Bisphosphonates inhibit the adhesion of breast cancer cells to bone matrices in vitro.

Bisphosphonates are used with increasing frequency in the management of skeletal complications in patients with breast cancer. In this paper, we have investigated whether bisphosphonates, besides their known beneficial effects on tumor-associated osteoclastic resorption, are capable of inhibiting breast cancer cell adhesion to bone matrix. For that we used two in vitro models for bone matrix (cortical bone slices and cryostat sections of trabecular bone from neonatal mouse tails). Four bone matrix-bound nitrogen-containing bisphosphonates (pamidronate, olpadronate, alendronate, and ibandronate) inhibited adhesion and spreading of breast cancer cells to bone dose-dependently, whereas etidronate and clodronate had little or no effect. Strikingly, the relative order of potency of the bisphosphonates in inhibiting the adhesion of cancer cells to cortical and trabecular bone corresponded to their relative antiresorptive potencies in vivo as well as their ranking in in vitro bone resorption assays with predictive value for their clinical efficacy. It appears that nitrogen-containing bisphosphonates alter selectively the adhesive properties of the extracellular bone matrix preventing the attachment of breast cancer cells to it. Besides the beneficial effects of bisphosphonates on tumor-induced osteoclastic resorption, the previously unrecognized effect presented in this paper makes these agents suitable for earlier pharmacologic intervention in patients with breast cancer at risk of developing bone metastases.

A zebrafish xenograft model for studying human cancer stem cells in distant metastasis and therapy response.

Lethal and incurable bone metastasis is one of the main causes of death in multiple types of cancer. A small subpopulation of cancer stem/progenitor-like cells (CSCs), also known as tumor-initiating cells from heterogenetic cancer is considered to mediate bone metastasis. Although over the past decades numerous studies have been performed in different types of cancer, it is still difficult to track small numbers of CSCs during the onset of metastasis. With use of noninvasive high-resolution imaging, transparent zebrafish embryos can be employed to dynamically visualize cancer progression and reciprocal interaction with stroma in a living organism. Recently we established a zebrafish CSC-xenograft model to visually and functionally analyze the role of CSCs and their interactions with the microenvironment at the onset of metastasis. Given the highly conserved human and zebrafish genome, transplanted human cancer cells are able to respond to zebrafish cytokines, modulate the zebrafish microenvironment, and take advantage of the zebrafish stroma during cancer progression. This chapter delineates the zebrafish CSC-xenograft model as a useful tool for both CSC biological study and anticancer drug screening.

CRIPTO and its signaling partner GRP78 drive the metastatic phenotype in human osteotropic prostate cancer.

CRIPTO (CR-1, TDGF1) is a cell surface/secreted oncoprotein actively involved in development and cancer. Here, we report that high expression of CRIPTO correlates with poor survival in stratified risk groups of prostate cancer (PCa) patients. CRIPTO and its signaling partner glucose-regulated protein 78 (GRP78) are highly expressed in PCa metastases and display higher levels in the metastatic ALDHhigh sub-population of PC-3M-Pro4Luc2 PCa cells compared with non-metastatic ALDHlow. Coculture of the osteotropic PC-3M-Pro4Luc2 PCa cells with differentiated primary human osteoblasts induced CRIPTO and GRP78 expression in cancer cells and increases the size of the ALDHhigh sub-population. Additionally, CRIPTO or GRP78 knockdown decreases proliferation, migration, clonogenicity and the size of the metastasis-initiating ALDHhigh sub-population. CRIPTO knockdown reduces the invasion of PC-3M-Pro4Luc2 cells in zebrafish and inhibits bone metastasis in a preclinical mouse model. These results highlight a functional role for CRIPTO and GRP78 in PCa metastasis and suggest that targeting CRIPTO/GRP78 signaling may have significant therapeutic potential.

Bone sialoprotein peptides are potent inhibitors of breast cancer cell adhesion to bone.

Bone and bone marrow are important sites of metastasis formation in breast cancer. Extracellular matrix proteins with attachment properties are generally believed to play a key role in tumorigenesis and metastasis formation. We have investigated whether mammary carcinoma cells (MDA-MB-231) can recognize constructs of the fairly bone-specific human bone sialoprotein, which encompass the RGD sequence (EPRGD-NYR). Exogenously added bone sialoprotein peptides with this amino acid sequence in their backbone structure, but not the more common fibronectin-derived GRGDS peptide, strongly inhibited breast cancer cell adhesion to extracellular bone matrix at micromolar concentrations. Most cyclic derivatives with the EPRGDNYR sequence were more effective inhibitors of tumor cell adhesion to bone than their linear equivalents. Furthermore, changes in the RGD-tripeptide of the backbone structure of the constructs, removal of the NYR flanking sequence, or a different tertiary cyclic structure significantly decreased their inhibitory potencies. In addition, the RGE-analogue EPRGENYR was capable of inhibiting breast cancer cell adhesion to bone, albeit to a lesser extent. We conclude therefore, that the inhibitory potency of the bone sialoprotein-derived peptides on breast cancer cell adhesion to bone is not solely due to a properly positioned RGD-motif alone but is also determined by its flanking regions, together with the tertiary structure of the EPRGDNYR peptide. Synthetic cyclic constructs with the EPRGDNYR sequence may, therefore, be potentially useful as antiadhesive agents for cancer cells to bone in vivo.

miR-25 Modulates Invasiveness and Dissemination of Human Prostate Cancer Cells via Regulation of αv- and α6-Integrin Expression.

Altered microRNA (miRNA; miR) expression is associated with tumor formation and progression of various solid cancers. A major challenge in miRNA expression profiling of bulk tumors is represented by the heterogeneity of the subpopulations of cells that constitute the organ, as well as the tumor tissue. Here, we analyzed the expression of miRNAs in a subpopulation of epithelial stem/progenitor-like cells in human prostate cancer [prostate cancer stem cell (PCSC)] and compared their expression profile to more differentiated cancer cells. In both cell lines and clinical prostate cancer specimens, we identified that miR-25 expression in PCSCs was low/absent and steadily increased during their differentiation into cells with a luminal epithelial phenotype. Functional studies revealed that overexpression of miR-25 in prostate cancer cell lines and selected subpopulation of highly metastatic and tumorigenic cells (ALDH(high)) strongly affected the invasive cytoskeleton, causing reduced migration in vitro and metastasis via attenuation of extravasation in vivo. Here, we show, for the first time, that miR-25 can act as a tumor suppressor in highly metastatic PCSCs by direct functional interaction with the 3'-untranslated regions of proinvasive αv- and α6-integrins. Taken together, our observations suggest that miR-25 is a key regulator of invasiveness in human prostate cancer through its direct interactions with αv- and α6-integrin expression.

The role of geranylgeranylation in bone resorption and its suppression by bisphosphonates in fetal bone explants in vitro: A clue to the mechanism of action of nitrogen-containing bisphosphonates.

Bisphosphonates, synthetic compounds used in the treatment of skeletal disorders, suppress osteoclast-mediated bone resorption by a yet unidentified mechanism. Previous studies showed that some bisphosphonates can inhibit enzymes of the mevalonate pathway, and nitrogen-containing bisphosphonates inhibit protein prenylation in mouse macrophages. In the present study, we examined the involvement of the mevalonate pathway in basal and bisphosphonate-inhibited osteoclastic resorption in fetal mouse long bone explants, an experimental model representative of the in vivo action of bisphosphonates. Mevastatin inhibited bone resorption at concentrations similar to those of the potent bisphosphonate ibandronate. This effect could be totally reversed by the addition of mevalnate and geranylgeraniol but not farnesol. The first two intermediates but not the latter could also stimulate basal bone resorption. The inhibitory effect of ibandronate on bone resorption could be totally reversed by the addition of geranylgeraniol and to a small extent only by mevalonate and farnesol, indicating that the bisphosphonate acts at a level of the mevalonate pathway different from that of mevastatin. Histologic sections of ibandronate-treated bone explants showed further rescue of functioning osteoclasts during concomitant treatment with geranylgeraniol. Finally, the reversibility of bisphosphonate inhibited osteoclastic resorption by geranylgeraniol was also demonstrated for the potent nitrogen-containing bisphosphonates alendronate, olpadronate, and risedronate but not for the non-nitrogen-containing bisphosphonates clodronate and etidronate. These studies demonstrate that protein geranylgeranylation but not farnesylation is important for osteoclast-mediated bone resorption and that nitrogen-containing bisphosphonates exert their antiresorptive action probably by affecting enzymes of the mevalonate pathway involved in the generation of geranylgeranyl pyrophosphate.

Integrins and osteoclastic resorption in three bone organ cultures: differential sensitivity to synthetic Arg-Gly-Asp peptides during osteoclast formation.

We investigated possible inhibitory effects of five synthetic Arg-Gly-Asp (RGD)-containing peptides on osteoclastic resorption in three distinct in vitro resorption assays (17-day-old fetal mouse bone organ cultures) that differ in stages of osteoclast differentiation. RGD peptides, which can bind the adhesion receptors called integrins, inhibited osteoclastic resorption (45Ca release) in fetal mouse bone explants in which osteoclast precursors have yet to adhere to the mineralized matrix and develop into mature osteoclasts (metacarpals and coculture system). Treatment of metacarpals with RGD peptides inhibited the formation of multinucleated TRAP+ osteoclasts in the mineralized matrix because their mononuclear TRAP+ osteoclast precursors remained localized in the periosteum. In particular, echistatin, a viper venom protein with known affinity for alpha v beta 3 integrin, and GdRGDSP inhibited osteoclastic resorption dose dependently in these systems (ED50 10(-9) and 10(-4) M, respectively) but did not alter the activity of mature resorbing osteoclasts in radii. In addition, 45Ca release was significantly inhibited by the cyclic peptide GPenGRGDSPCA, which has a relatively higher affinity for the vitronectin than fibronectin receptor(s). In contrast, GRDGdSP, which has a much higher affinity for the fibronectin receptor (than the vitronectin receptors), had no effect on resorption at similar concentrations in any resorption system used. In summary, the data presented in this paper show that peptides with RGD motifs are capable of inhibiting osteoclastic resorption in bone organ cultures. Our studies not only support the hypothesis concerning the importance of alpha v beta 3 in osteoclastic resorption but also suggest an important role of integrin(s) in events preceding the actual resorption of calcified matrix by osteoclasts.

Monitoring metastatic behavior of human tumor cells in mice with species-specific polymerase chain reaction: elevated expression of angiogenesis and bone resorption stimulators by breast cancer in bone metastases.

Tumor-stroma interactions are of primary importance in determining the pathogenesis of metastasis. Here, we describe the application of sensitive competitive polymerase chain reaction (PCR) techniques for detection and quantitation of human breast cancer cells (MDA-MB-231) in an in vivo mouse model of experimental metastasis. Human-specific oligonucleotide primers in competitive PCR reactions were used to quantify the amount of MDA-MB-231 cells per tissue per organ. Using this species-specific (semi)quantitative PCR approach, gene expression patterns of (human) tumor cells or (mouse) stromal cells in metastatic lesions in the skeleton or soft tissues were investigated and compared. In all metastatic lesions, MDA-MB-231 cells express angiogenic factors (vascular endothelial growth factors [VEGFs]; VEGF-A, -B, and -C) and bone-acting cytokines (parathyroid hormone-related protein [PTHrP] and macrophage colony-stimulating factor [M-CSF]). In these metastases, PECAM-1-positive blood vessels and stromal cells of mouse origin are detected. The latter express angiogenic factors and markers of sprouting vessels (VEGF receptors flt-1/flk - 1/flk-4 and CD31/PECAM-1). Strikingly, steady-state messenger RNA (mRNA) levels of VEGF-A and -B and the major bone resorption stimulators PTHrP and M-CSF by tumor cells were elevated significantly in bone versus soft tissues (p < or = 0.05, p < or = 0.0001, p < or = 0.001, and p < or = 0.05, respectively), indicating tissue-specific expression of these tumor progression factors. In conclusion, MDA-MB-231 breast cancer cells express a variety of factors in vivo that have been implicated in metastatic bone disease and that correlate with poor survival of patients with breast cancer. We hypothesize that the observed up-regulated expression of angiogenic and bone-resorbing factors by the breast cancer cells in the skeleton underlie the clinically observed osteotropism of breast cancer cells and pathogenesis of osteolytic bone metastases. The application of the species-specific competitive PCR-based assay in vivo can provide new information concerning the involvement of gene families in tumor progression and metastatic disease and greatly facilitates the study of tumor-stroma interactions in cancer invasion and metastasis.

Migration and phenotypic transformation of osteoclast precursors into mature osteoclasts: the effect of a bisphosphonate.

Osteoclast-devoid bone explants were cultured together with embryonic liver as a source of osteoclast precursors, but separated from each other by a filter. Cells migrated through the filter toward the calcified matrix and acquired the characteristics of mature, tartrate-resistant acid phosphatase-positive (TRAP+) osteoclasts upon contact with the bone explant. Migration and attachment could be visualized separately. Progressive reduction of filter pore size resulted in progressive reduction of resorption because the use of smaller pores made it increasingly difficult for cells to pass. Indeed, the use of 0.22-micron filters, through which no cells can pass, but which still allow full passage of medium, completely blocked the resorption. When migrating cells from fetal liver were arrested for 10 days by using a combination of filters with different pore sizes, the arrested cells showed a tendency to fuse just opposite the mineralized matrix. Furthermore, a great number of the arrested cells expressed the macrophage-specific cell-surface antigen F4/80 and showed acid phosphatase activity, but none of these cells were tartrate resistant. The acquisition of tartrate-resistant acid phosphatase activity upon contact with the bone explant and subsequent resorption of this explant could be prevented by exposure of the system to the bisphosphonate dimethyl-APD (Me2-APD), whereas migration of cells through the filter was not affected. We suggest that the bisphosphonate interferes with a matrix factor that is essential for the attachment and subsequent transformation of the osteoclast precursor into the mature phenotype.

Interleukin-6 and the acute phase response during treatment of patients with Paget's disease with the nitrogen-containing bisphosphonate dimethylaminohydroxypropylidene bisphosphonate.

Bisphosphonates suppress bone resorption and are used in the management of bone diseases with increasing frequency. In some patients treated for the first time with potent nitrogen-containing bisphosphonates, there is a transient febrile reaction and transient hematological changes suggestive of an acute phase response. Because IL-6 is considered to be an important mediator of the acute phase response, we examined the changes in circulating IL-6 bioactivity in 38 patients with Paget's disease treated with the nitrogen-containing bisphosphonate (3-dimethyl-amino-1-hydroxypropylidene)-1,1-bisphosphonate (dimethyl-APD). 16 patients who had never received such bisphosphonate were treated with oral dimethyl-APD (100-400 mg/day) and 22 (9 for the first time) with intravenous dimethyl-APD 4 mg/day. Treatment was given for 10 days. Eleven of 38 patients, all first treatments, showed an increase in body temperature of more than 0.5 degrees C exceeding 37 degrees C associated with a significant decrease in lymphocyte count and an increase in serum CRP values. These changes were transient and did not occur in the patients with no febrile response. In patients with a febrile reaction circulating IL-6 bioactivity increased significantly and this increase generally preceeded the rise in temperature. Moreover, patients with an acute phase response had significantly higher peak IL-6 values than those without (128 +/- 30 vs. 31 +/- 4 U/ml, p < 0.001). The peaks in plasma IL-6 were further correlated with the peaks in temperature and in serum CRP values (r = 0.49, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Disodium 1-hydroxy-3-(1-pyrrolidinyl)-propylidene-1,1-bisphosphonate (EB-1053) is a potent inhibitor of bone resorption in vitro and in vivo.

The ability of the new nitrogen-containing bisphosphonate disodium-1-hydroxy-3-(1-pyrrolidinyl)-propylidene-1,1-bisphosphona te (EB-1053) to inhibit osteoclastic resorption was examined in vitro and in vivo. Results were compared to those obtained with 3-amino-1-hydroxypropylidene-1,1-bisphosphonate (pamidronate or APD). In vitro, when tested in osteoclast precursor-dependent systems (fetal mouse metacarpals and a coculture system), EB-1053 suppressed 45Ca release effectively and was found to be about 10 times more potent than pamidronate (ED50 = 2.5 x 10(-7) versus 2.5 x 10(-6) M, respectively). The EB-1053-inhibited osteoclastic resorption could be reversed by treatment with parathyroid hormone (PTH). In vivo, daily subcutaneous injections of EB-1053 to young growing rats for 7 days increased metaphyseal bone mass in tibiae dose dependently. In these experiments EB-1053 was about 50 times more potent than pamidronate. These studies show that EB-1053 is a very potent bisphosphonate that has potential use in the treatment of skeletal disorders.

Modulation of PTH-stimulated osteoclastic resorption by bisphosphonates in fetal mouse bone explants.

We examined the effects of the bisphosphonates Cl2MDP, APD, and Me2APD on osteoclastic resorption in the absence and presence of PTH using fetal mouse osteoclast-free bone explants cocultured with fetal liver as a source of osteoclast precursors. Results revealed qualitative and quantitative differences among the bisphosphonates tested. With Cl2MDP and APD fractional inhibition of resorption (measured as 45Ca release) in the presence of PTH was proportional to that obtained in its absence. In contrast, Me2APD, which is the most potent inhibitor of the three, was found at low concentrations (less than or equal to 5 x 10(-7) M) to enhance the PTH-stimulated osteoclastic resorption. APD as well, at concentrations that could not inhibit resorption, had a similar effect, but Cl2MDP did not. These studies describe a new phenomenon, that low doses of nitrogen-containing bisphosphonates can act synergistically with PTH and enhance osteoclastic resorption. These findings may have clinical implications in the management of patients with increased osteoclastic resorption due to parathyroid overactivity.

Structure and molecular regulation of bone matrix proteins.

The organic matrix of bone contains several protein families, including collagens, proteoglycans, and glycoproteins, all of which may be extensively modified by posttranslational events, such as phosphorylation and sulfation. Many of the glycoproteins contain Arg-Gly-Asp (RGD), the integrin-binding sequence, within their structure, whereas other constituent proteins contain gamma-carboxyglutamic acid. The deposition of bone matrix by cells in the osteoblastic lineage is regulated by extrinsic factors, such as systemic and local growth factors and physical forces, and factors that are intrinsic to the cell, such as position in the cell cycle, maturational stage, and developmental age of the donor. Recent studies of several bone matrix gene promoters have identified cis- and trans-acting elements that are responsible for gene activity, although the precise sequence of regulatory events is not known. Development of in vitro assays, coupled with studies of the appearance of these proteins during development in vivo, provides insight into the functions of these proteins during the various stages of bone metabolism. Potential roles for these proteins include proliferation and maturation of stem cells, formation of matrix scaffolding elaborated by bone-forming cells, modeling, and remodeling. Changes in the functional properties of the extracellular matrix may be involved in a variety of disease processes, including osteoporosis and oral bone loss.

Two distinct effects of recombinant human tumor necrosis factor-alpha on osteoclast development and subsequent resorption of mineralized matrix.

The multifunctional cytokine tumor necrosis factor-alpha (TNF alpha) stimulates osteoclastic resorption. It is not known which steps in osteoclast formation are affected by TNF alpha. We have investigated the effects of recombinant human TNF alpha (rhTNF alpha) on osteoclast development and osteoclastic resorption in two different in vitro resorption systems which are each characterized by a different stage of development of the osteoclast. The effects were further compared to those of bovine PTH-(1-84). rhTNF alpha at concentrations between 0.01-50 ng/ml (3 x 10(-13) to 1.5 x 10(-9) M) did not alter the activity of mature osteoclasts, measured as 45Ca release in fetal mouse radii. In the osteoclast precursor-dependent system (fetal mouse metacarpals) rhTNF alpha had a biphasic effect. It stimulated resorption dose-dependently from 0.01 ng/ml onward, with a maximal response at 0.5 ng/ml. At concentrations above 10 ng/ml rhTNF alpha, resorption was inhibited. In experiments in which irradiation was used to block replication, it was found that TNF alpha stimulates the proliferation of osteoclast progenitors at both low and high concentrations. As a result, at relatively low concentrations, more osteoclasts were formed in the calcified matrix, coinciding with an increased release of 45Ca. However, at relatively high concentrations, the increase in osteoclast progenitors did not lead to increased resorption, since the putative osteoclast progenitors were arrested in the periosteum. In comparison, bovine PTH-(1-84) stimulated resorption independent of proliferation by enhancing the differentiation of postmitotic osteoclast precursors and activating mature osteoclasts. In conclusion, the effects of TNF alpha on osteoclastic resorption are dependent on the stage of osteoclast development and the concentrations applied.

Effect of macrophage colony-stimulating factor on in vitro osteoclast generation and bone resorption.

To investigate the role of recombinant human macrophage colony-stimulating factor (rhM-CSF) on in vitro bone resorption, two bone explants, each at a different developmental stage, were adopted, namely 1) radii and 2) metatarsals of 17-day-old embryonic mice. At this stage of gestation, bone resorption in the radii is exclusively dependent upon fusion of osteoclast precursors and activation of mature osteoclasts, whereas in metatarsals it is dependent upon the generation of new osteoclasts. rhM-CSF showed no effect in radii, but stimulated 45Ca release in metatarsals, when they were either intact or periosteum stripped in coculture with embryonal liver as a source of hemopoietic progenitors. The rhM-CSF-induced increase in 45Ca release was paralleled by a higher number of osteoclasts. The stimulating effect was found to be in a concentration range between 250-500 U/ml M-CSF. The action of rhM-CSF was blocked by irradiation, indicating that it is dependent upon cell proliferation. These results, thus, show that M-CSF stimulates bone resorption only when it is dependent on generation of new osteoclasts. M-CSF does not appear to have any effect on the activity of mature osteoclasts. The mechanism of action might be direct on osteoclast precursors or indirect on accessory cells influencing osteoclast generation.

Beneficial effects of retinoic acid on extracellular matrix degradation and attachment behaviour in follicular thyroid carcinoma cell lines.

The prognosis of patients with metastasised follicular thyroid carcinoma (FTC) is limited, necessitating the search for new treatment options. Beneficial effects of retinoids have been suggested in thyroid cancer and the present study was performed to investigate the effects of retinoic acid (RA) on important determinants of metastatic behaviour in FTC: the disengagement of tumour cells from the primary tumour and the degradation of extracellular matrix, focusing on the role of the plasmin activation system and the integrin and E-cadherin families of attachment molecules. Three FTC cell lines were studied: FTC-133, derived from the primary tumour; and FTC-236 and FTC-238, derived from metastases. FTC cell lines were cultured with 0.1, 1 and 10 microM 13-cis-RA or with the solvent DMSO for 1 and 5 days. Extracellular matrix degradation by these cell lines was studied by assessing the 48-h release of radioactivity from (35)S-methionine labelled extracellular matrix proteins synthesised by the MC3T3 cell line coated onto plastic. The involvement of constituents of the plasmin activation system was investigated by semi-quantitative RT-PCR and zymography. Attachment to extracellular matrix was studied by determining the number of adhering FTC cells to extracellular matrix coated onto plastic, 3 h after seeding. The involvement of attachment molecules was studied by RT-PCR with primers for integrin subclasses and E-cadherin and immunofluorescence for E-cadherin. Five days culturing with 10 microM RA reduced the degradation of extracellular matrix significantly in all cell lines: FTC-133 by 35%, FTC-236 by 74% and FTC-238 by 31%. Zymography revealed diminished activity of urokinase type plasminogen activator (uPA) in FTC-236 and FTC-238, but not in FTC-133 cultured with RA. mRNA expression of the uPA receptor was diminished in FTC-236. In the attachment assay, 10 microM RA for 5 days increased the number of adherent cells to extracellular matrix significantly by 91% in FTC-133, 64% in FTC-236 and 87% in FTC-238. No effects of RA on integrin or E-cadherin mRNA expression were observed. Immunofluorescence, however, revealed enhanced organisation of E-cadherin along the cell membrane by RA treatment. In conclusion, the present study demonstrates beneficial effects of RA on important determinants of metastatic behaviour in FTC cell lines, e.g. decreased degradation of extracellular matrix which may in part be explained by effects on the plasmin activation system and enhanced attachment to extracellular matrix. These findings may add to the explanations for beneficial effects of retinoids in thyroid cancer.

Role of integrins in the attachment of metastatic follicular thyroid carcinoma cell lines to bone.

One of the principle targets for metastasis of follicular thyroid carcinoma (FTC) is the skeleton. Because no data are available on the role of the integrin adhesion molecule family in the attachment of FTC to bone, we studied the attachment characteristics of three FTC cell lines to bone and the role of integrins. Three cell lines were used from the same patient, one (FTC-133) from the primary tumor and two (FTC-236 and FTC-238) from metastases. Attachment of FTC cell lines to bone was assessed on conditioned medium of an osteoblastic cell line, coated onto plastic, as an in vitro model of bone matrix. The synthetic RGD (Arg-Gly-Asp) peptide GRGDS impaired attachment of the FTC cell lines to bone matrix, demonstrating the role of integrins in the attachment of FTC to bone. Attachment of FTC-133 to bone matrix was blocked completely by GRGDS, whereas attachment of FTC-236 and FTC-238 could not be impaired completely. Semiquantitative polymerase chain reaction (PCR) of cDNA from the cell lines indicated stronger expression of alpha5 integrin mRNA in FTC-133 than in the other cell lines. In line with this, attachment of FTC-133 to bone matrix could be inhibited almost completely by anti alpha5 and beta1 integrin antibodies, indicating the importance of the fibronectin receptor in the attachment of FTC-133 to bone. Binding of FTC-236 and FTC-238 to bone matrix could not be inhibited completely by anti-integrin antibodies, suggesting an additional role of nonintegrin adhesion molecules in the attachment of FTC-236 and FTC-238 to bone. The synthetic bone sialoprotein cyclic peptide, CNB, revealed antiadhesive effects in the binding of FTC to bone. In conclusion, integrins play an important role in the attachment of metastatic FTC to bone. Differences in the functional involvement of integrins in the attachment to bone are observed between the three cell lines studied. From the present results, antiadhesive interventions with synthetic RGD peptides in FTC may be designed.

Degradation of extracellular matrix by metastatic follicular thyroid carcinoma cell lines: role of the plasmin activation system.

The plasmin activation system plays a key role in extracellular matrix degradation in many malignant tumors. Because no data are available on the involvement of the plasmin activation system in matrix degradation by thyroid carcinoma, the present study was performed using follicular thyroid carcinoma cell lines obtained from a primary tumor (FTC-133) and metastases (FTC-236 and FTC-238) of one patient. Matrix degradation by these cell lines was studied assessing the release of radioactivity from S35-methionine labeled extracellular matrix coated onto plastic. The involvement of constituents of the plasmin activation system as well as matrix metalloproteinases (MMPs), another class of proteolytic enzymes, which can be activated by plasmin, were assessed by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and zymography. In the matrix degradation experiment, S35 release by FTC-133 was significantly higher than FTC-236 and FTC-238. S35 degradation could be inhibited by the plasmin inhibitor aprotinin and by anti-human urokinase-type plasminogen activator (uPA) antibody, indicating the involvement of the plasmin activation system. Matrix degradation could also be inhibited by the MMP inhibitor marimastat, thus demonstrating the involvement of MMPs in matrix degradation by these cell lines. Zymographic assays revealed activity of uPA in all cell lines. However, in contrast with FTC-236 and FTC-238, no plasminogen activator inhibitor (PAI) or PAI1 mRNA were found in FTC-133. Therefore, the differences in PAI activity as observed between the cell lines may originate from differences in PAI1 gene transcription. Differences in PAI1 expression did not affect the attachment of these cell lines to vitronectin. We conclude that the plasmin activation system is involved in extracellular matrix degradation by these metastatic follicular thyroid carcinoma cell lines. Differences in extracellular matrix degradation between the cell lines correspond with differences in PAI1 gene expression, indicating the significance of PAI1 in extracellular matrix degradation by metastatic follicular thyroid carcinoma.

Reestablishment of in vitro and in vivo iodide uptake by transfection of the human sodium iodide symporter (hNIS) in a hNIS defective human thyroid carcinoma cell line.

Uptake of iodide is a prerequisite for radioiodine therapy in thyroid cancer. However, loss of iodide uptake is frequently observed in metastasized thyroid cancer, which may be explained by diminished expression of the human sodium iodide symporter (hNIS). Strategies to restore iodide uptake in thyroid cancer include the exploration of hNIS gene transfer into hNIS defective thyroid cancer. In this study, we report the stable transfection of a hNIS expression vector into the hNIS defective follicular thyroid carcinoma cell line FTC133. Stablely transfected colonies exhibited high uptake of Na125I, which could be blocked completely with sodiumperchlorate. hNIS mRNA expression corresponded with iodide uptake in semiquantitative polymerase chain reaction. Iodide uptake was maximal after 60 minutes, whereas iodide efflux was complete after 120 minutes. hNIS transfected FTC133 and control cell lines injected subcutaneously in nude mice formed tumors after 6 weeks. Iodide uptake in the hNIS transfected tumor was much higher than in the nontransfected tumor, which corresponded with hNIS mRNA expression in tumors.

The BMP2/7 heterodimer inhibits the human breast cancer stem cell subpopulation and bone metastases formation.

Accumulating evidence suggests that a subpopulation of breast cancer cells, referred to as cancer stem cells (CSCs), have the ability to propagate a tumor and potentially seed new metastases. Furthermore, stimulation of an epithelial-to-mesenchymal transition by factors like transforming growth factor-ß (TGFß) is accompanied with the generation of breast CSCs. Previous observations indicated that bone morphogenetic protein-7 (BMP7) antagonizes the protumorigenic and prometastatic actions of TGFß, but whether BMP7 action is mechanistically linked to breast CSCs has remained elusive. Here, we have studied the effects of BMP7, BMP2 and a BMP2/7 heterodimer on the formation of human breast CSCs (ALDH(hi)/CD44(hi)/CD24(-/low)) and bone metastases formation in a preclinical model of intra-cardiac injection of MDA-MB-231 cells in athymic nude (Balb/c nu/nu) mice. The BMP2/7 heterodimer was the most efficient stimulator of BMP signaling and very effectively reduced TGFß-driven Smad signaling and cancer cell invasiveness. The tested BMPs-particularly the heterodimeric BMP2/7-strongly reduced the size of the ALDH(hi)/CD44(hi)/CD24(-/low) CSC subpopulation. In keeping with these in vitro observations, pretreatment of cancer cells with BMPs for 72 h prior to systemic inoculation of the cancer cells inhibited the formation of bone metastases. Collectively, our data support the notion that breast CSCs are involved in bone metastasis formation and describe heterodimeric BMP2/7 as a powerful TGFß antagonist with anti-metastatic potency.