Breast cancer cells release factors that induced apoptosis in human bone marrow stromal cells

Bone metastatic mammary tumor cell-derived extracellular vesicles inhibit osteoblast maturation via JNK signaling

The metastases of breast cancer to bone often cause osteolytic lesions not only by stimulating osteoclasts to resorb the bone but also by inhibiting osteoblasts from bone formation. Although tumor cell-derived extracellular vesicles (EVs) promote osteoclast differentiation and bone resorption, their roles in osteoblast differentiation and functions have not been elucidated. In this study, we investigated the effects of breast cancer cell-derived EVs on osteoblast differentiation and functions in vitro. We found that upon osteogenic induction, 4T1 bone metastatic mouse mammary tumor cell-derived EVs (4T1-EVs) were inhibited matrix mineralization of ST2 mouse bone marrow stromal cells. Temporal expression analysis of osteoblast marker genes, including runt-related transcription factor 2 (Runx2), osterix (Osx), alkaline phosphatase (Alp), collagen type I (Col1a1), bone sialoprotein (Bsp), and osteocalcin (Bglap) revealed that 4T1-EVs decreased their expression during the late stage of osteoblast differentiation. Elevated levels of c-Jun N-terminal kinase (JNK) phosphorylation, upon osteogenic induction, were diminished by 4T1-EVs, significantly. In contrast, the nullification of reduced JNK phosphorylation by anisomycin, a potent JNK activator, increased the expression levels of osteoblast differentiation markers. Overall, our data indicated that 4T1-EVs affect osteoblast maturation, at least partially, through the regulation of JNK activity, which provides novel insights into the pathological impact of osteolytic bone metastasis and the role of EVs in osteoblast differentiation.

Myofibroblast androgen receptor expression determines cell survival in co-cultures of myofibroblasts and prostate cancer cells in vitro

Fibroblasts express androgen receptor (AR) in the normal prostate and during prostate cancer development. We have reported that loss of AR expression in prostate cancer-associated fibroblasts is a poor prognostic indicator. Here we report outcomes of direct and indirect co-cultures of immortalised AR-positive (PShTert-AR) or AR-negative (PShTert) myofibroblasts with prostate cancer cells.

In the initial co-cultures the AR-negative PC3 cell line was used so AR expression and signalling were restricted to the myofibroblasts. In both direct and indirect co-culture with PShTert-AR myofibroblasts, paracrine signalling to the PC3 cells slowed proliferation and induced apoptosis. In contrast, PC3 cells proliferated with PShTert myofibroblasts irrespective of the co-culture method. In direct co-culture PC3 cells induced apoptosis in and destroyed PShTerts by direct signalling. Similar results were seen in direct co-cultures with AR-negative DU145 and AR-positive LNCaP and C4-2B prostate cancer cell lines. The AR ligand 5α-dihydrotestosterone (DHT) inhibited the proliferation of the PShTert-AR myofibroblasts, thereby reducing the extent of their inhibitory effect on cancer cell growth.

These results suggest loss of stromal AR would favour prostate cancer cell growth in vivo, providing an explanation for the clinical observation that reduced stromal AR is associated with a poorer outcome.

Anti-resorptive osteonecrosis of the jaws: facts forgotten, questions answered, lessons learned

Osteonecrosis of the jaws associated with bisphosphonate and other anti-resorptive medications (ARONJ) has historically been a poorly understood disease process in terms of its pathophysiology, prevention and treatment since it was originally described in 2003. In association with its original discovery 11 years ago, non-evidence based speculation of these issues have been published in the international literature and are currently being challenged. A critical analysis of cancer patients with ARONJ, for example, reveals that their osteonecrosis is nearly identical to that of cancer patients who are naive to anti-resorptive medications. In addition, osteonecrosis of the jaws is not unique to patients exposed to anti-resorptive medications, but is also seen in patients with osteomyelitis and other pathologic processes of the jaws. This article represents a review of facts forgotten, questions answered, and lessons learned in general regarding osteonecrosis of the jaws.

Effects of methylthiouracil on the proliferation and apoptosis of rat bone marrow stromal cells

The aim of the present study was to investigate the effects of methylthiouracil (MTU) on the proliferation and apoptosis of rat bone marrow stromal cells (BMSCs). Rat BMSCs were isolated, cultured in vitro and treated with various concentrations of MTU. Cell growth curves were determined using the Cell Counting Kit-8 method and the effect of MTU on BMSCs in a logarithmic growth phase was observed. BMSC apoptosis following MTU treatment was detected by flow cytometry. The experimental results demonstrated that the proliferation-inhibition effect was gradually enhanced with increasing MTU concentrations and the extension of treatment time. Statistically significant differences were observed between the treatment and the control groups (P<0.05). In addition, the BMSC apoptosis rate gradually increased with increasing drug concentrations and treatment time extension; statistically significant differences were observed between the treatment and the control groups (P<0.05). Therefore, the results of the present study demonstrated that MTU inhibited the proliferation of BMSCs and promoted apoptosis, indicating the cytotoxic effects of MTU on BMSCs.

Behaviour of mesenchymal stem cells from bone marrow of untreated advanced breast and lung cancer patients without bone osteolytic metastasis

Tumour cells can find in bone marrow (BM) a niche rich in growth factors and cytokines that promote their self-renewal, proliferation and survival. In turn, tumour cells affect the homeostasis of the BM and bone, as well as the balance among haematopoiesis, osteogenesis, osteoclastogenesis and bone-resorption. As a result, growth and survival factors normally sequestered in the bone matrix are released, favouring tumour development. Mesenchymal stem cells (MSCs) from BM can become tumour-associated fibroblasts, have immunosuppressive function, and facilitate metastasis by epithelial-to-mesenchymal transition. Moreover, MSCs generate osteoblasts and osteocytes and regulate osteoclastogenesis. Therefore, MSCs can play an important pro-tumorigenic role in the formation of a microenvironment that promotes BM and bone metastasis. In this study we showed that BM MSCs from untreated advanced breast and lung cancer patients, without bone metastasis, had low osteogenic and adipogenic differentiation capacity compared to that of healthy volunteers. In contrast, chondrogenic differentiation was increased. Moreover, MSCs from patients had lower expression of CD146. Finally, our data showed higher levels of Dkk-1 in peripheral blood plasma from patients compared with healthy volunteers. Because no patient had any bone disorder by the time of the study we propose that the primary tumour altered the plasticity of MSCs. As over 70 % of advanced breast cancer patients and 30-40 % of lung cancer patients will develop osteolytic bone metastasis for which there is no total cure, our findings could possibly be used as predictive tools indicating the first signs of future bone disease. In addition, as the MSCs present in the BM of these patients may not be able to regenerate bone after the tumour cells invasion into BM/bone, it is possible that they promote the cycle between tumour cell growth and bone destruction.

The role of versican G3 domain in regulating breast cancer cell motility including effects on osteoblast cell growth and differentiation in vitro - evaluation towards understanding breast cancer cell bone metastasis

BACKGROUND

Versican is detected in the interstitial tissues at the invasive margins of breast carcinoma, is predictive of relapse, and negatively impacts overall survival rates. The versican G3 domain is important in breast cancer cell growth, migration and bone metastasis. However, mechanistic studies evaluating versican G3 enhanced breast cancer bone metastasis are limited.

METHODS

A versican G3 construct was exogenously expressed in the 66c14 and the MC3T3-E1 cell line. Cells were observed through light microscopy and viability analyzed by Coulter Counter or determined with colorimetric proliferation assays. The Annexin V-FITC apoptosis detection kit was used to detect apoptotic activity. Modified Chemotactic Boyden chamber migration invasion assays were applied to observe tumor migration and invasion to bone stromal cells and MC3T3-E1 cells. Alkaline phosphatase (ALP) staining and ALP ELISA assays were performed to observe ALP activity in MC3T3-E1 cells.

RESULTS

In the four mouse breast cancer cell lines 67NR, 66c14, 4T07, and 4T1, 4T1 cells expressed higher levels of versican, and showed higher migration and invasion ability to MC3T3-E1 cells and primary bone stromal cells. 4T1 conditioned medium (CM) inhibited MC3T3-E1 cell growth, and even lead to apoptosis. Only 4T1 CM prevented MC3T3-E1 cell differentiation, noted by inhibition of alkaline phosphatase (ALP) activity. We exogenously expressed a versican G3 construct in a cell line that expresses low versican levels (66c14), and observed that the G3-expressing 66c14 cells showed enhanced cell migration and invasion to bone stromal and MC3T3-E1 cells. This observation was prevented by selective EGFR inhibitor AG1478, selective MEK inhibitor PD 98059, and selective AKT inhibitor Triciribine, but not by selective JNK inhibitor SP 600125. Versican G3 enhanced breast cancer cell invasion to bone stromal cells or osteoblast cells appears to occur through enhancing EGFR/ERK or AKT signaling. G3 expressing MC3T3-E1 cells showed inhibited cell growth and cell differentiation when cultured with TGF-β1 (1 ng/ml), and expressed enhanced cell apoptosis when cultured with TNF-α (2 ng/ml). Enhanced EGFR/JNK signaling appears to be responsible for G3 enhanced osteoblast apoptosis and inhibited osteoblast differentiation. Whereas repressed expression of GSK-3β (S9P) contributes to G3 inhibited osteoblast growth. Versican G3 functionality was dependent on its EGF-like motifs. Without the structure of EGF-like repeats, the G3 domain would not confer enhancement of tumor cell migration and invasion to bone with concordant inhibition of osteoblast differentiation and promotion of osteoblast apoptosis.

CONCLUSIONS

Versican enhances breast cancer bone metastasis not only through enhancing tumor cell mobility, invasion, and survival in bone tissues, but also by inhibiting pre-osteoblast cell growth, differentiation, which supply favorable microenvironments for tumor metastasis.

The Casitas B lineage lymphoma (Cbl) mutant G306E enhances osteogenic differentiation in human mesenchymal stromal cells in part by decreased Cbl-mediated platelet-derived growth factor receptor alpha and fibroblast growth factor receptor 2 ubiquitination

Human bone marrow-derived mesenchymal stromal cells (hMSCs) have the capacity to differentiate into several cell types including osteoblasts and are therefore an important cell source for bone tissue regeneration. A crucial issue is to identify mechanisms that trigger hMSC osteoblast differentiation to promote osteogenic potential. Casitas B lineage lymphoma (Cbl) is an E3 ubiquitin ligase that ubiquitinates and targets several molecules for degradation. We hypothesized that attenuation of Cbl-mediated degradation of receptor tyrosine kinases (RTKs) may promote osteogenic differentiation in hMSCs. We show here that specific inhibition of Cbl interaction with RTKs using a Cbl mutant (G306E) promotes expression of osteoblast markers (Runx2, alkaline phosphatase, type 1 collagen, osteocalcin) and increases osteogenic differentiation in clonal bone marrow-derived hMSCs and primary hMSCs. Analysis of molecular mechanisms revealed that the Cbl mutant increased PDGF receptor α and FGF receptor 2 but not EGF receptor expression in hMSCs, resulting in increased ERK1/2 and PI3K signaling. Pharmacological inhibition of FGFR or PDGFR abrogated in vitro osteogenesis induced by the Cbl mutant. The data reveal that specific inhibition of Cbl interaction with RTKs promotes the osteogenic differentiation program in hMSCs in part by decreased Cbl-mediated PDGFRα and FGFR2 ubiquitination, providing a novel mechanistic approach targeting Cbl to promote the osteogenic capacity of hMSCs.

Collagen supramolecular and suprafibrillar organizations on osteoblasts long-term behavior: benefits for bone healing materials

This study compares the behavior of osteoblastic cells seeded on three structurally distinct collagen-based materials. Adhesion and long-term behavior were evaluated in vitro in regard to collagen scaffolds forming loose or dense fibrillar networks or exempt of fibrils. In this purpose collagen solutions at concentrations of 5 and 40 mg/mL were processed by freeze-drying or by sol/gel fibrillogenesis to form either sponges or hydrogels. Macroscopic and microscopic images of sponges showed a light material exhibiting large pores surrounded by dense collagen walls made of thin unstriated microfibrils of 20 nm in diameter. In comparison collagen hydrogels are more homogeneous materials, at 5 mg/mL the material consists of a regular network of cross-striated collagen fibrils of 100 nm in diameter. At 40 mg/mL the material appears stiffer, the ultrastructure exhibits cross-striated collagen fibrils packed in large bundles of 300-800 nm of width. Human osteoblastic cells seeded on top of the 5 mg/mL matrices exhibit a squared shaped osteoblast-like morphology over 28 days of culture and express both alkaline phosphatase and osteocalcin. Osteoblastic cells seeded on top of sponges or of 40 mg/mL matrices exhibit both flat and elongated resting-osteoblast morphology. Osteoblastic cells have mineralized the three collagen-based materials after 28 days of culture but collagen sponges spontaneously mineralized in absence of cells. These results highlight, in an in vitro cell culture approach, the benefit of fibrils and of dense fibrillar networks close to in vivo-like tissues, as positive criteria for new bone tissue repair materials.

Tumor-supportive and osteoclastogenic changes induced by breast cancer-derived factors are reversed by inhibition of {gamma}-secretase

During breast cancer metastasis to bone, tumor cells home to bone marrow, likely targeting the stem cell niche, and stimulate osteoclasts, which mediate osteolysis required for tumor expansion. Although osteoblasts contribute to the regulation of the hematopoietic stem cell niche and control osteoclastogenesis through production of proresorptive cytokine RANKL (receptor activator of NF-κB ligand), their role in cancer metastases to bone is not fully understood. C57BL/6J mouse bone marrow cells were treated for 3–12 days with ascorbic acid (50 μg/ml) in the presence or absence of 10% medium conditioned by breast carcinoma cells MDA-MB-231, 4T1, or MCF7. Treatment with cancer-derived factors resulted in a sustained 40–60% decrease in osteoblast differentiation markers, compared with treatment with ascorbic acid alone, and induced an osteoclastogenic change in the RANKL/osteoprotegerin ratio. Importantly, exposure of bone cells to breast cancer-derived factors stimulated the subsequent attachment of cancer cells to immature osteoblasts. Inhibition of γ-secretase using pharmacological inhibitors DAPT and Compound E completely reversed cancer-induced osteoclastogenesis as well as cancer-induced enhancement of cancer cell attachment, identifying γ-secretase activity as a key mediator of these effects. Thus, we have uncovered osteoblasts as critical intermediary of premetastatic signaling by breast cancer cells and pinpointed γ-secretase as a robust target for developing therapeutics potentially capable of reducing both homing and progression of cancer metastases to bone.

High Wnt signaling represses the proapoptotic proteoglycan syndecan-2 in osteosarcoma cells

Osteosarcoma is characterized by frequent relapse and metastatic disease associated with resistance to chemotherapy. We previously showed that syndecan-2 is a mediator of the antioncogenic effect of chemotherapeutic drugs. The purpose of this work was to elucidate molecular mechanisms responsible for the low expression of syndecan-2 in osteosarcoma. We compared the regulatory activity of cis-acting DNA sequences of the syndecan-2 gene in osteosarcoma and osteoblastic cell lines. We identified a DNA region that negatively regulates syndecan-2 transcription in the osteosarcoma cells. T-cell factors (TCF) bind to this sequence in vivo. Wnt3a stimulation, beta-catenin activation, and TCF overexpression resulted in syndecan-2 repression, whereas Wnt inhibition using sFRP-1 increased syndecan-2 expression in U2OS cells. RhoA activation blunted the stimulatory effect of sFRP-1 on syndecan-2 transcription, whereas RhoA inhibition enhanced syndecan-2 expression. These results indicate that Wnt/beta-catenin and Wnt/RhoA signaling contribute to syndecan-2 repression. The alteration of syndecan-2 expression in osteosarcoma cell lines also seemed to be related to a higher shedding, controlled by Wnt/RhoA. Conversely, syndecan-2 was found to activate its own expression in U2OS cells through RhoA inhibition. These data identify a molecular network that may contribute to the low expression of the proapoptotic proteoglycan syndecan-2 in osteosarcoma cells. The high activity of the canonical Wnt pathway in the different osteosarcoma cells induces a constitutive repression of syndecan-2 transcription, whereas Wnt/RhoA signaling blocks the amplification loop of syndecan-2 expression. Our results identify syndecan-2 as a Wnt target and bring new insights into a possible pathologic role of Wnt signaling in osteosarcoma.

Topographically induced self-deformation of the nuclei of cells: dependence on cell type and proposed mechanisms

Osteosarcoma-derived cell lines (SaOs-2, MG63) have recently been shown to deform their nucleus considerably in response to surface topography. Such a deformation had not been described previously. Here we present results on additional cell lines, including cancerous (OHS4, U2OS), immortalized (F/STRO-1(+)A and FHSO6) and healthy cells (HOP). The cancerous cells were found to deform extensively, the immortalized cells showed small deformations, whereas the healthy cells showed deformation only at short incubation times. These results suggest a strong link between the malignant transformation of cells and the state of the cytoskeletal network. We propose mechanisms to explain the deformation in which the cytoskeleton either pushes down on the nucleus during spreading or pulls it down upon adhesion to the pillars.

Death receptor pathways mediate targeted and non-targeted effects of ionizing radiations in breast cancer cells

Delayed cell death by mitotic catastrophe is a frequent mode of solid tumor cell death after γ-irradiation, a widely used treatment of cancer. Whereas the mechanisms that underlie the early γ-irradiation-induced cell death are well documented, those that drive the delayed cell death are largely unknown. Here we show that the Fas, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and tumor necrosis factor (TNF)-α death receptor pathways mediate the delayed cell death observed after γ-irradiation of breast cancer cells. Early after irradiation, we observe the increased expression of Fas, TRAIL-R and TNF-R that first sensitizes cells to apoptosis. Later, the increased expression of FasL, TRAIL and TNF-α permit the apoptosis engagement linked to mitotic catastrophe. Treatments with TNF-α, TRAIL or anti-Fas antibody, early after radiation exposure, induce apoptosis, whereas the neutralization of the three death receptors pathways impairs the delayed cell death. We also show for the first time that irradiated breast cancer cells excrete soluble forms of the three ligands that can induce the death of sensitive bystander cells. Overall, these results define the molecular basis of the delayed cell death of irradiated cancer cells and identify the death receptors pathways as crucial actors in apoptosis induced by targeted as well as non-targeted effects of ionizing radiation.

Blockade of the RhoA-JNK-c-Jun-MMP2 cascade by atorvastatin reduces osteosarcoma cell invasion

Osteosarcoma is characterized by a high malignant and metastatic potential, which points to the need for new therapeutic strategies to prevent cell metastasis. In this study, we show that statin-induced HMG-CoA reductase inhibition reduces cell migration and invasion in human and murine osteosarcoma cells, independently of the genotype. The statin-induced reduction of cell migration and invasion was independent of induction of apoptosis and was geranylgeranylpyrophosphate-dependent. The statin reduced matrix metalloproteinase (MMP) 2, 9, and 14 and TIMP2 expression or activity in invading cells. Forced expression of MMP2 and MMP14 overcame the inhibitory effect of the statin on cell invasion, suggesting a role for these MMPs in invasive potential. We also investigated the mechanisms involved in the reduced MMP2 activity and cell invasion. Inhibition of JNK, but not ERK1/2 signaling, reduced MMP2 activity. Pharmacological or constitutive activation of JNK overcame the reduced MMP2 activity and cell invasion induced by the statin. The statin decreased JNK phosphorylation and c-Jun nuclear translocation, suggesting that HMG-CoA reductase inhibition targets the JNK-c-Jun signaling pathway. We showed that mevalonate or geranylgeranylpyrophosphate treatment prevented the statin-induced reduction in JNK phosphorylation, MMP2 activity, and cell invasion. Forced expression of a constitutively active form of RhoA increased JNK phosphorylation and overcame the inhibitory effect of atorvastatin on MMP2 activity and cell invasion. The data establish a link between RhoA, JNK, c-Jun, and MMP2 activity that is functionally involved in the reduction in osteosarcoma cell invasion by the statin. This suggests a novel strategy targeting RhoA-JNK-c-Jun signaling to reduce osteosarcoma cell tumorigenesis.

In vitro age-related responses of endothelial cells to breast cancer cell addition

AIM

The purpose of this study was to determine if the in vitro age of endothelial cells alters endothelial response(s) to breast cancer cells.

METHOD

After characterizing lower passage ("young"; passages 10-16) and higher passage ("old"; passages 30-36) bovine pulmonary artery endothelial cells (BPAECs), fluorescently labeled MCF-7 breast cancer cells were added to confluent monolayers of young and old BPAECs.

RESULTS

Transient gaps that peaked in size by 12 h and closed by 48h occurred between the young BPAECs, while large persistent gaps formed between the old BPAECs. Gap formation did not occur when 184A1 cells, a non-malignant mammary epithelial cell line, were added in place of MCF-7 cells, suggesting that the age-related responses of the endothelial cells to MCF-7 cell addition were specific to the tumor cell addition. Additionally, more MCF-7 cells migrated through old BPAEC monolayers, than young BPAEC monolayers, grown on Matrigel-coated filters. Finally, DNA fragmentation and fluorescent annexin-V binding assays suggested increased MCF-7 cell-induced apoptosis in older BPAECs, though results from a caspase-3 activation assay were equivocal.

CONCLUSIONS

In sum, our findings support the notion that aged endothelial cells are more susceptible to breast cancer-induced injury, perhaps due to increased apoptosis.

Cytokines secreted by bone-metastatic breast cancer cells alter the expression pattern of f-actin and reduce focal adhesion plaques in osteoblasts through PI3K

Breast cancer frequently metastasizes to bone, resulting in osteolytic lesions. These lesions, formed by activated osteoclasts, cause pain, an increased susceptibility to fractures, and hypercalcemia. It has been shown that breast cancer cells communicate with osteoblasts and subsequently stimulate osteoclast activity; however, little research has focused on understanding the interaction between breast cancer cells and osteoblasts. We recently reported that conditioned medium from MDA-MB-231 breast cancer cells inhibited the differentiation of MC3T3-E1 osteoblasts through the secretion of transforming growth factor beta (TGFbeta). In addition, the breast cancer conditioned medium altered MC3T3-E1 morphology, the pattern of actin stress fibers, and reduced focal adhesion plaques. In the current study, we identified the mechanism used by MDA-MB-231 cells to cause these effects. When MC3T3-E1 osteoblasts were cultured with MDA-MB-231 conditioned medium preincubated with neutralizing antibodies to platelet derived growth factor (PDGF), insulin-like growth factorII (IGFII), and TGFbeta, focal adhesion plaques and actin stress fiber formation were restored. These cytokines were further found to signal through PI3Kinase and Rac. In conclusion, TGFbeta, PDGF, and IGFII might be good therapeutic targets for treating breast cancer-induced osteolytic lesions.

Metastatic breast cancer cells suppress osteoblast adhesion and differentiation

Bone is a primary target for colonization of metastatic breast cancer cells. Once present, the breast cancer cells activate osteoclasts, thereby stimulating bone loss. Bone degradation is accompanied by pain and increased susceptibility to fractures. However, targeted inhibition of osteoclasts does not completely prevent lesion progression, nor does it heal the lesions. This suggests that breast cancer cells may also affect osteoblasts, cells that build bone. The focus of this study was to determine the ability of breast cancer cells to alter osteoblast function. MC3T3-E1 osteoblasts were cultured with conditioned medium from MDA-MB-231 breast cancer cells and subsequently assayed for changes in differentiation. Osteoblast differentiation was monitored by expression of osteocalcin, bone sialoprotein and alkaline phosphatase, and by mineralization. Osteoblasts cultured with MDA-MB-231 conditioned medium did not express these mature bone proteins, nor did they mineralize a matrix. Inhibition of osteoblast differentiation was found to be due to transforming growth factor beta present in MDA-MB-231 conditioned medium. Interestingly, breast cancer conditioned medium also altered cell adhesion. When osteoblasts were assayed for adhesion properties using interference reflection microscopy and scanning acoustic microscopy, there was a reduction in focal adhesion plaques and sites of detachment were clearly visible. F-actin was disassembled and punctate in osteoblasts cultured with MDA-MB-231 conditioned medium rather than organized in long stress fibers. Taken together, these observations suggest that metastatic breast cancer cells alter osteoblast adhesion and prevent differentiation. These affects could account for the continued loss of bone after osteoclast inhibition in patients with bone-metastatic breast cancer.

Breast cancer cells induce osteoblast apoptosis: a possible contributor to bone degradation

Breast cancer cells exhibit a predilection for metastasis to bone. There, the metastases usually bring about bone loss with accompanying pain and loss of function. One way that breast cancer cells disrupt the normal pattern of bone remodeling is by activating osteoclasts, the bone degrading cells. Nevertheless, targeting the osteoclasts does not cure the disease or result in bone repair. These observations indicate that osteoblast function also may be compromised. The objective of this study was to investigate the interaction of metastatic breast cancer cells with osteoblasts. Human metastatic breast cancer cells, MDA-MB-435 or MDA-MB-231, or their conditioned media were co-cultured with a human osteoblast line hFOB1.19. The breast cancer cells caused an increase in the prevalence of apoptotic osteoblasts. Apoptotic osteoblasts detected by the TUNEL assay or by caspase activity increased approximately two to fivefold. This increase was not seen with non-metastatic MDA-MB-468 cells. In an investigation of the mechanism, it was determined that the hFOB1.19 cells expressed fas and that fas was functional. Likewise the hFOB1.19 cells were susceptible to TNF-alpha, but this cytokine was not detected in the conditioned medium of the breast cancer cells. This study indicates that osteoblasts are the target of breast cancer cell-induced apoptosis, but fas/fas-ligand and TNF-alpha, two common initiators of cell death, are probably not involved in this aspect of the metastases/bone cell axis. There are several mechanisms that remain to be explored in order to determine how breast cancer cells bring about osteoblast apoptosis. Even though the specific initiator of apoptosis remains to be identified, the results of this study suggest that the mechanism is likely to be novel.

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

Bone remodelling is severely affected in myeloma bone disease as a consequence of skeletal metastatization of malignant plasma cells. We investigated whether defective bone replacement is dependent on increased osteoblast apoptosis and/or on deregulated events within the bone microenvironment. Circulating tumour necrosis factor (TNF)-alpha, interferon-gamma, interleukin (IL)-1beta, and IL-6 levels were higher in myeloma patients with overt bone disease, whose osteoblasts constitutively overexpressed Fas, DR4/DR5 complex as receptors to TNF-related apoptosis inducing ligand, intercellular adhesion molecule-1 (ICAM-1), and monocyte chemotactic protein-1 (MCP-1). They were functionally exhausted and promptly underwent apoptosis in vitro, in contrast to the minor tendency to death detected in control osteoblasts from patients without bone involvement and normal donors. Osteoblasts dramatically enhanced their apoptosis in co-cultures with MCC-2 myeloma cells and upregulated both ICAM-1 and MCP-1 in a manner similar to control osteoblasts. Pretreating MCC-2 cells with soluble ICAM-1 led to a striking inhibition of their adhesion to osteoblasts, suggesting that the ICAM-1/lymphocyte function-associated antigen-1 system plays a role in the reciprocal membrane contact to trigger apoptogenic signals. Our data suggest that, in the myeloma bone microenvironment, both high cytokine levels and physical interaction of malignant plasma cells with osteoblasts drive the accelerated apoptosis in these cells leading to defective new bone formation.

Extracellular calcium downregulates estrogen receptor alpha and increases its transcriptional activity through calcium-sensing receptor in breast cancer cells

Skeleton is the most common organ targeted by breast cancer cells, especially from estrogen receptor alpha (ER)-positive neoplasms. Metastatic cells can stimulate directly or indirectly osteoclast-mediated bone resorption. Tumor-induced osteolysis is often extensive and leads to the release of large quantities of calcium. Metastatic cancer cells can be thus exposed to high calcium concentrations (40 mM has been reported at the resorption site). However, the effects of Ca2+ on breast cancer cells have been minimally examined. We showed that 20-mM extracellular Ca2+ induced a downregulation of ER protein in MCF-7 cells and caused ER-mediated transactivation of a reporter gene by 55 +/- 10% (mean +/- SD) in MVLN cells (MCF-7 cells stably transfected with ERE and luciferase reporter gene). Moreover, 3 mM Ca2+ increased progesterone receptor (PgR) expression by 45 +/- 8%. Mg2+ tested at up to 20 mM did not exert any effects, while 17beta-estradiol downregulated ER, transactivated the reporter gene, and enhanced PgR expression. The pure antiestrogen ICI 182,780 was able to abrogate the transactivation of the reporter gene and the increase in PgR levels induced by Ca2+, indicating that Ca2+ may exert a weak and specific estrogenic effect in MCF-7 cells. Ca2+ effects on ER probably start at the cell membrane level since a large Ca2+ influx caused by the ionophore A23187 failed to activate ER. We have thus studied the involvement of the membrane calcium-sensing receptor (CaR) that is known to be expressed notably in MCF-7 cells. We first tested the effects of a specific activator of CaR. Exposure to 10(-4) M calcimimetic NPS R-467 mirrored the changes observed with extracellular Ca2+ by inducing a marked decrease in ER protein levels, increasing the transcriptional activity of ER (67 +/- 12%) and stimulating PgR expression (41 +/- 4%). As expected, the NPS S-467 isomer was less effective. Furthermore, a highly selective CaR antagonist partly suppressed the downregulation of ER as well as transactivation of the reporter gene induced by Ca(2+). Our results suggest that the effects of extracellular Ca2+ on ER expression and activity are mediated, at least in part, by the CaR. In summary, calcium released during the process of metastatic bone destruction could modulate the functions of the estrogen receptor, a key receptor involved in breast cancer cells growth and function, and thus participate in the pathogenesis of tumor-induced osteolysis.

Modulation of survival in osteoblasts from postmenopausal women

Osteoblast survival is one of the determinants of postmenopausal osteoporosis development. Recent data from animal experiments suggest that cytokines, in particular Fas ligand (FasL), contribute to postmenopausal osteoporosis. We now address the effect of Fas activation in postmenopausal osteoblast survival and the potential modulatory effect of estrogen and raloxifene analog (LY117018). The expression of Fas mRNA, Fas protein, and the sensitivity to Fas-induced apoptosis were studied in primary cultures of human osteoblasts from postmenopausal women and in osteoblastic MG-63 cells. Human postmenopausal osteoblasts constitutively expressed Fas receptors in the cell surface. TNFalpha increased the expression of Fas mRNA and cell surface Fas expression. Neither estradiol nor raloxifene analog prevented this increase in Fas expression. In addition, activation of Fas receptor resulted in apoptosis of postmenopausal osteoblasts. While TNFalpha did not induce human osteoblast apoptosis, it did increase the lethal effect of Fas activation. Therapeutic concentrations of estradiol or raloxifene analog did not modulate lethal cytokine-induced apoptosis. Both postmenopausal osteoblasts and MG-63 cells express FasL. FasL expression was not modulated by TNFalpha. In conclusion, estrogen and raloxifene analog do not appear to affect the sensitivity of postmenopausal osteoblasts to Fas-mediated apoptosis.

Upregulation of osteoblast apoptosis by malignant plasma cells: a role in myeloma bone disease

Typical features of multiple myeloma (MM) are osteolytic lesions and severely affected bone regeneration. This study of 53 MM patients demonstrates an enhancement of osteoblast cytotoxicity by malignant myeloma cells via the upregulation of apoptogenic receptors, including Fas ligand (Fas-L) and tumour-necrosis-factor-related apoptosis inducing ligand (TRAIL). Both were significantly increased in the marrow myeloma cells of patients with extensive osteolytic lesions in a fashion similar to the highly malignant human myeloma cell line MCC-2. Osteoblasts from these subjects over-expressed Fas and death receptor (DR) 4/5 and underwent dramatic apoptosis when co-cultured with either MCC-2 or autologous myeloma cells. In osteoblast and myeloma cell co-cultures, monocyte chemoattractant protein 1 (MCP-1) mRNA was upregulated in osteoblasts from patients with severe bone disease in parallel with increased CC-chemokine receptor R2 (CCR2) expression, the ligand of MCP-1, in the myeloma cells. This chemokine was shown to activate malignant cell migration in vitro. An upregulation of ICAM-1 expression occurred in osteoblasts from patients with active skeleton disease. This upregulation appeared to be an effect of malignant plasma cell contact, as MCC-2 co-culture greatly enhanced ICAM-1 production by resting osteoblasts from patients without skeleton involvement. Our results suggest that osteoblasts in active myeloma are functionally exhausted and promptly undergo apoptosis in the presence of myeloma cells from patients with severe bone disease. It is suggested that this cytotoxic effect plays a pivotal role in the pathogenesis of defective bone repair.

Bisphosphonates in the treatment of metastatic breast cancer

The skeleton is the most common site of metastatic disease in breast cancer and the most common site of first distant relapse. Bone metastases in breast cancer are the source of considerable morbidity, including severe pain, pathological fractures, need for radiotherapy or surgery, and hypercalcemia. Bisphosphonates are potent inhibitors of osteoclast-mediated bone resorption, and it is well known that breast cancer cells in bone can stimulate osteoclast formation and activity leading to the release of growth factors and cytokines, which will further stimulate cancer cell growth and their secretion of osteolytic factors. We are thus typically dealing with a vicious cycle, as the bone resorption-induced release of growth factors from the bone matrix will stimulate breast cancer cell growth (probably mainly by IGFs) and the production of the osteolytic factor PTHrP (probably mainly by TGF-beta but also by extracellular calcium). Clodronate, but not the aminobisphosphonates, can be metabolized to an ATP analog that is toxic for osteoclasts. Nitrogen-containing bisphosphonates, such as pamidronate, ibandronate, and zoledronate, interfere with the mevalonate pathway that is crucial to maintain cell membrane integrity. The net result, regardless of the mechanism, is osteoclast apoptosis, notably through the induction of caspase-3. Bisphosphonates are now the standard treatment for cancer hypercalcemia. Repeated bisphosphonate infusions also exert clinically relevant analgesic effects in at least one half of the patients with metastatic bone pain. Most importantly, prolonged administration of bisphosphonates (for at least 1 year) reduces the frequency of morbid skeletal events by 30-40% in breast cancer metastatic to bone and in up to 50% in patients with multiple myeloma. Newer bisphosphonates, such as ibandronate and zoledronate, will simplify the current therapeutic schemes and improve the cost-effectiveness ratio, and they have the potential to improve the therapeutic efficacy, at least in patients with aggressive osteolytic disease or in the adjuvant setting.