Involvement of cell-cell and cell-matrix interactions in bone destruction induced by metastatic MDA-MB-231 human breast cancer cells in nude mice

Parathyroid hormone-related protein (PTHrP)-dependent modulation of gene expression signatures in cancer cells

PTHrP is encoded by PTHLH gene which can generate by alternative promoter usage and splicing mechanisms at least three mature peptides of 139, 141 and 173 amino acids with distinct carboxy terminus. PTHrP may undergo proteolytic processing into smaller bioactive forms, comprising an amino terminus peptide, which is the mediator of the "classical" PTH-like effect, as well as midregion and carboxy terminus peptides that act as multifaceted critical regulator of proliferation, differentiation and apoptosis via the reprogramming of gene expression in normal and neoplastic cells. Moreover, a nuclear/nucleolar localization signal sequence is present in the [87-107] domain allowing PTHrP nuclear import and "intracrine" effect additional to the autocrine/paracrine one. Within the large number of data available in the literature on PTHrP bioactivities, the goal of this chapter is to pick up selected studies that report the detection of molecular signatures of cancer cell exposure to PTHrP, either as full-length protein or discrete peptides, demonstrated by individual gene or whole genome expression profiling, briefly recapitulating the biological implications associated with the specific gene activation or silencing.

Inhibitory effect of cathepsin K inhibitor (ODN-MK-0822) on invasion, migration and adhesion of human breast cancer cells in vitro

Approximately 90% of patients with advanced breast cancer develop bone metastases; an event that results in severe decrease of quality of life and a drastic deterioration in prognosis. Therefore, to increase the survival of breast cancer patients, the development of new therapeutic strategies to impair metastatic process and skeletal complications is critical. Previous studies on the role of cathepsin K (CTSK) in metastatic spreading led to several strategies for inhibition of this molecule such as MIV-711 (Medivir), balicatib and odanacatib (ODN) which were on trial in the past. The present study intended to assess the anti-metastatic efficacy of ODN in breast cancer cells. Human breast cancer cell lines MDA-MB-231 were treated with different concentrations of ODN and performed invasion, adhesion and migration assays and, RT-PCR and western blot to evaluate the effect of ODN on the metastatic potential of breast cancer cells. ODN markedly decreased wound healing cell migration, invasion and adhesion at a dose dependent manner. ODN inhibits cell invasion by decreasing the matrix metalloproteinase (MMP-9) with the upregulation of TIMP-1 expression. ODN effectively inhibited the phosphorylation of extracellular signal-regulated kinase (ERK), p38, and c-Jun N-terminal Kinase (JNK), and blocked the expression of β-integrins and FAK proteins. ODN also significantly inhibited PI3K downstream targets Rac1, Cdc42, paxillin and Src which are critical for cell adhesion, migration and cytoskeletal reorganization. ODN exerts anti-metastatic action through inhibition of signaling pathway for MMP-9, PI3K and MAPK. This indicates potential therapeutic effects of ODN in the treatment of metastatic breast cancer.

Bone metastasis: Interaction between cancer cells and bone microenvironment

BACKGROUND

Bone is one of the most common target organs for cancer metastasis, especially in patients with advanced breast and prostate cancers. Despite recent advances in therapeutic approaches, bone metastases remain incurable and produce multiple complications called skeletal-related events, including hypercalcemia, pathological fractures, spinal compression, and bone pain, which are associated with poor prognosis.

HIGHLIGHT

Although the precise mechanisms are yet to be fully elucidated, accumulating evidence suggests that bone provides a favorable microenvironment that enables circulating cancer cells to home, proliferate, and colonize, resulting in the formation of metastasis. Cancer cells that metastasize to bone also possess unique features, enabling them to utilize the bone microenvironment. Thus, communication between cancer cells and bone is believed to be critical for the development and progression of bone metastases.

CONCLUSION

Continued studies are warranted to understand the molecular mechanisms underlying bone metastases and to develop mechanism-based and effective therapeutic interventions.

BRCA1 haploinsufficiency cell-autonomously activates RANKL expression and generates denosumab-responsive breast cancer-initiating cells

Denosumab, a monoclonal antibody to the receptor activator of nuclear factor-κB ligand (RANKL), might be a novel preventative therapy for BRCA1-mutation carriers at high risk of developing breast cancer. Beyond its well-recognized bone-targeted activity impeding osteoclastogenesis, denosumab has been proposed to interfere with the cross-talk between RANKL-producing sensor cells and cancer-initiating RANK+ responder cells that reside within premalignant tissues of BRCA1-mutation carriers. We herein tested the alternative but not mutually exclusive hypothesis that BRCA1 deficiency might cell-autonomously activate RANKL expression to generate cellular states with cancer stem cell (CSC)-like properties. Using isogenic pairs of normal-like human breast epithelial cells in which the inactivation of a single BRCA1 allele results in genomic instability, we assessed the impact of BRCA1 haploinsufficiency on the expression status of RANK and RANKL. RANK expression remained unaltered but RANKL was dramatically up-regulated in BRCA1mut/+ haploinsufficient cells relative to isogenic BRCA1+/+ parental cells. Neutralizing RANKL with denosumab significantly abrogated the ability of BRCA1 haploinsufficient cells to survive and proliferate as floating microtumors or "mammospheres" under non-adherent/non-differentiating conditions, an accepted surrogate of the relative proportion and survival of CSCs. Intriguingly, CSC-like states driven by epithelial-to-mesenchymal transition or HER2 overexpression traits responded to some extent to denosumab. We propose that breast epithelium-specific mono-allelic inactivation of BRCA1 might suffice to cell-autonomously generate RANKL-addicted, denosumab-responsive CSC-like states. The convergent addiction to a hyperactive RANKL/RANK axis of CSC-like states from genetically diverse breast cancer subtypes might inaugurate a new era of cancer prevention and treatment based on denosumab as a CSC-targeted agent.

ITGBL1 Is a Runx2 Transcriptional Target and Promotes Breast Cancer Bone Metastasis by Activating the TGFβ Signaling Pathway

Bone metastasis affects more than 70% of advanced breast cancer patients, but the molecular mechanisms of this process remain unclear. Here, we present clinical and experimental evidence to clarify the role of the integrin β-like 1 (ITGBL1) as a key contributor to bone metastasis of breast cancer. In an in vivo model system and in vitro experiments, ITGBL1 expression promoted formation of osteomimetic breast cancers, facilitating recruitment, residence, and growth of cancer cells in bone microenvironment along with osteoclast maturation there to form osteolytic lesions. Mechanistic investigations identified the TGFβ signaling pathway as a downstream effector of ITGBL1 and the transcription factor Runx2 as an upstream activator of ITGBL1 expression. In support of these findings, we also found that ITGBL1 was an essential mediator of Runx2-induced bone metastasis of breast cancer. Overall, our results illuminate how bone metastasis occurs in breast cancer, and they provide functional evidence for new candidate biomarkers and therapeutic targets to identify risk, to prevent, and to treat this dismal feature of advanced breast cancer.

In vitro microenvironments to study breast cancer bone colonisation

Bone metastasis occurs frequently in patients with advanced breast cancer and is a major cause of morbidity and mortality in these patients. In order to advance current therapies, the mechanisms leading to the formation of bone metastases and their pathophysiology have to be better understood. Several in vitro models have been developed for systematic studies of interactions between breast cancer cells and the bone microenvironment. Such models can provide insights into the molecular basis of bone metastatic colonisation and also may provide a useful platform to design more physiologically relevant drug testing assays. This review describes different in vitro approaches and discusses their advantages and disadvantages.

Targeting RANKL in metastasis

Acting through its cognate receptor, receptor activator of nuclear factor-κB (RANK), RANK ligand (RANKL) is an essential mediator of osteoclast function and survival. Preclinical data have now firmly established that blockade of tumor-induced osteoclastogenesis by RANKL inhibition will not only protect against bone destruction but will also inhibit the progression of established bone metastases and delay the formation of de novo bone metastases in cancer models. In patients with bone metastases, skeletal complications are driven by increased osteoclastic activity and may result in pathological fractures, spinal cord compression and the need for radiotherapy to the bone or orthopedic surgery (collectively known as skeletal-related events (SREs)). Denosumab, a fully human monoclonal antibody against RANKL, has been demonstrated to prevent or delay SREs in patients with solid tumors that have metastasized to bone. In addition to its central role in tumor-induced osteolysis, bone destruction and skeletal tumor progression, there is emerging evidence for direct pro-metastatic effects of RANKL, independent of osteoclasts. For example, RANKL also stimulates metastasis via activity on RANK-expressing cancer cells, resulting in increased invasion and migration. Pharmacological inhibition of RANKL may also reduce bone and lung metastasis through blockade of the direct action of RANKL on metastatic cells. This review describes these distinct but potentially overlapping mechanisms by which RANKL may promote metastases.

DHA is a more potent inhibitor of breast cancer metastasis to bone and related osteolysis than EPA

Breast cancer patients often develop bone metastasis evidenced by osteolytic lesions, leading to severe pain and bone fracture. Attenuation of breast cancer metastasis to bone and associated osteolysis by fish oil, rich in EPA and DHA, has been demonstrated previously. However, it was not known whether EPA and DHA differentially or similarly affect breast cancer bone metastasis and associated osteolysis. In vitro culture of parental and luciferase gene encoded MDA-MB-231 human breast cancer cell lines treated with EPA and DHA revealed that DHA inhibits proliferation and invasion of breast cancer cells more potently than EPA. Intra-cardiac injection of parental and luciferase gene encoded MDA-MB-231 cells to athymic NCr nu/nu mice demonstrated that DHA-treated mice had significantly less breast cancer cell burden in bone, and also significantly less osteolytic lesions than EPA-treated mice. In vivo cell migration assay as measured by luciferase intensity revealed that DHA attenuated cell migration specifically to the bone. Moreover, the DHA-treated group showed reduced levels of CD44 and TRAP positive area in bone compared to EPA-treated group. Breast cancer cell burden and osteolytic lesions were also examined in intra-tibially breast cancer cell injected mice and found less breast cancer cell growth and associated osteolysis in DHA-treated mice as compared to EPA-treated mice. Finally, doxorubicin-resistant MCF-7 (MCF-7dox) human breast cancer cell line was used to examine if DHA can improve sensitization of MCF-7dox cells to doxorubicin. DHA improved the inhibitory effect of doxorubicin on proliferation and invasion of MCF-7dox cells. Interestingly, drug resistance gene P-gp was also down-regulated in DHA plus doxorubicin-treated cells. In conclusion, DHA attenuates breast cancer bone metastasis and associated osteolysis more potently than EPA, possibly by inhibiting migration of breast cancer cell to the bone as well as by inhibiting osteoclastic bone resorption.

Delineating breast cancer cell interactions with engineered bone microenvironments

The mechanisms leading to colonization of metastatic breast cancer cells (BCa) in the skeleton are still not fully understood. Here, we demonstrate that mineralized extracellular matrices secreted by primary human osteoblasts (hOBM) modulate cellular processes associated with BCa colonization of bone. A panel of four BCa cell lines of different bone-metastatic potential (T47D, SUM1315, MDA-MB-231, and the bone-seeking subline MDA-MB-231BO) was cultured on hOBM. After 3 days, the metastatic BCa cells had undergone morphological changes on hOBM and were aligned along the hOBM's collagen type I fibrils that were decorated with bone-specific proteins. In contrast, nonmetastatic BCa cells showed a random orientation on hOBM. Atomic force microscopy-based single-cell force spectroscopy revealed that the metastatic cell lines adhered more strongly to hOBM compared with nonmetastatic cells. Function-blocking experiments indicated that β1 -integrins mediated cell adhesion to hOBM. In addition, metastatic BCa cells migrated directionally and invaded hOBM, which was accompanied by enhanced MMP-2 and -9 secretion. Furthermore, we observed gene expression changes associated with osteomimickry in BCa cultured on hOBM. As such, osteopontin mRNA levels were significantly increased in SUM1315 and MDA-MB-231BO cells in a β1 -integrin-dependent manner after growing for 3 days on hOBM compared with tissue culture plastic. In conclusion, our results show that extracellular matrices derived from human osteoblasts represent a powerful experimental platform to dissect mechanisms underlying critical steps in the development of bone metastases.

Cancer stem-like cell marker CD44 promotes bone metastases by enhancing tumorigenicity, cell motility, and hyaluronan production

CD44, an adhesion molecule that binds to the extracellular matrix, primarily to hyaluronan (HA), has been implicated in cancer cell migration, invasion, and metastasis. CD44 has also recently been recognized as a marker for stem cells of several types of cancer. However, the roles of CD44 in the development of bone metastasis are unclear. Here, we addressed this issue by using bone metastatic cancer cell lines, in which CD44 was stably knocked down. Tumor sphere formation and cell migration and invasion were significantly inhibited by CD44 knockdown. Furthermore, the downregulation of CD44 markedly suppressed tumorigenicity and bone metastases in nude mice. Of note, the number of osteoclasts decreased in the bone metastases. Microarray analysis revealed that the expression of HA synthase 2 was downregulated in CD44-knockdown cells. The localization of HA in the bone metastatic tumors was also markedly reduced. We then examined the roles of CD44-HA interaction in bone metastasis using 4-methylumbelliferone (4-MU), an inhibitor of HA synthesis. 4-MU decreased tumor sphere and osteoclast-like cell formation in vitro. Moreover, 4-MU inhibited bone metastases in vivo with reduced number of osteoclasts. These results collectively suggest that CD44 expression in cancer cells promotes bone metastases by enhancing tumorigenicity, cell migration and invasion, and HA production. Our results also suggest the possible involvement of CD44-expressing cancer stem cells in the development of bone metastases through interaction with HA. CD44-HA interaction could be a potential target for therapeutic intervention for bone metastases.

Integrin α(v)β₃ as a PET imaging biomarker for osteoclast number in mouse models of negative and positive osteoclast regulation

PURPOSE

The goal of this study was to determine the specificity of ⁶⁴Cu-CB-TE2A-c(RGDyK) (⁶⁴Cu-RGD) for osteoclast-related diseases, such as Paget's disease or rheumatoid arthritis.

PROCEDURES

C57BL/6 mice were treated systemically with osteoprotegerin (OPG) for 15 days or RANKL for 11 days to suppress and stimulate osteoclastogenesis, respectively. The mice were then imaged by positron emission tomography/computed tomography using ⁶⁴Cu-RGD, followed by determination of serum TRAP5b and bone histology. Standard uptake values were determined to quantify ⁶⁴Cu-RGD in bones and other tissues.

RESULTS

Mice treated with OPG showed decreased bone uptake of ⁶⁴Cu-RGD at 1, 2, and 24 h post-injection of the tracer (p < 0.01 for all time points) compared to vehicle controls, which correlated with a post-treatment decrease in serum TRAP5b. In contrast, mice treated with RANKL showed significantly increased bone uptake at 2 h post-injection of (⁶⁴Cu-RGD (p < 0.05) compared to the vehicle control group, corresponding to increased serum TRAP5b and OC numbers as determined by bone histology.

CONCLUSIONS

These data demonstrate that ⁶⁴Cu-RGD localizes to areas in bone with increased osteoclast numbers and support the use of ⁶⁴Cu-RGD as an imaging biomarker for osteoclast number that could be used to monitor osteoclast-related pathologies and their treatments.

Evaluating the effects of mixed osteolytic/osteoblastic metastasis on vertebral bone quality in a new rat model

Spinal metastases often show mixed areas of enhanced (osteoblastic) bone growth adjacent to areas of thinning (osteolytic) bone. This study aims to quantitatively characterize bone quality and tumor burden within a new rat model of mixed osteolytic/osteoblastic spinal metastases. Mixed vertebral metastases were analyzed in nude rats 21-days post intracardiac injection of Ace-1 canine prostate cancer cells. Vertebral micro-architecture was assessed in µCT images. Histologic processing quantified tumor burden (PTHrP), osteoclast activity (TRAP), and osteoid formation (Goldner's Trichrome) in ½ of all samples. Remaining samples were mechanically tested to failure in compression. Metastatically involved vertebrae exhibited extreme osteolysis, evident through an increase in osteoclasts leading to significantly reduced trabecular bone volume. Metastatically involved vertebrae also exhibited increased osteoid characteristic of osteoblastic lesions. While mechanical properties in tumor-bearing vertebrae were not significantly decreased compared to controls, a strong correlation was found between trabecular volumetric BMD and ultimate force. The highly aggressive Ace-1 skeletal metastases demonstrated predominant osteolysis with some areas of immature, new osteoblastic bone formation. Bone quality resulting from these lesions consisted of decreased structural properties, but without a significant impact on mechanical integrity.

The reaction of bone to tumor growth from human breast cancer cells in a rat spine single metastasis model

STUDY DESIGN

In vivo experiments to develop a rat spine single metastasis model by using human breast cancer cells.

OBJECTIVE

To study the survival and tumorigenesis of the human breast cancer cells after transplantation to vertebral body (VB) by intraosseous injection as a model for therapeutic studies of spine metastatic tumor.

SUMMARY OF BACKGROUND DATA

VBs are the most common bones involved in the metastases of breast cancer. To develop experimental therapeutics requires an appropriate animal model. Moreover, it is also important to establish accurate and sensitive detection methods for the evaluation.

METHODS

MDA-MB-231 human breast cancer cells were injected into 3-week-old female athymic rats. The tumorigenesis was assayed with quantitative in vivo bioluminescence (IVIS), microcomputed tomography (micro-CT), quantitative CT (qCT), micro position emission tomography (micro-PET), and histologic studies.

RESULTS

A spine single metastasis model of human breast cancer was successfully developed in rats. The IVIS signal intensity from the cancer cells increased after 2 weeks. Signal from the tumor in spine can be detected by micro-PET at day 1. The signal intensity decreased after 1 week and then recovered and continually increased afterwards. Bone destruction was demonstrated in the qCT and micro-CT images. However, both qCT and micro-CT found that the bone density in the cancer cell-injected VB increased before the appearance of osteolysis. The growth of tumor and the reaction of bone in the VB were observed simultaneously by histology.

CONCLUSION

A spine single metastasis model was developed by injection of human breast cancer cells into the VB of athymic rats. This is the first report of quantitative evaluation with micro-PET in a spine metastasis model. In addition, the detection of osteogenesis after the introduction of MDA-MB-231 cells in vivo is a novel observation.

Simvastatin prevents skeletal metastasis of breast cancer by an antagonistic interplay between p53 and CD44

Substantial data from clinical trials and epidemiological studies show promising results for use of statins in many cancers, including mammary carcinoma. Breast tumor primarily metastasizes to bone to form osteolytic lesions, causing severe pain and pathological fracture. Here, we report that simvastatin acts as an inhibitor of osteolysis in a mouse model of breast cancer skeletal metastasis of human mammary cancer cell MDA-MB-231, which expresses the mutant p53R280K. Simvastatin and lovastatin attenuated migration and invasion of MDA-MB-231 and BT-20 breast tumor cells in culture. Acquisition of phenotype to express the cancer stem cell marker, CD44, leads to invasive potential of the tumor cells. Interestingly, statins significantly decreased the expression of CD44 protein via a transcriptional mechanism. shRNA-mediated down-regulation of CD44 markedly reduced the migration and invasion of breast cancer cells in culture. We identified that in the MDA-MB-231 cells, simvastatin elevated the levels of mutated p53R280K, which was remarkably active as a transcription factor. shRNA-derived inhibition of mutant p53R280K augmented the expression of CD44, leading to increased migration and invasion. Finally, we demonstrate an inverse correlation between expression of p53 and CD44 in the tumors of mice that received simvastatin. Our results reveal a unique function of statins, which foster enhanced expression of mutant p53R280K to prevent breast cancer cell metastasis to bone.

PDGFR signaling blockade in marrow stroma impairs lung cancer bone metastasis

Bone microenvironment and cell-cell interactions are crucial for the initiation and development of metastasis. By means of a pharmacologic approach, using the multitargeted tyrosine kinase inhibitor sunitinib, we tested the relevance of the platelet-derived growth factor receptor (PDGFR) axis in the bone marrow (BM) stromal compartment for the initiation and development of lung cancer metastasis to bone. PDGFRβ was found to be the main tyrosine kinase target of sunitinib expressed in BM stromal ST-2 and MC3T3-E1 preosteoblastic cells. In contrast, no expression of sunitinib-targeted receptors was found in A549M1 and low levels in H460M5 lung cancer metastatic cells. Incubation of ST-2 and human BM endothelial cells with sunitinib led to potent cell growth inhibition and induction of apoptosis in a dose-dependent manner. Similarly, sunitinib induced a robust proapoptotic effect in vivo on BM stromal PDGFRβ(+) cells and produced extensive disruption of tissue architecture and vessel leakage in the BM cavity. Pretreatment of ST-2 cells with sunitinib also hindered heterotypic adhesion to lung cancer cell lines. These effects were correlated with changes in cell-cell and cell-matrix molecules in both stromal and tumor cells. Pretreatment of mice with sunitinib before intracardiac inoculation of A549M1 or H460M5 cells caused marked inhibition of tumor cells homing to bone, whereas no effect was found when tumor cells were pretreated before inoculation. Treatment with sunitinib dramatically increased overall survival and prevented tumor colonization but not bone lesions, whereas combination with zoledronic acid resulted in marked reduction of osteolytic lesions and osseous tumor burden. Thus, disruption of the PDGFR axis in the BM stroma alters heterotypic tumor-stromal and tumor-matrix interactions, thereby preventing efficient engagement required for bone homing and osseous colonization. These results support the notion that concomitant targeting of the tumor and stromal compartment is a more effective approach for blocking bone metastasis.

Fish oil prevents breast cancer cell metastasis to bone

The data derived from epidemiological and animal models confirm a beneficial effect of fish oil (rich in ω-3 polyunsaturated fatty acids) in the amelioration of tumor growth and progression, including breast cancer. The breast cancer patients often develop bone metastasis evidenced by osteolytic lesions, leading to severe pain and bone fracture. Using a mouse model of MDA-MB-231 human breast cancer cell metastasis to bone, here we show that fish oil diet enriched in DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid) prevents the formation of osteolytic lesions in bone, indicating suppression of cancer cell metastasis to bone. These results are supported by our data showing both DHA and EPA significantly attenuate the migration/invasion of MDA-MB-231 breast cancer cells in culture. The mechanism that limits breast cancer cells to selective metastasis to bone remains hitherto unexplored. Aberrant increased expression of CD44 is associated with generation of cancer stem cells, which contribute to metastasis of breast cancer cells. We demonstrate that DHA and EPA significantly inhibit the expression of CD44 protein and mRNA by a transcriptional mechanism. Furthermore, we show markedly reduced levels of CD44 mRNA and protein in the tumors of mice, which were fed fish oil diet than those in control diet. Our data provide the first evidence for a salutary effect of fish oil on breast cancer metastasis to bone. Our results identify a novel function of the fish oil active components, DHA and EPA, which target the cell-intrinsic pro-metastatic molecule CD44 to inhibit migration/invasion.

US-guided interstitial chemotherapy using paclitaxel temperature-responsive gel for breast cancer treatment in rat

INTRODUCTION

This study aims to investigate the therapeutic effect of paclitaxel temperature-responsive gel (PTRG) for interstitial chemotherapy on breast cancer, and to explore a new minimally invasive treatment for breast cancer.

MATERIALS AND METHODS

Breast cancer models were induced in rats using subcutaneous transplantation of tumor cells. The rats were then divided into control, paclitaxel injection, gel injection and paclitaxel-gel (PG) group. Following treatment, all animals were checked regularly by ultrasonography to observe changes in the tumors. Biopsy tumor tissues were processed for histopathological examination, and apoptotic index was determined by the terminal deoxynucleotidyl transferase dUTP nick end labeling method. In addition, blood cell count and liver transaminase activity were monitored, and the survival time of rats with cancer recorded.

RESULTS

Rats in PG group exhibited liquefaction necrosis of tumors. Ninety days after the experiment, four rats exhibited complete extinction of tumors, indicating full recovery. Pathological examination revealed that the tumor tissues in these rats were mostly necrotic, and the apoptotic index of tumor cells increased markedly compared to PI group. Also, the red blood cell, hemoglobin and white blood cell levels declined significantly in the PI group compared with PG group, while glutamic-pyruvic transaminase and glutamic-oxalacetic transaminase activities significantly increased. Meanwhile, no toxicity due to treatment was observed in PG group.

CONCLUSION

Interstitial chemotherapy mediated by PTRG appeared to be a safe and effective treatment for breast cancer in rats. It might have clinical applications for treating human breast cancer.