New Insights in Myeloma-induced Osteolysis

Pathways of Angiogenic and Inflammatory Cytokines in Multiple Myeloma: Role in Plasma Cell Clonal Expansion and Drug Resistance

Multiple myeloma (MM) is the second most common hematological malignancy, and despite the introduction of innovative therapies, remains an incurable disease. Identifying early and minimally or non-invasive biomarkers for predicting clinical outcomes and therapeutic responses is an active field of investigation. Malignant plasma cells (PCs) reside in the bone marrow (BM) microenvironment (BMME) which comprises cells (e.g., tumour, immune, stromal cells), components of the extracellular matrix (ECM) and vesicular and non-vesicular (soluble) molecules, all factors that support PCs’ survival and proliferation. The interaction between PCs and BM stromal cells (BMSCs), a hallmark of MM progression, is based not only on intercellular interactions but also on autocrine and paracrine circuits mediated by soluble or vesicular components. In fact, PCs and BMSCs secrete various cytokines, including angiogenic cytokines, essential for the formation of specialized niches called “osteoblastic and vascular niches”, thus supporting neovascularization and bone disease, vital processes that modulate the pathophysiological PCs–BMME interactions, and ultimately promoting disease progression. Here, we aim to discuss the roles of cytokines and growth factors in pathogenetic pathways in MM and as prognostic and predictive biomarkers. We also discuss the potential of targeted drugs that simultaneously block PCs’ proliferation and survival, PCs–BMSCs interactions and BMSCs activity, which may represent the future goal of MM therapy.

Cervical spine multiple myeloma and isolated radiotherapy

Multiple myeloma is a hematologic malignancy frequently presenting with spinal lytic lesions. The authors report the case of a patient with an extensively destructive osteolytic MM lesion in the cervical spine treated exclusively with radiotherapy. Computed tomography and magnetic resonance imaging scans showed an arrest of further progression of instability and resolution of the lytic lesion, showing signs of new bone formation. Whereas surgery should be considered for cases of spinal instability and potential neurological injury, this case demonstrates that isolated radiotherapy can be used in select cases to treat MM lesions and restore the structural integrity of the spinal elements.

Evaluation of in vitro effects of various targeted drugs on plasma cells and putative neoplastic stem cells in patients with multiple myeloma

Multiple myeloma (MM) is a malignancy characterized by monoclonal paraproteinemia and tissue plasmocytosis. In advanced MM cytopenia and osteopathy may occur. Although several effective treatment strategies have been developed in recent years, there is still a need to identify new drug targets and to develop more effective therapies for patients with advanced MM. We examined the effects of 15 targeted drugs on growth and survival of primary MM cells and 5 MM cell lines (MM.1S, NCI-H929, OPM-2, RPMI-8226, U-266). The PI3-kinase blocker BEZ235, the pan-BCL-2 inhibitor obatoclax, the Hsp90-targeting drug 17AAG, and the Polo-like kinase-1 inhibitor BI2536, were found to exert major growth-inhibitory effects in all 5 MM cell lines tested. Moreover, these drugs suppressed the in vitro proliferation of primary bone marrow-derived MM cells and induced apoptosis at pharmacologic drug concentrations. Apoptosis-inducing effects were not only seen in the bulk of MM cells but also in MM stem cell-containing CD138⁻/CD20⁺/CD27⁺ memory B-cell fractions. Synergistic growth-inhibitory effects were observed in MM cell lines using various drug combinations, including 17AAG+BI2536 in MM.1S, OPM-2, RPMI-8226, and U-266 cells, 17AAG+BEZ235 in MM.1S, OPM-2, RPMI-8226, and U-266 cells, 17AAG+obatoclax in MM.1S, NCI-H929, OPM-2, and RPMI-8226 cells, BI2536+BEZ235 in MM.1S, NCI-H929, OPM-2, and RPMI-8226 cells, BI2536+obatoclax in MM.1S, OPM-2 and RPMI-8226 cells, and BEZ235+obatoclax in MM.1S and RPMI-8226 cells. Together, our data show that various targeted drugs induce profound and often synergistic anti-neoplastic effects in MM cells which may have clinical implications and may contribute to the development of novel treatment strategies in advanced MM.

Interleukin-32α promotes the proliferation of multiple myeloma cells by inducing production of IL-6 in bone marrow stromal cells

Multiple myeloma (MM) is a malignant plasma disease closely associated with inflammation. In MM bone marrow microenvironment, bone marrow stromal cells (BMSCs) are the primary source of interleukin-6 (IL-6) secretion, which promotes the proliferation and progression of MM cells. However, it is still unknown how the microenvironment stimulates BMSCs to secrete IL-6. Interleukin-32 (IL-32) is a newly identified pro-inflammatory factor. It was reported that in solid tumors, IL-32 induces changes in other inflammatory factors including IL-6, IL-10, and TNF-α. The aim of this study was to investigate the expression of IL-32 and the role of IL-32 in the MM bone marrow microenvironment. Our data illustrate that MM patients have higher expression of IL-32 than healthy individuals in both bone marrow and peripheral blood. We used ELISA and qRT-PCR to find that malignant plasma cells are the primary source of IL-32 production in MM bone marrow. ELISA and Western blot analysis revealed that recombinant IL-32α induces production of IL-6 in BMSCs by activating NF-κB and STAT3 signaling pathways, konckdown of IL-32 receptor PR3 inhibit this process. Knockdown of IL-32 by shRNA decreased the proliferation in MM cells that induced by BMSCs. In conclusion, IL-32 secreted from MM cells has paracrine effect to induce production of IL-6 in BMSCs, thus feedback to promote MM cells growth.

Activation of LTBP3 gene by a long noncoding RNA (lncRNA) MALAT1 transcript in mesenchymal stem cells from multiple myeloma

Long noncoding RNAs (lncRNAs) are emerging as important regulatory molecules in tumor suppressor and oncogenic pathways. However, the magnitude of the contribution of lncRNA expression to normal human tissues and cancers has not been investigated in a comprehensive manner. Here we explored the biology of the lncRNA MALAT1 and considered the potential significance in mesenchymal stem cells from myeloma patients. By using assays such as RNA interference, luciferase, chromatin immunoprecipitation, and RNA immunoprecipitation, we showed that in mesenchymal stem cells MALAT1 promoted the activation effect of the key transcription factor Sp1 on LTBP3 promoter by modulating recruitment of Sp1 to the LTBP3 gene that regulated the bioavailability of TGF-β in particular. Our data suggested that lncRNA MALAT1 directly interacted with Sp1 and LTBP3 promoter to increase expression of LTBP3 gene. The specificity and efficiency of activation were ensured by the formation of a stable complex between MALAT1 and the LTBP3 promoter, direct interaction of MALAT1 with Sp1, and recruitment of Sp1 to the promoter. In this study, we showed that the mechanism of transcriptional activation of LTBP3 promoter depended on MALAT1 initiated from neighboring gene LTBP3 and involved both the direct interaction of the Sp1 and promoter-specific activation. Our knowledge of the role of MALAT1 in cellular transformation is pointing toward its potential use as a biomarker and a target for novel therapeutic approaches in multiple myeloma.

The effect of the combination of bisphosphonates and conventional chemotherapy on bone metabolic markers in multiple myeloma patients

PURPOSE

Urinary N-terminal telopeptides of type I collagen (uNTX), serum bone alkaline phosphatase (sBAP) have been acknowledged in observing bone metastases of solid tumors. The paper is designed to study the value of clinical application of uNTX and sBAP in the treatment of multiple myeloma (MM), as well as the action of bisphosphonates for osteolytic bone lesion.

METHODOLOGY

Thirty-three MM cases were treated with bisphosphonates (hereinafter called clodronate therapy group) and 20 MM cases were treated with simple chemotherapy (hereinafter called control group). uNTX and sBAP were tested during the courses of treatment three times (pretreatment, 3 months, and 6 months). uNTX was tested by enzyme-linked immunosorbent assay. sBAP was tested by chemiluminescence analysis. All the results were analyzed with t-test by using SPSS 11.0.

RESULTS

There were no significant differences between therapy and control groups: in uNTX (173.74 ± 14.55) and (129.79 ± 12.13) μg/l before treatment (P > 0.05). After 6 months there were significant differences between them: (85.71 ± 8.23) and (121.59 ± 12.43) μg/l (P < 0.05). And also there were significant differences among the courses in the therapy group. There were no significant differences between therapy and control groups in sBAP concentration: (4.78 ± 0.55) and (8.42 ± 1.32) μg/l before treatment (P > 0.05). After 6 months there were significant differences between them: (16.01 ± 0.52) and (9.62 ± 1.29) μg/l (P < 0.001). And also there were significant differences among the courses in the therapy group.

CONCLUSION

uNTX and sBAP were important to measure the situation of the osteolytic bone lesion in MM. Bisphosphonates can significantly reduce bone degradation and metabolism, improve the synthesis, which is valuable for the treatment of MM cases.

Stable changes in mesenchymal stromal cells from multiple myeloma patients revealed through their responses to Toll-like receptor ligands and epidermal growth factor

In human multiple myeloma (MM), the tumor cells exhibit strict dependence on bone marrow (BM) stromal elements. It has been suggested that, in turn, MM cells modify multipotent stromal cells (MSCs), diverting them to support the myeloma. We investigated MM-derived MSCs by comparing their toll-like receptor (TLR) responses to those of MSCs derived from healthy controls. We now report that MM-derived MSCs manifested intact proliferation responses and IL-6 secretion and their adipose and osteogenic differentiation responses to TLR ligands were also similar to those of healthy controls, ranging from augmentation to inhibition. However, MM-derived MSCs were found to be defective in IL-8 secretion and ERK1/2 phosphorylation following TLR-2 activation. Moreover, MM-derived MSCs failed to respond to EGF by elevation of ERK1/2 phosphorylation. The persistence of these changes in extensively cultured MM-derived MSCs, suggests that these cells are stably, if not irreversibly modified.

Novel strategies for immunotherapy in multiple myeloma: previous experience and future directions

Multiple myeloma (MM) is a life-threatening haematological malignancy for which standard therapy is inadequate. Autologous stem cell transplantation is a relatively effective treatment, but residual malignant sites may cause relapse. Allogeneic transplantation may result in durable responses due to antitumour immunity mediated by donor lymphocytes. However, morbidity and mortality related to graft-versus-host disease remain a challenge. Recent advances in understanding the interaction between the immune system of the patient and the malignant cells are influencing the design of clinically more efficient study protocols for MM. Cellular immunotherapy using specific antigen-presenting cells (APCs), to overcome aspects of immune incompetence in MM patients, has received great attention, and numerous clinical trials have evaluated the potential for dendritic cell (DC) vaccines as a novel immunotherapeutic approach. This paper will summarize the data investigating aspects of immunity concerning MM, immunotherapy for patients with MM, and strategies, on the way, to target the plasma cell more selectively. We also include the MM antigens and their specific antibodies that are of potential use for MM humoral immunotherapy, because they have demonstrated the most promising preclinical results.

Macrophage infiltration predicts a poor prognosis for human ewing sarcoma

Ewing sarcoma-primitive neuroectodermal tumor (EWS) is associated with the most unfavorable prognosis of all primary musculoskeletal tumors. The objective of the present study was to investigate whether tumor-associated macrophages (TAMs) affect the development of EWS. TAMs were isolated from mouse xenografts using CD11b magnetic beads and examined for their cytokine expression and osteoclastic differentiation. To evaluate the role of TAMs in xenograft formation, liposome-encapsulated clodronate was used to deplete TAMs in mice. Macrophage infiltration and tumor microvascular density were histologically evaluated in 41 patients with EWS, and association with prognosis was examined using Kaplan-Meier survival analysis. In mouse EWS xenografts, TAMs expressed higher concentrations of cytokines including interleukin-6, keratinocyte-derived chemokine, and monocyte chemotactic protein-1. TAMs were more capable than normal monocytes of differentiating into tartrate-resistant acid phosphatase-positive giant cells. Depleting macrophages using liposome-encapsulated clodronate significantly inhibited development of EWS xenografts. In human EWS samples, higher levels of CD68-positive macrophages were associated with poorer overall survival. In addition, enhanced vascularity, increase in the amount of C-reactive protein, and higher white blood cell counts were also associated with poor prognosis and macrophage infiltration. TAMs seem to enhance the progression of EWS by stimulating both angiogenesis and osteoclastogenesis. Further investigation of the behavior of TAMs may lead to development of biologically targeted therapies for EWS.

The role of RANK-ligand inhibition in cancer: the story of denosumab

The diagnosis of bone metastases is an event with certain consequences for the patient. They often mean pain and can also mean pathological fractures, hypercalcemia, and spinal cord compression, all synonymous with a diminished quality of life and often also hospitalization. Since the advent of the intravenous bisphosphonates, things began to look a bit brighter for patients with bone metastases-bone destruction was kept at bay a little longer. The next generation of bone metastasis treatments is well on its way in clinical development, and among them, the most advanced drug is denosumab. Denosumab is a fully human monoclonal antibody that inhibits osteoclast maturation, activation, and function by binding to receptor activator of nuclear factor kappa B ligand, with the final result being a reduced rate of bone resorption. In this review, we give an overview of relevant preclinical and clinical data regarding the use of denosumab in patients with solid tumors in general and prostate cancer in particular.

Heparanase enhances local and systemic osteolysis in multiple myeloma by upregulating the expression and secretion of RANKL

Excessive bone destruction is a major cause of morbidity in myeloma patients. However, the biological mechanisms involved in the pathogenesis of myeloma-induced bone disease are not fully understood. Heparanase, an enzyme that cleaves the heparan sulfate chains of proteoglycans, is upregulated in a variety of human tumors, including multiple myeloma. We previously showed that heparanase promotes robust myeloma tumor growth and supports spontaneous metastasis of tumor cells to bone. In the present study, we show, for the first time, that the expression of heparanase by myeloma tumor cells remarkably enhances bone destruction locally within the tumor microenvironment. In addition, enhanced heparanase expression in the primary tumor also stimulated systemic osteoclastogenesis and osteolysis, thus mimicking the systemic osteoporosis often seen in myeloma patients. These effects occur, at least in part, as the result of a significant elevation in the expression and secretion of receptor activator of NF-κB ligand (RANKL) by heparanase-expressing myeloma cells. Moreover, analysis of bone marrow biopsies from myeloma patients reveals a positive correlation between the level of expression of heparanase and RANKL. Together, these discoveries reveal a novel and key role for heparanase in promoting tumor osteolysis and show that RANKL is central to the mechanism of heparanase-mediated osteolysis in myeloma.

Computed microtomography of bone specimens for rapid analysis of bone changes associated with malignancy

Breast and prostate cancers are specially metastasizing to bone. Metastases from breast cancer usually exhibit a mixed osteolytic/osteosclerotic aspect, with osteolysis predominating. Osteosclerosis is a common finding in prostatic cancer although osteolysis occurs within the sclerotic lesions. B-cell malignancies (lymphoma, myeloma) are also associated with marked osteolysis. Histopathological examination of bone biopsies was used for the diagnosis of malignancies and, prior to embedding, microcomputed tomography (microCT) was done on the bone specimens. Patients (247) who presented either a bone metastasis, an overt myeloma, a lymphoma or a monoclonal gammopathy of undetermined significance were studied. All patients had a bone biopsy studied by 2D histomorphometry for the histopathology. During the fixation time, the bone cores were analyzed by microCT. On the 3D reconstructed models provided by microCT, signs of osteolysis/osteosclerosis were searched: excess of bone resorption, focal disorganization of microarchitecture, bone metaplasia, osteosclerosis. A strong agreement was obtained between histomorphometry and microCT results using Cohen's kappa test (kappa = 0.713). MicroCT identified excess bone resorption on trabecular surfaces when eroded surfaces were >10.5% by histomorphometry. MicroCT failed to identify some patients with smoldering myeloma or some lymphomas with microresorption. MicroCT data are obtained within 4 hr and suggest the malignant invasion of bone marrow when excess of bone resorption/formation is obtained. MicroCT can be used in the immediate postbiopsy period making possible a fast identification of malignancy. However these signs are not specific and must be confirmed by histopathological analysis.

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.

Advances in the understanding of myeloma bone disease and tumour growth

Advances in multiple myeloma support the notion that the associated bone disease, characterized by increased osteoclastogenesis and suppressed osteoblastogenesis, is both a consequence and necessity of tumour progression. Osteoblastogenesis is suppressed by secreted inhibitors and dysregulation of cell-surface 'coupling' factors on osteogenic cells. Osteoclastogenesis is increased as a consequence of osteoblast deactivation and of production of osteoclast-activating factors. Osteoclasts express soluble and cell-surface factors that stimulate myeloma growth, while osteoblasts produce bone-building factors that restrain growth of myeloma cells that are dependent on the microenvironment; detailed molecular mechanisms are discussed. Experimental and clinical findings indicate that pharmacological and experimental osteoblast-activating agents that effectively promote bone formation also reduce growth of myeloma cells within bone, seemingly by simultaneously stimulating osteoblastogenesis and restraining osteoclastogenesis. Unravelling mechanisms of myeloma bone disease expands horizons for developing novel interventions and also facilitates better understanding of the association between induction of osteolysis and disease progression.

[Pelvic and spinal MR follow-up of multiple myeloma patients after high-dose chemotherapy and autologous peripheral blood stem cell transplant]

PURPOSE

To evaluate the changes of bone marrow lesions on pelvic and spinal MR in patients with multiple myeloma after high-dose chemotherapy and autologous peripheral blood stem cell transplant.

PATIENTS AND METHODS

Pelvic and spinal MR examinations were obtained at presentation (myeloma diagnosis) and 1 year after transplant in 20 patients that were part of a group of 39 patients enrolled in a prospective study. The type of marrow replacement (classified in stages with stage 0: normal; stage 1: salt and pepper; stage 2: focal infiltration; stage 3: diffuse infiltration), the number and size of marrow lesions and the number of vertebral compression fractures were recorded. We have compared the findings prior to and following transplant, with correlation to the response to treatment and the use of biphosphonates.

RESULTS

The type of marrow replacement was improved following transplant in 65% of patients (not statistically significant). The number and size of nodules > 20 mm showed significant reduction (p = 0.0224 and p = 0.0237 respectively). Lesions on MR improved in 50% of patients with good response and 75% of patients with poor response to treatment. Patients receiving biphosphonates showed more vertebral compression fractures.

CONCLUSION

The evolution of marrow replacing lesions on MR is discordant compared to the biological and clinical response to treatment. Pelvic and spinal MR evaluation at the time of diagnosis does not appear to be a good predictive factor of response to treatment. Biphosphonates do not appear to prevent new vertebral compression fractures. Pelvic and spinal MR provides interesting data in the follow-up of patients with myeloma following autologous transplant, especially in the local evolution of marrow replacing lesions, but our results do not justify its use in routine clinical practice.

Bone lesions and macrophage inflammatory protein-1 alpha (MIP-1α) in human multiple myeloma

Bone lesions are a prominent feature accompanying multiple myeloma. Elucidation of the mechanisms regulating osteolysis is crucial in achieving a good quality of life, as such patients suffer from bone pain even after achieving improvement of the disease by high-dose chemotherapy. Recent research has revealed that bone lysis in myeloma patients is the result of both inhibited bone formation and enhanced bone destruction. It has been considered that bone absorption is regulated by activation of osteoclasts mediated by osteoclast activating factor (OAF) produced from myeloma cells. Macrophage inflammatory protein-1 alpha (MIP-1a) is a member of the chemokine family, and was originally determined as a soluble factor secreted from activated macrophages. Many candidates for OAF had been proposed and MIP-1a is now considered a major OAF. In this review, the significance of MIP-1a in myeloma bone disease is summarized.

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.

The proteasome inhibitor, bortezomib suppresses primary myeloma and stimulates bone formation in myelomatous and nonmyelomatous bones in vivo

Multiple myeloma (MM), a hematologic malignancy of terminally differentiated plasma cells is closely associated with induction of osteolytic bone disease, induced by stimulation of osteoclastogenesis and suppression of osteoblastogenesis. The ubiquitin-proteasome pathway regulates differentiation of bone cells and MM cell growth. The proteasome inhibitor, bortezomib, is a clinical potent antimyeloma agent. The main goal of this study was to investigate the effect of bortezomib on myeloma-induced bone resorption and tumor growth in SCID-rab mice engrafted with MM cells from 16 patients. Antimyeloma response of bortezomib, which was evident in >50% of 16 experiments and resembled clinical response, was associated with significant increased bone mineral density (BMD) and osteoblast numbers, and reduced osteoclast numbers in myelomatous bones. This bone anabolic effect, which was also visualized on X-ray radiographs and confirmed by static and dynamic histomorphometric analyses, was unique to bortezomib and was not observed in hosts responding to melphalan, a chemotherapeutic drug widely used to treat MM. Bortezomib also increased BMD and osteoblasts number and reduced osteoclasts number in nonmyelomatous implanted bones. In vitro bortezomib directly suppressed human osteoclast formation and promoted maturation of osteoblasts. We conclude that bortezomib promotes bone formation in myelomatous and nonmyelomatous bones by simultaneously inhibiting osteoclastogenesis and stimulating osteoblastogenesis. As clinical and experimental studies indicate that bone disease is both a consequence and necessity of MM progression our results suggest and that bortezomib's effects on bone remodeling contribute to the antimyeloma efficacy of this drug.

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.

Elevated tumor necrosis factor-alpha suppresses TAZ expression and impairs osteogenic potential of Flk-1+ mesenchymal stem cells in patients with multiple myeloma

One of the clinical features of multiple myeloma (MM) is the occurrence of skeletal events, which are characterized by increased bone resorption and decreased bone formation. In contrast to enhanced osteoclastogenesis, little is known about the mechanism of impaired bone formation in MM. Because TAZ, a Runx2/Cbfa1 transcriptional co-activator, has recently been shown to modulate mesenchymal stem cell (MSC) differentiation in favor of osteoblast differentiation, we investigated whether the regulation of TAZ expression played a role in the decreased bone formation of MM. We isolated and purified Flk-1(+)CD31(-)CD34(-) cells with MSC characters from bone marrow (BM) of myeloma patients and healthy donors. We found the osteogenic potential of the MSCs from myeloma patients decreased significantly, and TAZ expression of these cells was lower than that of healthy donors. Human myeloma cell lines (HMCLs) and CD138(+) myeloma cells (MCs) from myeloma patients inhibited osteogenesis of the MSCs from healthy volunteers, which were accompanied by a reduced TAZ expression and elevated TNF-alpha concentration in the supernatant of co-culture systems. The repressed osteogenesis and TAZ expression were both partially restored by neutralization of TNF-alpha. Thus, the decreased osteogenic potential of MSCs of myeloma patients was in part due to TNF-alpha suppressed TAZ expression.

Predictive value of alkaline phosphatase for response and time to progression in bortezomib-treated multiple myeloma patients

Myeloma bone disease is characterized by osteolytic destruction associated with suppressed osteoblastic activity. Using data from the APEX (Richardson et al., N Engl J Med 2005;352:2487-2498) study, we have assessed the relationship of changes in alkaline phosphatase (ALP) levels during bortezomib therapy with response and time to progression on this therapy. The percentage of ALP increments in responders (complete and partial response) and nonresponders was analyzed at different thresholds and time points. For all bortezomib-treated patients enrolled in the trial (N = 333), at least a 25% increase in ALP from the baseline at 6 week was the most powerful predictor of treatment response (P < 0.0001) and time to progression (206 vs. 169 days) relative to patients with less than a 25% increase in ALP (P = 0.01). Markers of osteoblastic activation may predict quality and duration of response in multiple myeloma. In addition, our data suggest that bone anabolism could inhibit myeloma growth.

Antibody-based inhibition of DKK1 suppresses tumor-induced bone resorption and multiple myeloma growth in vivo

Dickkopf-1 (DKK1), a soluble inhibitor of Wnt signaling secreted by multiple myeloma (MM) cells contributes to osteolytic bone disease by inhibiting the differentiation of osteoblasts. In this study, we tested the effect of anti-DKK1 therapy on bone metabolism and tumor growth in a SCID-rab system. SCID-rab mice were engrafted with primary MM cells expressing varying levels of DKK1 from 11 patients and treated with control and DKK1-neutralizing antibodies for 4 to 6 weeks. Whereas bone mineral density (BMD) of the implanted myelomatous bone in control mice was reduced during the experimental period, the BMD in mice treated with anti-DKK1 increased from pretreatment levels (P < .001). Histologic examination revealed that myelomatous bones of anti-DKK1-treated mice had increased numbers of osteocalcin-expressing osteoblasts and reduced number of multinucleated TRAP-expressing osteoclasts. The bone anabolic effect of anti-DKK1 was associated with reduced MM burden (P < .04). Anti-DKK1 also significantly increased BMD of the implanted bone and murine femur in nonmyelomatous SCID-rab mice, suggesting that DKK1 is physiologically an important regulator of bone remodeling in adults. We conclude that DKK1 is a key player in MM bone disease and that blocking DKK1 activity in myelomatous bones reduces osteolytic bone resorption, increases bone formation, and helps control MM growth.

Multiple myeloma of the cervical spine: treatment strategies for pain and spinal instability

OBJECT

Metastases of multiple myeloma often occur in the cervical spine. These metastases may cause pain and associated spinal instability. The authors report the results of radiotherapy and surgical treatment for myeloma involving the cervical spine. The results of radiation therapy for multiple myeloma metastases to the cervical spine that cause clinical or radiographically documented instability have not been reported previously.

METHODS

A retrospective chart review of patients with multiple myeloma metastases to the cervical spine was undertaken. Between 1993 and 2005, 35 patients were treated with external-beam radiation and/or surgical stabilization at the University of Texas M. D. Anderson Cancer Center in Houston, Texas. Nineteen of 20 patients with sufficient follow-up data experienced resolution of their pain when treated with radiation without surgical intervention. Twenty-three patients had evidence of spinal instability on radiographic images; 15 of these were treated with radiation alone. Of these, 10 had sufficient follow-up data, and none showed any clinical progression of instability. Radiographic follow-up images demonstrated an arrest of further progression of instability and, in some cases, healing of pathological fractures by means of radiation alone.

CONCLUSIONS

The results of this series suggest that, in selected cases, external-beam radiation for multiple myeloma metastases to the cervical spine is an effective palliative treatment, even in cases involving clinical or radiographically documented instability.

Multiple myeloma bone disease: Pathophysiology of osteoblast inhibition

Multiple myeloma (MM) is a plasma cell malignancy characterized by a high capacity to induce osteolytic bone lesions. Bone destruction in MM results from increased osteoclast formation and activity that occur in close proximity to myeloma cells. However, histomorphometric studies have demonstrated that MM patients with osteolytic bone lesions have lower numbers of osteoblasts and decreased bone formation. This impaired bone formation plays a critical role in the bone-destructive process. Recently, the biologic mechanisms involved in the osteoblast inhibition induced by MM cells have begun to be elucidated. In this article, the pathophysiology underlying osteoblast inhibition in MM is reviewed.

The phenotypic plasticity of myeloma plasma cells as expressed by dedifferentiation into an immature, resilient, and apoptosis-resistant phenotype

PURPOSE

We previously showed the ability of osteoclasts to support myeloma plasma cell survival and proliferation in vivo and ex vivo. The aim of the current study was to investigate osteoclast-induced phenotypic changes associated with long-term survival of myeloma cells in coculture.

EXPERIMENTAL DESIGN

CD138-selected myeloma plasma cells from 16 patients were cocultured with human osteoclasts for up to 20 weeks.

RESULTS

Precultured cells were typically CD45(low/intermediate) CD38(high) CD138(high), CD19(-)CD34(-). After >6 weeks, the phenotype of cocultured myeloma cells consistently shifted to cells expressing CD45(intermediate/high) CD19(low) CD34(low). Expression of CD38 and CD138 were reduced to subpopulations with CD38(intermediate) and CD138(low) levels. Morphologically, cocultured plasma cells became plasmablastic. Blocking interleukin-6 activity did not affect the immature phenotype of myeloma cells. The effect of dexamethasone on myeloma cells cultured alone or in cocultures at baseline and after 6 weeks of coculture was determined. When baseline myeloma cells were cultured alone, dexamethasone significantly increased the percentage of apoptotic cells over the spontaneous rate. Conversely, myeloma cells recovered from cocultures had high survival rates and were resistant to dexamethasone-induced apoptosis. Long-term coculture of normal CD34-expressing hematopoietic stem cells (HSC) resulted in loss of CD34 expression, suggesting a common mechanism for osteoclast-induced myeloma and HSC plasticity.

CONCLUSIONS

This study indicates that myeloma cells have plasticity expressed by their ability to reprogram, dedifferentiate, and acquire autonomous survival properties.

A crosstalk between myeloma cells and marrow stromal cells stimulates production of DKK1 and interleukin-6: a potential role in the development of lytic bone disease and tumor progression in multiple myeloma

Multiple myeloma (MM) is a malignancy of antibody-secreting plasma cells. B-cell plasmacytomas stimulate bone resorption and angiogenesis, resulting in osteolytic lesions in the skeleton which persist upon successful treatment of the malignancy with chemotherapy. We found that an interaction between MM cells and mesenchymal stem cells (MSCs) from bone marrow stroma results in the formation and persistence of osteolytic bone lesions. It is known that MM cells activate osteoclast activity and secrete high levels of the Wnt inhibitor, Dickkopf-1, which prevents MSCs from differentiating into osteoblasts. We show that the Wnt signaling activator 6-bromoindirubin-3'-monoxime (BIO) releases MSCs from the osteoinhibitory effects of Dickkopf-1, whereas LiCl treatment does not. Additionally, we show that the >5-kDa fraction of MSC-conditioned medium promotes the proliferation of Dickkopf-1-secreting MM cells and that an interleukin-6 (IL-6)-neutralizing antibody blocks this effect. IL-6 expression levels were higher in undifferentiated MSCs than in MSCs treated with osteogenic medium, remained high in the presence of Dkk1, and were reduced by BIO treatment. Therefore, BIO treatment reduces the MSC-stimulated proliferation of MM cells and may enable MSCs to repair existing osteolytic lesions.

Myeloma cells block RUNX2/CBFA1 activity in human bone marrow osteoblast progenitors and inhibit osteoblast formation and differentiation

Decreased bone formation contributes to the development of bone lesions in multiple myeloma (MM) patients. In this study, we have investigated the effects of myeloma cells on osteoblast formation and differentiation and the potential role of the critical osteoblast transcription factor RUNX2/CBFA1 (Runt-related transcription factor 2/core-binding factor Runt domain alpha subunit 1) in the inhibition of osteoblastogenesis in MM. We found that human myeloma cells suppress the formation of human osteoblast progenitors in bone marrow (BM) cultures. Moreover, an inhibitory effect on osteocalcin, alkaline phosphatase, collagen I mRNA, protein expression, and RUNX2/CBFA1 activity by human preosteoblastic cells was observed in cocultures with myeloma cells. The inhibitory effect was more pronounced in the cell-to-cell contact conditions compared with those without the contact and involved the very late antigen 4 (VLA-4) integrin system. Among the soluble osteoblast inhibitors screened, we show the potential contribution of interleukin-7 (IL-7) in the inhibitory effect on osteoblast formation and RUNX2/CBFA1 activity by human myeloma cells in coculture. Finally, our in vitro results were supported in vivo by the finding of a significant reduction in the number of Runx2/Cbfa1-positive cells in the BM biopsies of patients with MM who had osteolytic lesions compared with those who did not have bone lesions, suggesting the critical involvement of RUNX2/CBFA1 in the decreased bone formation in MM.

Osteoprotegerin in the Inner Ear May Inhibit Bone Remodeling in the Otic Capsule

OBJECTIVES

To elucidate factors that may be responsible for the inhibition of remodeling of bone within the otic capsule.

METHODS

Expression of osteoprotegerin (OPG), receptor activator of nuclear factor kappa B (RANK), and RANK ligand (RANKL) were assayed in samples of bone obtained from the otic capsule, calvarium, and femur, and from the soft tissue within the cochlea using semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) in mice. Immunostaining was used for histologic localization of the gene products. An enzyme-linked immunosorbent assay (ELISA) was used to quantify the amount of OPG within perilymph, serum, and cerebrospinal fluid. The micro-anatomy of the interface between the otic capsule and the fluid spaces of the cochlea was investigated by brightfield and phase-contrast microscopy and by three-dimensional reconstruction in the mouse and human.

RESULTS

OPG, a powerful inhibitor of bone remodeling, was expressed at extremely high levels within the soft tissue of the cochlea and was present in the perilymph at very high concentrations. The OPG produced within the inner ear may diffuse into the surrounding otic capsule, where it may be responsible for inhibition of bone turnover. Our anatomic studies revealed an extensive system of interconnected canaliculi within the otic capsule that had direct openings into the fluid spaces of the inner ear, thus providing a possible anatomic route for the diffusion of OPG from the inner ear into the surrounding bone.

CONCLUSION

OPG, a potent inhibitor of osteoclast formation and function, is expressed at high levels within the inner ear and is secreted into the perilymph and the surrounding bone and may serve to inhibit active bone remodeling within the otic capsule, especially immediately adjacent to the cochlea. By this means, the cochlear soft tissue may control the nature of the surrounding petrous bone.

CCR1 chemokines promote the chemotactic recruitment, RANKL development, and motility of osteoclasts and are induced by inflammatory cytokines in osteoblasts

Chemoattractants that recruit OC precursors to locally inflamed sites of resorption are not well known. A chemokine receptor, CCR1, was expressed in OC precursors and elevated in mature OCs, and its ligands promoted OC precursor recruitment, RANKL development, and OC motility. Cytokines induced OB release of such chemokines, which may therefore significantly contribute to inflammatory bone loss.

INTRODUCTION

Chemokines, primarily of two major (CXC, CC) families, are essential signals for the trafficking and localization of circulating hematopoietic cells into tissues. However, little is known about their potential roles in osteoclast (OC) recruitment, development, or function. Previously, we analyzed CXC receptors in murine OC precursors and found high expression of CXCR4 that mediated their stromal-derived factor-1(SDF-1)-induced chemotaxis and collagen invasion. Here, we investigated if CC receptors and ligands, which are elevated in inflammatory and other osteolytic diseases, also play important roles in the recruitment, formation, or activity of murine bone-resorptive OCs.

MATERIALS AND METHODS

CC chemokine receptor (CCR) mRNA expression was analyzed during OC formation induced by RANKL in murine RAW 264.7 cells and primary marrow cells. Corresponding CC chemokines were tested for their ability to elicit precursor chemotaxis or OC development, or to influence motility, bone resorption, adhesion, or survival in RANKL-differentiated OCs. Constitutive and inflammatory cytokine-induced release of the chemokines macrophage inflammatory protein-1alpha (MIP-1alpha) and regulated on activation, normal T-cell expressed and secreted (RANTES) was measured by ELISA for OCs, osteoblasts (OBs), and their precursor cells.

RESULTS

CCR1 was expressed in murine marrow cells, the most prominent CCR in RAW cells, and upregulated by RANKL in marrow or RAW cells. Chemokines that bind CCR1 (MIP-1alpha, RANTES, and monocyte chemoattractant protein-3 [MCP-3]) were produced to varying degrees by murine OCs, OBs, and their precursors, and markedly increased by interleukin (IL)-1alpha and TNFalpha in differentiating OBs. RANTES, and especially MIP-1alpha, increased mature OC motility, but did not alter OC resorption activity, adhesion, or survival. All three chemokines stimulated chemotaxis of marrow or RAW cell precursors, leading to the greater formation of OCs (in number and size) after RANKL development of such chemoattracted marrow cells. All three chemokines also directly and dramatically enhanced OC formation in marrow cultures, through a pathway dependent on the presence of RANKL but without altering RANK expression.

CONCLUSIONS

Pathological increases in secretion of these chemokines from activated OBs or other cells may potently stimulate the chemotactic recruitment and RANKL formation of bone-resorptive OCs, thereby exacerbating local osteolysis in multiple skeletal diseases.

T cells support osteoclastogenesis in an in vitro model derived from human multiple myeloma bone disease: the role of the OPG/TRAIL interaction

The development of multiple myeloma (MM) bone disease is mediated by increased number and activity of osteoclasts (OCs). Using an in vitro osteoclastogenesis model consisting of unstimulated and unfractionated peripheral blood mononuclear cells (PBMCs) from patients with MM, we showed that T cells support the formation of OCs with longer survival. Different from T-cell-depleted MM PBMC cultures, exogenous macrophage-colony stimulating factor (M-CSF) and receptor activator of nuclear factor-kappaB ligand (RANKL) were necessary for the formation of OCs; however, they did not exhibit longer survival. We found up-regulated production of RANKL, osteoprotegerin (OPG), and TNF-related apoptosis-inducing ligand (TRAIL) by fresh MM T cells. Despite high OPG levels, the persistence of osteoclastogenesis can be related to the formation of the OPG/TRAIL complex demonstrated by immunoprecipitation experiments and the addition of anti-TRAIL antibody which decreases OC formation. OCs overexpressed TRAIL decoy receptor DcR2 in the presence of MM T cells and death receptor DR4 in T-cell-depleted cultures. In addition, increased Bcl-2/Bax (B-cell lymphoma-2/Bcl2-associated protein X) ratio, following Bcl-2 up-regulation, was detected in OCs generated in the presence of T cells. Our results highlight that MM T cells support OC formation and survival, possibly involving OPG/TRAIL interaction and unbalanced OC expression of TRAIL death and decoy receptors.