Activity

Hematopoietic stem progenitor cells (HSPCs) follow the diurnal circulation rhythm in peripheral blood (PB) with nadir during late night and peak at early morning hours. The level of these cells in PB correlates with activation of innate immunity pathways, including complement cascade (ComC) that drives activation of Nlrp3 inflammasome. To support this, mice both in defective ComC activation as well as Nlrp3 inflammasome do not show typical changes in the diurnal level of circulating HSPCs. Migration of HSPCs is also impaired at the intracellular level by the anti-inflammatory enzyme heme oxygenase-1 (HO-1) which is an inhibitor of Nlrp3 inflammasome. It is also well known that circadian rhythm mediates PB level of melatonin released from the pineal gland. Since trafficking of HSPCs is driven by innate immunity-induced sterile inflammation and melatonin has an anti-inflammatory effect, we hypothesized that melatonin could negatively impact the release of HSPCs from BM into PB by inhibiting Nlrp3 inflammasome activation. We provide an evidence that melatonin being a ''sleep regulating pineal hormone'' directly inhibits migration of HSPCs both in vitro migration assays and in vivo during pharmacological mobilization. This correlated with inhibition of cholesterol synthesis required for a proper membrane lipid raft (MLRs) formation and an increase in expression of HO-1-an inhibitor of Nlrp3 inflammasome. Since melatonin is a commonly used drug, this should be considered while preparing a patient for the procedure of HSPCs mobilization. More importantly, our studies shed more mechanistic light on a role of melatonin in the diurnal circulation of HSPCs.

The expression mechanism of programmed cell death 1 ligand 1 and its role in immunomodulatory ability of mesenchymal stem cells

Programmed cell death 1 ligand 1 (PD-L1) is an important immunosuppressive molecule, which inhibits the function of T cells and other immune cells by binding to the receptor programmed cell death-1. The PD-L1 expression disorder plays an important role in the occurrence, development, and treatment of sepsis or other inflammatory diseases, and has become an important target for the treatment of these diseases. Mesenchymal stem cells (MSCs) are a kind of pluripotent stem cells with multiple differentiation potential. In recent years, MSCs have been found to have a strong immunosuppressive ability and are used to treat various inflammatory insults caused by hyperimmune diseases. Moreover, PD-L1 is deeply involved in the immunosuppressive events of MSCs and plays an important role in the treatment of various diseases. In this review, we will summarize the main regulatory mechanism of PD-L1 expression, and discuss various biological functions of PD-L1 in the immune regulation of MSCs.

Hematopoietic stem cells on the crossroad between purinergic signaling and innate immunity

Hematopoiesis is regulated by several mediators such as peptide-based growth factors, cytokines, and chemokines, whose biological effects have been studied for many years. However, several other mediators have been identified recently that affect the fate of hematopoietic stem/progenitor cells (HSPC) as well as non-hematopoietic cells in the bone marrow microenvironment. These new mediators comprise members of purinergic signaling pathways and are active mediators of the soluble arm of innate immunity, the complement cascade (ComC). In this review, we will discuss the coordinated effects of these pathways in regulating the biology of HSPC. Importantly, both purinergic signaling and the ComC are activated in stress situations and interact with specific receptors expressed on HSPC. Evidence has accumulated indicating that some of the purinergic as well as ComC receptors could also be activated intracellularly by intrinsically expressed ligands. To support this recent evidence, our work indicates that the major mediator of purinergic signaling, adenosine triphosphate, and the cleavage product of the fifth component of the ComC (C5), C5a anaphylatoxin, can activate their corresponding receptors expressed on the outer mitochondrial membrane in an autocrine manner. We will also discuss recent evidence that these responses, mediated by purinergic signaling and the ComC network, are coordinated by activation of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 - reactive oxygen species - NLR family pyrin domain containing 3 (NLRP3) inflammasome (Nox2-ROS-NLRP3) axis.

Synthesis and structure-activity relationships of ticlopidine derivatives and analogs as inhibitors of ectonucleotidase CD39

Ticlopidine is an antithrombotic prodrug of the thienotetrahydropyridine family. For platelet inhibition it has to undergo oxidative ring-opening by cytochrome P450 enzymes. The resulting thiol reacts with a cysteine residue of the purinergic P2Y₁₂ receptor on thrombocytes resulting in covalent receptor blockade. Ticlopidine in its intact, not-metabolized form was previously shown to inhibit ecto-nucleoside triphosphate diphosphohydrolase-1 (NTPDase1, also known as cluster of differentiation (CD) 39). CD39 catalyzes the extracellular hydrolysis of ATP via ADP to AMP, which is further hydrolyzed by ecto-5'-nucleotidase (CD73) to adenosine. CD39 inhibition has been proposed as a novel strategy to increase the extracellular concentration of antiproliferative ATP, while decreasing immunosuppressive and cancer-promoting adenosine levels. In the present study, we performed an extensive structure-activity relationship (SAR) analysis of ticlopidine derivatives and analogs as CD39 inhibitors followed by an in-depth characterization of selected compounds. Altogether 74 compounds were synthesized, 41 of which are new, not previously described in literature. Benzotetrahydropyridines, in which the metabolically labile thiophene is replaced by a benzene ring, were discovered as a new class of allosteric CD39 inhibitors.

Purinergic Signaling and Its Role in Mobilization of Bone Marrow Stem Cells

Mobilization or egress of stem cells from bone marrow (BM) into peripheral blood (PB) is an evolutionary preserved and important mechanism in an organism for self-defense and regeneration. BM-derived stem cells circulate always at steady-state conditions in PB, and their number increases during stress situations related to (a) infections, (b) tissue organ injury, (c) stress, and (d) strenuous exercise. Stem cells also show a circadian pattern of their PB circulating level with peak in early morning hours and nadir late at night. The number of circulating in PB stem cells could be pharmacologically increased after administration of some drugs such as cytokine granulocyte colony-stimulating factor (G-CSF) or small molecular antagonist of CXCR4 receptor AMD3100 (Plerixafor) that promote their egress from BM into PB and lymphatic vessels. Circulating can be isolated from PB for transplantation purposes by leukapheresis. This important homeostatic mechanism is governed by several intrinsic complementary pathways. In this chapter, we will discuss the role of purinergic signaling and extracellular nucleotides in regulating this process and review experimental strategies to study their involvement in mobilization of various types of stem cells that reside in murine BM.

Repurposing of Commercially Existing Molecular Target Therapies to Boost the Clinical Efficacy of Immune Checkpoint Blockade

Immune checkpoint blockade (ICB) is now standard of care for several metastatic epithelial cancers and prolongs life expectancy for a significant fraction of patients. A hostile tumor microenvironment (TME) induced by intrinsic oncogenic signaling induces an immunosuppressive niche that protects the tumor cells, limiting the durability and efficacy of ICB therapies. Addition of receptor tyrosine kinase inhibitors (RTKi) as potential modulators of an unfavorable local immune environment has resulted in moderate life expectancy improvement. Though the combination strategy of ICB and RTKi has shown significantly better results compared to individual treatment, the benefits and adverse events are additive whereas synergy of benefit would be preferable. There is therefore a need to investigate the potential of inhibitors other than RTKs to reduce malignant cell survival while enhancing anti-tumor immunity. In the last five years, preclinical studies have focused on using small molecule inhibitors targeting cell cycle and DNA damage regulators such as CDK4/6, CHK1 and poly ADP ribosyl polymerase (PARP) to selectively kill tumor cells and enhance cytotoxic immune responses. This review provides a comprehensive overview of the available drugs that attenuate immunosuppression and overcome hostile TME that could be used to boost FDA-approved ICB efficacy in the near future.

Adenosine signaling: Optimal target for gastric cancer immunotherapy

Gastric cancer (GC) is one of the most common malignancy and leading cause of cancer-related deaths worldwide. Due to asymptomatic or only nonspecific early symptoms, GC patients are usually in the advanced stage at first diagnosis and miss the best opportunity of treatment. Immunotherapies, especially immune checkpoint inhibitors (ICIs), have dramatically changed the landscape of available treatment options for advanced-stage cancer patients. However, with regards to existing ICIs, the clinical benefit of monotherapy for advanced gastric cancer (AGC) is quite limited. Therefore, it is urgent to explore an optimal target for the treatment of GC. In this review, we summarize the expression profiles and prognostic value of 20 common immune checkpoint-related genes in GC from Gene Expression Profiling Interactive Analysis (GEPIA) database, and then find that the adenosinergic pathway plays an indispensable role in the occurrence and development of GC. Moreover, we discuss the pathophysiological function of adenosinergic pathway in cancers. The accumulation of extracellular adenosine inhibits the normal function of immune effector cells and facilitate the effect of immunosuppressive cells to foster GC cells proliferation and migration. Finally, we provide insights into potential clinical application of adenosinergic-targeting therapies for GC patients.

Radiofrequency ablation in combination with CD73 inhibitor AB680 reduces tumor growth and enhances anti-tumor immunity in a syngeneic model of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma presents a 5-year overall survival rate of 11%, placing an imperative need for the discovery and application of innovative treatments. Radiofrequency ablation represents a promising therapy for PDA, as studies show it induces coagulative necrosis and a host adaptive immune response. In this work we evaluated the effects of RFA treatment in vivo by establishing a syngeneic mouse model of PDA and performing tumor ablation in one flank. Our studies revealed RFA acutely impaired PDA tumor growth; however, such effects were not sustained one week after treatment. Adenosine (ADO) pathway represents a strong immunosuppressive mechanism that was shown to play a role in PDA progression and preliminary data from ongoing clinical studies suggest ADO pathway inhibition may improve therapeutic outcomes. Thus, to investigate whether ADO generation may be involved in tumor growth relapse after RFA, we evaluated adenosine-monophosphate (AMP), ADO and inosine (INO) levels by HPLC and found they were acutely increased after treatment. Thus, we evaluated an in vivo CD73 inhibition in combination with RFA to study ADO pathway implication in RFA response. Results showed combination therapy of RFA and a CD73 small molecule inhibitor (AB680) in vivo promoted sustained tumor growth impairment up to 10 days after treatment as evidenced by increased necrosis and anti-tumor immunity, suggesting RFA in combination with CD73 inhibitors may improve PDA patient response.

Protein kinase inhibitor ceritinib blocks ectonucleotidase CD39 - a promising target for cancer immunotherapy

Background

An important mechanism, by which cancer cells achieve immune escape, is the release of extracellular adenosine into their microenvironment. Adenosine activates adenosine A_2A and A_2B receptors on immune cells constituting one of the strongest immunosuppressive mediators. In addition, extracellular adenosine promotes angiogenesis, tumor cell proliferation, and metastasis. Cancer cells upregulate ectonucleotidases, most importantly CD39 and CD73, which catalyze the hydrolysis of extracellular ATP to AMP (CD39) and further to adenosine (CD73). Inhibition of CD39 is thus expected to be an effective strategy for the (immuno)therapy of cancer. However, suitable small molecule inhibitors for CD39 are not available. Our aim was to identify drug-like CD39 inhibitors and evaluate them in vitro.

Methods

We pursued a repurposing approach by screening a self-compiled collection of approved, mostly ATP-competitive protein kinase inhibitors, on human CD39. The best hit compound was further characterized and evaluated in various orthogonal assays and enzyme preparations, and on human immune and cancer cells.

Results

The tyrosine kinase inhibitor ceritinib, a potent anticancer drug used for the treatment of anaplastic lymphoma kinase (ALK)-positive metastatic non-small cell lung cancer, was found to strongly inhibit CD39 showing selectivity versus other ectonucleotidases. The drug displays a non-competitive, allosteric mechanism of CD39 inhibition exhibiting potency in the low micromolar range, which is independent of substrate (ATP) concentration. We could show that ceritinib inhibits ATP dephosphorylation in peripheral blood mononuclear cells in a dose-dependent manner, resulting in a significant increase in ATP concentrations and preventing adenosine formation from ATP. Importantly, ceritinib (1–10 µM) substantially inhibited ATP hydrolysis in triple negative breast cancer and melanoma cells with high native expression of CD39.

Conclusions

CD39 inhibition might contribute to the effects of the powerful anticancer drug ceritinib. Ceritinib is a novel CD39 inhibitor with high metabolic stability and optimized physicochemical properties; according to our knowledge, it is the first brain-permeant CD39 inhibitor. Our discovery will provide the basis (i) to develop more potent and balanced dual CD39/ALK inhibitors, and (ii) to optimize the ceritinib scaffold towards interaction with CD39 to obtain potent and selective drug-like CD39 inhibitors for future in vivo studies.

Extracellular Adenosine (eAdo) - A2B Receptor Axis Inhibits in Nlrp3 Inflammasome-dependent Manner Trafficking of Hematopoietic Stem/progenitor Cells

We postulated that mobilization, homing, and engraftment of hematopoietic stem/progenitor cells (HSCPs) is facilitated by a state of sterile inflammation induced in bone marrow (BM) after administration of pro-mobilizing drugs or in response to pre-transplant myeloablative conditioning. An important role in this phenomenon plays purinergic signaling that by the release of extracellular adenosine triphosphate (eATP) activates in HSPCs and in cells in the hematopoietic microenvironment an intracellular pattern recognition receptor (PPR) known as Nlrp3 inflammasome. We reported recently that its deficiency results in defective trafficking of HSPCs. Moreover, it is known that eATP after release into extracellular space is processed by cell surface expressed ectonucleotidases CD39 and CD73 to extracellular adenosine (eAdo) that in contrast to eATP shows an anti-inflammatory effect. Based on data that the state of sterile inflammation promotes trafficking of HSPCs, and since eAdo is endowed with anti-inflammatory properties we become interested in how eAdo will affect the mobilization, homing, and engraftment of HSPCs and which of eAdo receptors are involved in these processes. As expected, eAdo impaired HSPCs trafficking and this occurred in autocrine- and paracrine-dependent manner by direct stimulation of these cells or by affecting cells in the BM microenvironment. We report herein for the first time that this defect is mediated by activation of the A2B receptor and a specific inhibitor of this receptor improves eAdo-aggravated trafficking of HSPCs. To explain this at the molecular level eAdo-A2B receptor interaction upregulates in HSPCs in NF-kB-, NRF2- and cAMP-dependent manner heme oxygenase-1 (HO-1), that is Nlrp3 inflammasome inhibitor. This corroborated with our analysis of proteomics signature in murine HSPCs exposed to eAdo that revealed that A2B inhibition promotes cell migration and proliferation. Based on this we postulate that blockage of A2B receptor may accelerate the mobilization of HSPCs as well as their hematopoietic reconstitution and this approach could be potentially considered in the future to be tested in the clinic.

Graphical Abstract

CD73-Positive Small Extracellular Vesicles Derived From Umbilical Cord Mesenchymal Stem Cells Promote the Proliferation and Migration of Pediatric Urethral Smooth Muscle Cells Through Adenosine Pathway

Smooth muscle cells (SMCs) are the main functional component of urethral tissue, but are difficult to proliferate in vitro. Mesenchymal stem cells (MSCs) and mesenchymal stem cell-derived small extracellular vesicles (MSC-sEV) have been shown to promote tissue repair by regulating the proliferation and migration of different types of cells. In this study, we investigated the effect of umbilical cord mesenchymal stem cell-derived sEV (UCMSC-sEV) on the proliferation and migration of pediatric urethral smooth muscle cells (PUSMCs) and the mechanism by which sEV regulates the function of PUSMCs. We observed that UCMSC-sEV can significantly promote the proliferation and migration of PUSMCs in vitro. UCMSC-sEV exerted proliferation and migration promotion effects by carrying the CD73 to PUSMCs and catalyzing the production of adenosine. Conversely, the effect of UCMSC-sEV on the proliferation and migration of PUSMCs were no longer observed with addition of the PSB12379 as a CD73 inhibitor. It was found that the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway in PUSMCs was activated by adenosine or UCMSC-sEV intervention. In summary, UCMSC-sEV promoted proliferation and migration of PUSMCs in vitro by activating CD73/adenosine signaling axis and downstream PI3K/AKT pathway. Thus, we concluded that UCMSC-sEV may be suggested as a new solution strategy for the urethral tissue repair.

The P2X4 purinergic receptor has emerged as a potent regulator of hematopoietic stem/progenitor cell mobilization and homing-a novel view of P2X4 and P2X7 receptor interaction in orchestrating stem cell trafficking

Recent evidence indicates that extracellular adenosine triphosphate (eATP), as a major mediator of purinergic signaling, plays an important role in regulating the mobilization and homing of hematopoietic stem progenitor cells (HSPCs). In our previous work we demonstrated that eATP activates the P2X7 ion channel receptor in HSPCs and that its deficiency impairs stem cell trafficking. To learn more about the role of the P2X purinergic receptor family in hematopoiesis, we phenotyped murine and human HSPCs with respect to the seven P2X receptors and observed that, these cells also highly express P2X4 receptors, which shows ~50% sequence similarity to P2X7 subtypes, but that P2X4 cells are more sensitive to eATP and signal much more rapidly. Using the selective P2X4 receptor antagonist PSB12054 as well as P2X4-KO mice, we found that the P2X4 receptor, similar to P2X7 receptor, promotes trafficking of HSPCs in that its deficiency leads to impaired chemotaxis of HSPCs in response to a stromal-derived factor 1 (SDF-1) gradient, less effective pharmacological mobilization, and defective homing and engraftment of HSPCs after transplantation into myeloablated hosts. This correlated with a decrease in SDF-1 expression in the BM microenvironment. Overall, our results confirm the proposed cooperative dependence of both receptors in response to eATP signaling. In G-CSF-induced mobilization, a lack of one receptor is not compensated by the presence of the other one, which supports their mutual dependence in regulating HSPC trafficking.

Identification of Novel CD39 Inhibitors Based on Virtual Screening and Enzymatic Assays

The accumulation of adenosine in the tumor microenvironment mediates immunosuppression and promotes tumor growth and proliferation. Intervention of the adenosine pathway is an important direction of antitumor immunity research. CD39 is an important ecto-nucleotidases for adenosine generation, therefore targeting the CD39-adenosine pathway is an emerging immune checkpoint for anticancer treatment. However, currently no CD39 inhibitor has been approved by the U.S. Food and Drug Administration. The development of CD39 drugs is urgent for clinical application. In this study, we combined homology modeling, virtual screening, and in vitro enzymatic activity to characterize the structural features of the CD39 protein and identify a triazinoindole-based compound as a CD39 inhibitor. The identified inhibitor and one of its analogues could effectively prevent the enzymatic activity of CD39 with IC₅₀ values of 27.42 ± 5.52 and 79.24 ± 12.21 μM, respectively. At the same time, the inhibitor significantly inhibited the adenosine monophosphate production in colorectal cancer cell lines (HT29 and MC38) and thereafter prevented cell proliferation. Molecular docking studies, mutagenesis, and microscale thermophoresis indicated that residues such as R85 could be the main contributor in binding triazinoindole compounds. The binding mode can potentially be utilized for hit-to-lead optimization, and the identified inhibitor can be further tested for its anticancer activity in vivo or may serve as a chemical agent to study CD39-related functions.

Intracoronary Delivery of Porcine Cardiac Progenitor Cells Overexpressing IGF-1 and HGF in a Pig Model of Sub-Acute Myocardial Infarction

Human cardiac progenitor cells (hCPC) are considered a good candidate in cell therapy for ischemic heart disease, demonstrating capacity to improve functional recovery after myocardial infarction (MI), both in small and large preclinical animal models. However, improvements are required in terms of cell engraftment and efficacy. Based on previously published reports, insulin-growth factor 1 (IGF-1) and hepatocyte growth factor (HGF) have demonstrated substantial cardioprotective, repair and regeneration activities, so they are good candidates to be evaluated in large animal model of MI. We have validated porcine cardiac progenitor cells (pCPC) and lentiviral vectors to overexpress IGF-1 (co-expressing eGFP) and HGF (co-expressing mCherry). pCPC were transduced and IGF1-eGFP^pos and HGF-mCherry^pos populations were purified by cell sorting and further expanded. Overexpression of IGF-1 has a limited impact on pCPC expression profile, whereas results indicated that pCPC-HGF-mCherry cultures could be counter selecting high expresser cells. In addition, pCPC-IGF1-eGFP showed a higher cardiogenic response, evaluated in co-cultures with decellularized extracellular matrix, compared with native pCPC or pCPC-HGF-mCherry. In vivo intracoronary co-administration of pCPC-IGF1-eGFP and pCPC-HFG-mCherry (1:1; 40 × 10⁶/animal), one week after the induction of an MI model in swine, revealed no significant improvement in cardiac function.

The Nlrp3 inflammasome - the evolving story of its positive and negative effects on hematopoiesis

PURPOSE OF REVIEW

Hematopoiesis is co-regulated by innate immunity, which is an ancient evolutionary defense mechanism also involved in the development and regeneration of damaged tissues. This review seeks to shed more light on the workings of the Nlrp3 inflammasome, which is an intracellular innate immunity pattern recognition receptor and sensor of changes in the hematopoietic microenvironment, and focus on its role in hematopoieisis.

RECENT FINDINGS

Hematopoietic stem progenitor cells (HSPCs) are exposed to several external mediators of innate immunity. Moreover, since hemato/lymphopoietic cells develop from a common stem cell, their behavior and fate are coregulated by intracellular innate immunity pathways. Therefore, the Nlrp3 inflammasome is functional both in immune cells and in HSPCs and affects hematopoiesis in either a positive or negative way, depending on its activity level. Specifically, while a physiological level of activation regulates the trafficking of HSPCs and most likely maintains their pool in the bone marrow, hyperactivation may lead to irreversible cell damage by pyroptosis and HSPC senescence and contribute to the origination of myelodysplasia and hematopoietic malignancies.

SUMMARY

Modulation of the level of Nrp3 inflammasome activation will enable improvements in HSPC mobilization, homing, and engraftment strategies. It may also control pathological activation of this protein complex during HSPC senescence, graft-versus-host disease, the induction of cytokine storms, and the development of hematopoietic malignancies.

Comparison of the efficacy of hematopoietic stem cell mobilization regimens: a systematic review and network meta-analysis of preclinical studies

BACKGROUND

Mobilization failure may occur when the conventional hematopoietic stem cells (HSCs) mobilization agent granulocyte colony-stimulating factor (G-CSF) is used alone, new regimens were developed to improve mobilization efficacy. Multiple studies have been performed to investigate the efficacy of these regimens via animal models, but the results are inconsistent. We aim to compare the efficacy of different HSC mobilization regimens and identify new promising regimens with a network meta-analysis of preclinical studies.

METHODS

We searched Medline and Embase databases for the eligible animal studies that compared the efficacy of different HSC mobilization regimens. Primary outcome is the number of total colony-forming cells (CFCs) in per milliliter of peripheral blood (/ml PB), and the secondary outcome is the number of Lin^- Sca1⁺ Kit⁺ (LSK) cells/ml PB. Bayesian network meta-analyses were performed following the guidelines of the National Institute for Health and Care Excellence Decision Support Unit (NICE DSU) with WinBUGS version 1.4.3. G-CSF-based regimens were classified into the SD (standard dose, 200-250 μg/kg/day) group and the LD (low dose, 100-150 μg/kg/day) group based on doses, and were classified into the short-term (2-3 days) group and the long-term (4-5 days) group based on administration duration. Long-term SD G-CSF was chosen as the reference treatment. Results are presented as the mean differences (MD) with the associated 95% credibility interval (95% CrI) for each regimen.

RESULTS

We included 95 eligible studies and reviewed the efficacy of 94 mobilization agents. Then 21 studies using the poor mobilizer mice model (C57BL/6 mice) to investigate the efficacy of different mobilization regimens were included for network meta-analysis. Network meta-analyses indicated that compared with long-term SD G-CSF alone, 14 regimens including long-term SD G-CSF + Me6, long-term SD G-CSF + AMD3100 + EP80031, long-term SD G-CSF + AMD3100 + FG-4497, long-term SD G-CSF + ML141, long-term SD G-CSF + desipramine, AMD3100 + meloxicam, long-term SD G-CSF + reboxetine, AMD3100 + VPC01091, long-term SD G-CSF + FG-4497, Me6, long-term SD G-CSF + EP80031, POL5551, long-term SD G-CSF + AMD3100, AMD1300 + EP80031 and long-term LD G-CSF + meloxicam significantly increased the collections of total CFCs. G-CSF + Me6 ranked first among these regimens in consideration of the number of harvested CFCs/ml PB (MD 2168.0, 95% CrI 2062.0-2272.0). In addition, 7 regimens including long-term SD G-CSF + AMD3100, AMD3100 + EP80031, long-term SD G-CSF + EP80031, short-term SD G-CSF + AMD3100 + IL-33, long-term SD G-CSF + ML141, short-term LD G-CSF + ARL67156, and long-term LD G-CSF + meloxicam significantly increased the collections of LSK cells compared with G-CSF alone. Long-term SD G-CSF + AMD3100 ranked first among these regimens in consideration of the number of harvested LSK cells/ml PB (MD 2577.0, 95% CrI 2422.0-2733.0).

CONCLUSIONS

Considering the number of CFC and LSK cells in PB as outcomes, G-CSF plus AMD3100, Me6, EP80031, ML141, FG-4497, IL-33, ARL67156, meloxicam, desipramine, and reboxetine are all promising mobilizing regimens for future investigation.

New insights into cytotoxic mechanisms of bozepinib against glioblastoma

Glioblastoma (GBM) is the most frequent and aggressive brain tumor in adults and the current treatments only have a modest effect on patient survival. Recent studies show that bozepinib (BZP), a purine derivative, has potential applications in cancer treatment. The aim of this study was to evaluate the effect of BZP against GBM cells, specially concerning the purinergic system. Thus, GBM cells (C6 and U138 cell lines) were treated with BZP and cell viability, cell cycle, and annexin/PI assays, and active caspase-3 measurements were carried out. Besides, the effect of BZP over the purinergic system was also evaluated in silico and in vitro. Finally, we evaluate the action of BZP against important markers related to cancer progression, such as Akt, NF-κB, and CD133. We demonstrate here that BZP reduces GBM cell viability (IC₅₀ = 5.7 ± 0.3 µM and 12.7 ± 1.5 µM, in C6 and U138 cells, respectively), inducing cell death through caspase-dependent apoptosis, autophagosome formation, activation of NF-κB, without any change in cell cycle progression or on the Akt pathway. Also, BZP modulates the purinergic system, inducing an increase in CD39 enzyme expression and activity, while inhibiting CD73 activity and adenosine formation, without altering CD73 enzyme expression. Curiously, one cycle of treatment resulted in enrichment of GBM cells expressing NF-κB and CD133⁺, suggesting resistant cells selection. However, after another treatment round, the resistant cells were eliminated. Altogether, BZP presented in vitro anti-glioma activity, encouraging further in vivo studies in order to better understand its mechanism of action.

Postnatal Pluripotent Cells: Quarter of a Century of Research

Almost quarter of a century long studies aimed at identification, isolation, culturing, and use of postnatal pluripotent cells for the development of cell-based technologies have not met with success and failed to provide reliable and reproducible protocols of cell isolation, identification, and culturing. At the same time, experimental data in this field suggest that postnatal pluripotent cells are not the copies of embryonic cells and, therefore, the tests routinely used for identification of embryonic pluripotent cells are not fully adequate for characterization of their postnatal analogues. Therefore, cell lineage tracing methods showing the differentiation routes of the studied cells in human or animal body after birth should be developed and used.

The adenosinergic pathway in mesenchymal stem cell fate and functions

Mesenchymal stem cells (MSCs) play an important role in tissue homeostasis and damage repair through their ability to differentiate into cells of different tissues, trophic support, and immunomodulation. These properties made them attractive for clinical applications in regenerative medicine, immune disorders, and cell transplantation. However, despite multiple preclinical and clinical studies demonstrating beneficial effects of MSCs, their native identity and mechanisms of action remain inconclusive. Since its discovery, the CD73/ecto-5'-nucleotidase is known as a classic marker for MSCs, but its role goes far beyond a phenotypic characterization antigen. CD73 contributes to adenosine production, therefore, is an essential component of purinergic signaling, a pathway composed of different nucleotides and nucleosides, which concentrations are finely regulated by the ectoenzymes and receptors. Thus, purinergic signaling controls pathophysiological functions such as proliferation, migration, cell fate, and immune responses. Despite the remarkable progress already achieved in considering adenosinergic pathway as a therapeutic target in different pathologies, its role is not fully explored in the context of the therapeutic functions of MSCs. Therefore, in this review, we provide an overview of the role of CD73 and adenosine-mediated signaling in the functions ascribed to MSCs, such as homing and proliferation, cell differentiation, and immunomodulation. Additionally, we will discuss the pathophysiological role of MSCs, via CD73 and adenosine, in different diseases, as well as in tumor development and progression. A better understanding of the adenosinergic pathway in the regulation of MSCs functions will help to provide improved therapeutic strategies applicable in regenerative medicine.

Extracellular Adenosine Triphosphate (eATP) and Its Metabolite, Extracellular Adenosine (eAdo), as Opposing "Yin-Yang" Regulators of Nlrp3 Inflammasome in the Trafficking of Hematopoietic Stem/Progenitor Cells

Nlrp3 inflammasome plays a pleiotropic role in hematopoietic cells. On the one hand, physiological activation of this intracellular protein complex is crucial to maintaining normal hematopoiesis and the trafficking of hematopoietic stem progenitor cells (HSPCs). On the other hand, its hyperactivation may lead to cell death by pyroptosis, and prolonged activity is associated with sterile inflammation of the BM and, as a consequence, with the HSPCs aging and origination of myelodysplasia and leukemia. Thus, we need to understand better this protein complex’s actions to define the boundaries of its safety window and study the transition from being beneficial to being detrimental. As demonstrated, the Nlrp3 inflammasome is expressed and active both in HSPCs and in the non-hematopoietic cells that are constituents of the bone marrow (BM) microenvironment. Importantly, the Nlrp3 inflammasome responds to mediators of purinergic signaling, and while extracellular adenosine triphosphate (eATP) activates this protein complex, its metabolite extracellular adenosine (eAdo) has the opposite effect. In this review, we will discuss and focus on the physiological consequences of the balance between eATP and eAdo in regulating the trafficking of HSPCs in an Nlrp3 inflammasome-dependent manner, as seen during pharmacological mobilization from BM into peripheral blood (PB) and in the reverse mechanism of homing from PB to BM and engraftment. We propose that both mediators of purinergic signaling and the Nlrp3 inflammasome itself may become important therapeutic targets in optimizing the trafficking of HSPCs in clinical settings.

Inflammasomes and the Maintenance of Hematopoietic Homeostasis: New Perspectives and Opportunities

Hematopoietic stem cells (HSCs) regularly produce various blood cells throughout life via their self-renewal, proliferation, and differentiation abilities. Most HSCs remain quiescent in the bone marrow (BM) and respond in a timely manner to either physiological or pathological cues, but the underlying mechanisms remain to be further elucidated. In the past few years, accumulating evidence has highlighted an intermediate role of inflammasome activation in hematopoietic maintenance, post-hematopoietic transplantation complications, and senescence. As a cytosolic protein complex, the inflammasome participates in immune responses by generating a caspase cascade and inducing cytokine secretion. This process is generally triggered by signals from purinergic receptors that integrate extracellular stimuli such as the metabolic factor ATP via P2 receptors. Furthermore, targeted modulation/inhibition of specific inflammasomes may help to maintain/restore adequate hematopoietic homeostasis. In this review, we will first summarize the possible relationships between inflammasome activation and homeostasis based on certain interesting phenomena. The cellular and molecular mechanism by which purinergic receptors integrate extracellular cues to activate inflammasomes inside HSCs will then be described. We will also discuss the therapeutic potential of targeting inflammasomes and their components in some diseases through pharmacological or genetic strategies.

Mesenchymal Stromal Cell Immunology for Efficient and Safe Treatment of Osteoarthritis

Mesenchymal stem cell (MSC) therapy represents a promising approach for the treatment of osteoarthritis (OA). MSCs can be readily isolated from multiple sources and expanded ex vivo for possible clinical application. They possess a unique immunological profile and regulatory machinery that underline their therapeutic effects. They also have the capacity to sense the changes within the tissue environment to display the adequate response. Indeed, there is a close interaction between MSCs and the host cells. Accordingly, MSCs demonstrate encouraging results for a variety of diseases including OA. However, their effectiveness needs to be improved. In this review, we selected to discuss the importance of the immunological features of MSCs, including the type of transplantation and the immune and blood compatibility. It is important to consider MSC immune evasive rather than immune privileged. We also highlighted some of the actions/mechanisms that are displayed during tissue healing including the response of MSCs to injury signals, their interaction with the immune system, and the impact of their lifespan. Finally, we briefly summarized the results of clinical studies reporting on the application of MSCs for the treatment of OA. The research field of MSCs is inspiring and innovative but requires more knowledge about the immunobiological properties of these cells. A better understanding of these features will be key for developing a safe and efficient medicinal product for clinical use in OA.

CD39 Identifies the CD4+ Tumor-Specific T-cell Population in Human Cancer

The accumulation of tumor-specific CD4⁺ and CD8⁺ effector T cells is key to an effective antitumor response. Locally, CD4⁺ T cells promote the recruitment and effector function of tumor-specific CD8⁺ T cells and activate innate killer cells in the tumor. Here, we show that tumor-specific CD4⁺ T cells were predominantly present in the CD39⁺ subset of tumor-infiltrating lymphocytes (TIL). The CD39⁺ CD4⁺ and CD8⁺ TILs were detected in three different tumor types, and displayed an activated (PD-1⁺, HLA-DR⁺) effector memory phenotype. CD4⁺CD39⁺ single-cell RNA-sequenced TILs shared similar well-known activation, tissue residency, and effector cell-associated genes with CD8⁺CD39⁺CD103⁺ TILs. Finally, analysis of directly ex vivo cell-sorted and in vitro expanded pure populations of CD39-positive and negative CD4⁺ and CD8⁺ TILs revealed that tumor-specific antigen reactivity was almost exclusively detected among CD39⁺ cells. Immunotherapy of cancer is based on the activation of tumor-reactive CD4⁺ and CD8⁺ T cells. We show that the expression of CD39 can be used to identify, isolate, and expand tumor-reactive T-cell populations in cancers.

Extracellular Adenine Nucleotides and Adenosine Modulate the Growth and Survival of THP-1 Leukemia Cells

A new approach to improve the effectiveness of acute myeloid leukemia (AML) treatment is to use the properties of purinergic signaling molecules secreted into the bone marrow milieu in response to leukemic cell growth. Therefore, our study aimed to evaluate the effects of extracellular adenine nucleotides and adenosine on the growth and death parameters in the leukemic THP-1 cell line. Cells were exposed to ATP, ADP, AMP, adenosine and nonhydrolyzable analogues of ATP and ADP (ATPγS and ADPβS) in a 1–1000 μM broad concentration range. The basal mRNA expression of the P1 and P2 receptors was evaluated by real-time PCR. Changes in the processes of cell growth and death were assessed by flow cytometry analysis of proliferation, cell cycle and apoptosis. Chemotaxis toward stromal cell-derived factor-1 (SDF-1) was performed using the modified Boyden chamber assay, and chemokine receptor type 4 (CXCR4) surface expression was quantified by flow cytometry. We indicated several antileukemic actions. High micromolar concentrations (100–1000 μM) of extracellular adenine nucleotides and adenosine inhibit the growth of cells by arresting the cell cycle and/or inducing apoptosis. ATP is characterized by the highest potency and widest range of effects, and is responsible for the cell cycle arrest and the apoptosis induction. Compared to ATP, the effect of ADP is slightly weaker. Adenosine mostly has a cytotoxic effect, with the induction of apoptosis. The last studied nucleotide, AMP, demonstrated only a weak cytotoxic effect without affecting the cell cycle. In addition, cell migration towards SDF-1 was inhibited by low micromolar concentrations (10 μM). One of the reasons for this action of ATPγS and adenosine was a reduction in CXCR4 surface expression, but this only partially explains the mechanism of antimigratory action. In summary, extracellular adenine nucleotides and adenosine inhibit THP-1 cell growth, cause death of cells and modulate the functioning of the SDF-1/CXCR4 axis. Thus, they negatively affect the processes that are responsible for the progression of AML and the difficulties in AML treatment.

Innate immunity orchestrates the mobilization and homing of hematopoietic stem/progenitor cells by engaging purinergic signaling-an update

Bone marrow (BM) as an active hematopoietic organ is highly sensitive to changes in body microenvironments and responds to external physical stimuli from the surrounding environment. In particular, BM tissue responds to several cues related to infections, strenuous exercise, tissue/organ damage, circadian rhythms, and physical challenges such as irradiation. These multiple stimuli affect BM cells to a large degree through a coordinated response of the innate immunity network as an important guardian for maintaining homeostasis of the body. In this review, we will foc++us on the role of purinergic signaling and innate immunity in the trafficking of hematopoietic stem/progenitor cells (HSPCs) during their egression from the BM into peripheral blood (PB), as seen along pharmacological mobilization, and in the process of homing and subsequent engraftment into BM after hematopoietic transplantation. Innate immunity mediates these processes by engaging, in addition to certain peptide-based factors, other important non-peptide mediators, including bioactive phosphosphingolipids and extracellular nucleotides, as the main topic of this review. Elucidation of these mechanisms will allow development of more efficient stem cell mobilization protocols to harvest the required number of HSPCs for transplantation and to accelerate hematopoietic reconstitution in transplanted patients.

The Nlrp3 inflammasome as a "rising star" in studies of normal and malignant hematopoiesis

Recent investigations indicate that hematopoiesis is coregulated by innate immunity signals and by pathways characteristic of the activation of innate immunity cells that also operate in normal hematopoietic stem progenitor cells (HSPCs). This should not be surprising because of the common developmental origin of these cells from a hemato/lymphopoietic stem cell. An important integrating factor is the Nlrp3 inflammasome, which has emerged as a major sensor of changes in body microenvironments, cell activation, and cell metabolic activity. It is currently the best-studied member of the inflammasome family expressed in hematopoietic and lymphopoietic cells, including also HSPCs. It is proposed as playing a role in (i) the development and expansion of HSPCs, (ii) their release from bone marrow (BM) into peripheral blood (PB) in stress situations and during pharmacological mobilization, (iii) their homing to BM after transplantation, and (iv) their aging and the regulation of hematopoietic cell metabolism. The Nlrp3 inflammasome is also involved in certain hematological pathologies, including (i) myelodysplastic syndrome, (ii) myeloproliferative neoplasms, (iii) leukemia, and (iv) graft-versus-host disease (GvHD) after transplantation. The aim of this review is to shed more light on this intriguing intracellular protein complex that has become a “rising star” in studies focused on both normal steady-state and pathological hematopoiesis.

Involvement of P2 receptors in hematopoiesis and hematopoietic disorders, and as pharmacological targets

Several reports have shown the presence of P2 receptors in hematopoietic stem cells (HSCs). These receptors are activated by extracellular nucleotides released from different sources. In the hematopoietic niche, the release of purines and pyrimidines in the milieu by lytic and nonlytic mechanisms has been described. The expression of P2 receptors from HSCs until maturity is still intriguing scientists. Several reports have shown the participation of P2 receptors in events associated with modulation of the immune system, but their participation in other physiological processes is under investigation. The presence of P2 receptors in HSCs and their ability to modulate this population have awakened interest in exploring the involvement of P2 receptors in hematopoiesis and their participation in hematopoietic disorders. Among the P2 receptors, the receptor P2X7 is of particular interest, because of its different roles in hematopoietic cells (e.g., infection, inflammation, cell death and survival, leukemias and lymphomas), making the P2X7 receptor a promising pharmacological target. Additionally, the role of P2Y12 receptor in platelet activation has been well-documented and is the main example of the importance of the pharmacological modulation of P2 receptor activity. In this review, we focus on the role of P2 receptors in the hematopoietic system, addressing these receptors as potential pharmacological targets.

The NLRP3 inflammasome: a therapeutic target for inflammation-associated cancers

Introduction: Inflammasomes are large multimeric intracellular complexes that are capable of maturation and secretion of pro-inflammatory cytokines, IL-1β and IL-18, in response to danger signal molecules. As a member of the inflammasome family, the NLRP3 inflammasome has recently been under intense investigation revealing its possible role in several human diseases especially cancers.Areas covered: In this review, we will discuss the biology and mechanism of NLRP3 inflammasome activation, its role in specific types of tumors and the novel therapeutic modalities targeting this complex.Expert opinion: The NLRP3 inflammasome and its components including the adapter apoptosis-associated speck-like (ASC) protein and caspase-1 impose different and sometimes contrasting effects in tumorigenesis depending on various contexts. Considering the novel role of this complex in the initiation and progression of neoplasia, the NLRP3 inflammasome and its pathways provide desirable therapeutic targets for prevention, treatment, and prognosis of certain types of cancer. To date, several agents have been introduced for this purpose, some of which have shown promising results in the clinic.