IL-1ß in breast cancer bone metastasis.

Bone is the most common site for advanced breast cancer to metastasise. The proinflammatory cytokine, interleukin-1ß (IL-1ß) plays a complex and contradictory role in this process. Recent studies have demonstrated that breast cancer patients whose primary tumours express IL-1ß are more likely to experience relapse in bone or other organs. Importantly, IL-1ß affects different stages of the metastatic process including growth of the primary tumour, epithelial to mesenchymal transition (EMT), dissemination of tumour cells into the blood stream, tumour cell homing to the bone microenvironment and, once in bone, this cytokine participates in the interaction between cancer cells and bone cells, promoting metastatic outgrowth at this site. Interestingly, although inhibition of IL-1ß signalling has been shown to have potent anti-metastatic effects, inhibition of the activity of this cytokine has contradictory effects on primary tumours, sometimes reducing but often promoting their growth. In this review, we focus on the complex roles of IL-1ß on breast cancer bone metastasis: specifically, we discuss the distinct effects of IL-1ß derived from tumour cells and/or microenvironment on inhibition/induction of primary breast tumour growth, induction of the metastatic process through the EMT, promotion of tumour cell dissemination into the bone metastatic niche and formation of overt metastases.

The IL-1/IL-1R axis induces greater fibroblast-derived chemokine release in human papillomavirus-negative compared to positive oropharyngeal cancer.

Human papillomavirus (HPV) is now recognised as a major aetiological agent in the pathogenesis of oropharyngeal carcinoma (OPC). HPV-positive tumours are associated with better outcomes compared to HPV-negative tumours, possibly due to differences in their aetiology and/or the tumour microenvironment. Increased numbers of tumour-associated leukocytes have been observed in many cancers including OPC, with variable influence on prognosis depending on the leukocyte subpopulation investigated. Whether HPV status influences leukocyte recruitment to OPC remains unknown. This in-vitro study examined differences in the chemoattractant capacity of HPV-positive and HPV-negative OPC cell lines. Gene and protein expression analysis demonstrated that whilst both monocultures of HPV-positive and HPV-negative cell lines, along with normal tonsillar fibroblasts (NTF), expressed low chemokine levels, NTF cultured with conditioned medium from HPV-negative OPC cells expressed significantly higher levels of all chemokines tested compared to NTF incubated with the medium from HPV-positive OPC cell lines. HPV-negative OPC lines expressed IL-1ß mRNA whereas HPV-positive cells did not, and NTF constitutively expressed IL-1R1. Pre-treatment with the IL-R antagonist, anakinra or siRNA to IL-1R1 significantly reduced chemokine secretion from NTF stimulated with conditioned medium from HPV-negative tumour cells or recombinant IL-1ß (p < 0.05). These data suggest that secretion of chemokines is driven by the interaction between HPV-negative OPC cells and stromal fibroblasts through an IL-1/IL-1R-mediated mechanism that is less prominent within the HPV-positive tumour microenvironment. These observations may explain differences in leukocyte sub-populations recruited to HPV-positive versus negative OPC and indicate that HPV status is a key determinant in controlling the inflammatory tumour microenvironment.

Parathyroid Hormone (PTH) Increases Skeletal Tumour Growth and Alters Tumour Distribution in an In Vivo Model of Breast Cancer.

Breast cancer cells colonize the skeleton by homing to specific niches, but the involvement of osteoblasts in tumour cell seeding, colonization, and progression is unknown. We used an in vivo model to determine how increasing the number of cells of the osteoblast lineage with parathyroid hormone (PTH) modified subsequent skeletal colonization by breast cancer cells. BALB/c nude mice were injected for five consecutive days with PBS (control) or PTH and then injected with DiD-labelled breast cancer cells via the intra-cardiac route. Effects of PTH on the bone microenvironment and tumour cell colonization and growth was analyzed using bioluminescence imaging, two-photon microscopy, and histological analysis. PTH treatment caused a significant, transient increase in osteoblast numbers compared to control, whereas bone volume/structure in the tibia was unaffected. There were no differences in the number of tumour cells seeding to the tibias, or in the number of tumours in the hind legs, between the control and PTH group. However, animals pre-treated with PTH had a significantly higher number of tumour colonies distributed throughout skeletal sites outside the hind limbs. This is the first demonstration that PTH-induced stimulation of osteoblastic cells may result in alternative skeletal sites becoming available for breast cancer cell colonization.

Mitotic quiescence, but not unique "stemness," marks the phenotype of bone metastasis-initiating cells in prostate cancer.

This study aimed to identify subpopulations of prostate cancer cells that are responsible for the initiation of bone metastases. Using rapidly dividing human prostate cancer cell lines, we identified mitotically quiescent subpopulations (<1%), which we compared with the rapidly dividing populations for patterns of gene expression and for their ability to migrate to the skeletons of athymic mice. The study used 2-photon microscopy to map the presence/distribution of fluorescently labeled, quiescent cells and luciferase expression to determine the presence of growing bone metastases. We showed that the mitotically quiescent cells were very significantly more tumorigenic in forming bone metastases than fast-growing cells (55 vs. 15%) and had a unique gene expression profile. The quiescent cells were not uniquely stem cell like, with no expression of CD133 but had the same level expression of other putative prostate stem cell markers (CD44 and integrins α2/ß1), when compared to the rapidly proliferating population. In addition, mitotic quiescence was associated with very high levels of C-X-C chemokine receptor type 4 (CXCR4) production. Inhibition of CXCR4 activity altered the homing of quiescent tumor cells to bone. Our studies suggest that mitotic dormancy is a unique phenotype that facilitates tumor cell colonization of the skeleton in prostate cancer.

OPG-Fc inhibits ovariectomy-induced growth of disseminated breast cancer cells in bone.

Dormant disseminated tumour cells can be detected in the bone marrow of breast cancer patients several years after resection of the primary tumour. The majority of these patients will remain asymptomatic, however, ∼ 15% will go on to develop overt bone metastases and this condition is currently incurable. The reason why these dormant cells are stimulated to proliferate and form bone tumours in some patients and not others remains to be elucidated. We have recently shown that in an in vivo model, increasing bone turnover by ovariectomy stimulated proliferation of disseminated tumour cells, resulting in formation of bone metastasis. We now show for the first time that osteoclast mediated mechanisms induce growth of tumours from dormant MDA-MB-231 cells disseminated in the bone. We also show that disruption of RANK-RANKL interactions following administration of OPG-Fc inhibits growth of these dormant tumour cells in vivo. Our data support early intervention with anti-resorptive therapy in a low-oestrogen environment to prevent development of bone metastases.

The role of IL-1B in breast cancer bone metastasis.

Interleukin-1B (IL-1B) is a potent pro-inflammatory cytokine that plays multiple, pivotal roles, in the complex interplay between breast cancer cells and the bone microenvironment. IL-1B is involved in the growth of the primary tumours, regulation of inflammation within the tumour microenvironment, promotion of epithelial to mesenchymal transition (EMT), migration and invasion. Moreover, when breast cancer cells arrive in the bone microenvironment there is an upregulation of IL-1B which promotes the creation of a conducive niche for metastatic breast cancer cells as well as stimulating initiation of the vicious cycle of bone metastasis. Pre-clinical studies have demonstrated that inhibition of IL-1 signalling reduces bone metastasis from oestrogen receptor positive/triple-negative breast cancers in various mouse models. However, effects on primary tumours and soft tissue metastasis remain controversial with some studies showing increased tumour growth in these sites, whilst others show no effects. Notably, combining anti-IL-1 therapy with standard-of-care treatments, such as chemotherapy and immunotherapy, has been demonstrated to reduce the growth of primary tumours, bone metastasis, as well as metastatic outgrowth in other organs. This review focuses on the mechanisms by which IL-1B promotes breast cancer bone metastasis.

The CDK4/6 Inhibitor Palbociclib Inhibits Estrogen-Positive and Triple Negative Breast Cancer Bone Metastasis In Vivo.

CDK 4/6 inhibitors have demonstrated significant improved survival for patients with estrogen receptor (ER) positive breast cancer (BC). However, the ability of these promising agents to inhibit bone metastasis from either ER+ve or triple negative BC (TNBC) remains to be established. We therefore investigated the effects of the CDK 4/6 inhibitor, palbociclib, using in vivo models of breast cancer bone metastasis. In an ER+ve T47D model of spontaneous breast cancer metastasis from the mammary fat pad to bone, primary tumour growth and the number of hind limb skeletal tumours were significantly lower in palbociclib treated animals compared to vehicle controls. In the TNBC MDA-MB-231 model of metastatic outgrowth in bone (intracardiac route), continuous palbociclib treatment significantly inhibited tumour growth in bone compared to vehicle. When a 7-day break was introduced after 28 days (mimicking the clinical schedule), tumour growth resumed and was not inhibited by a second cycle of palbociclib, either alone or when combined with the bone-targeted agent, zoledronic acid (Zol), or a CDK7 inhibitor. Downstream phosphoprotein analysis of the MAPK pathway identified a number of phosphoproteins, such as p38, that may contribute to drug-insensitive tumour growth. These data encourage further investigation of targeting alternative pathways in CDK 4/6-insensitive tumour growth.

Loss of plakoglobin promotes decreased cell-cell contact, increased invasion, and breast cancer cell dissemination in vivo.

INTRODUCTION: The majority of deaths from breast cancer are a result of metastases; however, little is understood about the genetic alterations underlying their onset. Genetic profiling has identified the adhesion molecule plakoglobin as being three-fold reduced in expression in primary breast tumors that have metastasized compared with nonmetastatic tumors. In this study, we demonstrate a functional role for plakoglobin in the shedding of tumor cells from the primary site into the circulation. METHODS: We investigated the effects of plakoglobin knockdown on breast cancer cell proliferation, migration, adhesion, and invasion in vitro and on tumor growth and intravasation in vivo. MCF7 and T47D cells were stably transfected with miRNA sequences targeting the plakoglobin gene, or scramble vector. Gene and protein expression was monitored by quantitative polymerase chain reaction (qPCR) and Western blot. Cell proliferation, adhesion, migration, and invasion were measured by cell counting, flow cytometry, and scratch and Boyden Chamber assays. For in vivo experiments, plakoglobin knockdown and control cells were inoculated into mammary fat pads of mice, and tumor growth, shedding of tumor cells into the bloodstream, and evidence of metastatic bone lesions were monitored with caliper measurement, flow cytometry, and microcomputed tomography (µCT), respectively. RESULTS: Plakoglobin and γ-catenin expression were reduced by more than 80% in all knockdown cell lines used but were unaltered after transfection with the scrambled sequence. Reduced plakoglobin resulted in significantly increased in MCF7 and T47D cell proliferation in vitro and in vivo, compared with control, with significantly more tumor cells being shed into the bloodstream of mice bearing plakoglobin knockdown tumors. In addition, plakoglobin knockdown cells showed a >250% increase in invasion through basement membrane and exhibited reduced cell-to-cell adhesion compared with control cells. CONCLUSION: Decreased plakoglobin expression increases the invasive behavior of breast cancer cells. This is the first demonstration of a functional role for plakoglobin/γ-catenin in the metastatic process, indicating that this molecule may represent a target for antimetastatic therapies.

Combination therapy inhibits development and progression of mammary tumours in immunocompetent mice.

We have determined the effect of combining the chemotherapy agent doxorubicin and the anti-resorptive drug zoledronic acid on the early stages of spontaneous mammary tumour development using the immunocompetent PyMT mouse model that closely mimics human breast cancer development. 6-week-old PyMT mice were treated weekly for 6 weeks with PBS, 2 mg/kg doxorubicin, 100 µg/kg zoledronic acid or doxorubicin followed 24 h later by zoledronic acid (n = 15/group). Untreated, 6-week-old animals were used for comparison of tumour development. Tumour volume, apoptosis and angiogenesis were analysed on H&E, caspase 3, CD31 and CD34 stained histological sections. Proliferation was measured by BrdU incorporation and Ki67 staining and tumour macrophage infiltration assessed by F4/80 immunohistochemistry. Animals treated with doxorubicin followed by zoledronic acid did not develop palpable mammary tumours, whereas in all other treatment groups tumours progressed to late stage adenocarcinomas. Tumours from the combination treatment group were of comparable size to those in 6-week-old untreated animals, remaining pre-malignant with well-differentiated acinar arrangements and with tumour volume only reaching on average 26% of that in the PBS control group. Tumour cell apoptosis and proliferation was significantly reduced compared to control, single agent or untreated 6-week-old mice. Significantly fewer circulating tumour cells were present in animals following sequential treatment compared to all other groups. Combination treatment with doxorubicin followed by zoledronic acid inhibits development and progression of spontaneously occurring mammary tumours.

Novel Methods of Targeting IL-1 Signalling for the Treatment of Breast Cancer Bone Metastasis.

Breast cancer bone metastasis is currently incurable. Evidence suggests that inhibiting IL-1 signalling with the IL1R antagonist, Anakinra, or the IL1ß antibody, Canakinumab, prevents metastasis and almost eliminates breast cancer growth in the bone. However, these drugs increase primary tumour growth. We, therefore, investigated whether targeting other members of the IL-1 pathway (Caspase-1, IL1ß or IRAK1) could reduce bone metastases without increasing tumour growth outside of the bone. Inhibition of IL-1 via MLX01 (IL1ß secretion inhibitor), VRT043198/VX765 (Caspase-1 inhibitor), Pacritinib (IRAK1 inhibitor) or Anakinra (IL1R antagonist) on tumour cell viability, migration and invasion were assessed in mouse mammary E0771 and Py8119 cells in vitro and on primary tumour growth, spontaneous metastasis and metastatic outgrowth in vivo. In vitro, Inhibition of IL-1 signalling by MLX01, VRT043198 and Anakinra reduced migration of E0771 and Py8119 cells and reversed tumour-derived IL1ß induced-increased invasion and migration towards bone cells. In vivo, VX765 and Anakinra significantly reduced spontaneous metastasis and metastatic outgrowth in the bone, whereas MLX01 reduced primary tumour growth and bone metastasis. Pacritinib had no effect on metastasis in vitro or in vivo. Targeting IL-1 signalling with small molecule inhibitors may provide a new therapeutic strategy for breast cancer bone metastasis.

The kinetochore protein Cenp-F is a potential novel target for zoledronic acid in breast cancer cells.

The anti-resorptive agent zoledronic acid inhibits key enzymes in the mevalonate pathway, disrupting post-translational modification and thereby correct protein localization and function. Inhibition of prenylation may also be responsible for the reported anti-tumour effects of zoledronic acid, but the specific molecular targets have not been identified. Cenp-F/mitosin, a kinetochore-associated protein involved in the correct separation of chromosomes during mitosis, has been shown to undergo post-translational prenylation and may therefore be a novel target contributing to the anti-tumour effects of zoledronic acid. We investigated whether zoledronic acid causes loss of Cenp-F from the kinetochore in breast cancer cells, to determine if the reported anti-tumour effects may be mediated by impairing correct chromosome separation. MDA-MB-436, MDA-MB-231 and MCF-7 breast cancer cells and MCF-10A non-malignant breast epithelial cells were treated with zoledronic acid in vitro, and the effect on Cenp-F localization was analysed by immunoflourescence microscopy. Zoledronic acid caused loss of Cenp-F from the kinetochore, accompanied by an increase in the number of cells in pro-, /prometa- and metaphase in all of the cancer cell lines. There was also a significant increase in the number of lagging chromosomes in mitotic cells. The effects of zoledronic acid could be reversed by inclusion of an intermediary of the mevalonate pathway, showing that the loss of Cenp-F from the kinetochore was caused by the inhibition of farnesylation. In contrast, no effect was seen on Cenp-F in non-malignant MCF-10A cells. This is the first report showing a specific effect of zoledronic acid on a protein involved in the regulation of chromosome segregation, identifying Cenp-F as a potential new molecular target for NBPs in tumour cells.

Transcriptomic Profiling Reveals Novel Candidate Genes and Signalling Programs in Breast Cancer Quiescence and Dormancy.

Metastatic recurrence, the major cause of breast cancer mortality, is driven by reactivation of dormant disseminated tumour cells that are defined by mitotic quiescence and chemoresistance. The molecular mechanisms underpinning mitotic quiescence in cancer are poorly understood, severely limiting the development of novel therapies for removal of residual, metastasis-initiating tumour cells. Here, we present a molecular portrait of the quiescent breast cancer cell transcriptome across the four main breast cancer sub-types (luminal, HER2-enriched, basal-like and claudin-low) and identify a novel quiescence-associated 22-gene signature using an established lipophilic-dye (Vybrant® DiD) retention model and whole-transcriptomic profiling (mRNA-Seq). Using functional association network analysis, we elucidate the molecular interactors of these signature genes. We then go on to demonstrate that our novel 22-gene signature strongly correlates with low tumoural proliferative activity, and with dormant disease and late metastatic recurrence (≥5 years after primary tumour diagnosis) in metastatic breast cancer in multiple clinical cohorts. These genes may govern the formation and persistence of disseminated tumour cell populations responsible for breast cancer recurrence, and therefore represent prospective novel candidates to inform future development of therapeutic strategies to target disseminated tumour cells in breast cancer, eliminate minimal residual disease and prevent metastatic recurrence.

Oestradiol Contributes to Differential Antitumour Effects of Adjuvant Zoledronic Acid Observed Between Pre- and Post-Menopausal Women.

Clinical trials have demonstrated that adding zoledronic acid (Zol) to (neo)adjuvant standard of care has differential antitumour effects in pre- and post-menopausal women: Both benefit from reduced recurrence in bone; however, while postmenopausal women also incur survival benefit, none is seen in premenopausal women treated with adjuvant bisphosphonates. In the current study, we have used mouse models to investigate the role of oestradiol in modulating potential antitumour effects of Zol. Pre-, peri-, and post-menopausal concentrations of oestradiol were modelled in BALB/c wild-type, BALB/c nude, and C57BL/6 mice by ovariectomy followed by supplementation with oestradiol. Mice also received 40 mg/kg/day goserelin to prevent ovariectomy-induced increases in follicle-stimulating hormone (FSH). Metastasis was modelled following injection of MDA-MB-231, 4T1, or E0771 cells after ovariectomy and saline or 100 µg/kg Zol administered weekly. Supplementing ovariectomised mice with 12.5 mg/ml, 1.38 mg/ml, and 0 ng/ml oestradiol, in the presence of goserelin, resulted in serum concentrations of 153.16 ± 18.10 pg/ml, 48.64 ± 18.44 pg/ml, and 1.00 ± 0.27 pg/ml oestradiol, which are equivalent to concentrations found in pre-, peri-, and post-menopausal humans. Osteoclast activity was increased 1.5-1.8-fold with peri- and post-menopausal compared with premenopausal oestradiol, resulting in a 1.34-1.69-fold reduction in trabecular bone. Zol increased trabecular bone in all groups but did not restore bone to volumes observed under premenopausal conditions. In tumour-bearing mice, Zol reduced bone metastases in BALB/c (wild-type and nude), with greatest effects seen under pre- and post-menopausal concentrations of oestradiol. Zol did not affect soft tissue metastases in immunocompetent BALB/c mice but increased metastases 3.95-fold in C57BL/6 mice under premenopausal concentrations of oestradiol. In contrast, Zol significantly reduced soft tissue metastases 2.07 and 4.69-fold in immunocompetent BALB/c and C57BL/6 mice under postmenopausal oestradiol, mirroring the results of the clinical trials of (neo)adjuvant bisphosphonates. No effects on soft tissue metastases were observed in immunocompromised mice, and differences in antitumour response did not correlate with musculoaponeurotic fibrosarcoma (MAF), macrophage capping protein (CAPG), or PDZ domain containing protein GIPC1 (GIPC1) expression. In conclusion, oestradiol contributes to altered antitumour effects of Zol observed between pre- and post-menopausal women. However, other immunological/microenvironmental factors are also likely to contribute to this phenomenon.

Increased Abundance of Tumour-Associated Neutrophils in HPV-Negative Compared to HPV-Positive Oropharyngeal Squamous Cell Carcinoma Is Mediated by IL-1R Signalling.

The incidence of human papillomavirus (HPV)-associated cancer is increasing and HPV is now implicated in the aetiology of more than 60% of all oropharyngeal squamous cell carcinomas (OPSCC). In OPSCC, innate immune cells such as neutrophils and macrophages generally correlate with poor prognosis, whilst adaptive immune cells, such as lymphocytes, tend to correlate with improved prognosis. This may, in part, be due to differences in the immune response within the tumour microenvironment leading to the recruitment of specific tumour-associated leukocyte sub-populations. In this study, we aimed to examine if differences exist in the levels of infiltrated leukocyte sub-populations, with particular emphasis on tumour-associated neutrophils (TAN), and to determine the mechanism of chemokine-induced leukocyte recruitment in HPV-positive compared to HPV-negative OPSCC. Immunohistochemical analysis showed that HPV-negative OPSCC contained significantly more neutrophils than HPV-positive tumours, whilst levels of CD68+ macrophages and CD3+ lymphocytes were similar. Using a 3D tissue culture model to represent tumour-stromal interactions, we demonstrated that HPV-negative tumour-stromal co-cultures expressed significantly higher levels of CXCL8, leading to increased neutrophil recruitment compared to their HPV-positive counterparts. HPV-negative OPSCC cells have previously been shown to express higher levels of IL-1 than their HPV-positive counterparts, indicating that this cytokine may be responsible for driving increased chemokine production in the HPV-negative 3D model. Inhibition of IL-1R in the tumour-stromal models using the receptor-specific antagonist, anakinra, dramatically reduced chemokine secretion and significantly impaired neutrophil and monocyte recruitment, suggesting that this tumour-stromal response is mediated by the IL-1/IL-1R axis. Here, we identify a mechanism by which HPV-negative OPSCC may recruit more TAN than HPV-positive OPSCC. Since TAN are associated with poor prognosis in OPSCC, our study identifies potential therapeutic targets aimed at redressing the chemokine imbalance to reduce innate immune cell infiltration with the aim of improving patient outcome.

Osteoblast-Derived Paracrine and Juxtacrine Signals Protect Disseminated Breast Cancer Cells from Stress.

Metastatic breast cancer in bone is incurable and there is an urgent need to develop new therapeutic approaches to improve survival. Key to this is understanding the mechanisms governing cancer cell survival and growth in bone, which involves interplay between malignant and accessory cell types. Here, we performed a cellular and molecular comparison of the bone microenvironment in mouse models representing either metastatic indolence or growth, to identify mechanisms regulating cancer cell survival and fate. In vivo, we show that regardless of their fate, breast cancer cells in bone occupy niches rich in osteoblastic cells. As the number of osteoblasts in bone declines, so does the ability to sustain large numbers of breast cancer cells and support metastatic outgrowth. In vitro, osteoblasts protected breast cancer cells from death induced by cell stress and signaling via gap junctions was found to provide important juxtacrine protective mechanisms between osteoblasts and both MDA-MB-231 (TNBC) and MCF7 (ER+) breast cancer cells. Combined with mathematical modelling, these findings indicate that the fate of DTCs is not controlled through the association with specific vessel subtypes. Instead, numbers of osteoblasts dictate availability of protective niches which breast cancer cells can colonize prior to stimulation of metastatic outgrowth.

IL-1B drives opposing responses in primary tumours and bone metastases; harnessing combination therapies to improve outcome in breast cancer.

Breast cancer bone metastasis is currently incurable, ~75% of patients with late-stage breast cancer develop disease recurrence in bone and available treatments are only palliative. We have previously shown that production of the pro-inflammatory cytokine interleukin-1B (IL-1B) by breast cancer cells drives bone metastasis in patients and in preclinical in vivo models. In the current study, we have investigated how IL-1B from tumour cells and the microenvironment interact to affect primary tumour growth and bone metastasis through regulation of the immune system, and whether targeting IL-1 driven changes to the immune response improves standard of care therapy for breast cancer bone metastasis. Using syngeneic IL-1B/IL1R1 knock out mouse models in combination with genetic manipulation of tumour cells to overexpress IL-1B/IL1R1, we found that IL-1B signalling elicited an opposite response in primary tumours compared with bone metastases. In primary tumours, IL-1B inhibited growth, by impairing the infiltration of innate immune cell subsets with potential anti-cancer functions but promoted enhanced tumour cell migration. In bone, IL-1B stimulated the development of osteolytic metastases. In syngeneic models of breast cancer, combining standard of care treatments (Doxorubicin and Zoledronic acid) with the IL-1 receptor antagonist Anakinra inhibited both primary tumour growth and metastasis. Anakinra had opposite effects on the immune response compared to standard of care treatment, and its anti-inflammatory signature was maintained in the combination therapy. These data suggest that targeting IL-1B signalling may provide a useful therapeutic approach to inhibit bone metastasis and improve efficacy of current treatments for breast cancer patients.

Sustained inhibition of tumor growth and prolonged survival following sequential administration of doxorubicin and zoledronic acid in a breast cancer model.

Combination therapy, using agents that target the microenvironment as well as the cancer cells, is common in the treatment of advanced breast cancer. Here, we show that a 6-week course of weekly sequential administration of the cytotoxic drug doxorubicin (2 mg/kg), followed 24 hr later by the antiresorptive agent zoledronic acid (100 microg/kg), causes substantial inhibition of subcutaneous MDA-MB-436 breast tumor growth in immunocompromised mice, leading to significantly increased survival. Tumor growth did not resume following withdrawal of treatment after 6 weeks, with 60% of the animals in this group surviving for more than 160 days. In comparison, animals receiving single-agent therapy all died within 50 days. Molecular analysis of the tumors showed no effect on cell cycle or apoptosis following administration of 100 microg/kg zoledronic acid or 2 mg/kg doxorubicin alone. When doxorubicin was administered 24 hr before zoledronic acid, tumors displayed decreased expression of CYCLINS E1, B, D1 and D3 as well as CDK2, CDC2, CDK4 and CDK7, indicative of cell-cycle inhibition. Tumors from animals receiving sequential treatment also showed induction of both intrinsic- and extrinsic-apoptotic pathways, with increased expression of BAX, decreased expression of BCL-2 and activation of CASPASE 3, 8 and 9. Accumulation of the unprenylated form of RAP1a, a surrogate marker for uptake of zoledronic acid, was only detected in tumors from animals treated with doxorubicin 24 hr before zoledronic acid. Our data are the first to show a sustained antitumor effect in vivo following a limited course of sequential administration of doxorubicin followed by zoledronic acid.

Combined administration of a small-molecule inhibitor of TRAF6 and Docetaxel reduces breast cancer skeletal metastasis and osteolysis.

Tumour necrosis factor receptor-associated factor 6 (TRAF6) has been implicated in breast cancer and osteoclastic bone destruction. Here, we report that 6877002, a verified small-molecule inhibitor of TRAF6, reduced metastasis, osteolysis and osteoclastogenesis in models of osteotropic human and mouse breast cancer. First, we observed that TRAF6 is highly expressed in osteotropic breast cancer cells and its level of expression was higher in patients with bone metastasis. Pre-exposure of osteoclasts and osteoblasts to non-cytotoxic concentrations of 6877002 inhibited cytokine-induced NFκB activation and osteoclastogenesis, and reduced the ability of osteotropic human MDA-MB-231 and mouse 4T1 breast cancer cells to support bone cell activity. 6877002 inhibited human MDA-MB-231-induced osteolysis in the mouse calvaria organ system, and reduced soft tissue and bone metastases in immuno-competent mice following intra-cardiac injection of mouse 4T1-Luc2 cells. Of clinical relevance, combined administration of 6877002 with Docetaxel reduced metastasis and inhibited osteolytic bone damage in mice bearing 4T1-Luc2 cells. Thus, TRAF6 inhibitors such as 6877002 - alone or in combination with conventional chemotherapy - show promise for the treatment of metastatic breast cancer.

Differential effect of doxorubicin and zoledronic acid on intraosseous versus extraosseous breast tumor growth in vivo.

PURPOSE: Breast cancer patients with bone metastases are commonly treated with chemotherapeutic agents such as doxorubicin and zoledronic acid to control their bone disease. Sequential administration of doxorubicin followed by zoledronic acid has been shown to increase tumor cell apoptosis in vitro. We have therefore investigated the antitumor effects of clinically relevant doses of these drugs in a mouse model of breast cancer bone metastasis. EXPERIMENTAL DESIGN: MDA-MB-231/BO2 cells were injected via the tail vein into athymic mice. Tumor-induced osteolytic lesions were detected in all animals following X-ray analysis 18 days after tumor cell inoculation (day 18). Mice were administered saline, 100 microg/kg zoledronic acid, 2 mg/kg doxorubicin, doxorubicin and zoledronic acid simultaneously, or doxorubicin followed 24 h later by zoledronic acid. Doxorubicin-treated animals received a second injection on day 25. Tumor growth in the marrow cavity and on the outside surface of the bone was measured as well as tumor cell apoptosis and proliferation. The effects of treatments on bone were evaluated following X-ray and muCT analysis. RESULTS: Sequential treatment with doxorubicin followed by zoledronic acid caused decreased intraosseous tumor burden, which was accompanied by increased levels of tumor cell apoptosis and decreased levels of proliferation, whereas extraosseous parts of the same tumors were unaffected. Administration of zoledronic acid, alone or in combination with doxorubicin, resulted in significantly smaller tumor-induced osteolytic lesions compared with control or doxorubicin-treated animals. CONCLUSIONS: This is the first study to show that sequential treatment with clinically relevant doses of doxorubicin, followed 24 h later by zoledronic acid, reduces intraosseous but not extraosseous growth of BO2 breast tumors. Our results suggest that breast cancer patients with metastatic bone disease may benefit from sequential treatment using doxorubicin and zoledronic acid.