Analyzing the metastatic phenotype

Serpin E2 promotes breast cancer metastasis by remodeling the tumor matrix and polarizing tumor associated macrophages

The extracellular serine protease inhibitor serpinE2 is overexpressed in breast cancer and has been shown to foster metastatic spread. Here, we investigated the hypothesis that serpinE2 creates tumor-promoting conditions in the tumor microenvironment (TME) by affecting extracellular matrix remodeling. Using two different breast cancer models, we show that blocking serpinE2, either by knock-down (KD) in tumor cells or in response to a serpinE2 binding antibody, decreases metastatic dissemination from primary tumors to the lungs. We demonstrate that in response to serpinE2 KD or antibody treatment there are dramatic changes in the TME. Multiphoton intravital imaging revealed deposition of a dense extracellular collagen I matrix encapsulating serpinE2 KD or antibody-treated tumors. This is accompanied by a reduction in the population of tumor-promoting macrophages, as well as a decrease in chemokine ligand 2, which is known to affect macrophage abundance and polarization. In addition, TIMP-1 secretion is increased, which may directly inhibit matrix metalloproteases critical for collagen degradation in the tumor. In summary, our findings suggest that serpinE2 is required in the extracellular milieu of tumors where it acts in multiple ways to regulate tumor matrix deposition, thereby controlling tumor cell dissemination.

The Notch-1 receptor in prostate tumorigenesis

The Notch signalling pathway plays a fundamental role in tissue development due to its involvement in cell fate determination and postnatal tissue differentiation. Its capacity to regulate cell growth and development has been linked to the occurrence of several cancers including that of the prostate. The transmembrane receptor Notch-1 of this pathway has been linked to the oncogenic role of Notch signalling in prostate adenocarcinoma. Other studies have suggested a tumour suppressive function for Notch-1. This review focuses on the role of Notch-1 in prostate cancer development and maintenance and relates this to the fundamental role of Notch in normal prostate development. The current understanding of the aberrant Notch signalling characteristic of prostate cancer is discussed, and recent therapeutic advances in this field are presented.

Mouse models of advanced spontaneous metastasis for experimental therapeutics

An enduring problem in cancer research is the failure to reproduce highly encouraging preclinical therapeutic findings using transplanted or spontaneous primary tumours in mice in clinical trials of patients with advanced metastatic disease. There are several reasons for this, including the failure to model established, visceral metastatic disease. We therefore developed various models of aggressive multi-organ spontaneous metastasis after surgical resection of orthotopically transplanted human tumour xenografts. In this Opinion article we provide a personal perspective summarizing the prospect of their increased clinical relevance. This includes the reduced efficacy of certain targeted anticancer drugs, the late emergence of spontaneous brain metastases and the clinical trial results evaluating a highly effective therapeutic strategy previously tested using such models.

Mendelian analysis of a metastasis-prone substrain of BALB/c nude mice using a subcutaneously inoculated human tumour

Most nude mice do not allow the formation of metastases after heterotransplantation of human malignant tumours. Here we describe a substrain of BALB/c nude mice (BALB/c/AnNCr) that reproducibly allows some human cancers to metastasize. By Mendelian analysis of hybrids between this substrain and C57BL/6J +/+ mice we found that the ability to allow a human tumour (MDA-MB-435 BAG) to express its metastatic phenotype is determined by a recessively inheritable trait in the mouse host. We are presently working to identify the genetics responsible for development of metastases. The study also includes immunohistochemical and electron microscopic analysis of the test tumour, originally assumed to be a human mammary carcinoma, but shown to possess characteristics of a malignant melanoma (1). The ultimate aim of our ongoing study is to establish a substrain of nude mice that will allow metastasis in all recipients.

In situ analysis of breast cancer progression in murine models using a macroscopic fluorescence imaging system

BACKGROUND AND OBJECTIVE

The goal of this study was to use an inexpensive macroscopic imaging system to monitor tumor progression in mouse models in real-time with minimal intervention.

STUDY DESIGN/MATERIALS AND METHODS

Illumination is provided via a xenon arc lamp and a fiber optic probe which delivers white light or quasi-monochromatic excitation via specific bandpass filters. Fluorescence emission from SCID and nude mice following mammary fat pad injection of red fluorescence protein (RFP)-expressing human breast cancer cell lines was recorded and quantified using a single lens reflex (SLR) digital camera.

RESULTS

This simple system enabled the verification of successful tumor take and temporal quantification of tumor progression in mouse models.

CONCLUSION

The macroscopic fluorescence imaging system represents an inexpensive and portable tool to facilitate non-invasive in situ cancer detection with the potential to monitor fluorescent tumor formation and investigation of the efficacy of potential cancer therapeutics.

ErbB3-dependent motility and intravasation in breast cancer metastasis

A better understanding of how epidermal growth factor receptor family members (ErbBs) contribute to metastasis is important for evaluating ErbB-directed therapies. Activation of ErbB3/ErbB2 heterodimers can affect both proliferation and motility. We find that increasing ErbB3-dependent signaling in orthotopic injection models of breast cancer can enhance intravasation and lung metastasis with no effect on primary tumor growth or microvessel density. Enhanced metastatic ability due to increased expression of ErbB2 or ErbB3 correlated with stronger chemotaxis and invasion responses to heregulin beta1. Suppression of ErbB3 expression reduced both intravasation and metastasis. A human breast cancer tumor tissue microarray showed a significant association between ErbB3 and ErbB2 expression and metastasis independent of tumor size. These results indicate that ErbB3-dependent signaling through ErbB3/ErbB2 heterodimers can contribute to metastasis through enhancing tumor cell invasion and intravasation in vivo and that ErbB-directed therapies may be useful for the inhibition of invasion independent of effects on tumor growth.

Common origins of MDA-MB-435 cells from various sources with those shown to have melanoma properties

Recently, the tissue origin of MDA-MB-435 cell line has been the subject of considerable debate. In this study, we set out to determine whether MDA-MB-435-DTP cells shown to express melanoma-specific genes were identical to various other MDA-MB-435 cell stocks worldwide. CGH-microarray, genetic polymorphism genotyping, microsatellite fingerprint analysis and/or chromosomal number confirmed that the MDA-MB-435 cells maintained at the Lombardi Comprehensive Cancer Center (MDA-MB-435-LCC) are almost identical to the MDA-MB-435-DTP cells, and showed a very similar profile to those obtained from the same original source (MD Anderson Cancer Center) but maintained independently (MDA-MB-435-PMCC). Gene expression profile analysis confirmed common expression of genes among different MDA-MB-435-LCC cell stocks, and identified some unique gene products in MDA-MB-435-PMCC cells. RT-PCR analysis confirmed the expression of the melanoma marker tyrosinase across multiple MDA-MB-435 cell stocks. Collectively, our results show that the MDA-MB-435 cells used widely have identical origins to those that exhibit a melanoma-like gene expression signature, but exhibit a small degree of genotypic and phenotypic drift.

Animal models for studying lung cancer and evaluating novel intervention strategies

The pathogenesis of lung cancer progression, invasion and metastasis remains undefined. Clinically relevant laboratory models of the disease could greatly facilitate its clarification. Model systems of lung cancer that accurately reflect different biologic properties and disease stages are necessary to ensure proper experimental design of studies aimed at increasing our understanding of the disease. Such models are also essential tools to accelerate development of new therapies for lung cancer. In this review we summarize the available lung cancer model systems in use today and define both their utility and limitations.

Validation of an orthotopic model of human lung cancer with regional and systemic metastases

BACKGROUND

We developed an orthotopic model of human lung cancer that exhibits highly predictable regional and systemic metastases. This study examines the response of the model when treated with conventional and experimental chemotherapy.

METHODS

NCI-H460 tumor fragments were implanted into the right caudal lung lobe of a nude rat. Treatment commenced 2 weeks later. We assessed response by comparing primary tumor and mediastinal lymph node weights, total body weight, and length of survival with untreated, tumor-bearing control animals. We also calculated the incidence of metastasis to kidney, bone, brain, and contralateral lung in treated versus untreated animals.

RESULTS

Mitomycin and cisplatin showed broad activity against primary and metastatic disease. The matrix metalloproteinase inhibitor batimastat, low-dose cisplatin, and mitomycin significantly prolonged survival. High-dose cisplatin caused renal toxicity that shortened survival. Brain metastases did not respond to mitomycin, consistent with its poor blood-brain barrier penetration.

CONCLUSIONS

Responses were similar to NCI-H460 in vitro data and consistent with clinical experience for these drugs. Drug-related toxicities similar to those seen in clinical practice were detected.

Clinical targets for anti-metastasis therapy

Metastasis is responsible for most cancer deaths. Therapeutic strategies to prevent development of metastases thus have potential to impact on cancer mortality. Development of these therapies requires a better understanding of the biology and molecular events of the metastatic process. Metastasis is usually defined, clinically and experimentally, by evidence of the endpoint of the process, that is, the presence of metastatic tumors. Endpoint assays are suitable for determining if a therapeutic approach is effective, but can provide little information on how a treatment works in vivo and what steps in metastasis are affected. We describe here two methodological advances in the study of metastasis as a process: in vivo videomicroscopy, which permits direct observation of steps in metastasis, and a "cell accounting" technique that permits quantification of the fate of cells over time. These procedures have provided new and unexpected insights into the biology of the metastatic process. Based on these insights, we consider which steps in the metastatic process are biologically and clinically most appropriate as therapeutic targets for development of anti-metastasis therapies. We conclude that the most promising stage of the metastasis process for therapeutic targeting is the growth phase, after cancer cells have arrested in the microcirculation in secondary sites and have completed extravasation. Earlier phases in the process are either biologically inappropriate or clinically inaccessible, except in specific cases (e.g., chemoprevention strategies). The role of "seed" and "soil" in determining organ-specific metastasis is also discussed. The metastatic growth phase fortunately is a clinically broad target, and any treatment that limits growth of metastases prior to their causing irreversible harm to the patient has the potential to be clinically useful. A variety of therapeutic approaches to target this phase are under active development, including inhibition of angiogenesis or signal transduction pathways needed to support the growth of metastatic cells.

Metastatic burden in nude mice organs measured using prostate tumor PC-3 cells expressing the luciferase gene as a quantifiable tumor cell marker

BACKGROUND

Sensitive procedures for quantitative measurement of tumor cell spread as a function of time and primary tumor size are necessary to generate models of metastasis and formulate therapies.

METHODS

Prostate carcinoma cells PC-3.luc expressing the luciferase gene were intramuscularly inoculated in nude mice to generate experimental tumors. Metastatic cells in target organs were easily counted by their capacity to produce light.

RESULTS

Tumor cells were very mobile and migrated to all the target organs examined: lymph nodes, brain, bone, lungs, liver, kidney, spleen, testicles, prostate, seminal vesicle, and scrotum. Organ colonization started very early, 14 days after inoculation, when primary tumors were very small and produced an amount of light equivalent to that generated by 2 x 10(4) tumor cells in vitro (tumor cell equivalents, TCEs). Tumor cell burden could be quantitatively described by power functions of time or primary tumor light-producing capacity. The ratio of metastatic TCEs to primary tumor TCEs clustered around organ characteristic values: 10(-3) for femur and lumbar lymph nodes, 10(-6) for the spleen, and 10(-3) for the added set of organs.

CONCLUSIONS

Dispersal of PC-3 tumor cells from IM experimental tumors started early before the third week postinoculation and when primary tumors had 2 x 10(4) TCEs. Tumor cells were found widely spread in all the organs tested. The possibility of easily quantifying tumor cell burden should make this approach useful for the study of metastasis and the development of antimetastatic therapies.

Characterization of spontaneous metastasis in an aggressive breast carcinoma model using flow cytometry

Studies of metastasis can be accelerated and provide more mechanistic information using cell lines which reproducibly and aggressively metastasize, and which are accurately and easily detected in tissues at all stages of the metastatic process. Although reporter proteins such as green fluorescent protein (GFP) and beta-galactosidase have improved the tracking of tumor cells in vivo, their measurement has often been limited to visual observation and manual counting. In this study, we exploited the highly sensitive and objective quantitation provided by flow cytometry to characterize, in detail, the sequence of events associated with orthotopic metastasis in a highly aggressive mouse model. Following stable transfection of the MDA-MB-435 breast carcinoma cell line with GFP, we utilized an in vivo selection process to isolate a variant exhibiting increased primary tumor growth and metastasis. As few as one fluorescent tumor cell per 200,000 host cells could be accurately detected in dissociated tissues by flow cytometry, allowing us to demonstrate that metastatic cells migrate to the lungs of SCID mice very early after orthotopic implantation. Tumor burden in lungs increased in a smooth continuous manner, until death approximately eight weeks later. Levels of circulating tumor cells in blood were also detectable at an early timepoint, but remained relatively low throughout the course of secondary tumor development in the lungs. Surgical removal of the primary tumor at various times after inoculation significantly affected lung tumor burden, supporting the concept that circulating tumor cells in blood inefficiently initiate distal metastases. Furthermore, the continuing contribution to metastasis by the primary tumor was independent of tumor mass. The combined characteristics of enhanced orthotopic metastasis and quantitative detection in blood and tissues will make this a useful new model for the characterization of the multi-stage progression of cancer, and the preclinical evaluation of anti-neoplastic therapies.

Phosphoinositide 3-kinase is involved in the tumor-specific activation of human breast cancer cell Na(+)/H(+) exchange, motility, and invasion induced by serum deprivation

Whereas the tumor acidic extracellular pH plays a crucial role in the invasive process, the mechanism(s) behind this acidification, especially in low nutrient conditions, are unclear. The regulation of the Na(+)/H(+) exchanger (NHE) and invasion by serum deprivation were studied in a series of breast epithelial cell lines representing progression from non-tumor to highly metastatic cells. Whereas serum deprivation reduced lactate production in all three cells lines, it inhibited NHE activity in the non-tumor cells and stimulated it in the tumor cells with a larger stimulation in the metastatic cells. The stimulation of NHE in the tumor cell lines was the result of an increased affinity of the internal H(+) regulatory site of the NHE without changes in sodium kinetics or expression. Serum deprivation conferred increased cell motility and invasive ability that were abrogated by specific inhibition of the NHE. Inhibition of phosphoinositide 3-kinase by overexpression of a dominant-negative mutant or wortmannin incubation inhibited NHE activity and invasion in serum replete conditions while potentiating the serum deprivation-dependent activation of the NHE and invasion. These results indicate that the up-regulation of the NHE by a phosphoinositide 3-kinase-dependent mechanism plays an essential role in increased tumor cell invasion induced by serum deprivation.

Molecular evidence for derivation of metastatic cells from minor subclones of primary clear renal cell carcinomas

The production of metastases depends on changes in a large number of genes. It is also connected with the interaction of tumor cells with the environment. It has been reported that primary tumor clone domination is also an important factor in metastasizing, and in many neoplasms dominating clones are the metastatic forerunners. Up to now it is unknown whether domination of a given clone in a primary renal cell carcinoma is a crucial factor in forming metastases or rather presence or absence of specific genes imposes the major advantage in the metastatic process. To study the presence or absence of the duplication and mitotic nondisjunction event as one of the phenomenon in the creation of metastases, as well as possible derivation of metastatic cells from the minor subclone of primary tumor, we examined three metastatic renal clear-cell carcinomas in which by comparative genomic hybridization we detected the loss of 3p in the primary tumor and two copies of 3p in the corresponding metastasis. Loss of heterozygosity analyses using markers for 3p25 (D3S1038), 3p21.1 (D3S1295), and 3p14.2 (D3S1481) proved heterozygosity of at least two 3p loci in all metastatic tumors, which indicates the absence of mitotic nondisjunction event as a cause of occurrence of two copies of 3p in metastases. Our results suggest that in some of the clear-cell renal carcinomas metastatic cells may derive from minor subclones of primary tumors.

Molecular mechanisms regulating the hyaluronan binding activity of the adhesion protein CD44

In the present study, we describe the isolation and characterization of a cDNA clone designated B6F1.3, that appears to 'activate' the hyaluronan-binding capacity of CD44 upon transfection into the murine fibroblastoid cell line MOP8. Sequence analysis indicates that the putative regulatory molecule encoded by this clone is identical to the murine interleukin-2 receptor gamma chain (mIL-2R gamma), a recently described type 1 transmembrane protein that constitutes an integral component of the cell surface receptors that bind a number of cytokines including IL-2, IL-4, IL-7, IL-9, IL-15 and perhaps also IL-13. Mutations in this molecule have been shown to be responsible for X-linked severe combined immunodeficiency (XSCID) in humans. With the exception of bone marrow, the mIL-2R gamma chain was found to be expressed at high levels on all hemopoietic cell lines and tissue types examined. Non-hemopoietic tissues are generally negative. FACS analysis and Western blot analysis indicated respectively that B6F1.3 does not mediate its effects by upregulating the expression of CD44 or by altering the alternative splicing of the molecule. Removal of the cytoplasmic tail of the mIL-2R gamma chain, including a Src homology region 2 (SH2) subdomain, abolished its ability to enhance CD44-mediated binding to hyaluronan suggesting the involvement of signal transduction events triggered via the cytoplasmic domain in the 'activation' process. Determining whether activating molecules such as B6F1.3 are co-expressed within tumor cells may help improve the potential value of CD44 as a diagnostic marker of metastatic disease.

In vitro invasiveness of DU-145 human prostate carcinoma cells is modulated by EGF receptor-mediated signals

Prostate carcinomas often present an autocrine stimulatory loop in which the transformed cells both express the EGF receptor (EGFR) and produce activating ligands (TGF alpha and EGF forms). Up-regulated EGFR signalling has been correlated with tumor progression in other human neoplasia; however, the cell behaviour which is promoted remains undefined. To determine whether an EGFR-induced response contributes to cell invasiveness, we transduced DU-145 human prostate carcinoma cells with either a full-length (WT) or a mitogenically-active but motility-deficient truncated (c'973) EGFR. The DU-145 Parental and two transgene sublines all produced EGFR and TGF alpha, but the transduced WT and c'973 EGFR underwent autocrine downregulation to a lesser degree, with more receptor remaining intact. DU-145 cells transduced with WT EGFR transmigrated a human amniotic basement membrane matrix (Amgel) to a greater extent than did Parental DU-145 cells (175 +/- 22%). Cells expressing the c'973 EGFR invaded through the Amgel only to about two thirds the extent of the Parental cells (62 +/- 23%). A monoclonal antibody which prevents ligand-induced activation of EGFR decreased the invasiveness of WT-expressing cells by half and Parental cells by a fifth, but had little effect on the invasiveness of c'973-expressing cells; with the result that in the presence of antibody, all three cell lines transmigrated the Amgel to the same extent. The different levels of invasiveness between the three sublines were independent of cell proliferation. These findings demonstrated that EGFR-mediated signals increase tumor cell invasiveness and suggested that domains in the carboxy-terminus are required to signal invasiveness. As an initial investigation into the mechanisms underlying the EGFR-mediated enhanced invasiveness, we determined whether these cells presented different collagenolytic activity, as the major constituents of Amgel are collagen types I and IV. All three sublines secreted easily detectable levels of gelatin-directed proteases and TIMP-1, with WT cells secreting equivalent or lower levels of proteases. The proteolytic balance in these cells did not correlate with invasiveness. These data suggest that the TGF alpha-EGFR autocrine loop promotes invasiveness and that this is accomplished by signalling cell properties other than differential secretion of collagenolytic activity.