Multiple myeloma disrupts the TRANCE/ osteoprotegerin cytokine axis to trigger bone destruction and promote tumor progression

Good Cop, Bad Cop: Profiling the Immune Landscape in Multiple Myeloma

Multiple myeloma (MM) is a dyscrasia of plasma cells (PCs) characterized by abnormal immunoglobulin (Ig) production. The disease remains incurable due to a multitude of mutations and structural abnormalities in MM cells, coupled with a favorable microenvironment and immune suppression that eventually contribute to the development of drug resistance. The bone marrow microenvironment (BMME) is composed of a cellular component comprising stromal cells, endothelial cells, osteoclasts, osteoblasts, and immune cells, and a non-cellular component made of the extracellular matrix (ECM) and the liquid milieu, which contains cytokines, growth factors, and chemokines. The bone marrow stromal cells (BMSCs) are involved in the adhesion of MM cells, promote the growth, proliferation, invasion, and drug resistance of MM cells, and are also crucial in angiogenesis and the formation of lytic bone lesions. Classical immunophenotyping in combination with advanced immune profiling using single-cell sequencing technologies has enabled immune cell-specific gene expression analysis in MM to further elucidate the roles of specific immune cell fractions from peripheral blood and bone marrow (BM) in myelomagenesis and progression, immune evasion and exhaustion mechanisms, and development of drug resistance and relapse. The review describes the role of BMME components in MM development and ongoing clinical trials using immunotherapeutic approaches.

Effect of pilose antler polypeptide on the mechanism of bone homeostasis in osteoporosis

Osteoporosis stands out as a prevalent metabolic disorder, bearing significant repercussions on human well-being and overall quality of life. It remains an urgent concern within the global public health framework due to its widespread occurrence. Osteoporosis arises from an abnormal metabolism in osteoblasts and osteoclasts, resulting in a disruption of the delicate equilibrium between bone formation and bone resorption. Within this context, deer antler peptides emerge as natural active compounds, wielding a pivotal role in governing the differentiation, proliferation, and mineralization of osteoblasts, as well as influencing the activity of osteoclasts. This article aims to consolidate our comprehension of the mechanisms underpinning the dynamic balance between bone formation and resorption, meticulously orchestrated by osteoblasts and osteoclasts in osteoporosis. Furthermore, it offers a comprehensive overview of how deer antler peptides, through their modulation of relevant signaling pathways, contribute to the enhancement of bone homeostasis. These insights deepen our understanding of the pathological processes through which deer antler peptides ameliorate bone homeostasis, while also presenting novel strategies for osteoporosis management.

The molecular mechanism of Gorham syndrome: an update

Gorham syndrome, also known as "vanishing osteopathy" and "invasive hemangiomatosis," is a rare clinical syndrome whose etiology is unknown and can invade the whole-body skeleton. At present, more than 300 cases have been reported at home and abroad, usually manifesting as spontaneous chronic osteolysis with no periosteal reaction at the lysis site and occult onset, often with fractures, scoliosis, chylothorax, etc. When waiting for medical treatment, the condition is serious, and the prognosis is poor. At present, there is no effective treatment. The main pathological manifestations of Gorham syndrome are the non-neoplastic abnormal proliferation of lymphatic vessels or blood vessels and osteolysis caused by osteoclast proliferation or increased activity. At present, there is no unified conclusion regarding Gorham syndrome's pathogenesis. This paper starts with the two most studied osteolysis methods at present, osteoclast osteolysis and osteolysis caused by vascular and lymphatic proliferation and summarizes the corresponding most possible molecular mechanisms in recent years to provide more ideas for Gorham syndrome treatment.

RANKL and RANK in Cancer Therapy

Receptor activator of nuclear factor-κB (RANK) and its ligand (RANKL) are key regulators of mammalian physiology such as bone metabolism, immune tolerance and antitumor immunity, and mammary gland biology. Here, we explore the multiple functions of RANKL/RANK in physiology and pathophysiology and discuss underlying principles and strategies to modulate the RANKL/RANK pathway as a therapeutic target in immune-mediated cancer treatment.

Myeloma bone disease: pathogenesis and management in the era of new anti-myeloma agents

INTRODUCTION

Multiple myeloma (MM) is a malignancy of plasma cells with characteristic bone disease. Despite recent great strides achieved in MM treatment owing to the implementation of new anti-MM agents, MM is still incurable and bone destruction remains a serious unmet issue in patients with MM.

APPROACH

In this review, we will summarize and discuss the mechanisms of the formation of bone disease in MM and the available preclinical and clinical evidence on the treatment for MM bone disease.

CONCLUSIONS

MM cells produce a variety of cytokines to stimulate receptor activator of nuclear factor-κB ligand-mediated osteoclastogenesis and suppress osteoblastic differentiation from bone marrow stromal cells, leading to extensive bone destruction with rapid loss of bone. MM cells alter the microenvironment through bone destruction where they colonize, which in turn favors tumor growth and survival, thereby forming a vicious cycle between tumor progression and bone destruction. Denosumab or zoledronic acid is currently recommended to be administered at the start of treatment in newly diagnosed patients with MM with bone disease. Proteasome inhibitors and the anti-CD38 monoclonal antibody daratumumab have been demonstrated to exert bone-modifying activity in responders. Besides their anti-tumor activity, the effects of new anti-MM agents on bone metabolism should be more precisely analyzed in patients with MM. Because prognosis in patients with MM has been significantly improved owing to the implementation of new agents, the therapeutic impact of bone-modifying agents should be re-estimated in the era of these new agents.

The use of bone-modifying agents in multiple myeloma

Multiple myeloma is a hematological neoplasm characterized by abnormal proliferation of plasma cells in the bone marrow and is usually associated with increased bone pain and skeletal-related events such as pathological fracture and/or spinal cord compression. Myeloma bone disease results in changes in the bone-marrow microenvironment evidenced by increased osteoclastic activity and/or decreased osteoblastic activity, which negatively affect quality of life. Treatment of myeloma bone disease includes bisphosphonates or denosumab (bone-modifying agents). These agents do not induce the formation of new bone or repair existing bone damage, but they can decrease bone pain and the risk of pathological fracture. While these agents improve quality of life, it is not known whether they improve overall survival. This review focuses on different classes of bone-modifying agents, their mechanisms of action, time of initiation, duration of therapy, and potential survival benefits.

Current perspectives on interethnic variability in multiple myeloma: Single cell technology, population pharmacogenetics and molecular signal transduction

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This review discusses the emerging single cell technologies and applications in Multiple myeloma (MM), population pharmacogenetics of MM, resistance to chemotherapy, genetic determinants of drug-induced toxicity, molecular signal transduction.

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The role(s) of epigenetics and noncoding RNAs including microRNAs (miRNAs) and long noncoding RNAs (lncRNAs) that influence the risk and severity of MM are also discussed.

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It is understood that ethnic component acts as a driver of variable response to chemotherapy in different sub-populations globally.

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This review augments our understanding of genetic variability in ‘myelomagenesis’ and drug-induced toxicity, myeloma microenvironment at the molecular and cellular level, and developing precision medicine strategies to combat this malignancy.

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The emerging single cell technologies hold great promise for enhancing our understanding of MM tumor heterogeneity and clonal diversity.

Multiple myeloma (MM) is an aggressive cancer characterised by malignancy of the plasma cells and a rising global incidence. The gold standard for optimum response is aggressive chemotherapy followed by autologous stem cell transplantation (ASCT). However, majority of the patients are above 60 years and this presents the clinician with complications such as ineligibility for ASCT, frailty, drug-induced toxicity and differential/partial response to treatment. The latter is partly driven by heterogenous genotypes of the disease in different subpopulations. In this review, we discuss emerging single cell technologies and applications in MM, population pharmacogenetics of MM, resistance to chemotherapy, genetic determinants of drug-induced toxicity, molecular signal transduction, as well as the role(s) played by epigenetics and noncoding RNAs including microRNAs (miRNAs) and long noncoding RNAs (lncRNAs) that influence the risk and severity of the disease. Taken together, our discussions further our understanding of genetic variability in ‘myelomagenesis’ and drug-induced toxicity, augment our understanding of the myeloma microenvironment at the molecular and cellular level and provide a basis for developing precision medicine strategies to combat this malignancy.

Parathyroid hormone-related protein (PTHrP) and malignancy

PTHrP (parathyroid hormone related protein) is an important mediator of malignancy-related tumor progression and hypercalcemia that shares considerable homology and functionality with parathyroid hormone. In this chapter, we review what has been elucidated to date regarding PTHrP's role in malignancies. Starting with a review of calcium metabolism and regulation, we then summarize the discovery and structure of PTHrP and development of sensitive immunoassays for specific measurement. Subsequently, we explore its role in tumor progression, with emphasis on the primary tumor as well as skeletal and non-osseus metastases. We then consider the clinical implications of PTHrP in cancer before concluding with a discussion of both established and potential treatments for malignancy associated hypercalcemia and bone metastases.

Contribution of the Tumor Microenvironment to Metabolic Changes Triggering Resistance of Multiple Myeloma to Proteasome Inhibitors

Virtually all patients with multiple myeloma become unresponsive to treatment with proteasome inhibitors over time. Relapsed/refractory multiple myeloma is accompanied by the clonal evolution of myeloma cells with heterogeneous genomic aberrations, diverse proteomic and metabolic alterations, and profound changes of the bone marrow microenvironment. However, the molecular mechanisms that drive resistance to proteasome inhibitors within the context of the bone marrow microenvironment remain elusive. In this review article, we summarize the latest knowledge about the complex interaction of malignant plasma cells with its surrounding microenvironment. We discuss the pivotal role of metabolic reprograming of malignant plasma cells within the tumor microenvironment with a subsequent focus on metabolic rewiring in plasma cells upon treatment with proteasome inhibitors, driving multiple ways of adaptation to the treatment. At the same time, mutual interaction of plasma cells with the surrounding tumor microenvironment drives multiple metabolic alterations in the bone marrow. This provides a tumor-promoting environment, but at the same time may offer novel therapeutic options for the treatment of relapsed/refractory myeloma patients.

The Osteoclast Traces the Route to Bone Tumors and Metastases

Osteoclasts are highly specialized cells of the bone, with a unique apparatus responsible for resorption in the process of bone remodeling. They are derived from differentiation and fusion of hematopoietic precursors, committed to form mature osteoclasts in response to finely regulated stimuli produced by bone marrow–derived cells belonging to the stromal lineage. Despite a highly specific function confined to bone degradation, emerging evidence supports their relevant implication in bone tumors and metastases. In this review, we summarize the physiological role of osteoclasts and then focus our attention on their involvement in skeletal tumors, both primary and metastatic. We highlight how osteoclast-mediated bone erosion confers increased aggressiveness to primary tumors, even those with benign features. We also outline how breast and pancreas cancer cells promote osteoclastogenesis to fuel their metastatic process to the bone. Furthermore, we emphasize the role of osteoclasts in reactivating dormant cancer cells within the bone marrow niches for manifestation of overt metastases, even decades after homing of latent disseminated cells. Finally, we point out the importance of counteracting tumor progression and dissemination through pharmacological treatments based on a better understanding of molecular mechanisms underlying osteoclast lytic activity and their recruitment from cancer cells.

A systematic review and meta-analysis of interventional studies of bisphosphonates and denosumab in multiple myeloma and future perspectives

Bisphosphonates (BPs) and denosumab (DENOS), due to their ability to inhibit osteoclast activity, are used to prevent skeletal complications in multiple myeloma (MM) patients. The NCBI PubMed, Web of Science, Scopus and ClinicalTrials.gov databases, were systematically searched for interventional studies, assessing the use of BP and DENOS in MM patients. Overall survival, disease progression, skeletal-related events, bone pain, osteonecrosis of the jaw (ONJ) and renal toxicity were the outcomes of interest. A total of 993 studies were retrieved and 43 were used for qualitative synthesis. Clodronate (CLOD) and zoledronic acid (ZOL) were effective in reducing skeletal complications compared to placebo. Results are mixed regarding the efficacy of pamidronate in reducing skeletal related events. ONJ rates were higher for ZOL, but under 5%, with CLOD having the safest profile. DENOS demonstrated non-inferiority to ZOL, in improving overall survival [pooled Hazard Ratio(HR) 1.02(95% CI 0.72,1.44)], progression free survival [pooled HR 0.92(95% CI 0.76,1.11)] and in reducing skeletal related events [pooled HR 1.03(95% CI 0.92,1.16)], with similar rates of ONJ and better safety profile regarding renal toxicity. Denosumab has comparable efficacy and safety with ZOL and may even replace BPs in the future, in the management of myeloma bone disease.

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.

B cell acute lymphoblastic leukemia cells mediate RANK-RANKL-dependent bone destruction

Although most children survive B cell acute lymphoblastic leukemia (B-ALL), they frequently experience long-term, treatment-related health problems, including osteopenia and osteonecrosis. Because some children present with fractures at ALL diagnosis, we considered the possibility that leukemic B cells contribute directly to bone pathology. To identify potential mechanisms of B-ALL-driven bone destruction, we examined the p53 ^-/-; Rag2 ^-/-; Prkdc^scid/scid triple mutant (TM) mice and p53 ^-/-; Prkdc^scid/scid double mutant (DM) mouse models of spontaneous B-ALL. In contrast to DM animals, leukemic TM mice displayed brittle bones, and the TM leukemic cells overexpressed Rankl, encoding receptor activator of nuclear factor κB ligand. RANKL is a key regulator of osteoclast differentiation and bone loss. Transfer of TM leukemic cells into immunodeficient recipient mice caused trabecular bone loss. To determine whether human B-ALL can exert similar effects, we evaluated primary human B-ALL blasts isolated at diagnosis for RANKL expression and their impact on bone pathology after their transplantation into NOD.Prkdc^scid/scidIl2rg^tm1Wjl /SzJ (NSG) recipient mice. Primary B-ALL cells conferred bone destruction evident in increased multinucleated osteoclasts, trabecular bone loss, destruction of the metaphyseal growth plate, and reduction in adipocyte mass in these patient-derived xenografts (PDXs). Treating PDX mice with the RANKL antagonist recombinant osteoprotegerin-Fc (rOPG-Fc) protected the bone from B-ALL-induced destruction even under conditions of heavy tumor burden. Our data demonstrate a critical role of the RANK-RANKL axis in causing B-ALL-mediated bone pathology and provide preclinical support for RANKL-targeted therapy trials to reduce acute and long-term bone destruction in these patients.

Myeloma Bone Disease: A Comprehensive Review

Multiple myeloma (MM) is a neoplastic clonal proliferation of plasma cells in the bone marrow microenvironment, characterized by overproduction of heavy- and light-chain monoclonal proteins (M-protein). These proteins are mainly found in the serum and/or urine. Reduction in normal gammaglobulins (immunoparesis) leads to an increased risk of infection. The primary site of origin is the bone marrow for nearly all patients affected by MM with disseminated marrow involvement in most cases. MM is known to involve bones and result in myeloma bone disease. Osteolytic lesions are seen in 80% of patients with MM which are complicated frequently by skeletal-related events (SRE) such as hypercalcemia, bone pain, pathological fractures, vertebral collapse, and spinal cord compression. These deteriorate the patient's quality of life and affect the overall survival of the patient. The underlying pathogenesis of myeloma bone disease involves uncoupling of the bone remodeling processes. Interaction of myeloma cells with the bone marrow microenvironment promotes the release of many biochemical markers including osteoclast activating factors and osteoblast inhibitory factors. Elevated levels of osteoclast activating factors such as RANK/RANKL/OPG, MIP-1-α., TNF-α, IL-3, IL-6, and IL-11 increase bone resorption by osteoclast stimulation, differentiation, and maturation, whereas osteoblast inhibitory factors such as the Wnt/DKK1 pathway, secreted frizzle related protein-2, and runt-related transcription factor 2 inhibit osteoblast differentiation and formation leading to decreased bone formation. These biochemical factors also help in development and utilization of appropriate anti-myeloma treatments in myeloma patients. This review article summarizes the pathophysiology and the recent developments of abnormal bone remodeling in MM, while reviewing various approved and potential treatments for myeloma bone disease.

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.

Monocyte Subsets and Serum Inflammatory and Bone-Associated Markers in Monoclonal Gammopathy of Undetermined Significance and Multiple Myeloma

BACKGROUND

Monocyte/macrophages have been shown to be altered in monoclonal gammopathy of undetermined significance (MGUS), smoldering (SMM) and active multiple myeloma (MM), with an impact on the disruption of the homeostasis of the normal bone marrow (BM) microenvironment.

METHODS

We investigated the distribution of different subsets of monocytes (Mo) in blood and BM of newly-diagnosed untreated MGUS (n = 23), SMM (n = 14) and MM (n = 99) patients vs. healthy donors (HD; n = 107), in parallel to a large panel of cytokines and bone-associated serum biomarkers.

RESULTS

Our results showed normal production of monocyte precursors and classical Mo (cMo) in MGUS, while decreased in SMM and MM (p ≤ 0.02), in association with lower blood counts of recently-produced CD62L⁺ cMo in SMM (p = 0.004) and of all subsets of (CD62L⁺, CD62L^- and FcεRI⁺) cMo in MM (p ≤ 0.02). In contrast, intermediate and end-stage non-classical Mo were increased in BM of MGUS (p ≤ 0.03), SMM (p ≤ 0.03) and MM (p ≤ 0.002), while normal (MGUS and SMM) or decreased (MM; p = 0.01) in blood. In parallel, increased serum levels of interleukin (IL)1β were observed in MGUS (p = 0.007) and SMM (p = 0.01), higher concentrations of serum IL8 were found in SMM (p = 0.01) and MM (p = 0.002), and higher serum IL6 (p = 0.002), RANKL (p = 0.01) and bone alkaline phosphatase (BALP) levels (p = 0.01) with decreased counts of FcεRI⁺ cMo, were restricted to MM presenting with osteolytic lesions. This translated into three distinct immune/bone profiles: (1) normal (typical of HD and most MGUS cases); (2) senescent-like (increased IL1β and/or IL8, found in a minority of MGUS, most SMM and few MM cases with no bone lesions); and (3) pro-inflammatory-high serum IL6, RANKL and BALP with significantly (p = 0.01) decreased blood counts of immunomodulatory FcεRI⁺ cMo-, typical of MM presenting with bone lesions.

CONCLUSIONS

These results provide new insight into the pathogenesis of plasma cell neoplasms and the potential role of FcεRI⁺ cMo in normal bone homeostasis.

Multiple Myeloma Bone Disease: Implication of MicroRNAs in Its Molecular Background

Multiple myeloma (MM) is a common hematological malignancy arising from terminally differentiated plasma cells. In the majority of cases, symptomatic disease is characterized by the presence of bone disease. Multiple myeloma bone disease (MMBD) is a result of an imbalance in the bone-remodeling process that leads to increased osteoclast activity and decreased osteoblast activity. The molecular background of MMBD appears intriguingly complex, as several signaling pathways and cell-to-cell interactions are implicated in the pathophysiology of MMBD. MicroRNAs (miRNAs) are small non-coding RNA molecules that regulate the expression of their target mRNAs. Numerous miRNAs have been witnessed to be involved in cancer and hematological malignancies and their role has been characterized either as oncogenic or oncosuppressive. Recently, scientific research turned towards miRNAs as regulators of MMBD. Scientific data support that miRNAs finely regulate the majority of the signaling pathways implicated in MMBD. In this review, we provide concise information regarding the molecular pathways with a significant role in MMBD and the miRNAs implicated in their regulation. Moreover, we discuss their utility as molecular biomarkers and highlight the putative usage of miRNAs as novel molecular targets for targeted therapy in MMBD.

Denosumab compared with zoledronic acid on PFS in multiple myeloma: exploratory results of an international phase 3 study

An exploratory end point from a recent trial in patients with newly diagnosed multiple myeloma showed that median progression-free survival (PFS) was increased by 10.7 months with denosumab vs zoledronic acid. We performed additional analyses to identify factors that may have contributed to the favorable PFS with denosumab. Ad hoc analyses were performed for patients intending to undergo autologous stem cell transplantation (ASCT; ASCT intent), not intending to undergo ASCT (ASCT no intent), and intent-to-treat according to age (<70 or ≥70 years) and baseline renal function (≤60 mL/min or >60 mL/min creatinine clearance [CrCl]). Of 1718 patients, 930 (54.1%) were in the ASCT-intent subgroup, and 788 (45.9%) were in the ASCT-no-intent subgroup. In the ASCT-intent subgroup, frontline triplet (median PFS, not estimable vs 35.7 months; hazard ratio [HR] [95% confidence interval (CI)], 0.65 [0.47-0.90]; descriptive P = .009) or bortezomib-only (median PFS, not estimable vs not estimable; HR [95% CI], 0.61 [0.39-0.95]; descriptive P = .029) induction regimens demonstrated the strongest PFS benefit favoring denosumab vs zoledronic acid. In the ASCT-no-intent subgroup, no benefit with denosumab vs zoledronic acid was observed. PFS favored denosumab vs zoledronic acid in patients with CrCl >60 mL/min and in patients <70 years old, but no difference was observed in patients with CrCl ≤60 mL/min or patients ≥70 years old. The PFS difference observed with denosumab is one of the notable benefits reported in newly diagnosed multiple myeloma and was most pronounced in patients intending to undergo ASCT and those who received proteasome inhibitor (PI)-based triplet regimens. This study was registered at www.clinicaltrials.gov as #NCT01345019.

Game of Bones: How Myeloma Manipulates Its Microenvironment

Multiple myeloma is a clonal disease of long-lived plasma cells and is the second most common hematological cancer behind Non-Hodgkin’s Lymphoma. Malignant transformation of plasma cells imparts the ability to proliferate, causing harmful lesions in patients. In advanced stages myeloma cells become independent of their bone marrow microenvironment and form extramedullary disease. Plasma cells depend on a rich array of signals from neighboring cells within the bone marrow for survival which myeloma cells exploit for growth and proliferation. Recent evidence suggests, however, that both the myeloma cells and the microenvironment have undergone alterations as early as during precursor stages of the disease. There are no current therapies routinely used for treating myeloma in early stages, and while recent therapeutic efforts have improved patients’ median survival, most will eventually relapse. This is due to mutations in myeloma cells that not only allow them to utilize its bone marrow niche but also facilitate autocrine pro-survival signaling loops for further progression. This review will discuss the stages of myeloma cell progression and how myeloma cells progress within and outside of the bone marrow microenvironment.

Use of bisphosphonates in multiple myeloma patients in Denmark, 2005-2015

PURPOSE

To describe use of bisphosphonates in newly diagnosed multiple myeloma patients in Denmark.

METHODS

Using data from the Danish National Multiple Myeloma Registry, we conducted a population-based cohort study. Among patients newly diagnosed with multiple myeloma from 2005 to 2015, we examined use of bisphosphonates at first- and at progression/second-line anti-myeloma treatment overall, by patient characteristics, and myeloma complications.

RESULTS

Of 2947 patients starting first-line anti-myeloma treatment, 2207 patients (74.9%) received bisphosphonates. During a median follow-up of 27.6 (quartiles, 10.6-52.5) months, disease progression post-first-line treatment was recorded in 1546 patients, of whom 1065 (68.9%) were treated with bisphosphonates. Altogether, 80.9% of patients with and 37.6% of patients without myeloma bone disease were treated with bisphosphonates at first line and 73.0% and 42.7%, respectively, at progression/second line. Moreover, the proportion of patients treated with bisphosphonates decreased with increasing severity of renal impairment at first and at progression/second-line treatment.

CONCLUSION

The proportion of patients treated with bisphosphonates as part of first- and second-line anti-myeloma treatment increased with presence of myeloma bone disease and decreased by presence and severity of renal impairment. Overall, 25% of newly diagnosed multiple myeloma patients had no record of bisphosphonate treatment, potentially indicating an unmet need.

Role of RANKL in cancer development and metastasis

Bone metastasis involves tumor-induced osteoclast activation, resulting in skeletal tumor progression as well as skeletal disorders. Aberrant expression of receptor activator of NF-κB ligand (RANKL), an essential cytokine for osteoclast differentiation, induced by the metastatic tumor cells is responsible for the pathological bone resorption in bone metastasis. A fully human anti-RANKL neutralizing antibody has been developed to block osteoclast activation and is now used for the treatment of patients with bone metastasis and multiple myeloma. On the other hand, numerous studies have revealed that the RANKL/RANK system also contributes to primary tumorigenesis as well as metastasis through osteoclast-independent processes. Furthermore, emerging clinical and preclinical evidence has suggested anti-tumor immune effects of RANKL blockade when added to immune checkpoint inhibitor therapies. Study on the pleiotropic functions of RANKL in tumorigenesis and metastasis is now expanding beyond the bone field and has been established as one of the most important areas of "RANKL biology".

Controversies in the use of new bone-modifying therapies in multiple myeloma

Bone-modifying therapies are essential in the treatment of patients with multiple myeloma. Zoledronic acid is preferred over other bisphosphonates due to its superiority in reducing the incidence of skeletal-related events and improving survival. The anti-receptor activator of nuclear factor-κΒ ligand (RANKL)-targeted agent denosumab has shown its non-inferiority compared to bisphosphonates in preventing skeletal-related events among newly diagnosed patients with myeloma bone disease. Denosumab may confer a survival benefit in patients eligible for autologous transplantation. Denosumab may present a safer profile for patients with renal impairment. Discontinuation of bone-directed therapies can be considered for patients with deep responses and after an adequate time period on treatment; however, a rebound effect may become evident especially in the case of denosumab. Three-monthly infusions of zoledronic acid or at-home denosumab administration should be considered during the coronavirus disease 2019 (COVID-19) pandemic. Measures to prevent hypocalcaemia, renal toxicity and osteonecrosis of the jaw are important for all bone-modifying agents.

Bone metastases

Bone is the most frequent site for metastasis for many cancers, notably for tumours originating in the breast and the prostate. Tumour cells can escape from the primary tumour site and colonize the bone microenvironment. Within the bone, these disseminated tumour cells, as well as those arising in the context of multiple myeloma, may assume a state of dormancy, remaining quiescent for years before resuming proliferation and causing overt metastasis, which causes bone destruction via activation of osteoclast-mediated osteolysis. This structural damage can lead to considerable morbidity, including pain, fractures and impaired quality of life. Although treatment of bone metastases and myeloma bone disease is rarely curative, disease control is often possible for many years through the use of systemic anticancer treatments on a background of multidisciplinary supportive care. This care should include bone-targeted agents to inhibit tumour-associated osteolysis and prevent skeletal morbidity as well as use of appropriate local treatments such as radiation therapy, orthopaedic surgery and specialist palliative care to minimize the impact of metastatic bone disease on physical functioning. In this Primer, we provide an overview of the clinical features, the pathophysiology and the specific treatment approaches to prevent and treat bone metastases from solid tumours as well as myeloma bone disease.

Old and new generation proteasome inhibitors in multiple myeloma

Proteasome inhibitors (PIs) represent a recently developed drug class that inhibit the ubiquitin-proteasome system, thus interfering with the intracellular machinery who has the duty of misfolded proteins disposal. Myeloma plasma cells are structurally aimed at the production of large quantities of immunoglobulins. This explains their vulnerability to any perturbation of intracellular protein homeostasis. Bortezomib is the first-in-class PI and nowadays, in combination with other compounds, is the cornerstone of multiple myeloma (MM) treatment in several settings. Bortezomib has several attractive features for its inclusion in the induction phase of therapy: high efficacy, rapid cytoreduction, absence of nephrotoxicity, fast reduction of plasmacytomas, and fast pain control. However, the safety profile of bortezomib is characterized by a not negligible peripheral neuropathy. Newer PIs, such as carfilzomib and ixazomib, have been developed and each offers specific advantages. Carfilzomib is extremely efficient in proteasome inhibition. This results in high efficacy but suffers from a significant cardiotoxicity. Ixazomib is the first oral PI with a proteasome inhibition profile similar to bortezomib, with lower neurotoxicity. PIs mechanism of action is complementary with other drug classes, and this explains the synergism between PIs and other drugs, in particular steroids and immunomodulators. PIs are frequently used in doublets and triplets. Also, they can be associated with anti-CD38 monoclonal antibodies. This review summarizes the principal biological and clinical features of PIs in the MM treatment.

Non-Coding RNAs in Multiple Myeloma Bone Disease Pathophysiology

Bone remodeling is uncoupled in the multiple myeloma (MM) bone marrow niche, resulting in enhanced osteoclastogenesis responsible of MM-related bone disease (MMBD). Several studies have disclosed the mechanisms underlying increased osteoclast formation and activity triggered by the various cellular components of the MM bone marrow microenvironment, leading to the identification of novel targets for therapeutic intervention. In this regard, recent attention has been given to non-coding RNA (ncRNA) molecules, that finely tune gene expression programs involved in bone homeostasis both in physiological and pathological settings. In this review, we will analyze major signaling pathways involved in MMBD pathophysiology, and report emerging evidence of their regulation by different classes of ncRNAs.

Bone Marrow-Derived Mesenchymal Stromal Cells: A Novel Target to Optimize Hematopoietic Stem Cell Transplantation Protocols in Hematological Malignancies and Rare Genetic Disorders

: Mesenchymal stromal cells (MSCs) are crucial elements in the bone marrow (BM) niche where they provide physical support and secrete soluble factors to control and maintain hematopoietic stem progenitor cells (HSPCs). Given their role in the BM niche and HSPC support, MSCs have been employed in the clinical setting to expand ex-vivo HSPCs, as well as to facilitate HSPC engraftment in vivo. Specific alterations in the mesenchymal compartment have been described in hematological malignancies, as well as in rare genetic disorders, diseases that are amenable to allogeneic hematopoietic stem cell transplantation (HSCT), and ex-vivo HSPC-gene therapy (HSC-GT). Dissecting the in vivo function of human MSCs and studying their biological and functional properties in these diseases is a critical requirement to optimize transplantation outcomes. In this review, the role of MSCs in the orchestration of the BM niche will be revised, and alterations in the mesenchymal compartment in specific disorders will be discussed, focusing on the need to correct and restore a proper microenvironment to ameliorate transplantation procedures, and more in general disease outcomes.

Prevention Of Skeletal Related Events In Multiple Myeloma: Focus On The RANK-L Pathway In The Treatment Of Multiple Myeloma

More than 90% of patients with multiple myeloma (MM) have osteolytic bone lesions which increase the risk of skeletal-related events (SRE). The cytokine milieu in the bone marrow microenvironment (BMME) of MM plays a key role in myeloma bone disease by impairing the balance between osteoclastogenesis and osteoblastogenesis. This is orchestrated by the malignant plasma cell (MPC) with the ultimate outcome of MPC proliferation and survival at the expense of excess osteoclast activation resulting in osteolytic bone lesions. Prevention of SRE is currently accomplished by the inhibition of osteoclasts. Bisphosphonates (BPs) are pyrophosphate analogues that cause apoptosis of osteoclasts and have been proven to prevent and delay SRE. Denosumab, a fully humanized monoclonal antibody that binds and inhibits receptor activator of nuclear factor-ĸB ligand (RANKL), a key molecule in the BMME crucial for osteoclastogenesis, is also approved for the prevention of SRE in MM. The addition of BPs and denosumab to standard MM treatment affords a survival benefit for patients with MM. Specifically, the addition of denosumab to standard MM treatments results in superior PFS compared to BPs, highlighting the key role of the RANKL pathway in MM. This review focuses on the pathophysiology of myeloma bone disease as well as on the importance of targeting the RANK-L pathway for the treatment of MM and prevention of SRE.

Monoclonal antibodies against RANKL and sclerostin for myeloma-related bone disease: can they change the standard of care?

Introduction: Over 80% of the patients with multiple myeloma (MM) develop myeloma bone disease (MBD) during the disease course. The clinical consequences include serious skeletal-related events (SRE) that impact survival and quality of life. Bisphosphonates are the mainstay in the treatment of MBD. Currently, new therapeutic strategies are being introduced and broaden the therapeutic options in MBD. Areas covered: The purpose of this review is to summarize the current clinical management of MBD and present novel data regarding monoclonal antibodies against the receptor activator of NF-kappa B ligand (RANKL) and sclerostin that may change the clinical practice. Expert opinion: Our better understanding of the pathophysiology of MBD has identified several factors as potential therapeutic targets. Recent data have shown that the RANKL inhibitor denosumab constitutes a new promising option. The non-inferiority compared with bisphosphonates in terms of SRE prevention, the potential survival benefit, the convenience of subcutaneous administration, and the favorable toxicity profile makes denosumab a valuable alternative for physicians in the current treatment of MBD. Anti-sclerostin antibodies are currently under clinical development. Further investigations are needed to address open questions in the field including the value of anabolic agents combined with anti-resorptive and anti-MM drugs in MBD.

Upregulation of interleukin-8 and activin A induces osteoclastogenesis in ameloblastoma

Ameloblastoma is a common odontogenic benign tumor located in the jaws and is characterized by severe local bone destruction. The current study aimed to investigate the effect of interactions between tumor cells and bone marrow stromal cells (BMSCs) on osteoclast formation in ameloblastoma. The impact of ameloblastoma/BMSC interactions on cytokine production, gene expression and osteoclastogenesis was examined using an immortalized ameloblastoma cell line that the authors' previously established. The results demonstrated that interactions between ameloblastoma cells and BMSCs increased interleukin (IL)‑8 and activin A secretion by BMSCs. IL‑8 expression in BMSCs was modulated by tumor‑derived tumor necrosis factor‑α and IL‑8 contributed to osteoclast formation not only directly but also by stimulating receptor activator of NF‑κB ligand (RANKL) expression in BMSCs. Activin A secretion in BMSCs was stimulated by ameloblastoma cells via cell‑to‑cell‑mediated activation of c‑Jun N‑terminal kinase activation, acting as a cofactor of RANKL to induce osteoclast formation and function. The present study highlights the critical role of communication between BMSCs and ameloblastoma cells in bone resorption in ameloblastoma.

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.

Identification of an Epigenetic Signature of Osteoporosis in Blood DNA of Postmenopausal Women

Osteoporosis is one of the most common age-related progressive bone diseases in elderly people. Approximately one in three women and one in five men are predisposed to developing osteoporosis. In postmenopausal women, a reduction in BMD leads to an increased risk of fractures. In the current study, we delineated the DNA methylation signatures in whole blood samples of postmenopausal osteoporotic women. We obtained whole blood DNA from 22 normal women and 22 postmenopausal osteoporotic women (51 to 89 years old) from the Canadian Multicenter Osteoporosis Study (CaMos) cohort. These DNA samples were subjected to Illumina Infinium human methylation 450 K analysis. Illumina 450K raw data were analyzed by Genome Studio software. Analysis of the female participants with early and advanced osteoporosis resulted in the generation of a list of 1233 differentially methylated CpG sites when compared with age-matched normal women. T test, ANOVA, and post hoc statistical analyses were performed, and 77 significantly differentially methylated CpG sites were identified. From the 13 most significant genes, ZNF267, ABLIM2, RHOJ, CDKL5, and PDCD1 were selected for their potential role in bone biology. A weighted polygenic DNA methylation score of these genes predicted osteoporosis at an early stage with high sensitivity and specificity and correlated with measures of bone density. Pyrosequencing analysis of these genes was performed to validate the results obtained from Illumina 450 K methylation analysis. The current study provides proof of principal for the role of DNA methylation in osteoporosis. Using whole blood DNA methylation analysis, women at risk of developing osteoporosis can be identified before a diagnosis of osteoporosis is made using BMD as a screening method. Early diagnosis will help to select patients who might benefit from early therapeutic intervention. © 2018 American Society for Bone and Mineral Research.

LIGHT/TNFSF14 as a New Biomarker of Bone Disease in Multiple Myeloma Patients Experiencing Therapeutic Regimens

We have previously shown that through the production of high LIGHT levels, immune cells contribute to both osteoclastogenesis and bone destruction in Multiple Myeloma (MM)-related bone disease. With the aim of further exploring the mechanisms underlying the development of MM-related bone disease, here we focused on a possible role of LIGHT in MM patients with active bone disease despite the treatment received. We detected LIGHT over-expression by circulating CD14⁺ monocytes from MM patients still showing active bone disease, despite the treatment. In addition, we found over-expression of receptor activator of nuclear factor kappa-B ligand (RANKL), whose pro-osteoclastogenic role is well-known, in T-lymphocytes isolated from the same patients. Although the percentages of circulating osteoclast progenitors, CD14⁺CD16⁺ monocytes, were higher in all the MM patients than in the controls spontaneous osteoclastogenesis occurred only in the cultures derived from PBMCs of MM patients with unresponsive bone disease. Of note, in the same cultures osteoclastogenesis was partially or completely inhibited, in a dose-dependent manner, by the addition of RANK-Fc or anti-LIGHT neutralizing antibody, demonstrating the contribution of both LIGHT and RANKL to the enhanced osteoclast formation observed. In addition, high serum levels of TRAP5b and CTX, the two markers of osteoclast activity, were detected in MM patients with bone disease not responsive to treatment. In conclusion, our study indicates a prominent role of LIGHT in the crosstalk among osteoclasts and immune cells, co-involved together with RANKL in the pathophysiological mechanisms leading to MM-related bone disease. This TNF superfamily member may thus be a possible new therapeutic target in MM-related bone disease.

Osteoclast Immunosuppressive Effects in Multiple Myeloma: Role of Programmed Cell Death Ligand 1

Immunomodulatory drugs and monoclonal antibody-based immunotherapies have significantly improved the prognosis of the patients with multiple myeloma (MM) in the recent years. These new classes of reagents target malignant plasma cells (PCs) and further modulate the immune microenvironment, which prolongs anti-MM responses and may prevent tumor occurrence. Since MM remains an incurable cancer for most patients, there continues to be a need to identify new tumor target molecules and investigate alternative cellular approaches using gene therapeutic strategies and novel treatment mechanisms. Osteoclasts (OCs), as critical multi-nucleated large cells responsible for bone destruction in >80% MM patients, have become an attractive cellular target for the development of novel MM immunotherapies. In MM, OCs are induced and activated by malignant PCs in a reciprocal manner, leading to osteolytic bone disease commonly associated with this malignancy. Significantly, bidirectional interactions between OCs and MM cells create a positive feedback loop to promote MM cell progression, increase angiogenesis, and inhibit immune surveillance via both cell-cell contact and abnormal production of multiple cytokines/chemokines. Most recently, hyper-activated OCs have been associated with activation of programmed cell death protein 1 (PD-1)/programmed cell death ligand 1 (PD-L1) pathway, which impairs T cell proliferation and cytotoxicity against MM cells. Importantly, therapeutic anti-CD38 monoclonal antibodies and checkpoint inhibitors can alleviate OC-induced immune suppression. Furthermore, a proliferation-inducing ligand, abundantly secreted by OCs and OC precursors, significantly upregulates PD-L1 expression on MM cells, in addition to directly promoting MM cell proliferation and survival. Coupled with increased PD-L1 expression in other immune-suppressive cells, i.e., myeloid-derived suppressor cells and tumor-associated macrophages, these results strongly suggest that OCs contribute to the immunosuppressive MM BM microenvironment. Based on these findings and ongoing osteoimmunology studies, therapeutic interventions targeting OC number and function are under development to diminish both MM bone disease and related immune suppression. In this review, we discuss the classical and novel roles of OCs in the patho-immunology of MM. We also describe novel therapeutic strategies simultaneously targeting OCs and MM interactions, including PD-1/PD-L1 axis, to overcome the immune-suppressive microenvironment and improve patient outcome.

Role of the RANK/RANKL Pathway in Multiple Myeloma

Receptor activator of nuclear factor-kappa B (RANK) and its ligand, RANKL, are expressed in a variety of tissues throughout the body; their primary role is in the regulation of bone remodeling and development of the immune system. Consistent with these functions, evidence exists for a role of RANK/RANKL in all stages of tumorigenesis, from cell proliferation and carcinogenesis to epithelial-mesenchymal transition to neoangiogenesis and intravasation to metastasis to bone resorption and tumor growth in bone. Results from current studies also point to a role of RANK/RANKL signaling in patients with multiple myeloma, who have increased serum levels of soluble RANKL and an imbalance in RANKL and osteoprotegerin. Current therapies for patients with multiple myeloma demonstrate that RANKL may be released by tumor cells or osteoprogenitor cells. This article will review currently available evidence supporting a role for RANK/RANKL signaling in tumorigenesis, with a focus on patients with multiple myeloma.

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.

Micro RNAs from DNA Viruses are Found Widely in Plasma in a Large Observational Human Population

Viral infections associate with disease risk and select families of viruses encode miRNAs that control an efficient viral cycle. The association of viral miRNA expression with disease in a large human population has not been previously explored. We sequenced plasma RNA from 40 participants of the Framingham Heart Study (FHS, Offspring Cohort, Visit 8) and identified 3 viral miRNAs from 3 different human Herpesviridae. These miRNAs were mostly related to viral latency and have not been previously detected in human plasma. Viral miRNA expression was then screened in the plasma of 2763 participants of the remaining cohort utilizing high-throughput RT-qPCR. All 3 viral miRNAs associated with combinations of inflammatory or prothrombotic circulating biomarkers (sTNFRII, IL-6, sICAM1, OPG, P-selectin) but did not associate with hypertension, coronary heart disease or cancer. Using a large observational population, we demonstrate that the presence of select viral miRNAs in the human circulation associate with inflammatory biomarkers and possibly immune response, but fail to associate with overt disease. This study greatly extends smaller singular observations of viral miRNAs in the human circulation and suggests that select viral miRNAs, such as those for latency, may not impact disease manifestation.

Possible targets to treat myeloma-related osteoclastogenesis

INTRODUCTION

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

Biology and treatment of myeloma related bone disease

Myeloma bone disease (MBD) is the most common complication of multiple myeloma (MM), resulting in skeleton-related events (SREs) such as severe bone pain, pathologic fractures, vertebral collapse, hypercalcemia, and spinal cord compression that cause significant morbidity and mortality. It is due to an increased activity of osteoclasts coupled to the suppressed bone formation by osteoblasts. Novel molecules and pathways that are implicated in osteoclast activation and osteoblast inhibition have recently been described, including the receptor activator of nuclear factor-kB ligand/osteoprotegerin pathway, activin-A and the wingless-type signaling inhibitors, dickkopf-1 (DKK-1) and sclerostin. These molecules interfere with tumor growth and survival, providing possible targets for the development of novel drugs for the management of lytic disease in myeloma but also for the treatment of MM itself. Currently, bisphosphonates are the mainstay of the treatment of myeloma bone disease although several novel agents such as denosumab and sotatercept appear promising. This review focuses on recent advances in MBD pathophysiology and treatment, in addition to the established therapeutic guidelines.

A vicious cycle between acid sensing and survival signaling in myeloma cells: acid-induced epigenetic alteration

Myeloma (MM) cells and osteoclasts are mutually interacted to enhance MM growth while creating acidic bone lesions. Here, we explored acid sensing of MM cells and its role in MM cell response to acidic conditions. Acidic conditions activated the PI3K-Akt signaling in MM cells while upregulating the pH sensor transient receptor potential cation channel subfamily V member 1 (TRPV1) in a manner inhibitable by PI3K inhibition. The acid-activated PI3K-Akt signaling facilitated the nuclear localization of the transcription factor Sp1 to trigger the expression of its target genes, including TRPV1 and HDAC1. Consistently, histone deacetylation was enhanced in MM cells in acidic conditions, while repressing a wide variety of genes, including DR4. Indeed, acidic conditions deacetylated histone H3K9 in a DR4 gene promoter and curtailed DR4 expression in MM cells. However, inhibition of HDAC as well as either Sp1 or PI3K was able to restore DR4 expression in MM cells suppressed in acidic conditions. These results collectively demonstrate that acid activates the TRPV1-PI3K-Akt-Sp1 signaling in MM cells while inducing HDAC-mediated gene repression, and suggest that a positive feedback loop between acid sensing and the PI3K-Akt signaling is formed in MM cells, leading to MM cell response to acidic bone lesions.

The cell biology and role of resorptive cells in diseases: A review

Resorptive cells are responsible for the resorption of mineralized matrix of hard tissues. Bone-resorbing cells are called osteoclasts; however, they can resorb mineralized dental tissues or calcified cartilage and then they are called odontoclasts and chondroclasts, respectively. Resorptive cells form when mononuclear precursors derived from a monocyte–macrophage cell lineage are attracted to certain mineralized surfaces and subsequently fuse and adhere onto them for exerting their resorbing activity. These cells are responsible for degradation of calcified extracellular matrix composed of organic molecules and hydroxyapatite. The activity of these cells can be observed in both physiological and pathological processes throughout life and their activity is mainly required in bone turnover and growth, spontaneous and induced (orthodontic) tooth movement, tooth eruption, and bone fracture healing, as well as in pathological conditions such as osteoporosis, osteoarthritis, and bone metastasis. In addition, they are responsible for daily control of calcium homeostasis. Clastic cells also resorb the primary teeth for shedding before the permanent teeth erupt into the oral cavity.

TAK1 inhibition subverts the osteoclastogenic action of TRAIL while potentiating its antimyeloma effects

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) agonists induce tumor-specific apoptosis indicating that they may be an attractive therapeutic strategy against cancers, including multiple myeloma (MM). Osteoclastogenesis is highly induced in MM, which in turn enhances MM growth, thereby forming a vicious cycle between MM tumor expansion and bone destruction. However, the effects of TRAIL on MM-enhanced osteoclastogenesis remain largely unknown. Here, we show that TRAIL induced apoptosis in MM cells, but not in osteoclasts (OCs), and that it rather facilitated receptor activator of NF-κB ligand-induced osteoclastogenesis along with upregulation of cellular FLICE inhibitory protein (c-FLIP). TRAIL did not induce death-inducing signaling complex formation in OCs, but formed secondary complex (complex II) with the phosphorylation of transforming growth factor β-activated kinase-1 (TAK1), and thus activated NF-κB signaling. c-FLIP knockdown abolished complex II formation, thus permitting TRAIL induction of OC cell death. The TAK1 inhibitor LLZ1640-2 abrogated the TRAIL-induced c-FLIP upregulation and NF-κB activation, and triggered TRAIL-induced caspase-8 activation and cell death in OCs. Interestingly, the TRAIL-induced caspase-8 activation caused enzymatic degradation of the transcription factor Sp1 to noticeably reduce c-FLIP expression, which further sensitized OCs to TRAIL-induced apoptosis. Furthermore, the TAK1 inhibition induced antiosteoclastogenic activity by TRAIL even in cocultures with MM cells while potentiating TRAIL's anti-MM effects. These results demonstrated that osteoclastic lineage cells use TRAIL for their differentiation and activation through tilting caspase-8-dependent apoptosis toward NF-κB activation, and that TAK1 inhibition subverts TRAIL-mediated NF-κB activation to resume TRAIL-induced apoptosis in OCs while further enhancing MM cell death in combination with TRAIL.

Denosumab for the treatment of bone disease in solid tumors and multiple myeloma

Bone is a common site for malignant involvement, either as a site of metastasis, especially in breast or prostate cancer, or as a defining characteristic of the disease, as in multiple myeloma. Bone disease is a major source of morbidity, and half of patients with bone involvement develop skeletal-related events such as pathological fractures or cord compression requiring surgery and/or radiation. Skeletal involvement also increases mortality, as pathologic fractures increase the risk of dying by 20-40%. Osteoclast inhibition with bisphosphonates such as zoledronic acid and recently denosumab has been a significant improvement for bone disease. This review will focus on denosumab in the treatment of bone metastases and highlight the recent findings in multiple myeloma.

Myeloma and Bone Disease

PURPOSE OF REVIEW

Bone disease is a defining characteristic of multiple myeloma (MM) and the major cause of morbidity. It manifests as lytic lesions or osteopenia and is often associated with severe pain, pathological fracture, spinal cord compression, vertebral collapse, and hypercalcemia. Here, we have reviewed recent data on understanding its biology and treatment.

RECENT FINDINGS

The imbalance between bone regeneration and bone resorption underlies the pathogenesis of osteolytic bone disease. Increased osteoclast proliferation and activity accompanied by inhibition of bone-forming osteoblasts leads to progressive bone loss and lytic lesions. Although tremendous progress has been made, MM remains an incurable disease. Novel agents targeting bone disease are under investigation with the goal of not only preventing bone loss and improving bone quality but also harnessing MM tumor growth. Current data illustrate that the interactions between MM cells and the tumor-bone microenvironment contribute to the bone disease and continued MM progression. A better understanding of this microenvironment is critical for novel therapeutic treatments of both MM and associated bone disease.

Mechanisms of bone destruction in multiple myeloma

Osteolytic bone disease is a frequent complication of multiple myeloma, resulting in skeletal complications that are a significant cause of morbidity and mortality. It is the result of an increased activity of osteoclasts, which is not followed by reactive bone formation by osteoblasts. Recent studies have revealed novel molecules and pathways that are implicated in osteoclast activation and osteoblast inhibition. Among them, the most important include the receptor activator of nuclear factor-kappa B ligand/osteoprotegerin pathway, the macrophage inflammatory proteins and the activin-A that play a crucial role in osteoclast stimulation in myeloma, while the wingless-type (Wnt) signalling inhibitors (sclerostin and dickkopf-1) along with the growth factor independence-1 are considered the most important factors for the osteoblast dysfunction of myeloma patients. Finally, the role of osteocytes, which is the key cell for normal bone remodelling, has also revealed during the last years through their interaction with myeloma cells that leads to their apoptosis and the release of RANKL and sclerostin maintaining bone loss in these patients. This review focuses on the latest available data for the mechanisms of bone destruction in multiple myeloma.