A novel in vitro assay system for transendothelial tumor cell invasion: significance of E-selectin and alpha 3 integrin in the transendothelial invasion by HT1080 fibrosarcoma cells

Unique cartilage matrix-associated protein inhibits the migratory and invasive potential of triple-negative breast cancer

Triple-negative breast cancer (TNBC) that lacks expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) is a breast cancer subtype with very aggressive metastasis and poor prognosis. Unique cartilage matrix-associated protein (UCMA) is a vitamin K-dependent protein (VKDP) with a high-density γ-carboxyglutamic acid (Gla) domain due to the action of vitamin K. UCMA promotes osteoblast differentiation and mineral deposition in bone and suppresses calcification in vessels. However, correlation between UCMA and TNBC is unknown. This study investigated the inhibitory effect of UCMA on TNBC cell in vitro migration, invasion, and colony formation in addition to in vivo tumorigenesis. Cell migration and invasion significantly decreased in Ucma-overexpressing MDA-MB-231 and 4T1 cells compared to the mock control cells. Also, colony formation and the number of colonies significantly decreased in Ucma-overexpressing MDA-MB-231 and 4T1 cells. These results indicate that UCMA significantly inhibits the migration, invasion, and colony formation of TNBC cells. In an in vivo xenograft mouse model, tumor growth significantly decreased in mice bearing Ucma-overexpressing TNBC cells compared to the mock control cells, indicating that UCMA reduced in vivo tumor growth, similar to the inhibitory role of UCMA in vitro. Survival analysis using publicly available database showed that high UCMA expression significantly correlated with favorable relapse-free survival in TNBC patients compared to those with the other VKDPs, matrix Gla protein (MGP) and osteocalcin (OCN). Collectively, this study suggests that UCMA is a promising new therapeutic agent for TNBC.

PKCε Is an Essential Mediator of Prostate Cancer Bone Metastasis

The bone is a preferred site for metastatic homing of prostate cancer cells. Once prostate cancer patients develop skeletal metastases, they eventually succumb to the disease; therefore, it is imperative to identify key molecular drivers of this process. This study examines the involvement of protein kinase C epsilon (PKCε), an oncogenic protein that is abnormally overexpressed in human tumor specimens and cell lines, on prostate cancer cell bone metastasis. PC3-ML cells, a highly invasive prostate cancer PC3 derivative with bone metastatic colonization properties, failed to induce skeletal metastatic foci upon inoculation into nude mice when PKCε expression was silenced using shRNA. Interestingly, while PKCε depletion had only marginal effects on the proliferative, adhesive, and migratory capacities of PC3-ML cells in vitro or in the growth of xenografts upon s.c. inoculation, it caused a significant reduction in cell invasiveness. Notably, PKCε was required for transendothelial cell migration (TEM) as well as for the growth of PC3-ML cells in a bone biomimetic environment. At a mechanistic level, PKCε depletion abrogates the expression of IL1β, a cytokine implicated in skeletal metastasis. Taken together, PKCε is a key factor for driving the formation of bone metastasis by prostate cancer cells and is a potential therapeutic target for advanced stages of the disease.

IMPLICATIONS

This study uncovers an important new function of PKCε in the dissemination of cancer cells to the bone; thus, highlighting the promising potential of this oncogenic kinase as a therapeutic target for skeletal metastasis.

Combretastatin A-4 derived imidazoles show cytotoxic, antivascular, and antimetastatic effects based on cytoskeletal reorganisation

INTRODUCTION

Combretastatin A-4 (CA-4) is a natural cis-stilbene which interferes with the cellular tubulin dynamics and which selectively destroys tumour blood vessels. Its pharmacological shortcomings such as insufficient chemical stability, water solubility, and cytotoxicity can be remedied by employing its imidazole derivatives.

METHODS

We studied 11 halogenated imidazole derivatives of CA-4 for their effects on the microtubule and actin cytoskeletons of cancer and endothelial cells and on the propensity of these cells to migrate across tissue barriers or to form blood vessel-like tubular structures.

RESULTS

A series of N-methyl-4-aryl-5-(4-ethoxyphenyl)-imidazoles proved far more efficacious than the lead CA-4 in growth inhibition assays against CA-4-resistant HT-29 colon carcinoma cells and generally more selective for cancer over nonmalignant cells. Et-brimamin (6), the most active compound, inhibited the growth of various cancer cell lines with IC50 (72 h) values in the low nanomolar range. Active imidazoles such as 6 reduced the motility and invasiveness of cancer cells by initiating the formation of actin stress fibres and focal adhesions as a response to the extensive microtubule disruption. The antimetastatic properties were ascertained in 3D-transwell migration assays which simulated the transgression of highly invasive melanoma cells through the extracellular matrix of solid tumours and through the endothelium of blood vessels. The studied imidazoles exhibited vascular-disrupting effects also against tumour xenografts that are refractory to CA-4. They were also less toxic and better tolerated by mice.

CONCLUSIONS

We deem the new imidazoles promising drug candidates for combination regimens with antiangiogenic VEGFR inhibitors.

Regulation of CXCR4-mediated invasion by DARPP-32 in gastric cancer cells

Although Dopamine and cAMP-regulated phosphoprotein, Mr 32000 (DARPP-32) is overexpressed in two-thirds of gastric cancers, its impact on molecular functions has not been fully characterized. In this study, we examined the role of DARPP-32 in gastric cancer cell invasion. Using matrigel-coated Boyden chamber invasion assay, DARPP-32-overexpressing AGS cells showed a three-fold increase in invasion relative to the vector control (P < 0.01). We also tested the transendothelial cell invasion as a measure of cell aggressiveness using the impedance-based human umbilical vein endothelial cells invasion assay and obtained similar results (P < 0.001). Western blot analysis indicated that overexpression of DARPP-32 mediated an increase in the membrane-type 1 matrix metalloproteinase (MT1-MMP) and CXCR4 protein levels. Consistent with the role of MT1-MMP in cleaving extracellular matrix proteins initiating the activation of soluble MMPs, we detected a robust increase in MMP-2 activity in DARPP-32-overexpressing cells. The knockdown of endogenous DARPP-32 in the MKN-45 cells reversed these signaling events and decreased cell invasive activity. We tested whether the invasive activity mediated by DARPP-32 might involve sustained signaling via CXCR4-dependent activation of the MT1-MMP/MMP-2 pathway. The small-molecule CXCR4 antagonist (AMD3100) and CXCR4-siRNA blocked DARPP-32-induced cell invasion. We further examined our hypothesis that DARPP-32 could interact with CXCR4 and stabilize its levels following stimulation with its ligand, CXCL12. Using reciprocal coimmunoprecipitation and immunofluorescence experiments, we found that DARPP-32 and CXCR4 coexist in the same protein complex. DARPP-32 prolonged the CXCR4 protein half-life and reduced ubiquitination of the CXCR4 protein, following treatment with its ligand, CXCL12. In conclusion, these findings show a novel mechanism by which DARPP-32 promotes cell invasion by regulating CXCR4-mediated activation of the MT1-MMP/MMP-2 pathway.

α3β1 integrins regulate CD151 complex assembly and membrane dynamics in carcinoma cells within 3D environments

Integrins are extracellular matrix (ECM) receptors that are key players in the regulation of tumour cell invasion. The laminin-binding integrin α3β1 has previously been shown to regulate adhesion and migration of carcinoma cells in part through co-operative signalling with the tetraspanin family of transmembrane proteins. However, the spatial and temporal regulation of crosstalk between these families of transmembrane proteins in intact cells remains poorly understood. Here we have used fluorescence resonance energy transfer (FRET) to demonstrate for the first time that α3β1 and the tetraspanin CD151 directly associate at the front and retracting rear of polarised migrating breast carcinoma cells in both two-dimentional (2D) and three-dimentional (3D)matrices. Furthermore, localised α3β1-CD151 binding correlates with lower CD151 homodimerisation in cells migrating on laminin or within matrigel. Loss of α3β1 integrin leads to increased CD151 homodimer formation, increased activation of Rho GTPase, loss of cell polarity and decreased invasion in 3D ECM. As a result, α3-silenced cells show decreased actin-based membrane protrusion and retraction in both 2D and 3D environments. These data demonstrate that associations between α3β1 and CD151 occur dynamically within discrete subcellular compartments and act to establish local GTPase signalling to promote tumour cell invasion. These novel findings shed light on the complex crosstalk and switching between receptor complexes in response to different extracellular cues during cell invasion in 3D environments.

In vitro mesothelial clearance assay that models the early steps of ovarian cancer metastasis

Ovarian cancer is the fifth leading cause of cancer related deaths in the United States(1). Despite a positive initial response to therapies, 70 to 90 percent of women with ovarian cancer develop new metastases, and the recurrence is often fatal(2). It is, therefore, necessary to understand how secondary metastases arise in order to develop better treatments for intermediate and late stage ovarian cancer. Ovarian cancer metastasis occurs when malignant cells detach from the primary tumor site and disseminate throughout the peritoneal cavity. The disseminated cells can form multicellular clusters, or spheroids, that will either remain unattached, or implant onto organs within the peritoneal cavity(3) (Figure 1, Movie 1). All of the organs within the peritoneal cavity are lined with a single, continuous, layer of mesothelial cells(4-6) (Figure 2). However, mesothelial cells are absent from underneath peritoneal tumor masses, as revealed by electron micrograph studies of excised human tumor tissue sections(3,5-7) (Figure 2). This suggests that mesothelial cells are excluded from underneath the tumor mass by an unknown process. Previous in vitro experiments demonstrated that primary ovarian cancer cells attach more efficiently to extracellular matrix than to mesothelial cells(8), and more recent studies showed that primary peritoneal mesothelial cells actually provide a barrier to ovarian cancer cell adhesion and invasion (as compared to adhesion and invasion on substrates that were not covered with mesothelial cells)(9,10). This would suggest that mesothelial cells act as a barrier against ovarian cancer metastasis. The cellular and molecular mechanisms by which ovarian cancer cells breach this barrier, and exclude the mesothelium have, until recently, remained unknown. Here we describe the methodology for an in vitro assay that models the interaction between ovarian cancer cell spheroids and mesothelial cells in vivo (Figure 3, Movie 2). Our protocol was adapted from previously described methods for analyzing ovarian tumor cell interactions with mesothelial monolayers(8-16), and was first described in a report showing that ovarian tumor cells utilize an integrin -dependent activation of myosin and traction force to promote the exclusion of the mesothelial cells from under a tumor spheroid(17). This model takes advantage of time-lapse fluorescence microscopy to monitor the two cell populations in real time, providing spatial and temporal information on the interaction. The ovarian cancer cells express red fluorescent protein (RFP) while the mesothelial cells express green fluorescent protein (GFP). RFP-expressing ovarian cancer cell spheroids attach to the GFP-expressing mesothelial monolayer. The spheroids spread, invade, and force the mesothelial cells aside creating a hole in the monolayer. This hole is visualized as the negative space (black) in the GFP image. The area of the hole can then be measured to quantitatively analyze differences in clearance activity between control and experimental populations of ovarian cancer and/ or mesothelial cells. This assay requires only a small number of ovarian cancer cells (100 cells per spheroid X 20-30 spheroids per condition), so it is feasible to perform this assay using precious primary tumor cell samples. Furthermore, this assay can be easily adapted for high throughput screening.

ZEB1 enhances transendothelial migration and represses the epithelial phenotype of prostate cancer cells

Metastatic colonization involves cancer cell lodgment or adherence in the microvasculature and subsequent migration of those cells across the endothelium into a secondary organ site. To study this process further, we analyzed transendothelial migration of human PC-3 prostate cancer cells in vitro. We isolated a subpopulation of cells, TEM4-18, that crossed an endothelial barrier more efficiently, but surprisingly, were less invasive than parental PC-3 cells in other contexts in vitro. Importantly, TEM4-18 cells were more aggressive than PC-3 cells in a murine metastatic colonization model. Microarray and FACS analysis of these cells showed that the expression of many genes previously associated with leukocyte trafficking and cancer cell extravasation were either unchanged or down-regulated. Instead, TEM4-18 cells exhibited characteristic molecular markers of an epithelial-to-mesenchymal transition (EMT), including frank loss of E-cadherin expression and up-regulation of the E-cadherin repressor ZEB1. Silencing ZEB1 in TEM4-18 cells resulted in increased E-cadherin and reduced transendothelial migration. TEM4-18 cells also express N-cadherin, which was found to be necessary, but not sufficient for increased transendothelial migration. Our results extend the role of EMT in metastasis to transendothelial migration and implicate ZEB1 and N-cadherin in this process in prostate cancer cells.

Tumorigenicity of IL-1alpha- and IL-1beta-deficient fibrosarcoma cells

Analyzing the growth of fibrosarcoma lines derived from IL-1alpha-, IL-1beta- , or IL-1alphabeta-knockout (-/-) mice in the immunocompetent host revealed that tumor-derived IL-1alpha and IL-1beta exert strong and opposing effects on immune response induction, which prohibited the evaluation of a potential impact on tumorigenicity. Therefore, in vivo growth of IL-1-deficient tumor lines was evaluated in nu/nu mice and was compared with in vitro growth characteristics. All IL-1-deficient fibrosarcoma lines grow in immunocompromised mice. However, IL-1alpha(-/-)beta-competent (comp) lines grow more aggressively, efficiently induce angiogenesis, and recruit inflammatory cells. Despite stronger tumorigenicity of IL-1beta(comp) lines, IL-1alpha strengthens anchorage-independent growth, but both IL-1alpha and IL-1beta support drug resistance. Corresponding to the aggressive growth, IL-1beta(comp) cells display increased matrix adhesion, motility, and cable formation on matrigel, likely supported by elevated alpha(v)/beta3 and matrix metalloroteinase expression. Recruitment of myeloid cells requires IL-1beta but is regulated by IL-1alpha, because inflammatory chemokine and cytokine expression is stronger in IL-1alpha(-/-)beta(comp) than in IL-1(wt) lines. This regulatory effect of tumor-derived IL-1alpha is restricted to the tumor environment and does not affect systemic inflammatory response induction by tumor-derived IL-1beta. Both sarcoma cell-derived IL-1alpha and IL-1beta promote tumor growth. However, IL-1alpha exerts regulatory activity on the tumor cell-matrix cross-talk, and only IL-1beta initiates systemic inflammation.

The differential effect of endothelial cell factors on in vitro motility of malignant and non-malignant cells

Motility of cancer cells plays a critical role in tumor metastasis, and as such is a target for intervention. The motility of malignant Calu-1 human lung epithelial carcinoma cells is upregulated when placed on a human umbilical vein endothelial cell monolayer, while that of non-malignant L132 human lung epithelial cells is not. To dissect the factor(s) causing such differential behaviors, the motile responses of both cell lines to endothelial cell factors-secreted to the media, on the endothelial cell surface, and secreted to the extracellular matrix-and to individual extracellular matrix proteins were compared. Cell motility was quantified by tracking the cell movement on a surface with time-lapse video microscopy, which was analyzed with the persistent random walk model of motility. None of the factors tested had a remarkable effect on L132 cell motility, but the Calu-1 cell motility was significantly upregulated by endothelial cell extracellular matrix and by laminin, fibronectin, collagen I and collagen VI individually. Flow cytometry analysis revealed significantly higher expression levels of integrin subunits beta1, alpha2, alpha3, and alpha6, which are known receptors for these extracellular matrix proteins, on the Calu-1 than L132 cells, implicating a role of these integrins in the observed motile behaviors of these cell lines.

Stepping out of the flow: capillary extravasation in cancer metastasis

In order for cancer cells to successfully colonize a metastatic site, they must detach from the primary tumor using extracellular matrix-degrading proteases, intravasate and survive in the circulation, evade the immune response, and extravasate the vasculature to invade the target tissue parenchyma, where metastatic foci are established. Though many of the steps of metastasis are widely studied, the precise cellular interactions and molecular alterations associated with extravasation are unknown, and further study is needed to elucidate the mechanisms inherent to this process. Studies of leukocytes localized to inflamed tissue during the immune response may be used to elucidate the process of cancer extravasation, since leukocyte diapedesis through the vasculature involves critical adhesive interactions with endothelial cells, and both leukocytes and cancer cells express similar surface receptors capable of binding endothelial adhesion molecules. Thus, leukocyte extravasation during the inflammatory response has provided a model for transendothelial migration (TEM) of cancer cells. Leukocyte extravasation is characterized by a process whereby rolling mediated by cytokine-activated endothelial selectins is followed by firmer adhesions with beta1 and beta2 integrin subunits to an activated endothelium and subsequent diapedesis, which most likely involves activation of Rho GTPases, regulators of cytoskeletal rearrangements and motility. It is controversial whether such selectin-mediated rolling is necessary for TEM of cancer cells. However, it has been established that similar stable adhesions between tumor and endothelial cells precede cancer cell transmigration through the endothelium. Additionally, there is support for the preferential attachment of tumor cells to the endothelium and, accordingly, site-specific metastasis of cancer cells. Rho GTPases are critical to TEM of cancer cells as well, and some progress has been made in understanding the specific roles of the Rho GTPase family, though much is still unknown. As the mechanisms of cancer TEM are elucidated, new approaches to study and target metastasis may be utilized and developed.

Tumor-endothelial cell interactions: therapeutic potential

Metastasis is the primary cause of death in cancer patients. However, the molecular mechanism of the metastatic process is poorly understood because it involves multiple steps with a high degree of complexity. A critical step for successful establishment of secondary colonization is the hematogenous dissemination of malignant cells. During this process, the attachment of cancer cells to the endothelial cells on microvasculature is considered to be an essential step and many adhesion molecules as well as chemokines have been found to be involved in this process. This interaction of cancer-endothelial cell is considered not only to determine the physical site of metastasis, but also to provide the necessary anchorage to facilitate tumor cell extravasation. However, recent evidence indicates that this interaction also serves as a host defense mechanism and hinders the process of metastasis. The tumor metastases suppressor gene, KAI1, has been known to block metastatic process without affecting the primary tumor growth, and this protein has been found to be able to bind to the chemokine receptor, Duffy antigen receptor for chemokines (DARC), which is expressed on endothelial cells. Importantly, this interaction markedly induces senescence of tumor cells. This novel finding is not only significant in the context of molecular dissection of metastatic process but also in the therapeutic implication to develop drugs inhibiting metastasis.

A critical role for tetraspanin CD151 in alpha3beta1 and alpha6beta4 integrin-dependent tumor cell functions on laminin-5

The basement membrane protein laminin-5 supports tumor cell adhesion and motility and is implicated at multiple steps of the metastatic cascade. Tetraspanin CD151 engages in lateral, cell surface complexes with both of the major laminin-5 receptors, integrins alpha3beta1 and alpha6beta4. To determine the role of CD151 in tumor cell responses to laminin-5, we used retroviral RNA interference to efficiently silence CD151 expression in epidermal carcinoma cells. Near total loss of CD151 had no effect on steady state cell surface expression of alpha3beta1, alpha6beta4, or other integrins with which CD151 associates. However, CD151-silenced carcinoma cells displayed markedly impaired motility on laminin-5, accompanied by unusually persistent lateral and trailing edge adhesive contacts. CD151 silencing disrupted alpha3beta1 integrin association with tetraspanin-enriched microdomains, reduced the bulk detergent extractability of alpha3beta1, and impaired alpha3beta1 internalization in cells migrating on laminin-5. Both alpha3beta1- and alpha6beta4-dependent cell adhesion to laminin-5 were also impaired in CD151-silenced cells. Reexpressing CD151 in CD151-silenced cells reversed the adhesion and motility defects. Finally, loss of CD151 also impaired migration but not adhesion on substrates other than laminin-5. These data show that CD151 plays a critical role in tumor cell responses to laminin-5 and reveal promotion of integrin recycling as a novel potential mechanism whereby CD151 regulates tumor cell migration.

Studies of the interactions between melatonin and 2 Hz, 0.3 mT PEMF on the proliferation and invasion of human breast cancer cells

Interactions between the hormone melatonin at pharmacological concentrations (10(-3) M) and 2 Hz, 0.3 mT pulsed electromagnetic fields (PEMF) on the proliferation and invasion of human breast cancer cells were studied in vitro. Three types of human breast cancer cells were used in this study: MDA-MB-435, MDA-MB-231, and MCF-7. Results showed that cellular growth of MDA-MB-231 cells, which were reported to be lowly metastatic, and MCF-7 cells, which were reported to be nonmetastatic, were both significantly reduced by melatonin regardless of the presence of the field. Results also showed that MDA-MB-435 and MDA-MB-231 cells were invasive, with MDA-MB-231 cells being more invasive than the MDA-MB-435 cells for both unexposed and experimental-PEMF groups. In addition, invasion studies showed that MCF-7 cells were not invasive and that melatonin did not have any effects on the invasion of these cells, with or without the PEMF. It is also suggested that since metastasis requires growth and invasion into tissue, anti-invasion agents can be used in conjunction with melatonin to prevent formation of secondary metastases. The overall studies suggest that PEMF at 2 Hz, 0.3 mT does not influence cancer metastasis; while having clinical merit in the healing of soft tissue injury, this field has shown no influence on cancer cells as 60 Hz power line fields have.

Molecular detection of disseminated cancer cells in the peripheral blood and expression of sialylated antigens in colon cancers

BACKGROUND AND OBJECTIVES

To improve the survival rate of patients with colon cancer, liver metastases must be eradicated in a clinically occult state. This study was designed to find a predictor for potential liver metastases or micrometastases in colon cancer.

METHODS

Peripheral blood samples and tumor specimens were obtained from 36 patients with colon cancers. The blood samples were subjected to reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, and the expression of sialylated carbohydrates was also investigated in the tumors immunohistochemically.

RESULTS

A carcinoembryonic antigen (CEA)-specific signal in the blood was detected in 9 of 12 (75%) patients with liver metastasis and in 8 of 24 (33%) patients without liver metastasis, respectively (P < 0.05). The positive rates of sialyl Lewis A (sLeA) and sialyl Lewis X (sLeX) were 36.3% and 40% in tumors without liver metastasis vs. 58.3% and 100% with liver metastasis, respectively. Within a year after surgery, liver metastases became clinically evident in three of the four patients without liver metastasis who showed a CEA-positive signal in their blood preoperatively and who had tumors with a strong expression of sLeX.

CONCLUSIONS

A combination of both markers may provide prognostic information for liver metastases in colon cancer.

Significance of VLA-4-VCAM-1 interaction and CD44 for transendothelial invasion in a bone marrow metastatic myeloma model

In previous work, we established the B9/BM1 syngeneic murine bone marrow metastasis model. Interleukin (IL)-6-dependent. IL-1-producing B9/BM1 cells, which colonize the vertebral and femoral marrow after i.v. injection, show great similarity in cell surface phenotype to human myeloma cells, especially the expression of 3 adhesion molecules, CD44, VLA-4 and ICAM-1. Here we investigated the function of these adhesion molecules by binding and transendothelial invasion assays using a newly established bone marrow-derived endothelial cell line (BMEC). A combination of monoclonal antibodies against CD44 and VLA-4 significantly inhibited the adherence of B9/BM1 cells to BMEC and anti-CD44 mAb especially blocked B9/BM1 transendothelial invasion of unstimulated BMEC cells. Results of additional experiments, in which the cells were treated with anti-CD44 and hyaluronidase, demonstrated that the interaction of CD44 molecules on B9/BM1 cells with hyaluronan on BMEC cells was a critical factor in both adhesion and transendothelial invasion in this model. However, stimulation of BMEC with TNFalpha resulted in increased invasion by B9/BM1 cells, which was completely suppressed by anti-VCAM-1 mAb, implicating a significant role of this adhesion molecule in this process during inflammation.

Interactions between cancer cells and the endothelium in metastasis

The haematogenous phase of cancer metastasis facilitates the transport of metastatic cells within the blood and incorporates a sequence of interactions between circulating intravascular cancer cells and the endothelium of blood vessels at the sites of tumour cell arrest. Initial interactions involve mechanical contact and transient adhesion, mediated by endothelial selectins and their ligands on the neoplastic cells. This contact initiates a sequence of activation pathways that involves cytokines, growth factors, bioactive lipids, and reactive oxygen species produced by either the cancer cell or the endothelium. These molecules elicit expression of integrin adhesion molecules in cancer cells and the endothelium, matrix metalloproteinases, and chemotactic factors that promote the attachment of tumour cells to the vessel wall and/or transvascular penetration. Induction of endothelial free radicals can be cytotoxic to cancer cells. Collectively, the sum of these interactions constitutes an interdependent relationship, the outcome of which determines the fate of the metastatic process.

A modified Boyden chamber assay for tumor cell transendothelial migration in vitro

We have developed a modified Boyden chamber system for assessing tumor cell transmigration across endothelial monolayer in vitro. This radiometric-based method allows us to take into account the cells which have traversed but detached from the filter, a significant fraction not included in the existing method of visual counting. The method was applied to examine six malignant and one non-malignant cell lines. The variable invasive potentials of these cells were found to correlate with their ability to disrupt the endothelial cell monolayers.

Enhancement of metastatic activity of colon cancer as influenced by expression of cell surface antigens

BACKGROUND

Cell surface antigens are contributory factors toward metastatic activity. There have been no detailed studies on changes in cell surface antigens of colon cancer cell lines. To control life-threatening metastasis, it is necessary to evaluate what types of changes in cell surface antigens exert an influence on metastatic activity.

MATERIALS AND METHODS

In vivo selection was performed using the human colon cancer-derived cell line KM12SM to obtain variants of metastatic activity. A murine spleen injection-liver metastasis procedure reflecting the latter half of the metastatic process was adopted and repeated four times. Flow cytometric analyses were carried out to detect expression of antigens: Lewis a (Lea), Lewis x (Lex), sialyl Lewis a (sLea), sialyl Lewis x (sLex), E-cadherin, CD44v6, integrin alpha2 (CD49b), integrin alpha3 (CD49c), integrin alpha4 (CD49d), integrin alpha5 (CD49e), and integrin beta1 (CD29).

RESULTS

In vivo selection produced variants with higher metastatic activity. In the original line KM12SM, sLea, E-cadherin, CD49b, CD49c, or CD29 were positive in more than 40% of the cells. After selection, the percentage of cells positive for Lea, sLea, and all examined integrins significantly increased. Lex, sLex, and CD44v6 increased slightly, while E-cadherin decreased slightly.

CONCLUSIONS

In vivo selection and flow cytometric analysis revealed that Lea, sLea, CD49b, CD49c, and CD29 appear to be involved in the increase of metastatic activity. The changes of integrin expression in this study suggest that integrins collaborate in the promotion of adhesion to an extracellular matrix.

Enhancement of type IV collagenases by highly metastatic variants of HT1080 fibrosarcoma cells established by a transendothelial invasion system in vitro

A novel in vitro invasion assay system was established in this laboratory, in which the invasion of tumor cells after interaction with endothelial cells could be examined. Two variant cell lines (FP-10, FP-21) were established from parental HT1080 cells using this assay system. FP-10 and FP-21 cells had higher invasive and metastatic potential than the parental cells both in vitro and in vivo. The activity of anchorage-independent proliferation and the adhesion to the HUVEC monolayer of FP-10 and FP-21 was greater than the parental cells. The secretion of type IV collagenase (both MMP-2 and MMP-9) was also increased more significantly by the variant cells than by the parental cells, and the expression of uPA mRNA was higher in FP-10 and FP-21. Treatment of variant cells with human TIMP-2 remarkably suppressed the increment of the in vitro invasion to the same level as parental cells. These results suggest that this in vitro transendothelial invasion system accelerates multiple mechanisms of the metastasis by HT1080, especially the production of type IV collagenases. It can thus provide a useful model of tumor metastasis.

Inhibition of osteolytic bone metastasis of breast cancer by combined treatment with the bisphosphonate ibandronate and tissue inhibitor of the matrix metalloproteinase-2

Multiple steps are involved in the metastasis of cancer cells from primary sites to distant organs. These steps should be considered in the design of pharmacologic approaches to prevent or inhibit the metastatic process. In the present study, we have compared the effects of inhibiting several steps involved in the bone metastatic process individually with inhibition of both together. The steps we chose were matrix metalloproteinase (MMP) secretion, likely involved in tumor cell invasion, and osteoclastic bone resorption, the final step in the process. We used an experimental model in which inoculation of human estrogen-independent breast cancer MDA-231 cells into the left cardiac ventricle of female nude mice causes osteolytic lesions in bone. To inhibit cancer invasiveness, the tissue inhibitor of the MMP-2 (TIMP-2), which is a natural inhibitor of MMPs, was overexpressed in MDA-231 cells. To inhibit bone resorption, a potent bisphosphonate, ibandronate (4 microg/mouse) was daily administered subcutaneously. Nude mice received either; (a) nontransfected MDA-231 cells; (b) nontransfected MDA231 cells and ibandronate; (c) TIMP-2-transfected MDA-231 cells; or (d) TIMP-2-transfected MDA-231 cells and ibandronate. In mice from group a, radiographs revealed multiple osteolytic lesions. However, in mice from group b or group c, osteolytic lesions were markedly decreased. Of particular note, in animals from group d receiving both ibandronate and TIMP-2-transfected MDA-231 cells, there were no radiologically detectable osteolytic lesions. Survival rate was increased in mice of groups c and d. There was no difference in local enlargement in the mammary fat pad between nontransfected and TIMP-2-transfected MDA-231 cells. These results suggest that inhibition of both MMPs and osteoclastic bone resorption are more efficacious treatment for prevention of osteolytic lesions than either alone, and suggest that when therapies are designed based on the uniqueness of the bone microenvironment and combined with several common steps in the metastatic process, osteolytic bone metastases can be more efficiently and selectively inhibited.

Role of VLA-integrin receptor in invasion and metastasis of human fibrosarcoma cells

Anti-invasive and anti-metastatic effects of anti-integrin antibodies (against VLA-alpha 2, alpha 4, beta 1) were examined on human fibrosarcoma cells using in vitro invasion assay in a reconstituted basement membrane (Matrigel) and experimental metastatic assay in a chick embryo. The effects of anti-integrin antibodies were compared with those of RGD-containing peptides (GRGDS), which have been known as effective inhibitors of tumor cell metastasis. Although slight differences in effective concentration among antibodies were observed, invasion and metastasis were significantly inhibited by anti-integrin antibodies. The results also showed partial inhibitory effect of GRGDS on the invasion and metastasis of human fibrosarcoma cells. These results indicate that integrin receptors mediating cell-cell/cell-extracellular matrix components interactions play a key role in the invasion and metastasis of human fibrosarcoma cells.

Metastasis from human breast cancer cell lines

Immunodeficient animals, principally nude mice, when used in appropriately designed studies have been shown to be useful for the experimental analysis of human breast cancer metastasis. As with many other human tumors, the implantation of breast cancer cells into an anatomically appropriate tissue (the mammary fatpad) results in increased tumor take and incidence of metastasis for certain cell lines compared with subcutaneous injection. Testing a number of widely available human breast cancer cell lines identified the MDA-MB-435 cell line as the most metastatic, producing lung and lymph node metastases in a high proportion of nude and severe combined immunodeficient (SCID) mice after injection in the mammary fatpad. Mixing human breast cancer cells with normal fibroblasts or with Matrigel also increases the tumor incidence and growth rates in nude mice. Different routes of injection can be used to assess the ability of human breast cancer cells to form metastatic lesions in the lungs (i.v. injection), the liver (injection in the spleen), the brain (direct or intracarotid artery injection) and the bone marrow and bone (injection into the left ventricle of the heart). These different approaches demonstrate the potential of experimental studies of human breast cancer growth and metastasis using immunodeficient mice; this model is valuable for experiments that test the role of metastasis-associated genes and the efficacy of novel forms of therapy.

Adhesion molecules involved in the binding of murine myeloma cells to bone marrow stromal elements

In previous work, we reported the development of the B9/BMI syngeneic murine bone marrow metastasis model. Interleukin (IL)-6-dependent, IL-I-producing B9/BMI cells, which preferentially home to and colonise the vertebral and femoral marrow after i.v. injection, exhibit striking similarity in cell surface phenotype to human myeloma cells, especially the expression of 3 adhesion molecules, CD44, VLA-4 and ICAM-I. Because the haematopoietic microenvironment consists of different cell types, such as endothelial cells, fibroblasts, adipocytes and macrophages, we investigated the functional significance of these adhesion molecules in heterotypic binding assays between B9/BMI cells and a newly established bone marrow-derived endothelial cell line (BMEC), a fibroblastoid pre-adipocyte cell line (BMS2.2) and primary bone marrow-derived macrophages. B9/BMI cells adhered well to all stromal elements: a combination of monoclonal antibodies (MAbs) against CD44 and VLA-4 significantly inhibited the adherence of B9/BMI cells to BMEC and BMS2.2 cells, whereas binding of B9/BMI cells to macrophages was partially blocked with an anti-ICAM-I MAb. Our results implicate multiple recognition mechanisms, including those involving CD44, VLA-4 and ICAM-I, in the retention of B9/BMI cells in the bone marrow.