Serial Plasma Osteopontin Levels Have Prognostic Value in Metastatic Breast Cancer

Melatonin inhibits the migration of human lung adenocarcinoma A549 cell lines involving JNK/MAPK pathway

Objective

Melatonin, an indolamine produced and secreted predominately by the pineal gland, exhibits a variety of physiological functions, possesses antioxidant and antitumor properties. But, the mechanisms for the anti-cancer effects are unknown. The present study explored the effects of melatonin on the migration of human lung adenocarcinoma A549 cells and its mechanism.

Methods

MTT assay was employed to measure the viability of A549 cells treated with different concentrations of melatonin. The effect of melatonin on the migration of A549 cells was analyzed by wound healing assay. Occludin location was observed by immunofluorescence. The expression of occludin, osteopontin (OPN), myosin light chain kinase (MLCK) and phosphorylation of myosin light chain (MLC), JNK were detected by western blots.

Results

After A549 cells were treated with melatonin, the viability and migration of the cells were inhibited significantly. The relative migration rate of A549 cells treated with melatonin was only about 20% at 24 h. The expression level of OPN, MLCK and phosphorylation of MLC of A549 cells were reduced, while the expression of occludin was conversely elevated, and occludin located on the cell surface was obviously increased. The phosphorylation status of JNK in A549 cells was also reduced when cells were treated by melatonin.

Conclusions

Melatonin significantly inhibits the migration of A549 cells, and this may be associated with the down-regulation of the expression of OPN, MLCK, phosphorylation of MLC, and up-regulation of the expression of occludin involving JNK/MAPK pathway.

Role of osteopontin in the pathophysiology of cancer

Osteopontin (OPN) is a multifunctional cytokine that impacts cell proliferation, survival, drug resistance, invasion, and stem like behavior. Due to its critical involvement in regulating cellular functions, its aberrant expression and/or splicing is functionally responsible for undesirable alterations in disease pathologies, specifically cancer. It is implicated in promoting invasive and metastatic progression of many carcinomas. Due to its autocrine and paracrine activities OPN has been shown to be a crucial mediator of cellular cross talk and an influential factor in the tumor microenvironment. OPN has been implicated as a prognostic and diagnostic marker for several cancer types. It has also been explored as a possible target for treatment. In this article we hope to provide a broad perspective on the importance of OPN in the pathophysiology of cancer.

Extracellular matrix components in breast cancer progression and metastasis

The extracellular matrix (ECM) is composed of highly variable and dynamic components that regulate cell behavior. The protein composition and physical properties of the ECM govern cell fate through biochemical and biomechanical mechanisms. This requires a carefully orchestrated and thorough regulation considering that a disturbed ECM can have serious consequences and lead to pathological conditions like cancer. In breast cancer, many ECM proteins are significantly deregulated and specific matrix components promote tumor progression and metastatic spread. Intriguingly, several ECM proteins that are associated with breast cancer development, overlap substantially with a group of ECM proteins induced during the state of tissue remodeling such as mammary gland involution. Fibrillar collagens, fibronectin, hyaluronan and matricellular proteins are matrix components that are common to both involution and cancer. Moreover, some of these proteins have in recent years been identified as important constituents of metastatic niches in breast cancer. In addition, specific ECM molecules, their receptors or enzymatic modifiers are significantly involved in resistance to therapeutic intervention. Further analysis of these ECM proteins and the downstream ECM mediated signaling pathways may provide a range of possibilities to identify druggable targets against advanced breast cancer.

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.

Bone sialoprotein and osteopontin in bone metastasis of osteotropic cancers

The mechanisms underlying malignant cell metastasis to secondary sites such as bone are complex and no doubt multifactorial. Members of the small integrin-binding ligand N-linked glycoproteins (SIBLINGs) family, particularly bone sialoprotein (BSP) and osteopontin (OPN), exhibit multiple activities known to promote malignant cell proliferation, detachment, invasion, and metastasis of several osteotropic cancers. The expression level of BSP and OPN is elevated in a variety of human cancers, particularly those that metastasize preferentially to the skeleton. Recent studies suggest that the "osteomimicry" of malignant cells is not only conferred by transmembrane receptors bound by BSP and OPN, but includes the "switch" in gene expression repertoire typically expressed in cells of skeletal lineage. Understanding the role of BSP and OPN in tumor progression, altered pathophysiology of bone microenvironment, and tumor metastasis to bone will likely result in development of better diagnostic approaches and therapeutic regimens for osteotropic malignant diseases.

Osteopontin is a promoter for hepatocellular carcinoma metastasis: a summary of 10 years of studies

In this review, we summarize the novel findings from our series of studies on the leading metastasis-related gene, osteopontin (OPN). In our previous gene expression profiling study, OPN was identified as one of the leading genes associated with the metastasis of hepatocellular carcinoma (HCC). We focused on OPN to evaluate its prognostic values and important roles in HCC metastasis. A retrospective study of large cohorts of HCC patients demonstrated that plasma OPN level was one of the leading independent prognostic factors for HCC patients, even in the early stage of HCC, and could serve as a surrogate serologic biomarker for monitoring the treatment response and tumor recurrence after HCC resection. Using both in vitro and in vivo investigations, we found that OPN has an important role in metastasis and tumor growth of HCC and is an attractive potential therapeutic target for combating HCC metastasis. We also found that OPN⁺ HCC cells have much more amplifications at chromosomal regions, and promoter polymorphisms are important in the regulation of OPN expression and tumor growth and lung metastasis of HCC.

Assessment of osteopontin in early breast cancer: correlative study in a randomised clinical trial

INTRODUCTION

Osteopontin (OPN) is a malignancy-associated glycoprotein that contributes functionally to tumor aggressiveness. In metastatic breast cancer, we previously demonstrated that elevated OPN in primary tumor and blood was associated with poor prognosis.

METHODS

We measured OPN in plasma by ELISA, and in tumors by immunohistochemistry, in 624 (94%) and 462 (69%), respectively, of 667 postmenopausal women with hormone responsive early breast cancer treated by surgery followed by adjuvant treatment with tamoxifen +/- octreotide in a randomized trial (NCIC CTG MA.14; National Cancer Institute of Canada Clinical Trials Group Mammary.14).

RESULTS

Plasma OPN was measured in 2,540 samples; 688 at baseline and 1,852 collected during follow-up. Mean baseline plasma OPN was 46 ng/ml (range 22.6 to 290) which did not differ from normal levels. Mean percentage OPN tumor cell positivity was 33.9 (95% CI: 30.2 to 37.9). There was no correlation between plasma and tumor OPN values. In multivariate analysis, neither was associated with event-free survival (EFS), relapse-free survival (RFS), overall survival (OS), bone RFS or non-bone RFS. An exploratory analysis in patients with recurrence showed higher mean OPN plasma levels 60.7 ng/ml (23.9 to 543) in the recurrence period compared with baseline levels.

CONCLUSIONS

The hypothesis that OPN tumor expression would have independent prognostic value in early breast cancer was not supported by multivariate analysis of this study population. Plasma OPN levels in women with hormone responsive early breast cancer in the MA.14 trial were not elevated and there was no evidence for prognostic value of plasma OPN in this defined group of patients. However, our finding of elevated mean OPN plasma level around the time of recurrence warrants further study.

TRIAL REGISTRATION

NCT00002864, http://clinicaltrials.gov/show/NCT00002864.

Plasma osteopontin is a useful diagnostic biomarker for advanced non-small cell lung cancer

Background

Osteopontin (OPN) and carbonic anhydrase IX (CAIX), which are expressed on the surface of tumor cells, are associated with hypoxia during tumor development and progression. However, the roles of these proteins in the plasma of patients with non-small cell lung cancer (NSCLC) are poorly understood. Herein, we hypothesized that plasma OPN and CAIX levels could be used as diagnostic and prognostic tumor markers in patients with NSCLC.

Methods

Fifty-three patients with NSCLC and 50 healthy control subjects were enrolled. We selected controls without malignancy and matched them with NSCLC patient cases according to age and gender. Blood samples were collected at the time of diagnosis; the plasma levels of OPN and CAIX were measured by enzyme-linked immunosorbent assays.

Results

The plasma levels of OPN in the patients with NSCLC were significantly elevated as compared to those in the controls (p=0.016). However, there was no difference in the plasma level of CAIX between the NSCLC patients and controls. NSCLC patients with a distant metastasis had a remarkable increase in plasma OPN compared with patients without metastasis (p=0.026), but no such correlation was found for CAIX. There was no difference in overall survival rates according to the plasma level of OPN between the two groups (by Kaplan-Meier survival analysis).

Conclusion

Plasma OPN levels were elevated in patients with NSCLC as compared with the controls, with greater elevation of OPN levels in the advanced stages of disease. Therefore, plasma OPN may have utility as a diagnostic, but not prognostic, biomarker of advanced NSCLC.

Osteopontin promoter polymorphisms at locus -443 significantly affect the metastasis and prognosis of human hepatocellular carcinoma

Osteopontin (OPN) plays a crucial role in hepatocellular carcinoma (HCC) metastasis. However, little is known about the impact of OPN polymorphisms on cancer progression. In this study, we first identified the single nucleotide polymorphisms (SNPs) in the OPN promoter region by direct sequencing in 30 HCCs, and then evaluated the prognostic values of the selected ones in two large cohorts of 826 HCC patients. The identified SNPs were functionally analyzed using in vitro and in vivo assays and their correlations with OPN levels were also evaluated. Only SNP at locus -443 and their related haplotypes (Ht2: -1748A/-616G/-443T/-155* [*indicates base deletion]; Ht3: -1748A/-616G/-443C/-155*) were significantly associated with overall survival (OS) and time to recurrence (TTR). The patients with the -443TT/TC genotype or Ht2 had a shorter OS and TTR compared with those with -443CC genotype or Ht3. This was further confirmed in the validation cohort. Moreover, this correlation remained significant in patients with small HCCs (≤5 cm). Multivariate analyses indicated that the prognostic performance of the -443 genotypes (OS, P=0.031; TTR, P=0.005) and their related haplotypes (OS, P=0.002; TTR, P=0.001) was independent of other clinicopathological factors. The Ht2 and -443TT genotype could significantly increase the promoter transcriptional activity and expression level of OPN compared with the Ht3 or -443CC genotype, and lead to an obvious increase in both in vitro invasion and in vivo tumor growth and lung metastasis of HCC cells (P<0.05).

CONCLUSION

The genetic variation at locus -443 of the OPN promoter plays important roles in the regulation of OPN expression and cancer progression of HCCs, which is a novel determinant and target for HCC metastasis and prognosis.

Upregulation of drug transporter expression by osteopontin in prostate cancer cells

Multidrug resistance is a major cause of chemotherapy failure. Recent studies indicate that drug resistance can be rapidly induced by some soluble factors, such as cytokines, chemokines, growth factors, and cell adhesion factors in the tumor microenvironment. Osteopontin (OPN), an extracellular matrix protein, has a functional arginine-glycine-aspartic acid (RGD) domain for binding to integrin. Here we found OPN expression to be upregulated by hypoxic condition in PC-3 prostate tumor cells. OPN increased the mRNA and protein expression of p-glycoprotein (P-gp), a subfamily of ATP-binding cassette transporter in a concentration- and time-dependent manner. The increase in P-gp transporter by OPN was mediated by binding to αvβ3 integrin. Daunomycin (DUN), a chemotherapeutic agent with autofluorescence, was used to evaluate the pump activity, and OPN increased the drug pumping-out activity. OPN inhibited DUN-induced cell death, which was antagonized by αvβ3 monoclonal antibody. Long-term treatment with DUN further enhanced the expression of OPN. Knockdown of endogenous OPN potentiated the DUN-induced apoptosis of PC-3 cells. Furthermore, knockdown of OPN enhanced cell death caused by other drugs, including paclitaxel, doxorubicin, actinomycin-D, and rapamycin, which are also P-gp substrates. The animal studies also showed that OPN knockdown enhanced the cytotoxic action of DUN. These results indicate that OPN is a potential therapeutic target for cancer therapy to reduce drug resistance in sensitive tumors.

Matricellular proteins: priming the tumour microenvironment for cancer development and metastasis

Matricellular proteins have been classified as a family of non-structural matrix proteins capable of modulating a variety of biological processes within the extracellular matrix (ECM). These proteins are expressed dynamically and their cellular functions are highly dependent upon cues from the local environment. Recent studies have shown an increasing appreciation of the key roles these ECM proteins play within the tumour microenvironment. Induced by either tumour cells or tumour stromal components, matricellular proteins initiate downstream signalling events that lead to proliferation, invasion, matrix remodelling and dissemination to pre-metastatic niches in other organs. In this review, we summarise and discuss the current knowledge of the diverse roles these proteins play within the microenvironment that influences tumour progression and potential for future therapies targeting the tumour microenvironment.

A bead-based multiplexed immunoassay to evaluate breast cancer biomarkers for early detection in pre-diagnostic serum

This study investigates whether a set of ten potential breast cancer serum biomarkers and cancer antigens (osteopontin (OPN), haptoglobin, cancer antigen 15-3 (CA15-3), carcinoembryonic antigen (CEA), cancer antigen 125 (CA-125), prolactin, cancer antigen 19-9 (CA19-9), α-fetoprotein (AFP), leptin and migration inhibitory factor (MIF)) can predict early stage breast cancer in samples collected before clinical diagnosis (phase III samples). We performed a nested case-control study within the Prospect-EPIC (European Prospective Investigation into Cancer and nutrition) cohort. We examined to what extent the biomarker panel could discriminate between 68 women diagnosed with breast cancer up to three years after enrollment and 68 matched healthy controls (all 56-64 years at baseline). Using a quantitative bead-based multiplexed assay, we determined protein concentrations in serum samples collected at enrollment. Principal Component Analysis (PCA) and Random Forest (RF) analysis revealed that on the basis of all ten proteins, early cases could not be separated from controls. When we combined serum protein concentrations and subject characteristics related to breast cancer risk in the RF analysis, this did not result in classification accuracy scores that could correctly classify the samples (sensitivity: 50%, specificity: 50%). Our findings indicate that this panel of selected tumor markers cannot be used for diagnosis of early breast cancer.

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.

Microarray-to-microarray transfer of reagents by snapping of two chips for cross-reactivity-free multiplex immunoassays

Whereas microarray and microfluidic technologies have progressed on many fronts, servicing microchips with minute amounts of reagents still constitutes an important challenge for many applications. Recently, chip-to-chip reagent transfer methods were introduced that simplify the delivery of reagents but required manual, visual alignment, custom-built microwells, and only showed the reaction of a single sample with multiple chemicals. Here, we present the snap chip, which uses common glass slides for transfer, back-side alignment for achieving precise alignment in spite of mirroring, and a snap-apparatus for facile transfer of arrays of chemicals at once by snapping the two slides together. We recently established that cross-reactivity was a significant problem in multiplex assays both theoretically and experimentally and found that it can be eliminated by avoiding mixing, but which necessitates delivering each detection antibody to a single spot with the cognate capture antibody. Using the snap chip, multiplexed sandwich immunoassays without mixing were performed: a slide with multiple arrays of 10 different capture antibodies was incubated with a sample, and then all detection antibodies transferred at once by snapping, each to the single cognate spot. All binding curves were established and limits of detection in the pg/mL range were obtained. Snap chips were stored up to 3 months prior to usage. The snap chip, by dissociating microarray production, which requires expensive equipment, from assay execution, which can be achieved using a hand-held alignment apparatus, will allow for multiplex reactions to be performed using a user-friendly kit. This new liquid handling format can be easily adapted to other applications that require transfer of minute amounts of different reagents in parallel.

Silencing of skeletal metastasis-associated genes impairs migration of breast cancer cells and reduces osteolytic bone lesions

Bone sialoprotein (BSP) and osteopontin (OPN) are important factors in the metastasis of breast cancer, which were examined as targets for antineoplastic therapy by siRNA. In addition, the effect of gene silencing on their transcription factor Runx2 and their interaction partners integrin β(3) and matrix metalloproteinase 2 was studied. The effect of siRNAs directed against these genes was assessed by monitoring expression levels followed by functional assays in cell culture as well as skeletal metastases caused by human MDA-MB-231(luc) breast cancer cells in nude rats. Upon silencing of the targets, cell migration was profoundly impaired (p < 0.001 for BSP-siRNA), but the impact on proliferation was low. Systemic administration by osmotic mini-pumps of BSP-siRNA but not OPN-siRNA decreased osteolytic lesions (p = 0.067). Extraosseous tumour growth was not affected. As an alternative approach, non-viral, polymeric based formulations of siRNAs in nanoparticles (NP) were developed. Locoregional administration of the two siRNAs targeting OPN and BSP encapsulated in these biodegradable NP reduced skeletal lesions even more efficiently (p = 0.03). Compared to systemic administration, this treatment caused not only a more pronounced anti-osteolytic effect at a 25-fold lower total siRNA dose, but also had a slight reducing effect on tumour incidence (p = 0.095). In conclusion, the siRNA treatment had a small effect on cellular proliferation but a significant efficacy against migration of and osteolysis induced by MDA-MB-231 cells. Our data underline that siRNA mediated knockdown is a powerful tool for identifying targets for pharmacological intervention. In addition, encapsulation of siRNA into biodegradable NP is a strategy, which promises well for using siRNA.

Matricellular proteins: a sticky affair with cancers

The multistep process of metastasis is a major hallmark of cancer progression involving the cointeraction and coevolution of the tumor and its microenvironment. In the tumor microenvironment, tumor cells and the surrounding stromal cells aberrantly secrete matricellular proteins, which are a family of nonstructural proteins in the extracellular matrix (ECM) that exert regulatory roles via a variety of molecular mechanisms. Matricellular proteins provide signals that support tumorigenic activities characteristic of the metastastic cascade such as epithelial-to-mesenchymal (EMT) transition, angiogenesis, tumor cell motility, proliferation, invasion, evasion from immune surveillance, and survival of anoikis. Herein, we review the current understanding of the following matricellular proteins and highlight their pivotal and multifacted roles in metastatic progression: angiopoietin-like protein 4 (ANGPTL4), CCN family members cysteine-rich angiogenic inducer 61 (Cyr61/CCN1) and CCN6, osteopontin (OPN), secreted protein acidic and rich in cysteine (SPARC), tenascin C (TNC), and thrombospondin-1 and -2 (TSP1, TSP2). Insights into the signaling mechanisms resulting from the interaction of these matricellular proteins and their respective molecular partner(s), as well as their subsequent contribution to tumor metastasis, are discussed. In addition, emerging evidences of their promising potential as therapeutic options and/or targets in the treatment of cancer are also highlighted.

Up-regulation of osteopontin expression by aryl hydrocarbon receptor via both ligand-dependent and ligand-independent pathways in lung cancer

The secreted glycol-phosphoprotein OPN not only plays important roles in immune responses and tissue remodeling but is also intimately involved in tumorigenesis. It is up-regulated in various cancers and correlated with poor prognosis. It is evident by enhancing growth and migration of cancer cells. However, the mechanisms that participate in up-regulation of OPN in lung cancer are largely unknown. Up-regulation of aryl hydrocarbon receptor (AhR), a transcription factor activated by xenobiotics, has been observed in lung cancer as well as premalignant lesions. In this study we demonstrated that AhR positively regulates OPN expression in lung cancer. We observed positive correlation of OPN and AhR expression in lung cancer specimen. Knockdown or overexpression of AhR exhibited down- or up-regulation of OPN expression in lung cancer cells. We identified an OPN promoter region between positions -268 and +435 that was activated by both ligand-independent and ligand-activated AhR. However, this region does not contain AhR response element/dioxin response element (DRE/XRE). Further truncations and internal deletions of the promoter revealed that the ligand-independent and ligand-activated AhR function through different regions of OPN promoter. The region between -268 and -100 was required for ligand-independent AhR activity. This region contains several cis-elements including AP2, C/EBP, SP1 and AP1 sites. On the other hand, the ligand-activated AhR up-regulates OPN activity through two regions of OPN promoter; one contains NFκB site at +137 and the other is between positions -100 and +126. This study suggested that both overexpression of un-induced AhR (in cases of non-smokers with high level of AhR) and ligand-activated AhR (such as smokers) contribute to up-regulation of OPN that in turn leads to lung tumorigenesis.

Pharmacokinetic characterization of an RNA aptamer against osteopontin and demonstration of in vivo efficacy in reversing growth of human breast cancer cells

BACKGROUND

We report pharmacokinetic (PK) data, evaluation of modifications for increased stability, evaluation for cellular uptake, and mediation of regression of breast cancer for the aptamer OPN-R3.

METHODS

The OPN-R3 aptamer was assessed for PK data in vivo with additional comparison of IV and subcutaneous dosing. Five aptamer variants were generated by differential 2'-O-methylation for comparison with parent. OPN-R3-Cy3 was incubated with MDA-MB231 cells and cellular uptake evaluated under confocal microscopy. Mice were treated with OPN-R3, mutant, or saline 3 weeks after inoculation with MDA-MB231 cells and tumor size was evaluated.

RESULTS

OPN-R3 PK data were: t(1/2) 7.76 hours, T(max) 3 hours, C(max) 13.2 mmol/L, mean residence time 9 hours, AUC (0-t) 161.9 mmol/hr/L, and K(d) 57.2 nmol/L. The half-life was higher when given intravenously versus subcutaneously (E(1/2) 7.93 vs 0.74 hours). The 2' methylation of all available bases increased unmodified aptamer stability and affinity (t(1/2) 6.2 hours; K(d) 520 nmol/L), but this did not improve on parent aptamer (t(1/2) 7.78 hours, K(d) 18 nmol/L). The aptamer remained extracellular. OPN-R3 caused regression of tumor to levels seen at 1 week after tumor inoculation.

CONCLUSION

We show the efficacy of OPN-R3 for reversing growth of breast cancer cells with adequate PK stability for clinical application.

Pre- and post-translational regulation of osteopontin in cancer

Osteopontin (OPN) is a matricellular protein that binds to a number of cell surface receptors including integrins and CD44. It is expressed in many tissues and secreted into body fluids including blood, milk and urine. OPN plays important physiological roles in bone remodeling, immune response and inflammation. It is also a tumour-associated protein, and elevated OPN levels are associated with tumour formation, progression and metastasis. Research has revealed a promising role for OPN as a cancer biomarker. OPN is subject to alternative splicing, as well as post-translational modifications such as phosphorylation, glycosylation and proteolytic cleavage. Functional differences have been revealed for different isoforms and post-translational modifications. The pattern of isoform expression and post-translational modification is cell-type specific and may influence the potential role of OPN in malignancy and as a cancer biomarker.

Plasma versus serum levels of osteopontin and mesothelin in patients with malignant mesothelioma--which is best?

BACKGROUND

Blood-based markers for malignant mesothelioma (MM), particularly soluble mesothelin and osteopontin, are currently of great clinical interest. As there is some concern about the sensitivity of osteopontin in serum versus plasma, we compared them in the same patient population to mesothelin.

METHODS

Soluble mesothelin and osteopontin concentrations were determined by commercial assays in blood samples from 66 patients with pleural MM, 47 patients with non-malignant asbestos-related lung or pleural disease, 42 patients with other benign pleural and lung diseases and 21 patients with lung cancer.

RESULTS

Soluble mesothelin and osteopontin in serum and plasma were significantly elevated in MM patients compared to patients with benign lung and pleural disease. At a level of specificity of 95% relative to patients with benign disease, the sensitivity of mesothelin in serum and plasma at presentation with symptoms was 67%, and for osteopontin in the plasma was 40% and in the serum was 20% for MM patients. Combining the serum mesothelin and plasma osteopontin markers using a logistic regression model did not significantly increase the area under the receiver operator curve.

CONCLUSION

Plasma osteopontin has a superior diagnostic accuracy to serum. As the choice of blood sample type has limit effect on soluble mesothelin sensitivity, plasma should be collected for biomarker evaluation in patients suspected of having mesothelioma.

Osteopontin promotes CCL5-mesenchymal stromal cell-mediated breast cancer metastasis

The interaction between cancer and its local microenvironment can determine properties of growth and metastasis. A critical component of the tumor microenvironment in this context is the cancer-associated fibroblast (CAF), which can promote tumor growth, angiogenesis and metastasis. It has been hypothesized that CAF may be derived from mesenchymal stromal cells (MSC), derived from local or distant sources. However, the signaling mechanisms by which tumors and MSCs interact to promote CAF-dependent cancer growth are largely unknown. In this study with in vitro and in vivo models using MDA-MB231 human breast cancer cells, we demonstrate that tumor-derived osteopontin (OPN) induces MSC production of CCL5; the mechanism involves OPN binding to integrin cell surface receptors and activator protein-1 c-jun homodimer transactivation. In a murine xenograft model, concomitant inoculation of MSC with MDA-MB231 cells induces: (i) significantly increased growth and metastasis of MB231 cells and (ii) increased MSC migration to metastatic sites in lung and liver; this mechanism is both OPN and CCL5 dependent. MSCs retrieved from sites of metastases exhibit OPN-dependent expression of the CAF markers, α-smooth muscle actin, tenascin-c, CXCL12 (or stromal cell-derived factor 1) and fibroblast-specific protein-1 and the matrix metalloproteinases (MMP)-2 and MMP-9. Based upon these results, we propose that tumor-derived OPN promotes tumor progression via the transformation of MSC into CAF.

Deletion of the thrombin cleavage domain of osteopontin mediates breast cancer cell adhesion, proteolytic activity, tumorgenicity, and metastasis

BACKGROUND

Osteopontin (OPN) is a secreted phosphoprotein often overexpressed at high levels in the blood and primary tumors of breast cancer patients. OPN contains two integrin-binding sites and a thrombin cleavage domain located in close proximity to each other.

METHODS

To study the role of the thrombin cleavage site of OPN, MDA-MB-468 human breast cancer cells were stably transfected with either wildtype OPN (468-OPN), mutant OPN lacking the thrombin cleavage domain (468-ΔTC) or an empty vector (468-CON) and assessed for in vitro and in vivo functional differences in malignant/metastatic behavior.

RESULTS

All three cell lines were found to equivalently express thrombin, tissue factor, CD44, αvβ5 integrin and β1 integrin. Relative to 468-OPN and 468-CON cells, 468-ΔTC cells expressing OPN with a deleted thrombin cleavage domain demonstrated decreased cell adhesion (p < 0.001), decreased mRNA expression of MCAM, maspin and TRAIL (p < 0.01), and increased uPA expression and activity (p < 0.01) in vitro. Furthermore, injection of 468-ΔTC cells into the mammary fat pad of nude mice resulted in decreased primary tumor latency time (p < 0.01) and increased primary tumor growth and lymph node metastatic burden (p < 0.001) compared to 468-OPN and 468-CON cells.

CONCLUSIONS

The results presented here suggest that expression of thrombin-uncleavable OPN imparts an early tumor formation advantage as well as a metastatic advantage for breast cancer cells, possibly due to increased proteolytic activity and decreased adhesion and apoptosis. Clarification of the mechanisms responsible for these observations and the translation of this knowledge into the clinic could ultimately provide new therapeutic opportunities for combating breast cancer.

Osteopontin as a potential biomarker of proliferation and invasiveness for lung cancer

PURPOSE

Lung cancer is one of the most malignant tumors and poses a significant threat to human health. Osteopontin (OPN) is a variably expressed, secreted glycophosphoprotein that mediates the growth and metastases of several carcinoma types. In this study, we aimed to understand the role of OPN in lung cancer cell proliferation and invasiveness.

METHODS

Expression of OPN was examined using an immunohistochemical method in paraffin-embedded sections collected from 49 patients with lung cancer. We silenced OPN expression by lentivirus-mediated OPN-specific small interfering RNA (siRNA) and examined the proliferation and invasiveness of OPN-silenced lung cancer cell (A549) through MTT, BrdU, flow cytometry, and Matrigel assay. In addition, we tested the role of individual OPN splice variants in A549 cell growth and invasion by constructing OPN overexpression lentiviruses.

RESULT

Downregulation of OPN inhibited A549 cell proliferation and in vivo tumor growth, abrogated augmentation of invasion, induced G1-phase cell cycle arrest, and induced cell late apoptosis and necrosis. Moreover, the proliferation and invasiveness was linked to different OPN splice variants, of which OPN-b affected the cell proliferation and OPN-c showed significant correlation with invasion behavior.

CONCLUSIONS

Our data suggested that OPN served as a potential biomarker for invasive lung cancer and provided new molecular-targeted therapy for lung cancer based on lentivirus-mediated RNA interference.

Hedgehog signaling induced by breast cancer cells promotes osteoclastogenesis and osteolysis

Bone integrity is maintained by a dynamic equilibrium between the activities of bone-forming osteoblasts and bone-resorbing osteoclasts. Osteolytic lesions are a painful consequence of metastasis of breast cancer cells to bone in an overwhelming majority of breast cancer patients. Factors secreted by breast cancer cells propel a cascade of events that trigger osteoclastogenesis and elevated bone resorption. In the present study, we show that the Hedgehog (Hh) ligands secreted by breast cancer cells promote osteoclast differentiation and potentiate the activity of mature osteoclasts. Paracrine Hh signaling induced by breast cancer cells mediates a detrimental chain of events by the up-regulation of osteopontin (OPN), which in turn enhances osteoclastic activity by up-regulating cathepsin K and MMP9. Hh signaling is essential for osteoclasts because blocking the Hh pathway using the pharmacological Hh inhibitor, cyclopamine, results in an overall decrease in osteoclastogenesis and resorptive activity. Our studies suggest that inhibiting Hh signaling interferes with the ability of pre-osteoclasts to respond to the stimulatory effects of the breast cancer cells, indicating that Hh signaling is vital to osteoclast activity.

Effects of osteopontin inhibition on radiosensitivity of MDA-MB-231 breast cancer cells

Background

Osteopontin (OPN) is a secreted glycophosphoprotein that is overexpressed in various tumors, and high levels of OPN have been associated with poor prognosis of cancer patients. In patients with head and neck cancer, high OPN plasma levels have been associated with poor prognosis following radiotherapy. Since little is known about the relationship between OPN expression and radiosensitivity, we investigated the cellular and radiation induced effects of OPN siRNA in human MDA-MB-231 breast cancer cells.

Methods

MDA-MB-231 cells were transfected with OPN-specific siRNAs and irradiated after 24 h. To verify the OPN knockdown, we measured the OPN mRNA and protein levels using qRT-PCR and Western blot analysis. Furthermore, the functional effects of OPN siRNAs were studied by assays to assess clonogenic survival, migration and induction of apoptosis.

Results

Treatment of MDA-MB-231 cells with OPN siRNAs resulted in an 80% decrease in the OPN mRNA level and in a decrease in extracellular OPN protein level. Transfection reduced clonogenic survival to 42% (p = 0.008), decreased the migration rate to 60% (p = 0.15) and increased apoptosis from 0.3% to 1.7% (p = 0.04). Combination of OPN siRNA and irradiation at 2 Gy resulted in a further reduction of clonogenic survival to 27% (p < 0.001), decreased the migration rate to 40% (p = 0.03) and increased apoptosis to 4% (p < 0.005). Furthermore, OPN knockdown caused a weak radiosensitization with an enhancement factor of 1.5 at 6 Gy (p = 0.09) and a dose modifying factor (DMF₁₀) of 1.1.

Conclusion

Our results suggest that an OPN knockdown improves radiobiological effects in MDA-MB-231 cells. Therefore, OPN seems to be an attractive target to improve the effectiveness of radiotherapy.

Osteopontin is up-regulated and associated with neutrophil and macrophage infiltration in glioblastoma

Osteopontin (OPN) is a glycophosphoprotein with multiple intracellular and extracellular functions. In vitro, OPN enhances migration of mouse neutrophils and macrophages. In cancer, extracellular OPN facilitates migration of cancer cells via its RGD sequence. The present study was designed to investigate whether osteopontin is responsible for neutrophil and macrophage infiltration in human cancer and in particular in glioblastoma. We found that in vitro mouse neutrophil migration was RGD-dependent. In silico, we found that the OPN gene was one of the 5% most highly expressed genes in 20 out of 35 cancer microarray data sets in comparison with normal tissue in at least 30% of cancer patients. In some types of cancer, such as ovarian cancer, lung cancer and melanoma, the OPN gene was one of those with the highest expression levels in at least 90% of cancer patients. In glioblastoma, the most invasive type of brain tumours/glioma, but not in lower grades of glioma it was one of the 5% highest expressed genes in 90% of patients. In situ, we found increased protein levels of OPN in human glioblastoma versus normal human brain confirming in silico results. OPN protein expression was co-localized with neutrophils and macrophages. In conclusion, OPN in tumours not only induces migration of cancer cells but also of leucocytes.

Matricellular proteins: from homeostasis to inflammation, cancer, and metastasis

The family of matricellular proteins comprises molecules with disparate biology. The main characteristic of matricellular proteins is to be expressed during tissue renewal and repair in order to "normalize" the tissue. Tumors are wound that do not heal, and tumor growth and metastasis can be viewed as a consequence of aberrant homeostasis, during which matricellular proteins are often upregulated. In the tumor microenvironment, they can be produced by both tumor cells and surrounding stromal cells, such as fibroblasts and macrophages. In this context, matricellular proteins can exert several functions that actively contribute to tumor progression. They may (a) regulate cellular adhesion and migration and extracellular matrix deposition, (b) control tumor infiltration by macrophages or other leukocytes, (c) affect tumor angiogenesis, (d) regulate TGFbeta and other growth factor receptor signals, (e) directly stimulate integrin receptors to transduce pro-survival or pro-migratory signals, and (f) regulate the wnt/beta-catenin pathways. Most of these functions contribute to settle a chronic low inflammatory state, whose involvement in tissue transformation and tumor progression is now established.

Osteopontin: an effector and an effect of tumor metastasis

Osteopontin (OPN) is a matricellular protein that is produced by multiple tissues in our body and is most abundant in bone. It is also produced by cancer cells and plays a determinative role in the growth, progression and metastasis of cancer. Clinically, OPN has been reported to be upregulated in tumor cells per se; this is also reflected by increased levels of OPN in the circulation. Thus, increased OPN levels the plasma are an effect of tumor growth and progression. Functionally, high OPN levels are determinative of higher incidence of bone metastases in mouse models and are clinically correlated with metastatic bone disease and bone resorption in advanced breast cancer patients. Several research efforts have been made to therapeutically target and inhibit the activities of OPN. In this article we have reviewed OPN in its role as an effector of critical steps in tumor progression and metastasis, with a particular emphasis on its role in facilitating bone metastasis of breast cancer. We have also addressed the role of the host-derived OPN in influencing the malignant behavior of the tumor cells.

Osteopontin can act as an effector for a germline mutation of BRCA1 in malignant transformation of breast cancer-related cells

Breast cancer-associated 1 (BRCA1) plays an important role in breast cancer initiation and progression through its functions in the cell cycle and DNA repair processes; however, its role in metastatic development in human breast cancer is still poorly understood. We have previously shown that osteopontin (OPN) expression was suppressed by wild-type BRCA1 (Wt.BRCA1) and that a natural mutant allele of BRCA1 (Mut.BRCA1) diminished the effect of Wt.BRCA1 on OPN in vitro. In this study, we show that while Wt.BRCA1 suppresses OPN-induced metastasis in a rat syngeneic system, Mut.BRCA1 enhances the development of metastasis through OPN, suggesting that OPN and BRCA1 work closely to regulate metastatic development in the rat. To test whether these findings are relevant to human breast cancer, we have investigated the relationship between BRCA1, OPN, and metastatic properties in human breast cancer-related cells. Using western blot analysis, we show that Wt.BRCA1 suppresses, while Mut.BRCA1 enhances, OPN protein expression; and in parallel that Wt.BRCA1 suppresses, while Mut.BRCA1 enhances, OPN-mediated in vitro properties associated with the metastatic state in both MCF-7 and MDA MB435s cells. Overall, these results suggest that Mut.BRCA1 can elicit some of the changes involved in metastatic progression in human breast cancer via the overexpression of OPN.

Microdialysis combined with proteomics for protein identification in breast tumor microenvironment in vivo

Tumor microenvironment constitutes a reservoir for proteins released from tumor cells and the host, which can contribute significantly to tumor growth and invasion. This study aims to apply a method of combining in vivo microdialysis and proteomics to identify proteins in mammary tumor interstitial fluids, a major component of tumor microenvironment. In vivo microdialysis was performed in polyomavirus middle T antigen (PyVmT) transgenic mouse mammary tumors and age-matched control wild-type mammary glands. Over four hundred proteins were identified from the microdialysis perfusates, using the Multidimensional Protein Identification Technology. Osteopontin (OPN) is one of the proteins overexpressed in breast tumor perfusates, as confirmed with immunoassays. OPN was also found to be present in tumor-associated stroma in both PyVmT and human breast tumors, using immunohistochemistry. Specifically, fibroblasts were further shown to express OPN at both mRNA and protein levels. In vitro assays showed that OPN can stimulate PyVmT breast carcinoma cell proliferation and migration. Finally, the expression of OPN was significantly higher in the peripheral blood of mice bearing breast tumors, compared to wild-type mice. Overall, microdialysis combined with proteomics is a unique technique for identifying proteins in a tumor microenvironment in vivo. Mammary fibroblasts can secrete OPN, and its overexpression in mammary tumor microenvironment may contribute significantly to mammary tumor progression.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s12307-010-0046-3) contains supplementary material, which is available to authorized users.

Small integrin-binding proteins as serum markers for prostate cancer detection

PURPOSE

The small integrin-binding ligand N-linked glycoprotein (SIBLING) gene family includes bone sialoprotein (BSP), dentin matrix protein 1 (DMP1), dentin sialophosphoprotein (DSPP), matrix extracellular phosphoglycoprotein (MEPE), and osteopontin (OPN). Previous studies have separately reported elevated expression of BSP, OPN, or DSPP in prostate tumor paraffin sections. We hypothesized that SIBLINGs may be informative serum markers for subjects with prostate cancer.

METHODS

Expression levels of SIBLINGs in biopsies of normal tissue and tumors from prostate were determined by cDNA array and by immunohistochemical staining with monoclonal antibodies. Competitive ELISAs for measuring total BSP, DSPP, MEPE, and OPN were applied to a test group of 102 subjects with prostate cancer and 110 normal subjects and a validation group of 90 subjects.

RESULTS

BSP, DMP1, DSPP, and OPN exhibited elevated mRNA expression and protein levels in biopsies. BSP, DSPP, and OPN were elevated in serum from prostate cancer subjects, with serum DSPP exhibiting the greatest difference, yielding an area under the receiver operator characteristic curve value of 0.98. Serum BSP and OPN levels were significantly elevated only in late stages, whereas DSPP was significantly elevated at all stages. Optimal serum value cutoff points derived for BSP, OPN, and DSPP were applied as a validation test to a new group of 90 subjects and DSPP yielded a sensitivity of 90% and a specificity of 100%.

CONCLUSION

Of the SIBLING gene family members, DSPP appears to be a strong candidate for use in serum assays for prostate cancer detection.

Spheroid-forming subpopulation of breast cancer cells demonstrates vasculogenic mimicry via hsa-miR-299-5p regulated de novo expression of osteopontin

The growth of cancer cells as multicellular spheroids has frequently been reported to mimic the in vivo tumour architecture and physiology and has been utilized to study antitumour drugs. In order to determine the distinctive characteristics of the spheroid-derived cells compared to the corresponding monolayer-derived cells, we enriched multicellular spheroid-forming subpopulations of cells from three human breast cancer cell lines (MCF7, MCF10AT and MCF10DCIS.com). These spheroid-derived cells were injected into female athymic nude mice to assess their tumorigenic potential and were profiled for their characteristic miRNA signature. We discovered that the spheroid-derived cells expressed increased levels of osteopontin (OPN), an oncogenic protein that has been clinically correlated with increased tumour burden and adverse prognosis in patients with breast cancer metastasis. Our studies further show that increased OPN levels are brought about in part, by decreased levels of hsa-mir-299–5p in the spheroid-forming population from all three cell lines. Moreover, the spheroid-forming cells can organize into vascular structures in response to nutritional limitation; these structures recapitulate a vascular phenotype by the expression of endothelial markers CD31, Angiopoeitin-1 and Endoglin. In this study, we have validated that hsa-mir-299–5p targets OPN; de novo expression of OPN in turn plays a critical role in enhancing proliferation, tumorigenicity and the ability to display vasculogenic mimicry of the spheroid-forming cells.

Extracellular and intracellular mechanisms that mediate the metastatic activity of exogenous osteopontin

BACKGROUND

Osteopontin affects several steps of the metastatic cascade. Despite direct correlation with metastasis in experimental systems and in patient studies, the extracellular and intracellular basis for these observations remains unsolved. In this study, the authors used human melanoma and sarcoma cell lines to evaluate the effects of soluble osteopontin on metastasis.

METHODS

Exogenous osteopontin or negative controls, including a site-directed mutant osteopontin, were used in functional assays in vitro, ex vivo, and in vivo that were designed to test the extracellular and intracellular mechanisms involved in experimental metastasis.

RESULTS

In the extracellular environment, the results confirmed that soluble osteopontin is required for its prometastatic effects; this phenomenon is specific, arginine-glycine-aspartic acid (RGD)-dependent, and evident in experimental models of metastasis. In the intracellular environment, osteopontin initially induced rapid tyrosine 418 (Tyr-418) dephosphorylation of the cellular homolog of the Rous sarcoma virus (c-Src), with decreases in actin stress fibers and increased binding to the vascular endothelium. This heretofore undescribed Tyr dephosphorylation was followed by a tandem c-Src phosphorylation after tumor cell attachment to the metastatic site.

CONCLUSIONS

The results of this study revealed a complex molecular interaction as well as a dual role for osteopontin in metastasis that depends on whether tumor cells are in circulation or attached. Such context-dependent functional insights may contribute to antimetastasis strategies.

New Dual Monoclonal ELISA for Measuring Plasma Osteopontin as a Biomarker Associated with Survival in Prostate Cancer: Clinical Validation and Comparison of Multiple ELISAs

Background: A previously developed monoclonal/polyclonal ELISA (Mono/Poly) to detect plasma concentrations of osteopontin (OPN) was shown to provide prognostic information in breast, prostate, and other cancers. Here we describe the clinical validation of a new dual monoclonal (Dual Mono) assay. We compared both assays with 4 assays that recognize defined regions of OPN protein (dual polyclonal systems 5-1, 4-1, 4-3 and polyclonal-monoclonal system 1-3).

Methods: OPN sequences recognized by the monoclonal antibodies that make up the Dual Mono ELISA were identified by Pepscan CLIPS™ analysis. Using the 6 ELISAs, we measured OPN in plasma from 66 patients with castration-resistant prostate cancer, and we assessed the ability of each assay to predict patient survival.

Results: The assays varied in measured plasma OPN concentrations, with median values ranging from 112 to 1740 μg/L, and ability to predict patient survival. By Cox univariable regression of survival by tertiles of OPN, the Mono/Poly and Dual Mono ELISAs had the highest log-rank χ2 values. After adjustment for risk factors independently associated with survival in our samples, OPN remained associated with survival only for the Mono/Poly and Dual Mono systems.

Conclusions: OPN plasma values varied significantly depending on the assay used. Only the Mono/Poly and Dual Mono systems were independently associated with survival in a population of men with castration-resistant prostate cancer. The availability of a clinically validated, dual monoclonal–based ELISA will provide consistent reagents for studies of OPN plasma concentrations in cancer and other pathologies.

Comprehensive study on the prognostic role of osteopontin expression in oral squamous cell carcinoma

Osteopontin is a tumor-associated protein that promotes tumor development and metastasis. The preoperative blood samples of 94 oral squamous cell carcinoma (OSCC) patients and 28 healthy individuals were analyzed for plasma osteopontin levels, and another 256 paraffin-embedded OSCC specimens were analyzed by osteopontin immunostaining. The patients with advanced tumor (T) stage (T3/T4 vs. T1/T2) and positive nodal (N) status had significantly higher plasma levels of osteopontin (both p<0.001). Positive osteopontin immunostaining also correlated significantly with advanced T stage (p<0.001), positive N status (p<0.001), advanced TNM stage (p<0.001) and male gender (p=0.016). Unfavorable cumulative 5-year overall survival rates correlated significantly with positive osteopontin immunostaining (p<0.001), advanced T stage (p<0.001), positive N status (p<0.001) and advanced TNM stage (p<0.001). However, Cox regression analysis revealed that T stage and N status were independent prognostic factors for survival (both p<0.001) and osteopontin immunostaining was marginally significant for survival (p=0.056). The present study demonstrated that high expression level of osteopontin in either the plasma or the tumor of the patients with OSCC was associated with tumor progression, suggesting that osteopontin expression is an important prognostic factor for OSCC.

Activation of the osteopontin/matrix metalloproteinase-9 pathway correlates with prostate cancer progression

PURPOSE

Prostate cancer remains the second most frequent cause of tumor-related deaths in the Western world. Additional markers for the identification of prostate cancer development and progression are needed. Osteopontin (OPN), which activates matrix metalloproteinases (MMP), is considered a prognostic biomarker in several cancers. "In silico" and experimental approaches were used to determine whether OPN-mediated MMP activation may be a signal of prostate cancer progression.

EXPERIMENTAL DESIGN

Pearson correlation coefficients were computed for each OPN/MMP pair across seven publicly available prostate cancer gene expression data sets. Using Gene Set Enrichment Analysis, 101 cancer-related gene sets were analyzed for association with OPN and MMP-9 expression. OPN, MMP-9, MMP-2 tissue inhibitor of metalloproteinase-1 plasma levels, and MMP gelatinase activity were measured by ELISA and zymography in 96 and 92 patients with prostate cancer and benign prostatic hyperplasia, respectively, and 125 age-matched healthy men.

RESULTS

Computational analyses identified a significant correlation only between MMP-9 and OPN, and showed significant enrichment scores in "cell proliferation", "genes constituting the phosphoinositide-3-kinase predictor", "proliferation signature", and "tumor metastasis" gene sets in association with both OPN and MMP-9. Plasma analyses revealed a significant increase in OPN and MMP-9 levels and activity in patients with prostate cancer in association with clinical variables (prostate-specific antigen > 4 ng/mL and Gleason score > 7). Significant correlation between OPN and MMP-9 levels were also observed. Mean plasma levels of OPN and MMP-9 decreased in patients with prostate cancer within 6 months after prostatectomy.

CONCLUSIONS

The concordant computational and experimental data indicate that the extent of OPN pathway activation correlates with prostate cancer progression.

Lower osteopontin plasma levels are associated with superior outcomes in advanced non-small-cell lung cancer patients receiving platinum-based chemotherapy: SWOG Study S0003

PURPOSE

S0003 was a phase III trial of carboplatin/paclitaxel with or without the hypoxic cytotoxin tirapazamine in patients with advanced or metastatic non-small-cell lung cancer (NSCLC). We investigated the relationship between clinical outcomes and plasma levels of the hypoxia-associated protein osteopontin (OPN) in patients on this protocol.

PATIENTS AND METHODS

Baseline plasma was obtained from 172 patients. In 56 patients, sequential plasma was obtained after one or two cycles. Concentrations of OPN, as well as plasminogen activator inhibitor-1 (PAI-1) and vascular endothelial growth factor (VEGF), were measured using enzyme-linked immunosorbent assay. Tumor expression of OPN was assessed by immunohistochemistry in 61 matched archival specimens.

RESULTS

Patients with lower OPN levels (below the median) had a significantly superior overall survival compared with patients with higher levels, regardless of treatment arm (hazard ratio [HR] = 0.60, P = .002). A similar correlation was observed for progression-free survival (HR = 0.69, P = .02). When examined as a continuous variable, OPN maintained its significant association with both progression-free (HR = 1.05, P = .01) and overall survival (HR = 1.09, P < .0001). Patients with lower plasma OPN levels were significantly more likely to have tumor response (P = .03). No differences were observed between treatment arms. Tumor OPN levels did not correlate with patient outcomes or with plasma levels. No associations were observed between patient outcomes and VEGF or PAI-1 levels; however, plasma concentrations of these markers were significantly interrelated (P < .0001) and significantly decreased after treatment (P = .0002 and P = .03, respectively).

CONCLUSION

Pretreatment plasma levels of OPN are significantly associated with patient response, progression-free survival, and overall survival in chemotherapy-treated patients with advanced NSCLC.

Practical approaches to proteomic biomarkers within prostate cancer radiotherapy trials

INTRODUCTION

Proteomic biomarkers may be useful for monitoring therapeutic response and to triage cancer patients to best therapy.

OBJECTIVES

In this review, we highlight the importance of specimen acquisition, preparation and analysis in radiotherapy proteomic studies. We also discuss practical approaches for the design and execution of clinical proteomic studies using our recent experience based on specimens accrued during prostate cancer radiation therapy.

DISCUSSION AND CONCLUSIONS

Numerous proteomic methods are being employed, including high-throughput mass spectrometry and immunoassays, and using solid tissues, blood and urine for analysis. Given the potential complexity of cytokine and other protein responses, there is a need to assess proteomic signatures within serial samples as longitudinal studies during a course of fractionated radiotherapy (RT).

RAN GTPase is an effector of the invasive/metastatic phenotype induced by osteopontin

Osteopontin (OPN) is a phosphorylated glycoprotein that binds to alpha v-containing integrins and is important in malignant transformation and cancer. Previously, we have utilized suppressive subtractive hybridization between mRNAs isolated from the Rama 37 (R37) rat mammary cell line and a subclone rendered invasive and metastatic by stable transfection with an expression vector for OPN to identify RAN GTPase (RAN) as the most overexpressed gene, in addition to that of OPN. Here we show that transfection of noninvasive R37 cells with an expression vector for RAN resulted in increased anchorage-independent growth, cell attachment and invasion through Matrigel in vitro, and metastasis in syngeneic rats. This induction of a malignant phenotype was induced independently of the expression of OPN, and was reversed by specifically reducing the expression of RAN using small-interfering RNAs. By using a combination of mutant protein and inhibitors, it was found that RAN signal transduction occurred through the c-Met receptor and PI3 kinase. This study therefore identifies RAN as a novel effector of OPN-mediated malignant transformation and some of its downstream signaling events in a mammary epithelial model of cancer invasion/metastasis.

Downregulation of osteopontin contributes to metastasis suppression by breast cancer metastasis suppressor 1

Breast cancer metastasis suppressor 1 (BRMS1) inhibits the ability of multiple human and murine cancer cell lines to metastasize to lymph nodes, bones and lungs. Comparison of mRNA expression in metastatic MDA-MB-435 human carcinoma cells (435) and metastasis-suppressed BRMS1 transfectants (435/BRMS1) showed a marked (>90%) reduction of osteopontin (OPN) mRNA and protein expression in BRMS1-overexpressing cells. OPN expression is associated with disease progression in patients, with higher levels of OPN produced by cancer cells associated with poorer patient survival. Furthermore, OPN has been suggested to promote survival of cancer cells in response to stress, although the mechanisms by which this may occur remain poorly understood. This study tested the hypothesis that re-expression of OPN in metastasis-suppressed 435/BRMS1 cells would reverse metastasis suppression and confer protection from stress-induced apoptosis. A stable pooled population of OPN overexpressing 435/BRMS1 cells was created (435/BRMS1/OPN). OPN re-expression did not affect in vitro cell growth rates; however, increased anchorage independent growth/survival and protection from hypoxia-induced apoptosis was observed (p < 0.05). In vivo, OPN re-expression in BRMS1 transfected cells did not affect in vivo primary tumor growth but did increase the incidence of spontaneous metastasis to lymph nodes and lungs in mice. These novel findings suggest that OPN downregulation by BRMS1 may be responsible, at least in part, for BRMS1-mediated metastasis suppression by sensitizing cancer cells to stress induced apoptosis. These studies clarify one mechanism by which BRMS1 can suppress metastasis.

Osteopontin: regulation in tumor metastasis

Osteopontin is a secreted phosphoprotein that has been implicated as an important mediator of tumor metastasis and has been investigated for use as a biomarker for advanced disease and as a potential therapeutic target in the regulation of cancer metastasis. The OPN DNA sequence is highly conserved and the protein contains several important functional domains including alpha(v)beta integrin and CD44 binding sites. High levels of OPN expression correlate with tumor invasion, progression or metastasis in multiple cancer. Studies demonstrate that osteopontin mediates the molecular mechanisms which determine metastatic spread, such as prevention of apoptosis, extracellular matrix proteolysis and remodeling, cell migration, evasion of host-immune cells and neovascularization. Transcriptional regulation of OPN is complex and involves multiple pathways, including AP-1, Myc, v-Src, Runx/CBF, TGF-B/BMPs/Smad/Hox, and Wnt/ss-catenin/APC/GSK-3ss/Tcf-4. The current state of knowledge of OPN biology suggests that it is an attractive target for therapeutic modulation of metastatic disease.