Of mice and (wo)men: mouse models of breast cancer metastasis to bone

Neutrophil Elastase Remodels Mammary Tumors to Facilitate Lung Metastasis

Metastatic disease remains the leading cause of death due to cancer, yet the mechanism(s) of metastasis and its timely detection remain to be elucidated. Neutrophil elastase (NE), a serine protease secreted by neutrophils, is a crucial mediator of chronic inflammation and tumor progression. In this study, we used the PyMT model (NE+/+ and NE-/-) of breast cancer to interrogate the tumor-intrinsic and -extrinsic mechanisms by which NE can promote metastasis. Our results showed that genetic ablation of NE significantly reduced lung metastasis and improved metastasis-free survival. RNA-sequencing analysis of primary tumors indicated differential regulation of tumor-intrinsic actin cytoskeleton signaling pathways by NE. These NE-regulated pathways are critical for cell-to-cell contact and motility and consistent with the delay in metastasis in NE-/- mice. To evaluate whether pharmacologic inhibition of NE inhibited pulmonary metastasis and phenotypically mimicked PyMT NE-/- mice, we utilized AZD9668, a clinically available and specific NE inhibitor. We found AZD9668 treated PyMT-NE+/+ mice showed significantly reduced lung metastases, improved recurrence-free, metastasis-free and overall survival, and their tumors showed similar molecular alterations as those observed in PyMT-NE-/- tumors. Finally, we identified a NE-specific signature that predicts recurrence and metastasis in patients with breast cancer. Collectively, our studies suggest that genetic ablation and pharmacologic inhibition of NE reduces metastasis and extends survival of mouse models of breast cancer, providing rationale to examine NE inhibitors as a treatment strategy for the clinical management of patients with metastatic breast cancer.

Biomimetic Microfluidic Platforms for the Assessment of Breast Cancer Metastasis

Of around half a million women dying of breast cancer each year, more than 90% die due to metastasis. Models necessary to understand the metastatic process, particularly breast cancer cell extravasation and colonization, are currently limited and urgently needed to develop therapeutic interventions necessary to prevent breast cancer metastasis. Microfluidic approaches aim to reconstitute functional units of organs that cannot be modeled easily in traditional cell culture or animal studies by reproducing vascular networks and parenchyma on a chip in a three-dimensional, physiologically relevant in vitro system. In recent years, microfluidics models utilizing innovative biomaterials and micro-engineering technologies have shown great potential in our effort of mechanistic understanding of the breast cancer metastasis cascade by providing 3D constructs that can mimic in vivo cellular microenvironment and the ability to visualize and monitor cellular interactions in real-time. In this review, we will provide readers with a detailed discussion on the application of the most up-to-date, state-of-the-art microfluidics-based breast cancer models, with a special focus on their application in the engineering approaches to recapitulate the metastasis process, including invasion, intravasation, extravasation, breast cancer metastasis organotropism, and metastasis niche formation.

Spatiotemporal assessment of spontaneous metastasis formation using multimodal in vivo imaging in HER2+ and triple negative metastatic breast cancer xenograft models in mice

Background

Preclinical breast cancer models recapitulating the clinical course of metastatic disease are crucial for drug development. Highly metastatic cell lines forming spontaneous metastasis following orthotopic implantation were previously developed and characterized regarding their biological and histological characteristics. This study aimed to non-invasively and longitudinally characterize the spatiotemporal pattern of metastasis formation and progression in the MDA-MB-231-derived triple negative LM2-4 and HER2⁺ LM2-4H2N cell lines, using bioluminescence imaging (BLI), contrast enhanced computed tomography (CT), fluorescence imaging, and 2-deoxy-2-[fluorine-18]fluoro-D-glucose positron emission tomography ([¹⁸F]FDG-PET).

Material and methods

LM2-4, LM2-4H2N, and MDA-MB-231 tumors were established in the right inguinal mammary fat pad (MFP) of female SCID mice and resected 14–16 days later. Metastasis formation was monitored using BLI. Metabolic activity of primary and metastatic lesions in mice bearing LM2-4 or LM2-4H2N was assessed by [¹⁸F]FDG-PET. Metastatic burden at study endpoint was assessed by CT and fluorescence imaging following intravenous dual-modality liposome agent administration.

Results

Comparable temporal metastasis patterns were observed using BLI for the highly metastatic cell lines LM2-4 and LM2-4H2N, while metastasis formed about 10 days later for MDA-MB-231. 21 days post primary tumor resection, metastases were detected in 86% of LM2-4, 69% of LM2-4H2N, and 60% of MDA-MB-231 inoculated mice, predominantly in the axillary region, contralateral MFP, and liver/lung. LM2-4 and LM2-4H2N tumors displayed high metabolism based on [¹⁸F]FDG-PET uptake. Lung metastases were detected as the [¹⁸F]FDG-PET uptake increased significantly between pre- and post-metastasis scan. Using a liposomal dual-modality agent, CT and fluorescence confirmed BLI detected lesions and identified additional metastatic nodules in the intraperitoneal cavity and lung.

Conclusions

The combination of complementary anatomical and functional imaging techniques can provide high sensitivity characterization of metastatic disease spread, progression and overall disease burden. The described models and imaging toolset can be implemented as an effective means for quantitative treatment response evaluation in metastatic breast cancer.

Orthotopic Xenograft Mouse Model of Cervical Cancer for Studying the Role of MicroRNA-21 in Promoting Lymph Node Metastasis

Cervical cancer is the most frequent cause of gynecologic cancer-associated death worldwide. Animal models that demonstrate metastatic patterns consistent with the clinical course of cervical cancer are urgently needed to conduct studies focused on understanding the mechanisms of the disease and identifying optimal treatments. To address this, we established an orthotopic xenograft model of cervical cancer in female NOD-SCID mice using SiHa and ME180 cell lines stably expressing green fluorescent protein to evaluate the role of microRNA-21 (miR-21) in spontaneous lymph node metastasis in vivo. In this case, SiHa and ME180 cells were transduced by lentivirus to stably express green fluorescent protein and miR-21. Overexpression of miR-21 promoted proliferation, migration, and invasion of SiHa and ME180 cells in vitro. Finally, an orthotopic xenograft model of human cervical cancer was successfully established in NOD-SCID mice. Using this model, we confirmed that overexpression of miR-21 resulted in an increase in the size of primary tumors and in the frequency of spontaneous lymph node metastasis at the time of excision. Therefore, the use of the orthotopic xenograft model should allow for the investigation of novel factors that affect metastasis of cervical cancer and presents an opportunity to evaluate potential therapeutic agents that may inhibit the spread of the disease.

Feline Mammary Cancer

Feline mammary carcinoma (FMC) is similar to human breast cancer in the late age of onset, incidence, histopathologic features, biological behavior, and pattern of metastasis. Therefore, FMC has been proposed as a relevant model for aggressive human breast cancer. The goals of this study were to develop a nude mouse model of FMC tumor growth and metastasis and to measure the expression of genes responsible for lymphangiogenesis, angiogenesis, tumor progression, and lymph node metastasis in FMC tissues and cell lines. Two primary FMC tissues were injected subcutaneously, and 6 FMC cell lines were injected into 3 sites (subcutaneous, intratibial, and intracardiac) in nude mice. Tumors and metastases were monitored using bioluminescent imaging and characterized by gross necropsy, radiology, and histopathology. Molecular characterization of invasion and metastasis genes in FMC was conducted using quantitative real-time reverse transcription polymerase chain reaction in 6 primary FMC tissues, 2 subcutaneous FMC xenografts, and 6 FMC cell lines. The histologic appearance of the subcutaneous xenografts resembled the primary tumors. No metastasis was evident following subcutaneous injection of tumor tissues and cell lines, whereas lung, brain, liver, kidney, eye, and bone metastases were confirmed following intratibial and intracardiac injection of FMC cell lines. Finally, 15 genes were differentially expressed in the FMC tissues and cell lines. The highly expressed genes in all samples were PDGFA, PDGFB, PDGFC, FGF2, EGFR, ERBB2, ERBB3, VEGFD, VEGFR3, and MYOF. Three genes ( PDGFD, ANGPT2, and VEGFC) were confirmed to be of stromal origin. This investigation demonstrated the usefulness of nude mouse models of experimental FMC and identified molecular targets of FMC progression and metastasis.

Use of Animal Models in Understanding Cancer-induced Bone Pain

Many common cancers have a propensity to metastasize to bone. Although malignancies often go undetected in their native tissues, bone metastases produce excruciating pain that severely compromises patient quality of life. Cancer-induced bone pain (CIBP) is poorly managed with existing medications, and its multifaceted etiology remains to be fully elucidated. Novel analgesic targets arise as more is learned about this complex and distinct pain state. Over the past two decades, multiple animal models have been developed to study CIBP’s unique pathology and identify therapeutic targets. Here, we review animal models of CIBP and the mechanistic insights gained as these models evolve. Findings from immunocompromised and immunocompetent host systems are discussed separately to highlight the effect of model choice on outcome. Gaining an understanding of the unique neuromolecular profile of cancer pain through the use of appropriate animal models will aid in the development of more effective therapeutics for CIBP.

Multimodal imaging of bone metastases: From preclinical to clinical applications

Metastases to the skeletal system are commonly observed in cancer patients, highly affecting the patients' quality of life. Imaging plays a major role in detection, follow-up, and molecular characterisation of metastatic disease. Thus, imaging techniques have been optimised and combined in a multimodal and multiparametric manner for assessment of complementary aspects in osseous metastases. This review summarises both application of the most relevant imaging techniques for bone metastasis in preclinical models and the clinical setting.

Methods for culturing human femur tissue explants to study breast cancer cell colonization of the metastatic niche

Bone is the most common site of breast cancer metastasis. Although it is widely accepted that the microenvironment influences cancer cell behavior, little is known about breast cancer cell properties and behaviors within the native microenvironment of human bone tissue.We have developed approaches to track, quantify and modulate human breast cancer cells within the microenvironment of cultured human bone tissue fragments isolated from discarded femoral heads following total hip replacement surgeries. Using breast cancer cells engineered for luciferase and enhanced green fluorescent protein (EGFP) expression, we are able to reproducibly quantitate migration and proliferation patterns using bioluminescence imaging (BLI), track cell interactions within the bone fragments using fluorescence microscopy, and evaluate breast cells after colonization with flow cytometry. The key advantages of this model include: 1) a native, architecturally intact tissue microenvironment that includes relevant human cell types, and 2) direct access to the microenvironment, which facilitates rapid quantitative and qualitative monitoring and perturbation of breast and bone cell properties, behaviors and interactions. A primary limitation, at present, is the finite viability of the tissue fragments, which confines the window of study to short-term culture. Applications of the model system include studying the basic biology of breast cancer and other bone-seeking malignancies within the metastatic niche, and developing therapeutic strategies to effectively target breast cancer cells in bone tissues.

Monitoring dynamic interactions between breast cancer cells and human bone tissue in a co-culture model

PURPOSE

Bone is a preferential site of breast cancer metastasis, and models are needed to study this process at the level of the microenvironment. We have used bioluminescence imaging (BLI) and multiplex biomarker immunoassays to monitor dynamic breast cancer cell behaviors in co-culture with human bone tissue.

PROCEDURES

Femur tissue fragments harvested from hip replacement surgeries were co-cultured with luciferase-positive MDA-MB-231-fLuc cells. BLI was performed to quantify breast cell proliferation and track migration relative to bone tissue. Breast cell colonization of bone tissues was assessed with immunohistochemistry. Biomarkers in co-culture supernatants were profiled with MILLIPLEX(®) immunoassays.

RESULTS

BLI demonstrated increased MDA-MB-231-fLuc cell proliferation (p < 0.001) in the presence vs. absence of bones and revealed breast cell migration toward bone. Immunohistochemistry illustrated MDA-MB-231-fLuc cell colonization of bone, and MILLIPLEX(®) profiles of culture supernatants suggested breast/bone crosstalk.

CONCLUSIONS

Breast cell behaviors that facilitate metastasis occur reproducibly in human bone tissue co-cultures and can be monitored and quantified using BLI and multiplex immunoassays.

Prediction of individual response to anticancer therapy: historical and future perspectives

Since the introduction of chemotherapy for cancer treatment in the early 20th century considerable efforts have been made to maximize drug efficiency and at the same time minimize side effects. As there is a great interpatient variability in response to chemotherapy, the development of predictive biomarkers is an ambitious aim for the rapidly growing research area of personalized molecular medicine. The individual prediction of response will improve treatment and thus increase survival and life quality of patients. In the past, cell cultures were used as in vitro models to predict in vivo response to chemotherapy. Several in vitro chemosensitivity assays served as tools to measure miscellaneous endpoints such as DNA damage, apoptosis and cytotoxicity or growth inhibition. Twenty years ago, the development of high-throughput technologies, e.g. cDNA microarrays enabled a more detailed analysis of drug responses. Thousands of genes were screened and expression levels were correlated to drug responses. In addition, mutation analysis became more and more important for the prediction of therapeutic success. Today, as research enters the area of -omics technologies, identification of signaling pathways is a tool to understand molecular mechanism underlying drug resistance. Combining new tissue models, e.g. 3D organoid cultures with modern technologies for biomarker discovery will offer new opportunities to identify new drug targets and in parallel predict individual responses to anticancer therapy. In this review, we present different currently used chemosensitivity assays including 2D and 3D cell culture models and several -omics approaches for the discovery of predictive biomarkers. Furthermore, we discuss the potential of these assays and biomarkers to predict the clinical outcome of individual patients and future perspectives.

Fusion of HepG2 cells with mesenchymal stem cells increases cancer‑associated and malignant properties: an in vivo metastasis model

In the present study, we have tested the hypothesis that fusion between an altered cell and a mesenchymal stem cell produces a hybrid cell with enhanced characteristics associated with metastatic cancer cells, and we have developed a flexible model for investigating the mechanisms of metastasis. Human HepG2 cells with low metastatic potential were induced to fuse with rat bone marrow mesenchymal stem cells, and the progeny were compared with the parental cells for possession of enhanced in vitro and in vivo characteristics of malignant cells. Compared to the parental cells, the fused cells exhibited enhanced expression of E-cadherin, vimentin, Twist, Snail, matrix metalloproteinase 2 and 9 activities, aneuploidy and enhanced in vitro invasion and migration. In an in vivo xenograft assay, the fused cells generated increased numbers of metastatic liver and lung lesions. This model system is a flexible tool for investigation of the mechanisms of stem cell fusion in carcinogenesis and metastasis and for the discovery of new therapeutic targets to inhibit metastasis.

A microfluidic 3D in vitro model for specificity of breast cancer metastasis to bone

Cancer metastases arise following extravasation of circulating tumor cells with certain tumors exhibiting high organ specificity. Here, we developed a 3D microfluidic model to analyze the specificity of human breast cancer metastases to bone, recreating a vascularized osteo-cell conditioned microenvironment with human osteo-differentiated bone marrow-derived mesenchymal stem cells and endothelial cells. The tri-culture system allowed us to study the transendothelial migration of highly metastatic breast cancer cells and to monitor their behavior within the bone-like matrix. Extravasation, quantified 24 h after cancer cell injection, was significantly higher in the osteo-cell conditioned microenvironment compared to collagen gel-only matrices (77.5 ± 3.7% vs. 37.6 ± 7.3%), and the migration distance was also significantly greater (50.8 ± 6.2 μm vs. 31.8 ± 5.0 μm). Extravasated cells proliferated to form micrometastases of various sizes containing 4 to more than 60 cells by day 5. We demonstrated that the breast cancer cell receptor CXCR2 and the bone-secreted chemokine CXCL5 play a major role in the extravasation process, influencing extravasation rate and traveled distance. Our study provides novel 3D in vitro quantitative data on extravasation and micrometastasis generation of breast cancer cells within a bone-like microenvironment and demonstrates the potential value of microfluidic systems to better understand cancer biology and screen for new therapeutics.

Humanised xenograft models of bone metastasis revisited: novel insights into species-specific mechanisms of cancer cell osteotropism

The determinants and key mechanisms of cancer cell osteotropism have not been identified, mainly due to the lack of reproducible animal models representing the biological, genetic and clinical features seen in humans. An ideal model should be capable of recapitulating as many steps of the metastatic cascade as possible, thus facilitating the development of prognostic markers and novel therapeutic strategies. Most animal models of bone metastasis still have to be derived experimentally as most syngeneic and transgeneic approaches do not provide a robust skeletal phenotype and do not recapitulate the biological processes seen in humans. The xenotransplantation of human cancer cells or tumour tissue into immunocompromised murine hosts provides the possibility to simulate early and late stages of the human disease. Human bone or tissue-engineered human bone constructs can be implanted into the animal to recapitulate more subtle, species-specific aspects of the mutual interaction between human cancer cells and the human bone microenvironment. Moreover, the replication of the entire "organ" bone makes it possible to analyse the interaction between cancer cells and the haematopoietic niche and to confer at least a partial human immunity to the murine host. This process of humanisation is facilitated by novel immunocompromised mouse strains that allow a high engraftment rate of human cells or tissue. These humanised xenograft models provide an important research tool to study human biological processes of bone metastasis.

In vitro models of the metastatic cascade: from local invasion to extravasation

A crucial event in the metastatic cascade is the extravasation of circulating cancer cells from blood capillaries to the surrounding tissues. The past 5 years have been characterized by a significant evolution in the development of in vitro extravasation models, which moved from traditional transmigration chambers to more sophisticated microfluidic devices, enabling the study of complex cell-cell and cell-matrix interactions in multicellular, controlled environments. These advanced assays could be applied to screen easily and rapidly a broad spectrum of molecules inhibiting cancer cell endothelial adhesion and extravasation, thus contributing to the design of more focused in vivo tests.

Novel mouse mammary cell lines for in vivo bioluminescence imaging (BLI) of bone metastasis

BACKGROUND

Tumor cell lines that can be tracked in vivo during tumorigenesis and metastasis provide vital tools for studying the specific cellular mechanisms that mediate these processes as well as investigating therapeutic targets to inhibit them. The goal of this study was to engineer imageable mouse mammary tumor cell lines with discrete propensities to metastasize to bone in vivo. Two novel luciferase expressing cell lines were developed and characterized for use in the study of breast cancer metastasis to bone in a syngeneic mouse model.

RESULTS

The 4 T1.2 luc3 and 66c14 luc2 cell lines were shown to have high levels of bioluminescence intensity in vitro and in vivo after orthotopic injection into mouse mammary fat pads. The 4 T1.2 luc3 cell line was found to closely model the sites of metastases seen in human patients including lung, liver, and bone. Specifically, 4 T1.2 luc3 cells demonstrated a high incidence of metastasis to spine, with an ex-vivo BLI intensity three orders of magnitude above the commercially available 4 T1 luc2 cells. 66c14 luc2 cells also demonstrated metastasis to spine, which was lower than that of 4 T1.2 luc3 cells but higher than 4 T1 luc2 cells, in addition to previously unreported metastases in the liver. High osteolytic activity of the 4 T1.2 luc3 cells in vivo in the bone microenvironment was also detected.

CONCLUSIONS

The engineered 4 T1.2 luc3 and 66c14 luc2 cell lines described in this study are valuable tools for studying the cellular events moderating the metastasis of breast tumor cells to bone.

"A novel in vivo model for the study of human breast cancer metastasis using primary breast tumor-initiating cells from patient biopsies"

Background

The study of breast cancer metastasis depends on the use of established breast cancer cell lines that do not accurately represent the heterogeneity and complexity of human breast tumors. A tumor model was developed using primary breast tumor-initiating cells isolated from patient core biopsies that would more accurately reflect human breast cancer metastasis.

Methods

Tumorspheres were isolated under serum-free culture conditions from core biopsies collected from five patients with clinical diagnosis of invasive ductal carcinoma (IDC). Isolated tumorspheres were transplanted into the mammary fat pad of NUDE mice to establish tumorigenicity in vivo. Tumors and metastatic lesions were analyzed by hematoxylin and eosin (H+E) staining and immunohistochemistry (IHC).

Results

Tumorspheres were successfully isolated from all patient core biopsies, independent of the estrogen receptor α (ERα)/progesterone receptor (PR)/Her2/neu status or tumor grade. Each tumorsphere was estimated to contain 50-100 cells. Transplantation of 50 tumorspheres (1-5 × 10³ cells) in combination with Matrigel into the mammary fat pad of NUDE mice resulted in small, palpable tumors that were sustained up to 12 months post-injection. Tumors were serially transplanted three times by re-isolation of tumorspheres from the tumors and injection into the mammary fat pad of NUDE mice. At 3 months post-injection, micrometastases to the lung, liver, kidneys, brain and femur were detected by measuring content of human chromosome 17. Visible macrometastases were detected in the lung, liver and kidneys by 6 months post-injection. Primary tumors variably expressed cytokeratins, Her2/neu, cytoplasmic E-cadherin, nuclear β catenin and fibronectin but were negative for ERα and vimentin. In lung and liver metastases, variable redistribution of E-cadherin and β catenin to the membrane of tumor cells was observed. ERα was re-expressed in lung metastatic cells in two of five samples.

Conclusions

Tumorspheres isolated under defined culture conditions from patient core biopsies were tumorigenic when transplanted into the mammary fat pad of NUDE mice, and metastasized to multiple mouse organs. Micrometastases in mouse organs demonstrated a dormancy period prior to outgrowth of macrometastases. The development of macrometastases with organ-specific phenotypic distinctions provides a superior model for the investigation of organ-specific effects on metastatic cancer cell survival and growth.