Brain metastasis model in athymic nude mice using a novel MUC1-secreting human breast-cancer cell line, MA11

Breast cancer brain metastasis: from etiology to state-of-the-art modeling

Currently, breast carcinoma is the most common form of malignancy and the main cause of cancer mortality in women worldwide. The metastasis of cancer cells from the primary tumor site to other organs in the body, notably the lungs, bones, brain, and liver, is what causes breast cancer to ultimately be fatal. Brain metastases occur in as many as 30% of patients with advanced breast cancer, and the 1-year survival rate of these patients is around 20%. Many researchers have focused on brain metastasis, but due to its complexities, many aspects of this process are still relatively unclear. To develop and test novel therapies for this fatal condition, pre-clinical models are required that can mimic the biological processes involved in breast cancer brain metastasis (BCBM). The application of many breakthroughs in the area of tissue engineering has resulted in the development of scaffold or matrix-based culture methods that more accurately imitate the original extracellular matrix (ECM) of metastatic tumors. Furthermore, specific cell lines are now being used to create three-dimensional (3D) cultures that can be used to model metastasis. These 3D cultures satisfy the requirement for in vitro methodologies that allow for a more accurate investigation of the molecular pathways as well as a more in-depth examination of the effects of the medication being tested. In this review, we talk about the latest advances in modeling BCBM using cell lines, animals, and tissue engineering methods.

Preclinical Models of Brain Metastases in Breast Cancer

Breast cancer remains a leading cause of mortality among women worldwide. Brain metastases confer extremely poor prognosis due to a lack of understanding of their specific biology, unique physiologic and anatomic features of the brain, and limited treatment strategies. A major roadblock in advancing the treatment of breast cancer brain metastases (BCBM) is the scarcity of representative experimental preclinical models. Current models are predominantly based on the use of animal xenograft models with immortalized breast cancer cell lines that poorly capture the disease’s heterogeneity. Recent years have witnessed the development of patient-derived in vitro and in vivo breast cancer culturing systems that more closely recapitulate the biology from individual patients. These advances led to the development of modern patient-tissue-based experimental models for BCBM. The success of preclinical models is also based on the imaging technologies used to detect metastases. Advances in animal brain imaging, including cellular MRI and multimodality imaging, allow sensitive and specific detection of brain metastases and monitoring treatment responses. These imaging technologies, together with novel translational breast cancer models based on patient-derived cancer tissues, represent a unique opportunity to advance our understanding of brain metastases biology and develop novel treatment approaches. This review discusses the state-of-the-art knowledge in preclinical models of this disease.

Novel human melanoma brain metastasis models in athymic nude fox1nu mice: Site-specific metastasis patterns reflecting their clinical origin

BACKGROUND

Malignant melanomas frequently metastasize to the brain, but metastases in the cerebellum are underrepresented compared with metastases in the cerebrum.

METHODS

We established animal models by injecting intracardially in athymic nude fox1nu mice two human melanoma cell lines, originating from a cerebral metastasis (HM19) and a cerebellar metastasis (HM86).

RESULTS

Using magnetic resonance imaging (MRI), metastases were first detected after a mean of 34.5 days. Mean survival time was 59.6 days for the mice in the HM86 group and significantly shorter (43.7 days) for HM19-injected animals (p < 0.001). In the HM86 group, the first detectable metastasis was located in the cerebellum in 15/55 (29%) mice compared with none in the HM19 group (p < 0.001). At sacrifice, cerebellar metastases were found in 34/55 (63%) HM86-injected mice compared with 1/53 (2%) in the HM19-injected (p < 0.001) mice. At that time, all mice in both groups had detectable metastases in the cerebrum. Comparing macroscopic and histologic appearances of the brain metastases with their clinical counterparts, the cell line-based tumors had kept their original morphologic characteristics.

CONCLUSIONS

The present work demonstrates that human brain-metastatic melanoma cells injected intracardially in mice had retained inherent characteristics also in reproducing interaction with subtle microenvironmental brain tissue compartment-specific features. The models offer new possibilities for investigating tumor- and host-associated factors involved in determining tissue specificity of brain metastasis.

Atlas of Lobular Breast Cancer Models: Challenges and Strategic Directions

Invasive lobular carcinoma (ILC) accounts for up to 15% of all breast cancer (BC) cases and responds well to endocrine treatment when estrogen receptor α-positive (ER+) yet differs in many biological aspects from other ER+ BC subtypes. Up to 30% of patients with ILC will develop late-onset metastatic disease up to ten years after initial tumor diagnosis and may experience failure of systemic therapy. Unfortunately, preclinical models to study ILC progression and predict the efficacy of novel therapeutics are scarce. Here, we review the current advances in ILC modeling, including cell lines and organotypic models, genetically engineered mouse models, and patient-derived xenografts. We also underscore four critical challenges that can be addressed using ILC models: drug resistance, lobular tumor microenvironment, tumor dormancy, and metastasis. Finally, we highlight the advantages of shared experimental ILC resources and provide essential considerations from the perspective of the European Lobular Breast Cancer Consortium (ELBCC), which is devoted to better understanding and translating the molecular cues that underpin ILC to clinical diagnosis and intervention. This review will guide investigators who are considering the implementation of ILC models in their research programs.

Experimental Models as Refined Translational Tools for Breast Cancer Research

Breast cancer is one of the most common cancers worldwide, which makes it a very impactful malignancy in the society. Breast cancers can be classified through different systems based on the main tumor features and gene, protein, and cell receptors expression, which will determine the most advisable therapeutic course and expected outcomes. Multiple therapeutic options have already been proposed and implemented for breast cancer treatment. Nonetheless, their use and efficacy still greatly depend on the tumor classification, and treatments are commonly associated with invasiveness, pain, discomfort, severe side effects, and poor specificity. This has demanded an investment in the research of the mechanisms behind the disease progression, evolution, and associated risk factors, and on novel diagnostic and therapeutic techniques. However, advances in the understanding and assessment of breast cancer are dependent on the ability to mimic the properties and microenvironment of tumors in vivo, which can be achieved through experimentation on animal models. This review covers an overview of the main animal models used in breast cancer research, namely in vitro models, in vivo models, in silico models, and other models. For each model, the main characteristics, advantages, and challenges associated to their use are highlighted.

Basal-like breast cancer engages tumor-supportive macrophages via secreted factors induced by extracellular S100A4

The tumor microenvironment (TME) may influence both cancer progression and therapeutic response. In breast cancer, particularly in the aggressive triple‐negative/basal‐like subgroup, patient outcome is strongly associated with the tumor's inflammatory profile. Tumor‐associated macrophages (TAMs) are among the most abundant immune cells in the TME, shown to be linked to poor prognosis and therapeutic resistance. In this study, we investigated the effect of the metastasis‐ and inflammation‐associated microenvironmental factor S100A4 on breast cancer cells (BCCs) of different subtypes and explored their further interactions with myeloid cells. We demonstrated that extracellular S100A4 activates BCCs, particularly the basal‐like subtype, to elevate secretion of pro‐inflammatory cytokines. The secreted factors promoted conversion of monocytes to TAM‐like cells that exhibited protumorigenic activities: stimulated epithelial–mesenchymal transition, proliferation, chemoresistance, and motility in cancer cells. In conclusion, we have shown that extracellular S100A4 instigates a tumor‐supportive microenvironment, involving a network of cytokines and TAM‐like cells, which was particularly characteristic for basal‐like BCCs and potentiated their aggressive properties. The S100A4–BCC–TAM interaction cascade could be an important contributor to the aggressive behavior of this subtype and should be further explored for therapeutic targeting.

Canine mammary tumors as a model for human disease

Animal models for examining human breast cancer (HBC) carcinogenesis have been extensively studied and proposed. With the recent advent of immunotherapy, significant attention has been focused on the dog as a model for human cancer. Dogs develop mammary tumors and other cancer types spontaneously with an intact immune system, which exhibit a number of clinical and molecular similarities to HBC. In addition to the spontaneous tumor presentation, the clinical similarities between human and canine mammary tumors (CMT) include the age at onset, hormonal etiology and course of the diseases. Furthermore, factors that affect the disease outcome, including tumor size, stage and lymph node invasion, are similar in HBC and CMT. Similarly, the molecular characteristics of steroid receptor, epidermal growth factor, proliferation marker, metalloproteinase and cyclooxygenase expression, and the mutation of the p53 tumor suppressor gene in CMT, mimic HBC. Furthermore, ductal carcinomas in situ in human and canine mammary glands are particularly similar in their pathological, molecular and visual characteristics. These CMT characteristics and their similarities to HBC indicate that the dog could be an excellent model for the study of human disease. These similarities are discussed in detail in the present review, and are compared with the in vitro and other in vivo animal models available.

Breast Cancer Cell Line Classification and Its Relevance with Breast Tumor Subtyping

Breast cancer cell lines have been widely used for breast cancer modelling which encompasses a panel of diseases with distinct phenotypical associations. Though cell lines provide unlimited homogenous materials for tumor studies and are relatively easy to culture, they are known to accumulate mutations duringthe initial establishment and subsequent series of cultivations. Thus, whether breast cancer cell line heterogeneity reflects that of carcinoma remains an important issue to resolve before drawing any reliable conclusion at the tumor level using cell lines. Inconsistent nomenclatures used for breast cancer cell line subtyping and the different number of subtypes grouped for cell lines and tumors make their direct matching elusive. By analyzing the molecular features of 92 breast cancer cell lines as documented by different literatures, we categorize 84 cell lines into 5 groups to be consistent with breast tumor classification. After combing through these cell lines, we summarized the molecular features, genetically and epigenetically, of each subtype, and manually documented 10 cell lines lacking explicit information on subtyping. Nine cell lines, either found inconsistent on their primary molecular features from different studies or being contaminated at the origin, are not suggested as the first choice for experimental use. We conclude that breast tumor cell lines, though having a high mutational frequency with many uncertainties and could not fully capture breast cancer heterogeneity, are feasible but crude models for tumors of the same subtype. New cell lines with enriched interferon regulated genes need to be established to enlarge the coverage of cell lines on tumor heterogeneity.

Distinct Small RNA Signatures in Extracellular Vesicles Derived from Breast Cancer Cell Lines

Breast cancer is a heterogeneous disease, and different subtypes of breast cancer show distinct cellular morphology, gene expression, metabolism, motility, proliferation, and metastatic potential. Understanding the molecular features responsible for this heterogeneity is important for correct diagnosis and better treatment strategies. Extracellular vesicles (EVs) and their associated molecules have gained much attention as players in intercellular communication, ability to precondition specific organs for metastatic invasion, and for their potential role as circulating cancer biomarkers. EVs are released from the cells and contain proteins, DNA, and long and small RNA species. Here we show by high-throughput small RNA-sequencing that EVs from nine different breast cancer cell lines share common characteristics in terms of small RNA content that are distinct from their originating cells. Most strikingly, a highly abundant small RNA molecule derived from the nuclear 28S rRNA is vastly enriched in EVs. The miRNA profiles in EVs correlate with the cellular miRNA expression pattern, but with a few exceptions that includes miR-21. This cancer-associated miRNA is retained in breast cancer cell lines. Finally, we report that EVs from breast cancer cell lines cluster together based on their small RNA signature when compared to EVs derived from other cancer cell lines. Altogether, our data demonstrate that breast cancer cell lines manifest a specific small RNA signature in their released EVs. This opens up for further evaluation of EVs as breast cancer biomarkers.

Tetraspanin CD9 determines invasiveness and tumorigenicity of human breast cancer cells

Interaction of breast cancer cells (BCCs) with stromal components is critical for tumor growth and metastasis. Here, we assessed the role of CD9 in adhesion, migration and invasiveness of BCCs. We used co-cultures of BCCs and bone marrow-derived multipotent mesenchymal stromal cells (MSCs), and analyzed their behavior and morphology by dynamic total internal reflection fluorescence, confocal and scanning electron microscopy. 83, 16 and 10% of contacts between MDA-MB-231 (MDA), MA-11 or MCF-7 cells and MSCs, respectively, resulted in MSC invasion. MDA cells developed long magnupodia, lamellipodia and dorsal microvilli, whereas long microvilli emerged from MA-11 cells. MCF-7 cells displayed large dorsal ruffles. CD9 knockdown and antibody blockage in MDA cells inhibited MSC invasion by 95 and 70%, respectively, suggesting that CD9 is required for this process. Remarkably, CD9-deficient MDA cells displayed significant alteration of their plasma membrane, harboring numerous peripheral and dorsal membrane ruffles instead of intact magnupodium/lamellipodium and microvillus, respectively. Such modification might explain the delayed adhesion, and hence MSC invasion. In agreement with this hypothesis, CD9-knockdown suppressed the metastatic capacity of MDA cells in mouse xenografts. Our data indicate that CD9 is implicated in BCC invasiveness and metastases by cellular mechanisms that involve specific CD9⁺ plasma membrane protrusions of BCCs.

Emerging nanomedicine approaches fighting tumor metastasis: animal models, metastasis-targeted drug delivery, phototherapy, and immunotherapy

Nanomedicine approaches may bring new opportunities for tumor metastasis treatment.

Understanding Heterogeneity and Permeability of Brain Metastases in Murine Models of HER2-Positive Breast Cancer Through Magnetic Resonance Imaging: Implications for Detection and Therapy

OBJECTIVES: Brain metastases due to breast cancer are increasing, and the prognosis is poor. Lack of effective therapy is attributed to heterogeneity of breast cancers and their resulting metastases, as well as impermeability of the blood–brain barrier (BBB), which hinders delivery of therapeutics to the brain. This work investigates three experimental models of HER2 + breast cancer brain metastasis to better understand the inherent heterogeneity of the disease. We use magnetic resonance imaging (MRI) to quantify brain metastatic growth and explore its relationship with BBB permeability. DESIGN: Brain metastases due to breast cancer cells (SUM190-BR3, JIMT-1-BR3, or MDA-MB-231-BR-HER2) were imaged at 3 T using balanced steady-state free precession and contrast-enhanced T1-weighted spin echo sequences. The histology and immunohistochemistry corresponding to MRI were also analyzed. RESULTS: There were differences in metastatic tumor appearance by MRI, histology, and immunohistochemistry (Ki67, CD31, CD105) across the three models. The mean volume of an MDA-MB-231-BR-HER2 tumor was significantly larger compared to other models (F_2,12 = 5.845, P < .05); interestingly, this model also had a significantly higher proportion of Gd-impermeable tumors (F_2,12 = 22.18, P < .0001). Ki67 staining indicated that Gd-impermeable tumors had significantly more proliferative nuclei compared to Gd-permeable tumors (t[24] = 2.389, P < .05) in the MDA-MB-231-BR-HER2 model. CD31 and CD105 staining suggested no difference in new vasculature patterns between permeable and impermeable tumors in any model. CONCLUSION: Significant heterogeneity is present in these models of brain metastases from HER2 + breast cancer. Understanding this heterogeneity, especially as it relates to BBB permeability, is important for improvement in brain metastasis detection and treatment delivery.

Lobular breast cancer: molecular basis, mouse and cellular models

Infiltrating lobular breast cancer (ILC) is the most common special breast cancer subtype. With mutational or epigenetic inactivation of the cell adhesion molecule E-cadherin (CDH1) being confined almost exclusively to ILC, this tumor entity stands out from all other types of breast cancers. The molecular basis of ILC is linked to loss of E-cadherin, as evidenced by human CDH1 germline mutations and conditional knockout mouse models. A better understanding of ILC beyond the level of descriptive studies depends on physiologically relevant and functional tools. This review provides a detailed overview on ILC models, including well-characterized cell lines, xenograft tumors and genetically engineered mouse models. We consider advantages and limitations of these models and evaluate their representativeness for human ILC. The still incompletely defined mechanisms by which loss of E-cadherin drives malignant transformation are discussed based on recent findings in these models. Moreover, candidate genes and signaling pathways potentially involved in ILC development and progression as well as anticancer drug and endocrine resistance are highlighted.

The nuclear pool of tetraspanin CD9 contributes to mitotic processes in human breast carcinoma

Tetraspanin-29 (CD9) is an integral membrane protein involved in several fundamental cell processes and in cancer metastasis. Here, characterization of a panel of breast cancer cells revealed a nuclear pool of CD9, not present in normal human mammary epithelial cells. Antibody binding to surface CD9 of breast cancer cells resulted in increased nuclear CD9 fluorescence. CD9 was also found, along with a plasma membrane-associated pool, in the nuclei of all primary ductal breast carcinoma patient specimens analyzed. In all patients, about 40% of the total CD9 cellular fluorescence was nuclear. CD9 colocalized at the nuclear level with CEP97, a protein implicated in centrosome function, and with the IGSF8, an established CD9 partner in the plasma membrane. Co-immunoprecipitation of CEP97 and IGSF8 with CD9 was shown in nuclear extracts from breast cancer cells expressing a CD9-GFP fusion protein. However, by fluorescence resonance energy transfer (FRET) analysis, no direct binding of CD9 with either protein was observed, suggesting that CD9 is part of a larger nuclear protein complex. CD9 depletion or exposure of parental breast cancer cells to anti-CD9 mAb resulted in polynucleation and multipolar mitoses. These data indicate that the nuclear CD9 pool has an important role in the mitotic process.

IMPLICATIONS

The discovery of a nuclear pool of CD9 has prognostic and/or therapeutic potential for patients with ductal carcinoma of the breast.

CNS metastases in breast cancer: old challenge, new frontiers

Despite major therapeutic advances in the management of patients with breast cancer, central nervous system (CNS) metastases remain an intractable problem, particularly in patients with metastatic HER2-positive and triple-negative breast cancer. As systemic therapies to treat extracranial disease improve, some patients are surviving longer, and the frequency of CNS involvement seems to be increasing. Furthermore, in the early-stage setting, the CNS remains a potential sanctuary site for relapse. This review highlights advances in the development of biologically relevant preclinical models, including the development of brain-tropic cell lines for testing of agents to prevent and treat brain metastases, and summarizes our current understanding of the biology of CNS relapse. From a clinical perspective, a variety of therapeutic approaches are discussed, including methods to improve drug delivery, novel cytotoxic agents, and targeted therapies. Challenges in current trial design and endpoints are reviewed. Finally, we discuss promising new directions, including novel trial designs, correlative imaging techniques, and enhanced translational opportunities.

Brain metastases from breast cancer: lessons from experimental magnetic resonance imaging studies and clinical implications

Breast cancer that has metastasized to the brain presents difficult clinical challenges. This diagnosis comes with high mortality rates, largely due to complexities in early detection and ineffective therapies associated with both dormancy and impermeability of the blood-brain barrier (BBB). Magnetic resonance imaging (MRI) is the current gold standard for diagnosis and assessment of brain tumors. It has been used clinically to investigate metastatic development as well as monitor response to therapy. Here, we describe preclinical imaging strategies that we have used to study the development of brain metastases due to breast cancer. Using this approach, we have identified three subsets of metastatic disease: permeable metastases, nonpermeable metastases, and solitary, dormant cancer cells, which likely have very different biology and responses to therapy. The ability to simultaneously monitor the spatial and temporal distribution of dormant cancer cells, metastatic growth, and associated tumor permeability can provide great insight into factors that contribute to malignant proliferation. Our preclinical findings suggest that standard clinical detection strategies may underestimate the true metastatic burden of breast cancer that has metastasized to the brain. A better understanding of true metastatic burden in brains will be important to assist in the development of more effective chemotherapeutics-particularly those targeted to cross the BBB-as well as detection of small nonpermeable metastases.

MUC1 and metastatic cancer: expression, function and therapeutic targeting

MUC1 is a transmembrane mucin that is often overexpressed in metastatic cancers and often used as a diagnostic marker for metastatic progression. The extracellular domain of MUC1 can serve as a ligand for stromal and endothelial cell adhesion receptors, and the cytoplasmic domain engages in several interactions that can result in increased migration and invasion, as well as survival. In this review, we address the role of MUC1 in metastatic progression by assessing clinical studies reporting MUC1 levels at various disease stages, reviewing mouse models utilized to study the role of MUC1 in metastatic progression, discuss mechanisms of MUC1 upregulation, and detail MUC1 protein interactions and signaling events. We review interactions between MUC1 and the extracellular environment, with proteins colocalized in the plasma membrane and/or cytoplasmic proteins, and summarize the role of MUC1 in the nucleus as a transcriptional cofactor. Finally, we review recent publications describing current therapies targeting MUC1 in patients with advanced disease and the stage of these therapies in preclinical development or clinical trials.

Relationship between tumor cell invasiveness and polyploidization

A number of studies have shown that tumor cells fuse with other tumor and non-tumor cells. In the present study on tumor cell lines derived from glioblastoma, breast cancer, and melanoma, we estimated the frequency of fusion between tumor cells by establishing the fraction of cells with whole tumor-genome duplication in each cell line. Together with this, the capacity of the tumor cell lines to spread through a basement membrane scaffold was assessed, in order to test the hypothesis that pericellular proteolysis by enzymatic release in the spaces of intercellular contact could account for differences in the fusogenicity of tumor cells. The difference in invasiveness between the cell lines accounted for their specific amount of cells with tumor-genome duplication, which, depending on the cell line analyzed, ranged from 2% to 25% of the total cells. These results support the hypothesis that cell-to-cell invasion eliciting membrane fusion causes polyploidization in tumor cells.

Spontaneous formation of tumorigenic hybrids between breast cancer and multipotent stromal cells is a source of tumor heterogeneity

Breast cancer progression involves cancer cell heterogeneity, with generation of invasive/metastatic breast cancer cells within populations of nonmetastatic cells of the primary tumor. Sequential genetic mutations, epithelial-to-mesenchymal transition, interaction with local stroma, and formation of hybrids between cancer cells and normal bone marrow-derived cells have been advocated as tumor progression mechanisms. We report herein the spontaneous in vitro formation of heterotypic hybrids between human bone marrow-derived multipotent stromal cells (MSCs) and two different breast carcinoma cell lines, MDA-MB-231 (MDA) and MA11. Hybrids showed predominantly mesenchymal morphological characteristics, mixed gene expression profiles, and increased DNA ploidy. Both MA11 and MDA hybrids were tumorigenic in immunodeficient mice, and some MDA hybrids had an increased metastatic capacity. Both in culture and as xenografts, hybrids underwent DNA ploidy reduction and morphological reversal to breast carcinoma-like morphological characteristics, while maintaining a mixed breast cancer-mesenchymal expression profile. Analysis of coding single-nucleotide polymorphisms by RNA sequencing revealed genetic contributions from both parental partners to hybrid tumors and metastasis. Because MSCs migrate and localize to breast carcinoma, our findings indicate that formation of MSC-breast cancer cell hybrids is a potential mechanism of the generation of invasive/metastatic breast cancer cells. Our findings reconcile the fusion theory of cancer progression with the common observation that breast cancer metastases are generally aneuploid, but not tetraploid, and are histopathologically similar to the primary neoplasm.

MicroRNA profiling and prediction of recurrence/relapse-free survival in stage I lung cancer

About 30% stage I non-small cell lung cancer (NSCLC) patients undergoing resection will recur. Robust prognostic markers are required to better manage therapy options. MicroRNAs (miRNAs) are a class of small non-coding RNAs of 19-25 nt and play important roles in gene regulation in human cancers. The purpose of this study is to identify miRNA expression profiles that would better predict prognosis of stage I NSCLC. MiRNAs extracted from 527 stage I NSCLC patients were profiled on the human miRNA expression profiling v2 panel (Illumina). The expression profiles were analyzed for their association with cancer subtypes, lung cancer brain metastasis and recurrence/relapse free survival (RFS). MiRNA expression patterns between lung adenocarcinoma and squamous cell carcinoma differed significantly with 171 miRNAs, including Let-7 family members and miR-205. Ten miRNAs associated with brain metastasis were identified including miR-145*, which inhibit cell invasion and metastasis. Two miRNA signatures that are highly predictive of RFS were identified. The first contained 34 miRNAs derived from 357 stage I NSCLC patients independent of cancer subtype, whereas the second containing 27 miRNAs was adenocarcinoma specific. Both signatures were validated using formalin-fixed paraffin embedded and/or fresh frozen tissues in independent data set with 170 stage I patients. Our findings have important prognostic or therapeutic implications for the management of stage I lung cancer patients. The identified miRNAs hold great potential as targets for histology-specific treatment or prevention and treatment of recurrent disease.

Strongly amphiphilic photosensitizers are not substrates of the cancer stem cell marker ABCG2 and provides specific and efficient light-triggered drug delivery of an EGFR-targeted cytotoxic drug

A wide range of anti-cancer drugs are substrates of the ATP-binding cassette transporter ABCG2/CD338/BCRP/MXR, which is thought to play an important role in multi-drug resistance (MDR) and protection of cancer stem cells (CSC) against chemotherapeutics and photodynamic therapy (PDT). Hence, it is of importance to develop drugs that are not substrates of ABCG2. The aim of this study was to elucidate if photosensitizers utilized for the endo-lysosomal release drug delivery method photochemical internalization (PCI) are substrates for ABCG2. The breast carcinoma cell line MA11, with a Hoechst 33342 side population of >50% was used as an ABCG2high model. The photosensitizer Pheophorbide A (PhA) and Hoechst 33342 were used as positive control substrates of ABCG2. ABCG2-inhibition by fumitremorgin C (FTC) did neither induce an increased accumulation of three different PCI-photosensitizers (di-sulfonated meso-tetraphenylporphine (TPPS(2a)), di-sulfonated meso-tetraphenylchlorin (TPCS(2a)) and di-sulfonated aluminium phtalocyanine (AlPcS(2a))) nor enhanced the photosensitization (P=0.65 for TPCS(2a)-PDT) of these PCI-based photosensitizers in the MA11 cells. The same results were also obtained with TPPS(2a) in the malignant glioma cell line U87 having a SP of ~0.1%. In contrast, both uptake and PDT-induced cytotoxicity was strongly enhanced for PhA when combined with FTC (P<0.001)). Specific and efficient light-controlled killing of EGFR+/ABCG2+ MA11 cells was obtained by PCI of the targeting toxin EGF-saporin. The novel data obtained in this study demonstrates that strongly amphiphilic photosensitizers used for PCI-based drug delivery are not substrates of ABCG2. This important findings warrant further development of the PCI technology as a strategy for efficient and site-specific eradication of MDR cells and CSC.

In vivo single scan detection of both iron-labeled cells and breast cancer metastases in the mouse brain using balanced steady-state free precession imaging at 1.5 T

PURPOSE

To simultaneously detect iron-labeled cancer cells and brain tumors in vivo in one scan, the balanced steady-state free precession (b-SSFP) imaging sequence was optimized at 1.5 T on mice developing brain metastases subsequent to the injection of micron-sized iron oxide particle-labeled human breast cancer cells.

MATERIALS AND METHODS

b-SSFP sequence parameters (repetition time, flip angle, and receiver bandwidth) were varied and the signal-to-noise ratio, contrast between the brain and tumors, and the number of detected iron-labeled cells were evaluated.

RESULTS

Optimal b-SSFP images were acquired with a 26 msec repetition time, 35° flip angle, and bandwidth of ±21 kHz. b-SSFP images were compared with T(2) -weighted 2D fast spin echo (FSE) and 3D spoiled gradient recalled echo (SPGR) images. The mean tumor-brain contrast-to-noise ratio and the ability to detect iron-labeled cells were the highest in the b-SSFP images.

CONCLUSION

A single b-SSFP scan can be used to visualize both iron-labeled cells and brain metastases.

Brain metastases as preventive and therapeutic targets

The incidence of metastasis to the brain is apparently rising in cancer patients and threatens to limit the gains that have been made by new systemic treatments. The brain is considered a 'sanctuary site' as the blood-tumour barrier limits the ability of drugs to enter and kill tumour cells. Translational research examining metastasis to the brain needs to be multi-disciplinary, marrying advanced chemistry, blood-brain barrier pharmacokinetics, neurocognitive testing and radiation biology with metastasis biology, to develop and implement new clinical trial designs. Advances in the chemoprevention of brain metastases, the validation of tumour radiation sensitizers and the amelioration of cognitive deficits caused by whole-brain radiation therapy are discussed.

The biology of brain metastases-translation to new therapies

Brain metastases are a serious obstacle in the treatment of patients with solid tumors and contribute to the morbidity and mortality of these cancers. It is speculated that the frequency of brain metastasis is increasing for several reasons, including improved systemic therapy and survival, and detection of metastases in asymptomatic patients. The lack of preclinical models that recapitulate the clinical setting and the exclusion of patients with brain metastases from most clinical trials have slowed progress. Molecular factors contributing to brain metastases are being elucidated, such as genes involved in cell adhesion, extravasation, metabolism, and cellular signaling. Furthermore, the role of the unique brain microenvironment is beginning to be explored. Although the presence and function of the blood-brain barrier in metastatic tumors is still poorly understood, it is likely that some tumor cells are protected from therapeutics by the blood-tumor barrier, creating a sanctuary site. This Review discusses what is known about the biology of brain metastases, what preclinical models are available to study the disease, and which novel therapeutic strategies are being studied in patients.

A novel human recombinant single-chain antibody targeting CD166/ALCAM inhibits cancer cell invasion in vitro and in vivo tumour growth

Screening a phage-display single-chain antibody library for binding to the breast cancer cell line PM-1 an antibody, scFv173, recognising activated leukocyte cell adhesion molecule (ALCAM, CD166) was isolated and its binding profile was characterized. Positive ALCAM immunohistochemical staining of frozen human tumour sections was observed. No ALCAM staining was observed in the majority of tested normal human tissues (nine of ten). Flow cytometry analyses revealed binding to 22 of 26 cancer cell lines of various origins and no binding to normal blood and bone marrow cells. Antibody binding inhibited invasion of the breast cancer cell line MDA-MB-231 by 50% in an in vitro Matrigel-coated membrane invasion assay. Reduced growth of tumours in nude mice was observed in an in vivo model in which the mice were injected subcutaneously with colorectal carcinoma HCT 116 cells and treated with scFv173 when compared to control. In summary, we have characterized a novel fully human scFv antibody recognising ALCAM on cancer cells and in tumour tissues that reduces cancer cell invasion and tumour growth in accordance with the hypothesised role for ALCAM in cell growth and migration control.

Cystatin E/M suppresses legumain activity and invasion of human melanoma

Background

High activity of cysteine proteases such as legumain and the cathepsins have been shown to facilitate growth and invasion of a variety of tumor types. In breast cancer, several recent studies have indicated that loss of the cysteine protease inhibitor cystatin E/M leads to increased growth and metastasis. Although cystatin E/M is normally expressed in the skin, its role in cysteine protease regulation and progression of malignant melanoma has not been studied.

Methods

A panel of various non-melanoma and melanoma cell lines was used. Cystatin E/M and C were analyzed in cell media by immunoblotting and ELISA. Legumain, cathepsin B and L were analyzed in cell lysates by immunoblotting and their enzymatic activities were analyzed by peptide substrates. Two melanoma cell lines lacking detectable secretion of cystatin E/M were transfected with a cystatin E/M expression plasmid (pCST6), and migration and invasiveness were studied by a Matrigel invasion assay.

Results

Cystatin E/M was undetectable in media from all established melanoma cell lines examined, whereas strong immunobands were detected in two of five primary melanoma lines and in two of six lines derived from patients with metastatic disease. Among the four melanoma lines secreting cystatin E/M, the glycosylated form (17 kD) was predominant compared to the non-glycosylated form (14 kD). Legumain, cathepsin B and L were expressed and active in most of the cell lines, although at low levels in the melanomas expressing cystatin E/M. In the melanoma lines where cystatin E/M was secreted, cystatin C was generally absent or expressed at a very low level. When melanoma cells lacking secretion of cystatin E/M were transfected with pCST6, their intracellular legumain activity was significantly inhibited. In contrast, cathepsin B activity was not affected. Furthermore, invasion was suppressed in cystatin E/M over-expressing melanoma cell lines as measured by the transwell Matrigel assay.

Conclusions

These results suggest that the level of cystatin E/M regulates legumain activity and hence the invasive potential of human melanoma cells.

Synergistic anti-cancer effects of immunotoxin and cyclosporin in vitro and in vivo

BACKGROUND

The clinical use of immunotoxins (ITs) has been hampered by hepatotoxicity, and the induction of a strong human-anti-IT response. The human-anti-IT response results in neutralisation of the immunoconjugates, rendering repetitive treatment inefficacious.

METHODS

We evaluated the combination of cyclosporin A (CsA) with various Pseudomonas exotoxin A-based ITs in human breast, cervical, and prostate cancer cell lines measured by protein synthesis, cell viability, and TUNEL assay. Furthermore, expression of essential proteins were analysed by western blot. We used cervical cancer model in nude rats to evaluate the anti-metastatic effect of the combination. The anti-immunogenic response by the CsA treatment was investigated in immunocompetent rats.

RESULTS

The combination of CsA with ITs caused remarkable synergistic cytotoxicity, in several cancer cell lines, characterised by protein synthesis inhibition, decreased cell viability, and an increased apoptotic index. Furthermore, the combination strongly inhibited formation of metastases in a cervical cancer model in nude rats with a statistically significant increase in median survival time of the combination-treated animals, as compared with those receiving a suboptimal dose of IT alone. Notably, we found in immunocompetent rats that the anti-IT immunoresponse elicited by repeated administration of IT was efficiently abrogated by CsA; notably the antibody responds towards the highly immunogenic PE was shown to be prevented.

CONCLUSION

The combination of ITs and CsA might constitute a significant improvement in the clinical potential of systemic IT treatment of cancer patients.

Multi-modality therapeutics with potent anti-tumor effects: photochemical internalization enhances delivery of the fusion toxin scFvMEL/rGel

BACKGROUND

There is a need for drug delivery systems (DDS) that can enhance cytosolic delivery of anti-cancer drugs trapped in the endo-lysosomal compartments. Exposure of cells to specific photosensitizers followed by light exposure (photochemical internalization, PCI) results in transfer of agents from the endocytic compartment into the cytosol.

METHODOLOGY AND PRINCIPAL FINDINGS

The recombinant single-chain fusion construct scFvMEL/rGel is composed of an antibody targeting the progenitor marker HMW-MAA/NG2/MGP/gp240 and the highly effective toxin gelonin (rGel). Here we demonstrate enhanced tumor cell selectivity, cytosolic delivery and anti-tumor activity by applying PCI of scFvMEL/rGel. PCI performed by light activation of cells co-incubated with scFvMEL/rGel and the endo-lysosomal targeting photosensitizers AlPcS(2a) or TPPS(2a) resulted in enhanced cytotoxic effects against antigen-positive cell lines, while no differences in cytotoxicity between the scFvMEL/rGel and rGel were observed in antigen-negative cells. Mice bearing well-developed melanoma (A-375) xenografts (50-100 mm(3)) were treated with PCI of scFvMEL/rGel. By 30 days after injection, approximately 100% of mice in the control groups had tumors>800 mm(3). In contrast, by day 40, 50% of mice in the PCI of scFvMEL/rGel combination group had tumors<800 mm(3) with no increase in tumor size up to 110 days. PCI of scFvMEL/rGel resulted in a synergistic effect (p<0.05) and complete regression (CR) in 33% of tumor-bearing mice (n = 12).

CONCLUSIONS/SIGNIFICANCE

This is a unique demonstration that a non-invasive multi-modality approach combining a recombinant, targeted therapeutic such as scFvMEL/rGel and PCI act in concert to provide potent in vivo efficacy without sacrificing selectivity or enhancing toxicity. The present DDS warrants further evaluation of its clinical potential.

The melanoma specific 9.2.27PE immunotoxin efficiently kills melanoma cells in vitro

Malignant melanomas are generally drug resistant and have a very poor prognosis. We have studied the effects of a chemical conjugate of pseudomonas exotoxin A (PE) and the antibody 9.2.27, which recognizes the high molecular weight melanoma associated antigen (HMW-MAA) expressed in most malignant melanomas and melanoma cell lines. We demonstrate that the 9.2.27PE immunotoxin (IT) induces cell death in malignant melanoma cells through protein synthesis inhibition followed by some morphological and biochemical features of apoptosis, like rounding up of cells, chromatin condensation and inactivation of PARP. Unlike previous results with the 425.3PE IT in breast cancer cells, we detected no depolarization of the mitochondrial membrane after 9.2.27PE IT treatment. This is likely due to the lack of strong activation of caspase-8 and caspase-3. The lack of depolarization suggests that cytochrome c, a molecule that triggers activation of caspase-3, was retained within the mitochondria. In addition, the protein level of the antiapoptotic Bcl-2 did not decrease in contrast to other antiapoptotic molecules belonging to the inhibitor of apoptosis and the Bcl-2 family. This suggests that Bcl-2 may play a role in maintaining the mitochondrial membrane integrity in the 9.2.27PE-treated cells. Nevertheless, 9.2.27PE IT efficiently killed malignant melanoma cells that can be ascribed to inhibition of protein synthesis followed by some morphological and biochemical features of apoptosis.

Reactive glia are recruited by highly proliferative brain metastases of breast cancer and promote tumor cell colonization

Interactions between tumor cells and the microenvironment are crucial to tumor formation and metastasis. The central nervous system serves as a "sanctuary" site for metastasis, resulting in poor prognosis in diagnosed patients. The incidence of brain metastasis is increasing; however, little is known about interactions between the brain and metastatic cells. Brain pathology was examined in an experimental model system of brain metastasis, using a subline of MDA-MB-231 human breast cancer cells. The results were compared with an analysis of sixteen resected human brain metastases of breast cancer. Experimental metastases formed preferentially in specific brain regions, with a distribution similar to clinical cases. In both the 231-BR model, and in human specimens, Ki67 expression indicated that metastases were highly proliferative (approximately 50%). Little apoptosis was observed in either set of tumors. In the model system, metastases elicited a brain inflammatory response, with extensive reactive gliosis surrounding metastases. Similarly, large numbers of glial cells were found within the inner tumor mass of human brain metastases. In vitro co-cultures demonstrated that glia induced a approximately 5-fold increase in metastatic cell proliferation (P<0.001), suggesting that brain tissue secretes factors conducive to tumor cell growth. Molecules used to signal between tumor cells and the surrounding glia could provide a new avenue of therapeutic targets for brain metastases.

PreTect HPV-Proofer: real-time detection and typing of E6/E7 mRNA from carcinogenic human papillomaviruses

Monitoring human papillomavirus (HPV) E6/E7 mRNA expression may provide an accurate and informative diagnostic approach for detection of oncogene activity related to the development of severe dysplasia or cervical carcinoma. A multiplex nucleic acid sequence based amplification (NASBA) assay, utilizing molecular beacon probes for real-time detection was developed for the identification of E6/E7 mRNA from HPV types 16, 18, 31, 33 and 45. The assay is called PreTect HPV-Proofer and this report describes the development and the analytical performance of the assay. The reproducibility of PreTect HPV-Proofer with regard to a positive result was found to be between 96 and 100%, depending on HPV type. The melting temperature for the different molecular beacons was in the range of 48-55 degrees C, indicating conformational stability, i.e. the molecular beacons will not get activated by the 41 degrees C annealing temperature, but will be activated by the annealing to the target itself. The limit of detection for HPV 16 was ten SiHa or CaSki cells and for HPV 18 one HeLa cell. No cross reactivity was observed with E6/E7 mRNA from the other tested HPV types. mRNA from cervical cells was also successfully amplified after more than one year of storage. In conclusion, the PreTect HPV-Proofer assay, individually identifying E6/E7 mRNA expression from five carcinogenic HPV types, is a reproducible assay that may serve as a valuable tool in monitoring HPV infections producing proteins with a transforming potential.

The Biology of Metastasis to a Sanctuary Site

Metastasis to the brain is prevalent in solid tumors and lymphomas, and is associated with shortened survival. The brain is regarded as a sanctuary site for metastatic tumor cells where they exist partially protected from drugs by the blood-tumor barrier. Model systems for brain metastasis have been developed and are now yielding mechanistic insights into the roles of angiogenesis, energy metabolism, the Her-2 and Stat3 signaling pathways, and dormancy. Specific, new approaches to combat brain metastatic disease are needed.

Delivery of chemotherapy and antibodies across the blood-brain barrier and the role of chemoprotection, in primary and metastatic brain tumors: report of the Eleventh Annual Blood-Brain Barrier Consortium meeting

Although knowledge of molecular biology and cellular physiology has advanced at a rapid pace, much remains to be learned about delivering chemotherapy and antibodies across the blood-brain barrier (BBB) for the diagnosis and treatment of central nervous system (CNS) disease. A meeting, partially funded by an NIH R13 grant, was convened to discuss the state of the science, current knowledge gaps, and future directions in the delivery of drugs and proteins to the CNS, for the treatment of primary and metastatic brain tumors. Meeting topics included CNS metastases and the BBB, and chemoprotection and chemoenhancement in CNS disorders. The discussions regarding CNS metastases generated possibilities of chemoprotection as a means not only to decrease treatment-related toxicity but also to increase chemotherapy dose intensity. The increasing incidence of sanctuary brain metastasis from breast cancer, in part due to the difficulty of monoclonal antibodies (mAbs) such as herceptin to cross the BBB, was one of the most salient "take home" messages of the meeting.

AMP-activated protein kinase protects against anti-epidermal growth factor receptor-Pseudomonas exotoxin A immunotoxin-induced MA11 breast cancer cell death

We have shown previously that our 425.3PE immunotoxin inhibits protein synthesis and induces apoptosis in human breast cancer cells. In attempts to further elucidate the intracellular pathways implicated in its cellular effects, we found that the immunotoxin induced an initial stress response, which rapidly caused an imbalance in the cellular energy status with an increase in reactive oxygen species. The AMP-activated protein kinase (AMPK), a sensor of increased cellular AMP/ATP ratio, was activated by 425.3PE. An immunotoxin-induced activation of c-Jun NH2-terminal kinase (JNK) preceded and overlapped caspase-mediated cleavage of the alpha-subunit of AMPK in a time- and dose-dependent manner. The JNK activation occurred already at a dose level too low to induce any detectable changes in the apoptotic machinery or protein synthesis. In contrast, cycloheximide, even at a concentration causing a 90% inhibition of protein synthesis, did neither affect the ATP level nor activate JNK and AMPK. Pretreatment of the cells with the specific AMPK inhibitor compound C and JNK inhibitor SP600125 blocked activation of AMPK and JNK, respectively, and subsequently sensitized the cells to 425.3PE-induced cell death. Whereas the antioxidant N-acetyl-l-cysteine blocked the generation of reactive oxygen species and activation of JNK and AMPK, it did not block immunotoxin-induced apoptosis. Together, the results show that 425.3PE induces several parallel signaling events, observed initially as an early activation of survival pathways, protecting the cells against the toxic effects of the immunotoxin, followed by subsequent apoptosis induction and protein synthesis inhibition. Conceivably, therapeutic manipulation of the signaling intermediates AMPK and JNK might provide a means to maximize the anticancer effects of the 425.3 immunotoxin.

Breast cancer metastasis to the central nervous system

Clinically symptomatic metastases to the central nervous system (CNS) occur in approximately 10 to 15% of patients with metastatic beast cancer. CNS metastases are traditionally viewed as a late complication of systemic disease, for which few effective treatment options exist. Recently, patients with Her-2-positive breast tumors who were treated with trastuzumab have been reported to develop CNS metastases at higher rates, often while responding favorably to treatment. The blood:brain barrier and the unique brain microenvironment are hypothesized to promote distinct molecular features in CNS metastases that may require tailored therapeutic approaches. New research approaches using cell lines that reliably and preferentially metastasize in vivo to the brain have been reported. Using such model systems, as well as in vitro analogs of blood-brain barrier penetration and tissue-based studies, new molecular leads into this disease are unfolding.

Cell cycle checkpoint signaling involved in histone deacetylase inhibition and radiation-induced cell death

In breast cancer, radiation has a central role in the treatment of brain metastasis, although tumor sensitivity might be limited. The tumor cell defense response to ionizing radiation involves activation of cell cycle checkpoint signaling. Histone deacetylase (HDAC) inhibitors, agents that cause hyperacetylation of histone proteins and thereby aberrations in the chromatin structure, may also override the DNA damage defense response and facilitate the radiation-induced mitotic cell death. In experimental metastasis models, the human breast carcinoma cell line MA-11 invariably disseminates to the central nervous system. We compared profiles of in vitro MA-11 cell cycle response to ionizing radiation and HDAC inhibition. After radiation exposure, the G2-M phase accumulation and the preceding repression of the G2 phase regulatory factors Polo-like kinase-1 and cyclin B1 required intact G2 checkpoint signaling through the checkpoint kinase CHK1, whereas the similar phenotypic changes observed with HDAC inhibition did not. MA-11 cells did not show radiation-induced expression of the G1 cell cycle inhibitor p21, indicative of a defective G1 checkpoint and consistent with a point mutation detected in the tumor suppressor TP53 gene. Increase in the p21 level, however, was observed with HDAC inhibition. Following pretreatment with the HDAC inhibitor, the efficiency of clonogenic regrowth after irradiation was reduced, which is in accordance with the concept of increased probability of mitotic cell death when the chromatin structure is disrupted. Among molecular cell cycle-targeted drugs currently in the pipeline for testing in early-phase clinical trials, HDAC inhibitors may have therapeutic potential as radiosensitizers.

Downregulation of the antiapoptotic MCL-1 protein and apoptosis in MA-11 breast cancer cells induced by an anti-epidermal growth factor receptor-Pseudomonas exotoxin a immunotoxin

Pseudomonas exotoxin (PE)-containing immunotoxins (ITs) act by arresting protein synthesis and promoting apoptosis, but the mechanisms of the induced apoptosis and the relationship to protein synthesis inhibition is not well elucidated. We studied these effects in MA-11 human breast cancer cells treated with 425.3PE, an unmodified PE covalently linked to the 425.3 antibody, which targets the EGF receptor. This IT induced efficient inhibition of protein synthesis with simultaneous induction of apoptosis. Thus, treatment of cells with 10 ng/ml of IT for 5 hr caused 85% inhibition of protein synthesis in parallel with caspase-3, -8 and -9 activation and PARP inactivation. Even after 72 hr of IT treatment, preincubation with the broad-spectrum caspase inhibitor z-VAD-FMK caused a significant increase in cell survival without affecting IT-induced protein synthesis inhibition. Interestingly, a combination of z-VAD-FMK and the cathepsin B/L inhibitor z-FA-FMK prevented completely IT-induced cell death in MA-11 cells after 24 hr, indicating that cathepsin activation may be important for optimal induction of IT-induced cell death. IT treatment caused after 2.5 hr a significant decrease in the level of the antiapoptotic protein Mcl-1 but not of Bcl-2 and Bcl-XL. Furthermore, Mcl-1 expression was not sensitive to caspase inhibitors but was totally prevented by the lactacystin proteasome inhibitor, suggesting that IT-induced apoptosis may be triggered by a reduction in the Mcl-1 level. Mitochondrial membrane potential (DeltaPsi mito) decreased concurrently with caspase activation, showing the involvement of DeltaPsi mito as a regulator of IT-induced apoptosis. Our results demonstrate that 425.3PE-mediated cell death involves simultaneous induction of apoptosis and protein synthesis inhibition in MA-11 cells, thus contributing to an understanding of the mechanisms involved in IT-induced apoptosis.

Relevance of breast cancer cell lines as models for breast tumours: an update

The number of available breast cancer cell (BCC) lines is small, and only a very few of them have been extensively studied. Whether they are representative of the tumours from which they originated remains a matter of debate. Whether their diversity mirrors the well-known inter-tumoural heterogeneity is another essential question. While numerous similarities have long been found between cell lines and tumours, recent technical advances, including the use of micro-arrays and comparative genetic analysis, have brought new data to the discussion. This paper presents most of the BCC lines that have been described in some detail to date. It evaluates the accuracy of the few of them widely used (MCF-7, T-47D, BT-474, SK-BR-3, MDA-MB-231, Hs578T) as tumour models. It is concluded that BCC lines are likely to reflect, to a large extent, the features of cancer cells in vivo. The importance of oestrogen receptor-alpha (gene ESR1 ) and Her-2/ neu ( ERBB2 ) as classifiers for cell lines and tumours is underlined. The recourse to a larger set of cell lines is suggested since the exact origin of some of the widely used lines remains ambiguous. Investigations on additional specific lines are expected to improve our knowledge of BCC and of the dialogue that these maintain with their surrounding normal cells in vivo.

Imaging of murine brain tumors using a 1.5 Tesla clinical MRI system

BACKGROUND

In this study, we investigated the feasibility of using a 1.5 Tesla (T) clinical magnetic resonance imaging (MRI) system for in vivo assessment of three histopathologically different brain tumor models in mice.

METHODS

We selected mouse models in which tumor growth was observed in different intracranial compartments: Patched+/- heterozygous knock-out mice for tumor growth in the cerebellum (n = 5); U87 MG human astrocytoma cells xenografted to the frontal lobe of athymic mice (n = 15); and F5 (n = 15) or IOMM Lee (n = 15) human malignant meningioma cells xenotransplanted to the athymic mouse skull base or convexity. Mice were imaged using a small receiver surface coil and a clinical 1.5 T MRI system. T1- and fast spin echo T2-weighted image sequences were obtained in all animals. Gadolinium was injected via tail vein to better delineate the intracranial tumors. Twenty mice were followed by serial MRI to study tumor growth over time. In these mice, images were typically performed after tumor implantation, and at two week intervals. Mice were euthanized following their last imaging procedure, and their tumors were examined by histopathology. The histopathological preparations were then compared to the last MR images to correlate the imaging features with the pathology.

RESULTS

Magnetic resonance imaging delineated th tumors in the cerebellum, frontal lobes and skull base in all mouse models. The detection of intracranial tumors was enhanced with prio administration of gadolinium, and the limit of resolution of brain tumors in the mice was 1-2 mm3. Sequential images performed at different time intervals showed progressive tumor growth in all animals. The MR images of tumor size and location correlated accurately with th results of the histopathological analysis.

CONCLUSION

Magnetic resonance imaging of murine brain tumors in different intracrania compartments is feasible with a 1.5 T clinical MR system and a specially designed surface coil. Tumors as small as 1-2 mm3 can be detecte with good image resolution. Mice harbouring nascent brain tumors can be followed sequentially by serial MR imaging. This may allow for a noninvasive means by which tumor growth can be measured, and novel therapies tested without resorting to sacrifice of the mice.

Models of breast cancer: is merging human and animal models the future?

Survival rates of patients with early breast cancer in the United Kingdom and in the United States have improved steadily over the past 15 years. The only way to continue or even accelerate this progress, however, is the discovery and development of new preventative and therapeutic strategies. With the massive explosion in potential therapeutic strategies becoming available, in the postgenomic era, better and more representative breast cancer models are urgently required for preclinical trials. Development of better in vivo models of human breast cancer are thus of crucial importance in the development of new cancer therapeutics.

Clinical significance of proliferative potential of occult metastatic cells in bone marrow of patients with breast cancer

There is increasing statistical evidence that the presence of tumour cells in bone marrow detected by immunocytochemistry represents an important prognostic indicator in breast cancer, but their individual capacity to become clinical metastases is unknown. The aim of this study was to assess the proliferative capacity of these occult metastatic cells in the bone marrow of patients with various stages of breast cancer. We obtained bone marrow aspirates from 60 patients with breast cancer before treatment with chemotherapy: 17 stage II, 12 stage III and 31 stage IV. After bone marrow culture for 6-34 days (median: 17 days) under specific cell culture conditions, viable epithelial cells were detected by cytokeratin staining in 40 patients (66%). Expansion of tumour cells was poorly correlated with tumour cell detection on primary screening (P=0.06). There was a nonsignificant correlation between the number and the presence of expanded tumour cells and the UICC stage of the patients. On primary screening, tumour cell detection was positive in 56% of patients and was correlated with clinical UICC stage (P=0.01). However, with a median follow-up of 23 months, expansion of tumour cells from bone marrow was associated with decreased patient survival (P=0.04), whereas the survival difference according to detection of CK-positive cells on primary screening was not statistically significant. In conclusion, viable tumour cells can be detected in the bone marrow of breast cancer patients. Their proliferative potential could be predictive of outcome and deserves further investigation.

Differential display analysis of breast carcinoma cells enriched by immunomagnetic target cell selection: gene expression profiles in bone marrow target cells

The red bone marrow (BM) is an important indicator organ of hematogenous micrometastatic spread of carcinomas. Characterization of biological properties specific for BM micrometastatic cells, however, is technically challenging due to the limited number of target cells usually available for the purpose. This report provides referrals to qualitative gene expression profiling of BM micrometastatic cells enriched by immunomagnetic selection. First, an experimental strategy was used to study regulatory mechanisms involved when BM micrometastatic cells colonize distant organs. The MA-11 cells, originating from BM micrometastases in a breast cancer patient clinically devoid of overt metastatic disease, were injected into immunodeficient rats. Metastatic MA-11 cells were subsequently immunoselected from the resulting in vivo lesions. The selected cell populations were compared to the injected cells by differential display analysis, and several genes possibly involved in tumor cell invasion and proliferation were confirmed as differentially expressed among the various MA-11 cell populations. A direct approach to qualitative gene expression profiling of BM micrometastatic cells was also explored. Carcinoma cells were immunoselected from BM and axillary lymph nodes obtained from breast cancer patients, and the isolated cell populations were compared by differential display analysis. Two candidate genes, identified as factors involved in cellular growth control, appeared as differentially expressed by the target cells from BM. Our study provides detailed information on how to combine an immunomagnetic selection procedure and differential display analysis to reveal gene expression profiles that may characterize BM micrometastatic cells.

Complete cytogenetic characterization of the human breast cancer cell line MA11 combining G-banding, comparative genomic hybridization, multicolor fluorescence in situ hybridization, RxFISH, and chromosome-specific painting

The MA11 cell line was established from malignant cells isolated from the bone marrow of a breast cancer patient. It metastasizes selectively to the brain in athymic mice. Since the genomic rearrangements of only a few breast cancer cell lines have been characterized completely, we analyzed MA11 cytogenetically. Because the G-banding analysis revealed a very complex karyotype with several markers and chromosomes with additional material of unknown origin, we used multicolor fluorescence in situ hybridization (M-FISH), cross-species color banding (RxFISH), comparative genomic hybridization (CGH), and chromosome-specific probes to better characterize the chromosome abnormalities. The use of these FISH-based screening techniques allowed us to detect previously unsuspected chromosomal changes and determine the identity of chromosomal markers. Multicolor FISH was especially useful to identify the rearranged chromosomes, whereas RxFISH, G-banding, and CGH were instrumental in determining breakpoint positions, although some uncertainties were removed only after hybridization with chromosome-specific probes. The combined analysis revealed a near-triploid karyotype with no less than 20 chromosomes demonstrating structural rearrangements. The resulting imbalances included several of those known to be common in primary breast carcinomas (gain of 1q, 8q, and 20q and loss of 8p, 11q, and 13q), indicating that the MA11 cell line may serve as a good model to study breast carcinogenesis. The full cytogenetic characterization we present may guide future searches for the mechanism of organ-selective metastasis in this model system and, possibly, also in vivo.

Systemic immunotoxin treatment inhibits formation of human breast cancer metastasis and tumor growth in nude rats

Adjuvant chemotherapy in breast cancer patients has had limited success, which is possibly because of lack of effect on non-proliferating cells accompanied by the emergence of drug-resistant cell clones. Since immunotoxins (ITs) are known to exert proliferation-independent cytotoxicity, we investigated the efficacy of systemically administered anti-carcinoma ITs in nude rat models, simulating micrometastatic disease. The monoclonal antibodies MOC31, BM7 and 425.3, which recognize epithelial glycoprotein 2, MUC-1 mucin and the epidermal growth factor receptor, chemically conjugated to Pseudomonas exotoxin A (PE), inhibited protein synthesis of the 2 breast cancer cell lines at concentrations of 0.3-0.4 ng/ml, except for BM7-PE, which was less efficacious (65 ng/ml). In the MA-11 model in nude rats, a single i. v. dose of 20 microg MOC31-PE prevented development of metastasis in the spinal cord in 11/19 (58%) of the animals. Similarly, 425.3-PE treatment gave 6/9 (66%) long-term survivors. In rats injected intracardially or intratibially with MT-1 cells, treatment with 425. 3-PE prevented metastasis in 4/10 (40%) and intratibial tumor growth in 17/18 (94%) of the rats. Importantly, an equimolar dose of free 425.3 (antibody) was ineffective, whereas PE alone was toxic. With BM7-PE, 5/17 (29%) cures were obtained in the intratibial model. The results demonstrate that systemic short-term treatment with non-toxic doses of the 3 ITs tested can effectively inhibit the development of experimental breast cancer metastasis and/or local tumor growth in bone. The results support the development of the ITs towards clinical evaluation for possible use as short-term adjuvant therapy in patients at high risk of early relapse.

Heterogeneity of MUC1 expression by human breast carcinoma cell lines in vivo and in vitro

Increased expression of the epithelial mucin MUC1 has been linked to tumor aggressiveness in human breast carcinoma. Recent studies have demonstrated that overexpression of MUC1 interferes with cell-substrate and cell-cell adhesion by masking cell surface integrins and E-cadherin. Additionally, the cytoplasmic tail of MUC1 is involved in signal transduction and interactions with catenins. In the present study, we have examined the in vitro expression of MUC1 mRNA and protein in a panel of 14 human breast cancer cell lines using northern blotting, western blotting, immunocytochemistry, and flow cytometry. Considerable variability of expression was noted not only between cell lines but also within several individual lines. Many cell lines such as BT 20, KPL-1, and T47D expressed abundant MUC1 whilst others such as MDA-MB-231 and MCF-7 showed intermediate expression, and MDA-MB-435 and MDA-MB-453 expressed very low levels. Low levels of MUC1 expression were associated with decreased expression of cytokeratin and increased expression of vimentin. Additionally, 12 of the cell lines were established as xenografts in immunocompromised (SCID) mice, and MUC1 expression in both the primary tumors as well as metastases was assessed immunohistochemically. In general, in vivo expression mirrored in vitro expression, although there was reduced in vivo expression in T47D and ZR-75-1 xenografts. Although we showed no correlation between tumorigenicity or metastasis and MUC1 expression, this study will assist development of experimental models to assess the influence of MUC1 of on breast cancer progression.

Site-specific experimental metastasis patterns of two human breast cancer cell lines in nude rats

Animal models for breast cancer metastasis are valuable tools for studying mechanisms of metastasis and for preclinical testing of anti-metastatic therapy regimens. Using MA-11 and MT-1, two oestrogen and progesterone receptor-negative human breast cancer cell lines, we developed new models in nude rats with patterns of experimental metastasis resembling those frequently observed in humans. MA-11 cells showed a clear preference for growth in the CNS. Fourteen of 15 animals injected with MA-11 cells into the left ventricle of the heart developed hind-leg paralysis, and tumours were observed in the spinal cord. MT-1 cells consistently exhibited bone/bone marrow metastases after intracardial injection, in addition to tumours in the brain and spinal cord. When injected into the cisterna magna, both cell lines gave rise to leptomeningeal neoplastic disease. Injection of MA-11 cells into the tibial bone marrow resulted in tumours in only 2 of 13 rats, whereas all animals injected with MT-1 cells developed tumours. Only 2 of 6 rats injected i.v. with MA-11 cells developed lung colonies compared with all 9 animals injected with MT-1 cells. Cell-surface expression of the following was examined: EGP2; MUC1; EGFr; E- and N-cadherin; the alpha2, alpha3, alpha5, beta1 and beta4 integrins; c-erb-B2; and N-CAM. c-erb-B2 was expressed in a higher percentage of the bone-metastasizing MT-1 cells than the MA-11 cells, whereas E-cadherin was expressed in MA-11 but not MT-1 cells. In animals injected with MA-11 and MT-1 cells in the left cardiac ventricle, treatment with cisplatin and doxorubicin did not improve survival. In summary, these clinically relevant animal models may be used for studies related to site-specific growth and metastasis and for assessing effects of experimental therapy against human breast cancer.

Detection and clinical importance of micrometastatic disease

Metastatic relapse in patients with solid tumors is caused by systemic preoperative or perioperative dissemination of tumor cells. The presence of individual tumor cells in bone marrow and in peripheral blood can be detected by immunologic or molecular methods and is being regarded increasingly as a clinically relevant prognostic factor. Because the goal of adjuvant therapy is the eradication of occult micrometastatic tumor cells before metastatic disease becomes clinically evident, the early detection of micrometastases could identify the patients who are most (and least) likely to benefit from adjuvant therapy. In addition, more sensitive methods for detecting such cells should increase knowledge about the biologic mechanisms of metastasis and improve the diagnosis and treatment of micrometastatic disease. In contrast to solid metastatic tumors, micrometastatic tumor cells are appropriate targets for intravenously applied agents because macromolecules and immunocompetent effector cells should have access to the tumor cells. Because the majority of micrometastatic tumor cells may be nonproliferative (G0 phase), standard cytotoxic chemotherapies aimed at proliferating cells may be less effective, which might explain, in part, the failure of chemotherapy. Thus, adjuvant therapies that are aimed at dividing and quiescent cells, such as antibody-based therapies, are of considerable interest. From a literature search that used the databases MEDLINE(R), CANCERLIT(R), Biosis(R), Embase(R), and SciSearch(R), we discuss the current state of research on minimal residual cancer in patients with epithelial tumors and the diagnostic and clinical implications of these findings.