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The relationship between bone and immune cells is well established both in physiological and pathological conditions. Multiple myeloma (MM) is a plasma cell malignancy characterized by an increase of number and activity of osteoclasts (OCLs) and a decrease of osteoblasts (OBs). These events are responsible for bone lesions of MM patients. OCLs support MM cells survival in vitro and in vivo. Recently, the possible role of OCLs as immunosuppressive cells in the MM BM microenvironment has been underlined. OCLs protect MM cells against T cell-mediated cytotoxicity through the expression of several molecules including programmed death-ligand (PD-L) 1, galectin (Gal) 9, CD200, and indoleamine-2,3-dioxygenase (IDO). Among the molecules that could be involved in the link between immune-microenvironment and osteoclastogenesis the role of CD38 has been hypothesized. CD38 is a well-known adhesion molecule and an ectoenzyme highly expressed by MM cells. Moreover, CD38 is expressed by OCLs and at the surface level on OCL precursors. Targeting CD38 with monoclonal antibodies showed inhibition of both osteoclastogenesis and OCL-mediated suppression of T cell function. This review elucidates this evidence indicating that osteoclastogenesis affect MM immune-microenvironment being a potential target to improve anti-MM immunity and to ameliorate bone disease., (Copyright © 2018 European Federation of Immunological Societies. Published by Elsevier B.V. All rights reserved.)

Osteocytes are terminally differentiated cells of the osteoblast lineage. They are involved in the regulation of bone remodeling by increasing osteoclast formation or decreasing bone formation by the secretion of the osteoblast inhibitor sclerostin. Monoclonal antibody anti-sclerostin, Romosozumab, has been developed and tested in clinical trials in patients with osteoporosis. In the last years, the role of osteocytes in the development of osteolytic bone lesions that occurs in multiple myeloma, have been underlined. Myeloma cells increase osteocyte death through the up-regulation of both apoptosis and autophagy that, in turn, triggers osteoclast formation, and activity. When compared to healthy controls, myeloma patients with bone disease have higher osteocyte cell death, but the treatment with proteasome inhibitor bortezomib has been shown to maintain osteocyte viability. In preclinical mouse models of multiple myeloma, treatment with blocking anti-sclerostin antibody increased osteoblast numbers and bone formation rate reducing osteolytic bone lesions. Moreover, the combination of anti-sclerostin antibody and the osteoclast inhibitor zoledronic acid increased bone mass and fracture resistance synergistically. However, anti-sclerostin antibody did not affect tumor burden in vivo or the efficacy of anti-myeloma drugs in vitro . Nevertheless, the combination therapy of anti-sclerostin antibody and the proteasome inhibitor carfilzomib, displayed potent anti-myeloma activity as well as positive effects on bone disease in vivo . In conclusion, all these data suggest that osteocytes are involved in myeloma bone disease and may be considered a novel target for the use of antibody-mediated anti-sclerostin therapy also in multiple myeloma patients.

Introduction: Bone destruction is the hallmark of multiple myeloma (MM). About 80% of MM patients at diagnosis presents myeloma bone disease (MBD) leading to bone pain and pathological fractures, significantly affecting patients' quality of life. Bisphosphonates are the treatment of choice for MBD, but osteolytic lesions remain a critical issue in the current management of MM patients. Several studies clarified the mechanisms involved in MM-induced osteoclast formation and activation, leading to the identification of new possible targets and the development of better bone-directed therapies, that are discussed in this review. Areas covered: This review summarizes the latest advances in the knowledge of the pathophysiology of the osteoclast formation and activation induced by MM cells, and the new therapeutic targets identified. Recently, neutralizing antibodies (i.e. denosumab, siltuximab, daratumumab), as well as recombinant fusion proteins, and receptor molecular inhibitors, have been developed to block these targets. Clinical trials testing their anti-MBD potential are ongoing. The emerging role of exosomes and microRNAs in the regulation of osteoclast differentiation has been also discussed. Expert commentary: Although further studies are needed to arrive at a clinical approving, the basis for the development of better bone-directed therapies has been established.

Bone marrow monocytes are primarily committed to osteoclast formation. It is, however, unknown whether potential primary alterations are specifically present in bone marrow monocytes from patients with multiple myeloma, smoldering myeloma or monoclonal gammopathy of undetermined significance. We analyzed the immunophenotypic and transcriptional profiles of bone marrow CD14 + monocytes in a cohort of patients with different types of monoclonal gammopathies to identify alterations involved in myeloma-enhanced osteoclastogenesis. The number of bone marrow CD14 + CD16 + cells was higher in patients with active myeloma than in those with smoldering myeloma or monoclonal gammopathy of undetermined significance. Interestingly, sorted bone marrow CD14 + CD16 + cells from myeloma patients were more pro-osteoclastogenic than CD14 + CD16-cells in cultures ex vivo Moreover, transcriptional analysis demonstrated that bone marrow CD14 + cells from patients with multiple myeloma (but neither monoclonal gammopathy of undetermined significance nor smoldering myeloma) significantly upregulated genes involved in osteoclast formation, including IL21R IL21R mRNA over-expression by bone marrow CD14 + cells was independent of the presence of interleukin-21. Consistently, interleukin-21 production by T cells as well as levels of interleukin-21 in the bone marrow were not significantly different among monoclonal gammopathies. Thereafter, we showed that IL21R over-expression in CD14 + cells of myeloma patients. Our results indicate that bone marrow monocytes from multiple myeloma patients show distinct features compared to those from patients with indolent monoclonal gammopathies, supporting the role of + cells of myeloma patients. Our results indicate that bone marrow monocytes from multiple myeloma patients show distinct features compared to those from patients with indolent monoclonal gammopathies, supporting the role of IL21R over-expression by bone marrow CD14 + cells in enhanced osteoclast formation., (Copyright© Ferrata Storti Foundation.)

The skin is a possible site of extramedullary localization in multiple myeloma (MM) patients; however, the mechanisms involved in this process are poorly understood. We describe the case of a refractory MM patient who developed a cutaneous localization under bortezomib treatment and we further expanded observations in other eight MM patients. We focused on the expression of genes involved in plasma cell skin homing, including CCR10, which was highly expressed. Moreover, we observed a lack of CXCR4 surface expression and the down-regulation of ICAM1/CD54 throughout the progression of the disease, suggesting a possible mechanism driving the escape of MM cells from the bone marrow into the skin.

Galectin-1 (Gal-1) is involved in tumoral angiogenesis, hypoxia and metastases. Actually the Gal-1 expression profile in multiple myeloma (MM) patients and its pathophysiological role in MM-induced angiogenesis and tumoral growth are unknown. In this study, we found that Gal-1 expression by MM cells was upregulated in hypoxic conditions and that stable knockdown of hypoxia inducible factor-1α significantly downregulated its expression. Therefore, we performed Gal-1 inhibition using lentivirus transfection of shRNA anti-Gal-1 in human myeloma cell lines (HMCLs), and showed that its suppression modified transcriptional profiles in both hypoxic and normoxic conditions. Interestingly, Gal-1 inhibition in MM cells downregulated proangiogenic genes, including MMP9 and CCL2, and upregulated the antiangiogenic ones SEMA3A and CXCL10. Consistently, Gal-1 suppression in MM cells significantly decreased their proangiogenic properties in vitro. This was confirmed in vivo, in two different mouse models injected with HMCLs transfected with anti-Gal-1 shRNA or the control vector. Gal-1 suppression in both models significantly reduced tumor burden and microvascular density as compared with the control mice. Moreover, Gal-1 suppression induced smaller lytic lesions on X-ray in the intratibial model. Overall, our data indicate that Gal-1 is a new potential therapeutic target in MM blocking angiogenesis.

The importance of glutamine (Gln) metabolism in multiple myeloma (MM) cells and its potential role as a therapeutic target are still unknown, although it has been reported that human myeloma cell lines (HMCLs) are highly sensitive to Gln depletion. In this study, we found that both HMCLs and primary bone marrow (BM) CD138(+) cells produced large amounts of ammonium in the presence of Gln. MM patients have lower BM plasma Gln with higher ammonium and glutamate than patients with indolent monoclonal gammopathies. Interestingly, HMCLs expressed glutaminase (GLS1) and were sensitive to its inhibition, whereas they exhibited negligible expression of glutamine synthetase (GS). High GLS1 and low GS expression were also observed in primary CD138(+) cells. Gln-free incubation or treatment with the glutaminolytic enzyme l-asparaginase depleted the cell contents of Gln, glutamate, and the anaplerotic substrate 2-oxoglutarate, inhibiting MM cell growth. Consistent with the dependence of MM cells on extracellular Gln, a gene expression profile analysis, on both proprietary and published datasets, showed an increased expression of the Gln transporters SNAT1, ASCT2, and LAT1 by CD138(+) cells across the progression of monoclonal gammopathies. Among these transporters, only ASCT2 inhibition in HMCLs caused a marked decrease in Gln uptake and a significant fall in cell growth. Consistently, stable ASCT2 downregulation by a lentiviral approach inhibited HMCL growth in vitro and in a murine model. In conclusion, MM cells strictly depend on extracellular Gln and show features of Gln addiction. Therefore, the inhibition of Gln uptake is a new attractive therapeutic strategy for MM., (© 2016 by The American Society of Hematology.)

Multiple myeloma (MM) is characterized by severely imbalanced bone remodeling. In this study, we investigated the potential effect of proteasome inhibitors (PIs), a class of drugs known to stimulate bone formation, on the mechanisms involved in osteocyte death induced by MM cells. First, we performed a histological analysis of osteocyte viability on bone biopsies on a cohort of 37 MM patients with symptomatic disease. A significantly higher number of viable osteocytes was detected in patients treated with a bortezomib (BOR)-based regimen compared with those treated without BOR. Interestingly, both osteocyte autophagy and apoptosis were affected in vivo by BOR treatment. Thereafter, we checked the in vitro effect of BOR to understand the mechanisms whereby BOR maintains osteocyte viability in bone from MM patients. We found that osteocyte and preosteocyte autophagic death was triggered during coculturing with MM cells. Our evaluation was conducted by analyzing either autophagy markers microtubule-associated protein light chain 3 beta (LC3B) and SQSTM1/sequestome 1 (p62) levels, or the cell ultrastructure by transmission electron microscopy. PIs were found to increase the basal levels of LC3 expression in the osteocytes while blunting the myeloma-induced osteocyte death. PIs also reduced the autophagic death of osteocytes induced by high-dose dexamethasone (DEX) and potentiated the anabolic effect of PTH(1-34). Our data identify osteocyte autophagy as a new potential target in MM bone disease and support the use of PIs to maintain osteocyte viability and improve bone integrity in MM patients., (© 2015 American Society for Bone and Mineral Research.)

The relationship between bone marrow (BM) cytokine and chemokine levels, cytogenetic profiles and skeletal involvement in multiple myeloma (MM) patients is not yet defined. This study investigated a cohort of 455 patients including monoclonal gammopathy of uncertain significance (MGUS), smoldering MM and symptomatic MM patients. Skeletal surveys, positron emission tomography (PET)/computerized tomography (CT) and magnetic resonance imaging (MRI) were used to identify myeloma bone disease. Significantly higher median BM levels of both C-C motif Ligand (CCL)3 and CCL20 were found in MM patients with radiographic evidence of osteolytic lesions as compared with those without, and in all MM patients with positive PET/CT scans. BM levels of CCL3, CCL20, Activin-A and Dickkopf-1 (DKK-1) were significantly higher in patients with high bone disease as compared with patients with low bone disease. Moreover, CCL20 BM levels were significant predictors of osteolysis on X-rays by multivariate logistic analysis. On the other hand, DKK-1 levels were related to the presence of MRI lesions independently of the osteolysis at the X-rays. Our data define the relationship between bone disease and the BM cytokine and chemokine patterns highlighting the tight relationship between CCL20 BM levels and osteolysis in MM.

The osteoblastic niche has a critical role in the regulation of hemopoietic stem cell (HSC) quiescence and self-renewal and in the support of hematopoiesis. Several mechanisms are involved in the crosstalk between stem cells and osteoblasts, including soluble cytokines, adhesion molecules, and signal pathways such as the wingless-Int (Wnt), Notch, and parathyroid hormone pathways. According to the most recent evidence, there is an overlap between osteoblastic and perivascular niches that affects HSC function involving mesenchymal stromal and endothelial cells and a gradient of oxygen regulated by hypoxia inducible factor (HIF)-1α. Derived from plasma cells, multiple myeloma (MM) is a hematopoietic malignancy characterized by a peculiar dependency on the bone microenvironment. Quiescent MM cells may reside in the osteoblastic niche for protection from apoptotic stimuli; in turn, MM cells suppress osteoblast formation and function, leading to impairment of bone formation and the development of osteolytic lesions. Several recent studies have investigated the mechanisms involved in the relationship between osteoblasts and MM cells and identified potential therapeutic targets in the osteoblastic niche, including the HIF-1α, Runx2, and Wnt (both canonical and noncanonical) signaling pathways., (© 2014 New York Academy of Sciences.)

The bone marrow provides a protected environment for generating a vast array of cell types. Bones are thus a dynamic source of structural components and soluble factors used either locally or at a distance from their site of production. We discuss the role of ectoenzymes in the bone niche where human myeloma grows. Selected ectoenzymes have been tested for their ability to promote production of substrates involved in signaling, synthesis of growth factors and hormones, and modulation of the immune response. Because of the difficulty of simultaneously tracking all these activities, we narrow our focus to events potentially influencing synthesis of adenosine (ADO), an important regulator of multiple biological functions, including local immunological tolerance. Our working hypothesis, to be discussed and partially tested herein, is that CD38, and likely BST1/CD157--both NAD(+) -consuming enzymes, are active in the myeloma niche and lead a discontinuous chain of ectoenzymes whose final products are exploited by the neoplastic plasma cell as part of its local survival strategy. Coadjuvant ectoenzymes include PC-1/CD203a, CD39, and CD73, which control the production of ADO. Results discussed here and from ongoing experiments indicate that the myeloma niche hosts the canonical, as well as alternative, pathways of ADO generation. Other possibilities are presented and discussed., (© 2014 New York Academy of Sciences.)

Multiple myeloma (MM) is characterized by a high capacity to induce alterations in the bone remodeling process. The increase in osteoclastogenesis and the suppression of osteoblast formation are both involved in the pathophysiology of the bone lesions in MM. The proteasome inhibitor (PI) bortezomib is the first drug designed and approved for the treatment of MM patients by targeting the proteasome. However, recently novel PIs have been developed to overcome bortezomib resistance. Interestingly, several preclinical data indicate that the proteasome complex is involved in both osteoclast and osteoblast formation. It is also evident that bortezomib either inhibits osteoclast differentiation induced by the receptor activator of nuclear factor kappa B (NF-κB) ligand (RANKL) or stimulates the osteoblast differentiation. Similarly, the new PIs including carfilzomib and ixazomib can inhibit bone resorption and stimulate the osteoblast differentiation. In a clinical setting, PIs restore the abnormal bone remodeling by normalizing the levels of bone turnover markers. In addition, a bone anabolic effect was described in responding MM patients treated with PIs, as demonstrated by the increase in the osteoblast number. This review summarizes the preclinical and clinical evidence on the effects of bortezomib and other new PIs on myeloma bone disease.

Hypoxia-inducible transcription factor-1 (HIF-1α) is overexpressed in multiple myeloma (MM) cells within the hypoxic microenvironment. Herein, we explored the effect of persistent HIF-1α inhibition by a lentivirus short hairpin RNA pool on MM cell growth either in vitro or in vivo and on the transcriptional and pro-angiogenic profiles of MM cells. HIF-1α suppression did not have a significant impact on MM cell proliferation and survival in vitro although, increased the antiproliferative effect of lenalidomide. On the other hand, we found that HIF-1α inhibition in MM cells downregulates the pro-angiogenic genes VEGF, IL8, IL10, CCL2, CCL5 and MMP9. Pro-osteoclastogenic cytokines were also inhibited, such as IL-7 and CCL3/MIP-1α. The effect of HIF-1α inhibition was assessed in vivo in nonobese diabetic/severe combined immunodeficiency mice both in a subcutaneous and an intratibial MM model. HIF-1α inhibition caused a dramatic reduction in the weight and volume of the tumor burden in both mouse models. Moreover, a significant reduction of the number of vessels and vascular endothelial growth factors (VEGFs) immunostaining was observed. Finally, in the intratibial experiments, HIF-1α inhibition significantly blocked bone destruction. Overall, our data indicate that HIF-1α suppression in MM cells significantly blocks MM-induced angiogenesis and reduces MM tumor burden and bone destruction in vivo, supporting HIF-1α as a potential therapeutic target in MM.

Multiple myeloma (MM) is characterized by the impaired osteogenic differentiation of human mesenchymal stromal cells (hMSCs). Canonical Wnt signaling is critical for the regulation of bone formation, however, recent evidence suggests that the non-canonical Wnt agonist Wnt5a stimulates human osteoblastogenesis through its co-receptor Ror2. The effects of MM cells on non-canonical Wnt signaling and the effect of the activation of this pathway on MM-induced osteoblast exhaustion are not known and were investigated in this study. We found that the osteogenic differentiation of bone marrow hMSCs toward osteoprogenitor cells (PreOB) significantly increased Ror2 expression, and that MM cells inhibit Ror2 expression by PreOB in co-culture by inhibiting the non-canonical Wnt5a signaling. The activation of the non-canonical Wnt pathway in hMSCs by means of Wnt5a treatment and the overexpression of Wnt5 or Ror2 by lentiviral vectors increased the osteogenic differentiation of hMSCs and blunted the inhibitory effect of MM in co-culture. Consistently, Wnt5a inhibition by specific small interfering RNA reduced the hMSC expression of osteogenic markers. Our findings demonstrate that the Wnt5a/Ror2 pathway is involved in the pathophysiology of MM-induced bone disease and that the activation of the non-canonical Wnt5a/Ror2 pathway in hMSCs increases osteogenic differentiation and may counterbalance the inhibitory effect of MM cells.

The involvement of osteocytes in multiple myeloma (MM)-induced osteoclast (OCL) formation and bone lesions is still unknown. Osteocytes regulate bone remodelling at least partially, as a result of their cell death triggering OCL recruitment. In this study, we found that the number of viable osteocytes was significantly smaller in MM patients than in healthy controls, and negatively correlated with the number of OCLs. Moreover, the MM patients with bone lesions had a significantly smaller number of viable osteocytes than those without, partly because of increased apoptosis. These findings were further confirmed by ultrastructural in vitro analyses of human preosteocyte cells cocultured with MM cells, which showed that MM cells increased preosteocyte death and apoptosis. A micro-array analysis showed that MM cells affect the transcriptional profiles of preosteocytes by upregulating the production of osteoclastogenic cytokines such as interleukin (IL)-11, and increasing their pro-osteoclastogenic properties. Finally, the osteocyte expression of IL-11 was higher in the MM patients with than in those without bone lesions. Our data suggest that MM patients are characterized by a reduced number of viable osteocytes related to the presence of bone lesions, and that this is involved in MM-induced OCL formation.

Homeobox (HOX) gene transcription factors are frequently deregulated in hematologic malignancies and involved in leukemogenic transformation [1]. Moreover, their overexpression has been associated with tumoral-induced neoangiogenesis in solid cancer [2]. The expression and the role of these genes have not yet been completely elucidated in multiple myeloma (MM). Recently, we reported that a small fraction of MM patients shows a HOXB7 overexpression as compared with normal samples and that HOXB7 expression correlates with bone marrow angiogenesis and the production of the proangiogenic factors by MM cells [3]. Other authors previously reported that HOXA cluster genes are expressed in a small fraction of MM patients [4]. Herein, we extended our previous evidences with the evaluation of the expression level of HOXB7 and the other gene family members in a large number of primary MM cells in relationship with the different molecular subgroups of MM and the presence of specific chromosome translocations. We found that HOXB7 and other genes of HOX family have a preferential distribution based on the characteristics of molecular MM subtypes based on the translocations/cyclins (TC) classification, suggesting a potential relationship between HOX genes expression, angiogenesis, and molecular features of MM patients.

The deregulation of the homeobox genes as homeoboxB (HOXB)-7 has been previously associated to tumor progression and angiogenesis; here we investigated the potential role of HOXB7 in the pro-angiogenic properties of multiple myeloma (MM) cells. We found that HOXB7 was expressed in 10 out of 22 MM patients analyzed at the diagnosis related to high bone marrow angiogenesis and overexpressed in about 40% of myeloma cell lines compared with normal plasma cells. Enforced HOXB7 expression in MM cells by a lentiviral vector significantly modified their transcriptional and angiogenic profile, checked by combined microarray and angiogenesis PCR analyses, upregulating VEGFA, FGF2, MMP2, WNT5a and PDGFA and downregulating thrombospoindin-2. The pro- and anti-angiogenic HOXB7-related gene signature was also validated in a large independent dataset of MM patients. Accordingly, MM-induced vessel formation was significantly increased by HOXB7 overexpression both in vitro angiogenic and chorioallantoic membrane assays, as well as the HOXB7 silencing by small interfering RNA inhibited the production of angiogenic factors, and the pro-angiogenic properties of MM cells. Finally, in SCID-NOD mice we confirmed that HOXB7 overexpression by MM cells stimulated tumor growth, increased MM-associated angiogenesis and the expression of pro-angiogenic genes by microarray analysis supporting the critical role of HOXB7 in the angiogenic switch in MM.

Objective: Multiple myeloma (MM) cells are extremely resistant to drug-induced apoptosis due to both intrinsic- and bone marrow (BM) microenvironment-dependent drug resistance particularly supported by bone cells. Growing evidence suggest that the osteoclast inhibitor zoledronic acid (ZOL) exerts both indirect and direct anti-tumoral effects, including an in vitro proapoptotic effect on MM cells, although this property has not yet been clearly observed in MM patients., Materials and Methods: In this study, we attempt to better define the cytotoxic effect of ZOL on MM cells in order to identify novel drug combinations able to potentiate its proapoptotic effect., Results: Our data shows that ZOL at concentrations ranging from 10 to 100 μM was able to induce MM cell apoptosis overcoming the prosurvival effect of both stromal cells and osteoclasts and independent of the intrinsic bortezomib resistance of MM cells. Interestingly, we found that the capacity of ZOL to induce apoptosis in bortezomib-resistant cells was associated with a downregulation of the proapoptotic molecule myeloid cell leukemia-1. A transcriptional analysis by microarray was also performed to identify genes specifically modulated by ZOL in bortezomib-resistant MM cells. Finally, we show an additive effect of arsenic trioxide on apoptosis when used in combination with ZOL., Conclusions: Our in vitro data suggest that the use of ZOL at appropriate doses could be explored clinically in bortezomib-resistant MM patients and combined with arsenic trioxide to increase its proapoptotic effect., (Copyright © 2011 ISEH - Society for Hematology and Stem Cells. Published by Elsevier Inc. All rights reserved.)

Objective: Multiple myeloma (MM) is characterized by a high incidence of osteolytic bone lesions, which have been previously correlated with the gene expression profiles of MM cells. The aim of this study was to investigate the transcriptional patterns of cells in the bone microenvironment and their relationships with the presence of osteolysis in MM patients., Materials and Methods: Both mesenchymal (MSC) and osteoblastic (OB) cells were isolated directly from bone biopsies of MM patients and controls to perform gene expression profiling by microarrays and real-time polymerase chain reaction on selected bone-related genes., Results: We identified a series of upregulated and downregulated genes that were differentially expressed in the MSC cells of osteolytic and nonosteolytic patients. Comparison of the osteolytic and nonosteolytic samples also showed that the MSC cells and OB had distinct transcriptional patterns. No significantly modulated genes were found in the OBs of the osteolytic and nonosteolytic patients., Conclusions: Our data suggest that the gene expression profiles of cells of the bone microenvironment are different in MM patients and controls, and that MSC cells, but not OBs, have a distinct transcriptional pattern associated with the occurrence of bone lesions in MM patients. These data support the idea that alterations in MSC cells may be involved in MM bone disease., (Copyright 2010 ISEH - Society for Hematology and Stem Cells. Published by Elsevier Inc. All rights reserved.)

Multiple myeloma (MM) derives from malignant transformation of plasma cells (PC), which accumulate in the bone marrow (BM), where microenvironment supports tumor growth and inhibits anti-tumor immune responses. Adenosine (ADO), an immunosuppressive molecule, is produced within MM patients' BM by adenosinergic ectoenzymes, starting from ATP (CD39/CD73) or NAD+ [CD38/CD203a(PC-1)/CD73]. These ectoenzymes form a discontinuous network expressed by different BM cells. We investigated the expression and function of ectoenzymes on microvesicles (MVs) isolated from BM plasma samples of patients with MM, using asymptomatic forms of monoclonal gammopathy of undetermined significance (MGUS) and smoldering MM (SMM) as controls. The percentage of MVs expressing ectoenzymes at high levels was higher when derived from MM patients than controls. BM CD138+ PC from MM patients expressed high levels of all ectoenzymes. Paired MVs samples confirmed a higher percentage of MVs with high ectoenzymes expression in MM patients than controls. Pooled MVs from MM patients or controls were tested for ADO production. The catabolism of ATP, NAD+, ADPR and AMP to ADO was higher in MVs from MM patients than in those from controls. In conclusion, our results confirmed the hypothesis that MVs in MM niche are main contributor of ADO production. The ability of MVs to reach biological fluids strongly support the view that MVs may assume diagnostic and pathogenetic roles. [ABSTRACT FROM AUTHOR]

Multiple myeloma (MM) derives from malignant transformation of plasma cells (PC), which accumulate in the bone marrow (BM), where microenvironment supports tumor growth and inhibits anti-tumor immune responses. Adenosine (ADO), an immunosuppressive molecule, is produced within MM patients' BM by adenosinergic ectoenzymes, starting from ATP (CD39/CD73) or NAD+ [CD38/CD203a(PC-1)/CD73]. These ectoenzymes form a discontinuous network expressed by different BM cells. We investigated the expression and function of ectoenzymes on microvesicles (MVs) isolated from BM plasma samples of patients with MM, using asymptomatic forms of monoclonal gammopathy of undetermined significance (MGUS) and smoldering MM (SMM) as controls. The percentage of MVs expressing ectoenzymes at high levels was higher when derived from MM patients than controls. BM CD138+ PC from MM patients expressed high levels of all ectoenzymes. Paired MVs samples confirmed a higher percentage of MVs with high ectoenzymes expression in MM patients than controls. Pooled MVs from MM patients or controls were tested for ADO production. The catabolism of ATP, NAD+, ADPR and AMP to ADO was higher in MVs from MM patients than in those from controls. In conclusion, our results confirmed the hypothesis that MVs in MM niche are main contributor of ADO production. The ability of MVs to reach biological fluids strongly support the view that MVs may assume diagnostic and pathogenetic roles. [ABSTRACT FROM AUTHOR]