Osteoblast function in myeloma

Mechanistic insights into bone destruction in multiple myeloma: Cellular and molecular perspectives

Multiple myeloma (MM) is a hematological malignancy that leads to significant bone destruction, resulting in debilitating pain and skeletal-related events. The pathophysiology of osteolytic bone destruction in MM involves complex interactions between malignant plasma cells (PCs) and the bone marrow (BM) microenvironment. This review aims to provide a comprehensive synthesis of the cellular and molecular pathways underlying MM-associated bone disease. We discuss the role of osteoclast (OC), osteoblast (OB), osteocytes, along with the complex interactions between immune cells and the BM microenvironment in shaping disease progression. Additionally, we explore the molecular signaling pathways involved in bone disease as well as the influence of inflammatory cytokines, and the role of the metabolic alterations that characterize the MM BM. We also explore novel therapeutic strategies targeting these pathways to improve clinical outcomes. Understanding these mechanisms is crucial for the development of more effective treatments to prevent bone damage in MM patients.

Diagnostic Approach to Abnormal Alkaline Phosphatase Value

Alkaline phosphatase (ALP) is abundantly represented in nature, being fundamental for a number of processes. In addition to its fundamental function in skeletal mineralization, its roles in the pathogenesis of other diseases are being explored. The measurement of total ALP activity in serum or in plasma is a useful biomarker in clinical practice. Indeed, routine measurement of serum total ALP is a long-standing established part of initial biochemical evaluation of patients both in the hospital setting and on an ambulatory basis. Raised or reduced values of this enzyme activity are indicative of a number of diseases, most commonly affecting the skeleton and the biliary tract. Electrophoretic assays are preferable for visualizing and investigating the cause of increased serum total ALP activities, and bone ALP immunoassays are preferable for investigating and monitoring individuals with bone and mineral metabolic abnormalities. Here, we give a holistic vision of this fundamental enzyme, suggesting a clinical approach to the identification of diseases causing abnormal values. Finally, a therapeutic role has emerged as substitutive therapy in patients with hypophosphatasia, even though ongoing and future studies are exploring its role in other therapeutic areas. This narrative review was based on articles found by searching PubMed from its inception until July 2024 for the terms alkaline phosphatases, isozymes, isoforms, bone alkaline phosphatase, liver alkaline phosphatase, intestinal alkaline phosphatase, placental alkaline phosphatase, liver function tests, γ-glutamyltransferase, skeletal diseases, and liver diseases. We limited our research to papers published in the English language, with emphasis placed on those describing differential diagnosis whenever available.

Pre-Transplant Dual-Energy X-ray Absorptiometry (DXA)-Derived Body Composition Measures as Predictors of Treatment Outcomes and Early Post-Transplant Complications in Patients with Multiple Myeloma (MM) Treated with Autologous Hematopoietic Stem Cell Transplantation (AutoHSCT)

Background/Objectives: Changes in muscle mass and bone density are common in multiple myeloma (MM) patients. Dual-energy X-ray absorptiometry (DXA) offers precise, non-invasive insights into a patient's physical condition before autologous stem cell transplantation (autoHSCT). This study examines how pre-transplant body composition impacts treatment outcomes and early complications in MM patients undergoing autoHSCT. Methods: This study is a single-center, retrospective analysis of patients with MM who were treated with first or second autoHSCT and underwent DXA pre-transplant between 11 August 2019 and 12 June 2024. Results: We conducted a study of pre-transplant body composition in 127 patients with MM. Among them, 108 (85%) qualified for first autoHSCT, while 19 (15%) qualified for a second. The median age of the patients was 64 years (range 50-73). In the Cox proportional hazards regression conducted in the group of women, Total Body %Fat was a statistically significant predictor for progression-free survival (PFS) (HR = 0.07, 95% CI = 0.01,0.6, p = 0.0157). In the Mann-Whitney U test conducted on males, Lean Mass/Height2 and Appen. Lean Height2 were statistically significant predictors of early infections after autoHSCT (Z = 1.98, p = 0.0473 and Z = 2.32, p = 0.0204, respectively). In males, Fat Mass/Height2 was a significant predictor of non-infectious toxicity related to treatment (Z = -1.98, p = 0.0476). Conclusions: In women, higher levels of adipose tissue initially appear to exert a protective effect; however, this benefit diminishes over time, with greater fat mass eventually correlating with an increased risk of disease progression. In men, muscle mass has been identified as a significant predictor of early infection risk post-autoHSCT. Furthermore, our findings indicate that an increased amount of adipose tissue in men is statistically associated with a higher risk of non-infectious treatment-related toxicity. These conclusions highlight the critical need for further investigation into the role of body composition.

Communication between bone marrow mesenchymal stem cells and multiple myeloma cells: Impact on disease progression

Multiple myeloma (MM) is a hematological malignancy characterized by the accumulation of immunoglobulin-secreting clonal plasma cells at the bone marrow (BM). The interaction between MM cells and the BM microenvironment, and specifically BM mesenchymal stem cells (BM-MSCs), has a key role in the pathophysiology of this disease. Multiple data support the idea that BM-MSCs not only enhance the proliferation and survival of MM cells but are also involved in the resistance of MM cells to certain drugs, aiding the progression of this hematological tumor. The relation of MM cells with the resident BM-MSCs is a two-way interaction. MM modulate the behavior of BM-MSCs altering their expression profile, proliferation rate, osteogenic potential, and expression of senescence markers. In turn, modified BM-MSCs can produce a set of cytokines that would modulate the BM microenvironment to favor disease progression. The interaction between MM cells and BM-MSCs can be mediated by the secretion of a variety of soluble factors and extracellular vesicles carrying microRNAs, long non-coding RNAs or other molecules. However, the communication between these two types of cells could also involve a direct physical interaction through adhesion molecules or tunneling nanotubes. Thus, understanding the way this communication works and developing strategies to interfere in the process, would preclude the expansion of the MM cells and might offer alternative treatments for this incurable disease.

Molecular Crosstalk between Chromatin Remodeling and Tumor Microenvironment in Multiple Myeloma

Multiple myeloma (MM) is a complex disease driven by numerous genetic and epigenetic alterations that are acquired over time. Despite recent progress in the understanding of MM pathobiology and the availability of innovative drugs, which have pronounced clinical outcome, this malignancy eventually progresses to a drug-resistant lethal stage and, thus, novel therapeutic drugs/models always play an important role in effective management of MM. Modulation of tumor microenvironment is one of the hallmarks of cancer biology, including MM, which affects the myeloma genomic architecture and disease progression subtly through chromatin modifications. The bone marrow niche has a prime role in progression, survival, and drug resistance of multiple myeloma cells. Therefore, it is important to develop means for targeting the ecosystem between multiple myeloma bone marrow microenvironment and chromatin remodeling. Extensive gene expression profile analysis has indeed provided the framework for new risk stratification of MM patients and identifying novel molecular targets and therapeutics. However, key tumor microenvironment factors/immune cells and their interactions with chromatin remodeling complex proteins that drive MM cell growth and progression remain grossly undefined.

A Journey through the Inter-Cellular Interactions in the Bone Marrow in Multiple Myeloma: Implications for the Next Generation of Treatments

Tumors are composed of a plethora of extracellular matrix, tumor and non-tumor cells that form a tumor microenvironment (TME) that nurtures the tumor cells and creates a favorable environment where tumor cells grow and proliferate. In multiple myeloma (MM), the TME is the bone marrow (BM). Non-tumor cells can belong either to the non-hematological compartment that secretes soluble mediators to create a favorable environment for MM cells to grow, or to the immune cell compartment that perform an anti-MM activity in healthy conditions. Indeed, marrow-infiltrating lymphocytes (MILs) are associated with a good prognosis in MM patients and have served as the basis for developing different immunotherapy strategies. However, MM cells and other cells in the BM can polarize their phenotype and activity, creating an immunosuppressive environment where immune cells do not perform their cytotoxic activity properly, promoting tumor progression. Understanding cell-cell interactions in the BM and their impact on MM proliferation and the performance of tumor surveillance will help in designing efficient anti-MM therapies. Here, we take a journey through the BM, describing the interactions of MM cells with cells of the non-hematological and hematological compartment to highlight their impact on MM progression and the development of novel MM treatments.

Effect of Methionine Supplementation on Serum Metabolism and the Rumen Bacterial Community of Sika Deer (Cervus nippon)

Methionine is the first or second limiting amino acid for ruminants, such as sika deer, and has a variety of biological functions such as antioxidant activity, immune response, and protein synthesis. This study aimed to investigate the effects of methionine supplementation on antler growth, serum biochemistry, rumen fermentation, and the bacterial community of sika deer during the antler-growing period. Twelve 4-year-old male sika deer were randomly assigned to three dietary groups supplemented with 0 g/day (n = 4, CON), 4.0 g/day (n = 4, LMet), and 6.0 g/day (n = 4, HMet) methionine. No significant difference (p > 0.05) was found in the production performance between the three groups, but antler weight was higher in both the LMet and HMet groups than in the CON group. Methionine supplementation significantly increased the serum glutathione peroxidase activity (p < 0.05). The serum immunoglobulin G level was significantly higher in the HMet group than in the other two groups (p < 0.05). No significant effect was found on the apparent amino acid digestibility of the three groups, but cysteine and methionine digestibility were higher in the LMet group. The serum hydroxylysine level was significantly lower in the LMet and HMet groups, whereas the serum lysine level was significantly lower in the HMet group compared with the CON group (p < 0.05). The LMet group had the highest but a nonsignificant total volatile fatty acid content and significantly higher microbial protein content in the rumen than the CON group (p < 0.05). The phyla Bacteroidetes, Firmicutes, and Proteobacteria were dominant in the rumen of the sika deer. The principal coordinate analysis (PCoA) and analysis of similarities (ANOSIM) results showed a significant change in the bacterial composition of the three groups (p < 0.05). The relative abundance of Prevotella and Rikenellaceae-RC9 was significantly higher in the LMet group compared with the CON group and CON and HMet groups, respectively. These results revealed that methionine supplementation improved the antioxidant activity and immune status, affecting amino acid metabolism and rumen microbial composition of the sika deer.

Bone Disease in Multiple Myeloma: Biologic and Clinical Implications

Multiple Myeloma (MM) is a hematologic malignancy characterized by the proliferation of monoclonal plasma cells localized within the bone marrow. Bone disease with associated osteolytic lesions is a hallmark of MM and develops in the majority of MM patients. Approximately half of patients with bone disease will experience skeletal-related events (SREs), such as spinal cord compression and pathologic fractures, which increase the risk of mortality by 20–40%. At the cellular level, bone disease results from a tumor-cell-driven imbalance between osteoclast bone resorption and osteoblast bone formation, thereby creating a favorable cellular environment for bone resorption. The use of osteoclast inhibitory therapies with bisphosphonates, such as zoledronic acid and the RANKL inhibitor denosumab, have been shown to delay and lower the risk of SREs, as well as the need for surgery or radiation therapy to treat severe bone complications. This review outlines our current understanding of the molecular underpinnings of bone disease, available therapeutic options, and highlights recent advances in the management of MM-related bone disease.

Molecular Impact of the Tumor Microenvironment on Multiple Myeloma Dissemination and Extramedullary Disease

Multiple myeloma (MM) is the most common malignant monoclonal disease of plasma cells. Aside from classical chemotherapy and glucocorticoids, proteasome inhibitors, immunomodulatory agents and monoclonal antibodies are used in the current treatment scheme of MM. The tumor microenvironment (TME) plays a fundamental role in the development and progression of numerous solid and non-solid cancer entities. In MM, the survival and expansion of malignant plasma cell clones heavily depends on various direct and indirect signaling pathways provided by the surrounding bone marrow (BM) niche. In a number of MM patients, single plasma cell clones lose their BM dependency and are capable to engraft at distant body sites or organs. The resulting condition is defined as an extramedullary myeloma (EMM). EMMs are highly aggressive disease stages linked to a dismal prognosis. Emerging literature demonstrates that the dynamic interactions between the TME and malignant plasma cells affect myeloma dissemination. In this review, we aim to summarize how the cellular and non-cellular BM compartments can promote plasma cells to exit their BM niche and metastasize to distant intra-or extramedullary locations. In addition, we list selected therapy concepts that directly target the TME with the potential to prevent myeloma spread.

Pathogenesis and treatment of multiple myeloma bone disease

Multiple myeloma (Plasma cell myeloma), a malignancy of the plasma cells, exhibits tumor expansion preferentially in the bone marrow and the development of bone-destructive lesions. Multiple myeloma is still an incurable disease with changes in the bone marrow microenvironment in favor of the survival and proliferation of multiple myeloma cells and bone destruction. In this review, we described the recent findings on the regulators involved in the development of myeloma bone diseases, and succinctly summarize currently available therapeutic options and the development of novel bone modifying agents for myeloma treatment.

Bone Marrow Mesenchymal Stromal Cells in Multiple Myeloma: Their Role as Active Contributors to Myeloma Progression

Multiple myeloma (MM) is a hematological malignancy of plasma cells that proliferate and accumulate within the bone marrow (BM). Work from many groups has made evident that the complex microenvironment of the BM plays a crucial role in myeloma progression and response to therapeutic agents. Within the cellular components of the BM, we will specifically focus on mesenchymal stromal cells (MSCs), which are known to interact with myeloma cells and the other components of the BM through cell to cell, soluble factors and, as more recently evidenced, through extracellular vesicles. Multiple structural and functional abnormalities have been found when characterizing MSCs derived from myeloma patients (MM-MSCs) and comparing them to those from healthy donors (HD-MSCs). Other studies have identified differences in genomic, mRNA, microRNA, histone modification, and DNA methylation profiles. We discuss these distinctive features shaping MM-MSCs and propose a model for the transition from HD-MSCs to MM-MSCs as a consequence of the interaction with myeloma cells. Finally, we review the contribution of MM-MSCs to several aspects of myeloma pathology, specifically to myeloma growth and survival, drug resistance, dissemination and homing, myeloma bone disease, and the induction of a pro-inflammatory and immunosuppressive microenvironment.

The Role of Marrow Microenvironment in the Growth and Development of Malignant Plasma Cells in Multiple Myeloma

The development and effectiveness of novel therapies in multiple myeloma have been established in large clinical trials. However, multiple myeloma remains an incurable malignancy despite significant therapeutic advances. Accumulating data have elucidated our understanding of the genetic background of the malignant plasma cells along with the role of the bone marrow microenvironment. Currently, the interaction among myeloma cells and the components of the microenvironment are considered crucial in multiple myeloma pathogenesis. Adhesion molecules, cytokines and the extracellular matrix play a critical role in the interplay among genetically transformed clonal plasma cells and stromal cells, leading to the proliferation, progression and survival of myeloma cells. In this review, we provide an overview of the multifaceted role of the bone marrow microenvironment in the growth and development of malignant plasma cells in multiple myeloma.

P2X7 Receptor in Hematological Malignancies

The P2X7 receptor is an ion channel gated by the nucleotide ATP, known for its role in immune responses and recently emerging as a critical onco-promoting factor. Lymphocytes, myeloid cells, and their precursors were among the first cells proved to express a functional P2X7 receptor; therefore, it is not surprising that lymphoproliferative and myeloproliferative diseases, also known as hematological malignancies, were shown to be related in their insurgence and progression to P2X7 alterations. Here, we overview established and recent literature relating P2X7 with the biological mechanisms underlying leukemias, lymphomas, and multiple myeloma development. Particular attention is paid to studies published in the very recent past correlating P2X7 with ATP concentration in the leukemic microenvironment and P2X7 overexpression to acute myeloid leukemia aggressiveness and response to chemotherapy. The described literature strongly suggests that P2X7 and its genetic variants could be regarded as potential new biomarkers in hematological malignancies and that both P2X7 antagonists and agonists could emerge as new therapeutic tools alone or in combination with traditional chemotherapy.

Multiple Myeloma Cells Alter Adipogenesis, Increase Senescence-Related and Inflammatory Gene Transcript Expression, and Alter Metabolism in Preadipocytes

Within the bone marrow microenvironment, mesenchymal stromal cells (MSCs) are an essential precursor to bone marrow adipocytes and osteoblasts. The balance between this progenitor pool and mature cells (adipocytes and osteoblasts) is often skewed by disease and aging. In multiple myeloma (MM), a cancer of the plasma cell that predominantly grows within the bone marrow, as well as other cancers, MSCs, preadipocytes, and adipocytes have been shown to directly support tumor cell survival and proliferation. Increasing evidence supports the idea that MM-associated MSCs are distinct from healthy MSCs, and their gene expression profiles may be predictive of myeloma patient outcomes. Here we directly investigate how MM cells affect the differentiation capacity and gene expression profiles of preadipocytes and bone marrow MSCs. Our studies reveal that MM.1S cells cause a marked decrease in lipid accumulation in differentiating 3T3-L1 cells. Also, MM.1S cells or MM.1S-conditioned media altered gene expression profiles of both 3T3-L1 and mouse bone marrow MSCs. 3T3-L1 cells exposed to MM.1S cells before adipogenic differentiation displayed gene expression changes leading to significantly altered pathways involved in steroid biosynthesis, the cell cycle, and metabolism (oxidative phosphorylation and glycolysis) after adipogenesis. MM.1S cells induced a marked increase in 3T3-L1 expression of MM-supportive genes including Il-6 and Cxcl12 (SDF1), which was confirmed in mouse MSCs by qRT-PCR, suggesting a forward-feedback mechanism. In vitro experiments revealed that indirect MM exposure prior to differentiation drives a senescent-like phenotype in differentiating MSCs, and this trend was confirmed in MM-associated MSCs compared to MSCs from normal donors. In direct co-culture, human mesenchymal stem cells (hMSCs) exposed to MM.1S, RPMI-8226, and OPM-2 prior to and during differentiation, exhibited different levels of lipid accumulation as well as secreted cytokines. Combined, our results suggest that MM cells can inhibit adipogenic differentiation while stimulating expression of the senescence associated secretory phenotype (SASP) and other pro-myeloma molecules. This study provides insight into a novel way in which MM cells manipulate their microenvironment by altering the expression of supportive cytokines and skewing the cellular diversity of the marrow.

The Role of Tumor Microenvironment in Multiple Myeloma Development and Progression

Simple Summary

Multiple Myeloma (MM) is a hematologic malignancy caused by aberrant plasma cell proliferation in the bone marrow (BM) and constitutes the second most common hematological disease after non-Hodgkin lymphoma. The disease progression is drastically regulated by the immunosuppressive tumor microenvironment (TME) generated by soluble factors and different cells that naturally reside in the BM. This microenvironment does not remain unchanged and alterations favor cancer dissemination. Despite therapeutic advances over the past 15 years, MM remains incurable and therefore understanding the elements that control the TME in MM would allow better-targeted therapies to cure this disease. In this review, we discuss the main events and changes that occur in the BM milieu during MM development.

Abstract

Multiple myeloma (MM) is a hematologic cancer characterized by clonal proliferation of plasma cells in the bone marrow (BM). The progression, from the early stages of the disease as monoclonal gammopathy of undetermined significance (MGUS) and smoldering multiple myeloma (SMM) to MM and occasionally extramedullary disease, is drastically affected by the tumor microenvironment (TME). Soluble factors and direct cell–cell interactions regulate MM plasma cell trafficking and homing to the BM niche. Mesenchymal stromal cells, osteoclasts, osteoblasts, myeloid and lymphoid cells present in the BM create a unique milieu that favors MM plasma cell immune evasion and promotes disease progression. Moreover, TME is implicated in malignant cell protection against anti-tumor therapy. This review describes the main cellular and non-cellular components located in the BM, which condition the immunosuppressive environment and lead the MM establishment and progression.

Mathematical modelling of the role of GADD45β in the pathogenesis of multiple myeloma

Multiple myeloma (MM) is an incurable disease with relatively high morbidity and mortality rates. Great efforts were made to develop nuclear factor-kappa B (NF-κB)-targeted therapies against MM disease. However, these treatments influence MM cells as well as normal cells, inevitably causing serious side effects. Further research showed that NF-κB signalling promotes the survival of MM cells by interacting with JNK signalling through growth arrest and DNA damage-inducible beta (GADD45β), the downstream module of NF-κB signalling. The GADD45β-targeted intervention was suggested to be an effective and MM cell-specific treatment. However, the underlying mechanism through which GADD45β promotes the survival of MM cells is usually ignored in the previous models. A mathematical model of MM is built in this paper to investigate how NF-κB signalling acts along with JNK signalling through GADD45β and MKK7 to promote the survival of MM cells. The model cannot only mimic the variations in bone cells, the bone volume and MM cells with time, but it can also examine how the NF-κB pathway acts with the JNK pathway to promote the development of MM cells. In addition, the model also investigates the efficacies of GADD45β- and NF-κB-targeted treatments, suggesting that GADD45β-targeted therapy is more effective but has no apparent side effects. The simulation results match the experimental observations. It is anticipated that this model could be employed as a useful tool to initially investigate and even explore potential therapies involving the NF-κB and JNK pathways in the future.

Runx2 Deficiency in Osteoblasts Promotes Myeloma Progression by Altering the Bone Microenvironment at New Bone Sites

Multiple myeloma is a plasma cell malignancy that thrives in the bone marrow (BM), with frequent progression to new local and distant bone sites. Our previous studies demonstrated that multiple myeloma cells at primary sites secrete soluble factors and suppress osteoblastogenesis via the inhibition of Runt-related transcription factor 2 (Runx2) in pre- and immature osteoblasts (OB) in new bone sites, prior to the arrival of metastatic tumor cells. However, it is unknown whether OB-Runx2 suppression in new bone sites feeds back to promote multiple myeloma dissemination to and progression in these areas. Hence, we developed a syngeneic mouse model of multiple myeloma in which Runx2 is specifically deleted in the immature OBs of C57BL6/KaLwRij mice (OB-Runx2-/- mice) to study the effect of OB-Runx2 deficiency on multiple myeloma progression in new bone sites. In vivo studies with this model demonstrated that OB-Runx2 deficiency attracts multiple myeloma cells and promotes multiple myeloma tumor growth in bone. Mechanistic studies further revealed that OB-Runx2 deficiency induces an immunosuppressive microenvironment in BM that is marked by an increase in the concentration and activation of myeloid-derived suppressor cells (MDSC) and the suppression and exhaustion of cytotoxic CD8+ T cells. In contrast, MDSC depletion by either gemcitabine or 5-fluorouracil treatment in OB-Runx2-/- mice prevented these effects and inhibited multiple myeloma tumor growth in BM. These novel discoveries demonstrate that OB-Runx2 deficiency in new bone sites promotes multiple myeloma dissemination and progression by increasing metastatic cytokines and MDSCs in BM and inhibiting BM immunity. Importantly, MDSC depletion can block multiple myeloma progression promoted by OB-Runx2 deficiency.Significance: This study demonstrates that Runx2 deficiency in immature osteoblasts at distant bone sites attracts myeloma cells and allows myeloma progression in new bone sites via OB-secreted metastatic cytokines and MDSC-mediated suppression of bone marrow immunity.

Extracellular Vesicle microRNAs Contribute to the Osteogenic Inhibition of Mesenchymal Stem Cells in Multiple Myeloma

Osteolytic bone disease is the major complication associated with the progression of multiple myeloma (MM). Recently, extracellular vesicles (EVs) have emerged as mediators of MM-associated bone disease by inhibiting the osteogenic differentiation of human mesenchymal stem cells (hMSCs). Here, we investigated a correlation between the EV-mediated osteogenic inhibition and MM vesicle content, focusing on miRNAs. By the use of a MicroRNA Card, we identified a pool of miRNAs, highly expressed in EVs, from MM cell line (MM1.S EVs), expression of which was confirmed in EVs from bone marrow (BM) plasma of patients affected by smoldering myeloma (SMM) and MM. Notably, we found that miR-129-5p, which targets different osteoblast (OBs) differentiation markers, is enriched in MM-EVs compared to SMM-EVs, thus suggesting a selective packaging correlated with pathological grade. We found that miR-129-5p can be transported to hMSCs by MM-EVs and, by the use of miRNA mimics, we investigated its role in recipient cells. Our data demonstrated that the increase of miR-129-5p levels in hMSCs under osteoblastic differentiation stimuli inhibited the expression of the transcription factor Sp1, previously described as a positive modulator of osteoblastic differentiation, and of its target the Alkaline phosphatase (ALPL), thus identifying miR-129-5p among the players of vesicle-mediated bone disease.

Therapeutic targets in myeloma bone disease

Multiple myeloma (MM) is the second most common haematological malignancy and is characterized by a clonal proliferation of neoplastic plasma cells within the bone marrow. MM is the most frequent cancer involving the skeleton, causing osteolytic lesions, bone pain and pathological fractures that dramatically decrease MM patients' quality of life and survival. MM bone disease (MBD) results from uncoupling of bone remodelling in which excessive bone resorption is not compensated by new bone formation, due to a persistent suppression of osteoblast activity. Current management of MBD includes antiresorptive agents, bisphosphonates and denosumab, that are only partially effective due to their inability to repair the existing lesions. Thus, research into agents that prevent bone destruction and more importantly repair existing lesions by inducing new bone formation is essential. This review discusses the mechanisms regulating the uncoupled bone remodelling in MM and summarizes current advances in the treatment of MBD. LINKED ARTICLES: This article is part of a themed issue on The molecular pharmacology of bone and cancer-related bone diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.9/issuetoc.

Tumor-derived extracellular vesicles inhibit osteogenesis and exacerbate myeloma bone disease

Background: As a hallmark driver of multiple myeloma (MM), MM bone disease (MBD) is unique in that it is characterized by severely impaired osteoblast activity resulting from blocked osteogenesis in bone marrow-derived mesenchymal stem cells (BM-MSCs). The mechanisms underlying this preferential blockade are incompletely understood.

Methods: miRNA expression of MM cell-derived extracellular vesicles (MM-EVs) was detected by RNA sequencing. MM-EVs impaired osteogenesis and exacerbated MBD were in vitro and in vivo validated by histochemical staining, qPCR and micro-CT. We additionally examined the correlation between CD138⁺ circulating EVs (cirEVs) count and bone lesion in de novo MM patients.

Results: Here, by sequencing and bioinformatics analysis, we found that MM-EVs were enriched in various molecules negatively regulating osteogenesis. We experimentally verified that MM-EVs inhibited BM-MSC osteogenesis, induced elevated expression of miR-103a-3p inhibiting osteogenesis in BM-MSCs, and increased cell viability and interleukin-6 secretion in MM cells. In a mouse model, MM-EVs that were injected into the marrow space of the left tibia led to impaired osteogenesis and exacerbated MBD and MM progression. Furthermore, the levels of CD138⁺ cirEVs in the peripheral blood were positively correlated with the number of MM bone lesions in MM patients.

Conclusions: These findings suggest that MM-EVs play a pivotal role in the development of severely impaired osteoblast activity, which represents a novel biomarker for the precise diagnosis of MBD and a compelling rationale for exploring MM-EVs as a therapeutic target.

Bones in Multiple Myeloma: Imaging and Therapy

F-fluorodeoxyglucose (FDG)-PET/CT, MRI, and other novel imaging modalities in the management of disease in patients with plasma cell dyscrasias. We also review the state of the art in treatment of MM bone disease (MMBD) and the role of bisphosphonates and denosumab, a monoclonal antibody that binds and blocks the activity of receptor activator of nuclear factor-kappa B ligand (RANKL), which was recently approved by the U.S. Food and Drug Administration for MMBD.

Multiple Myeloma and Bone: The Fatal Interaction

Multiple myeloma (MM) is the second-most-common hematologic malignancy and the most frequent cancer to involve bone. MM bone disease (MMBD) has devastating consequences for patients, including dramatic bone loss, severe bone pain, and pathological fractures that markedly decrease the quality of life and impact survival of MM patients. MMBD results from excessive osteoclastic bone resorption and persistent suppressed osteoblastic bone formation, causing lytic lesions that do not heal, even when patients are in complete and prolonged remission. This review discusses the cellular and molecular mechanisms that regulate the uncoupling of bone remodeling in MM, the effects of MMBD on tumor growth, and potential therapeutic approaches that may prevent severe bone loss and repair damaged bone in MM patients.

Bisphosphonate guidelines for treatment and prevention of myeloma bone disease

Multiple myeloma (MM) is a haematological malignancy characterised by the clonal proliferation of plasma cells in the bone marrow. More than 80% of patients with MM display evidence of myeloma bone disease (MBD), characterised by the formation of osteolytic lesions throughout the axial and appendicular skeleton. MBD significantly increases the risk of skeletal-related events such as pathologic fracture, spinal cord compression and hypercalcaemia. MBD is the result of MM plasma cells-mediated activation of osteoclast activity and suppression of osteoblast activity. Bisphosphonates (BP), pyrophosphate analogues with high bone affinity, are the only pharmacological agents currently recommended for the treatment and prevention of MBD and remain the standard of care. Pamidronate and zoledronic acid are the most commonly used BP to treat MBD. Although generally safe, frequent high doses of BP are associated with adverse events such as renal toxicity and osteonecrosis of the jaw. As such, optimal duration and dosing of BP therapy is required in order to minimise BP-associated adverse events. The following guidelines provide currently available evidence for the adoption of a tailored approach when using BP for the management of MBD.

Thymic PTH Increases After Thyroparathyroidectomy in C57BL/KaLwRij Mice

We previously reported a substantial correlation between serum parathyroid hormone (PTH) levels and the myeloma response to proteasome inhibition that suggests a crucial role for the PTH receptor 1 system in the control of myeloma tumor growth. While investigating the role of PTH in the antimyeloma effect, we observed the recovery of serum PTH levels after thyroparathyroidectomy (TPTX). Although the presence of thymus-derived PTH has been reported previously, the existence or role of thymic PTH in the serum remains controversial. Here, TPTX was performed in 8- to 12-week-old C57BL/KaLwRij mice to delineate the potential source(s) for the recovery of serum PTH. Immediately after TPTX, the expected loss of measurable serum PTH was observed. Serum PTH levels recovered 3 to 4 weeks after TPTX. Thirteen endocrine organs from mice with recovered serum PTH were examined. The thymus from control mice expressed measurable and detectable Pth transcripts; however, the Pth transcript level was substantially elevated in tissue from TPTX mice. Western blot analysis of the thymus demonstrated a reproducible and distinct PTH band in thymus tissue that was significantly increased after TPTX. To directly confirm the identity of the distinct PTH band, immunoprecipitated proteins were isolated and subjected to tandem mass spectrometry. After fragmentation and direct peptide sequencing, PTH peptides PTH(1-13) and PTH(54-70), diagnostic for PTH, were identified. These data demonstrate that the murine thymus produces PTH and that after TPTX the thymus becomes the major source of serum PTH, compensating for the loss of the parathyroid glands and returning circulating PTH levels to normal.

Identification of the APC/C co-factor FZR1 as a novel therapeutic target for multiple myeloma

Multiple Myeloma (MM) is a haematological neoplasm characterised by the clonal proliferation of malignant plasma cells in the bone marrow. The success of proteasome inhibitors in the treatment of MM has highlighted the importance of the ubiquitin proteasome system (UPS) in the pathogenesis of this disease. In this study, we analysed gene expression of UPS components to identify novel therapeutic targets within this pathway in MM. Here we demonstrate how this approach identified previously validated and novel therapeutic targets. In addition we show that FZR1 (Fzr), a cofactor of the multi-subunit E3 ligase complex anaphase-promoting complex/cyclosome (APC/C), represents a novel therapeutic target in myeloma. The APC/C associates independently with two cofactors, Fzr and Cdc20, to control cell cycle progression. We found high levels of FZR1 in MM primary cells and cell lines and demonstrate that expression is further increased on adhesion to bone marrow stromal cells (BMSCs). Specific knockdown of either FZR1 or CDC20 reduced viability and induced growth arrest of MM cell lines, and resulted in accumulation of APC/C^Fzr substrate Topoisomerase IIα (TOPIIα) or APC/C^Cdc20 substrate Cyclin B. Similar effects were observed following treatment with proTAME, an inhibitor of both APC/C^Fzr and APC/C^Cdc20. Combinations of proTAME with topoisomerase inhibitors, etoposide and doxorubicin, significantly increased cell death in MM cell lines and primary cells, particularly if TOPIIα levels were first increased through pre-treatment with proTAME. Similarly, combinations of proTAME with the microtubule inhibitor vincristine resulted in enhanced cell death. This study demonstrates the potential of targeting the APC/C and its cofactors as a therapeutic approach in MM.

Bone marrow micro-environment is a crucial player for myelomagenesis and disease progression

Despite the advent of many therapeutic agents, such as bortezomib and lenalidomide that have significantly improved the overall survival, multiple myeloma remains an incurable disease. Failure to cure is multifactorial and can be attributed to the underlying genetic heterogeneity of the cancer and to the surrounding micro-environment. Understanding the mutual interaction between myeloma cells and micro-environment may lead to the development of novel treatment strategies able to eradicate this disease. In this review we discuss the principal molecules involved in the micro-environment network in multiple myeloma and the currently available therapies targeting them.

Expression of hsa-MIR-204, RUNX2, PPARγ, and BCL2 in Bone Marrow Derived Mesenchymal Stem Cells from Multiple Myeloma Patients and Normal Individuals

Objective

Multiple Myeloma (MM) is a heterogeneous cytogenetic disorder in which clonal plasma cells proliferate in the bone marrow (BM) and cause bone destruction. The BM microenvironment plays a crucial role in pathogenesis of this disease, and mesenchymal stem cells (MSCs) are one of the key players. Herein, we propose to investigate the expressions of hsa-MIR-204, runt-related transcription factor 2 (RUNX2), peroxisome proliferator-activated receptor gamma (PPARγ), and B-cell lymphoma 2 (BCL2) as factors involved in osteogenesis, adipogenesis, and MSC survival in BM-MSCs from MM patients and normal individuals.

Materials and Methods

In this experimental study, we isolated MSCs from BM aspirates of MM patients and healthy donors. Total RNA were extracted before and after co-culture with L363 myeloma cells. Gene expressions of RUNX2, PPARγ, BCL2, and hsa-MIR-204 were assessed by quantitive real time polymerase chain reaction (qRT-PCR).

Results

Higher levels of RUNX2, PPARγ, and hsa-MIR-204 expressions existed in MM- MSCs compared to normally derived (ND)-MSCs. BCL2 expression decreased in MM- MSCs. We observed different results in the co-culture model.

Conclusion

In general, the MM-MSCs gene expression profile differed compared to ND- MSCs. Upregulation of RUNX2, PPARγ, and hsa-MIR-204 in MM-MSCs compared to ND- MSCs would result in formation of bone defects. Downregulation of BCL2 would lead to MM-MSC cell death.

Automated "Bone Subtraction" Image Analysis Software Package for Improved and Faster CT Monitoring of Longitudinal Spine Involvement in Patients with Multiple Myeloma

RATIONALE AND OBJECTIVES

The study aimed to assess the diagnostic benefit of a novel computed tomography (CT) post-processing software generating subtraction maps of longitudinal non-enhanced CT examinations for monitoring the course of myeloma bone disease in the spine.

MATERIALS AND METHODS

The local institutional review board approved the retrospective data evaluation. Included were 82 consecutive myeloma patients (46 male; mean age, 65.08 ± 9.76) who underwent 188 repeated whole-body reduced-dose Multislice Detector Computed Tomography (MDCT) at our institution between December 2013 and January 2016. Lytic bone lesions were categorized as new or enlarging versus stable. Bone subtraction maps were read in combination with corresponding 1-mm source images comparing results to those of standard image reading of 5-mm axial and 2-mm multiplanar reformat reconstructions (MPR) scans and hematologic markers, and classified as either progressive disease (PD) or stable disease (SD or remission). The standard of reference was 1-mm axial CT image reading + hematologic response both confirmed at follow-up. For statistical purposes, we subgrouped the hematologic response categories similarly to those applied for CT imaging (progression vs stable/response).

RESULTS

According to the standard of reference, 16 patients experienced PD and 66 SD at follow-up. Th sensitivity, specificity, and accuracy for axial 5 mm + 2 mm MPR image versus bone subtraction maps in a "lesion-by-lesion" reading were 97.6%, 92.3%, and 97.2% versus 97.8%, 96.7%, and 97.7%, respectively. The use of bone subtraction maps resulted in a change of response classification in 9.7% of the patients (n = 8) versus 5 mm + 2 mm MPR image reading from SD to PD. Bone sclerosis lesions were detected in 52 out of 82 patients (63.4%). The reading time was significantly lower with the software bone subtraction compared to standard reading (P < 0.01) and 1-mm image reading (P < 0.001).

CONCLUSION

Accuracy of bone subtraction maps reading for monitoring multiple myeloma is slightly increased over that of conventional axial + MPR image reading and significantly speeds up the reading time.

Calcium and Bone Metabolism Indices

Calcium and inorganic phosphate are of critical importance for many body functions, thus the regulations of their plasma concentrations are tightly controlled by the concerted actions of reabsorption/excretion in the kidney, absorption in the intestines, and exchange from bone, the major reservoir for calcium and phosphate in the body. Parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D (1,25(OH)₂D) control calcium homeostasis, whereas PTH, 1,25(OH)₂D, and bone-derived fibroblast growth factor 23 (FGF 23) control phosphate homeostasis. Hypoparathyroidism can cause hypocalcemia and hyperphosphatemia, whereas deficient vitamin D actions can cause osteomalacia in adults and rickets in children. Hyperparathyroidism, alternatively, can cause hypercalcemia and hypophosphatemia. Laboratory tests of calcium, phosphate, PTH, and 25-hydroxyvitamin D are very useful in the diagnosis of abnormalities associated with calcium and/or phosphate metabolisms. Bone is constantly remodeled throughout life in response to mechanical stress and a need for calcium in extracellular fluids. Metabolic bone diseases such as osteoporosis, osteomalacia in adults or rickets in children, and renal osteodystrophy develop when bone resorption exceeds bone formation. Bone turnover markers (BTM) such as serum N-terminal propeptide of type I procollagen (P1NP) and C-terminal collagen cross-link (CTX) may be useful in predicting future fracture risk or monitoring the response to anti-resorptive therapy. There is a need to standardize sample collection protocols because certain BTMs exhibit large circadian variations and tend to be influenced by food intakes. In the United States, a project to standardize BTM sample collection protocols and to establish the reference intervals for serum P1NP and serum CTX is ongoing. We anticipate the outcome of this project to shine lights on the standardization of BTM assays, sample collection protocols, reference intervals in relation to age, sex, and ethnic origins, and clinical utilities of BTMs. This review will briefly discuss the regulations of calcium and phosphate homeostasis, laboratory's role in the diagnosis, and monitoring of bone and calcium metabolism, as well as the usefulness and controversies of the utilities of BTMs in the diagnosis and monitoring of metabolic bone diseases.

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.

Dissecting the multiple myeloma-bone microenvironment reveals new therapeutic opportunities

Multiple myeloma is a plasma cell skeletal malignancy. While therapeutic agents such as bortezomib and lenalidomide have significantly improved overall survival, the disease is currently incurable with the emergence of drug resistance limiting the efficacy of chemotherapeutic strategies. Failure to cure the disease is in part due to the underlying genetic heterogeneity of the cancer. Myeloma progression is critically dependent on the surrounding microenvironment. Defining the interactions between myeloma cells and the more genetically stable hematopoietic and mesenchymal components of the bone microenvironment is critical for the development of new therapeutic targets. In this review, we discuss recent advances in our understanding of how microenvironmental elements contribute to myeloma progression and, therapeutically, how those elements can or are currently being targeted in a bid to eradicate the disease.

Well plate-based perfusion culture device for tissue and tumor microenvironment replication

There are significant challenges in developing in vitro human tissue and tumor models that can be used to support new drug development and evaluate personalized therapeutics. The challenges include: (1) working with primary cells which are often difficult to maintain ex vivo, (2) mimicking native microenvironments from which primary cells are harvested, and (3) the lack of culture devices that can support these microenvironments to evaluate drug responses in a high-throughput manner. Here we report a versatile well plate-based perfusion culture device that was designed, fabricated and used to: (1) ascertain the role of perfusion in facilitating the expansion of human multiple myeloma cells and evaluate drug response of the cells, (2) preserve the physiological phenotype of primary murine osteocytes by reconstructing the 3D cellular network of osteocytes, and (3) circulate primary murine T cells through a layer of primary murine intestine epithelial cells to recapitulate the interaction of the immune cells with the epithelial cells. Through these diverse case studies, we demonstrate the device's design features to support: (1) the convenient and spatiotemporal placement of cells and biomaterials into the culture wells of the device; (2) the replication of tissues and tumor microenvironments using perfusion, stromal cells, and/or biomaterials; (3) the circulation of non-adherent cells through the culture chambers; and (4) conventional tissue and cell characterization by plate reading, histology, and flow cytometry. Future challenges are identified and discussed from the perspective of manufacturing the device and making its operation for routine and wide use.

Ex Vivo Maintenance of Primary Human Multiple Myeloma Cells through the Optimization of the Osteoblastic Niche

We previously reported a new approach for culturing difficult-to-preserve primary patient-derived multiple myeloma cells (MMC) using an osteoblast (OSB)-derived 3D tissue scaffold constructed in a perfused microfluidic environment and a culture medium supplemented with patient plasma. In the current study, we used this biomimetic model to show, for the first time, that the long-term survival of OSB is the most critical factor in maintaining the ex vivo viability and proliferative capacity of MMC. We found that the adhesion and retention of MMC to the tissue scaffold was meditated by osteoblastic N-cadherin, as one of potential mechanisms that regulate MMC-OSB interactions. However, in the presence of MMC and patient plasma, the viability and osteogenic activity of OSB became gradually compromised, and consequently MMC could not remain viable over 3 weeks. We demonstrated that the long-term survival of both OSB and MMC could be enhanced by: (1) optimizing perfusion flow rate and patient-derived plasma composition in the culture medium and (2) replenishing OSB during culture as a practical means of prolonging MMC's viability beyond several weeks. These findings were obtained using a high-throughput well plate-based perfusion device from the perspective of optimizing the ex vivo preservation of patient-derived MM biospecimens for downstream use in biological studies and chemosensitivity analyses.

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.

Gene-Lifestyle Interactions in Complex Diseases: Design and Description of the GLACIER and VIKING Studies

Most complex diseases have well-established genetic and non-genetic risk factors. In some instances, these risk factors are likely to interact, whereby their joint effects convey a level of risk that is either significantly more or less than the sum of these risks. Characterizing these gene-environment interactions may help elucidate the biology of complex diseases, as well as to guide strategies for their targeted prevention. In most cases, the detection of gene-environment interactions will require sample sizes in excess of those needed to detect the marginal effects of the genetic and environmental risk factors. Although many consortia have been formed, comprising multiple diverse cohorts to detect gene-environment interactions, few robust examples of such interactions have been discovered. This may be because combining data across studies, usually through meta-analysis of summary data from the contributing cohorts, is often a statistically inefficient approach for the detection of gene-environment interactions. Ideally, single, very large and well-genotyped prospective cohorts, with validated measures of environmental risk factor and disease outcomes should be used to study interactions. The presence of strong founder effects within those cohorts might further strengthen the capacity to detect novel genetic effects and gene-environment interactions. Access to accurate genealogical data would also aid in studying the diploid nature of the human genome, such as genomic imprinting (parent-of-origin effects). Here we describe two studies from northern Sweden (the GLACIER and VIKING studies) that fulfill these characteristics.

Myeloma bone disease: pathogenesis, current treatments and future targets

INTRODUCTION

Patients with myeloma develop localized and generalized bone loss leading to hypercalcaemia, accelerated osteoporosis, vertebral wedge fractures, other pathological fractures, spinal cord compression and bone pain. Bone loss is mediated by a variety of biological modifiers including osteoclast-activating factors (OAF) and osteoblast (OB) inhibitory factors produced either directly by malignant plasma cells (MPCs) or as a consequence of their interaction with the bone marrow microenvironment (BMM). Raised levels of OAFs such as receptor activator of nuclear factor-kappa B ligand (RANKL), macrophage inflammatory protein 1 alpha, tumour necrosis factor-alpha and interleukin 6 stimulate bone resorption by recruiting additional osteoclasts. Via opposing mechanisms, increases in OB inhibitory factors, such as dickkopf-1 (Dkk-1), soluble frizzled-related protein-3 and hepatocyte growth factor (HGF), suppress bone formation by inhibiting the differentiation and recruitment of OBs. These changes result in an uncoupling of physiological bone remodelling, leading to myeloma bone disease (MBD). Moreover, the altered BMM provides a fertile ground for the growth and survival of MPCs. Current clinical management of MBD is both reactive (to pain and fractures) and preventive, with bisphosphonates (BPs) being the mainstay of pharmacological treatment. However, side effects and uncertainties associated with BPs warrant the search for more targeted treatments for MBD. This review will summarize recent developments in understanding the intimate relationship between MBD and the BMM and the novel ways in which they are being therapeutically targeted.

SOURCES OF DATA

All data included were sourced and referenced from PubMed.

AREAS OF AGREEMENT

The clinical utility of BP therapy is well established. However, there is general acknowledgement that BPs are only partially successful in the treatment of MBD. The number of skeletal events attributable to myeloma are reduced by BPs but not totally eliminated. Furthermore, existing damage is not repaired. It is widely recognized that more effective treatments are needed.

AREAS OF CONTROVERSY

There remains controversy concerning the duration of BP therapy. Whether denosumab is a viable alternative to BP therapy is also contested. Many of the new therapeutic strategies discussed are yet to translate to clinical practice and demonstrate equal efficacy or superiority to BP therapy. It also remains controversial whether reported anti-tumour effects of bone-modulating therapies are clinically significant.

GROWING POINTS

The potential clinical utility of bone anabolic therapies including agents such as anti-Dkk-1, anti-sclerostin and anti-HGF is becoming increasingly recognized.

AREAS TIMELY FOR DEVELOPING RESEARCH

Further research effectively targeting the mediators of MBD, targeting both bone resorption and bone formation, is urgently needed. This should translate promptly to clinical trials of combination therapy comprising anti-resorptives and bone anabolic therapies to demonstrate efficacy and improved outcomes over BPs.

Carfilzomib promotes the osteogenic differentiation potential of mesenchymal stem cells derived from myeloma patients by inhibiting notch1 activity in vitro

Notch1 signaling plays a key role in the differentiation of mesenchymal stem cells (MSCs). Carfilzomib (CFZ), a second-generation proteasome inhibitor, has potent cytotoxicity against myeloma cells. In this study, we investigated the effects of CFZ on the osteogenic differentiation potential of MSCs derived from myeloma patients (MM-MSCs) in vitro. MM-MSCs showed decreased osteogenic differentiation ability, together with an impairment of notch1 deactivation. The notch1 inhibitor DAPT and the downregulation of notch1 by shRNA promoted osteogenesis in MM-MSCs. Additionally, CFZ treatment resulted in notch1 inhibition and enhanced osteogenesis in MM-MSCs. These findings suggest that CFZ stimulates osteogenesis via notch1 inhibition.

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.

Myeloma bone disease: Pathophysiology and management

Multiple myeloma bone disease is marked by severe dysfunction of both bone formation and resorption and serves as a model for understanding the regulation of osteoblasts (OBL) and osteoclasts (OCL) in cancer. Myeloma bone lesions are purely osteolytic and are associated with severe and debilitating bone pain, pathologic fractures, hypercalcemia, and spinal cord compression, as well as increased mortality. Interactions within the bone marrow microenvironment in myeloma are responsible for the abnormal bone remodeling in myeloma bone disease. Myeloma cells drive bone destruction that increases tumor growth, directly stimulates the OCL formation, and induces cells in the marrow microenvironment to produce factors that drive OCL formation and suppress OBL formation. Factors produced by marrow stromal cells and OCL promote tumor growth through direct action on myeloma cells and by increasing angiogenesis. Current therapies targeting MMBD focus on preventing osteoclastic bone destruction; however regulators of OBL inhibition in MMBD have also been identified, and targeted agents with a potential anabolic effect in MMBD are under investigation. This review will discuss the mechanisms responsible for MMBD and therapeutic approaches currently in use and in development for the management of MMBD.

[Occipito-cervical fixation in plasmocytoma. Method modification. Technical report]

Intraoperative modification of use and stabilization of the Axon system (Synthes) for occipito-cervical fusion in a patient treated oncologically due to plasmocytoma is presented. Pathological fracture, range of the process and damage of anterior cervical fusion necessitated the use of occipito-cervical stabilization. Different anatomical conditions within the occipital bone in the form of its thinning was observed. Fixing with screws was impossible due to the bone structure. In consequence, modification of stabilization with an ad hoc elaborated technique (burr holes in the occipital bone and stabilization with titanium wire) was implemented. Modifications and specific indications related to the clinical course of plasmocytoma are discussed.

Mineralized and osteoid tissue from dental pulp stem cells on micro-arc oxidation titanium in vitro

The presence of insufficient bone volume affects the implant healing and success. The aim of this study was to evaluate osteogenic capacity of dental pulp stem cells (DPSCs) on micro-arc oxidation (MAO) titanium surface. DPSCs were challenged at MAO and smooth titanium surface separately for different durations, and the bone marrow mesenchymal stem cells (BMSCs) served as the positive controls. The osteogenic capacity of DPSCs on MAO titanium surface was assessed by using scanning electron microscopy, energy dispersive spectroscopy, biochemical tests and real-time quantitative PCR. Data showed that DPSCs differentiated into osteoblasts and expressed bone morphogenetic genes on MAO titanium surface. The results of this study revealed that DPSCs had good potential to generate mineralized tissue on MAO titanium plates. The differential potential of DPSCs may be regulated by MAO titanium surface. The osteogenesis potential of DPSCs on the MAO titanium was similar with BMSCs.

Mechanisms of multiple myeloma bone disease

Multiple myeloma is the second most common hematological malignancy and the most frequent cancer to involve the skeleton. Multiple myeloma bone disease (MMBD) is characterized by abnormal bone remodeling with dysfunction of both bone resorption and bone formation, and thus can be used as a paradigm for other inflammatory bone diseases, and the regulation of osteoclasts and osteoblasts in malignancy. Studies of MMBD have identified novel regulators that increase osteoclastogenesis and osteoclast function, repress osteoblast differentiation, increase angiogenesis, or permanently alter stromal cells. This review will discuss the current understanding of mechanisms of osteoclast and osteoblast regulation in MMBD, and therapeutic approaches currently in use and under development that target mediators of bone destruction and blockade of bone formation for myeloma patients, including new anabolic therapies.

Therapeutic approaches to myeloma bone disease: an evolving story

Bone disease is a major morbidity factor in patients with multiple myeloma and significantly affects their overall survival. A complex interplay between malignant plasma cells and other marrow cells results in the generation of a microenvironment capable of enhancing both tumor growth and bone destruction. Bisphosphonates have consistently reduced the incidence of skeletal-related events in patients with multiple myeloma and other osteotropic tumors as well. However, their use is burdened with side-effects, including the risks of osteonecrosis of the jaw and kidney failure, suggesting that they should be discontinued after prolonged administration. New molecular targets of cell cross-talk in myeloma bone marrow are therefore under intensive investigation and new drugs are being explored in preclinical and clinical studies of myeloma bone disease. Compounds targeting osteoclast activation pathways, such as receptor activator of nuclear factor-κB/receptor activator of nuclear factor-κB ligand/osteoprotegerin, B-cell activating factor, mitogen-activated protein kinase and macrophage inflammatory protein-1α/chemokine receptor for macrophage inflammatory protein-1α axes, or soluble agents that improve osteoblast differentiation by modulating specific inhibitors such as Dickkopf-1 and transforming growth factor-β, as well as novel approaches of cytotherapy represent a new generation of promising drugs for the treatment of myeloma bone disease.

TRAF6 activation in multiple myeloma: a potential therapeutic target

Multiple myeloma (MM) is an incurable B-lymphocyte malignancy. New therapeutic options have become available during the past several years; however nearly all patients acquire resistance to currently available therapeutic agents. Mechanisms contributing to the pathogenesis and chemoresistance of MM include genetic abnormalities, chromosomal translocations, gene mutations, the interaction between MM cells and the bone marrow microenvironment, and defects in the apoptotic signaling pathways. Survival signaling pathways associated with the pathogenesis of MM and bone marrow stromal cells play crucial roles in promoting growth, survival, adhesion, immortalization, angiogenesis, and drug resistance. The receptor activator of nuclear factor-kappa B/receptor activator of nuclear factor-kappa B ligand/tumor necrosis factor receptor-associated factor (RANK/RANKL-TRAF6) signal pathway mediates osteolytic bone lesions through the activation of the NF-κB and Janus kinase/signal transducer and activator of transcription (JNK) pathways in osteoclast precursor cells and thus contributes to the main clinical manifestations of bone disease. TRAF6 has also been identified as a ligase for Akt ubiquitination and membrane recruitment and its phosphorylation on growth factor stimulation. The inhibition of TRAF6 by silencing RNA or by decoy peptides decreases MM tumor cell proliferation and increases apoptosis as well as bone resorption. Some proteasome inhibitors and benzoxadiazole derivatives showed inhibitory effects on the activity and function of TRAF6. Overall, we propose that TRAF6 may be considered as a potential therapeutic target for the treatment of MM.

Bone cell interactions through Eph/ephrin: bone modeling, remodeling and associated diseases

Bones cannot properly form or be maintained without cell-cell interactions through ephrin ligands and Eph receptors. Cell culture analysis and evaluation of genetic mouse models and human diseases reveal various ephrins and Eph functions in the skeletal system. Migration, attachment and spreading of mesenchymal stem cells are regulated by ephrinB ligands and EphB receptors. ephrinB1 loss-of-function is associated with craniofrontonasal syndrome (CFNS) in humans and mice. In bone remodeling, ephrinB2 is postulated to act as a “coupling stimulator.” In that case, bidirectional signaling between osteoclastic ephrinB2 and osteoblastic EphB4 suppresses osteoclastic bone resorption and enhances osteoblastic bone formation, facilitating the transition between these two states. Parathyroid hormone (PTH) induces ephrinB2 in osteoblasts and enhances osteoblastic bone formation. In contrast to ephrinB2, ephrinA2 acts as a “coupling inhibitor,” since ephrinA2 reverse signaling into osteoclasts enhances osteoclastogenesis and EphA2 forward signaling into osteoblasts suppresses osteoblastic bone formation and mineralization. Furthermore, ephrins and Ephs likely modulate pathological conditions such as osteoarthritis, rheumatoid arthritis, multiple myeloma and osteosarcoma. This review focuses on ephrin/Eph-mediated cell-cell interactions in bone biology.

Dual-energy X-ray absorptiometry and biochemical markers of bone turnover after autologous stem cell transplantation in myeloma

OBJECTIVES

To evaluate the effect of high-dose chemotherapy (HDT) followed by autologous stem cell transplantation (ASCT) on bone turnover and bone mineral density in a cohort of 39 consecutive patients with multiple myeloma (MM).

METHODS

Phosphorus and calcium parameters, bone turnover markers, and bone mineral density were studied. Timepoints were diagnosis (T1), just before ASCT (T2), 6 months (T3) after ASCT, and 1 yr (T4) after ASCT.

RESULTS

No bone mineral loss was shown on dual-energy X-ray absorptiometry (DXA) at T1 (lumbar Z-score -0.02, femoral neck Z-score 0.77) or during follow-up. Chronic vitamin D deficiency (25OHD3 11.7 ± 7.7 ng/mL at T1) and relative hyperparathyroidism from T2 to T4 were observed. In spite of this moderate hyperparathyroidism, serum C-telopeptide of type I collagen (CTX) decreased significantly between T1 and T4. Bone alkaline phosphatase levels were low at diagnosis and showed no significant change after ASCT, unlike DKK1 levels that were high at diagnosis and decreased 6 months after ASCT in patients not previously treated with bisphosphonates.

CONCLUSION

Bone demineralization is moderate in multiple myeloma. ASCT induces a decrease in bone resorption but no changes in bone formation, remaining low despite the decrease in DKK1. Bone mineral loss, evaluated by DXA, is moderate in multiple myeloma. High-dose chemotherapy followed by ASCT leads to decreased bone resorption but osteoblastic bone formation remains low, in spite of reduced circulating DKK1.