Tumor-host cell interactions in the bone disease of myeloma

The Leucine-Rich α2-Glycoprotein-1 Levels in Patients with Multiple Myeloma

INTRODUCTION

Angiogenesis is considered important in the pathogenesis of multiple myeloma (MM), as well as in the targeted treatment of the disease. Leucine-rich α2-glycoprotein 1 (LRG1) is a protein that participates in angiogenesis and its effect on solid organ tumors has been investigated recently. This study aimed to investigate the relationship between MM and LRG1.

METHODS

The MM patients who admitted to Hatay Mustafa Kemal University Hematology Clinic between September 2021 and October 2022 were included in the study. The study consists of a total of 4 groups: newly diagnosed MM (NDMM), relapsed refractory MM (RRMM), MM in remission (Rem-MM), and control group. Demographic data were retrieved from hospital records. Blood samples of our study groups were centrifuged at 1,500 × g for 10 min and serum was collected. LRG1, IL-6, IL-8, TGF-β1, HIF-1α, FGF-2, and VEGF levels were analyzed in all groups by ELISA method, and statistical analysis was performed.

RESULTS

A total of 112 individuals, including NDMM (n: 27), RRMM (n: 18), Rem-MM (n: 42), and control group (n: 25), were enrolled in the study. Based on the analyses, the NDMM group exhibited significantly elevated levels of LRG1 (p < 0.001), TGF-1 (p < 0.001), and HIF-1α (p = 0.046, p < 0.001, and p = 0.003 compared to the RRMM, Rem-MM, and control groups, respectively) compared to the other groups. LRG1 levels were positively correlated with creatinine (r: 0.363, p = 0.001), calcium (r: 0.344, p = 0.001), total protein (r: 0.473, p < 0.001), erythrocyte sedimentation rate (r: 0.547, p < 0.001), lactate dehydrogenase (r: 0.321, p = 0.003), beta-2-microglobulin (r: 0.312, p = 0.017), IL-6 (r: 0.478, p < 0.001), IL-8 (r: 0.240, p = 0.03), TGF-β1 (r: 0.521, p < 0.001), and HIF-1α (r: 0.321, p = 0.003) levels and were negatively correlated with hemoglobin (r: -0.512, p < 0.001) and albumin (r: -0.549, p < 0.001) levels. Receiver operating characteristics (ROC) analysis revealed the association of LRG1 with the highest AUC value of 0.959 (95% CI: 0.904-1, p < 0.001) and the optimal cut-off value of 534.95 ng/mL (sensitivity: 93% and specificity: 99%) in the NDMM group compared to the control group.

CONCLUSION

In this study, providing data for the first time on LRG1 levels in the setting of MM. LRG1 levels were found to be significantly higher in NDMM patients and in our study discriminate this patient population from RRMM, Rem-MM, and normal controls. Therefore, LRG1 seems to a potential biomarker that should be evaluated in future studies addressing the diagnosis, staging, follow-up, prognosis, and treatment target of MM.

Immunotherapy of cancer in single-cell RNA sequencing era: A precision medicine perspective

Immunotherapy has revolutionized cancer treatment and brought new aspects into tumor immunology. Effective immunotherapy will require using the suitable target antigens, optimizing the interaction between the antigenic peptide, the APC, and the T cell, and the simultaneous inhibitor of the negative regulatory process that inhibits immunotherapeutic effects and develop resistance. Tumor heterogeneity and its microenvironment is the leading cause of resistance in patients. Recently by emerging the single-cell RNA sequencing technology and its combination with immunotherapy, now we can specifically evaluate the mechanism of tumors in the face of immunotherapy agents at the single-cell resolution by detecting the transcriptional activity of immune checkpoints, screening neoantigens with high transcription levels, identifying rare cells, and other important processes. This review focuses on scRNA-seq, particularly on its application in cancer immunotherapy.

Genetic determinants of multiple myeloma risk within the Wnt/beta-catenin signaling pathway

BACKGROUND

Aberrant Wnt/beta-catenin pathway activation is implicated in Multiple Myeloma (MM) development, but little is known if genetic variants within this pathway contribute to MM susceptibility.

METHODS

We performed a discovery candidate pathway analysis in 269 non-Hispanic white MM cases and 272 controls focusing on 171 variants selected from 26 core genes within the Wnt/beta-catenin pathway. Significant candidate variants (P < 0.05) were selected for validation in internal and external non-Hispanic white populations totaling 818 cases and 1209 controls. We also examined significant variants in non-Hispanic black and Hispanic case/control study populations to identify potential differences by race/ethnicity. Possible biological functions of candidate variants were predicted in silico.

RESULTS

Seven variants were significantly associated with MM risk in non-Hispanic whites in the discovery population, of which LRP6:rs7966410 (OR: 0.57; 95 % CI: 0.38-0.88; P = 9.90 × 10^-3) and LRP6:rs7956971 (OR: 0.64; 95 % CI: 0.44-0.95; P = 0.027) remained significant in the internal and external populations. CSNK1D:rs9901910 replicated among all three racial/ethnic groups, with 2-6 fold increased risk of MM (OR: 2.40; 95 % CI: 1.67-3.45; P = 2.43 × 10^-6 - non-Hispanic white; OR: 6.42; 95 % CI: 2.47-16.7; P = 3.14 × 10^-4 - non-Hispanic black; OR: 4.31; 95 % CI: 1.83-10.1; P = 8.10 × 10^-4 - Hispanic). BTRC:rs7916830 was associated with a significant 37 % and 24 % reduced risk of MM in the non-Hispanic white (95 % CI: 0.49-0.82; P = 5.60 × 10^-4) and non-Hispanic Black (95 % CI: 0.60-0.97; P = 0.028) population, respectively. In silico tools predicted that these loci altered function through via gene regulation.

CONCLUSION

We identified several variants within the Wnt/beta-catenin pathway associated with MM susceptibility. Findings of this study highlight the potential genetic role of Wnt/beta-catenin signaling in MM etiology among a diverse patient population.

Management of Myeloma Bone Lesions

Multiple myeloma (MM) is a B-cell neoplasm characterized by clonal plasma-cell proliferation. The survival and prognosis of this condition have been significantly improved by treatment with active anti-MM drugs such as bortezomib or lenalidomide. Further, the discovery of novel agents has recently paved the way for new areas of investigation. However, MM, including myeloma-related bone diseases, remains fatal. Bone disease or bone destruction in MM is a consequence of skeletal involvement with bone pain, spinal cord compression, and bone fracture resulting from osteolytic lesions. These consequences affect disease outcomes, including patients' quality of life and survival. Several studies have sought to better understand MM bone disease (MBD) through the classification of its molecular mechanisms, including osteoclast activation and osteoblast inhibition. Bisphosphonates and the receptor activator of the nuclear factor-kappa B (NF-κB) ligand (RANKL) inhibitor, denosumab, prevent skeletal-related events in MM. In addition, several other bone-targeting agents, including bone-anabolic drugs, are currently used in preclinical and early clinical evaluations. This review summarizes the current knowledge of the pathogenesis of MBD and discusses novel agents that appear very promising and will soon enter clinical development.

Concomitant Primary Hyperparathyroidism in Patients with Multiple Myeloma: A Possible Link?

Hypercalcemia is a significant feature of patients with active multiple myeloma (MM) with extensive bone disease. Among the causes of non-neoplastic hypercalcemia, primary hyperparathyroidism (PHPT) is one of the most common, leading to osteoporosis and bone fractures. Interestingly, some preclinical data indicate that high secretion of parathyroid hormone (PTH) may have a negative impact on bone disease and MM progression. However, concomitant diagnosis of MM and PHPT has rarely been described. Here, we present 4 cases of patients with active MM and hypercalcemia with high or inappropriately normal PTH levels. Interestingly, CD138+ cells from these 4 MM patients lack PTH receptor 1 and PTH-related peptide expressions, indicating that PTH could have a paracrine rather than a direct pro-tumoral effect. Moreover, these cases suggest that the concomitant diagnosis of MM and PHTP may not be so rare and should be considered for the clinical management of MM patients with hypercalcemia.

Multiple myeloma increases nerve growth factor and other pain-related markers through interactions with the bone microenvironment

Interactions between multiple myeloma (MM) and bone marrow (BM) are well documented to support tumour growth, yet the cellular mechanisms underlying pain in MM are poorly understood. We have used in vivo murine models of MM to show significant induction of nerve growth factor (NGF) by the tumour-bearing bone microenvironment, alongside other known pain-related characteristics such as spinal glial cell activation and reduced locomotion. NGF was not expressed by MM cells, yet bone stromal cells such as osteoblasts expressed and upregulated NGF when cultured with MM cells, or MM-related factors such as TNF-α. Adiponectin is a known MM-suppressive BM-derived factor, and we show that TNF-α-mediated NGF induction is suppressed by adiponectin-directed therapeutics such as AdipoRON and L-4F, as well as NF-κB signalling inhibitor BMS-345541. Our study reveals a further mechanism by which cellular interactions within the tumour-bone microenvironment contribute to disease, by promoting pain-related properties, and suggests a novel direction for analgesic development.

Current Perspectives in Cancer Immunotherapy

Different immunotherapeutic approaches have proved to be of significant clinical value to many patients with different types of advanced cancer. However, we need more precise immunotherapies and predictive biomarkers to increase the successful response rates. The advent of next generation sequencing technologies and their applications in immuno-oncology has helped us tremendously towards this aim. We are now moving towards the realization of personalized medicine, thus, significantly increasing our expectations for a more successful management of the disease. Here, we discuss the current immunotherapeutic approaches against cancer, including immune checkpoint blockade with an emphasis on anti-PD-L1 and anti-CTLA-4 monoclonal antibodies. We also analyze a growing list of other co-inhibitory and co-stimulatory markers and emphasize the mechanism of action of the principal pathway for each of these, as well as on drugs that either have been FDA-approved or are under clinical investigation. We further discuss recent advances in other immunotherapies, including cytokine therapy, adoptive cell transfer therapy and therapeutic vaccines. We finally discuss the modulation of gut microbiota composition and response to immunotherapy, as well as how tumor-intrinsic factors and immunological processes influence the mutational and epigenetic landscape of progressing tumors and response to immunotherapy but also how immunotherapeutic intervention influences the landscape of cancer neoepitopes and tumor immunoediting.

Increased Osteoblastic Activity Suppressed Proliferation of Multiple Myeloma Plasma Cells

STUDY DESIGN

In vitro experimental study.

OBJECTIVE

To investigate the impact of increased osteoblastic activity on the proliferation and survival of multiple myeloma (MM) plasma cells in vitro SUMMARY OF BACKGROUND DATA.: MM is one of representative hematologic malignancies that cause skeletal-related events (SREs) and dysregulation of bone remodeling is known as a key pathomechanism of disease progression and skeletal-related events. However, decreased proliferation of MM at fracture sites is frequently noted in clinical situations regardless of systemic disease activity.

METHODS

Co-culture under various conditions was used to investigate effects of increased osteoblastic activity on survival and proliferation of MM plasma cells. MM plasma cells were cultured in culture media (control) and co-cultured with human mesenchymal stem cells (hMSCs, group I), osteoblasts (OBs) induced from hMSCs (group II) or bone morphogenic protein-2 (BMP-2, group III). Proliferation measured as extracellular signal-regulated kinase (ERK) and immunoglobulin G (Ig G) expression and apoptosis measured as fluorescence-activated cell sorting (FACS) with annexin V method, caspase-3, and stat-3 expression were assessed for cultured MM plasma cells, along with expression of sclerostin.

RESULTS

After 72 hours of co-culture, group II and III showed decreased ERK expression compared with controls. Lower Ig G expression was also noted for groups II and III compared with controls. Group I did not show significantly decreased Ig G and ERK expression compared with controls. Expressions of caspase-3 in groups II and III were higher than controls. Co-culture with hMSCs showed decreased caspase-3 expression compared with control. FACS with annexin V showed higher apoptosis in groups II and III. Sclerostin expression was also decreased in osteoblastic conditions compared with the control and hMSCs co-culture condition.

CONCLUSION

Collectively, our data suggest that increased osteoblastic conditions may provide not only prevention of SREs but also anti-tumor effects on MM cells in the bone marrow environment.

LEVEL OF EVIDENCE

N/A.

Tissue engineered models of healthy and malignant human bone marrow

Tissue engineering is becoming increasingly successful in providing in vitro models of human tissues that can be used for ex vivo recapitulation of functional tissues as well as predictive testing of drug efficacy and safety. From simple tissue models to microphysiological platforms comprising multiple tissue types connected by vascular perfusion, these "tissues on a chip" are emerging as a fast track application for tissue engineering, with great potential for modeling diseases and supporting the development of new drugs and therapeutic targets. We focus here on tissue engineering of the hematopoietic stem and progenitor cell compartment and the malignancies that can develop in the human bone marrow. Our overall goal is to demonstrate the utility and interconnectedness of improvements in bioengineering methods developed in one area of bone marrow studies for the remaining, seemingly disparate, bone marrow fields.

Multiple Myeloma Exemplifies a Model of Cancer Based on Tissue Disruption as the Initiator Event

The standard model of multiple myeloma (MM) oncogenesis is based on the genetic instability of MM cells and presents its evolution as the emergence of clones with more and more aggressive genotypes, giving them surviving and proliferating advantage. The micro-environment has a passive role. In contrast, many works have shown that the progression of MM is also characterized by the selection of clones with extended phenotypes able to destroy bone trabeculae, suggesting a major role for early micro-environmental disruption. We present a model of MM oncogenesis in which genetic instability is the consequence of the disruption of normal interactions between plasma cells and their environment, the bone remodeling compartment. These interactions, which normally ensure the stability of the genotypes and phenotypes of normal plasma cells could be disrupted by many factors as soon as the early steps of the disease (MGUS, pre-MGUS states). Therapeutical implications of the model are presented.

Improving knowledge on the activation of bone marrow fibroblasts in MGUS and MM disease through the automatic extraction of genes via a nonnegative matrix factorization approach on gene expression profiles

Background

Multiple myeloma (MM) is a cancer of terminally differentiated plasma that is part of a spectrum of blood diseases. The role of the micro-environment is crucial for MM clonal evolution.

Methods

This paper describes the analysis carried out on a limited number of genes automatically extracted by a nonnegative matrix factorization (NMF) based approach from gene expression profiles of bone marrow fibroblasts of patients with monoclonal gammopathy of undetermined significance (MGUS) and MM.

Results

Automatic exploration through NMF, combined with a motivated post-processing procedure and a pathways analysis of extracted genes, allowed to infer that a functional switch is required to lead fibroblasts to acquire pro-tumorigenic activity in the progression of the disease from MGUS to MM.

Conclusion

The extracted biologically relevant genes may be representative of the considered clinical conditions and may contribute to a deeper understanding of tumor behavior.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1589-1) contains supplementary material, which is available to authorized users.

Wnt signaling in multiple myeloma: a central player in disease with therapeutic potential

Multiple myeloma is the second most frequent hematological malignancy in the western world and remains incurable, predominantly due to acquired drug resistance and disease relapse. The highly conserved Wnt signal transduction pathway, which plays a key role in regulating cellular processes of proliferation, differentiation, migration, and stem cell self-renewal, is associated with multiple aspects of disease. Bone homeostasis is severely disturbed by Wnt antagonists that are secreted by the malignant plasma cells in the bone marrow. In the vast majority of patients, this results in osteolytic bone disease, which is associated with bone pain and pathological fractures and was reported to facilitate disease progression. More recently, cumulative evidence also indicates the importance of intrinsic Wnt signaling in the survival of multiple myeloma cells. However, Wnt pathway-activating gene mutations could not be identified. The search for factors or processes responsible for Wnt pathway activation currently focuses on aberrant ligand levels in the bone marrow microenvironment, increased expression of Wnt transcriptional co-factors and associated micro-RNAs, and disturbed epigenetics and post-translational modification processes. Furthermore, Wnt pathway activation is associated with acquired cell adhesion-mediated resistance of multiple myeloma cells to conventional drug therapies, including doxorubicin and lenalidomide. In this review, we present an overview of the relevance of Wnt signaling in multiple myeloma and highlight the Wnt pathway as a potential therapeutic target for this disease.

Impact of connexin 43 coupling on survival and migration of multiple myeloma cells

INTRODUCTION

Gap junctions (GJs) represent the best known intercellular communication (IC) system and are membrane-spanning channels that facilitate intercellular communication by allowing small signaling molecules to pass from cell to cell. In this study, we constructed an amino terminus of human Cx43 (Cx43NT-GFP), verified the overexpression of Cx43-NT in HUVEC cells and explored the impact of gap junctions (GJs) on multiple myeloma (MM).

MATERIAL AND METHODS

The levels of phosphorylated Cx43(s368) and the change of MAPK pathway associated molecules (ERK1/2, JNK, p38, NFκB) were also investigated in our cell models. Cx43 mRNA and proteins were detected in both MM cell lines and mesenchymal stem cells (MSCs). Dye transfer assays demonstrated that gap junction intercellular communication (GJIC) occurring via Cx43 situated between MM and MSCs or MM and HUVEC^Cx43NT is functional.

RESULTS

Our results present evidence for a channel-dependent modulator action of connexin 43 on the migratory activity of MM cells toward MSCs or HUVECCx43-N was higher than those of spontaneous migration (p < 0.05) and protection them from apoptosis in the presence of dexamethasone via cytokines secretion. In the meantime, the migration of MM cells involves an augmented response of p38 and JNK signaling pathway of carboxyl tail of the protein.

CONCLUSIONS

Our data suggest that GJIC between MM and MSCs is one of the essential factors in tumor cell proliferation and drug sensitivity, and is implicated in MM pathogenesis.

Cx43 expressed on bone marrow stromal cells plays an essential role in multiple myeloma cell survival and drug resistance

INTRODUCTION

Connexin-43 (Cx43), a connexin constituent of gap junctions (GJs) is mainly expressed in bone marrow stromal cells (BMSCs) and played a important role on hematopoiesis. In this study, we explored the role of gap junctions (GJs) formed by Cx43 between BMSCs and multiple myeloma (MM) cells.

MATERIAL AND METHODS

qPCR and western blot assays were employed to assay Cx43 expression in three MM cell lines (RPMI 8266, U266, and XG7), freshly isolated MM cells, and bone marrow stromal cells (BMSCs). Cx43 mRNA and proteins were detected in all three MM cell lines and six out of seven freshly isolated MM cells.

RESUTHS

The BMSCs from MM patients expressed Cx43 at higher levels than of normal donor (ND-BMSCs). Dye transfer assays demonstrated that gap junction intercellular communication (GJIC) occurring via Cx43 situated between MM and BMSCs is functional. Cytometry beads array (CBA) assays showed that cytokines production changed when the ND-BMSCs were co-cultured with MM cells, especially the levels of IL-6, SDF-1α and IL-10 were higher than those the cells cultured alone and decreased significantly in the presence of GJ inhibitor heptanol. Our results demonstrated that the cytotoxicity of BTZ to MM cells decreased significantly in the presence of BMSCs, an effect that was partially recovered in the presence of GJ inhibitor.

CONCLUSIONS

Our data suggest that GJIC between MM and BMSCs is a critical factor in tumor cell proliferation and drug sensitivity, and is implicated in MM pathogenesis.

Emerging treatment approaches for myeloma-related bone disease

INTRODUCTION

Multiple myeloma is characterized by the presence of osteolytic lesions that leads to devastating skeletal-related events in the majority of patients. Myeloma bone disease is attributed to increased osteoclastic and suppressed osteoblastic activity. Areas covered: Bisphosphonates remain the main treatment option, however they have limitations on their own. Understanding the pathogenesis of myeloma bone disease may provide a roadmap for new therapeutic approaches. The pathway of RANKRANKLOPG pathway has revealed denosumab, a monoclonal antibody targeting RANKL as a novel emerging therapy for myeloma-related bone disease. Furthermore, the Wnt signaling inhibitors dicckopf-1 and sclerostin that are implicated in the pathogenesis of bone destruction of myeloma are now targeted by novel monoclonal antibodies. Activin-A is a TGF-beta superfamily member which increases osteoclast activity and inhibits osteoblast function in myeloma; sotatercept and other molecules targeting activin-A have entered into clinical development. Several other molecules and pathways that play an important role in the pathogenesis of bone destruction in myeloma, such as periostin, adiponectin, Notch and BTK signaling are also targeted in an attempt to develop novel therapies for myeloma-related bone disease. Expert commentary: We summarize the current advances in the biology of myeloma bone disease and the potential therapeutic targets.

A virtual approach to evaluate therapies for management of multiple myeloma induced bone disease

Multiple myeloma bone disease is devastating for patients and a major cause of morbidity. The disease leads to bone destruction by inhibiting osteoblast activity while stimulating osteoclast activity. Recent advances in multiple myeloma research have improved our understanding of the pathogenesis of multiple myeloma-induced bone disease and suggest several potential therapeutic strategies. However, the effectiveness of some potential therapeutic strategies still requires further investigation and optimization. In this paper, a recently developed mathematical model is extended to mimic and then evaluate three therapies of the disease, namely: bisphosphonates, bortezomib and TGF-β inhibition. The model suggests that bisphosphonates and bortezomib treatments not only inhibit bone destruction, but also reduce the viability of myeloma cells. This contributes to the current debate as to whether bisphosphonate therapy has an anti-tumour effect. On the other hand, the analyses indicate that treatments designed to inhibit TGF-β do not reduce bone destruction, although it appears that they might reduce the viability of myeloma cells, which again contributes to the current controversy regarding the efficacy of TGF-β inhibition in multiple myeloma-induced bone disease.

Multiple myeloma in the marrow: pathogenesis and treatments

Multiple myeloma (MM) is a B cell malignancy resulting in osteolytic lesions and fractures. In the disease state, bone healing is limited owing to increased osteoclastic and decreased osteoblastic activity, as well as an MM-induced forward-feedback cycle where bone-embedded growth factors further enhance tumor progression as bone is resorbed. Recent work on somatic mutation in MM tumors has provided insight into cytogenetic changes associated with this disease; the initiating driver mutations causing MM are diverse because of the complexity and multitude of mutations inherent in MM tumor cells. This manuscript provides an overview of MM pathogenesis by summarizing cytogenic changes related to oncogenes and tumor suppressors associated with MM, reviewing risk factors, and describing the disease progression from monoclonal gammopathy of undetermined significance to overt MM. It also highlights the importance of the bone marrow microenvironment (BMM) in the establishment and progression of MM, as well as associated MM-induced bone disease, and the relationship of the bone marrow to current and future therapeutics. This review highlights why understanding the basic biology of the healthy and diseased BMM is crucial in the quest for better treatments and work toward a cure for genetically diverse diseases such as MM.

The Forkhead Transcription Factor FOXP2 Is Required for Regulation of p21WAF1/CIP1 in 143B Osteosarcoma Cell Growth Arrest

Mutations of the forkhead transcription factor FOXP2 gene have been implicated in inherited speech-and-language disorders, and specific Foxp2 expression patterns in neuronal populations and neuronal phenotypes arising from Foxp2 disruption have been described. However, molecular functions of FOXP2 are not completely understood. Here we report a requirement for FOXP2 in growth arrest of the osteosarcoma cell line 143B. We observed endogenous expression of this transcription factor both transiently in normally developing murine osteoblasts and constitutively in human SAOS-2 osteosarcoma cells blocked in early osteoblast development. Critically, we demonstrate that in 143B osteosarcoma cells with minimal endogenous expression, FOXP2 induced by growth arrest is required for up-regulation of p21^WAF1/CIP1. Upon growth factor withdrawal, FOXP2 induction occurs rapidly and precedes p21^WAF1/CIP1 activation. Additionally, FOXP2 expression could be induced by MAPK pathway inhibition in growth-arrested 143B cells, but not in traditional cell line models of osteoblast differentiation (MG-63, C2C12, MC3T3-E1). Our data are consistent with a model in which transient upregulation of Foxp2 in pre-osteoblast mesenchymal cells regulates a p21-dependent growth arrest checkpoint, which may have implications for normal mesenchymal and osteosarcoma biology.

Dynamic interplay between bone and multiple myeloma: emerging roles of the osteoblast

Multiple myeloma is a B-cell malignancy characterized by the unrelenting proliferation of plasma cells. Multiple myeloma causes osteolytic lesions and fractures that do not heal due to decreased osteoblastic and increased osteoclastic activity. However, the exact relationship between osteoblasts and myeloma cells remains elusive. Understanding the interactions between these dynamic bone-forming cells and myeloma cells is crucial to understanding how osteolytic lesions form and persist and how tumors grow within the bone marrow. This review provides a comprehensive overview of basic and translational research focused on the role of osteoblasts in multiple myeloma progression and their relationship to osteolytic lesions. Importantly, current challenges for in vitro studies exploring direct osteoblastic effects on myeloma cells, and gaps in understanding the role of the osteoblast in myeloma progression are delineated. Finally, successes and challenges in myeloma treatment with osteoanabolic therapy (i.e., any treatment that induces increased osteoblastic number or activity) are enumerated. Our goal is to illuminate novel mechanisms by which osteoblasts may contribute to multiple myeloma disease progression and osteolysis to better direct research efforts. Ultimately, we hope this may provide a roadmap for new approaches to the pathogenesis and treatment of multiple myeloma with a particular focus on the osteoblast.

The multiple myeloma bone eco-system and its relation to oncogenesis

Pure lytic bone lesions are the hallmark of myeloma (MM). MM is the only hematological malignancy associated with lytic bone lesions and the mechanisms of bone destruction are well documented both at the cellular and molecular levels. An uncoupling bone process characterizes MM, with stimulation of bone resorption and inhibition of bone formation. The capacity of MM cells to directly or indirectly inhibit bone formation is specific of MM, although many carcinomas have the capacity to stimulate bone resorption, directly or indirectly in a similar way to MM. Few MM do not develop bone lesions, while true sclerotic MM remain exceptional. Inhibition of bone formation is the major event explaining the transition from MGUS to overt MM. It is now well documented that bone cells regulate MM cell growth, osteoclast stimulating MM cell growth and osteoblasts inhibiting it. Progression of MM from MGUS is characterized by the selection of MM clones able to inhibit osteoblasts, favoring tumor growth. These data underline the interest of new treatments able to regenerate bone.

Glycosphingolipid synthesis inhibition limits osteoclast activation and myeloma bone disease

Glycosphingolipids (GSLs) are essential constituents of cell membranes and lipid rafts and can modulate signal transduction events. The contribution of GSLs in osteoclast (OC) activation and osteolytic bone diseases in malignancies such as the plasma cell dyscrasia multiple myeloma (MM) is not known. Here, we tested the hypothesis that pathological activation of OCs in MM requires de novo GSL synthesis and is further enhanced by myeloma cell-derived GSLs. Glucosylceramide synthase (GCS) inhibitors, including the clinically approved agent N-butyl-deoxynojirimycin (NB-DNJ), prevented OC development and activation by disrupting RANKL-induced localization of TRAF6 and c-SRC into lipid rafts and preventing nuclear accumulation of transcriptional activator NFATc1. GM3 was the prevailing GSL produced by patient-derived myeloma cells and MM cell lines, and exogenous addition of GM3 synergistically enhanced the ability of the pro-osteoclastogenic factors RANKL and insulin-like growth factor 1 (IGF-1) to induce osteoclastogenesis in precursors. In WT mice, administration of GM3 increased OC numbers and activity, an effect that was reversed by treatment with NB-DNJ. In a murine MM model, treatment with NB-DNJ markedly improved osteolytic bone disease symptoms. Together, these data demonstrate that both tumor-derived and de novo synthesized GSLs influence osteoclastogenesis and suggest that NB-DNJ may reduce pathological OC activation and bone destruction associated with MM.

unveiling skeletal fragility in patients diagnosed with MGUS: no longer a condition of undetermined significance?

Monoclonal gammopathy of undetermined significance (MGUS) is a common finding in clinical practice, affecting greater than 3% of adults aged 50 years and older. As originally described, the term MGUS reflected the inherent clinical uncertainty of distinguishing patients with a benign stable monoclonal plasma cell disorder from subjects destined to progress to malignancy. There is now clear epidemiologic evidence, however, that patients with MGUS suffer from a significantly increased fracture risk and that the prevalence of MGUS is increased in patients with osteoporosis. Despite this relationship, no clinical care guidelines exist for the routine evaluation or treatment of the skeletal health of patients with MGUS. Recent work has demonstrated that circulating levels of at least two cytokines (CCL3/MIP-1α and DKK1) with well-recognized roles in bone disease in the related monoclonal gammopathy multiple myeloma are also increased in patients with MGUS. Further, recent imaging studies using high-resolution peripheral quantitative CT have documented that patients with MGUS have substantial skeletal microarchitectural deterioration and deficits in biomechanical bone strength that likely underlie the increased skeletal fragility in these patients. Accordingly, this Perspective provides evidence that the "undetermined significance" portion of the MGUS acronym may be best replaced in favor of the term "monoclonal gammopathy of skeletal significance" (MGSS) in order to more accurately reflect the enhanced skeletal risks inherent in this condition.

Mathematical modelling of the pathogenesis of multiple myeloma-induced bone disease

Multiple myeloma (MM) is the second most common haematological malignancy and results in destructive bone lesions. The interaction between MM cells and the bone microenvironment plays an important role in the development of the tumour cells and MM-induced bone disease and forms a 'vicious cycle' of tumour development and bone destruction, intensified by suppression of osteoblast activity and promotion of osteoclast activity. In this paper, a mathematical model is proposed to simulate how the interaction between MM cells and the bone microenvironment facilitates the development of the tumour cells and the resultant bone destruction. It includes both the roles of inhibited osteoblast activity and stimulated osteoclast activity. The model is able to mimic the temporal variation of bone cell concentrations and resultant bone volume after the invasion and then removal of the tumour cells and explains why MM-induced bone lesions rarely heal even after the complete removal of MM cells. The behaviour of the model compares well with published experimental data. The model serves as a first step to understand the development of MM-induced bone disease and could be applied further to evaluate the current therapies against MM-induced bone disease and even suggests new potential therapeutic targets.

Peptide Decoration of Nanovehicles to Achieve Active Targeting and Pathology-Responsive Cellular Uptake for Bone Metastasis Chemotherapy

To improve bone metastases chemotherapy, a peptide-conjugated diblock copolymer consisting of chimeric peptide, poly(ethylene glycol) and poly(trimethylene carbonate) (Pep-b-PEG-b-PTMC) is fabricated as a drug carrier capable of bone-seeking targeting as well as pathology-responsive charge reversal to ensure effective cellular uptake at the lesion sites. The chimeric peptide CKGHPGGPQAsp₈ consists of an osteotropic anionic Asp8, a cathepsin K (CTSK)-cleavable substrate (HPGGPQ) and cationic residue tethered to polymer chain. Pep-b-PEG-b-PTMC can spontaneously self-assemble into negatively charged nanomicelles (~75 nm). As to the model drug of doxorubicin, Pep-b-PEG-b-PTM shows 30.0 ± 1 % and 90.1 ± 2 % for loading content and loading efficiency, respectively. High bone binding capability is demonstrated with that 66 % of Pep-b-PEG-b-PTMC micelles are able to bind to hydroxyl apatite, whereas less than 15 % is for Pep-free micelles. The nanomicelles exhibit a negative-to-positive charge conversion from -18.5 ± 1.9 mV to 15.2 ± 1.8 mV upon exposure to CTSK, an enzyme overexpressed in bone metastatic microenvironments. Such a pathology-responsive transition would lead to remarkably enhanced cellular uptake of the nanomicelles upon reaching lesion sites, thus improving the drug efficacy as verified by the in vitro cytotoxicity assay and the in vivo study in myeloma-bearing 5TGM1 mice model.

Contributions of the host microenvironment to cancer-induced bone disease

The bone marrow provides a specialized and highly supportive microenvironment for tumor growth and development of the associated bone disease. It is a preferred site for breast and prostate cancer bone metastasis and the hematologic malignancy, multiple myeloma. For many years, researchers have focused upon the interactions between tumor cells and the cells directly responsible for bone remodeling, namely osteoclasts and osteoblasts. However, there is ever-increasing evidence for a multitude of ways in which the bone marrow microenvironment can promote disease pathogenesis, including via cancer-associated fibroblasts, the hematopoietic stem cell niche, myeloid-derived suppressor cells, and the sympathetic nervous system. This review discusses the recent advances in our understanding of the contribution of the host microenvironment to the development of cancer-induced bone disease.

A novel Bruton's tyrosine kinase inhibitor CC-292 in combination with the proteasome inhibitor carfilzomib impacts the bone microenvironment in a multiple myeloma model with resultant antimyeloma activity

Bruton's tyrosine kinase (Btk) modulates B-cell development and activation and has an important role in antibody production. Interestingly, Btk may also affect human osteoclast (OC) function; however, the mechanism was unknown. Here we studied a potent and specific Btk inhibitor, CC-292, in multiple myeloma (MM). In this report, we demonstrate that, although CC-292 increased OC differentiation, it inhibited OC function via inhibition of c-Src, Pyk2 and cortactin, all involved in OC-sealing zone formation. As CC-292 did not show potent in vitro anti-MM activity, we next evaluated it in combination with the proteasome inhibitor, carfilzomib. We first studied the effect of carfilzomib on OC. Carfilzomib did not have an impact on OC-sealing zone formation but significantly inhibited OC differentiation. CC-292 combined with carfilzomib inhibited both sealing zone formation and OC differentiation, resulting in more profound inhibition of OC function than carfilzomib alone. Moreover, the combination treatment in an in vivo MM mouse model inhibited tumor burden compared with CC-292 alone; it also increased bone volume compared with carfilzomib alone. These results suggest that CC-292 combined with carfilzomib augments the inhibitory effects against OC within the bone microenvironment and has promising therapeutic potential for the treatment of MM and related bone disease.

Human umbilical cord blood-derived stromal cells: a new resource for the proliferation and apoptosis of myeloma cells

BACKGROUND/OBJECTIVE

Bone marrow stromal cells (BMSCs) can support multiple myeloma (MM) disease progression and resistance to chemotherapy. The proliferation of MM cells may be suppressed by modifying the hematopoietic microenvironment (HME). We have previously isolated human umbilical cord blood-derived stromal cells (hUCBDSCs) and observed that hUCBDSCs suppressed proliferation and induced apoptosis in KM3 cells. To examine the mechanism by which hUCBDSCs drive the inhibition of MM, KM3 cells were co-cultured with hUCBDSCs.

METHODS

Interleukin (IL)-6 and soluble IL-6 receptor (sIL-6R) expression levels were measured by enzyme-linked immunosorbent assay. The expression levels of membrane IL-6 receptor (mIL-6R), intercellular cell adhesion molecule-1 (ICAM-1), B-cell lymphoma/leukemia-2 (Bcl-2), and Bcl-XL as well as the location of nuclear factor κB (NF-κB) were assessed by laser confocal microscopy. The expression profiles of mIL-6R and ICAM-1 were also more precisely examined by flow cytometry, and Bcl-2, Bcl-XL and inhibitor kappa B expression levels were analyzed by western blot. The mRNA expression levels of IL-6R, ICAM-1, Bcl-2, and Bcl-XL were assessed by real-time polymerase chain reaction. NF-κB DNA-binding activity was examined by electrophoretic mobility shift assay.

RESULTS

The protein expression levels of both sIL-6R and mIL-6R were reduced in culture conditions when KM3 cells were co-cultured with hUCBDSCs; moreover, the mRNA expression levels of IL-6R were also reduced. Nuclear translocation of the NF-κB p65 subunit was inhibited in KM3 cells by co-culture with hUCBDSCs. Moreover, hUCBDSCs inhibited NF-κB DNA-binding activity, thereby resulting in the downregulation of NF-κB-regulated proteins.

CONCLUSION

hUCBDSCs can suppress proliferation and induce apoptosis in KM3 cells by both downregulating IL-6R expression and inhibiting NF-κB activity.

Genes associate with abnormal bone cell activity in bone metastasis

Bone is one of the most frequent sites of metastasis in patients with malignancies. Up to 90 % of patients with multiple myeloma, and 60 % to 75 % patients with prostate cancer and breast cancer develop bone metastasis at the later stages of their diseases. Bone metastases are responsible for tremendous morbidity in patients with cancer, including severe bone pain, pathologic fractures, spinal cord and nerve compression syndromes, life-threatening hypercalcemia, and increased mortality. Multiple factors produced by tumor cells or produced by the bone marrow microenvironment in response to tumor cells play important roles in activation of osteoclastic bone resorption and modulation of osteoblastic activity in patients with bone metastasis. In this chapter, we will review the genes that play important roles in bone destruction, tumor growth, and osteoblast activity in bone metastasis and discuss the potential therapies targeting the products of these genes to block both bone destruction and tumor growth.

Effect of the HDAC inhibitor vorinostat on the osteogenic differentiation of mesenchymal stem cells in vitro and bone formation in vivo

AIM

Vorinostat, a histone deacetylase (HDAC) inhibitor currently in a clinical phase III trial for multiple myeloma (MM) patients, has been reported to cause bone loss. The purpose of this study was to test whether, and to what extent, vorinostat influences the osteogenic differentiation of mesenchymal stem cells (MSCs) in vitro and bone formation in vivo.

METHODS

Bone marrow-derived MSCs were prepared from both normal donors and MM patients. The MSCs were cultured in an osteogenic differentiation induction medium to induce osteogenic differentiation, which was evaluated by alkaline phosphatase (ALP) staining, Alizarin Red S staining and the mRNA expression of osteogenic markers. Naïve mice were administered vorinostat (100 mg/kg, ip) every other day for 3 weeks. After the mice were sacrificed, bone formation was assessed based on serum osteocalcin level and histomorphometric analysis.

RESULTS

Vorinostat inhibited the viability of hMSCs in a concentration-dependent manner (the IC50 value was 15.57 μmol/L). The low concentration of vorinostat (1 μmol/L) did not significantly increase apoptosis in hMSCs, whereas pronounced apoptosis was observed following exposure to higher concentrations of vorinostat (10 and 50 μmol/L). In bone marrow-derived hMSCs from both normal donors and MM patients, vorinostat (1 μmol/L) significantly increased ALP activity, mRNA expression of osteogenic markers, and matrix mineralization. These effects were associated with upregulation of the bone-specifying transcription factor Runx2 and with the epigenetic alterations during normal hMSCs osteogenic differentiation. Importantly, the mice treated with vorinostat did not show any bone loss in response to the optimized treatment regimen.

CONCLUSION

Vorinostat, known as a potent anti-myeloma drug, stimulates MSC osteogenesis in vitro. With the optimized treatment regimen, any decrease in bone formation was not observed in vivo.

Clinical utility and implementation of gene-expression profiling in myeloma: current status and challenges

SUMMARY Multiple myeloma, a neoplasm of terminally differentiated plasma cell, is the second most frequent hematological malignancy after non-Hodgkin’s lymphoma. Gene-expression profiling is a powerful and sensitive tool that can detect global transcriptional changes in cells. This technology has been applied in myeloma studies in the last decade in diverse areas such as understanding molecular pathogenesis, role of microenvironment, molecular heterogeneity, prognosis prediction and identification of novel therapeutic targets. In this review, we will briefly retrace the achievements and consider the future perspectives of gene-expression profiling in multiple myeloma research.

Assessment of bone marrow fibrosis and angiogenesis in monitoring patients with multiple myeloma

The aim of our study was to emphasize the importance of accurate and standardized techniques for detailed monitoring of the microenvironment in multiple myeloma (MM). Bone marrow fibrosis, angiogenesis, and plasma cell infiltrates in bone marrow biopsy (BMB) samples at the time of diagnosis and on completion of therapy were analyzed for 42 patients with newly diagnosed MM. Computerized image analysis was used for all slides stained with anti-CD138 and anti-CD34. The patients with fibrosis in pretreatment BMB samples had significantly higher microvessel density (MVD) and plasma cell infiltrates. In posttreatment BMB samples, nonresponders had a significantly higher frequency and grade of fibrosis and higher values of MVD, total vascular area, and plasma cell percentage. The overall survival of nonresponders and patients with increased marrow fibrosis in posttreatment BMB samples was significantly shorter. The obtained results confirm that complex morphologic examination of the bone marrow microenvironment during the monitoring of MM can provide better prognostic significance.

Dasatinib as a bone-modifying agent: anabolic and anti-resorptive effects

BACKGROUND

Bone loss, in malignant or non-malignant diseases, is caused by increased osteoclast resorption and/or reduced osteoblast bone formation, and is commonly associated with skeletal complications. Thus, there is a need to identify new agents capable of influencing bone remodeling. We aimed to further pre-clinically evaluate the effects of dasatinib (BMS-354825), a multitargeted tyrosine kinase inhibitor, on osteoblast and osteoclast differentiation and function.

METHODS

For studies on osteoblasts, primary human bone marrow mensenchymal stem cells (hMSCs) together with the hMSC-TERT and the MG-63 cell lines were employed. Osteoclasts were generated from peripheral blood mononuclear cells (PBMC) of healthy volunteers. Skeletally-immature CD1 mice were used in the in vivo model.

RESULTS

Dasatinib inhibited the platelet derived growth factor receptor-β (PDGFR-β), c-Src and c-Kit phosphorylation in hMSC-TERT and MG-63 cell lines, which was associated with decreased cell proliferation and activation of canonical Wnt signaling. Treatment of MSCs from healthy donors, but also from multiple myeloma patients with low doses of dasatinib (2-5 nM), promoted its osteogenic differentiation and matrix mineralization. The bone anabolic effect of dasatinib was also observed in vivo by targeting endogenous osteoprogenitors, as assessed by elevated serum levels of bone formation markers, and increased trabecular microarchitecture and number of osteoblast-like cells. By in vitro exposure of hemopoietic progenitors to a similar range of dasatinib concentrations (1-2 nM), novel biological sequelae relative to inhibition of osteoclast formation and resorptive function were identified, including F-actin ring disruption, reduced levels of c-Fos and of nuclear factor of activated T cells 1 (NFATc1) in the nucleus, together with lowered cathepsin K, αVβ3 integrin and CCR1 expression.

CONCLUSIONS

Low dasatinib concentrations show convergent bone anabolic and reduced bone resorption effects, which suggests its potential use for the treatment of bone diseases such as osteoporosis, osteolytic bone metastasis and myeloma bone disease.

Premature loss of bone remodeling compartment canopies is associated with deficient bone formation: a study of healthy individuals and patients with Cushing's syndrome

A remarkable property of bone remodeling is that osteoblasts form bone matrix exactly where and when osteoclasts have removed it. The bone remodeling compartment (BRC) canopies that cover bone surfaces undergoing remodeling were proposed to be critical players in this mechanism. Here, we provide support to this hypothesis by analyzing the changes in prevalence of BRC canopies during the progress of the remodeling cycle in a cohort of healthy individuals and in patients with endogenous Cushing's syndrome (CS), and by relating these changes in prevalence with the extent of bone forming surfaces. Both cohorts showed almost 100% canopy coverage above resorbing osteoclasts, and only about 76% above bone forming surfaces. This indicates that BRC canopies are invariably associated with the early stage of the remodeling cycle, but may disappear later. Interestingly, in control and two-thirds of the CS patients, a significant decline in canopy coverage occurred only once bone formation was initiated, but in the remaining third of the CS patients the prevalence of canopies already decreased before bone formation. This canopy loss before initiation of bone formation coincided with significantly less bone-forming surface compared with canopy loss at a later stage. These observations support a model where bone restitution is compromised in the absence of BRC canopies, and apparently does not start when the BRC canopy is lost before initiation of the bone formation step. This model is discussed in the context of possible biological roles of BRC canopies. It suggests that BRC canopies could be privileged targets for treating patients suffering from a negative bone formation-resorption balance.

Effect of glycosphingolipids on osteoclastogenesis and osteolytic bone diseases

Alterations in glycosphingolipid (GSL) production results in lysosomal storage disorders associated with neurodegenerative changes. In Gaucher's disease, the patients also develop osteoporosis that is ameliorated upon treatment for the underlying defect in GSL metabolism. The role of GSLs in osteoclast and osteoblast formation is discussed here as well as the potential therapeutic uses of already approved drugs that limit GSL production in bone loss disorders such as multiple myeloma and periodontal disease.

Lower dose dexamethasone/thalidomide and zoledronic acid every 3 weeks in previously untreated multiple myeloma

BACKGROUND

Physicians in Asia have anecdotally reported that Asian patients with multiple myeloma (MM) are frequently intolerant of conventional doses of dexamethasone (Dex) and/or thalidomide (Thal). Since zoledronic acid (Zol) has an anti-MM effect in preclinical studies, we investigated whether the approved 3-times-weekly Zol combined with lower dose Dex/Thal could be an effective and better tolerated regimen in Asian patients.

PATIENTS AND METHODS

In this first Asian cooperative multicenter phase II study, previously untreated patients with MM (N = 44) received up to 6 cycles of 3-times-weekly low-dose Dex/Thal and 4 mg Zol (the dtZ regimen). Response was graded using Bladé criteria.

RESULTS

The average doses of Dex and Thal administered were 185.2 mg/month; and 87.5 mg/day, respectively. Thirty-nine (88.6%) patients demonstrated at least a partial response (PR), including 18.2% very good partial response (VGPR), 15.9% near complete response (nCR) and 18.2% complete response (CR). Achievement of CR/nCR was related to significant (P < .05), rapid, and sustained inhibition of osteoclasts (OCs) and OC precursors (pOCs) by Zol. Sepsis was the most frequently reported serious toxicity, contributing to 3 of 4 deaths. Importantly, there was no peripheral neuropathy, osteonecrosis of the jaw, or nephrotoxicity.

CONCLUSION

We conclude that the dtZ regimen is an effective and well-tolerated regimen for Asian patients with newly diagnosed MM. The high rate of VGPR/nCR/CR suggests that Zol could have a clinically relevant anti-MM effect. Since infections are the most frequent adverse event, it is probably wise to further lower the dose of Dex in future studies.

Host-derived adiponectin is tumor-suppressive and a novel therapeutic target for multiple myeloma and the associated bone disease

The contributions of the host microenvironment to the pathogenesis of multiple myeloma, including progression from the non-malignant disorder monoclonal gammopathy of undetermined significance, are poorly understood. In the present study, microarray analysis of a murine model requiring a unique host microenvironment for myeloma development identified decreased host-derived adiponectin compared with normal mice. In support, clinical analysis revealed decreased serum adiponectin concentrations in monoclonal gammopathy of undetermined significance patients who subsequently progressed to myeloma. We investigated the role of adiponectin in myeloma pathogenesis and as a treatment approach, using both mice deficient in adiponectin and pharmacologic enhancement of circulating adiponectin. Increased tumor burden and bone disease were observed in myeloma-bearing adiponectin-deficient mice, and adiponectin was found to induce myeloma cell apoptosis. The apolipoprotein peptide mimetic L-4F was used for pharmacologic enhancement of adiponectin. L-4F reduced tumor burden, increased survival of myeloma-bearing mice, and prevented myeloma bone disease. Collectively, our studies have identified a novel mechanism whereby decreased host-derived adiponectin promotes myeloma tumor growth and osteolysis. Furthermore, we have established the potential therapeutic benefit of increasing adiponectin for the treatment of myeloma and the associated bone disease.

Novel insights into the role of interleukin-27 and interleukin-23 in human malignant and normal plasma cells

Multiple myeloma is a monoclonal postgerminal center tumor that has phenotypic features of plasmablasts and/or plasma cells and usually localizes at multiple sites in the bone marrow. The pathogenesis of multiple myeloma is complex and dependent on the interactions between tumor cells and their microenvironment. Different cytokines, chemokines, and proangiogenic factors released in the tumor microenvironment are known to promote multiple myeloma cell growth. Here, we report recent advances on the role of 2 strictly related immunomodulatory cytokines, interleukin-27 (IL-27) and IL-23, in human normal and neoplastic plasma cells, highlighting their ability to (i) act directly against multiple myeloma cells, (ii) influence the multiple myeloma microenvironment by targeting osteoclast and osteoblast cells, and (iii) modulate normal plasma cell function. Finally, the therapeutic implication of these studies is discussed.

The backbone of progress--preclinical studies and innovations with zoledronic acid

Bisphosphonates (BPs) are antiresorptive agents that block pathologic bone resorption by inhibiting osteoclast function and later inducing osteoclast apoptosis. These agents localize to bone and break the vicious cycle of bone resorption that results from cross-stimulation between cancer cells and the bone remodeling cells, thereby reducing cancer-induced osteolysis and the tumor burden in bone. Thus nitrogen-containing BPs (N-BPs) have well established clinical benefits in the treatment of bone metastases from solid tumors and bone lesions from multiple myeloma. Preclinical data indicate that N-BPs, especially zoledronic acid (ZOL), can exert antimyeloma activity both in vitro and in vivo. Studies show that N-BPs can inhibit multiple intracellular processes essential for cancer cell proliferation and invasion and induce apoptosis. Furthermore, clinically relevant doses of N-BPs inhibit tumor-associated angiogenesis and can modulate macrophage phenotype in vivo, which is likely to contribute to anticancer effects.