Expression and localization of osteopontin, homing cell adhesion molecule/CD44, and integrin αvβ3 in pleomorphic adenoma, polymorphous low-grade adenocarcinoma, and adenoid cystic carcinoma

OBJECTIVES

Osteopontin (OPN) plays a role in tumor progression. This study aimed to determine the expression of OPN, CD44, and integrin αvβ3 in pleomorphic adenoma (PA), polymorphous low-grade adenocarcinoma (PLGA), and adenoid cystic carcinoma (ACC).

STUDY DESIGN

Immunohistochemistry was used to semiquantify the level of expression of OPN and its receptors in normal salivary glands (NSG; n = 20), PA (n = 20), PLGA (n = 16), and ACC (n = 22).

RESULTS

OPN expression was increased in PLGA and intermediate-/high-grade ACC compared with PA and NSG (median scores, 6, 5, 4, and 4, respectively). CD44 expression was reduced in PA, PLGA, and ACC. OPN expression levels were moderately correlated with CD44 in PLGA. Integrin αvβ3 was not expressed in PA and ACC and was seen in only 1 case of PLGA.

CONCLUSIONS

OPN is expressed in salivary gland tumors but does not correlate well with CD44 and αvβ3.

Expression and localization of osteopontin, homing cell adhesion molecule/CD44, and integrin αvβ3 in mucoepidermoid carcinoma and acinic cell adenocarcinoma of salivary gland origin

OBJECTIVE

Osteopontin (OPN) plays a role in tumor progression. This study aimed to determine the expression of OPN, CD44, and integrin αvβ3 in pleomorphic adenoma (PA), acinic cell adenocarcinoma (ACA), and mucoepidermoid carcinoma (MEC).

STUDY DESIGN

Immunohistochemistry was used to semiquantify the levels of expression of OPN and its receptors in normal salivary glands (NSG) (n = 20), PA (n = 20), ACA (n = 11), and MEC (n = 29).

RESULTS

OPN expression was increased in ACA and MEC compared with PA and NSG (median scores, 6, 6, 4, and 4, respectively). CD44 expression was increased in ACA and reduced in MEC and PA compared with NSG (median scores, 8, 4, 3, and 5, respectively). Integrin αvβ3 median scores were 5 in ACA, 1 in MEC, and 0 in PA and NSG.

CONCLUSIONS

OPN is expressed in salivary gland tumors and is at higher levels in ACA and MEC.

Abstract ES7-2: Tumor Dormancy from an Experimental Biologist's Perspective

Survival from breast cancer has improved steadily over the past decades. However, most breast cancer deaths are due to metastasis, and considerably less progress has been made against metastatic disease. We still know remarkably little about preventing or delaying metastatic recurrence or effectively treating the cancer if it does recur. Making breast cancer treatment even more challenging is the fact that breast cancer patients may appear to be cured of their disease, only to have it return later. These recurrences can happen even decades after apparently successful primary treatment. This creates years of uncertainty for breast cancer patients, who do not know if they have been cured or if the cancer will return, and makes clinical management difficult.

We have used experimental models, both in vitro and in vivo, to try to understand the process of breast cancer metastasis. We have found that a population of cancer cells can remain as dormant cells, and have shown that these cells can resist being killed by cytotoxic chemotherapy that successfully kills actively diving cells. Experimental studies raise questions that must be addressed clinically. For example, what is the prevalence of dormant cells in breast cancer patients – are they common or rare? Are there factors inherent to the cancer cells that influence the likelihood of dormant cells persisting and subsequently re-awakening? Conversely, are there host microenvironmental factors, such as diet, exercise or stress, that can influence whether dormant cells persist and re-awaken? This information will be important in learning better how to prevent, delay and treat metastatic breast cancer.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr ES7-2.

Plasma osteopontin as a biomarker of prostate cancer aggression: relationship to risk category and treatment response

BACKGROUND

High plasma osteopontin (OPN) has been linked to tumour hypoxia, metastasis, and poor prognosis. This study aims to assess whether plasma osteopontin was a biomarker of increasing progression within prostate cancer (PCa) prognostic groups and whether it reflected treatment response to local and systemic therapies.

METHODS

Baseline OPN was determined in men with localised (n=199), locally recurrent (n=9) and castrate-resistant, metastatic PCa (CRPC-MET; n=37). Receiver-operating curves (ROC) were generated to describe the accuracy of OPN for distinguishing between localised risk groups or localised vs metastatic disease. We also measured OPN pre- and posttreatment, following radical prostatectomy, external beam radiotherapy (EBRT), androgen deprivation (AD) or taxane-based chemotherapy.

RESULTS

The CRPC-MET patients had increased baseline values (mean 219; 56-513 ng ml(-1); P<0.0001) compared with the localised, non-metastatic group (mean 72; 12-438 ng ml(-1)). The area under the ROC to differentiate localised vs metastatic disease was improved when OPN was added to prostate-specific antigen (PSA) (0.943-0.969). Osteopontin neither distinguished high-risk PCa from other localised PCa nor correlated with serum PSA at baseline. Osteopontin levels reduced in low-risk patients after radical prostatectomy (P=0.005) and in CRPC-MET patients after chemotherapy (P=0.027), but not after EBRT or AD.

CONCLUSION

Plasma OPN is as good as PSA at predicting treatment response in CRPC-MET patients after chemotherapy. Our data do not support the use of plasma OPN as a biomarker of increasing tumour burden within localised PCa.

P2-12-28: Studies of a Malignancy-Associated Protein, Osteopontin, in NCIC CTG MA.14, a Randomized Trial of Tamoxifen Versus Combined Tamoxifen and Octreotide LAR in Adjuvant Treatment of Women with Early Breast Cancer

Background

We have shown, in women with metastatic breast cancer (BC), that high baseline plasma osteopontin (OPN) levels and increases over time are associated with poor survival. In primary BC, increased immunohistochemical (IHC) expression of OPN in tumour is associated with poorer survival and is elevated in lymph node metastases relative to primary tumour. Our current study evaluates tumour and baseline/serial plasma OPN levels after resection of primary BC.

Methods: In NCIC CTG MA.14, 667 postmenopausal women post surgery received 5 yrs Tamoxifen (T) +/− 2 yrs monthly Octreotide LAR. There were no differences in survival outcomes between arms. OPN was assayed by IHC in primary BC. OPN was measured in plasma at baseline (up to 4 mos post randomization) and serially in recurrent (18 mos time window) versus non-recurrent cases, by ELISA. Statistical Analysis: IHC and plasma OPN had Box-Cox variance stabilization transformations (power 0.5; logarithm). Descriptive characterization of both OPN measurements is provided for all patients, by baseline patient and tumour characteristics, and by recurrence status. Univariate stratified log-rank statistics and hazard ratios with 95% CI were generated for intention to treat (ITT), event free survival (EFS), relapse fee survival (RFS), overall survival, any bone RFS, and non-bone RFS. Stratified step-wise forward Cox regression was used, with factor added if p&lt;0.05.

Results: From 667 MA.14 patients, 647 patients were assessed for OPN: 462 (69%) by IHC; 387 (58%) at baseline in plasma (with 2,542 samples total from serial sampling). IHC % tumor positivity had mean 33.9% (95% CI 30.2%-37.9%), while baseline plasma OPN was mean 46.1 (44.6−47.6) ng/ml. In 80 women with recurrence, mean OPN during the recurrence window was 60.7 (52.8−69.8) ng/ml. Neither baseline IHC or plasma OPN levels were significantly associated with any of the endpoints in either univariate or multivariate analyses. Older age (p=0.02), greater nodal involvement (p=0.001), higher baseline body mass index (p&lt;0.0001), and higher tumour grade (p&lt;0.0001) were multivariately associated with shorter EFS. Baseline plasma OPN was not correlated with IHC OPN (Pearson 0.02, p=0.73).

Discussion: Mean baseline OPN plasma level 46.1 ng/ml (median 45 ng/ml) in MA.14 was similar to our previous findings in healthy women (median 47 ng/ml). In contrast, we previously showed that 63% of 158 women with a new diagnosis of metastatic BC had elevated OPN levels with median value 177 ng/ml. Our results thus far suggest that tumor and plasma levels, while associated with prognosis in metastatic BC, may not be so in primary BC following surgery. However, in MA.14, the 80 women with recurrent BC had significantly higher mean OPN in the recurrence window, 60.7 ng/ml, than at baseline. We will present further analyses exploring this finding.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-12-28.

P3-16-11: Prospective Evaluation of Radiation Pneumonitis in Neoadjuvant Concurrent Docetaxel and Radiation Therapy for Locally Advanced Breast Cancer

Background: Taxanes are known to have radiosensitizing properties, by causing cell arrest in the G2 and M phases of the cell cycle. As taxanes have become integrated into routine oncologic use, concerns have arisen over the association between taxanes and radiation toxicities such as pneumonitis. Pneumonitis has been reported to occur both with taxane administration alone or, more commonly, with concurrent or sequential radiation. The purpose of this study is to evaluate radiation pneumonitis from our institutional phase I/II protocol of neoadjuvant FEC chemotherapy followed by weekly docetaxel concurrent with radiotherapy in the treatment of locally advanced breast cancer (LABC).

Materials and Methods: Since August 2009, thirty-two LABC patients with stage IIB, IIIA, IIIB, or IIIC invasive breast cancer were enrolled to receive protocol based treatment consisting of 3 cycles of intravenous (IV) fluorouracil 500 mg/m2, epirubicin 100 mg/m2, and cyclophosphamide 500 mg/m2 (FEC) every 3 weeks. Following this, weekly IV docetaxel 35 mg/m2 was administered concurrently with locoregional external beam radiotherapy to a total dose of 45 Gy in 25 fractions followed by a boost of 5.4-9 Gy in 3–5 fractions to gross residual disease. Adverse events were scored using the National Cancer Institute Common Terminology Criteria for Adverse Events v3.0. A linear regression model was built used to evaluate potential parameters predictive of clinical pneumonitis (grade ≥2).

Results: Of the 32 patients enrolled on this prospective protocol, 7 were excluded from analysis (n = 6, follow-up &lt; 4 weeks; n = 1, converted to palliative radiotherapy due to metastatic disease). Twenty-five patients remained for analysis. The median age was 48 years (range 26 to 64). Thirteen patients were treated with intensity modulated radiation therapy while 12 were treated using 3D conformal radiotherapy. In total 13 patients (52%) experienced clinical pneumonitis with 6 of these patients (24%) transiently requiring supportive oxygen (grade 3). On linear regression modeling, the use of IMRT (p = 0.08), grade 3 skin toxicity (p = 0.08), and baseline left ventricular ejection fraction (LVEF, p = 0.05) were potentially predictive of symptomatic pneumonitis. Conversely, various heart and lung dose-volume histogram parameters, trastuzumab use, bolus use, disease laterality, total docetaxel dose, were not predictive of symptomatic pneumonitis (p &gt; 0.10). In multivariable modeling, the use of IMRT (p = 0.05) and baseline LVEF (0 = 0.03) remained predictive of symptomatic pneumonitis.

Conclusion: The use of concurrent weekly docetaxel-based chemoradiotherapy in LABC is associated with significant symptomatic pneumonitis and may be related to low baseline LVEF and the use of IMRT. However, conventional parameters of low dose volumes of lung and heart irradiated were not predictive of pneumonitis. The relationship of the use of IMRT and taxanes in the development of pnemonitis is likely complex and warrants further investigation.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-16-11.

Osteopontin expression in salivary gland tumours

Osteopontin (OPN) is expressed in numerous carcinomas and plays a role in tumour development, invasion and metastasis. This study examines by immunohistochemistry the expression of OPN in normal salivary gland tissue and three types of salivary gland tumour: pleomorphic adenoma (PA), adenoid cystic carcinoma (ACC) and polymorphous low grade adenocarcinoma (PLGA). PAs and PLGAs demonstrated higher levels of OPN than normal salivary gland tissue, while ACC, although showing a trend towards increased OPN, was not significantly different. The results of this study indicate that OPN expression is present in normal salivary gland tissue, and is increased in certain salivary gland tumours, but further investigation is necessary to clarify its role.

Volume measurement variability in three-dimensional high-frequency ultrasound images of murine liver metastases

The identification and quantification of tumour volume measurement variability is imperative for proper study design of longitudinal non-invasive imaging of pre-clinical mouse models of cancer. Measurement variability will dictate the minimum detectable volume change, which in turn influences the scheduling of imaging sessions and the interpretation of observed changes in tumour volume. In this paper, variability is quantified for tumour volume measurements from 3D high-frequency ultrasound images of murine liver metastases. Experimental B16F1 liver metastases were analysed in different size ranges including less than 1 mm3, 1-4 mm3, 4-8 mm3 and 8-70 mm3. The intra- and inter-observer repeatability was high over a large range of tumour volumes, but the coefficients of variation (COV) varied over the volume ranges. The minimum and maximum intra-observer COV were 4% and 14% for the 1-4 mm3 and <1 mm3 tumours, respectively. For tumour volumes measured by segmenting parallel planes, the maximum inter-slice distance that maintained acceptable measurement variability increased from 100 to 600 microm as tumour volume increased. Comparison of free breathing versus ventilated animals demonstrated that respiratory motion did not significantly change the measured volume. These results enable design of more efficient imaging studies by using the measured variability to estimate the time required to observe a significant change in tumour volume.

Genomic amplification of MET with boundaries within fragile site FRA7G and upregulation of MET pathways in esophageal adenocarcinoma

Esophageal adenocarcinoma (EA) is characterized by a poor prognosis making the identification of clinically targetable proteins essential for improving patient outcome. We report the involvement of multiple alterations of the MET pathway in EA development and progression. Microarray analysis of Barrett's metaplasia, dysplasia, and EA revealed overexpression of the MET oncogene in EAs but only those with MET gene amplification. STS-amplification mapping revealed that the boundary of the MET amplicon in these EAs is defined by fragile site FRA7G. We also identified an amplicon at 11p13 that resulted in amplification and overexpression of CD44, a gene involved in MET autophosphorylation upon HGF stimulation. Tissue microarrays with phospho-MET-specific antibodies demonstrated a uniformly high abundance of MET activation in primary EA and cells metastatic to lymph nodes but to a lesser extent in a subset of metaplastic and dysplastic Barrett's samples. Increased expression of multiple genes in the MET pathway associated with invasive growth, for example, many MMPs and osteopontin, also was found in EAs. Treatment of EA-derived cell lines with geldanamycin, an inhibitor for tyrosine kinases including MET receptor kinase, reduced cell migration and induced EA cell apoptosis. The data indicate that upregulation of the MET pathway may contribute to the poor outcome of EA patients and that therapeutic agents targeting this pathway may help improve patient survival.

Role of osteopontin in tumour progression

Since its first identification as a transformation-associated protein, osteopontin (OPN) has been recognised as important in the processes of tumorigenicity and metastasis. Here, we review the evidence that OPN might be considered as a candidate prognostic marker in human cancer. In animal systems, evidence from cell injection experiments and genetically manipulated mice suggest an important but complex role for the protein in tumour progression. Moreover, studies in a variety of human cancers associate high levels of OPN expression in tumours or in blood with more advanced cancers. The mechanism of action of OPN in promoting cancer is still unclear, and we consider aspects of OPN biology that can complicate interpretation of human studies. Nevertheless, growing evidence supports a role for OPN as a potential prognostic factor for various human cancers.

Inhibition of angiogenesis in liver metastases by carboxyamidotriazole (CAI)

Carboxyamidotriazole (CAI), an inhibitor of calcium-mediated signal transduction, is a promising new cytostatic anti-cancer drug which has entered Phase II clinical trials, and for which multiple modes of action have been proposed. We tested the hypothesis that CAI can inhibit tumor angiogenesis in vivo. The ability of orally administered CAI to inhibit experimental metastases of B16F1 melanoma cells in mouse liver was assessed. A computer-assisted stereological technique was then used to analyze images from histological sections of CAI-treated vs. control livers; the vascular volume percentage (percentage of tumor volume consisting of functional microvessels) was determined to assess the effect of CAI on tumor angiogenesis. CAI treatment significantly reduced the size (8 x reduction in volume; P = 0.02) but not the number of metastases. In association with this reduction in tumor size, CAI significantly decreased the vascular volume percentage within metastases by at least a factor of two (P = 0.001). A reduction in both number of microvessels/mm2 and microvessel size (cross-sectional area) was found to contribute to this decrease. CAI treatment did not affect the vascular volume percentage of normal liver tissue surrounding metastases (P = 0.8). This study documents for the first time that CAI can inhibit tumor angiogenesis within metastases in vivo.

Osteopontin(OPN)-induced increase in human mammary epithelial cell invasiveness is urokinase (uPA)-dependent

We have recently shown that either exogenous or endogenous, transfected OPN induces both uPA expression and increased invasiveness of 21 PT (non-tumorigenic) and 21 NT (tumorigenic) human mammary epithelial cells. Here we asked whether uPA contributes functionally to the increased invasiveness of these cells. The most invasive OPN-transfected cells were assessed for migration through Matrigel in transwell assays, in the presence or absence of various blocking antibodies and uPA inhibitors. Antibodies to both uPA and uPA receptor (uPAR) were shown to significantly inhibit cell invasion, as did the uPA inhibitors (plasminogen activator inhibitor-1 [PAI-1], p-aminobenzamidine [PABN], aprotinin, and amiloride). Both anti-uPA and anti-uPAR antibodies inhibited invasion to a level comparable to that of the control vector transfected cells. In contrast, non-specific IgG showed no antiinvasive effect. Cell migration experiments performed with the parental cell lines in the presence or absence of anti-uPA or anti-uPAR antibodies showed that uPA is also required for migratory responsiveness to exogenous OPN. These data thus provide direct evidence that OPN-induced invasion and migration of these cells requires uPA.

The functional and clinical roles of osteopontin in cancer and metastasis

Osteopontin (OPN) is a secreted and integrin-binding protein that has been implicated in a number of pathologies. In this review we will focus on the functional and clinical roles of OPN in cancer and metastasis, with a particular emphasis on breast cancer. While much evidence has suggested that OPN is associated with cancer, its functional contribution to cancer remains poorly understood. Here we will review evidence for mechanisms by which OPN may act to enhance malignancy, including evidence that signaling pathways directly induced by OPN, as well as interactions with growth factor receptor pathways, can combine to activate expression of genes and functions that contribute to metastasis. OPN has been shown to be over-expressed in a variety of human tumors and is present in elevated levels in the blood of some patients with metastatic cancers. We also will discuss recent clinical evidence that suggests that OPN is not only associated with several tumor types, but that levels of OPN in cancer patients' blood or tumors may provide prognostic information.

The role of osteopontin in breast cancer: clinical and experimental studies

Osteopontin (OPN) is a secreted, integrin-binding protein which has been implicated in cancer, as well as other pathologies and some aspects of normal development. Here we focus on the role of OPN in breast cancer. We describe studies that have shown that OPN plays a role in normal mammary gland development as well as in progression of breast cancer. We also summarize studies that have shown that OPN can play a functional role in malignancy of breast cancer. At least some of these effects are mediated by specific cell surface integrins (alpha(v)beta3 vs. alpha(v)beta1 and alpha(v)beta5) and lead to increased cell migration, activation of growth factor/receptor pathways (e.g. HGF and EGF), and increased proteolytic enzyme activity (e.g. uPA). We also summarize clinical studies that show that OPN levels in tumors and blood are elevated in women with metastatic breast cancer and may offer promise as prognostic markers in breast cancer.

Osteopontin and its receptor alphavbeta(3) integrin are coexpressed in the human endometrium during the menstrual cycle but regulated differentially

Osteopontin is an arginine-glycine-aspartic acid-containing acidic glycoprotein component of the extracellular matrix that is postulated to bind to integrin receptors at the cell surface to mediate cellular adhesion and migration during embryo implantation. The primary aim of this study was to examine the uterine expression of osteopontin throughout the menstrual cycle in normal fertile controls sampled prospectively based on urinary LH surge detection. Expression of osteopontin was documented using Northern blot analysis, in situ hybridization, and immunohistochemistry. Furthermore, the temporal pattern of osteopontin expression was compared with that of its receptor, the alphavbeta3 integrin. Using Ishikawa cells, a well differentiated endometrial adenocarcinoma cell line, the in vitro regulation of osteopontin and its receptor alphavbeta3 integrin was studied. By Northern blot analysis, osteopontin mRNA appears during the early secretory phase, with maximal expression occurring in mid to late secretory-phase endometrium. The in situ hybridization analyses showed that osteopontin mRNA specifically localized in epithelial cells within the endometrium. Immunostaining of osteopontin was detected in the glandular secretions and on the apical portions of surface (luminal) epithelium. The patterns of expression of osteopontin by Northern blotting, in situ hybridization, and immunohistochemistry are remarkably similar to the pattern for the alphavbeta3 integrin. Despite these similarities in distribution, in vitro studies demonstrate that osteopontin and beta3 integrin subunit expression are differentially regulated. The expression of osteopontin was primarily induced in response to progesterone, whereas the beta3 integrin subunit was up-regulated by epidermal growth factor or heparin-binding epidermal growth factor. The differential regulation of these two endometrial proteins suggests the existence of two separate pathways regulating epithelial gene expression in human endometrium during the window of implantation. In adhesion assays using Ishikawa cells, alphavbeta3 but not alphavbeta5 or beta1 integrins appear to be the primary receptors for osteopontin. These findings may better define the factors that favor the development of a receptive endometrium.

Solitary cancer cells as a possible source of tumour dormancy?

Metastasis can occur many years after primary tumour treatment. However, the status of the tumour during this period of dormancy is poorly understood. As part of our ongoing experimental studies on mechanisms of metastasis, we have discovered that large numbers of disseminated single cells may persist in secondary sites for extended time periods. Identification of these cells was facilitated by in vivo techniques developed to quantify the fate of individual cells during the metastatic process. Here we review these in vivo techniques and findings. We also discuss the potential clinical implications if dormant solitary cells exist in appreciable numbers in cancer patients.

Critical steps in hematogenous metastasis: an overview

Metastasis is responsible for most cancer deaths. A better understanding of the process provides opportunities to develop new treatments to prevent metastasis. This article summarizes findings from experimental in vivo videomicroscopy and quantitative studies on metastatic inefficiency, which indicate that early steps in hematogenous metastasis may be quite efficient, but that regulation of cancer cell growth in secondary sites determines metastatic outcome. The authors have identified three key stages of this growth regulation: survival of a subset of single cells, proliferation of a subset of these cells to form preangiogenic micrometastases, and persistence of growth of a subset of these to form vascularized metastases. Formation of clinically relevant metastases is determined by the proportion of cells that proceeds successfully through each stage, and surviving single cells and preangiogenic micrometastases both represent possible sources of tumor dormancy.

Functional analysis of bone sialoprotein: identification of the hydroxyapatite-nucleating and cell-binding domains by recombinant peptide expression and site-directed mutagenesis

Mammalian bone sialoprotein (BSP) is a mineralized tissue-specific protein containing an RGD (arginine-glycine-aspartic acid) cell-attachment sequence and two distinct glutamic acid (glu)-rich regions, with each containing one contiguous glu sequence. These regions have been proposed to contribute to the attachment of bone cells to the extracellular matrix and to the nucleation of hydroxyapatite (HA), respectively. To further delineate the domains responsible for these activities, porcine BSP cDNA was used to construct expression vectors coding for two partial-length recombinant BSP peptides: P2S (residues 42-87), containing the first glutamic acid-rich domain; and P1L (residues 69-300), containing the second glutamic acid-rich region and the RGD sequence. These peptides were expressed in Escherichia coli as his-tag fusion proteins and purified by nickel affinity columns and FPLC chromatography. Digestion with trypsin released the his-tag fusion peptide, which generated P2S-TY (residues 42-87) and P1L-TY (residues 132-239). Using a steady-state agarose gel system, P2S-TY promoted HA nucleation, whereas P2S, P1L, and P1L-TY did not. This implies that the minimum requirement for nucleation of HA resides within the amino acid sequence of the first glutamic acid-rich domain, whereas the second glutamic acid-rich domain may require posttranslational modifications for activity. P1L, but not P2S, promoted RGD-mediated attachment of human gingival fibroblasts in a manner similar to that of native BSP. Deletion of the RGD domain or conversion of it to RGE (arginine-glycine-glutamic acid) abolished the cell-attachment activity of P1L. This suggests that, at least for human gingival fibroblasts, the major cell-attachment activity in the recombinant BSP peptides studied (residues 42-87 and 69-300) requires the RGD sequence located at the C-terminal domain.

The role of osteopontin in the development of granulomatous lesions in lung

Osteopontin (OPN) has been shown to be expressed by cells in granulomas of various origins, but whether it plays a functional role in granuloma formation is not known. Here we used a cardiomyopathic hamster (TO2) model, to test the hypothesis that OPN contributes functionally to granuloma development. We immunized cardiomyopathic and normal hamsters by subcutaneous injection of bovine serum albumin in complete Freund's adjuvant, and assessed various tissues for both OPN RNA expression and granuloma formation. Cardiomyopathic hamsters expressed OPN, and formed granulomatous lesions, in heart tissue in both immunized and untreated animals. In addition, immunization induced expression of OPN in lung and lymph nodes of cardiomyopathic (but not normal) hamsters, and also induced granuloma formation in these organs. To test whether OPN expression could play a functional role in inducing granulomas, we produced an adenoviral vector containing the murine OPN gene, and introduced this vector intratracheally into the lungs of normal hamsters. The OPN-containing vector, but not the control vector, induced pulmonary granuloma formation. These studies provided direct in vivo evidence that OPN can contribute functionally to the formation of granulomatous lesions, and suggest that OPN expression may be a common factor involved in formation of granulomas of various origin.

Differential expression of drug resistance genes and chemosensitivity in glial cell lineages correlate with differential response of oligodendrogliomas and astrocytomas to chemotherapy

The two principal subtypes of glial neoplasms, astrocytomas and oligodendrogliomas, exhibit striking differences in response to chemotherapy. This differential chemosensitivity might be explained by the specific genetic alterations causing gliomas but could also be attributable to specific properties intrinsic to the cells from which gliomas arise. To examine the possibility that chemosensitivity might be associated with lineage-specific properties of potential ancestors of these tumors, we explored: (a) the expression of drug resistance genes in rat glial cells; (b) the sensitivity of rat glial subtypes to the bifunctional alkylating agent, 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU); and (c) the effect of O6-methylguanine-DNA methyltransferase (MGMT) and glutathione modulation on resistance to BCNU. Astrocytes, O-2A progenitors, and oligodendrocytes each displayed a unique pattern of expression of six drug resistance genes: MGMT, GST mu, GST pi,p53, MDR, and MT. Oligodendrocytes were more sensitive to BCNU than either astrocytes or O-2A progenitors. The increased resistance of astrocytes in comparison to oligodendrocytes was modulated, at least in part, by both O6-benzylguanine (BG) and DL-buthionine-(S,R)-sulfoximine, suggesting a role for both MGMT and glutathione in the resistance of astrocytes to BCNU. The sensitivity of O-2A progenitors to BCNU following BG pretreatment is virtually indistinguishable from that of oligodendrocytes depleted of MGMT, suggesting that the down-regulation of MGMT is sufficient to account for the increased sensitivity of oligodendrocyte lineage cells to BCNU as they differentiate. These experiments provide support for the hypothesis that properties of glial cells retained in gliomas may contribute to the differential chemosensitivity of glial neoplasms.

Osteopontin-induced, integrin-dependent migration of human mammary epithelial cells involves activation of the hepatocyte growth factor receptor (Met)

Osteopontin (OPN) is a secreted glycophosphoprotein which induces migration of mammary carcinoma cells, and has been implicated in the malignancy of breast carcinoma. Hepatocyte growth factor (HGF) induces cell migration of several mammary epithelial cell (MEC) lines, via activation of its cognate receptor (Met). This study examines the mechanism of OPN-induced MEC migration, in terms of the cell surface integrins involved and induction of the HGF/Met pathway. Three different MEC cell lines were used, representing different stages of tumor progression: 21PT, non-tumorigenic; 21NT, tumorigenic; non-metastatic; and MDA-MB-435, tumorigenic, highly metastatic. Human recombinant OPN was found to induce the migration of all three lines. OPN-induced migration of 21PT and 21NT cells was alphavbeta5 and beta1-integrin dependent, and alphavbeta3-independent, while that of MDA-MB-435 cells was alphavbeta3-dependent. HGF also induced migration of all three cell lines, and a synergistic response was seen to HGF and OPN together. The increased migration response to OPN was found to be associated with an initial increase in Met kinase activity (within 30 min), followed by an increase in Met mRNA and protein expression. OPN-induced cell migration is thus mediated by different cell surface integrins in MEC lines representing different stages of progression, and involves activation of the HGF receptor, Met.

Sequential steps in hematogenous metastasis of cancer cells studied by in vivo videomicroscopy

Understanding metastatic spread of cancer is of upmost importance to developing successful strategies to treat this disease. In this review, we present a picture of the process of hematogenous metastasis from the initial arrest of cancer cells, their extravasation, postextravasation migration, and their replication to form tumors, based on experimental results using in vivo videomicroscopy. The cancer cells are initially arrested by size constraints within minutes of entering the circulation and with little hemodynamic destruction. Within 24-48 h >80% of these cancer cells extravasate as single cells by adhesion to and spreading along the vessel wall, often using pseudopodial projections to move into the surrounding tissue without disrupting the microcirculation. Some of the extravasated cells also use pseudopodial projections to migrate to specific structures in the tissue where they can replicate. Many cancer cells can persist as dormant cells, neither dividing nor undergoing apoptosis. Only a small fraction of extravasated cells begin to divide to form micrometastases, and only a very small fraction of these micrometastases continue to grow to form tumors. Possible clinical implications are that (1) initial arrest and extravasation may be difficult to prevent and thus may be poor therapeutic targets; (2) dormant single cells will not be affected by conventional cancer therapies which are designed to treat actively growing cells; and (3) regulation of growth of cells after extravasation is key to determining whether clinically evident metastases form - this stage of metastasis thus offers promising targets for new antimetastasis drugs.

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.

Osteopontin-induced, integrin-dependent migration of human mammary epithelial cells involves activation of the hepatocyte growth factor receptor (Met)

Osteopontin (OPN) is a secreted glycophosphoprotein which induces migration of mammary carcinoma cells, and has been implicated in the malignancy of breast carcinoma. Hepatocyte growth factor (HGF) induces cell migration of several mammary epithelial cell (MEC) lines, via activation of its cognate receptor (Met). This study examines the mechanism of OPN-induced MEC migration, in terms of the cell surface integrins involved and induction of the HGF/Met pathway. Three different MEC cell lines were used, representing different stages of tumor progression: 21PT, non-tumorigenic; 21NT, tumorigenic; non-metastatic; and MDA-MB-435, tumorigenic, highly metastatic. Human recombinant OPN was found to induce the migration of all three lines. OPN-induced migration of 21PT and 21NT cells was alphavbeta5 and beta1-integrin dependent, and alphavbeta3-independent, while that of MDA-MB-435 cells was alphavbeta3-dependent. HGF also induced migration of all three cell lines, and a synergistic response was seen to HGF and OPN together. The increased migration response to OPN was found to be associated with an initial increase in Met kinase activity (within 30 min), followed by an increase in Met mRNA and protein expression. OPN-induced cell migration is thus mediated by different cell surface integrins in MEC lines representing different stages of progression, and involves activation of the HGF receptor, Met.

Temporal progression of metastasis in lung: cell survival, dormancy, and location dependence of metastatic inefficiency

Cancer metastasis is an inefficient process. The steps in metastasis responsible for this inefficiency and how metastatic inefficiency can vary in different locations within an organ remain poorly understood. B16F10 cells were injected to target mouse lung, and at sequential times thereafter we quantified in lung the time course of: (a) overall cell survival and metastatic development; and (b) local cell survival and growth with respect to the lung surface and specific interior structures. We found high rates of initial survival of cells trapped in the lung circulation, extravasation into lung tissue, and subsequent survival of extravasated solitary cells (74% at day 3) before metastasis formation. However, at the time of initial replication of metastatic cells a major loss of cells occurred. Although only a small proportion of injected cells started to form metastases, most of these developed into macroscopic tumors. Solitary cells found at later times were dormant. Thus, overall metastatic inefficiency was largely due to postextravasation events affecting solitary cells. Regionally within the lung, cells and metastases were randomly distributed to day 4, but by day 10 preferential tumor growth was found along the lung surface and around arterial and venous vessels. Thus, trapping and early growth of injected cells was unaffected by location within the lung, whereas subsequent metastatic growth was enhanced in specific microenvironments. This study: (a) quantifies early temporal and spatial progression of metastasis in lung; (b) documents persistence of solitary dormant cells; and (c) shows that metastatic inefficiency depends on the initiation of growth in a subset of extravasated cells, whereas continued growth of metastases occurs preferentially in specific tissue environments.

Transforming JB6 cells exhibit enhanced integrin-mediated adhesion to osteopontin

Transformation of preneoplastic epidermal JB6 cells with tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) is an in vitro model of late-stage tumor promotion. Osteopontin (OPN) is a secreted, adhesive protein that is highly expressed in JB6 cells with TPA treatment, and its expression persists for at least 4 days, which is the time required for subsequent expression of transformed phenotype. These observations suggest that OPN may play a role in promoting JB6 cell transformation. To function in transformation of JB6 cells, OPN must bind to the surface of the JB6 cell and subsequently signal within the cell. Therefore, we investigated whether JB6 cells adhere to OPN and, if so, to which surface receptors. TPA-treated JB6 cells had significantly (P < 0.05) increased adherence to OPN compared with dimethylsulfoxide-treated control cells. Enhanced attachment of JB6 cells to OPN was also observed after treatment with another tumor promoter phorbol dibutyrate but not with nontumor promoters (phorbol and 1alpha,25-dihydroxyvitamin D(3)), suggesting that tumor promoters specifically modulate attachment to OPN. The argininylglycylaspartic acid (RGD) cell-binding region of OPN mediates attachment of TPA-treated JB6 cells because RGD, but not argininylglycylglutamic acid (RGE), peptides inhibited adherence of these cells to OPN in a dose-dependent manner. Flow cytometric analyses, blocking adhesion assay using anti-alpha(v) antibody, and co-immunoprecipitation assay all indicated that TPA-treated cells had similar levels of alpha(v) and beta(5) but decreased levels of beta(1) compared with untreated cells and that cell adhesion to OPN is most likely mediated through the alpha(v)beta(5). Furthermore, calphostin C, a specific protein kinase C (PKC) inhibitor, decreased TPA-treated JB6 cell adhesion to OPN by 50%, suggesting that TPA increased integrin affinity or avidity for OPN through a PKC-mediated pathway. Collectively, these results indicate that transforming JB6 cells adhere to OPN through its RGD sequence. The most likely OPN receptor is the alpha(v)beta(5) integrin, which increases the affinity or avidity for OPN through a PKC-dependent pathway rather than increasing the number of receptors.

Antibodies to different peptides in osteopontin reveal complexities in the various secreted forms

We have generated synthetic peptides corresponding to various portions of human osteopontin (OPN) and have immunized rabbits and mice with these peptides to generate polyclonal and monoclonal antibodies specific to human OPN. We then generated six distinct sandwich enzyme-linked immunoabsorbent assay (ELISA) systems by using different pairs of polyclonal and monoclonal antibodies against human OPN. These systems allowed us to detect not only various isoforms and truncated forms of recombinant OPN, but also the glycosylated form of native urinary OPN. Most importantly, tumor-derived OPN was differentially detected by the six ELISA systems. The ELISA systems that we have developed will be useful for clarifying the functional roles for OPN in vivo in various physiologic and pathologic conditions.

Serum bound forms of PSP94 (prostate secretory protein of 94 amino acids) in prostate cancer patients

PSP94 (prostate secretory protein of 94 amino acids) was regarded as a possible prostate cancer marker, however, it has been controversial. All prior studies were designed to test the free form in serum using antibodies to PSP94. Results presented here demonstrate that PSP94 exists in prostate cancer patients in two forms, free and bound, and that the majority is present as serum bound complexes. This result was demonstrated by using both native and SDS-PAGE analyses of serum proteins from prostate cancer patients. Chromatographic separation of serum total proteins by a molecular sieve column generated two peaks (peak I and II), which were reactive with rabbit antiserum to human PSP94 in Western blot experiments. Peak I was eluted before the IgG fraction at a molecular weight larger than 150 kDa, and peak II appeared after serum albumin ( approximately 67 kDa) was eluted. By using a biotinylated PSP94 as an indicator of the free form of PSP94, we demonstrate that peak I contains serum PSP94-bound complexes and peak II is likely the free form of serum PSP94. Since the molecular weight of serum PSP94-bound complexes is close to IgG during molecular sieve separation, serum PSP94 complexes were further purified through two rounds of protein A column separation, followed by DEAE-ion exchange column chromatography. In vitro dissociation tests of the purified PSP94-bound complexes showed that the binding of serum PSP94-complexes is probably via disulfide bonds and is chemically stable. The results presented here indicate that serum PSP94-bound complexes must be considered in evaluating the clinical utility of PSP94 as a prostate cancer marker.

Restriction enzyme analysis of DNA methylation in "condensed" chromatin of Ha-ras-transformed NIH 3T3 cells

Increased amounts of chromatin condensation (i.e., localized areas of high DNA density, or chromatin higher order packing state) have been described in NIH 3T3 cells transformed with the Ha-ras oncogene. The structural basis for this oncogene-mediated alteration in nuclear organization is unknown. Since DNA methylation is likely to be involved in regulating the nucleosomal level of DNA packaging, we studied the role of DNA methylation in higher-order chromatin organization induced by Ha-ras. CpG-methylated DNA content was estimated in "condensed" chromatin of Ha-ras-transformed NIH 3T3 cell lines which differ in ras expression and ras-induced metastatic ability but present approximately the same values of "condensed" chromatin areas. The question posed was that if DNA methylation were involved with the chromatin higher-order organization induced by Ha-ras in these cell lines, the methylated DNA density in the "condensed" chromatin would also be the same. The DNA evaluation was performed by video image analysis in Feulgen-stained cells previously subjected to treatment with Msp I and Hpa II restriction enzymes, which distinguish between methylated and non-methylated DNA. The amount of methylated CpG sequences not digested by Hpa II in "condensed" chromatin regions was found to vary in the studied ras-transformed cell lines. DNA CpG methylation status is thus suggested not to be involved with the higher order chromatin condensation induced by ras transformation in the mentioned NIH 3T3 cell lines.

Molecular biology of breast cancer metastasis. Clinical implications of experimental studies on metastatic inefficiency

Recent technological advances have led to an increasing ability to detect isolated tumour cells and groups of tumour cells in patients' blood, lymph nodes or bone marrow. However, the clinical significance of these cells is unclear. Should they be considered as evidence of metastasis, necessitating aggressive treatment, or are they in some cases unrelated to clinical outcome? Quantitative experimental studies on the basic biology of metastatic inefficiency are providing clues that may help in understanding the significance of these cells. This understanding will be of use in guiding clinical studies to assess the significance of isolated tumour cells and micrometastases in cancer patients.

O(6)-methylguanine-DNA methyltransferase activity, p53 gene status and BCNU resistance in mouse astrocytes

We observed previously that wild-type p53 rendered neonatal mouse astrocytes resistant to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) in a gene dose-dependent fashion. This effect of p53 appeared to be unrelated to its cell cycle regulation or apoptotic functions. Because in many cell types O(6)-methylguanine-DNA methyltransferase (MGMT)-mediated DNA repair is an important mechanism of resistance to nitrosoureas, we measured MGMT activity in wild-type, heterozygous and p53 knockout neonatal mouse astrocytes. Wild-type p53 astrocytes had significantly greater MGMT activity than either heterozygous or p53 knockout astrocytes: MGMT activity was approximately 5-fold greater in wild-type p53 astrocytes than in p53 knockout cells. However, despite successful depletion of MGMT activity in wild-type astrocytes by O(6)-benzylguanine (BG), resistance to BCNU persisted unchanged. Moreover, we excluded the possibility that continued resistance to BCNU at the concentrations used could be explained by a compensatory induction of MGMT triggered by exposure to either BCNU or BG. Although these studies support a role for p53 regulation of MGMT in neonatal mouse astrocytes, BCNU resistance in wild-type cells appears to be mediated by a non-MGMT mechanism. Nevertheless, regulation of DNA repair by MGMT may be another mechanism by which alterations of the p53 gene promote tumor initiation or progression.

The metastatic process: basic research and clinical implications

Metastatic spread of cancer is responsible for most deaths due to cancer. An understanding of the process of metastasis at a level sufficient to permit the development of effective antimetastatic therapies thus has the potential to make an impact on mortality from cancer. Recent experimental studies using in vivo videomicroscopy, which have allowed direct observation and quantification of steps in metastasis as they occur in vivo, have led to new insights into the metastatic process and steps that result in metastatic inefficiency. It is important to learn if these findings are relevant to clinical cancer. If these experimental results reflect the situation that occurs during metastasis of human cancers, there are clinical implications that deserve evaluation. In this Commentary, these results are discussed in the context of human cancer, and the possible clinical implications of the experimental findings are considered. The findings are also discussed in the context of results that suggest that the timing of breast cancer surgery during the menstrual cycle in premenopausal women may affect probability of survival, and possible implications of the findings for tumor dormancy are discussed.

Serum bound forms of PSP94 (prostate secretory protein of 94 amino acids) in prostate cancer patients

PSP94 (prostate secretory protein of 94 amino acids) was regarded as a possible prostate cancer marker, however, it has been controversial. All prior studies were designed to test the free form in serum using antibodies to PSP94. Results presented here demonstrate that PSP94 exists in prostate cancer patients in two forms, free and bound, and that the majority is present as serum bound complexes. This result was demonstrated by using both native and SDS-PAGE analyses of serum proteins from prostate cancer patients. Chromatographic separation of serum total proteins by a molecular sieve column generated two peaks (peak I and II), which were reactive with rabbit antiserum to human PSP94 in Western blot experiments. Peak I was eluted before the IgG fraction at a molecular weight larger than 150 kDa, and peak II appeared after serum albumin ( approximately 67 kDa) was eluted. By using a biotinylated PSP94 as an indicator of the free form of PSP94, we demonstrate that peak I contains serum PSP94-bound complexes and peak II is likely the free form of serum PSP94. Since the molecular weight of serum PSP94-bound complexes is close to IgG during molecular sieve separation, serum PSP94 complexes were further purified through two rounds of protein A column separation, followed by DEAE-ion exchange column chromatography. In vitro dissociation tests of the purified PSP94-bound complexes showed that the binding of serum PSP94-complexes is probably via disulfide bonds and is chemically stable. The results presented here indicate that serum PSP94-bound complexes must be considered in evaluating the clinical utility of PSP94 as a prostate cancer marker.

Tumour metastasis to the liver, and the roles of proteinases and adhesion molecules: new concepts from in vivo videomicroscopy

Most preclinical studies of tumour metastasis and effects of molecular interventions have been based on end point assays, and little is known about the fate of cells at sequential steps in the metastatic process. In vivo videomicroscopy permits direct observations of sequential steps in hematogenous metastasis as they occur in living animals over time. These steps include initial arrest of cells in the microcirculation, extravasation, postextravasation migration and growth in the target organ. In the mouse liver model, cells are arrested in periportal sinusoids based on size restriction, survive in the circulation and extravasate into the tissue by 48 to 72 h regardless of metastatic potential. Thereafter, cells may migrate to preferred sites for growth. Critical steps responsible for cell losses and metastatic inefficiency occur at the level of postextravasation cell growth. Many extravasated cells may remain dormant, and growth to form micrometastases is initiated in only a small subset of cells. Most early micrometastases may disappear after a few days, and only a small subset continue growth into macroscopic tumours. Angiogenesis is a prerequisite for continued growth of metastases, as shown previously by others. Integrin based interventions can modulate postextravasation cell migration and cell growth. Matrix metalloproteinase inhibitors can inhibit tumour angiogenesis and thus reduce growth. Key targets against which future therapeutic strategies should be directed include the initiation and maintenance of growth of micrometastases, and the activation of dormant solitary cells.

Angiogenesis as a target for breast cancer therapy

Angiogenesis, the development of new blood vessels, is crucial for the growth of both primary tumors and metastases beyond a minimal size and the vasculature of tumors facilitates their metastatic spread. Inhibition of angiogenesis is thus seen as a potentially useful approach to anti-metastasis therapy, and is an area of active research and development. Here we discuss this therapeutic approach in the context of breast cancer. An overview of the contribution of angiogenesis to tumor development is provided and current treatment options for breast cancer are briefly summarized. Assessment of angiogenesis in primary breast tumors has been shown to provide independent prognostic information. There are opportunities for the application of anti-angiogenesis therapeutic strategies in the treatment of breast cancer. Clinical trial design must take into account the unique properties of anti-angiogenic agents to fully assess their potential clinical benefit.

Osteopontin induces increased invasiveness and plasminogen activator expression of human mammary epithelial cells

Osteopontin (OPN) has been associated with enhanced malignancy in breast cancer, but its functional role in this disease is poorly understood. To study the effect of OPN on cellular invasiveness, basal OPN expression was first assessed in members of a progression series of human mammary epithelial cell lines (21PT: immortalized, non-tumorigenic; 21NT: weakly tumorigenic; 21MT-1: tumorigenic, weakly metastatic; MDA-MB-435 cells: tumorigenic, highly metastatic). The two lines which expressed lowest basal levels of OPN (21PT, 21NT) were then examined for up-regulation of invasive behavior in response to exogenous or transfected (endogenous) OPN. Both 21PT and 21NT showed increased invasiveness through Matrigel when human recombinant (hr)OPN was added to the lower chamber of transwells. Both also showed a cell migration response to hrOPN. Populations of 21PT and 21NT cells stably transfected with an OPN-expression vector showed higher levels of cell invasiness than control vector transfectants. Examination of transfectants for mRNA of a number of secreted proteases showed that only urokinase-type plasminogen activator (uPA) expression was closely associated with OPN expression and cellular invasiveness. Treatment of the parental 21PT and 21NT cells with exogenous hrOPN resulted in increased uPA mRNA expression and increased urokinase activity of the conditioned media. Both increased cell migration and induction of uPA expression are thus potential mechanisms of increased invasiness of breast epithelial cells in response to OPN.

Reduced tolerance to acute renal ischemia in mice with a targeted disruption of the osteopontin gene

BACKGROUND

Mice with a targeted disruption of the osteopontin gene through homologous recombination in embryonic stem cells have recently been generated and shown to be characterized by unaltered fertility and normal embryonic and postnatal development, including renal development, but altered osteoclastogenesis from spleen progenitors. The lack of detectable pathological manifestations in kidneys of mice with the targeted disruption of the osteopontin gene (opn -/-) makes them an excellent model for studies of pathophysiological processes that are thought to be accompanied by changes in renal osteopontin expression. It has previously been suggested that osteopontin may play an important role in the pathophysiology of acute renal failure, thus prompting this study.

METHODS

Wild-type and opn -/- mice were subjected to 30 minutes of renal ischemia and were studied 24 hours later.

RESULTS

Control opn +/+ mice showed a significant retention of blood urea nitrogen and creatinine, which is indicative of the development of ischemic acute renal dysfunction. This was accompanied by a 2.7-fold increase in the immunodetectable osteopontin compared with sham-operated control. Animals with the disrupted osteopontin gene exhibited ischemia-induced renal dysfunction, which was twice as pronounced as that observed in mice with the intact osteopontin response to stress. In addition, the structural damage to the ischemic kidneys obtained from opn -/- mice was more pronounced than that observed in similarly treated wild-type mice. This was associated with the augmented expression of inducible nitric oxide synthase and the prevalence of nitrotyrosine residues in kidneys from opn -/- mice versus wild-type counterparts. In vitro studies with proximal tubular cells subjected to hypoxia in the presence of OPN, but not OPN with deleted arginine-glycine-aspartic acid (RGD) domain, resulted in cytoprotection.

CONCLUSIONS

The comparative analysis of functional and morphological sequelae of acute renal ischemia in opn +/+ and opn -/- mice provides strong evidence of renoprotective action of osteopontin in acute ischemia.

Cellular expression of green fluorescent protein, coupled with high-resolution in vivo videomicroscopy, to monitor steps in tumor metastasis

High resolution intravital videomicroscopy has provided a powerful tool for directly observing steps in the metastatic process, and for clarifying molecular mechanisms of metastasis and modes of action of anti-metastasis therapeutics. Cells previously have been identified in vivo using exogenously added fluorescent labels, limiting observations to a few cell divisions, or by natural markers (e.g. melanin) expressed only by specific cell types. Here we tested the utility of stable green fluorescent protein (GFP)-transfected cells for monitoring and quantifying sequential steps in the metastatic process. Using CHO-K1 cells that stably express GFP, we document the visualization and quantification by intravital videomicroscopy of sequential steps in metastasis within mouse liver, from initial arrest of cells in the microvasculature to the growth and angiogenesis of metastases. Individual, non-dividing cells, as well as micro- and macrometastases could clearly be detected and quantified, as could fine cellular details such as pseudopodial projections, even after extended periods of in vivo growth. We quantified the size distribution of micrometastases and their locations relative to the liver surface using 50 micrometer thick formalin-fixed tissue sections. The data suggest preferential growth and survival of micrometastases near the liver surface. Furthermore, we observed a small population of single cells that persisted over the 11 day observation period, which may represent dormant cells with potential for subsequent proliferation. This study demonstrates the advantages of GFP-expressing cells, coupled with real-time high resolution videomicroscopy, for long-term in vivo studies to visualize and quantify sequential steps of the metastatic process.

Preclinical assessment of anti-cancer therapeutic strategies using in vivo videomicroscopy

Preclinical in vivo studies of agents targeted against metastasis have to date been based primarily on end-point assays. Such assays can determine whether a treatment affects the number or size of metastases in an organ at a given time, but are poorly suited to determining how and at what stage in the process the treatment affected the end point. High resolution in vivo videomicroscopy permits direct observation of the process of metastasis as it occurs in living animals over time. Studies based on this technique and a cell accounting procedure we have devised, have shown that early steps in the metastatic process (survival in the circulation, extravasation) contribute relatively little to cell loss and metastatic inefficiency. Steps that occur after extravasation appear to be primarily responsible for the significant losses that result in metastatic inefficiency, and these steps may represent good targets for the design of new antimetastatic therapies. Matrix metalloproteinases have been implicated functionally in metastasis, and are viewed as an appropriate target in the development of inhibitors of metastasis. Using both endogenous and synthetic exogenous metalloproteinase inhibitors, we have shown that the inhibition of metastasis which these agents produce is not due to inhibition of cell extravasation from the circulation into the tissue, but to reduction of angiogenesis within metastases. A similar conclusion was reached concerning the mechanism of action, on metastasis, of carboxyamidotriazole, an inhibitor of calcium-mediated signal transduction which is currently in Phase II single agent clinical trials. In vivo videomicroscopy of sequential steps in metastasis, coupled with methods that allow precise quantification of cell loss at specific steps in the metastatic process, as well as standard histological assessment at stages identified as crucial, allow characterization of the details of metastasis as an ongoing process. This provides a powerful complement to end-point assays, for it allows mechanistic information to be obtained from in vivo experiments, an approach which provides better understanding of how and when a drug may function in vivo to inhibit metastasis.

Detection of various epitopes of murine osteopontin by monoclonal antibodies

We immunized rats with recombinant murine osteopontin protein and obtained four monoclonal antibodies recognizing distinct epitopes of murine osteopontin. OPN1.2 recognized the amino-terminal half of OPN, while OPN2.2, OPN2.3, and OPN3.1 recognized the carboxy-terminal half of OPN. The epitope recognized by OPN2.2 was destroyed by further cleavage of the carboxy half of OPN. The epitope recognized by OPN2.3 was located in the amino-terminal end of the carboxy half of OPN, whereas that recognized by OPN3.1 was located in the carboxy-terminal end of the carboxy half of OPN. OPN1.2 and OPN2.2 recognized thrombin-cleaved osteopontin, whereas thrombin-cleaved osteopontin was not recognized by OPN2.3 and OPN3.1. Thus, these monoclonal antibodies will be useful in structure/function studies of the role of osteopontin in murine models of disease.

The matrix metalloproteinase inhibitor batimastat inhibits angiogenesis in liver metastases of B16F1 melanoma cells

Matrix metalloproteinases (MMPs) have been shown to contribute functionally to tumor metastasis. MMP inhibitors are thus being assessed for clinical utility as anti-metastatic therapeutics. Batimastat (BB-94) is a synthetic MMP inhibitor that has been shown to inhibit tumor growth and metastasis in mice. Here we assessed the ability of batimastat to inhibit liver metastases of murine B16F1 cells, after injection of cells in mice via mesenteric vein to target the liver. We then determined which of the sequential steps in metastasis were affected by batimastat, in order to identify its mechanism of action in vivo. Intravital videomicroscopy was used to assess the effect on extravasation, and a 'cell accounting' procedure was used to determine the effect on initial survival of cells. Stereological quantification of functional blood vessels was used to determine the effect on tumor vascularity, thereby avoiding problems associated with immunohistochemical detection of liver sinusoidal endothelial cells. We found that batimastat (50 mg/kg i.p. 5 h prior to and after cell injection, daily thereafter) resulted in a 23% reduction in mean diameter of liver metastases (equivalent to a 54% reduction in tumor volume), while not reducing the number of metastases. Extravasation of cells from the liver circulation was not affected: at 8, 24 and 48 h after injection of cells, the same proportion of cells had extravasated from treated vs. control mice. Batimastat also did not inhibit early survival of cells. However, batimastat-treated mice had a significantly reduced percentage vascular volume within liver metastases, indicating inhibition of angiogenesis. This study demonstrates in vivo that the mechanism by which batimastat limits growth of B16F1 metastases in liver is not by affecting extravasation, but by inhibiting angiogenesis within metastases. This finding suggests that MMP inhibitors may be appropriate for use in patients with metastatic cells that have already extravasated in secondary sites.

Metastasis Research Society VII International Congress (Part II). 7-10 October 1998, San Diego, CA, USA

The Metastasis Research Society (MRS) has held its International Congress every two years since 1986, and alternates between European and North American meeting venues. The next MRS International Congress will be held in London, UK in the year 2000, and will be hosted by the current MRS President, Dr. Suzanne Eccles (Institute of Cancer Research, Sutton, UK). Dr. Eccles took over from the out-going President, Dr. William Stetler-Stevenson (National Institutes of Health, Bethesda, MD, USA), at the San Diego meeting. Information on joining the Metastasis Research Society, which includes a subscription to the Society's journal, Clinical and Experimental Metastasis, can be obtained from Dr. Eccles (suzan@icr.ac.uk) or from the newly-elected Secretary/Treasurer Dr. Danny Welch (Hershey, PA, USA; drw9@psu.edu). The meeting was organized by Darwin Medical Communications Ltd (Gill Heaton, Oxford, UK), who have placed the full program on the meeting web site (http:@www.sparks.co.uk/mrs). It is envisaged that full abstracts of all the presentations will be placed on the Metastasis Research Society web site, which is currently under construction. Corporate sponsors for the San Diego meeting included Agouron Pharmaceuticals, Becton Dickinson & Co, Zeneca Pharma SA, Schering AG, AntiCancer Inc, Oncogene Research Products, Daiichi Seiyaku Co Ltd and Novartis Pharma AG.

CD44 variants but not CD44s cooperate with beta1-containing integrins to permit cells to bind to osteopontin independently of arginine-glycine-aspartic acid, thereby stimulating cell motility and chemotaxis

The expression of osteopontin (OPN), CD44 variants, and integrins has been correlated with tumorigenesis and metastasis. Here we show that these proteins cooperate to enhance cell motility. First, we demonstrate that several different CD44 variants bind to OPN in an arginine-glycineaspartic acid-independent manner, but that the standard form of CD44 does not. These CD44 variants bind to both the amino- and COOH-terminal portions of OPN independently of the arginine-glycine-aspartic acid sequence, suggesting that multiple domains on OPN can be bound by the CD44 variants. Antibodies directed against the integrin beta1 subunit are able to inhibit this binding. The binding of CD44 variants to OPN is significantly augmented by both anti-CD44s and anti-CD44v antibodies. This augmentation by anti-CD44 antibodies is OPN specific and, again, can be blocked by anti-beta1 antibodies. Finally, we show that OPN binding by CD44 variants/beta1-containing integrins promotes cell spreading, motility, and chemotactic behavior.

Osteopontin inhibits inducible nitric oxide synthase activity in rat vascular tissue

We tested the hypothesis that osteopontin (OPN) can inhibit the induction of inducible nitric oxide synthase (iNOS) in vascular tissue. iNOS activity was induced in rat thoracic aortas by incubation of the tissue with lipopolysaccharide (LPS) and measured by conversion of L-[3H]arginine to L-[3H]citrulline. Addition of >/=1 nM recombinant OPN protein significantly reduced the LPS-induced increase in iNOS activity. Western blotting and the RT-PCR were used to determine the effect of LPS with and without OPN on tissue levels of iNOS protein and RNA, respectively. LPS resulted in an increase in iNOS protein and RNA, whereas OPN dose-dependently reduced tissue levels of iNOS activity, protein, and RNA. Mutated OPN proteins, in which the integrin-binding RGD amino acid sequence was deleted or mutated to RGE, resulted in complete and partial loss, respectively, of the ability of OPN to inhibit LPS-induced iNOS activity, implicating integrin binding in the effect. These results indicate that OPN can prevent induction of iNOS in vascular tissue.

Genetic background influences timing, morphology and dissemination of lymphomas in p53-deficient mice

To examine the influence of genetic background on tumorigenesis in p53-deficient mice, we used selective breeding to produce congenic mice with a null p53 gene mutation introduced into the VM inbred strain. Cohorts of homozygous p53 null (-/-) mice from the original C57B6/129Sv mixed strain and the VM congenic strain were monitored for spontaneous tumor development, as were control cohorts of wild-type (+/+) and heterozygous (+/-) animals. Twenty-six of 28 C57B6/129Sv (-/-) mice died by the study end date (median survival =184.5 days). Twenty-three of 26 VM (-/-) mice died and their survival was significantly shorter (111 days, P<0.0001). Of 26 C57B6/129Sv (-/-) mice that died, 21 were autopsied: all 21 had lymphomas. Of 26 VM mice that died (23 -/-, 3 +/-), 21 were autopsied: 19 developed lymphoma and two had sarcomas. Several mice had additional neoplasms. Lymphomas in VM mice were distinct from those in C57B6/129Sv mice in that they i) arose on average more than two months earlier, ii) involved thymus more often than spleen or lymph nodes and iii) were more often poorly differentiated, high grade tumors. These results demonstrate that genetic background alone influences the onset, morphology and dissemination of lymphomas in p53-deficient mice and suggest the presence of genes which modify the timing and biological nature of lymphomas in these mice.

Osteopontin expression in a group of lymph node negative breast cancer patients

The aim of this study was to examine the cellular distribution of osteopontin (OPN) protein [by immunohistochemical (IHC) analysis] and mRNA [by in situ hybridization (ISH)] in the primary tumors of lymph node negative (LNN) breast cancer patients and to determine whether the level of immunodetectable OPN may be associated with tumor aggressiveness. We examined OPN levels in tumors from 154 patients with LNN breast cancer who were followed for a median of 7 years (range 1.7-16.3 years). IHC staining for OPN was seen in tumor infiltrating macrophages and lymphocytes in 70% of these tumors, and in the carcinoma cells themselves in 26%. ISH was performed to determine cellular distribution of OPN mRNA expression in sections from selected tumors. OPN mRNA was detected in groups of tumor cells, individual tumor cells and tumor infiltrating macrophages and lymphocytes. Matched sections showed that some tumor cells with IHC staining for OPN protein were also positive for OPN mRNA by ISH, in contrast with previous studies which have shown OPN mRNA expression only in tumor infiltrating inflammatory cells. Our results thus indicate that OPN protein can be produced by breast cancer cells in vivo and suggest that it may also be taken up from the environment (i.e., secreted by inflammatory cells or other tumor cells). Tumor cell IHC staining intensity was then assessed using a semiquantitative scoring system. Univariate analysis showed tumor cell OPN positivity above an optimized cutpoint to be significantly associated with decreased disease-free survival (DFS) and overall survival (OS). The results of this pilot study thus suggest that the ability of breast cancer cells to either synthesize OPN or to bind and sequester OPN from the microenvironment may be associated with tumor aggressiveness and poor prognosis.

Multistep nature of metastatic inefficiency: dormancy of solitary cells after successful extravasation and limited survival of early micrometastases

In cancer metastasis, only a small percentage of cells released from a primary tumor successfully form distant lesions, but it is uncertain at which steps in the process cells are lost. Our goal was to determine what proportions of B16F1 melanoma cells injected intraportally to target mouse liver 1) survive and extravasate, 2) form micrometastases (4 to 16 cells) by day 3, 3) develop into macroscopic tumors by day 13, and 4) remain as solitary dormant cells. Using in vivo videomicroscopy, a novel cell accounting assay, and immunohistochemical markers for proliferation (Ki-67) and apoptosis (TUNEL), we found that 1) 80% of injected cells survived in the liver microcirculation and extravasated by day 3, 2) only a small subset of extravasated cells began to grow, with 1 in 40 forming micrometastases by day 3, 3) only a small subset of micrometastases continued to grow, with 1 in 100 progressing to form macroscopic tumors by day 13 (in fact, most micrometastases disappeared), and 4) 36% of injected cells remained by day 13 as solitary cancer cells, most of which were dormant (proliferation, 2%; apoptosis, 3%; in contrast to cells within macroscopic tumors: proliferation, 91%; apoptosis/necrosis, 6%). Thus, in this model, metastatic inefficiency is principally determined by two distinct aspects of cell growth after extravasation: failure of solitary cells to initiate growth and failure of early micrometastases to continue growth into macroscopic tumors.

Activation of MMP-2 by human GCT23 giant cell tumour cells induced by osteopontin, bone sialoprotein and GRGDSP peptides is RGD and cell shape change dependent

We show that osteopontin (OPN), bone sialoprotein (BSP) and GRGDSP peptides, in solution, induce activation of metalloproteinase-2 (MMP-2) secreted by human GCT23 giant cell tumour cells. Activation of MMP-2 is RGD sequence dependent, possibly involves anti-alphaVbeta3 integrins, is preceded by a change from spread to rounded cell morphology and is mimicked by the actin depolymerising agent cytochalasin B. Cells that had spread on OPN, BSP and GRGDSP substrata failed to activate MMP-2, but subsequent addition of soluble GRGDSP induced rounding and MMP-2 activation. Activation induced by GRGDSP and cytochalasin B was cell mediated, inhibited by EDTA, tissue inhibitor of metalloproteinase-2 (TIMP-2) and carboxyl terminal MMP-2 consistent with a role for membrane type (MT)-MMP but did not involve urokinase, plasmin or thrombin activity. Activation induced by GRGDSP and cytochalasin B, but not cell rounding, was inhibited by herbimycin A, cycloheximide and actinomycin D, suggesting a role for tyrosine kinases, protein and RNA synthesis, but was not associated with changes in mRNA for MT-MMP-1, MMP-1, MMP-2, TIMP-1 or TIMP-2. GRGDSP and cytochalasin B enhanced levels of membrane-associated pro- and active form MMP-1 and MMP-2 but not MT-MMP-1, stimulated cell surface MMP-1 staining and induced that of MT-MMP-1, MMP-2 and TIMP-2. This was consistent with the possible relocation of constitutive MT-MMP-1 to the cell surface as a prerequisite for subsequent cell surface MMP-2/TIMP-2/MT-MMP-1 complex formation and to the potential induction of conditions favourable for reciprocal cell surface MMP-1/MMP-2 activation. Our data provide a novel insight into interactions between RGD containing bone matrices, GCT cells and MMPs of potential relevance to GCT pathology.

Coordinate expression of OPN and associated receptors during monocyte/macrophage differentiation of HL-60 cells

Promyelocytic leukemia HL-60 cells promoted by PMA to differentiate along the monocyte pathway adhere to tissue culture plates. To explore the regulation of adhesion molecules in cells promoted to differentiate, the expression and secretion of osteopontin (OPN) and expression of associated cell surface receptors, CD44 and integrin subunits alpha(v), beta3, beta1, were examined. Results were as follows: 1) PMA induced OPN mRNA and OPN secretion into media; 2) untreated cells expressed beta1 and CD44 mRNA, and PMA induced alpha(v), and beta3 mRNA and increased beta1 and CD44 mRNA expression; 3) PMA increased levels of alpha(v), beta3, beta1 and CD44 protein on the cell surface; and 4) retinoic acid, which promotes granulocytic differentiation of HL-60 cells, did not affect OPN, alpha(v), beta3, beta1, or CD44 mRNA or protein expression. These data suggest that induction of OPN and associated receptors may play a role during monocytic differentiation of HL-60 cells.