Human breast cancer cells induced angiogenesis, recruitment, and activation of osteoclasts in osteolytic metastasis

Osteosarcoma and Metastasis Associated Bone Degradation-A Tale of Osteoclast and Malignant Cell Cooperativity

Cancer-induced bone degradation is part of the pathological process associated with both primary bone cancers, such as osteosarcoma, and bone metastases originating from, e.g., breast, prostate, and colon carcinomas. Typically, this includes a cancer-dependent hijacking of processes also occurring during physiological bone remodeling, including osteoclast-mediated disruption of the inorganic bone component and collagenolysis. Extensive research has revealed the significance of osteoclast-mediated bone resorption throughout the course of disease for both primary and secondary bone cancer. Nevertheless, cancer cells representing both primary bone cancer and bone metastasis have also been implicated directly in bone degradation. We will present and discuss observations on the contribution of osteoclasts and cancer cells in cancer-associated bone degradation and reciprocal modulatory actions between these cells. The focus of this review is osteosarcoma, but we will also include relevant observations from studies of bone metastasis. Additionally, we propose a model for cancer-associated bone degradation that involves a collaboration between osteoclasts and cancer cells and in which both cell types may directly participate in the degradation process.

Osteoclast Fusion: Physiological Regulation of Multinucleation through Heterogeneity-Potential Implications for Drug Sensitivity

Classically, osteoclast fusion consists of four basic steps: (1) attraction/migration, (2) recognition, (3) cell-cell adhesion, and (4) membrane fusion. In theory, this sounds like a straightforward simple linear process. However, it is not. Osteoclast fusion has to take place in a well-coordinated manner-something that is not simple. In vivo, the complex regulation of osteoclast formation takes place within the bone marrow-in time and space. The present review will focus on considering osteoclast fusion in the context of physiology and pathology. Special attention is given to: (1) regulation of osteoclast fusion in vivo, (2) heterogeneity of osteoclast fusion partners, (3) regulation of multi-nucleation, (4) implications for physiology and pathology, and (5) implications for drug sensitivity and side effects. The review will emphasize that more attention should be given to the human in vivo reality when interpreting the impact of in vitro and animal studies. This should be done in order to improve our understanding of human physiology and pathology, as well as to improve anti-resorptive treatment and reduce side effects.

Zoledronate Inhibits Osteoclast Differentiation via Suppressing Vascular Endothelial Growth Factor Receptor 2 Expression

Bisphosphonate-related osteonecrosis of the jaw (ONJ) is a major oral complication; however, its pathogenesis remains unclear. Impairment of osteoclast differentiation by bisphosphonates may be associated with the pathogenesis of ONJ. In our previous study, we reported that the expression of the gene encoding nuclear factor of activated T cells c1 (NFATc1), a known osteoclast differentiation marker, was significantly silenced by zoledronate, a bisphosphonate, in mouse osteoclast precursor cells (mOCPCs) using cDNA microarray. In the present study, the expression value of the NFATc1 gene was regarded as a cut-off and genes whose expression value was significantly decreased compared with that of the NFATc1 gene were extracted in mOCPCs. For validation, CD11b-positive (CD11b+) cells were used, which were purified from human peripheral blood mononuclear cells as human OCPCs. A total of 19 genes were identified; sequential expression analysis revealed that the gene encoding vascular endothelial growth factor receptor 2 (VEGFR2) was frequently silenced by zoledronate in CD11b+ cells. Furthermore, the number of tartrate-resistant acid phosphatase-positive multinucleated cells was decreased by VEGFR2 suppression using a VEGFR2 neutralizing antibody. Zoledronate inhibits human osteoclast differentiation via suppressing VEGFR2 expression. These results suggest that low expression of VEGFR2 in OCPCs may be involved in the pathogenesis of zoledronate-induced ONJ. The understanding of the role of VEGFR2 on bone remodeling is important to elucidate the pathogenesis of bisphosphonate-related ONJ.

Therapeutic inhibition of breast cancer bone metastasis progression and lung colonization: breaking the vicious cycle by targeting α5β1 integrin

At diagnosis, 10 % of breast cancer patients already have locally advanced or metastatic disease; moreover, metastasis eventually develops in at least 40 % of early breast cancer patients. Osteolytic bone colonization occurs in 80-85 % of metastatic breast cancer patients and is thought to be an early step in metastatic progression. Thus, breast cancer displays a strong preference for metastasis to bone, and most metastatic breast cancer patients will experience its complications. Our prior research has shown that the α5β1 integrin fibronectin receptor mediates both metastatic and angiogenic invasion. We invented a targeted peptide inhibitor of activated α5β1, Ac-PHSCN-NH2 (PHSCN), as a validated lead compound to impede both metastatic invasion and neovascularization. Systemic PHSCN monotherapy prevented disease progression for up to 14 months in Phase I clinical trial. Here, we report that the next-generation construct, Ac-PhScN-NH2 (PhScN), which contains D-isomers of histidine (h) and cysteine (c), is greater than 100,000-fold more potent than PHSCN at blocking basement membrane invasion. Moreover, PhScN is also up to 10,000-fold more potent than PHSCN at inhibiting lung extravasation and colonization in athymic mice for both MDA-MB-231 metastatic and SUM149PT inflammatory breast cancer cells. Furthermore, we show that systemic treatment with 50 mg/kg PhScN monotherapy reduces established intratibial MDA-MB-231 bone colony progression by 80 %. Thus, PhScN is a highly potent, well-tolerated inhibitor of both lung colonization and bone colony progression.

VEGF and bone cell signalling: an essential vessel for communication?

Vascular endothelial growth factor (VEGF) is an endothelial cell survival factor and is required for effective coupling of angiogenesis and osteogenesis. Although central to bone homeostasis, repair and the pathobiology that affect these processes, the precise mechanisms coupling endothelial cell function within bone formation and remodelling remain unclarified. This review will (i) focus on the potential directionality of VEGF signalling in adult bone by identifying the predominant source of VEGF within the bone microenvironment, (ii) will summarize current VEGF receptor expression studies by bone cells and (iii) will provide evidence for a role for VEGF signalling during postnatal repair and osteoporosis. A means of understanding the directionality of VEGF signalling in adult bone would allow us to most effectively target angiogenic pathways in diseases characterized by changes in bone remodelling rates and enhance bone repair when compromised.

Inhibition of p38-MAPK signaling pathway attenuates breast cancer induced bone pain and disease progression in a murine model of cancer-induced bone pain

BACKGROUND

Mechanisms driving cancer-induced bone pain are poorly understood. A central factor implicated to be a key player in the process of tumorigenesis, osteoclastogenesis and nociception is p38 MAPK. We determined the role of p38 MAPK in a mouse model of breast cancer induced bone pain in which mixed osteolytic and osteoblastic remodeling occurs.

RESULTS

In cancer-treated mice, acute as well as chronic inhibition of p38 MAPK with SB203580 blocked flinching and guarding behaviors in a dose-dependent manner whereas no effect on thresholds to tactile stimuli was observed. Radiographic analyses of bones demonstrated that chronic inhibition of p38 MAPK reduced bone loss and incidence of spontaneous fracture in cancer-treated mice. Histological analysis of bones collected from mice treated with the p38 MAPK inhibitor showed complete absence of osteoblastic growth in the intramedullary space as well as significantly reduced tumor burden.

CONCLUSIONS

Blockade of non-evoked pain behaviors but not hypersensitivity suggests differences in the underlying mechanisms of specific components of the pain syndrome and a possibility to individualize aspects of pain management. While it is not known whether the role of p38 MAPK signaling can be expanded to other cancers, the data suggest a need for understanding molecular mechanisms and cellular events that initiate and maintain cancer-induced bone pain for effective management for both ongoing pain as well as breakthrough pain.

Transforming growth factor-{beta} coordinately induces suppressor of cytokine signaling 3 and leukemia inhibitory factor to suppress osteoclast apoptosis

Local release of TGF-beta during times of high bone turnover leads to elevated levels within the bone microenvironment, and we have shown that TGF-beta suppresses osteoclast apoptosis. Therefore, understanding the influences of TGF-beta on bone resorbing osteoclasts is critical to the design of therapies to reduce excess bone loss. Here we investigated the mechanisms by which TGF-beta sustains suppression of osteoclast apoptosis. We found TGF-beta rapidly increased leukemia inhibitory factor (LIF) expression and secretion by phosphorylated mothers against decapentaplegic-dependent and -independent signaling pathways. TGF-beta also induced suppressor of cytokine signaling 3 (SOCS3) expression, which was required for TGF-beta or LIF to promote osteoclast survival by. Blocking LIF or SOCS3 blocked TGF-beta promotion of osteoclast survival, confirming that LIF and SOCS3 expression are necessary for TGF-beta-mediated suppression of osteoclast apoptosis. Investigation of the mechanisms by which LIF promotes osteoclast survival revealed that LIF-induced expression of Bcl-X(L) and repressed Bcl-2 interacting domain expression by activating MAPK kinase, AKT, and nuclear factor-kappaB pathways. Suppression of Janus kinase/signal transducer and activator of transcription signaling further increased Bcl-X(L) expression and enhanced osteoclast survival, supporting that this pathway is not involved in prosurvival effects of TGF-beta and LIF. These data show that TGF-beta coordinately induces LIF and SOCS3 to promote prosurvival signaling. This alters the ratio of prosurvival Bcl2 family member Bcl-X(L) to proapoptotic family member Bcl-2 interacting domain, leading to prolonged osteoclast survival.

High oxygen tension prolongs the survival of osteoclast precursors via macrophage colony-stimulating factor

The oxygen tension affects the function, differentiation, and transformation of various cells, including bone cells. In pathological conditions such as rheumatoid arthritis (RA), rapidly destructive arthropathy, and primary or metastatic tumors, severe bone destruction or osteolysis occurs. Abundant blood vessels are often observed around these destructive lesions. At such sites, we have confirmed the increased production of reactive oxygen species (ROS) induced by a high oxygen tension and/or oxidative stress, as well as numerous osteoclasts detectable by immunohistochemistry. These findings suggest that osteoclasts are influenced by the high oxygen tension in pathological bone lesions because the zone around blood vessels has a relatively high oxygen tension. In this study, we investigated the effects of oxygen tension on osteoclastogenesis by culturing human CD14-positive cells (osteoclast precursors) with or without osteoblast-like supporting cells (Saos-4/3 cells) under a normal oxygen tension (20% O(2)) or a high oxygen tension (40% O(2)). A high oxygen tension markedly prolonged the duration of osteoclast precursor formation in the presence of supporting cells, and also markedly and persistently increased the production of macrophage colony stimulating factor (M-CSF) by supporting cells. Furthermore, we found an increase of cells expressing M-CSF and cells positive for tartrate-resistant acid phosphatase (TRAP) in hypervascular destructive bone lesions of RA patients where ROS were also abundant.

Nitrogen-containing bisphosphonate, YM529/ONO-5920, inhibits macrophage inflammatory protein 1 alpha expression and secretion in mouse myeloma cells

Macrophage inflammatory protein 1 alpha (MIP-1 alpha) is detected at high concentrations in patients with multiple myeloma, and it is thought to play an important role in the etiology of multiple myeloma and osteolysis. Thus, we investigated whether or not YM529/ONO-5920, a new bisphosphonate, inhibited MIP-1 alpha mRNA expression in, and MIP-1 alpha secretion from, mouse myeloma cells. When the cells were stimulated by lipopolysaccharide, increased MIP-1 alpha mRNA expression and MIP-1 alpha secretion were observed. YM529/ONO-5920 inhibited MIP-1 alpha mRNA expression and MIP-1 alpha secretion in a concentration-dependent manner. A transient increase in the phosphorylation of extracellular-regulated kinase 1/2 (ERK1/2) and Akt was observed after lipopolysaccharide stimulation. After YM529/ONO-5920 was given, there was no transient increase in the phosphorylation of ERK1/2 or Akt. These results indicated that YM529/ONO-5920 inhibited the expression and secretion of MIP-1 alpha through blocking the signaling pathway of the Ras/mitogen-activated protein kinase kinase/ERK and Ras/phosphatidylinositol-3 kinase/Akt. Accordingly, YM529/ONO-5920 appears to have promise for use in effective future therapy for osteolysis and myeloma cell growth that depends on MIP-1 alpha.

A non-RGD-based integrin binding peptide (ATN-161) blocks breast cancer growth and metastasis in vivo

PURPOSE

Integrins are expressed by numerous tumor types including breast cancer, in which they play a crucial role in tumor growth and metastasis. In this study, we evaluated the ability of ATN-161 (Ac-PHSCN-NH2), a 5-mer capped peptide derived from the synergy region of fibronectin that binds to alpha5beta1 and alphavbeta3 in vitro, to block breast cancer growth and metastasis.

EXPERIMENTAL DESIGN

MDA-MB-231 human breast cancer cells were inoculated s.c. in the right flank, or cells transfected with green fluorescent protein (MDA-MB-231-GFP) were inoculated into the left ventricle of female BALB/c nu/nu mice, resulting in the development of skeletal metastasis. Animals were treated with vehicle alone or by i.v. infusion with ATN-161 (0.05-1 mg/kg thrice a week) for 10 weeks. Tumor volume was determined at weekly intervals and tumor metastasis was evaluated by X-ray, microcomputed tomography, and histology. Tumors were harvested for histologic evaluation.

RESULT

Treatment with ATN-161 caused a significant dose-dependent decrease in tumor volume and either completely blocked or caused a marked decrease in the incidence and number of skeletal as well as soft tissue metastases. This was confirmed histologically as well as radiographically using X-ray and microcomputed tomography. Treatment with ATN-161 resulted in a significant decrease in the expression of phosphorylated mitogen-activated protein kinase, microvessel density, and cell proliferation in tumors grown in vivo.

CONCLUSION

These studies show that ATN-161 can block breast cancer growth and metastasis, and provides a rationale for the clinical development of ATN-161 for the treatment of breast cancer.

Pathogenic role of connective tissue growth factor (CTGF/CCN2) in osteolytic metastasis of breast cancer

The role of CTGF/CCN2 in osteolytic metastasis by breast cancer cells and its mechanism of action were studied. Osteolytic metastasis accompanied by CCN2 and PTHrP overproduction was efficiently inhibited by an anti-CCN2 antibody. Furthermore, we found that CCN2 was induced by PTHrP through PKA-, PKC-, and ERK-mediated pathways therein.

INTRODUCTION

Connective tissue growth factor (CTGF/CCN2) is a mediator of local angiogenesis induced by breast cancer, but its role in osteolytic metastasis has not been evaluated. PTH-related peptide (PTHrP) is another critical factor in the development of the osteolytic metastasis. Using both in vivo and in vitro approaches, we studied whether/how neutralization of CCN2 prevented bone metastasis and how PTHrP signaling is related.

MATERIALS AND METHODS

A mouse model of bone metastasis by human breast cancer cell line MDA231 was treated with a CCN2-neutralizing antibody, and osteolytic bone metastases were assessed on radiographs and immunohistochemistry. Ccn2 gene expression and transcription were examined by Northern blot and luciferase analysis. Immunoblot analysis and kinase inhibitors were used to identify the signaling pathways implicated. Anti-angiogenic/osteoclastogenic effects of ccn2 downregulation were also evaluated.

RESULTS

Treatment of mice with a CCN2-neutralizing antibody greatly decreased osteolytic bone metastasis, microvasculature, and osteoclasts involved. The antibody also suppressed the growth of subcutaneous tumor in vivo and proliferation and migration of human umbilical vein endothelial cells (HUVECs) in vitro. Downregulation of ccn2 also repressed osteoclastogenesis. CCN2 expression was specifically observed in cancer cells producing PTHrP and type I PTH/PTHrP receptor (PTH1R) invaded the bone marrow, and PTHrP strongly upregulated ccn2 in MDA231 cells in vitro. Activation of protein kinase C (PKC) and protein kinase A (PKA) was necessary and sufficient for the stimulation of ccn2 by PTHrP. Indeed, inhibition of the extracellular signal-regulated kinase (ERK1/2), PKC, or PKA by specific inhibitors counteracted the stimulation of ccn2 expression. Incubation of MDA231 cells with PTHrP induced the activation of ERK1/2. Consistent with these findings, inhibition of PKC prevented PTHrP-induced ERK1/2 activation, whereas 12-O-tetradecanoylphorbol13-acetate (TPA), a stimulator of PKC, upregulated it.

CONCLUSIONS

CCN2 was critically involved in osteolytic metastasis and was induced by PKA- and PKC-dependent activation of ERK1/2 signaling by PTHrP. Thus, CCN2 may be a new molecular target for anti-osteolytic therapy to shut off the PTHrP-CCN2 signaling pathway.

Breast cancer cells with inhibition of p38alpha have decreased MMP-9 activity and exhibit decreased bone metastasis in mice

p38 belongs to a family of mitogen-activated protein kinases, which transfer extracellular signals into intracellular responses. p38 is also frequently detected in clinical breast cancer specimens, but its role as a prognostic factor is not known. Of the various p38 isoforms, p38alpha has been shown to mediate the in vitro invasiveness of breast cancer cells through up-regulation of urokinase plasminogen activator (uPA). We studied the role of p38alpha in breast cancer bone metastases, using dominant negative blockade approach. Human MDA-MB-231 breast cancer clones stably expressing dominant negative p38alpha (p38/AF) exhibited decreased basal MMP-9 activity. TGF-beta1-induced MMP-9 activity was also blunted in these clones, as compared with controls in which TGF-betal up-regulated MMP-9 activity. Consistent with these findings, SB202190, a specific p38 inhibitor, also inhibited TGF-beta1-induced MMP-9 activity in parental cells. The p38/AF clones exhibited also reduced uPA production after growth on vitronectin and decreased cell motility, as compared with controls. VEGF production levels in all the studied clones were similar. The p38/AF clone, which had similar in vitro growth rate as the control pcDNA3 clone, formed significantly less bone metastases in a mouse model, as compared with the control clone. In conclusion, inhibition of the p38alpha pathway results in decreased MMP-9 activity, impaired uPA expression and decreased motility, all of which may contribute to the decreased formation of bone metastasis.

Alterations of microvascular density in bone metastases of adenocarcinomas

Bone may provide an extremely fertile microenvironment for angiogenesis. Experimental investigations indicate angiogenesis as a major regulator of bone metastasis development. Vascularization and angiogenic potential is known for most of the primary tumor types, but no studies investigated angiogenesis in bone metastases of human cancers. We have evaluated microvessel density of bone metastases of various cancer types (all adenocarcinomas) and compared to their primary tumors in paraffin samples of 39 patients. Microvessel density was determined by using the hot spot method and the blood vessel marker, CD34. The most vascularized adenocarcinoma was found to be renal cell cancer followed by lung adenocarcinoma, while breast cancer was heterogenous in this respect. Two patterns of modulation of the angiogenic phenotype in the bone metastases emerged in this study, which seemed to be cancer type specific: decreased angiogenic potential characterizing 45% of renal cell cancers and breast cancers of high vascularity in their primary, and increased angiogenic potential characterizing 40% of lung adenocarcinomas and breast cancers of low vascularity in their primary lesion. Our data demonstrate that i., the vascularization of bone metastases is frequently altered compared to the primary tumors, ii., patterns are different in the case of various cancer types. The tumor-type specific alterations of the angiogenic phenotype of cancers, metastatic to the bone, can have a clinical significance when angiosuppressive therapies are considered.

Tumor necrosis factor-alpha induces interleukin-6 production via extracellular-regulated kinase 1 activation in breast cancer cells

Interleukin-6 (IL-6) and interleukin-11 (IL-11) are frequently produced by breast cancer cells. These interleukins promote osteoclast formation and may mediate osteolysis at the site of breast cancer bone metastases. Transforming growth factor-beta (TGF-beta), tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) up-regulate IL-6 and IL-11 production in a cytokine-dependent fashion in breast cancer cells, but very little is known about their intracellular signaling pathways in breast cancer cells. To study TGF-beta, TNF-alpha and IL-1beta regulation of IL-6 and IL-11 production in human MDA-MB-231 breast cancer cells, we established single cell clones stably expressing dominant negative (DN) forms of the mitogen-activated protein kinases p38 (p38/AF) or ERK1 (ERK1K71R). We show here, that while basal, TGF-beta and IL-1beta induced IL-6 production was similar in parental cells and in pcDNA3 control, ERK1K71R and p38/AF clones, TNF-alpha induced IL-6 production was blunted in the ERK1K71R clones. TGF-beta and IL-1beta, but not TNF-alpha, induced IL-11 production in parental MDA-MB-231 cells. Similar findings were detected in clones stably expressing p38/AF and ERK1K71R, which did not change basal IL-11 production either. In conclusion, TNF-alpha induced IL-6 production is mediated via ERK1 activation in MDA-MB-231 cells. These observations may be helpful in designing new anti-osteolytic therapies.

Bone marrow angiogenesis and its correlation with other disease characteristics in multiple myeloma in stage I versus stage II-III

PURPOSE

We studied bone marrow angiogenesis in different stages of multiple myeloma according to the Durie and Salmon classification and its correlations with other disease characteristics.

METHODS

Sixty-five immunohistochemical CD34-stained, paraffin-embedded bone marrow biopsies of multiple myeloma patients and 12 controls were studied. The mean number of microvessels per area in each sample was determined as the microvessel density (MVD). In addition, plasma cell infiltration of the bone marrow, serum beta2-microglobulin, immunoglobulin levels, C-reactive protein, and serum calcium concentration were measured in 22 patients with stage I multiple myeloma and in 43 patients in stage II-III.

RESULTS

In myeloma patients, the bone marrow MVD was significantly higher than in controls (P<0.001). In 43 patients with stage II-III multiple myeloma, MVD was significantly higher than in 22 patients with stage I (median MVD 46 and 21 vessels/mm(2), respectively, P=0.005). Additionally, in stage II-III the bone marrow MVD correlated positively with the bone marrow plasma cell infiltration (r=0.55, P<0.001) and the serum beta2-microglobulin level (r=0.53, P<0.001), while in stage I patients no correlation could be found.

CONCLUSIONS

Angiogenesis is significantly increased in stage II-III myeloma in comparison to stage I. In stages II-III, bone marrow angiogenesis is correlated with plasma cell infiltration and serum beta2-microglobulin levels.

Early detection of bone metastases in a murine model using fluorescent human breast cancer cells: application to the use of the bisphosphonate zoledronic acid in the treatment of osteolytic lesions

A very common metastatic site for human breast cancer is bone. The traditional bone metastasis model requires human MDA-MB-231 breast carcinoma cell inoculation into the left heart ventricle of nude mice. MDA-MB-231 cells usually develop osteolytic lesions 3-4 weeks after intracardiac inoculation in these animals. Here, we report a new approach to study the formation of bone metastasis in animals using breast carcinoma cells expressing the bioluminescent jellyfish protein (green fluorescent protein [GFP]). We first established a subclone of MDA-MB-231 cells by repeated in vivo passages in bone using the heart injection model. On stable transfection of this subclone with an expression vector for GFP and subsequent inoculation of GFP-expressing tumor cells (B02/GFP.2) in the mouse tail vein, B02/GFP.2 cells displayed a unique predilection for dissemination to bone. Externally fluorescence imaging of live animals allowed the detection of fluorescent bone metastases approximately 1 week before the occurrence of radiologically distinctive osteolytic lesions. The number, size, and intensity of fluorescent bone metastases increased progressively with time and was indicative of breast cancer cell progression within bone. Histological examination of fluorescent long bones from B02/GFP.2-bearing mice revealed the occurrence of profound bone destruction. Treatment of B02/GFP.2-bearing mice with the bisphosphonate zoledronic acid markedly inhibited the progression of established osteolytic lesions and the expansion of breast cancer cells within bone. Overall, this new bone metastasis model of breast cancer combining both fluorescence imaging and radiography should provide an invaluable tool to study the effectiveness of pharmaceutical agents that could suppress cancer colonization in bone.