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

Treatment affects load to failure and microdamage accumulation in healthy and osteolytic rat vertebrae

Bone turnover and microdamage are impacted by the presence of skeletal metastases which can contribute to increased fracture risk. Treatments for metastatic disease may further impact bone quality. This exploratory study aimed to establish an initial understanding of microdamage accumulation and load to failure in healthy and osteolytic rat vertebrae following focal and systemic cancer treatment (docetaxel (DTX), stereotactic body radiotherapy (SBRT), or zoledronic acid (ZA)). Osteolytic spine metastases were developed in 6-week-old athymic female rats via intracardiac injection of HeLa human cervical cancer cells (day 0). Additional rats served as healthy controls. Rats were either untreated, received SBRT to the T10-L6 vertebrae on day 14 (15 Gy, two fractions), DTX on day 7 or 14, or ZA on day 7. Rats were euthanized on day 21. Tumor burden was assessed with bioluminescence images acquired on day 14 and 21, histology of the excised T11 and L5 vertebrae, and ex-vivo μCT images of the T13-L4. Microstructural parameters (bone volume/total volume, trabecular number, spacing, thickness, and bone mineral density) were measured from L2 vertebrae. Load to failure was measured with axial compressive loading of the L1-L3 motion segments. Microdamage accumulation was labeled in T13 vertebrae with BaSO4 staining and was visualized with high resolution μCT imaging. Microdamage volume fraction was defined as the ratio of BaSO4 to bone volume. DTX administered on day 7 reduced tumor growth significantly (p < 0.05). Microdamage accumulation was found to be increased by the presence of metastases but was reduced by all treatments with ZA showing the largest improvement in HeLa cell injected rats. Load to failure was decreased in untreated and SBRT HeLa cell injected rats compared to healthy controls (p < 0.01). There was a moderate negative correlation between load to failure and microdamage volume fraction in vertebrae from rats injected with HeLa cells (R = -0.35, p = 0.031). Strong correlations were also found between microstructural parameters and load to failure and microdamage accumulation. Several factors, including the presence of osteolytic lesions and use of cancer therapies, influence microdamage accumulation and load to failure in rat vertebrae. Understanding the impact of these treatments on fracture risk of metastatic vertebrae is important to improve management of patients with spinal metastases.

Elevated Microdamage Spatially Correlates with Stress in Metastatic Vertebrae

Metastasis of cancer to the spine impacts bone quality. This study aims to characterize vertebral microdamage secondary to metastatic disease considering the pattern of damage and its relationship to stress and strain under load. Osteolytic and mixed osteolytic/osteoblastic vertebral metastases were produced in athymic rats via HeLa cervical or canine Ace-1 prostate cancer cell inoculation, respectively. After 21 days, excised motion segments (T12-L2) were µCT scanned, stained with BaSO₄ and re-imaged. T13-L2 motion segments were loaded in axial compression to induce microdamage, re-stained and re-imaged. L1 (loaded) and T12 (unloaded) vertebrae were fixed, sample blocks cut, polished and BSE imaged. µFE models were generated of all L1 vertebrae with displacement boundary conditions applied based on the loaded µCT images. µCT stereological analysis, BSE analysis and µFE derived von Mises stress and principal strains were quantitatively compared (ANOVA), spatial correlations determined and patterns of microdamage assessed qualitatively. BaSO₄ identified microdamage was found to be spatially correlated with regions of high stress in µFEA. Load-induced microdamage was shown to be elevated in the presence of osteolytic and mixed metastatic disease, with diffuse, crossed hatched areas of microdamage present in addition to linear microdamage and microfractures in metastatic tissue, suggesting diminished bone quality.

A model of breast cancer meningeal metastases: characterization with in vivo molecular imaging

Meningeal metastasis is a fatal complication of breast cancer which affects 8-15% of patients who experience severe neurological complications of cranial nerves, cerebrum, and spinal cord. Survival once diagnosed is less than 4 months. Currently there is no cure. Aggressive multimodal radiation, intra-CSF, or systemic chemotherapy is palliative. Investigation of urgently needed new treatment modalities is hindered by the lack of suitable animal models to effectively study tumor growth kinetics. We present a model of meningeal metastases where tumor growth and associated neurological symptoms have been characterized over 3 weeks by sequential molecular imaging, tumor growth kinetics, and histopathology. Meningeal metastases were induced by stereotaxic injection of human breast cancer cells (MDA-MB-231-Rluc) into the lateral ventricle. Tumor identified by Gd-MRI and Rluc-bioluminescence depict growth in 3 phases, namely lag, exponential, and plateau phase. Invasive tumor growth was highlighted by changes in contrast distribution in the meninges, ventricle and brain compartments over time where moderate contrast uptake in the early growth phase gave rise to a heavy tumor burden in the base of the brain in the latter phases. Tumor growth was accompanied with debilitating neurological symptoms and change in body mass. Tumor was confirmed by ex vivo histology. The reliability of the model to study novel therapeutics was confirmed by oncolytic virus delivered into the lateral ventricle showed potential for treatment. This effective and reliable model resembles human disease progression and is ideally suited to investigate novel treatments.

Mechanical behavior of metastatic vertebrae are influenced by tissue architecture, mineral content, and organic feature alterations

Diminished vertebral mechanical behavior with metastatic involvement is typically attributed to modified architecture and trabecular bone content. Previous work has identified organic and mineral phase bone quality changes in the presence of metastases, yet limited work exists on the potential influence of such tissue level modifications on vertebral mechanical characteristics. This work seeks to determine correlations between features of bone (structural and tissue level) and mechanical behavior in metastatically involved vertebral bone. It is hypothesized that tissue level properties (mineral and organic) will improve these correlations beyond architectural properties and BMD alone. Twenty-four female athymic rats were inoculated with HeLa or Ace-1 cancer cells lines producing osteolytic (N = 8) or mixed (osteolytic/osteoblastic, N = 7) metastases, respectively. Twenty-one days post-inoculation L1-L3 pathologic vertebral motion segments were excised and μCT imaged. 3D morphometric parameters and axial rigidity of the L2 vertebrae were quantified. Sequential loading and μCT imaging measured progression of failure, stiffness and peak force. Relationships between mechanical testing (whole bone and tissue-level) and tissue-level material property modifications with metastatic involvement were evaluated utilizing linear regression models. Osteolytic involvement reduced vertebral trabecular bone volume, structure, CT-derived axial rigidity, stiffness and failure force compared to healthy controls (N = 9). Mixed metastases demonstrated similar trends. Previously assessed collagen cross-linking and proline-based residues were correlated to mechanical behavior and improved the predictive ability of the regression models. Similarly, collagen organization improved predictive regression models for metastatic bone hardness. This work highlights the importance of both bone content/architecture and organic tissue-level features in characterizing metastatic vertebral mechanics. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3013-3022, 2018.

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.

Collagen fibril organization within rat vertebral bone modified with metastatic involvement

Metastatic involvement diminishes the mechanical integrity of vertebral bone, however its specific impact on the structural characteristics of a primary constituent of bone tissue, the collagen-I fibril matrix, has not been adequately characterized. Female athymic rats were inoculated with HeLa or Ace-1 cancer cells lines producing osteolytic or mixed (osteolytic & osteoblastic) metastases respectively. A maximum of 21days was allowed between inoculation and rat sacrifice for vertebrae extraction. Linear polarization-in, polarization-out (PIPO) second harmonic generation (SHG) and transmission electron microscopy (TEM) imaging was utilized to assess the impact of metastatic involvement on collagen fibril organization. Increased observations of deviations in the typical plywood motif or a parallel packing structure and an increased average measured susceptibility ratio (related to relative degree of in-plane vs. out-plane fibrils in the analyzed tissue area) in bone adjacent to metastatic involvement was indicative of change in fibrilar organization compared to healthy controls. In particular, collagen-I fibrils in tumour-induced osteoblastic bone growth showed no adherence to the plywood motif or parallel packing structure seen in healthy lamellar bone, exhibiting a much higher susceptibility ratio and degree of fibril disorder. Negative correlations were established between measured susceptibility ratios and the hardness and modulus of metastatic bone tissue assessed in a previous study. Characterizing modifications in tissue level properties is key in defining bone quality in the presence of metastatic disease and their potential impact on material behaviour.

Osteolytic and mixed cancer metastasis modulates collagen and mineral parameters within rat vertebral bone matrix

Metastatic involvement in vertebral bone diminishes the mechanical integrity of the spine; however minimal data exist on the potential impact of metastases on the intrinsic material characteristics of the bone matrix. Thirty-four (34) female athymic rats were inoculated with HeLa (N = 17) or Ace-1 (N = 17) cancer cells lines producing osteolytic or mixed (osteolytic and osteoblastic) metastases, respectively. A maximum of 21 days was allowed between inoculation and rat sacrifice for vertebrae extraction. High performance liquid chromatography (HPLC) was utilized to determine modifications in collagen-I parameters such as proline hydroxylation and the formation of specific enzymatic and non-enzymatic (pentosidine) cross-links. Raman spectroscopy was used to determine relative changes in mineral crystallinity, mineral carbonation, mineral/collagen matrix ratio, collagen quality ratio, and proline hydroxylation. HPLC results showed significant increase in the formation of pentosidine and decrease in the formation of the enzymatic cross-link deoxy-pryridinoline within osteolytic bone compared to mixed bone. Raman results showed decreased crystallinity, increased carbonation, and collagen quality (aka 1660/1690 sub-band) ratio with osteolytic bone compared to mixed bone and healthy controls along with an observed increase in proline hydroxylation with metastatic involvement. The mineral/matrix ratio decreased in both osteolytic and mixed bone compared to healthy controls. Quantifying modifications within the intrinsic characteristics of bone tissue will provide a foundation to assess the impact of current therapies on the material behavior of bone tissue in the metastatic spine and highlight targets for the development of new therapeutics and approaches for treatment. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2126-2136, 2016.

Matrix metalloproteinase-based photodynamic molecular beacons for targeted destruction of bone metastases in vivo

The metastatic spread of cancer from the primary site or organ is one of its most devastating aspects, being responsible for up to 90% of cancer-associated mortality. Bone is one of the common sites of metastatic spread, including the vertebrae. Regardless of the treatment strategy, the clinical goals for patients with vertebral metastases are to improve the quality of life by preventing neurologic decline, to achieve durable pain relief and enhance local tumor control. However, in part due to the close proximity of the spinal cord, current treatment options are limited. We propose a novel therapeutic strategy with the use of photodynamic molecular beacons (PMBs) for targeted destruction of spinal metastases, particularly to de-bulk lesions as an adjuvant to vertebroplasty or kyphoplasty in order to mechanically stabilize weak or fractured vertebrae. The PDT efficacy of a matrix metalloproteinase-specific PMB is reported in a metstatic model that recapitulates the clinical features of tumor growth within the bone. We demonstrate that not only does tumor cell destruction occur but also the killing of bone stromal cells. The potential of PMB-PDT to destroy metastatic tumors, disrupt the osteolytic cycle and better preserve critical organs with an increased therapeutic window compared with conventional photosensitizers is demonstrated.

Control of the blood-brain barrier function in cancer cell metastasis

Cerebral metastases are the most common brain neoplasms seen clinically in the adults and comprise more than half of all brain tumours. Actual treatment options for brain metastases that include surgical resection, radiotherapy and chemotherapy are rarely curative, although palliative treatment improves survival and life quality of patients carrying brain-metastatic tumours. Chemotherapy in particular has also shown limited or no activity in brain metastasis of most tumour types. Many chemotherapeutic agents used systemically do not cross the blood-brain barrier (BBB), whereas others may transiently weaken the BBB and allow extravasation of tumour cells from the circulation into the brain parenchyma. Increasing evidence points out that the interaction between the BBB and tumour cells plays a key role for implantation and growth of brain metastases in the central nervous system. The BBB, as the tightest endothelial barrier, prevents both early detection and treatment by creating a privileged microenvironment. Therefore, as observed in several in vivo studies, precise targetting the BBB by a specific transient opening of the structure making it permeable for therapeutic compounds, might potentially help to overcome this difficult clinical problem. Moreover, a better understanding of the molecular features of the BBB, its interrelation with metastatic tumour cells and the elucidation of cellular mechanisms responsible for establishing cerebral metastasis must be clearly outlined in order to promote treatment modalities that particularly involve chemotherapy. This in turn would substantially expand the survival and quality of life of patients with brain metastasis, and potentially increase the remission rate. Therefore, the focus of this review is to summarise the current knowledge on the role and function of the BBB in cancer metastasis.

In vitro and in vivo effects of photodynamic therapy on metastatic breast cancer cells pre-treated with zoledronic acid

BACKGROUND

Photodynamic therapy (PDT), a non-ionizing, minimally invasive drug-light treatment, has recently been shown to successfully ablate tumor within rat vertebrae with concurrent improvements in bone strength and architecture. The bisphosphonate zoledronic acid (zol), a current drug for patients with skeletal metastases, primarily works by inhibiting osteoclast activity, but direct anti-tumor effects have also been reported. However, it is unknown if or how pre-treatment with zol may alter the tumorcidal effect of PDT. The aim of this study was to evaluate the effect of PDT, both in vitro and in vivo, on zol-pretreated cancer cells.

MATERIALS AND METHODS

Human metastatic breast cancer cells (MT-1) were cultured in vitro and treated with zol (10μM) for 24h, followed by PDT treatment. Cell viability was assessed by fluorescence microscopy and flow cytometry. In vivo, MT-1 cells were injected (intracardiac) into athymic rats. On day 7, zol (60μg/kg) was administered subcutaneously. On day 14, PDT was applied (1mg/kg verteporfin; 75J; 690nm) to lumbar vertebrae. Histomorphometric assessment of tumor burden was evaluated on day 21.

RESULTS

The cell viability measured in vitro after PDT treatment decreased in cells pre-incubated with zol up to 20% compared to treatment with PDT alone. Zol alone had no influence on the MT-1 cell viability. In vivo, all treatments, either alone or combined, had a tumorcidal effect.

CONCLUSIONS

Pre-treatment with zol in vivo did not yield a synergistic effect on tumor ablation in contrast to the in vitro results, but neither did it abrogate the positive tumorcidal effect of PDT, so that those therapies may be applied in combination.

Geminin overexpression promotes imatinib sensitive breast cancer: a novel treatment approach for aggressive breast cancers, including a subset of triple negative

Breast cancer is the second leading cause of cancer-related deaths in women. Triple negative breast cancer (TNBC) is an aggressive subtype that affects 10–25% mostly African American women. TNBC has the poorest prognosis of all subtypes with rapid progression leading to mortality in younger patients. So far, there is no targeted treatment for TNBC. To that end, here we show that c-Abl is one of several tyrosine kinases that phosphorylate and activate geminin’s ability to promote TNBC. Analysis of >800 breast tumor samples showed that geminin is overexpressed in ∼50% of all tumors. Although c-Abl is overexpressed in ∼90% of all tumors, it is only nuclear in geminin overexpressing tumors. In geminin-negative tumors, c-Abl is only cytoplasmic. Inhibiting c-Abl expression or activity (using imatinib or nilotinib) prevented geminin Y150 phosphorylation, inactivated the protein, and most importantly converted overexpressed geminin from an oncogene to an apoptosis inducer. In pre-clinical orthotopic breast tumor models, geminin-overexpressing cells developed aneuploid and invasive tumors, which were suppressed when c-Abl expression was blocked. Moreover, established geminin overexpressing orthotopic tumors regressed when treated with imatinib or nilotinib. Our studies support imatinib/nilotonib as a novel treatment option for patients with aggressive breast cancer (including a subset of TNBCs)-overexpressing geminin and nuclear c-Abl.

Anticancer activity of Amauroderma rude

More and more medicinal mushrooms have been widely used as a miraculous herb for health promotion, especially by cancer patients. Here we report screening thirteen mushrooms for anti-cancer cell activities in eleven different cell lines. Of the herbal products tested, we found that the extract of Amauroderma rude exerted the highest activity in killing most of these cancer cell lines. Amauroderma rude is a fungus belonging to the Ganodermataceae family. The Amauroderma genus contains approximately 30 species widespread throughout the tropical areas. Since the biological function of Amauroderma rude is unknown, we examined its anti-cancer effect on breast carcinoma cell lines. We compared the anti-cancer activity of Amauroderma rude and Ganoderma lucidum, the most well-known medicinal mushrooms with anti-cancer activity and found that Amauroderma rude had significantly higher activity in killing cancer cells than Ganoderma lucidum. We then examined the effect of Amauroderma rude on breast cancer cells and found that at low concentrations, Amauroderma rude could inhibit cancer cell survival and induce apoptosis. Treated cancer cells also formed fewer and smaller colonies than the untreated cells. When nude mice bearing tumors were injected with Amauroderma rude extract, the tumors grew at a slower rate than the control. Examination of these tumors revealed extensive cell death, decreased proliferation rate as stained by Ki67, and increased apoptosis as stained by TUNEL. Suppression of c-myc expression appeared to be associated with these effects. Taken together, Amauroderma rude represented a powerful medicinal mushroom with anti-cancer activities.

Imaging of specific activation of photodynamic molecular beacons in breast cancer vertebral metastases

Breast cancer is the second leading cause of cancer-related death in women. Approximately 85% of patients with advanced cases will develop spinal metastases. The vertebral column is the most common site of breast cancer metastases, where overexpression of matrix metalloproteinases (MMPs) promotes the spread of cancer. Current therapies have significant limitations due to the high associated risk of damaging the spinal cord. An attractive alternative is photodynamic therapy providing noninvasive and site-selective treatment. However, current photosensitizers are limited by their nonspecific accumulation. Photodynamic molecular beacons (PP(MMP)B), activated by MMPs, offer another level of PDT selectivity and image-guidance preserving criticial tissues, specifically the spinal cord. Metastatic human breast carcinoma cells, MT-1, were used to model the metastatic behavior of spinal lesions. In vitro and in vivo evidence demonstrates MMP specific activation of PP(MMP)B in MT-1 cells. Using a clinically relevant metastatic model, fluorescent imaging establishes the specific activation of PP(MMP)B by vertebral metastases versus normal tissue (i.e., spinal cord) demonstrating the specificity of these beacons. Here, we validate that the metastasis-selective mechanism of PP(MMP)Bs can specifically image breast cancer vertebral metastases, thereby differentiating tumor and healthy tissue.

Phenotypic heterogeneity of breast cancer stem cells

Many types of tumors are organized in a hierarchy of heterogeneous cell populations, with only a small proportion of cancer stem cells (CSCs) capable of sustaining tumor formation and growth, giving rise to differentiated cells, which form the bulk of the tumor. Proof of the existence of CSC comes from clinical experience with germ-cell cancers, where the elimination of a subset of undifferentiated cells can cure patients (Horwich et al., 2006), and from the study of leukemic cells (Bonnet and Dick, 1997; Lapidot et al., 1994; and Yilmaz et al., 2006). The discovery of CSC in leukemias as well as in many solid malignancies, including breast carcinoma (Al-Hajj et al. 2003; Fang et al., 2005; Hemmati et al., 2003; Kim et al., 2005; Lawson et al., 2007; Li et al., 2007; Ricci-Vitiani et al., 2007; Singh et al., 2003; and Xin et al., 2005), has suggested a unifying CSC theory of cancer development. The reported general insensitivity of CSC to chemotherapy and radiation treatment (Bao et al., 2006) has suggested that current anticancer drugs, which inhibit bulk replicating cancer cells, may not effectively inhibit CSC. The clinical relevance of targeting CSC-associated genes is supported by several recent studies, including CD44 targeting for treatment of acute myeloid leukemia (Jin et al., 2006), CD24 targeting for treatment of colon and pancreatic cancer (Sagiv et al., 2008), and CD133 targeting for hepatocellular and gastric cancer (Smith et al., 2008). One promising approach is to target CSC survival signaling pathways, where leukemia stem cell research has already made some progress (Mikkola et al., 2010).

Angiogenesis and invasion in glioma

Despite advances in surgical and medical therapy, glioblastoma consistently remains a fatal disease. Over the last 20 years, no significant increase in survival has been achieved for patients with this disease. The formation of abnormal tumor vasculature and glioma cell invasion along white matter tracts are believed to be the major factors responsible for the resistance of these tumors to treatment. Therefore, investigation of angiogenesis and invasion in glioblastoma is essential for the development of a curative therapy. In our report, we first reviewed certain histopathological studies that focus on angiogenesis and invasion of human malignant gliomas. Second, we considered several animal models of glioma available for studying angiogenesis and invasion, including our novel animal models. Third, we focused on the molecular aspects of glioma angiogenesis and invasion, and the key mediators of these processes. Finally, we discussed the recent and ongoing clinical trials targeting tumor angiogenesis and invasion in glioma patients. A better understanding of the mechanism of glioma angiogenesis and invasion will lead to the development of new treatment methods.

Preclinical approaches to study the biology and treatment of brain metastases

Metastatic spread to the central nervous system (CNS) is a common and devastating manifestation of major cancer types. Its incidence is associated with poor prognosis manifested by neurological deterioration leading to diminished quality of life and an extremely short median survival. CNS metastasis is becoming an increasingly important clinical problem. This is especially the case for certain types of cancers for which effective treatments of visceral disease are available. As a result of the present limitations in treating CNS metastases, this manifestation of tumor progression remains an unmet clinical need. Despite its significance, our general understanding of the mechanisms that regulate the brain-metastatic phenotype is currently meager. Both the analysis of mechanistic aspects of brain metastasis and the development of effective treatments necessitate the use of appropriate in vivo models that recapitulate the interaction of the tumor cells with the microenvironment of the brain. Here we review the available preclinical models of CNS metastasis and their use as tools to advance knowledge of the biology of the disease (with the aim of identifying relevant molecular determinants, prognostic biomarkers, and therapeutic targets) as well as examining effective approaches for treatment.

Expression of CD44 3'-untranslated region regulates endogenous microRNA functions in tumorigenesis and angiogenesis

The non-coding 3'-untranslated region (UTR) plays an important role in the regulation of microRNA (miRNA) functions, since it can bind and inactivate multiple miRNAs. Here, we show the 3'-UTR of CD44 is able to antagonize cytoplasmic miRNAs, and result in the increased translation of CD44 and downstream target mRNA, CDC42. A series of cell function assays in the human breast cancer cell line, MT-1, have shown that the CD44 3'-UTR inhibits proliferation, colony formation and tumor growth. Furthermore, it modulated endothelial cell activities, favored angiogenesis, induced tumor cell apoptosis and increased sensitivity to Docetaxel. These results are due to the interaction of the CD44 3'-UTR with multiple miRNAs. Computational algorithms have predicted three miRNAs, miR-216a, miR-330 and miR-608, can bind to both the CD44 and CDC42 3'-UTRs. This was confirmed with luciferase assays, western blotting and immunohistochemical staining and correlated with a series of siRNA assays. Thus, the non-coding CD44 3'-UTR serves as a competitor for miRNA binding and subsequently inactivates miRNA functions, by freeing the target mRNAs from being repressed.

Phenotypic characterization of mammosphere-forming cells from the human MA-11 breast carcinoma cell line

The phenotypic diversity of breast carcinoma may be explained by the existence of a sub-population of breast cancer cells, endowed with stem cell-like properties and gene expression profiles, able to differentiate along different pathways. A stem cell-like population of CD44(+)CD24(-/low) breast cancer cells was originally identified using cells from metastatic pleural effusions of breast carcinoma patients. We have previously reported that upon in vitro culture as mammospheres under stem cell-like conditions, human MA-11 breast carcinoma cells acquired increased tumorigenicity and lost CD24 expression compared with the parental cell line. We now report that upon passage of MA-11 mammospheres into serum-supplemented cultures, CD24 expression was restored; the rapid increase in CD24 expression was consistent with up-regulation of the antigen, and not with in vitro selection of CD24(+) cells. In tumors derived from subcutaneous injection of MA-11 mammospheres in athymic nude mice, 76.1+/-9.7% of cells expressed CD24, vs. 0.5+/-1% in MA-11 cells dissociated from mammospheres before injection. The tumorigenicity of sorted CD44(+)CD24(-) and CD44(+)CD24(high) MA-11 cells was equal. Single cell-sorted CD24(-) and CD24(high) MA-11 gave rise in vitro to cell populations with heterogeneous CD24 expression. Also, subcutaneous tumors derived from sorted CD24(-) sub-populations and single-cell clones had levels of CD24 expression similar to the unsorted cells. To investigate whether the high expression of CD24 contributed to the tumorigenic potential of MA-11 cells, we silenced CD24 by shRNA. CD24 silencing (95%) resulted in no difference in tumorigenicity upon s.c. injection in athymic nude mice compared with mock-transduced MA-11 cells. Since CD24 silencing was maintained in vivo, our data suggest that the level of expression of CD24 is associated with but does not contribute to tumorigenicity. We then compared the molecular profile of the mammospheres with the adherent cell fraction. Gene expression profiling revealed that the increased tumorigenicity of MA-11 mammospheres was associated with changes in 10 signal transduction pathways, including MAP kinase, Notch and Wnt, and increased expression of aldehyde dehydrogenase, a cancer-initiating cell-associated marker. Our data demonstrate that (i) the level of CD24 expression is neither a stable feature of mammosphere-forming cells nor confers tumorigenic potential to MA-11 cells; (ii) cancer-initiating cell-enriched MA-11 mammospheres have activated specific signal transduction pathways, potential targets for anti-breast cancer therapy.

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.

The effect of versican G3 domain on local breast cancer invasiveness and bony metastasis

Introduction

Increased versican expression has been associated with local breast cancer invasiveness and a more aggressive tumor phenotype. The cellular mechanisms are not fully understood and this study evaluated versican G3 domain with its EGF-like motifs in influencing tumor invasion and metastasis.

Methods

One recombinant construct was synthesized (a signal peptide for product secretion and the versican G3 domain). The construct was stably transfected into human breast carcinoma MT-1 cells. Cell viability in vitro was evaluated in low serum and serum starvation conditions. In vivo study of tumor growth was evaluated in a nude mouse model. G3 effects on rodent vascular endothelial cells were evaluated in vitro on cell survival, apoptosis, migration, and vascular formation. The effects of VEGF, fibronectin, and G3 on vascular formation were examined. An intracardiac injection model of metastatic human breast carcinoma tested the effect of G3 on distant bony and soft tissue metastasis. Analysis of metastatic burden included histology, radiographs, and micro-CT quantification of osteolysis.

Results

A greater viability of cancer cells was observed in low serum and serum-free conditions in the presence of versican G3. Larger subcutaneous tumors were obtained in the G3 group following tumor cell injection into CD1 mice. G3 induced a greater degree of rodent vascular endothelial cell proliferation and migration in vitro. Simultaneous presence of fibronectin, VEGF, and G3 promoted endothelial cell migration in wound-healing assays as compared to the treatments containing none, one or two of these molecules. Systemic tumor burden to distant bony and soft tissue metastatic sites was greater in the G3 group using the intracardiac injection metastatic model

Conclusion

Versican G3 domain appears to be important in local and systemic tumor invasiveness of human breast cancer. Effects include enhancing cell viability, proliferation, migration and enhancing local tumor growth. Potential effects on angiogenesis include enhancing vascular endothelial proliferation, migration, and vessel formation. The interactions between tumor cells, surrounding stromal components and neo-vascularization in breast cancer may include interactions with VEGF and fibronectin. The propensity of versican G3 to influence tumor invasion to bone and the mechanisms of G3 mediated osteolysis warrants ongoing studies.

Neural stem cell markers, nestin and musashi proteins, in the progression of human glioma: correlation of nestin with prognosis of patient survival

BACKGROUND

The IF protein nestin and the RNA-binding protein musashi are expressed by neural progenitor cells during CNS development. Their expression in glial tumors was evaluated by immunohistochemistry, and the histopathological scores correlated with levels of cysteine cathepsins that are known prognostic markers in several tumors.

METHODS

The levels of nestin, musashi, and cathepsins B and L were assessed by immunohistochemical analysis of biopsies from 87 patients with primary CNS tumors. To confirm the immunohistochemical data, nestin expression was analyzed by real-time PCR in 12 brain tumor biopsies. The exact location of nestin-positive cells was determined by mapping the distribution of nestin in a highly invasive human glioma xenograft model.

RESULTS

Immunostaining revealed nestin to be expressed in 95.8% and musashi in 80% of the patient biopsies. The total IHC score for nestin was significantly higher in high- than in low-grade tumors (P < .0001). No difference was observed for musashi (P = .11). Real-time PCR of nestin expression confirmed the immunohistochemical data. Nestin expression was shown to be a strong prognostic marker for decreased overall survival (P = .0001), whereas musashi expression has no prognostic significance. Moreover, nestin was shown by Cox regression analysis to be a stronger prognostic marker than cathepsins B and L. IHC staining of nestin in a xenograft model showed that its expression is localized mainly in the invasive tumor cells at the tumor periphery.

CONCLUSIONS

Nestin is shown to be a strong prognostic marker for glioma malignancy. The presented data links the invasive glioma cells to CNS precursor cells, indicating that the most malignant cells in the gliomas may well be closely related to the glioma stem cells.

Carbohydrate status detecting by PNA is changeable through cancer prognosis from primary to metastatic nodal site: A possible prognostic factor in patient with node-positive lung adenocarcinoma

Carbohydrates antigens in cancer cells are considered to be important molecules, which may play a critical role for metastasis. To elucidate the prognostic relevance of the expression of peanut agglutinin (PNA) binding carbohydrates in patients with lung adenocarcinoma, we investigated the PNA binding carbohydrates immunohistochemically in both of primary tumors and involving nodal lesions. A total of 62 patients with node-positive primary lung adenocarcinoma, who had undergone complete resection and regional nodes dissection were subjected to this study. There were no significant correlations between PNA staining rates and clinicopathological variables. The survival rate of patients who had positive PNA staining in both of primary tumor and nodal lesion was significantly higher than those of patients in the other groups. Furthermore, the loss of the staining rate of PNA was an independent prognostic factor beside the lymphatic vessel invasion using multivariate analysis. The expression of PNA binding carbohydrates in tumor tissue and nodal lesion would be a novel significant prognostic factor for patients with node-positive lung adenocarcinomas.

Multimodality imaging for vertebral metastases in a rat osteolytic model

Imaging modalities facilitate the detection of early bony metastases. Few studies specifically address vertebral metastases in animal models for preclinical (early, asymptomatic) disease. We performed intracardiac injection of human breast cancer (MT-1) cells in 35 athymic nude rats. We evaluated potential temporal differences in appendicular versus axial metastases as detectable by longitudinal in vivo conventional radiography (ie, fine detail radiography and two-dimensional fluoroscopy). We compared bioluminescent reporter imaging with conventional radiographs in the detection of vertebral metastasis, and compared bioluminescent imaging with subsequent ex vivo microcomputed tomography analysis of osteolysis. The mean survival was 25 days in the animals that had metastases develop. Conventional radiographs identified appendicular osteolysis by 14 days; however, vertebral osteolysis was identified late in the metastatic spread (Days 25-28). Bioluminescence imaging was more sensitive in earlier detection of vertebral lesions in all imaged animals at Day 21, which corresponded to microcomputed tomography evaluation of osteolysis. Conventional radiographs do not appear useful for early detection of vertebral metastasis. Early identification of metastasis is important when considering the use of this model to evaluate therapeutic outcomes directed toward vertebral metastasis.

The detection of hamster connexins: a comparison of expression profiles with wild-type mouse and the cancer-prone Min mouse

The open reading frames of 17 connexins from Syrian hamster (using tissues) and 16 connexins from the Chinese hamster cell line V79, were fully (Cx30, Cx31, Cx37, Cx43 and Cx45) or partially sequenced. We have also detected, and partially sequenced, seven rat connexins that previously were unavailable. The expression of connexin genes was examined in some hamster organs and cultured hamster cells, and compared with wild-type mouse and the cancer-prone Min mouse. Although the expression patterns were similar for most organs and connexins in hamster and mouse, there were also some prominent differences (Cx29 and 30.3 in testis; Cx31.1 and 32 in eye; Cx46 in brain, kidney and testis; Cx47 in kidney). This suggests that some connexins have species-specific expression profiles. In contrast, there were minimal differences in expression profiles between wild type and Min mice. Species-specific expression profiles should be considered in attempts to make animal models of human connexin-associated diseases.

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.

Photodynamic therapy for the treatment of vertebral metastases in a rat model of human breast carcinoma

The feasibility and efficacy of photodynamic therapy (PDT) for the treatment of vertebral metastases using a minimally invasive surgical technique adapted from vertebroplasty was evaluated in a rodent model. Initial validation included photosensitizer (benzoporphyrin-derivative monoacid-ring A) drug uptake studies and in vitro confirmation of PDT efficacy. Intracardiac injection of human MT-1 breast cancer cells was performed in athymic rats. In 63 rats that developed vertebral metastases 21 days post-inoculation, single treatment of PDT was performed using a parapedicular approach placing an optical fiber adjacent to targeted vertebrae. Two milligrams per kilogram of photosensitizer drug was administered intravenously followed by 150 mW of 690 nm light illumination at varying drug-light intervals and light energies. Histologic and immunohistochemical analysis was performed assessing treatment effect. Local tumor viability and growth was quantified by bioluminescence imaging pre and 48 h post-treatment. PDT demonstrated an ablative effect on vertebral metastases (light energies 25-150 J). The effect varied in proportion to light energy with the greatest anti-tumor effect observed at 150 J using a 3 h drug-light interval. 9/22 rodents in the 3 h drug-light interval developed hindlimb paralysis following treatment, consistent with drug uptake studies demonstrating an increase in spinal cord uptake 3h following drug administration. The observations of paralysis following treatment highlight the importance of closely defining the therapeutic window of treatment in safety and efficacy.

First clinical experience with alpha-emitting radium-223 in the treatment of skeletal metastases

PURPOSE

The main goals were to study the safety and tolerability of the alpha-emitter radium-223 (223Ra) in breast and prostate cancer patients with skeletal metastases. In addition, pain palliation was evaluated.

EXPERIMENTAL DESIGN

Fifteen prostate and 10 breast cancer patients enrolled in a phase I trial received a single i.v. injection of 223Ra. Five patients were included at each of the dosages: 46, 93, 163, 213, or 250 kBq/kg and followed for 8 weeks. Palliative response was evaluated according to the pain scale of the European Organization for Research and Treatment of Cancer QLQ C30 questionnaire at baseline and at 1, 4, and 8 weeks after injection.

RESULTS

Weekly blood sampling during follow-up revealed mild and reversible myelosuppression with nadir 2 to 4 weeks after the injection. Importantly, for thrombocytes only grade 1 toxicity was reported. Grade 3 neutropenia and leucopenia occurred in two and three patients, respectively. Mild, transient diarrhea was observed in 10 of the 25 patients. Nausea and vomiting was more frequently observed in the highest dosage group. Serum alkaline phosphatase decreased with nadir averages of 29.5% in females and 52.1% in males. Pain relief was reported by 52%, 60%, and 56% of the patients after 7 days, 4, and 8 weeks, respectively. 223Ra cleared rapidly from blood and was below 1% of initial level at 24 hours. Gamma camera images indicated, in accordance with pretreatment (99m)Tc-MDP scans, accumulation of 223Ra in skeletal lesions. Elimination was mainly intestinal. Median survival exceeded 20 months.

CONCLUSIONS

223Ra was well tolerated at therapeutically relevant dosages. Phase II studies have therefore been initiated.

Photodynamic therapy for the treatment of metastatic lesions in bone: studies in rat and porcine models

This study represents the first reported use of photodynamic therapy (PDT) for metastatic bone lesions and specifically, as a treatment for spinal metastases. A model of bone metastasis in rat confirmed the efficacy of benzoporphyrin derivative-monoacid-mediated PDT for treating lesions within the spine and appendicular bone. Fluorimetry confirmed the selective accumulation of drug into the tumor(s) at 3 h post-injection. 48 h post-light delivery into the vertebral body of the rat spine loss of bioluminescent signal and histological analyses of sectioned spine confirmed MT-1 tumor cell kill in vivo as previously confirmed in vitro using an established cell viability assay. Porcine vertebrae provided a model comparable to that of human for light propagation and PDT response. Histological examination of vertebrae 48 h post-PDT revealed a necrotic radius of 0.6 cm with an average fluence rate of 4.3 mW/cm2. Non-necrotic tissue damage was evident up to 2 cm out from the treatment fiber. Results support the application of PDT to the treatment of primary or metastatic lesions within bone.

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.

Repression of mRNA for the PLK cell cycle gene after DNA damage requires BRCA1

DNA damage activates the G2 cell cycle checkpoint to allow time for DNA repair before mitotic entry. The mechanism involves inhibition of the enzymatic activity for polo-like kinase 1 (Plk1), rendering Cdc25C with a basal phosphatase activity that is insufficient for converting Cdc2 to the fully active G2/M transition kinase. We found that cell cycle arrest at the G2/M boundary after ionizing radiation (IR) of breast carcinoma cells may involve repression of the gene for Plk1, PLK, mediated by the tumor-suppressor protein BRCA1. The p53-defective MT-1 cell line had an apparent accumulation of G2/M phase cells 12 h after irradiation. This response was preceded by a transient downregulation of PLK mRNA expression with a barely detectable level 6 h after exposure to IR but recovered after 12 h. A significantly lower fraction of irradiated BRCA1(-/-) HCC1937 cells arrested in the G2/M phase after 12 h, and the transient response of PLK mRNA was also considerably impaired. After reconstitution of wild-type BRCA1 in the HCC1937 cells however, downregulation of PLK mRNA as well as Plk1 protein expression after IR was restored. Moreover, the suppression of PLK mRNA expression 6 h after irradiation was completely abolished by the specific CHEK1 kinase inhibitor UCN-01, further indicating that the effector mechanism of DNA damage on PLK signals through BRCA1 and its downstream CHEK1. Our observations provide new information about the diversity of regulatory mechanisms governed by BRCA1 in DNA damage checkpoint control.

Studies on the synthesis and biological properties of non-carrier-added [(125)I and (131)I]-labeled arylalkylidenebisphosphonates: potent bone-seekers for diagnosis and therapy of malignant osseous lesions

Arylalkylidenebisphosphonates labeled with nca [(125)I or (131)I] have been synthesized and their biological function investigated. The label was attached to the aromatic group in high yield and under mild conditions by means of iododesilylation. The bone affinities of the radioactive compounds were investigated in normal Balb/C mice. The compound 1-hydroxy(m-iodo[(125,131)I]-phenylethylidene)-1,1-bisphosphonate was found to possess superior bone affinity compared to others, and its in vivo deiodination was insignificant. The uptake in femur 24h after injection was 850 +/- 265% and 986 +/- 118% of injected dose per gram tissue times gram body weight in mice and rats, respectively. The therapeutic potential of the compound was investigated in two tumor models in athymic (nude) rats, one model for mixed lytic/sclerotic metastatic bone-lesions originating from breast cancer and the other model simulating osseous osteosarcoma. The effects in these models compare favorably to those observed for established treatment modalities. The experiments demonstrate that radioiodinated bisphosphonates may have a potential for diagnosis and therapy of malignant osseous lesions.

Intratumoral immunotoxin treatment of human malignant brain tumors in immunodeficient animals

Treatment of malignant brain tumors remains a clinical challenge. New treatment modalities are under investigation and among these are intratumoral infusion of immunotoxins that bind to specific cell surface molecules on the malignant cells. We have compared the efficacy of the 425.3-PE immunotoxin (which targets the epidermal growth factor [EGF] receptor) with the well-known immunotoxin Tfn-CRM107 (which targets the transferrin receptor), for the treatment of subcutaneous and intracranial human gliomas in nude animals. Bolus intratumoral administration of 1 microg Tfn-CRM107 or 425.3-PE into sc U87Mg tumors in nude mice reduced the tumor volume to 29 and 79%, respectively, of that in the control group 18 days after start of treatment. Higher doses of Tfn-CRM107 were toxic to the animals, whereas 425.3-PE was tolerated, with a dose-response relationship of up to 8 microg, a dose that reduced the tumor volume to 2% of control. In nude rats, treatment of intracerebral U87Mg tumors with Tfn-CRM107 proved ineffective and doses above 10 ng/animal were toxic to tumor-bearing rats. In contrast, intratumoral administration of 4 microg 425.3-PE increased symptom-free survival from 23 days to 40 days, with 2/9 surviving more than 90 days. We have recently shown that immunodeficient rats inoculated intracerebrally with precultured glioblastoma biopsy specimens develop highly infiltrative brain tumors. Direct interstitial infusion of immunotoxins into such tumors reduced the number of animals with detectable tumors at autopsy after 3 months, from 8/9 in the control animals to 4/6 and 2/6 in animals treated with Tfn-CRM107 and 425.3-PE, respectively. In conclusion, the anti-EGF receptor immunotoxin 425.3-PE exhibited promising efficacy, comparable to or better than that of Tfn-CRM107, an immunotoxin that in early clinical trials has been found to give responses in patients with brain tumors.

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.

Refinement of an orthotopic lung cancer model in the nude rat

Over 85% of people with lung cancer eventually succumb to this disease, largely because current chemotherapies are ineffective. The testing and validation of promising new approaches generally rely on achieving responses with cell lines in vitro or in tumor xenografts in nude mice. However, quite often the results seen with these models are not recapitulated in the clinic, thus necessitating the need for better animal models of lung cancer for preclinical testing of new therapies. One promising model is that of orthotopic lung cancer, where xenografts of human lung cancer are established in lungs of immunodeficient rodents. The problems associated with this model include poor rates of engraftment, limited tumor multiplicity, and a heightened risk for surgical trauma. The purpose of our study was to develop an efficient approach to engraftment of orthotopic tumors throughout the lungs of the Rowett nude rat. Initially, we augmented immunosuppression in the rats with whole-body X-irradiation and then used orotracheal cannulas to intratracheally instill human cancer cells from the Calu-6 cell line. This protocol produced a low rate of engraftment and low tumor multiplicity. The hypothesis that slight disruption of the pulmonary epithelium or the surfactant layer would allow better tumor engraftment was tested by coadministration of either pancreatic elastase or ethylenediaminetetraacetic acid (EDTA) along with the cell instillations. Lung tumor engraftment was evaluated 8 weeks after instillation. The inclusion of elastase or EDTA with the Calu-6 cells resulted in an 80-100% engraftment rate, respectively. Coadministration of EDTA resulted in significantly larger and greater numbers of tumors/lung than those in elastase-treated animals. Temporal studies demonstrated that small nodules were scattered throughout the lung parenchyma 5 weeks after instilling Calu-6 cells and EDTA. These nodules grew to coalesce and form large masses that effaced >75% of the parenchyma at 9 weeks postinstillation. The refinements made through our studies have led to the development of an orthotopic lung cancer model that should facilitate the evaluation of novel therapies designed to treat or impede lung cancer development.

The pattern of metastasis of human melanoma to the central nervous system is not influenced by integrin alpha(v)beta(3) expression

We investigated the effect of integrin alpha(v)beta(3) expression on the metastatic pattern of human melanoma cells in the central nervous system (CNS). For this purpose, we developed a hematogenous CNS melanoma metastasis model in nude mice using a modified internal carotid artery infusion technique. This protocol revealed 2 different patterns of CNS metastasis. The integrin alpha(v)beta(3)-expressing melanoma lines Mel57 and Zkr nearly exclusively produced metastases in the brain parenchyma, whereas cells of the BLM and MV3 lines, devoid of integrin alpha(v)beta(3) expression, preferentially metastasized to dura mater and leptomeninges. Treatment with hyaluronidase to obtain single BLM cell suspensions did not influence the metastatic pattern, indicating that this was not simply the result of entrapment of tumor cell aggregates in large-sized leptomeningeal vessels. The role of integrin alpha(v)beta(3) expression in the process of metastasis was tested by transfection of BLM, but did not lead to an altered pattern of metastasis. We did observe, however, slower growth of the transfected tumors, although the in vitro growth rate was unaltered, indicating a reduction in tumorigenicity. We conclude from our findings that CNS metastasis of melanoma cells in the mouse xenograft model occurs in at least 2 different but very reproducible patterns. Although it is predicted that adhesion of tumor cells to endothelial cells plays a role in this phenomenon, tumor cell integrin alpha(v)beta(3) expression per se does not explain the difference in metastatic behavior in the CNS. We assume that other, as yet unknown factors, must be involved.

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.

Pathophysiologic interactions in skeletal metastasis

BACKGROUND

This review summarizes evidence that the formation of bone metastases is the result of multiple synergistic cellular and molecular interactions between metastatic cells and the unique microenvironment in bone.

METHODS

Molecular technologies have been used to detect cancer cells in bone and to define their genotypic and phenotypic properties. Bone organ cultures have been employed to analyze the ability of tumor cells to modulate bone resorption and to study the effects of resorption products on the phenotypic properties of cancer cells. Experimental models of bone metastasis provide the ability to examine the effects of modulating specific host or tumor properties in vivo by quantifying their effects on the formation of bone tumors.

RESULTS

By means of the blood stream, cells from many common neoplasms seed bone marrow as an early clinical event. The subsequent growth of these cells into clinically significant metastatic lesions is associated with their ability to stimulate bone resorption through osteoclasts and macrophages or through a direct action on bone. In turn, the products of bone resorption, which include matrix-derived growth factors, act on the tumor cells to stimulate the expression of properties that promote their metastatic competence. These include the induction of integrin adhesion molecules, the stimulation of cell motility and chemotaxis, the enhanced expression of matrix metalloproteinases, and the stimulation of tumor cell growth.

CONCLUSIONS

The interdependency of tumor cells and bone was recognized by Steven Paget over 100 years ago, and it provides a rational basis for the development of current therapeutic strategies against bone metastasis.