Cellular mechanisms of bone resorption in breast carcinoma

Cannabinoid Receptor Type 2 Agonist, GW405833, Reduced the Impacts of MDA-MB-231 Breast Cancer Cells on Bone Cells

AIM

Breast cancer frequently metastasizes to bones. The interaction between breast cancer cells and bone cells results in osteolytic lesions by disrupting the balance between osteoblast-mediated bone production and osteoclast-mediated bone resorption. This study aims to investigate the effects of the cannabinoid receptor type 2 (CB2) agonist, GW405833, on interactions between breast cancer cells and osteoblasts as well as its impact on breast cancer-induced osteoclastogenesis.

MATERIALS & METHODS

MDA-MB-231, UMR-106, RAW 264.7 cells were used to represent breast cancer cells, osteoblast-like cells and macrophage-osteoclast precursor cells, respectively. Cell viability was evaluated by MTT assay, and breast cancer cell invasion was assessed by Transwell invasion assay. Tartrate-resistant acid phosphatase (TRAP) staining was utilized to evaluate osteoclastogenesis.

RESULTS

Our results demonstrated that GW405833 disrupted MDA-MB-231-induced UMR-106 cell death and promoted UMR-106 cell viability. The underlying mechanism of these effects was determined in this study. GW405833 reduced AKT phosphorylation in MDA-MB-231 cells without affecting mTOR protein expression or its phosphorylation. Conversely, in UMR-106 cells, GW405833 induced AKT and mTOR phosphorylated protein. Furthermore, the mTOR inhibitor reversed the GW405833-induced recovery of UMR-106 cell viability under MDA-MB-231-derived conditioned media (CM) exposure. These findings underscore the critical role of the AKT/mTOR pathway in mediating GW405833's inhibitory effects on cancer-bone interactions. Additionally, GW405833 suppressed osteoblast-enhanced breast cancer cell invasion and the expression of invasion-related proteins in both cell types, along with reducing osteoclastogenic factors induced by MDA-MB-231 CM in UMR-106 cells and suppressing MDA-MB-231 CM-enhanced osteoclastogenesis in RAW 264.7 cells.

CONCLUSION

This study highlights the therapeutic potential of cannabinoid receptor agonist for treating breast cancer bone metastasis and bone-related complications.

Detection of bone metastases in breast cancer patients in the PET/CT era: Do we still need the bone scan?

AIM

To examine the value of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) for the detection of bone metastasis in breast cancer patients and assess whether whole body bone scan (BS) with (99m)Tc-methylene diphosphonate provides any additional information.

MATERIAL AND METHODS

Study group comprised 150 patients, mean age 52 years (range 27-85) with breast cancer, suspected of having bone metastases. All patients had undergone both FDG-PET/CT and BS with or without single photon emission tomography/computed tomography (SPECT/CT) within a period of 6 weeks. The final diagnosis of bone metastasis was established by histopathological findings, additional imaging, or clinical follow-up longer than 10 months. Cancer antigen 15-3 (CA15-3) and carcinoembryogenic antigen (CEA) were measured in all patients.

RESULTS

Histologically 83%, 7% and 10% had infiltrating ductal, lobular and mixed carcinoma respectively. Confirmed bone metastases were present in 86 patients (57.3%) and absent in 64 (42.7%). Mean CA15-3 and CEA values in patients with bone metastases were 74.6ng/mL and 60.4U/mL respectively, compared to 21.3ng/mL and 3.2U/mL without metastases (p<0.001). The sensitivity of FDG-PET/CT for the detection of bone metastases was 97.6% compared to 89.5% with SPECT/CT. In 57 patients, FDG-PET/CT correctly identified additional pulmonary, hepatic, nodal and other soft tissue metastases, not detected by BS.

CONCLUSION

Our findings suggest that FDG-PET/CT is superior to BS with or without SPECT/CT.

Variability of the paracrine-induced osteoclastogenesis by human breast cancer cell lines

Breast cancer frequently metastasizes to the bone, often leading to the formation of osteolytic lesions. This work compares the paracrine-induced osteoclastogenesis mediated by four human breast cancer cell lines, the estrogen-receptor positive T47D and MCF-7 and the estrogen-negative SK-BR-3 and Hs-578T cell lines. Human osteoclast precursor cells were cultured in the presence of conditioned media from the breast cancer cell lines (10% and 20%), collected at different culture periods (48 h, 7 days, and 14 days). Cultures performed in the absence or the presence of M-CSF and RANKL served as negative and positive control, respectively. Results showed that the cell lines differentially expressed several osteoclastogenic genes. All cell lines exhibited a significant osteoclastogenic potential, evidenced by a high TRAP activity and number of osteoclastic cells, expression of several osteoclast-related genes, and, particularly, a high calcium phosphate resorption activity. Differences among the osteoclastogenic potential of the cell lines were noted. T47D and MCF-7 cell lines displayed the highest and the lowest osteoclastogenic response, respectively. Despite the variability observed, MEK and NF-κB signaling pathways, and, at a lesser extent, PGE2 production, seemed to have a central role on the observed osteoclastogenic response. In conclusion, the tested breast cancer cell lines exhibited a high osteoclastogenic potential, although with some variability on the cell response profile, a factor to be considered in the development of new therapeutic approaches for breast cancer-induced bone metastasis.

A tale of mice and (wo)men: development of and insights from an "all human" animal model of breast cancer metastasis to bone

There are 200,000 new cases of breast cancer (BrCa) annually in the United States. Metastasis to bone signals a life-threatening phase of this disease. Little progress has been made in understanding the pathogenesis of metastasis. Few validated drug targets have been identified. So there is a compelling need to understand the molecular mechanisms by which BrCa metastasizes to bone (osteotropism). There is need for animal models that reflect the complex biology of metastasis in humans. We performed research designed to elucidate the mechanisms of osteotropism from both sides of the tumor-stroma interface. We created an "all human" model in which human bone is transplanted into non-obese diabetic/severe combined immunodeficient immunodeficient (NOD/SCID) mice. Human BrCa cells injected into the mammary fat pad later metastasize to bone. We also found traffic in the opposite direction: bone marrow stem cells migrate from human bone to human breast tumors in the mouse. We are identifying osteotropism genes used by BrCa to metastasize to human bone.

Embelin suppresses osteoclastogenesis induced by receptor activator of NF-κB ligand and tumor cells in vitro through inhibition of the NF-κB cell signaling pathway

Most patients with cancer die not because of the tumor in the primary site, but because it has spread to other sites. Common tumors, such as breast, multiple myeloma, and prostate tumors, frequently metastasize to the bone. It is now well recognized that osteoclasts are responsible for the osteolysis observed in bone metastases of the tumor. Receptor activator of NF-κB ligand (RANKL), a member of the tumor necrosis factor superfamily and an activator of the NF-κB signaling pathway, has emerged as a major mediator of bone loss, commonly associated with cancer and other chronic inflammatory diseases. Embelin (2,5-dihydroxy-3-undecyl-1,4-benzoquinone), derived from the Ayurvedic medicinal plant Embelia ribes, has been shown to bind and inhibit X-linked inhibitor of apoptosis protein and inhibit inflammatory pathways. We investigated whether embelin could inhibit osteoclastogenesis-associated bone loss induced by RANKL and by tumor cells in vitro. We found that embelin suppressed the RANKL-induced differentiation of monocytes into osteoclasts. This benzoquinone also suppressed the osteoclastogenesis induced by multiple myeloma and by breast cancer cells. This effect of embelin correlated with the suppression of NF-κB activation and inhibition of IκBα phosphorylation and IκBα degradation. Inhibition of IκBα phosphorylation was due to the inhibition of IκBα kinase (IKK) activation. Furthermore, by using an inhibitor of the IKKγ or NF-κB essential modulator (NEMO), the regulatory component of the IKK complex, we showed that the NF-κB signaling pathway is mandatory for RAW 264.7 cell differentiation into osteoclasts. Thus, embelin, an inhibitor of RANKL-induced NF-κB activation has great potential as a therapeutic agent for osteoporosis and cancer-linked bone loss.

Fusion of metabolic function and morphology: sequential [18F]fluorodeoxyglucose positron-emission tomography/computed tomography studies yield new insights into the natural history of bone metastases in breast cancer

PURPOSE

By monitoring bone metastases with sequential [(18)F]fluorodeoxyglucose positron-emission tomography/computed tomography ([(18)F]FDG-PET/CT) imaging, this study investigates the clinical relevance of [(18)F]FDG uptake features of bone metastases with various radiographic appearances.

PATIENTS AND METHODS

Bone metastases were found in 67 of 408 consecutive patients with known/suspected recurrent breast cancer on [(18)F]FDG-PET/CT, characterized by CT morphology changes and/or bony [(18)F]FDG uptake. Twenty-five of the patients had sequential [(18)F]FDG-PET/CT examinations (86 studies) over an average follow-up period of 23 months. The temporal changes in [(18)F]FDG uptake and corresponding CT morphology features of 146 bone lesions identified in these 25 patients were followed up and correlated with therapeutic outcome retrospectively.

RESULTS

The 146 lesions were classified as osteolytic (77), osteoblastic (41), mixed-pattern (11), or no change/negative (17) on CT. The majority of the osteolytic (72; 93.5%) and mixed-pattern lesions (nine; 81.8%), but fewer of the osteoblastic lesions (25; 61%), showed increased [(18)F]FDG uptake. After treatment, 58 osteolytic lesions (80.5%) became [(18)F]FDG negative and osteoblastic on CT and only 14 relatively large lesions (19.5%) remained [(18)F]FDG avid. Of the 25 [(18)F]FDG-avid osteoblastic lesions, 13 (52%) became [(18)F]FDG negative, but 12 (48%) remained [(18)F]FDG avid and increased in size on CT. Five of the mixed-pattern lesions remained [(18)F]FDG avid after treatment. All 17 CT-negative lesions became [(18)F]FDG negative; however, nine of them became osteoblastic. None of the initially [(18)F]FDG-negative lesions showed [(18)F]FDG avidity during follow-up.

CONCLUSION

[(18)F]FDG uptake reflects the immediate tumor activity of bone metastases, whereas the radiographic morphology changes vary greatly with time among patients.

RANKL-dependent and RANKL-independent mechanisms of macrophage-osteoclast differentiation in breast cancer

The cellular and humoral mechanisms accounting for tumour osteolysis in metastatic breast cancer are uncertain. Osteoclasts, the specialised multinucleated cells responsible for tumour osteolysis, are derived from monocyte/macrophage precursors. Breast cancer-derived tumour-associated macrophages (TAMs) are capable of osteoclast differentiation but the cellular and humoral mechanisms controlling this activity are uncertain. In this study, TAMs were isolated from primary breast cancers and cultured in the presence and absence of cytokines/growth factors influencing osteoclastogenesis. Extensive TAM-osteoclast differentiation occurred only in the presence of RANKL and M-CSF; this process was inhibited by OPG and RANK:Fc, decoy receptors for RANKL. Breast cancer-derived fibroblasts and human bone stromal cells expressed mRNA for RANKL, OPG and TRAIL, and co-culture of these fibroblasts with human monocytes stimulated osteoclast formation by a RANKL-dependent mechanism. Osteoclast formation and lacunar resorption also occurred by a RANKL-independent mechanism when the conditioned medium from breast cancer cells, MDA-MB-231 and MCF-7, was added (with M-CSF) to monocyte cultures. Our findings indicate that TAMs in breast cancer are capable of osteoclast differentiation and that breast cancer-derived fibroblasts and breast cancer cells contribute to this process by producing soluble factors that influence osteoclast formation by RANKL-dependent and RANKL-independent mechanisms respectively.

1'-Acetoxychavicol acetate inhibits RANKL-induced osteoclastic differentiation of RAW 264.7 monocytic cells by suppressing nuclear factor-kappaB activation

Osteoclastogenesis is commonly associated with various age-related diseases, including cancer. A member of the tumor necrosis factor superfamily, receptor activator of nuclear factor-kappaB (NF-kappaB) ligand (RANKL), has been shown to play a critical role in osteoclast formation and bone resorption. Thus, agents that suppress RANKL signaling have a potential to suppress bone loss. In this report, we investigated the effect of 1'-acetoxychavicol acetate (ACA), a component of Alpina galanga, on RANKL signaling and consequent osteoclastogenesis in RAW 264.7 cells, a murine monocytic cell line. Treatment of these cells with RANKL activated NF-kappaB, and coexposure of the cells to ACA completely suppressed RANKL-induced NF-kappaB activation in a time- and concentration-dependent manner. The suppression of NF-kappaB by ACA was mediated through suppression of RANKL-induced activation of IkappaBalpha kinase, IkappaBalpha phosphorylation, and IkappaBalpha degradation. Furthermore, incubation of monocytic cells with RANKL induced osteoclastogenesis, and ACA suppressed it. Inhibition of osteoclastogenesis was maximal when cells were simultaneously exposed to ACA and RANKL and minimum when ACA was added 2 days after RANKL. ACA also inhibited the osteoclastogenesis induced by human breast cancer MCF-7 cells, multiple myeloma MM1 cells, and head and neck squamous cell carcinoma LICR-LON-HN5 cells. These results indicate that ACA is an effective blocker of RANKL-induced NF-kappaB activation and of osteoclastogenesis induced by RANKL and tumor cells, suggesting its potential as a therapeutic agent for osteoporosis and cancer-associated bone loss.

Guggulsterone inhibits osteoclastogenesis induced by receptor activator of nuclear factor-kappaB ligand and by tumor cells by suppressing nuclear factor-kappaB activation

Bone resorption is commonly associated with aging and with certain types of cancer, including multiple myeloma and breast cancer. What induces bone resorption is not fully understood, but the role of osteoclasts is well established. Recently, receptor activator of nuclear factor-kappaB (NF-kappaB) ligand (RANKL), a member of the tumor necrosis factor superfamily, was implicated as a major mediator of bone resorption, suggesting that agents that can suppress RANKL signaling have the potential to inhibit bone resorption or osteoclastogenesis. Guggulsterone [4,17(20)-pregnadiene-3,16-dione], isolated from the guggul tree Commiphora mukul and used to treat osteoarthritis and bone fractures, was recently shown to antagonize the farnesoid X receptor, decrease the expression of bile acid-activated genes, and suppress the NF-kappaB activation induced by various carcinogens. We investigated whether guggulsterone could modulate RANKL signaling and osteoclastogenesis induced by RANKL or tumor cells. We found that treatment of monocytes with guggulsterone suppressed RANKL-activated NF-kappaB activation (as indicated by gel-shift assay) and that this suppression correlated with inhibition of IkappaBalpha kinase and phosphorylation and degradation of IkappaBalpha, an inhibitor of NF-kappaB. Guggulsterone also suppressed the differentiation of monocytes to osteoclasts in a dose-dependent and time-dependent manner. Suppression of osteoclastogenesis by the NF-kappaB-specific inhibitory peptide implies a link between NF-kappaB and osteoclastogenesis. Finally, differentiation to osteoclasts induced by coincubating human breast tumor cells (MDA-MB-468) or human multiple myeloma (U266) cells with monocytes was also completely suppressed by guggulsterone. Collectively, our results indicate that guggulsterone suppresses RANKL and tumor cell-induced osteoclastogenesis by suppressing the activation of NF-kappaB.

SU11248 inhibits tumor growth and CSF-1R-dependent osteolysis in an experimental breast cancer bone metastasis model

The aim of the study was to investigate inhibitory effects of the receptor tyrosine kinase (RTK) inhibitor SU11248 against CSF-1R and osteoclast (OC) formation. We developed an in vivo model of breast cancer metastasis to evaluate efficacy of SU11248 against tumor growth and tumor-induced osteolysis in bone. The in vitro effects of SU11248 on CSF-1R phosphorylation, OC formation and function were evaluated. Effects on 435/HAL-Luc tumor growth in bone were monitored by in vivo bioluminescence imaging (BLI), and inhibition of osteolysis was evaluated by measurement of serum pyridinoline (PYD) concentration and histology. Phosphorylation of the receptor for M-CSF (CSF-1R) expressed by NIH3T3 cells was inhibited by SU11248 with an IC50 of 50-100 nM, consistent with CSF-1R belonging to the class III split kinase domain RTK family. The early M-CSF-dependent phase of in vitro murine OC development and function were inhibited by SU11248 at 10-100 nM. In vivo inhibition of osteolysis was confirmed by significant lowering of serum PYD levels following SU11248 treatment of tumor-bearing mice (P = 0.047). Using BLI, SU11248 treatment at 40 mg/kg/day for 21 days showed 64% inhibition of tumor growth in bone (P = 0.006), and at 80 mg/kg/day showed 89% inhibition (P = 0.001). Collectively, these data suggest that SU11248 may be an effective and tolerated therapy to inhibit growth of breast cancer bone metastases, with the additional advantage of inhibiting tumor-associated osteolysis.

The macrophage growth factor CSF-1 in mammary gland development and tumor progression

Colony stimulating factor 1 (CSF-1), a major regulator of the mononuclear phagocytic lineage, is expressed in more than 70% of human breast cancers and its expression is correlated with poor prognosis. Studies of CSF-1 null mutant mice demonstrated that CSF-1 plays an important role in normal mammary ductal development as well as in mammary tumor progression to metastasis. CSF-1 regulates these processes through the recruitment and regulation of macrophages, cells that become associated with mammary tumors and the terminal end buds at the end of the growing ducts. This phenomenon suggests that the tumors subvert normal developmental processes to allow invasion into the surrounding stroma, a process that gives the tumor access to the vasculature and consequently the promotion of metastasis. In addition, soluble CSF-1 secreted from the tumor acts to divert antitumor macrophage responses and suppresses the differentiation of mature tumor-antigen-presenting dendritic cell This review discusses these observations in detail and attempts to fit them into a larger picture of CSF-1 and macrophage action in the regulation of normal mammary gland development and tumor progression.