Impaired osteoblastogenesis in myeloma bone disease: role of upregulated apoptosis by cytokines and malignant plasma cells

Hypoxia-induced CREB cooperates MMSET to modify chromatin and promote DKK1 expression in multiple myeloma

Myeloma cells produce excessive levels of dickkopf-1 (DKK1), which mediates the inhibition of Wnt signaling in osteoblasts, leading to multiple myeloma (MM) bone disease. Nevertheless, the precise mechanisms underlying DKK1 overexpression in myeloma remain incompletely understood. Herein, we provide evidence that hypoxia promotes DKK1 expression in myeloma cells. Under hypoxic conditions, p38 kinase phosphorylated cAMP-responsive element-binding protein (CREB) and drove its nuclear import to activate DKK1 transcription. In addition, high levels of DKK1 were associated with the presence of focal bone lesions in patients with t(4;14) MM, overexpressing the histone methyltransferase MMSET, which was identified as a downstream target gene of hypoxia-inducible factor (HIF)-1α. Furthermore, we found that CREB could recruit MMSET, leading to the stabilization of HIF-1α protein and the increased dimethylation of histone H3 at lysine 36 on the DKK1 promoter. Knockdown of CREB in myeloma cells alleviated the suppression of osteoblastogenesis by myeloma-secreted DKK1 in vitro. Combined treatment with a CREB inhibitor and the hypoxia-activated prodrug TH-302 (evofosfamide) significantly reduced MM-induced bone destruction in vivo. Taken together, our findings reveal that hypoxia and a cytogenetic abnormality regulate DKK1 expression in myeloma cells, and provide an additional rationale for the development of therapeutic strategies that interrupt DKK1 to cure MM.

Current Understanding of Myelomatous Mesenchymal Stromal Cells Extended through Advances in Experimental Methods

Simple Summary

As the amount of information available has grown, now it is known that many types of non-hematopoietic cells, including mesenchymal stem/progenitor cells, mature mesenchymal cells, and endothelial cells, as well as mature hematopoietic cells such as monocytes, macrophages, T-cells, and B-cells, have roles in the pathogenesis of multiple myeloma. This review focuses on the role of mesenchymal cells in the microenvironment of multiple myeloma. We summarize the experimental strategies and current understanding of the biological roles in the pathogenesis of myeloma. Furthermore, we discuss the possible clinical applications targeting mesenchymal cells.

Abstract

Multiple myeloma is an incurable cancer formed by malignant plasma cells. For the proliferation and survival of myeloma cells, as well as the occurrence of the complications, numerous intra- and extra-cellular mechanisms are involved. The interaction of myeloma cells with the microenvironment is known to be one of the most critical mechanisms. A specific microenvironment could affect the progression and growth of tumor cells, as well as drug resistance. Among various microenvironment components, such as hematological and non-hematological cells, and soluble factors (cytokines, chemokines, and extracellular matrix (ECM) proteins), in this review, we focus on the role of mesenchymal cells. We aimed to summarize the experimental strategies used for conducting studies and current understanding of the biological roles in the pathogenesis of myeloma. Furthermore, we discuss the possible clinical applications targeting mesenchymal cells.

Role of the Bone Marrow Milieu in Multiple Myeloma Progression and Therapeutic Resistance

Multiple myeloma (MM) is a cancer of the plasma cells within the bone marrow (BM). Studies have shown that the cellular and noncellular components of the BM milieu, such as cytokines and exosomes, play an integral role in MM pathogenesis and progression by mediating drug resistance and inducing MM proliferation. Moreover, the BM microenvironment of patients with MM facilitates cancer tolerance and immune evasion through the expansion of regulatory immune cells, inhibition of antitumor effector cells, and disruption of the antigen presentation machinery. These are of special relevance, especially in the current era of cancer immunotherapy. An improved understanding of the supportive role of the MM BM microenvironment will allow for the development of future therapies targeting MM in the context of the BM milieu to elicit deeper and more durable responses. In the present review, we have discussed our current understanding of the role of the BM microenvironment in MM progression and resistance to therapy and discuss novel potential approaches to alter its pro-MM function.

Functional Comparison between Healthy and Multiple Myeloma Adipose Stromal Cells

Multiple myeloma (MM) is an incurable B cell neoplasia characterized by the accumulation of tumor plasma cells within the bone marrow (BM). As a consequence, bone osteolytic lesions develop in 80% of patients and remain even after complete disease remission. We and others had demonstrated that BM-derived mesenchymal stromal cells (MSCs) are abnormal in MM and thus cannot be used for autologous treatment to repair bone damage. Adipose stromal cells (ASCs) represent an interesting alternative to MSCs for cellular therapy. Thus, in this study, we wondered whether they could be a good candidate in repairing MM bone lesions. For the first time, we present a transcriptomic, phenotypic, and functional comparison of ASCs from MM patients and healthy donors (HDs) relying on their autologous MSC counterparts. In contrast to MM MSCs, MM ASCs did not exhibit major abnormalities. However, the changes observed in MM ASCs and the supportive property of ASCs on MM cells question their putative and safety uses at an autologous or allogenic level.

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.

Bortezomib could down-regulate the expression of RANKL, inhibit cell proliferation and induce cell apoptosis in the human myeloma cell line RPMI 8226 by activating casepase-3

OBJECTIVE

In spite of bortezomib being developed and demonstrated as a safe drug therapy for multiple myeloma (MM), the role of bortezomib-induced receptor activator of nuclear factor (NF)-κB ligand (RANKL) in the MM cell lines remains to be understood. Thus the present study aims to explore the impact of bortezomib on RANKL expression, cell growth and apoptosis in human myeloma cell line RPMI 8226.

METHODS

Four experiment groups were set according to different concentrations of bortezomib, namely blank group (treated with DMEM solution free of other drugs), low-dose group (treated with 10 nmol/L bortezomib), middle-dose group (treated with 20 nmol/L bortezomib) and high-dose group (treated with 40 nmol/L bortezomib). Western blotting was adopted to detect RANKL protein expression. MTT assay was performed to detect cell proliferation. Flow cytometry was used to analyze cell cycle and apoptosis. Spectrophotometry was applied to determine caspases-3 activity.

RESULTS

Compared with the blank group, the RANKL protein expression, cell number at the S stage was reduced while cell inhibition rate, cell apoptosis rate and caspase-3 activity enhanced remarkably in the low-dose, middle-dose and high-dose groups with dose-dependent manner. Compared with those treated with bortezomib (20 nmol/L and 40 nmol/L) for 6 h, the RANKL expression was down-regulated, cell inhibition rate was increased, cells at the S stage were reduced, cell apoptosis rate was enhanced, and caspase-3 activity elevated in the RPMI 8226 cells as treated with bortezomib for 24 h, with a dose- and time-dependent manner.

CONCLUSIONS

Bortezomib could reduce the RANKL expression, inhibit cell proliferation and activate caspase-3 activity to induce cell apoptosis in RPMI 8266 cells.

Dicer1 downregulation by multiple myeloma cells promotes the senescence and tumor-supporting capacity and decreases the differentiation potential of mesenchymal stem cells

Bone marrow mesenchymal stem cells (BMMSCs) facilitate the growth of multiple myeloma (MM) cells, but the underlying mechanisms remain unclear. This study demonstrates that the senescence of MM-MSCs significantly increased, as evidenced by a decrease in proliferation and increase in the number of cells positive for senescence-associated β-galactosidase activity. Senescent MM-MSCs displayed decreased differentiation potential and increased tumor-supporting capacity. Dicer1 knockdown in the MSCs of healthy controls promoted cellular senescence and tumor-supporting capacity, while decreasing the differentiation capacity. Dicer1 overexpression in MM-MSCs reversed the effects on differentiation and reduced cellular senescence. In addition, decreased expression of the microRNA-17 family was identified as a favorable element responsible for increasing senescence, with the expression of p21 increased in Dicer1 knockdown cells. Furthermore, we observed decreased expression of miR-93 and miR-20a in MM-MSCs, while upregulation of miR-93/miR-20a decreased cellular senescence, as evidenced by the increased p21 expression. Importantly, we found that myeloma cells could induce the senescence of MSCs from healthy controls, as observed from the decreased expression of Dicer1 and miR-93/miR-20a and increased expression of p21. Overall, MM cells downregulate Dicer1 in MSCs, which leads to senescence; in turn, senescent MSCs promote MM cell growth, which most likely contributes to disease progression.

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.

The Critical Role of Imaging in the Management of Multiple Myeloma

Multiple myeloma (MM) is characterized by abnormal proliferation of plasma cells in the bone marrow leading to symptoms of anemia, renal failure, hypercalcemia, and bone lesions. Bone imaging is critical for the diagnosis, staging, assessment for the presence and extent of bone lesions, and initial treatment of MM. Skeletal survey is the preferred initial imaging modality due to its availability and low cost. However, it has poor sensitivity and patients with occult myeloma may escape detection, delaying their diagnosis and treatment. New cross-sectional imaging modalities such as low-dose whole body CT, MRI, and PET-CT have high sensitivity and specificity for detecting lytic lesions and extramedullary relapse in MM. The combined use of cross-sectional imaging may provide complimentary information for staging, prognosis, and disease monitoring. In this review, we will discuss commonly used imaging modalities and their advantages and disadvantages in the management of MM.

Excessive Activation of TLR4/NF-κB Interactively Suppresses the Canonical Wnt/β-catenin Pathway and Induces SANFH in SD Rats

Nuclear factor-kappa B (NF-κB) interactively affects the Wnt/β-catenin pathway and is closely related to different diseases. However, such crosstalk effect in steroid-associated necrosis of femoral head (SANFH) has not been fully explored and evaluated. In this study, early-stage SANFH was induced by two doses of lipopolysaccharide (LPS, 2 mg/kg/day) and three doses of methylprednisolone (MPS, 40 mg/kg/day). LPS and pyrrolidine dithiocarbamate (PDTC) were administered to activate the TLR4/NF-κB pathway and selectively block the activation of NF-κB, respectively. Results showed that PDTC treatment significantly reduced NF-κB expression, diminished inflammation, and effectively decreased bone resorption processes (osteoclastogenesis, adipogenesis, and apoptosis), which were evidently reinforced after osteonecrosis induction. Moreover, PDTC remarkably increased the interfered Wnt/β-catenin pathway and elevated bone formation processes (osteogenesis and angiogenesis). Ultimately, PDTC treatment effectively reduced the incidence of SANFH. Therefore, the excessive activation of TLR4/NF-κB may interactively suppress the Wnt/β-catenin pathway and induce SANFH. Hence, we propose NF-κB-targeted treatment as a novel therapeutic strategy for SANFH.

Bone marrow mesenchymal stem cells regulate stemness of multiple myeloma cell lines via BTK signaling pathway

Bone marrow mesenchymal stem cells (BM-MSCs) are key components of bone marrow microenvironment. Although the importances of BM-MSCs activation in myeloma cells growth, development, progression, angiogenesis are well known, their role in the regulation of myeloma stemness is unclear. In this study, myeloma cell lines (LP-1, U266) were co-cultured with BM-MSCs, we found that BM-MSCs could up-regulate the expression of key stemness genes and proteins (OCT4, SOX2, NANOG) and increase clonogenicity. Similarly, the mechanisms underlying the BM-MSC activation of myeloma stemness remain unclear. Here, we found that PCI-32765, a Bruton tyrosine kinase (BTK) inhibitor, treatment significantly down- regulate expression of key stemness genes and proteins in vitro co-culture system. Together, our results revealed that BM-MSCs could increase myeloma stemness via activation of the BTK signal pathway.

Contact of myeloma cells induces a characteristic transcriptome signature in skeletal precursor cells -Implications for myeloma bone disease

Physical interaction of skeletal precursors with multiple myeloma cells has been shown to suppress their osteogenic potential while favoring their tumor-promoting features. Although several transcriptome analyses of myeloma patient-derived mesenchymal stem cells have displayed differences compared to their healthy counterparts, these analyses insufficiently reflect the signatures mediated by tumor cell contact, vary due to different methodologies, and lack results in lineage-committed precursors. To determine tumor cell contact-mediated changes on skeletal precursors, we performed transcriptome analyses of mesenchymal stem cells and osteogenic precursor cells cultured in contact with the myeloma cell line INA-6. Comparative analyses confirmed dysregulation of genes which code for known disease-relevant factors and additionally revealed upregulation of genes that are associated with plasma cell homing, adhesion, osteoclastogenesis, and angiogenesis. Osteoclast-derived coupling factors, a dysregulated adipogenic potential, and an imbalance in favor of anti-anabolic factors may play a role in the hampered osteoblast differentiation potential of mesenchymal stem cells. Angiopoietin-Like 4 (ANGPTL4) was selected from a list of differentially expressed genes as a myeloma cell contact-dependent target in skeletal precursor cells which warranted further functional analyses. Adhesion assays with full-length ANGPTL4-coated plates revealed a potential role of this protein in INA-6 cell attachment. This study expands knowledge of the myeloma cell contact-induced signature in the stromal compartment of myelomatous bones and thus offers potential targets that may allow detection and treatment of myeloma bone disease at an early stage.

Multiple myeloma-related bone disease: state-of-art and next future treatments

SUMMARY 

Multiple myeloma (MM) is a plasma cell malignancy associated with the development of life-threatening and/or severe osteolytic lesions, which significantly worsen the quality of life of affected patients. MM-related bone disease (BD) is the result of an overwhelming osteoclastic activity, while osteoblast-mediated bone formation is inhibited. Bisphosphonates are still the mainstay of therapy for BD. However, these drugs are associated with mid long-term sequelae. In this work, we review the pathogenesis and currently available therapies of MM-related BD. We describe the most recent and promising findings that may translate in changing the clinical practice in the next future.

Role of apoptosis in pathogenesis and treatment of bone-related diseases

In this article, bone cells and their intercellular communications have been reviewed. Gap junctions and hemichannels are the main routes of interactions in bone tissue. They play a substantial role in survival and cell death, since pro-apoptotic signals can propagate through them. Different adhesion molecules are required for apoptosis, particularly caspase family as well as noncaspase proteases. The disruption outcome of apoptosis could result in bone-related diseases such as osteonecrosis. Anti-apoptotic strategies include inhibition of caspase, poly [ADP-ribose] polymerase (PARP), and Bcl-2 proteins as well as induction of the PKB/Akt pathway and inhibitors of apoptosis (IAP) family of proteins. Thus, understanding the mechanism of apoptosis gives detailed insights of anti-apoptotic molecular targets. Based on these targets, different treatments were designed and produced such as estrogen replacement therapy, administration of different bisphosphonates, raloxifene, calcitonin, sodium fluoride, calcium, and vitamin D. As a result, new applicable drugs for treatment of related bone problems can be proposed for clinical approach especially in the early stage of diseases.

The effect of the PI3K inhibitor BKM120 on tumour growth and osteolytic bone disease in multiple myeloma

The plasma cell malignancy multiple myeloma (MM) is unique amongst haematological malignancies in its capacity to cause osteoclast-mediated skeletal destruction. The PI3K/Akt pathway mediates proliferation, survival and drug resistance in MM plasma cells and is also involved in regulating the formation and activity of bone-forming osteoblasts and bone-resorbing osteoclasts. NVP-BKM120 (Buparlisib, Novartis) is a PI3K inhibitor that is currently undergoing clinical evaluation in several tumour settings. In this study, we have examined the anti-tumorigenic effects of BKM120 in an immunocompetent mouse model of MM and its effects on osteoblast and osteoclast formation and function. BKM120 treatment (40 mg/kg) resulted in a significant decrease in serum paraprotein and tumour burden, and μCT analysis of the proximal tibia revealed a significant reduction in the number of osteolytic bone lesions in BKM120-treated animals. BKM120 also mediated a significant increase in serum levels of the osteoblast marker P1NP, and a significant decrease in serum levels of the osteoclast marker TRAcP5. In vitro, BKM120 decreased MM plasma cell proliferation, osteoclast formation and function, and promoted osteoblast formation and function. These findings suggest that, in addition to its anti-tumour properties, BKM120 could be used to treat osteolytic bone disease in MM patients.

Multiple myeloma mesenchymal stromal cells: Contribution to myeloma bone disease and therapeutics

Multiple myeloma is a hematological malignancy in which clonal plasma cells proliferate and accumulate within the bone marrow. The presence of osteolytic lesions due to increased osteoclast (OC) activity and suppressed osteoblast (OB) function is characteristic of the disease. The bone marrow mesenchymal stromal cells (MSCs) play a critical role in multiple myeloma pathophysiology, greatly promoting the growth, survival, drug resistance and migration of myeloma cells. Here, we specifically discuss on the relative contribution of MSCs to the pathophysiology of osteolytic lesions in light of the current knowledge of the biology of myeloma bone disease (MBD), together with the reported genomic, functional and gene expression differences between MSCs derived from myeloma patients (pMSCs) and their healthy counterparts (dMSCs). Being MSCs the progenitors of OBs, pMSCs primarily contribute to the pathogenesis of MBD because of their reduced osteogenic potential consequence of multiple OB inhibitory factors and direct interactions with myeloma cells in the bone marrow. Importantly, pMSCs also readily contribute to MBD by promoting OC formation and activity at various levels (i.e., increasing RANKL to OPG expression, augmenting secretion of activin A, uncoupling ephrinB2-EphB4 signaling, and through augmented production of Wnt5a), thus further contributing to OB/OC uncoupling in osteolytic lesions. In this review, we also look over main signaling pathways involved in the osteogenic differentiation of MSCs and/or OB activity, highlighting amenable therapeutic targets; in parallel, the reported activity of bone-anabolic agents (at preclinical or clinical stage) targeting those signaling pathways is commented.

Bortezomib enhances the osteogenic differentiation capacity of human mesenchymal stromal cells derived from bone marrow and placental tissues

Bortezomib (BZB) is a chemotherapeutic agent approved for treating multiple myeloma (MM) patients. In addition, there are several reports showing that bortezomib can induce murine mesenchymal stem cells (MSCs) to undergo osteogenic differentiation and increase bone formation in vivo. MSCs are the multipotent stem cells that have capacity to differentiate into several mesodermal derivatives including osteoblasts. Nowadays, MSCs mostly bone marrow derived have been considered as a valuable source of cell for tissue replacement therapy. In this study, the effect of bortezomib on the osteogenic differentiation of human MSCs derived from both bone marrow (BM-MSCs) and postnatal sources such as placenta (PL-MSCs) were investigated. The degree of osteogenic differentiation of BM-MSCs and PL-MSCs after bortezomib treatment was assessed by alkaline phosphatase (ALP) activity, matrix mineralization by Alizarin Red S staining and the expression profiles of osteogenic differentiation marker genes, Osterix, RUNX2 and BSP. The results showed that 1 nM and 2 nM BZB can induce osteogenic differentiation of BM-MSCs and PL-MSCs as demonstrated by increased ALP activity, increased matrix mineralization and up-regulation of osteogenic differentiation marker genes, Osterix, RUNX2 and BSP as compared to controls. The enhancement of osteogenic differentiation of MSCs by bortezomib may lead to the potential therapeutic applications in human diseases especially patients with osteopenia.

Concomitant activation of the PI3K/Akt and ERK1/2 signalling is involved in cyclic compressive force-induced IL-6 secretion in MLO-Y4 cells

IL-6 has a dual role in bone remodelling. The ERK1/2 pathway partially upregulated IL-6 secretion in osteocyte-like MLO-Y4 cells exposed to CCF. We have now investigated the possible role of phosphatidylinositol 3-kinase (PI3K)/Akt signalling pathway in the CCF-induced IL-6 expression. MLO-Y4 cells were treated with CCF 2,000 µstrain, 2 Hz, or 10, 30 min, 1, 3 and 6 h. IL-6 expression, Akt and ERK1/2 and PI3K/Akt phosphorylation were determined by RT-PCR, ELISA and Western blotting. Inhibition of PI3K/Akt with LY294002 or ERK1/2 with PD98059 significantly attenuated IL-6 upregulation, and IL-6 expression was abolished by inhibiting both pathways. Inhibition of one pathway downregulated the other's phosphorylation level. In conclusion, concomitant activation of PI3K/Akt and ERK1/2 pathways mediated IL-6 expression in MLO-Y4 cells under CCF.

Myeloma plasma cells alter the bone marrow microenvironment by stimulating the proliferation of mesenchymal stromal cells

Multiple myeloma is an incurable hematologic cancer characterized by the clonal proliferation of malignant plasma cells within the bone marrow. Numerous studies suggest that the myeloma plasma cells occupy and alter the stromal tissue of the bone marrow as a means of enhancing their survival and growth. However, the nature and magnitude of the changes to the stromal cell tissue remain to be determined. In this study, we used mesenchymal stromal cell and osteoblast-related cell surface marker expression (STRO-1 and alkaline phosphatase, respectively) and flow cytometry to enumerate mesenchymal stromal cell and osteoblast numbers in bone marrow recovered from myeloma patients at the time of diagnosis. Using this approach, we identified an increase in the number of STRO-1 positive colony forming mesenchymal stromal cells and a concomitant decrease in alkaline phophatase osteoblasts. Notably, this increase in mesenchymal stromal cell numbers correlated closely with plasma cell burden at the time of diagnosis. In addition, in comparison with the osteoblast population, the STRO-1+ mesenchymal stromal cell population was found to express higher levels of plasma cell- and osteoclast-activating factors, including RANKL and IL-6, providing a mechanism by which an increase in mesenchymal stromal cells may promote and aid the progression of myeloma. Importantly, these findings were faithfully replicated in the C57BL/KaLwRij murine model of myeloma, suggesting that this model may present a unique and clinically relevant system in which to identify and therapeutically modulate the bone microenvironment and, in turn, alter the progression of myeloma disease.

Proteasome inhibitors and bone disease

Bone disease in patients with multiple myeloma (MM) is characterized by increase in the numbers and activity of bone-resorpting osteoclasts and decrease in the number and function of bone-formation osteoblasts. MM-triggered inhibition of bone formation may stem from suppression of Wnt/β-catenin signaling, a pivotal pathway in the differentiation of mesenchymal stem cells (MSC) into osteoblasts, and regulating production of receptor activator of nuclear factor-κB ligand (RANKL)/osteoprotegerin (OPG) axis by osteoblasts. Proteasome inhibitors (PIs), such as bortezomib (Bz), induce activation of Wnt/β-catenin pathway and MSC differentiation toward osteoblasts. PIs also suppress osteoclastogenesis, possibly through regulating multiple pathways including NF-κB, Bim, and the ratio of RANKL/OPG. The critical role of PI in increasing osteoblast function and suppression of osteoclast activity is highlighted by clinical evidence of increases in bone formation and decreases in bone resorption makers. This review will discuss the function of PIs in stimulating bone formation and suppression of bone resorption, and the mechanism underlying this process that leads to inhibition bone disease in MM patients.

Tug of war in the haematopoietic stem cell niche: do myeloma plasma cells compete for the HSC niche?

In the adult mammal, normal haematopoiesis occurs predominantly in the bone marrow, where primitive haematopoietic stem cells (HSC) and their progeny reside in specialised microenvironments. The bone marrow microenvironment contains specific anatomical areas (termed niches) that are highly specialised for the development of certain blood cell types, for example HSCs. The HSC niche provides important cell–cell interactions and signalling molecules that regulate HSC self-renewal and differentiation processes. These same signals and interactions are also important in the progression of haematological malignancies, such as multiple myeloma (MM). This review provides an overview of the bone marrow microenvironment and its involvement in normal, physiological HSC maintenance and plasma cell growth throughout MM disease progression.

Bisphosphonate therapy in multiple myeloma in preventing vertebral collapses: preliminary report

PURPOSE

The aim of the study was to report and discuss the preliminary data obtained in a homogeneous series of 50 patients affected by multiple myeloma treated with bisphosphonates.

METHODS

Patients were followed for a minimum of 1 year. Main orthopaedic data were recorded. Visual Analogue Score and QLQ-C30 and MY 20 were used to assess the quality of life.

RESULTS

Statistical analysis showed less lytic lesions in the group with zoledronate therapy and stable primary disease compared with a greater number of lesions in the non-treated group. Results regarding VAS score and QLQ-C30 and MY were statistically better in the first group than in the second.

CONCLUSIONS

Our results confirm the efficacy of zoledronate in ensuring an acceptable quality of life restraining the aggressiveness of the myeloma on bone tissue, especially in spine although further prospective studies have to be conducted to determine its correct use in myeloma patients.

Emerging strategies for targeting cell adhesion in multiple myeloma

Multiple myeloma (MM) is an incurable hematological cancer involving proliferation of abnormal plasma cells that infiltrate the bone marrow (BM) and secrete monoclonal antibodies. The disease is clinically characterized by bone lesions, anemia, hypercalcemia, and renal failure. MM is presently treated with conventional therapies like melphalan, doxorubicin, and prednisone; or novel therapies like thalidomide, lenalidomide, and bortezomib; or with procedures like autologous stem cell transplantation. Unfortunately, these therapies fail to eliminate the minimal residual disease that remains persistent within the confines of the BM of MM patients. Mounting evidence indicates that components of the BM-including extracellular matrix, cytokines, chemokines, and growth factors-provide a sanctuary for subpopulations of MM. This co-dependent development of the disease in the context of the BM not only ensures the survival and growth of the plasma cells but contributes to de novo drug resistance. In addition, by fostering homing, angiogenesis, and osteolysis, this crosstalk plays a critical role in the progression of the disease. Not surprisingly then, over the past decade, several strategies have been developed to disrupt this communication between the plasma cells and the BM components including antibodies, peptides, and inhibitors of signaling pathways. Ultimately, the goal is to use these therapies in combination with the existing antimyeloma agents in order to further reduce or abolish minimal residual disease and improve patient outcomes.

Bone anabolic agents for the treatment of multiple myeloma

The majority of patients with multiple myeloma develop bone osteolytic lesions, which may lead to severe complications, including pain and fractures. The pathogenesis of bone disease depends on uncoupled bone remodeling, characterized by increased bone resorption due to upregulation of osteoclast activity and decreased bone formation due to osteoblast inhibition. In myeloma, impaired osteoblast differentiation and increased apoptosis have been described. Responsible for these effects are integrin-mediated adhesion to tumor cells and soluble factors, including WNT antagonists, BMP2 inhibitors and numerous cytokines. Based on the evidence of osteoblast suppression in myeloma, bone anabolic agents have been developed and are currently undergoing clinical evaluation. Due to bidirectional inhibitory effects characterizing tumor cells and osteoblasts interactions, agents targeting osteoblasts are expected to reduce tumor burden along with improvement of bone health. This review summarizes the current knowledge on osteoblast inhibition in myeloma and provides an overview on the clinical grade agents with bone anabolic properties, which represent new promising therapeutic strategies in myeloma.

Pathogenesis and management of myeloma bone disease

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 increased activity of osteoclasts that 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, including the RANKL/osteoprotegerin pathway, macrophage inflammatory proteins and the wingless type signaling pathway. These molecules also appear to interfere with tumor growth and survival, providing possible targets for the development of novel drugs for the management of lytic disease in myeloma. Currently, bisphosphonates are the mainstay of treatment for myeloma bone disease, although several novel agents appear promising. This review focuses on recent advances in understanding the biology of bone disease in multiple myeloma, diagnosis and recent progress in treatment options.

TGF-β-related mechanisms of bone destruction in multiple myeloma

In destructive bone lesions of multiple myeloma (MM), osteoclastic bone resorption is enhanced, while bone formation is suppressed with impaired osteoblast differentiation from their progenitor cells. As a result, a strong negative balance in bone turnover develops in MM bone lesions. The suppression of bone formation is mainly due to a secretion of Wnt signal inhibitors, secreted Frizzled-related protein (sFRP)-2 and 3 and dikkopf1 (DKK1). In addition, the enhanced bone resorption in MM bone lesions causes a marked increase in the release and activation of transforming growth factor (TGF)-β. Although TGF-β enhances the recruitment and proliferation of osteoblast progenitors, TGF-β potently inhibits later phases of osteoblast differentiation and maturation and suppresses matrix mineralization. Thus, TGF-β also plays a role in the suppression of bone formation in MM bone lesions. In fact, when TGF-β action is suppressed by inhibitors of TGF-β type I receptor kinase, the inhibition of terminal differentiation of osteoblasts and mineralization is abrogated. While immature mesenchymal stromal cells support the growth and survival of MM cells, mature osteoblasts enhance MM cell apoptosis and cell cycle arrest. Thus, the inhibition of TGF-β signaling by TGF-β type I receptor kinase inhibitor causes not only an enhancement of bone formation but also a suppression of MM cell growth. Inhibition of TGF-β signaling can become a new therapeutic approach against MM.

Bone disease from monoclonal gammopathy of undetermined significance to multiple myeloma: pathogenesis, interventions, and future opportunities

Manifestations of bone disease-osteopenia, osteolytic lesions, and fractures-are the hallmark of multiple myeloma (MM) and occur clinically in the vast majority of patients. These abnormalities can have devastating clinical effects by increasing both the morbidity and mortality of patients. Bone disease is usually found when patients are diagnosed with active MM; however, recent data suggest that it is present in early myelomagenesis, including patients with myeloma precursor disease, monoclonal gammopathy of undetermined significance (MGUS). The primary mechanisms of abnormal bone remodeling are increased osteoclastic activity, which occurs in close proximity to active myeloma cells, and decreased activity of the surrounding osteoblasts. Better understanding of the pathogenesis of bone disease in MM will allow us to enhance our current therapeutic options in the treatment of bone disease. In patients with active MM and at least one lytic lesion, intravenous bisphosphonates have been shown to decrease skeletal-related events and pain, improve performance status, and maintain quality of life. Emerging evidence suggests that intervention at earlier stages of disease may prevent skeletal-related events at time of progression, but there is no evidence that bisphosphonates in this setting change the natural history of the disease.

Examining the metastatic niche: targeting the microenvironment

Some of the most common cancer types, including breast cancer, prostate cancer, and lung cancer, show a predilection to metastasize to bone. The molecular basis of this preferential growth of cancer cells in the bone microenvironment has been an area of active investigation. Although the precise molecular mechanisms underlying this process remain to be elucidated, it is now increasingly being recognized that the unique characteristics of the bone niche provide homing signals to cancer cells, and create a microenvironment conducive for the cancer cells to colonize. Concomitantly, cancer cells release several regulatory factors that result in abnormal bone destruction and/or formation. This complex bidirectional interplay between tumor cells and bone microenvironment establishes a "vicious cycle" that leads to a selective growth advantage for the cancer cells. The molecular insights gained on the underpinnings of bone metastasis in recent years have also provided us with avenues to devise innovative approaches for therapeutic intervention. The goal of this review is to describe our current understanding of molecular pathophysiology of cancer metastases to bone, as well as its therapeutic implications.

Osteoblast physiology in normal and pathological conditions

Osteoblasts are mononucleated cells that are derived from mesenchymal stem cells and that are responsible for the synthesis and mineralization of bone during initial bone formation and later bone remodelling. Osteoblasts also have a role in the regulation of osteoclast activity through the receptor activator of nuclear factor κ-B ligand and osteoprotegerin. Abnormalities in osteoblast differentiation and activity occur in some common human diseases such as osteoporosis and osteoarthritis. Recent studies also suggest that osteoblast functions are compromised at sites of focal bone erosion in rheumatoid arthritis.

Protective actions of green tea polyphenols and alfacalcidol on bone microstructure in female rats with chronic inflammation

This study investigated the effects of green tea polyphenols (GTP) and alfacalcidol on bone microstructure and strength along with possible mechanisms in rats with chronic inflammation. A 12-week study using a 2 (no GTP vs. 0.5%, w/v GTP in drinking water)×2 (no alfacalcidol vs. 0.05 μg/kg alfacalcidol orally, 5×/week) factorial design was employed in lipopolysaccharide (LPS)-administered female rats. A group receiving placebo administration was used to compare with a group receiving LPS administration only to evaluate the effect of LPS. Changes in tibial and femoral microarchitecture and strength of femur were evaluated. Difference in expression of tumor necrosis factor-α (TNF-α) in proximal tibia using immunohistochemistry was examined. Compared to the placebo group, the LPS-administered-only group had significantly lower femoral mass, trabecular volume, thickness and number in proximal tibia and femur, and lower periosteal bone formation rate in tibial shafts but had significantly higher trabecular separation and osteoclast number in proximal tibia and eroded surface in endocortical tibial shafts. Both GTP and alfacalcidol reversed these LPS-induced detrimental changes in femur, proximal tibia and endocortical tibial shaft. Both GTP and alfacalcidol also significantly improved femoral strength, while significantly suppressed TNF-α expression in proximal tibia. There were significant interactions in femoral mass and strength, trabecular separation, osteoclast number and TNF-α expression in proximal tibia. A combination of both showed to sustain bone microarchitecture and strength. We conclude that a protective impact of GTP and alfacalcidol in bone microarchitecture during chronic inflammation may be due to a suppression of TNF-α.

Pathogenesis of myeloma bone disease

Multiple myeloma (MM) is the most common cancer to involve bone with up to 90% of patients developing bone lesions. The bone lesions are purely osteolytic in nature and do not heal in the vast majority of patients. Up to 60% of patients develop pathologic fractures over the course of their disease. Bone disease is a hallmark of MM, and myeloma bone disease differs from bone metastasis caused by other tumors. Although myeloma and other osteolytic metastases induce increased osteoclastic bone destruction, in contrast to other tumors, once myeloma tumor burden exceeds 50% in a local area, osteoblast activity is either severely depressed or absent. The basis for this severe imbalance between increased osteoclastic bone resorption and decreased bone formation has been the topic of intensive investigation over the last several years. These studies have helped to identify novel targets for treating myeloma bone disease and will be discussed in this chapter.

First-line treatment with bortezomib rapidly stimulates both osteoblast activity and bone matrix deposition in patients with multiple myeloma, and stimulates osteoblast proliferation and differentiation in vitro

OBJECTIVES

The aim of the study was to investigate the effect of bortezomib on osteoblast proliferation and differentiation, as well as on bone matrix deposition for the first time in bisphosphonate-naïve, previously untreated patients with myeloma.

METHODS

Twenty newly diagnosed patients received four cycles of bortezomib treatment, initially as monotherapy and then combined with a glucocorticoid from cycle two to four. Bone remodeling markers were monitored closely during treatment. Furthermore, the effects of bortezomib and a glucocorticoid on immature and mature osteoblasts were also studied in vitro.

RESULTS

Treatment with bortezomib caused a significant increase in bone-specific alkaline phosphatase and pro-collagen type I N-terminal propeptide, a novel bone formation marker. The addition of a glucocorticoid resulted in a transient decrease in collagen deposition. In vitro bortezomib induced osteoblast proliferation and differentiation. Differentiation but not proliferation was inhibited by glucocorticoid treatment.

CONCLUSIONS

Bortezomib used as first-line treatment significantly increased collagen deposition in patients with multiple myeloma and osteolytic lesions, but the addition of a glucocorticoid to the treatment transiently inhibited the positive effect of bortezomib, suggesting that bortezomib may result in better healing of osteolytic lesions when used without glucocorticoids in patients that have obtained remission with a previous therapy. The potential bone-healing properties of single-agent bortezomib are currently being explored in a clinical study in patients who have undergone high-dose therapy and autologous stem cell transplantation.

Multiple roles of chemokine (C-C motif) ligand 2 in promoting prostate cancer growth

Prostate cancer continues to be the most common nonskin cancer diagnosed and the second leading cause of cancer death in men in the United States. Prostate cancer that has metastasized to bone remains incurable. The interactions between prostate cancer cells and the various cells of the host microenvironment result in enhanced growth of tumor cells and activation of host cells that together culminate in osteoblastic bone metastases. These dynamic tumor-host interactions are mediated by cancer and host-produced cytokines and chemokines. Among them, chemokine (C-C motif) ligand 2 (CCL2) has been identified as a prominent modulator of metastatic growth in the bone microenvironment. CCL2 is produced by bone marrow osteoblasts, endothelial cells, stromal cells, and prostate cancer cells. It has been demonstrated to modulate tumor-associated macrophage migration and promote osteoclast maturation. In addition, CCL2 functions through binding to its receptor CCR2 to induce prostate cell proliferation, migration, and invasion in both autocrine and paracrine manners. CCL2 protects prostate cancer cells from autophagic death by activating survivin through a PI3K/AKT (phosphatidylinositol 3-kinase/protein kinase B)-dependent mechanism. Inhibition of CCL2 substantially decreases macrophage infiltration, decreases osteoclast function, and inhibits prostate cancer growth in bone in preclinical animal models. The multiple roles of CCL2 in the tumor microenvironment make it an attractive therapeutic target in metastatic prostate cancer as well as in other cancers.

Growth inhibition of human multiple myeloma cells by an oncolytic adenovirus carrying the CD40 ligand transgene

PURPOSE

The growth-inhibitory activity of recombinant CD40 ligand (CD40L) is well documented in human multiple myeloma (MM). We examined MM-targeted delivery of CD40L by a conditional replicative oncolytic adenovirus, AdEHCD40L.

EXPERIMENTAL DESIGN

The growth-regulatory activity of AdEHCD40L was determined in vitro and in vivo. Differential analysis with AdEHCD40L and parental virus (AdEHNull)-infected cultures allowed the identification of cellular and molecular pathways modulated by the CD40L transgene.

RESULTS

Conditional expression of viral E1A and CD40L transgene was shown in human MM lines RPMI 8226 [interleukin (IL)-6 independent] and Kas-6/1 (IL-6 dependent) under hypoxic conditions commonly found in MM in situ. AdEHCD40L inhibited MM cell growth more effectively than AdEHNull. This enhanced growth-inhibitory activity was abrogated by cotreatment with a CD40L antibody. Chemoresistant MM lines (MR20 and LR5) were similarly susceptible to AdEHCD40L treatment. AdEHCD40L induced apoptosis and S-phase cell cycle blockade while uniquely up-regulating the previously described proapoptotic elements tumor necrosis factor-related apoptosis-inducing ligand, Fas, and IL-8. Intratumoral injections of AdEHCD40L reduced the growth of severe combined immunodeficient/hu RPMI 8226 xenografts by >50% compared with 28% reduction by AdEHNull. Adenoviral hexon and CD40L were detected in AdEHCD40L-treated tumors at day 35 after infection primarily in necrotic areas, suggesting viral replicative activity.

CONCLUSIONS

These findings show that CD40L acts in concert with viral oncolysis to produce MM growth inhibition through activation of cellular apoptosis. The direct growth-inhibitory activity of AdEHCD40L, together with the well-known immune-potentiating features of CD40L, may be clinically applicable for the experimental treatment of MM or plasma cell leukemia.

Diet, tuberculosis, and the paleopathological record

Osseous manifestation of infectious disease is of paramount importance to paleopathologists seeking to interpret ancient health, but the relationships among infectious agent exposure, development of disease, and skeletal involvement are complex. The outcome of an exposure strongly depends on multiple factors, including ecology, diet, nutrition, immune function, and the genetics of pathogen and host. Mycobacterial diseases are often studied in ancient remains but also are especially influenced by these factors; individual and population differences in severity and course are apparent following onset of active disease. The osteological record for these diseases represents the complex interplay of host and pathogen characteristics influencing within- and among-individual skeletal lesion prevalence and distribution. However, many of these characteristics may be assessed independently through the archaeological record. Here, we explore the contributions of dietary protein and iron to immune function, particularly the course and outcome of infection with Mycobacterium tuberculosis. We emphasize how nutrition may influence the dissemination of bacilli to the skeleton and subsequent formation of diagnostic lesions. We then generate models and hypotheses informed by this interplay and apply them to four prehistoric New World areas. Finally, discrepancies between our expectations and the observed record are explored as a basis for new hypotheses.

In-vitro functional phenotypes of plasma cell lines from patients with multiple myeloma

Seven plasma cell lines from patients with smoldering (group A) and overt myeloma (group B) were investigated for both phenotypic markers and in-vitro properties, including sensitivity to apoptosis, cytotoxicity, cell adhesion, chemotaxis and bone interaction. Cell lines from group A underwent apoptosis whereas those from group B were apparently resistant, promoted cytotoxicity in target cells and enhanced both adhesion and migratory functions upon appropriate activators. In addition, MCC-2, a group B cell line from a patient with severe osteolytic disease of the skeleton produced erosive lacunae on bone substrates, whereas this effect was almost absent with cell lines from group A. Concurrent deregulation of relative markers, in combination with peculiar properties including resistance to apoptosis and high cytotoxic potential, as well as adhesion, chemotaxis and bone pathophysiology interactions, may thus identify myeloma cells with aggressive phenotype driving these biological activities in vitro and perhaps in vivo.

Bone-resorbing cells in multiple myeloma: osteoclasts, myeloma cell polykaryons, or both?

Myeloma bone disease (MBD) leads to progressive destruction of the skeleton and is the most severe cause of morbidity in multiple myeloma. Its pathogenetic mechanisms are not fully understood, though the current evidence points to osteoclast (OC) hyperactivity coupled with defective osteoblast function unable to counteract bone resorption. OCs are generated in bone marrow by myeloid progenitors through increased levels of receptor activator of nuclear factor kappaB ligand and M-CSF, whose intracellular pathways propagate signals that activate sequential transcription factors, resulting in the production of major OC enzymes that drive specific functions such as acidification and degradation of the bone matrix. Osteolytic lesions, however, are not characterized by massive OC content, whereas malignant plasma cells, which are usually present in a high number, may occur as large multinucleated cells. The possibility that myeloma cells fuse and generate polykaryons in vivo is suggested by the in vitro formation of multinuclear cells that express tartrate-resistant acid phosphatase and produce pits and erosive lacunae on experimental osteologic substrates. Further, the detection in vivo of polykaryons with chromosome translocations typical of myeloma cells lends support to the view that myeloma polykaryons may act as functional OCs and participate in the skeletal destruction by resorbing bone.

Activation of the acquired immune response reduces coupled bone formation in response to a periodontal pathogen

Osteoimmunolgy involves the interaction of the immune system with skeletal elements. This interaction can lead to the formation of osseous lesions. To investigate how the acquired immune response could contribute to osteolytic lesions, we injected the periodontal pathogen Porphyromonas gingivalis adjacent to calvarial bone with or without prior immunization against the bacterium. Activation of the acquired immune response increased osteoclastogenesis and decreased coupled bone formation. The latter was accompanied by an increase in nuclear translocation of the transcription factor FOXO1 in vivo, increased apoptosis of bone-lining cells measured by the TUNEL assay and number of activated caspase-3 positive cells and a decrease in bone lining cell density. Further studies were conducted with MC3T3 osteoblastic cells. Apoptosis and increased FOXO1 DNA binding activity were induced when a combination of cytokines was tested, IL-beta, TNF-alpha, and IFN-gamma. Knockdown of FOXO1 by small interfering RNA significantly reduced cytokine stimulated apoptosis, cleaved caspase-3/7 activity and decreased mRNA levels of the proapoptotic genes, TNF-alpha, FADD, and caspase-3, -8, and -9. These results indicate that activation of the acquired immunity by a periodontal pathogen reduces the coupling of bone formation and resorption. This may occur by enhancing bone lining cell apoptosis through a mechanism that involves increased FOXO1 activation. These studies give insight into inflammatory bone diseases such as periodontal disease and arthritis were the formation of lytic lesions occurs in conjunction with deficient bone formation and activation of an acquired immune response.

Novel targets for myeloma bone disease

BACKGROUND

Multiple myeloma (MM) is a plasma cell malignancy in which osteolytic bone lesions develop in over 80% of patients. The increased bone destruction results from increased osteoclast formation and activity, which occurs adjacent to marrow sites involved with MM cells. This is accompanied by suppressed or absent osteoblast differentiation and activity, resulting in severely impaired bone formation and development of purely osteolytic lesions.

OBJECTIVE

The pathophysiology underlying this bone remodeling is reviewed, and potential new strategies to treat MM bone disease are discussed.

RESULTS

Recent advances in our understanding of factors involved in pathogenesis of MM bone disease have identified novel therapeutic targets. Several of these are or will be in clinical trials soon.

CONCLUSION

Agents which target the tumor and bone-destructive process, such as the immunomodulatory drugs (IMiDs) or bortezomib, in combination with novel anti-resorptives should be effective. These combinations should be in clinical trials in the next few years. It is unclear if these treatments will be able to 'heal' bone lesions in MM patients.

Pathogenesis of myeloma bone disease

Bone disease in multiple myeloma (MM) is characterized by lytic bone lesions, which can cause severe bone pain, pathologic fractures and hypercalcemia. However, the lytic bone disease in MM differs from that in other cancer patients who have lytic bone metastases. Although increased osteoclastic bone destruction is involved in MM and other tumors involving bone, in contrast to other tumors, once the MM tumor burden exceeds 50% in a local area, osteoblast activity is either suppressed or absent. The basis for this severe imbalance between increased osteoclastic bone resorption and decreased bone formation has been a topic of intensive investigation over the last several years and will be reviewed in this article.

IL-6 receptor expression and IL-6 effects change during osteoblast differentiation

Studies of the effects of interleukin-6 on osteoblasts have yielded conflicting results. In several earlier in vitro studies it has been stated that IL-6 has no effects on osteoblasts unless soluble IL-6 receptor is added. These results are contradictory to the fact that IL-6 receptors are expressed in osteoblasts in vivo. In this study, MC3T3 preosteoblast cells and rat bone marrow stromal cells were cultured in bone inducing medium containing ascorbic acid, beta-glycerophosphate or dexamethasone. We found that IL-6 receptor expression increased in both types of cells during in vitro differentiation. Furthermore in MC3T3 cells IL-6 decreased proliferation and enhanced expression of two osteoblast-specific differentiation markers, Runx2 and osteocalcin, in proper sequential order. Interestingly, in both cell types IL-6-induced apoptosis only in later culture stages. We also found in MC3T3 cells that IL-6 induced STAT3 activation was significantly higher in later culture stages, i.e. when IL-6 receptor expression was high. The present study shows that IL-6 receptor expression increases during in vitro osteoblast differentiation and that IL-6 functions as a differentiation regulator of preosteoblast cells and an apoptosis initiator in more mature cells.

Abnormal cytokine production by bone marrow stromal cells of multiple myeloma patients in response to RPMI8226 myeloma cells

INTRODUCTION

Recent studies indicate that bone marrow stromal cells (BMSCs) derived from patients with multiple myeloma (MM) differ from those of healthy donors in their expression of extracellular matrix compounds and in cytokine production. It is not known whether these abnormalities are primary or are acquired by BMSCs on contact with MM cells.

MATERIALS AND METHODS

Interleukin (IL)-6, IL-11, IL-10, and tumor necrosis factor (TNF)-alpha production by CD166+ mesenchymal BMSCs and the CD38+/CD138+ RPMI8226 myeloma cell line cultivated in vitro in monocultures or co-cultivated under cell-to-cell contact or non-contact conditions in the presence of a tissue culture insert were measured. Intracellular cytokines were measured by flow cytometry analysis as the percentage of cytokine-producing cells or by mean fluorescence intensity as the level of cytokine expression in cells. Additionally, ELISA was used to measure IL-6, soluble IL-6 receptor (sIL-6R), IL-11, IL-10, TNF-alpha, B-cell-activating factor of the TNF family (BAFF), hepatocyte growth factor (HGF), and osteopontin (OPN) production in the supernatants of the cultures and co-cultures.

RESULTS

A higher ability of the BMSCs of MM patients than in controls was detected to produce IL-6, IL-10, TNF-alpha, OPN, and especially HGF and BAFF in response to the RPMI8226 cells. Moreover, the BMSCs of the MM patients significantly enhanced the production of sIL-6R by the RPMI8226 cells.

DISCUSSION

Cytokines over-expressed by BMSCs of MM patients can function as growth factors for myeloma cells (IL-6, IL-10, HGF), migration stimulatory factors for tumor plasma cells (TNF-alpha, HGF), adhesion stimulatory factors (HGF, BAFF and OPN), stimulators of osteoclastogenesis (IL-6, TNF-alpha), and angiogenic factors (TNF-alpha). The results of this experiment strongly suggest that the BMSCs from MM patients differed in spontaneous and myeloma cell-induced production of cytokines, especially of HGF and BAFF, and these abnormalities were both primary and acquired by the BMSCs on contact with the MM cells. This in turn suggests the presence of an undefined, autocrine stimulation pathway resulting in a prolonged production of cytokines even in long-term cultures in vitro and in vivo. These abnormalities might provide optimal conditions for the proliferation and differentiation of residual tumor cells or their precursors in the affected bone marrow.