Role of RANKL/RANK in primary and secondary breast cancer

Immunization With RANKL Inhibits Osteolytic Bone Metastasis in Breast Cancer

Breast cancer cells often metastasize to bone. Accumulating evidence suggests that inhibiting the receptor activator of nuclear factor-κB ligand (RANKL) not only leads to reduced bone metastasis of breast cancer but also has antitumoral effects. Here, we used mutant receptor activator of nuclear factor-κB ligand (RANKLM) as a vaccine for active immunization to induce antibodies for immunotherapy of bone metastatic cancer. We investigated whether anti-RANKL antibodies inhibit osteolytic bone metastasis in vitro and in a murine model. MC3T3 cells stimulated by MDA-MB-231 culture medium secreted growth differentiation factor-15 (GDF-15), which induced the nuclear factor-κB signaling cascade. In addition, RANKLM treatment-induced reduction of intraosseous growth of MDA-MB-231 cells correlated with decreased GDF-15 expression, a reduced number of osteolytic lesions, and slower tumor progression. In addition, vaccination with RANKLM led to significant improvement in overall survival and skeletal metastasis in tumor-bearing mice. Induction of anti-RANKL antibodies by RANKLM decreased GDF-15 production by deactivating nuclear factor-κB signaling, which in turn inhibited metastasis of MDA-MB-231 cells to bone. Taken together, the results demonstrate a role for RANKLM immunization in preventing bone metastasis of breast cancer.

Osteoclasts in Tumor Biology: Metastasis and Epithelial-Mesenchymal-Myeloid Transition

Osteoclast is a specialized cell that originates from monocytic lineage, communicates closely with osteoblasts under physiological conditions, participates in bone modeling and re-modeling, contributes to calcium homeostasis and osteoimmunity. In pathological conditions, it is involved in many tumors such as giant cell bone tumor (osteoclastoma), aneurysmal bone cyst, osteosarcoma, and metastatic cancers, and it usually causes local spread and progression of the tumor, working against the host. Since osteoclasts play an active role in primary bone tumors and bone metastases, the use of anti-osteoclastic agents significantly reduces the mortality and morbidity rates of patients by preventing the progression and local spread of tumors. Osteoclasts also accompany undifferentiated carcinomas of many organs, especially pancreas, thyroid, bladder and ovary. Undifferentiated carcinomas rich in osteoclasts have osteoclastoma-like histology. In these organs, osteoclastoma-like histology may accompany epithelial carcinomas, and de novo, benign and borderline tumors. Mature and immature myeloid cells, including osteoclasts, play an active role in the tumor progression in primary and metastatic tumor microenvironment, in epithelial-mesenchymal transition (EMT), mesenchymal-epithelial-transition (MET), and cancer stem cell formation. Additionally, they are the most suitable candidates for cancer cells in cell fusion due to their evolutionary fusion capabilities. Myeloid features and markers (CD163, CD33, CD68 etc.) can be seen in metastatic cancer cells. Consequently, they provide metastatic cancer cells with motility, margination, transmigration, chemotaxis, phagocytosis, angiogenesis, matrix degradation, and resistance to chemotherapy. For these reasons, we think that the concept of Epithelial-Mesencyhmal-Myeloid-Transition (EMMT) will be more accurate than EMT for cancer cells with myeloid properties.

How Different Are the Molecular Mechanisms of Nodal and Distant Metastasis in Luminal A Breast Cancer?

Lymph node status is one of the best prognostic factors in breast cancer, however, its association with distant metastasis is not straightforward. Here we compare molecular mechanisms of nodal and distant metastasis in molecular subtypes of breast cancer, with major focus on luminal A patients. We analyze a new cohort of 706 patients (MMCI_706) as well as an independent cohort of 836 primary tumors with full gene expression information (SUPERTAM_HGU133A). We evaluate the risk of distant metastasis, analyze targetable molecular mechanisms in Gene Set Enrichment Analysis and identify relevant inhibitors. Lymph node positivity is generally associated with NF-κB and Src pathways and is related to high risk (OR: 5.062 and 2.401 in MMCI_706 and SUPERTAM_HGU133A, respectively, p < 0.05) of distant metastasis in luminal A patients. However, a part (≤15%) of lymph node negative tumors at the diagnosis develop the distant metastasis which is related to cell proliferation control and thrombolysis. Distant metastasis of lymph node positive patients is mostly associated with immune response. These pro-metastatic mechanisms further vary in other molecular subtypes. Our data indicate that the management of breast cancer and prevention of distant metastasis requires stratified approach based on targeted strategies.

RANKL/RANK System-Based Mechanism for Breast Cancer Bone Metastasis and Related Therapeutic Strategies

Breast cancer remains one of the most life-threatening tumors affecting women. Most patients with advanced breast cancer eventually develop metastatic diseases, which cause significant morbidity and mortality. Approximately two-thirds of patients with advanced breast cancer exhibit osteolytic-type bone metastasis, which seriously reduce the quality of life. Therefore, development of novel therapeutic strategies for treating breast cancer patients with bone metastasis is urgently required. The "seed and soil" theory, which describes the interaction between the circulating breast cancer cells (seeds) and bone microenvironment (soil), is widely accepted as the mechanism underlying metastasis. Disruption of any step in this cycle might have promising anti-metastasis implications. The interaction of receptor activator of nuclear factor-κB ligand (RANKL) and its receptor RANK is fundamental in this vicious cycle and has been shown to be a novel effective therapeutic target. A series of therapeutic strategies have been developed to intervene in this cross-talk. Therefore, in this review, we have systematically introduced the functions of the RANKL/RANK signaling system in breast cancer and discussed related therapeutic strategies.

RANKL triggers resistance to TRAIL-induced cell death in oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) occurs as a malignancy of the oral cavity. RANK ligand (RANKL) is essential for osteoclast formation/bone resorption. Recently, we showed autoregulation of receptor activator of nuclear factor-κB ligand (RANKL) stimulates OSCC cell proliferation. OSCC cells show resistance to tumor necrosis factor related apoptosis inducing ligand (TRAIL) treatment. Therefore, we hypothesize that RANKL promotes resistance for TRAIL induction of OSCC apoptotic cell death. In this study, SCC14A and SCC74A cells cultured with TRAIL revealed high-level expression of RANKL which increased resistance to TRAIL inhibition of tumor cell proliferation. RANKL stimulation inhibited terminal deoxynucleotidyl transferase dUTP nick end labeling positive staining in TRAIL-treated cells. CRISPR/Cas-9 knockout of RANKL (RANKL-KO) increased caspase-9, caspase-3 activity and cytochrome c release in OSCC cells. RANKL inhibited proapoptotic proteins BAD and BAX expression. TRAIL treatment suppressed the SQSTM1/p62 and RANKL restored the expression. Interestingly, RANKL alone significantly increased proteasome activity. RANKL-KO in OSCC cells inhibited autophagic activity as evidenced by decreased light chain 3B-II and beclin-1 expression. Thus, RANKL stimulation of OSCC tumor cells triggered resistance for TRAIL-induced OSCC cell death. Taken together, blockade of RANKL may inhibit OSCC tumor progression and enhance the potential of TRAIL induced OSCC tumor cell apoptosis.

Prevention of breast cancer-induced osteolytic bone resorption by benzyl isothiocyanate

Osteolytic bone resorption is the primary cause of pain and suffering (e.g. pathological bone fracture) in women with metastatic breast cancer. The current standard of care for patients with bone metastasis for reducing the incidence of skeletal complications includes bisphosphonates and a humanized antibody (denosumab). However, a subset of patients on these therapies still develops new bone metastasis or experiences adverse effects. Moreover, some bisphosphonates have poor oral bioavailability. Therefore, orally-bioavailable and non-toxic inhibitors of breast cancer-induced osteolytic bone resorption are still clinically desirable. We have shown previously that benzyl isothiocyanate (BITC) decreases the incidence of breast cancer in a transgenic mouse model without any side effects. The present study provides in vivo evidence for inhibition of breast cancer-induced osteolytic bone resorption by BITC. Plasma achievable doses of BITC (0.5 and 1 μM) inhibited in vitro osteoclast differentiation induced by co-culture of osteoclast precursor cells (RAW264.7) and breast cancer cells representative of different subtypes. This effect was accompanied by downregulation of key mediators of osteoclast differentiation, including receptor activator of nuclear factor-κB ligand and runt-related transcription factor 2 (RUNX2), in BITC-treated breast cancer cells. Doxycycline-inducible knockdown of RUNX2 augmented BITC-mediated inhibition of osteoclast differentiation. Oral administration of 10 mg BITC/kg body weight, 5 times per week, inhibited MDA-MB-231-induced skeletal metastasis multiplicity by ~81% when compared with control (P = 0.04). The present study indicates that BITC has the ability to inhibit breast cancer-induced osteolytic bone resorption in vivo.

Decreased sensory nerve excitation and bone pain associated with mouse Lewis lung cancer in TRPV1-deficient mice

Bone pain is one of the most common and life-limiting complications of cancer metastasis to bone. Although the mechanism of bone pain still remains poorly understood, bone pain is evoked as a consequence of sensitization and excitation of sensory nerves (SNs) innervating bone by noxious stimuli produced in the microenvironment of bone metastases. We showed that bone is innervated by calcitonin gene-related protein (CGRP)⁺ SNs extending from dorsal root ganglia (DRG), the cell body of SNs, in mice. Mice intratibially injected with Lewis lung cancer (LLC) cells showed progressive bone pain evaluated by mechanical allodynia and flinching with increased CGRP⁺ SNs in bone and augmented SN excitation in DRG as indicated by elevated numbers of pERK- and pCREB-immunoreactive neurons. Immunohistochemical examination of LLC-injected bone revealed that the tumor microenvironment is acidic. Bafilomycin A1, a selective inhibitor of H⁺ secretion from vacuolar proton pump, significantly alleviated bone pain, indicating that the acidic microenvironment contributes to bone pain. We then determined whether the transient receptor potential vanilloid 1 (TRPV1), a major acid-sensing nociceptor predominantly expressed on SNs, plays a role in bone pain by intratibially injecting LLC cells in TRPV1-deficient mice. Bone pain and SN excitation in the DRG and spinal dorsal horn were significantly decreased in TRPV1 ^-/- mice compared with wild-type mice. Our results suggest that TRPV1 activation on SNs innervating bone by the acidic cancer microenvironment in bone contributes to SN activation and bone pain. Targeting acid-activated TRPV1 is a potential therapeutic approach to cancer-induced bone pain.

Autoregulation of RANK ligand in oral squamous cell carcinoma tumor cells

Oral squamous cell carcinoma (OSCC) is the most common malignancy among oral cancers and shows potent activity for local bone invasion. Receptor activator of nuclear factor κB (RANK) ligand (RANKL) is critical for bone-resorbing osteoclast formation. We previously demonstrated that OSCC tumor cells express high levels of RANKL. In this study, confocal microscopy demonstrated RANKL specific receptor, RANK expression in OSCC tumor cell lines (SCC1, SCC12, and SCC14a). We also confirmed the expression of RANK and RANKL in primary human OSCC tumor specimens. However, regulatory mechanisms of RANKL expression and a functional role in OSCC tumor progression are unclear. Interestingly, we identified that RANKL expression is autoregulated in OSCC tumor cells. The RANKL specific inhibitor osteoprotegerin (OPG) treatment to OSCC cells inhibits autoregulation of RANKL expression. Further, we showed conditioned media from RANKL CRISPR-Cas9 knockout OSCC cells significantly decreased osteoclast formation and bone resorption activity. In addition, RANKL increases OSCC tumor cell proliferation. RANKL treatment to OSCC cells demonstrated a dose-dependent increase in RANK intracellular adaptor protein, TRAF6 expression, and activation of IKK and IκB signaling molecules. We further identified that transcription factor NFATc2 mediates autoregulation of RANKL expression in OSCC cells. Thus, our results implicate RANKL autoregulation as a novel mechanism that facilitates OSCC tumor cell growth and osteoclast differentiation/bone destruction.

Pathologic conditions of hard tissue: role of osteoclasts in osteolytic lesion

Hard tissue homeostasis is regulated by the balance between bone formation by osteoblasts and bone resorption by osteoclasts. This physiologic process allows adaptation to mechanical loading and calcium homeostasis. Under pathologic conditions, however, this process is ill-balanced resulting in either over-resorption or over-formation of hard tissue. Local over-resorption by osteoclasts is typically observed in osteolytic metastases of malignancies, autoimmune arthritis, and giant cell tumor of bone (GCTB). In tumor-related local osteolysis, tumor-derived osteoclast-activating factors induce bone resorption not by directly acting on osteoclasts but by indirectly upregulating receptor activator of NFκB ligand (RANKL) on osteoblastic cells. Similarly, synovial tissue in the autoimmune arthritis model does overexpress RANKL and contains numerous osteoclast precursors, and like a landing craft, when it comes in contact with eroded bone surfaces, osteoclast precursors are immediately polarized to become mature osteoclasts, inducing rapidly progressive bone destruction at a late stage of the disease. GCTB, on the other hand, is a common primary bone tumor, usually arising at the metaphysis of the long bone in young adults. After the discovery of RANKL, the concept of GCTB as a tumor of RANKL-expressing stromal cells was established, and comprehensive exosome studies finally disclosed the causative single-point mutation at histone H3.3 (H3F3A) in stromal cells. Thus, osteolytic lesions under various pathological conditions are ultimately attributable to the overexpression of RANKL, which opens up a common, practical and useful therapeutic target for diverse osteolytic conditions.

Hypericin targets osteoclast and prevents breast cancer-induced bone metastasis via NFATc1 signaling pathway

Bone is the most common target organ of metastasis of breast cancers. This produces considerable morbidity due to skeletal-related events, and severely reduces the quality of life. Increased osteoclast activity is implicated in breast cancer outgrowth in the bone microenvironment. Our previous observation of an anti-osteoclastic activity of hypericin, a natural plant compound, led us to investigate whether hypericin could inhibit bone metastasis and osteolysis caused by breast cancer. We find that hypericin inhibited the upregulation of osteoclasts stimulated by breast cancer cells. The activity of hypericin on osteoclasts and breast cancer-mediated osteoclastogenesis was associated with the inhibition of NFATc1 signaling pathway and attenuation of Ca2+ oscillation. Furthermore, hypericin suppresses invasion and migration in breast cancer cells, but has little effect on breast cancer-cell induced RANKL/OPG ratio in osteoblast or the expression of osteoclast-activating factors. Administration of hypericin could reduce tumor burden, osteolysis induced by direct inoculation of MDA-MB-231 cells into the bone marrow cavity of the tibia as well as metastasis of bone and improve survival in an experimental metastasis model by intracardiac injection of MDA-MB-231 breast cancer cells. Taken together, these results suggest that hypericin may be a potential natural agent for preventing and treating bone destruction in patients with bone metastasis due to breast cancer.

Breast cancer is associated to impaired glucose/insulin homeostasis in premenopausal obese/overweight patients

The association between breast cancer (BCa) presence and altered glucose/insulin metabolism is controversial likely due to an inaccurate insulin resistance (IR) assessment and inappropriate stratification of patients by body-mass index (BMI) and menopausal state. 148 women with suspect of sporadic BCa were stratified by BMI and menopause. Fasting levels of glucose, insulin, glycohemoglobin and selected IR-related and tumor-derived markers were measured. Glucose/insulin levels during OGTT were used to calculate insulin resistance/sensitivity indexes. Analysis of 77 BCa-bearing patients and 71 controls showed an association between BCa and IR as demonstrated by impaired glucose/insulin homeostasis (increased fasting- and OGTT-induced glucose levels) and deteriorated IR indexes, which was especially patent in premenopausal women. The association between BCa presence and IR was markedly influenced by BMI, being obese BCa patients significantly more insulin resistant than controls. BCa presence was associated to elevated levels of IR (glucose, triglycerides) and tumor-derived (VEGF) markers, especially in overweight/obese patients. BCa presence is associated to IR in overweight/obese premenopausal but not in premenopausal normal weight or postmenopausal women. Our data support a bidirectional relationship between dysregulated/imbalanced glucose/insulin metabolism and BCa, as tumor- and IR-markers are correlated with the impairment of glucose/insulin metabolism in overweight/obese premenopausal BCa patients.

The ABC7 regimen: a new approach to metastatic breast cancer using seven common drugs to inhibit epithelial-to-mesenchymal transition and augment capecitabine efficacy

Breast cancer metastatic to bone has a poor prognosis despite recent advances in our understanding of the biology of both bone and breast cancer. This article presents a new approach, the ABC7 regimen (Adjuvant for Breast Cancer treatment using seven repurposed drugs), to metastatic breast cancer. ABC7 aims to defeat aspects of epithelial-to-mesenchymal transition (EMT) that lead to dissemination of breast cancer to bone. As add-on to current standard treatment with capecitabine, ABC7 uses ancillary attributes of seven already-marketed noncancer treatment drugs to stop both the natural EMT process inherent to breast cancer and the added EMT occurring as a response to current treatment modalities. Chemotherapy, radiation, and surgery provoke EMT in cancer generally and in breast cancer specifically. ABC7 uses standard doses of capecitabine as used in treating breast cancer today. In addition, ABC7 uses 1) an older psychiatric drug, quetiapine, to block RANK signaling; 2) pirfenidone, an anti-fibrosis drug to block TGF-beta signaling; 3) rifabutin, an antibiotic to block beta-catenin signaling; 4) metformin, a first-line antidiabetic drug to stimulate AMPK and inhibit mammalian target of rapamycin, (mTOR); 5) propranolol, a beta-blocker to block beta-adrenergic signaling; 6) agomelatine, a melatonergic antidepressant to stimulate M1 and M2 melatonergic receptors; and 7) ribavirin, an antiviral drug to prevent eIF4E phosphorylation. All these block the signaling pathways - RANK, TGF-beta, mTOR, beta-adrenergic receptors, and phosphorylated eIF4E - that have been shown to trigger EMT and enhance breast cancer growth and so are worthwhile targets to inhibit. Agonism at MT1 and MT2 melatonergic receptors has been shown to inhibit both breast cancer EMT and growth. This ensemble was designed to be safe and augment capecitabine efficacy. Given the expected outcome of metastatic breast cancer as it stands today, ABC7 warrants a cautious trial.

RANK Ligand Modulation of Autophagy in Oral Squamous Cell Carcinoma Tumor Cells

Autophagy is a cellular process to recycle nutrients and has been implicated in cancer treatment. Oral squamous cell carcinoma (OSCC) is the most common oral cancer which ranks 3% of cancers in men and 2% in women. In this study, immunohistochemical staining of OSCC tumor specimens from human subjects and an athymic mouse model demonstrated high levels of autophagy markers LC3-II and ATG5 expression. Further, we identified high levels LC3-II expression in OSCC tumor cell lines (SCC-1, SCC-12, and SCC-14a) compared to normal human epithelial (RWPE-1) cells. OSCC cells express high levels of RANK ligand (RANKL); however, a functional role in autophagy is unknown. Interestingly, RANKL stimulation significantly increased autophagosome-related gene expressions such as LC3, ATG5, BECN1, and PI3KC3 mRNA expression in OSCC cells. Further, Western blot analysis of total cell lysates demonstrated a dose-dependent increase in LC3-II and ATG5 expression in RANKL-stimulated cells. In addition, RANKL increased expression of LC3-I and LC3-II, essential for autophagosome formation. Confocal microscopy analysis of LC3-II and localization with lysosome further confirms autophagosome formation in response to RANKL treatment in OSCC cells. Collectively, our results indicate a novel function of RANKL to induce autophagosome formation, and could be a potential therapeutic target to control OSCC tumor progression.

Role of the RANK/RANKL pathway in breast cancer

The discovery of the OPG/RANK/RANKL pathway two decades ago has initiated novel insights into regulation of bone formation. More recently this pathway has been found to be also relevant in osteoclastic-independent mechanisms, mainly in mammary physiology and breast cancer. RANKL/RANK function is essential for epithelial cell proliferation and cellular survival as well as lobulo-alveolar development. The endogenous OPG functions as a soluble decoy receptor, binding the cytokine RANKL to prevent RANKL from activating its receptor RANK. The regulatory function of RANKL is one of the key factors in progesterone-induced proliferation of the breast. Progesterone has a direct action of progesterone on progesterone-receptor (PR) expressing cells but PR-negative cells are affected indirectly through RANKL-induced paracrine actions leading to proliferation of mammary epithelial PR-negative cells. RANK induces epithelial-mesenchymal transition and stemness in human mammary epithelial cells and promotes tumorigenesis and metastasis. Inhibition of the RANK/RANKL pathway using the monoclonal antibody denosumab can neutralize RANKL and inhibiting its interaction with its receptor RANK. Denosumab is currently used to treat osteoporosis and in prevention of skeletal related events in patients suffering from bone metastases due to solid tumors. As preclinical experiments suggest the RANKL/RANK pathway plays an important role in primary breast cancer development. The interference with the RANK/RANKL system could therefore serve as a potential target for prevention and treatment of breast cancer.

Acidic microenvironment and bone pain in cancer-colonized bone

Solid cancers and hematologic cancers frequently colonize bone and induce skeletal-related complications. Bone pain is one of the most common complications associated with cancer colonization in bone and a major cause of increased morbidity and diminished quality of life, leading to poor survival in cancer patients. Although the mechanisms responsible for cancer-associated bone pain (CABP) are poorly understood, it is likely that complex interactions among cancer cells, bone cells and peripheral nerve cells contribute to the pathophysiology of CABP. Clinical observations that specific inhibitors of osteoclasts reduce CABP indicate a critical role of osteoclasts. Osteoclasts are proton-secreting cells and acidify extracellular bone microenvironment. Cancer cell-colonized bone also releases proton/lactate to avoid intracellular acidification resulting from increased aerobic glycolysis known as the Warburg effect. Thus, extracellular microenvironment of cancer-colonized bone is acidic. Acidosis is algogenic for nociceptive sensory neurons. The bone is densely innervated by the sensory neurons that express acid-sensing nociceptors. Collectively, CABP is evoked by the activation of these nociceptors on the sensory neurons innervating bone by the acidic extracellular microenvironment created by bone-resorbing osteoclasts and bone-colonizing cancer cells. As current treatments do not satisfactorily control CABP and can elicit serious side effects, new therapeutic interventions are needed to manage CABP. Understanding of the cellular and molecular mechanism by which the acidic extracellular microenvironment is created in cancer-colonized bone and by which the expression and function of the acid-sensing nociceptors on the sensory neurons are regulated would facilitate to develop novel therapeutic approaches for the management of CABP.

Contribution of acidic extracellular microenvironment of cancer-colonized bone to bone pain

Solid and hematologic cancer colonized bone produces a number of pathologies. One of the most common complications is bone pain. Cancer-associated bone pain (CABP) is a major cause of increased morbidity and diminishes the quality of life and affects survival. Current treatments do not satisfactorily control CABP and can elicit adverse effects. Thus, new therapeutic interventions are needed to manage CABP. However, the mechanisms responsible for CABP are poorly understood. The observation that specific osteoclast inhibitors can reduce CABP in patients indicates a critical role of osteoclasts in the pathophysiology of CABP. Osteoclasts create an acidic extracellular microenvironment by secretion of protons via vacuolar proton pumps during bone resorption. In addition, bone-colonized cancer cells also release protons and lactate via plasma membrane pH regulators to avoid intracellular acidification resulting from increased aerobic glycolysis known as the Warburg effect. Since acidosis is algogenic for sensory neurons and bone is densely innervated by sensory neurons that express acid-sensing nociceptors, the acidic bone microenvironments can evoke CABP. Understanding of the mechanism by which the acidic extracellular microenvironment is created in cancer-colonized bone and the expression and function of the acid-sensing nociceptors are regulated should facilitate the development of novel approaches for management of CABP. Here, the contribution of the acidic microenvironment created in cancer-colonized bone to elicitation of CABP and potential therapeutic implications of blocking the development and recognition of acidic microenvironment will be described. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Elevated Pentraxin 3 in bone metastatic breast cancer is correlated with osteolytic function

Pentraxin 3 (PTX3), a modulator of tumor-associated inflammation, is known to be positively correlated with tumor grade and severity of malignancies, but its exact role remains unclear. This study found that PTX3 expression was up-regulated in distant bone metastases of breast cancer compared to lung, liver, and brain metastases in 64 human breast cancer patients. Elevated expression of PTX3 was correlated with poor survival in patients with breast cancer. PTX3 expression was also up-regulated in a bone metastatic breast cancer cell line and further enhanced by pro-inflammatory cytokine TNFα. Administration of PTX3 promoted the migratory potential of breast cancer cells and the mobilization of macrophages, a precursor of osteoclasts (OCs), toward breast cancer cells. In addition, elevated expression of PTX3 by TNFα led to enhanced OC formation, implying the distinct role of PTX3 in osteolytic bone metastasis of breast cancer cells. Furthermore, PTX3 silencing using siRNA-specific siRNA prevented breast cancer cell migration, macrophage Chemotaxis, and subsequent OC formation. These findings provide an important insight into the key role of PTX3 in inflammation-associated osteolytic complications of breast cancer.

Obtusifolin suppresses phthalate esters-induced breast cancer bone metastasis by targeting parathyroid hormone-related protein

This study is the first to demonstrate that parathyroid hormone-related protein (PTHrP), produced by human breast cancer cells after exposure to phthalate esters, contributes to bone metastasis by increasing osteoclastogenesis. This is also the first to reveal that obtusifolin reverses phthalate esters-mediated bone resorption. Human breast cancer cells were treated with dibutyl phthalate (DBP), harvested in conditioned medium, and cultured to osteoblasts or osteoclasts. Cultures of osteoblasts with DBP-MDA-MB-231-CM increased the osteoclastogenesis activator RANKL (receptor activator of nuclear factor κ-B ligand) and M-CSF (macrophage colony-stimulating factor). PTHrP was secreted in MDA-MB-231 cells. DBP-MDA-MB-231-CM reduced osteoblasts to produce osteoprotegerin, an osteoclastogenesis inhibitor, while DBP mediated PTHrP up-regulation, increasing IL-8 secretion in MDA-MB-231 and contributing to breast cancer-mediated osteoclast differentiation and bone resorption. Obtusifolin, a major bioactive compound present in Cassia tora L., suppressed phthalate esters-mediated bone resorption. Therefore, obtusifolin may be a novel anti-breast-cancer bone metastasis agent.

Wedelolactone inhibits breast cancer-induced osteoclastogenesis by decreasing Akt/mTOR signaling

The bone is the most common metastatic site of breast cancer. Bone metastasis causes pain, pathologic fractures, and severely reduces the quality of life. Breast cancer causes osteolytic bone metastasis, which is dependent on osteoclast-mediated bone resorption. While current treatments rely on palliative anti-resorptive agents, there is a need to develop a drug based on potential alternative therapies. This study is the first to determine that wedelolactone (WDL), a natural coumarin isolated from plants, can inhibit breast cancer-mediated osteoclastogenesis. Osteoclasts were generated from human CD14(+) monocytes cultured with M-CSF/RANKL and WDL suppressed human osteoclast differentiation and activity in vitro in a dose-dependent manner. Moreover, WDL inhibited the upregulation of osteoclasts stimulated by MDA‑MB‑231 breast cancer cells. The activity of WDL on osteoclasts and breast cancer-mediated osteoclastogenesis was associated with the inhibition of Akt/mammalian target of the rapamycin signaling pathway (mTOR). Blocking Akt and mTOR by specific inhibitors significantly decreased osteoclast differentiation and bone resorption. Furthermore, WDL regulated breast cancer-enhanced interaction of osteoblasts and osteoclasts by decreasing M-CSF expression in MDA‑MB‑231-stimulated osteoblasts. Thus, this study suggests that WDL may be a potential natural agent for preventing and treating bone destruction in patients with bone metastasis due to breast cancer.

STC1 expression is associated with tumor growth and metastasis in breast cancer

Stanniocalcin-1 (STC1) is a secreted glycoprotein implicated in several pathologies including retinal degeneration, cerebral ischemia, angiogenesis and inflammation. Aberrant STC1 expression has been reported in breast cancer but the significance of this is not clear. High levels of STC1 expression were found in the aggressive 4T1 murine mammary tumor cells and in the MDA-MB-231 human breast cancer line. To investigate its significance, stable clones with STC1 down-regulation using shRNA were generated in both tumor models. The consequences of STC1 down-regulation on cell proliferation, chemotactic invasion, tumor growth and metastasis were assessed. Down-regulation of STC1 in the 4T1 murine mammary tumor cells had a major impact on mammary tumor growth. This observation was replicated in a second tumor model with the MDA-MB-231 human breast cancer line, with a significant reduction in primary tumor formation and a major inhibition of metastasis as well. Interestingly, in both models, proliferation in vitro was not affected. Subsequent microarray gene expression profiling identified 30 genes to be significantly altered by STC1 down-regulation, the majority of which are associated with known hallmarks of carcinogenesis. Furthermore, bioinformatic analysis of breast cancer datasets revealed that high expression of STC1 is associated with poor survival. This is the first study to show definitively that STC1 plays an oncogenic role in breast cancer, and indicates that STC1 could be a potential therapeutic target for treatment of breast cancer patients.