Successful treatment of collagen-induced arthritis in non-human primates by chimeric anti-osteopontin antibody

Thrombin Cleavage of Osteopontin and the Host Anti-Tumor Immune Response

Osteopontin (OPN) is a multi-functional protein that is involved in various cellular processes such as cell adhesion, migration, and signaling. There is a single conserved thrombin cleavage site in OPN that, when cleaved, yields two fragments with different properties from full-length OPN. In cancer, OPN has tumor-promoting activity and plays a role in tumor growth and metastasis. High levels of OPN expression in cancer cells and tumor tissue are found in various types of cancer, including breast, lung, prostate, ovarian, colorectal, and pancreatic cancer, and are associated with poor prognosis and decreased survival rates. OPN promotes tumor progression and invasion by stimulating cell proliferation and angiogenesis and also facilitates the metastasis of cancer cells to other parts of the body by promoting cell adhesion and migration. Furthermore, OPN contributes to immune evasion by inhibiting the activity of immune cells. Thrombin cleavage of OPN initiates OPN's tumor-promoting activity, and thrombin cleavage fragments of OPN down-regulate the host immune anti-tumor response.

The Role and Clinical Relevance of Osteopontin in Allergic Airway Diseases

The airway epithelium is exposed to numerous external irritants including infectious agents, environmental allergens, and atmospheric pollutants, releasing epithelial cytokines including thymic stromal lymphopoietin (TSLP), IL-33, and IL-25 and initiating downstream type 2 (IL-4, IL-13, and IL-5) and IgE-driven pathways. These pathways trigger the initiation and progression of allergic airway diseases, including chronic rhinosinusitis with nasal polyps (CRSwNP), allergic rhinitis (AR), and allergic asthma. However, the use of biological agents that target downstream cytokines, such as IL-5, IL-4, and IL-13 receptors and IgE, might not be sufficient to manage some patients successfully. Instead of blocking downstream cytokines, targeting upstream epithelial cytokines has been proposed to address the complex immunologic networks associated with allergic airway diseases. Osteopontin (OPN), an extracellular matrix glyco-phosphoprotein, is a key mediator involved in Th1-related diseases, including systemic lupus erythematosus, multiple sclerosis, inflammatory bowel disease, and rheumatoid arthritis. Emerging evidence, including ours, indicates that epithelial-cell-derived OPN also plays an essential role in Th2-skewed airway diseases, including CRSwNP, AR, and allergic asthma involving the Th17 response. Therefore, we reviewed the current knowledge of epithelial-cell-derived OPN in the pathogenesis of three type-2-biased airway diseases and provided a direction for its future investigation and clinical relevance.

Osteopontin: A Bone-Derived Protein Involved in Rheumatoid Arthritis and Osteoarthritis Immunopathology

Osteopontin (OPN) is a bone-derived phosphoglycoprotein related to physiological and pathological mechanisms that nowadays has gained relevance due to its role in the immune system response to chronic degenerative diseases, including rheumatoid arthritis (RA) and osteoarthritis (OA). OPN is an extracellular matrix (ECM) glycoprotein that plays a critical role in bone remodeling. Therefore, it is an effector molecule that promotes joint and cartilage destruction observed in clinical studies, in vitro assays, and animal models of RA and OA. Since OPN undergoes multiple modifications, including posttranslational changes, proteolytic cleavage, and binding to a wide range of receptors, the mechanisms by which it produces its effects, in some cases, remain unclear. Although there is strong evidence that OPN contributes significantly to the immunopathology of RA and OA when considering it as a common denominator molecule, some experimental trial results argue for its protective role in rheumatic diseases. Elucidating in detail OPN involvement in bone and cartilage degeneration is of interest to the field of rheumatology. This review aims to provide evidence of the OPN’s multifaceted role in promoting joint and cartilage destruction and propose it as a common denominator of AR and OA immunopathology.

Osteopontin in autoimmune disorders: current knowledge and future perspective

Osteopontin (OPN) is a multifunctional cytokine and adhesion molecule, as well as an unusual regulator for both innate and adaptive immune responses. Several immune cells can produce OPN, including dendritic cells (DCs), macrophages, and T lymphocytes. OPN expression is reported to be increased in a wide range of disorders, including autoimmunity, cancer, and allergy. The overexpression of OPN in several autoimmune disorders, such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), multiple sclerosis (MS), Type 1 diabetes (T1D), inflammatory bowel disease (IBD), Sjögren's, and myasthenia gravis, have been shown to be correlated with disease severity. Regarding the important regulatory roles of OPN in the immune system, this study aimed to review the role of this molecule in autoimmune disorders and to provide a complete view of the current knowledge in this field.

Osteopontin Blockade Immunotherapy Increases Cytotoxic T Lymphocyte Lytic Activity and Suppresses Colon Tumor Progression

Simple Summary

Despite the breakthrough in human cancer immunotherapy, colorectal cancer, except for the small subset of microsatellite instable colorectal cancer (MSI, ~4% total cases), is one of the few human cancers that does not respond to current immune checkpoint inhibitor (ICI) immunotherapy. CTLs are present in both MSI and microsatellite stable (MSS) human colon carcinoma, suggesting that PD-L1-independent mechanisms may exist and suppress CTL activation in the colon tumor microenvironment. We determined that osteopontin (OPN) inhibits tumor-specific cytotoxic T lymphocyte (CTL) lytic activity to promote colon tumor growth in vivo. Accordingly, OPN blockade immunotherapy using OPN neutralization monoclonal antibodies 100D3 and 103D6 suppressed colon tumor growth in vivo. Our findings indicate that 100D3 and 103D6 has the potential to be further developed for colorectal cancer immunotherapy.

Abstract

Human colorectal cancers are mostly microsatellite-stable with no response to anti-PD-1 blockade immunotherapy, necessitating the development of a new immunotherapy. Osteopontin (OPN) is elevated in human colorectal cancer and may function as an immune checkpoint. We aimed at elucidating the mechanism of action of OPN and determining the efficacy of OPN blockade immunotherapy in suppression of colon cancer. We report here that OPN is primarily expressed in tumor cells, myeloid cells, and innate lymphoid cells in human colorectal carcinoma. Spp1 knock out mice exhibit a high incidence and fast growth rate of carcinogen-induced tumors. Knocking out Spp1 in colon tumor cells increased tumor-specific CTL cytotoxicity in vitro and resulted in decreased tumor growth in vivo. The OPN protein level is elevated in the peripheral blood of tumor-bearing mice. We developed four OPN neutralization monoclonal antibodies based on their efficacy in blocking OPN inhibition of T cell activation. OPN clones 100D3 and 103D6 increased the efficacy of tumor-specific CTLs in killing colon tumor cells in vitro and suppressed colon tumor growth in tumor-bearing mice in vivo. Our data indicate that OPN blockade immunotherapy with 100D3 and 103D6 has great potential to be further developed for colorectal cancer immunotherapy and for rendering a colorectal cancer response to anti-PD-1 immunotherapy.

Osteopontin: A Key Regulator of Tumor Progression and Immunomodulation

Simple Summary

Anti-PD-1/PD-L1 and anti-CTLA-4-based immune checkpoint blockade (ICB) immunotherapy have recently emerged as a breakthrough in human cancer treatment. Durable efficacy has been achieved in many types of human cancers. However, not all human cancers respond to current ICB immunotherapy and only a fraction of the responsive cancers exhibit efficacy. Osteopontin (OPN) expression is highly elevated in human cancers and functions as a tumor promoter. Emerging data suggest that OPN may also regulate immune cell function in the tumor microenvironment. This review aims at OPN function in human cancer progression and new findings of OPN as a new immune checkpoint. We propose that OPN compensates PD-L1 function to promote tumor immune evasion, which may underlie human cancer non-response to current ICB immunotherapy.

Abstract

OPN is a multifunctional phosphoglycoprotein expressed in a wide range of cells, including osteoclasts, osteoblasts, neurons, epithelial cells, T, B, NK, NK T, myeloid, and innate lymphoid cells. OPN plays an important role in diverse biological processes and is implicated in multiple diseases such as cardiovascular, diabetes, kidney, proinflammatory, fibrosis, nephrolithiasis, wound healing, and cancer. In cancer patients, overexpressed OPN is often detected in the tumor microenvironment and elevated serum OPN level is correlated with poor prognosis. Initially identified in activated T cells and termed as early T cell activation gene, OPN links innate cells to adaptive cells in immune response to infection and cancer. Recent single cell RNA sequencing revealed that OPN is primarily expressed in tumor cells and tumor-infiltrating myeloid cells in human cancer patients. Emerging experimental data reveal a key role of OPN is tumor immune evasion through regulating macrophage polarization, recruitment, and inhibition of T cell activation in the tumor microenvironment. Therefore, in addition to its well-established direct tumor cell promotion function, OPN also acts as an immune checkpoint to negatively regulate T cell activation. The OPN protein level is highly elevated in peripheral blood of human cancer patients. OPN blockade immunotherapy with OPN neutralization monoclonal antibodies (mAbs) thus represents an attractive approach in human cancer immunotherapy.

The establishment of a rheumatoid arthritis primate model in Macaca fascicularis

Background

Rheumatoid arthritis (RA) is a long-term autoimmune disorder that mostly affects the joints and leads to the destruction of cartilage. An RA model in non-human primates is especially useful because of their close phylogenetic relationship to humans in terms of cross-reactivity to compounds developed using modern drug technologies.

Methods

We used a collagen-induced arthritis (CIA) model in Macaca fascicularis. CIA was induced by the immunization of chicken type II collagen. Swelling was measured as the longitudinal and transverse axes of 16 proximal interphalangeal joints.

Results

A new system for visual evaluation was created, with a perfect score of 16. Individual behavioral analysis was also conducted. Serum was collected once a week after the first immunization. Blood chemistry and inflammatory cytokine parameters were higher in the CIA group than in the wild type group.

Conclusion

In conclusion, we established CIA in M. fascicularis, and the results can be used for drug evaluation models.

Neutralizing antibody against osteopontin attenuates non-alcoholic steatohepatitis in mice

Previously, we reported that an extracellular matrix protein, osteopontin (OPN), is involved in various autoimmune diseases using a neutralizing polyclonal antibody against OPN generated in rabbits. However, the antibody cannot be used for long-term mouse models of chronic inflammatory disease because of the induction of antibodies against anti-OPN rabbit IgG. In this study, we generated a new antibody, anti-mouse OPN mouse IgG (35B6). 35B6 inhibited the cell adhesion of mouse and human OPN to Chinese Hamster Ovary (CHO) cells or CHO cells expressing α4 or α9 integrin. It was reported that OPN is highly expressed and has an important role in a chronic liver disease, non-alcoholic steatohepatitis (NASH). 35B6 injection twice a week for 8 weeks attenuated liver inflammation and fibrosis in a NASH mouse model, suggesting 35B6 is beneficial for the treatment of NASH. 35B6 was preferable to the rabbit anti-OPN antibody for investigating the in vivo function of OPN in mouse models of long-term disease.

Assessing the Feasibility of Neutralizing Osteopontin with Various Therapeutic Antibody Modalities

Osteopontin is a secreted glycophosphoprotein that is highly implicated in many physiological and pathological processes such as biomineralization, cell-mediated immunity, inflammation, fibrosis, cell survival, tumorigenesis and metastasis. Antibodies against osteopontin have been actively pursued as potential therapeutics for various diseases by pharmaceutical companies and academic laboratories. Many studies have demonstrated the efficacy of osteopontin inhibition in a variety of preclinical models of diseases such as rheumatoid arthritis, cancer, nonalcoholic steatohepatitis, but clinical utility has not yet been demonstrated. To evaluate the feasibility of osteopontin neutralization with antibodies in a clinical setting, we measured its physiological turnover rate in humans, a sensitive parameter required for mechanistic pharmacokinetic and pharmacodynamic (PK/PD) modeling of biotherapeutics. Results from a stable isotope-labelled amino acid pulse-chase study in healthy human subjects followed by mass spectrometry showed that osteopontin undergoes very rapid turnover. PK/PD modeling and simulation of different theoretical scenarios reveal that achieving sufficient target coverage using antibodies can be very challenging mostly due to osteopontin’s fast turnover, as well as its relatively high plasma concentrations in human. Therapeutic antibodies against osteopontin would need to be engineered to have much extended PK than conventional antibodies, and be administered at high doses and with short dosing intervals.

Blocking osteopontin-fibronectin interactions reduce extracellular fibronectin deployment and arthritic immunopathology

Elevated levels of a thrombin-cleaved fragment of osteopontin (OPNT) are seen in synovial fluid (SF) and tissues of rheumatoid arthritis (RA) patients. OPNT binds to integrins on cell surfaces, inducing adhesion, migration and survival of inflammatory cells in the synovial joints, where OPNT binds to fibronectin to link fibroblast-like synoviocytes (FLS) with B cells, stimulating the latter to produce inflammatory cytokines. Our aim was to block OPNT-fibronectin interactions and examine whether this reduces inflammation. A human antibody (phage displayed) library was used to select scFv antibodies cognate to OPNT, and a particular scFv antibody (scFv 31) was evaluated. Adhesion, migration and fibronectin polymerization of FLS cells derived from RA patients were monitored, in cultures incorporating scFv 31. Also, scFv 31 was used in mice with CAIA (collagen antibody-induced arthritis), subjected to clinical and histological assessment, analysis of fibronectin and cartilage damage and induction of pro-inflammatory cytokines. The scFv antibody, scFv 31, appeared to cause significantly reduced migration of synovial fibroblasts, altered cell morphology, changes in actin stress fiber arrangement, and marked reduction in fibronectin. In CAIA mice, scFv 31 appeared to prevent arthritic changes through inhibition of synovial hypertrophy and loss of articular cartilage, decrease in fibronectin polymerization and expression of pro-inflammatory cytokines implicated in arthritis. Osteopontin-fibronectin interaction(s) appear to play a role in the expression of key inflammatory molecules by B cells infiltrating the synovial joint. The scFv antibody, scFv 31, provides a potential therapeutic lead for inhibition of some processes implicated in rheumatoid arthritis.

Peptide-based vaccination against OPN integrin binding sites does not improve cardio-metabolic disease in mice

Obesity causes insulin resistance via a chronic low-grade inflammation. This inflammation is characterized by elevated pro-inflammatory markers and macrophage accumulation in the adipose tissue (AT). AT inflammation is a key factor causing insulin resistance and thus type 2 diabetes, both linked to atherosclerotic cardiovascular disease. Osteopontin (OPN), a well-known inflammatory cytokine, is involved in obesity-linked complications including AT inflammation, insulin resistance, atherosclerosis and CVD. During inflammation, OPN is proteolytically cleaved by matrix metalloproteinases or thrombin leading to increased OPN activity. Therefore, OPN provides a new interesting target for immunological prevention and treatment of obesity-associated diseases. The aim of our study was to evaluate peptide-based vaccines against integrin binding sites of OPN and to examine whether these active immunotherapies are functional in reducing metabolic tissue inflammation, insulin resistance, and atherosclerosis in a cardio-metabolic (Ldlr^-/- mice) and a diet-induced obesity model (WT mice). However, atherosclerosis, insulin resistance and AT inflammation were not diminished after treatment with OPN-derived peptides in murine models. Lack of efficacy was based on a failure to induce antibodies capable to bind epitopes in the context of functional OPN protein. In conclusion, our data point to unexpected challenges in the immunotherapeutic targeting of adhesive motives, such as RGD containing sequences, on endogenous proteins.

Osteopontin as a biochemical marker and severity indicator for idiopathic hip osteoarthritis

INTRODUCTION

A diagnostic evaluation of the severity and progression of hip osteoarthritis (OA) using biochemical markers is lacking in the current medical literature. Osteopontin (OPN) has been proved to correlate with the progression and severity of knee OA. Therefore, the examination of plasma OPN levels in patients with idiopathic hip OA and its correlation with disease severity and progression was necessary.

METHODS

Our study included 21 patients displaying symptomatic severe idiopathic hip OA; the diagnosis of the disease was based on the checklist of the American College of Rheumatology and the severity was evaluated according to the K-L grading (Kellgran and Lawrence score).

RESULTS

14 patients showed radiological changes according K-L grade 3 (66.66%), and 7 patients showed radiological changes according K-L grade 4 (33.33%). We observed a highly statistically significant increase of plasma OPN levels in comparison with normal referenced values, the cut off value for differentiating between normal people and patients with hip OA was 193.6 ng/ml. Furthermore, the mean of plasma OPN levels in idiopathic hip osteoarthritis patients with K-L grade 4 (362.51 ± 83.31 ng/mL) was greater than those with K-L grade 3 (283.41 ± 56.31 ng/mL), the difference being statistically significant.

CONCLUSIONS

plasma OPN levels are increased in idiopathic hip OA and are correlated with the severity of the disease.

Inhibition of Cellular Adhesion by Immunological Targeting of Osteopontin Neoepitopes Generated through Matrix Metalloproteinase and Thrombin Cleavage

Osteopontin (OPN), a secreted protein involved in inflammatory processes and cancer, induces cell adhesion, migration, and activation of inflammatory pathways in various cell types. Cells bind OPN via integrins at a canonical RGD region in the full length form as well as to a contiguous cryptic site that some have shown is unmasked upon thrombin or matrix metalloproteinase cleavage. Thus, the adhesive capacity of osteopontin is enhanced by proteolytic cleavage that may occur in inflammatory conditions such as obesity, atherosclerosis, rheumatoid arthritis, tumor growth and metastasis. Our aim was to inhibit cellular adhesion to recombinant truncated proteins that correspond to the N-terminal cleavage products of thrombin- or matrix metalloproteinase-cleaved OPN in vitro. We specifically targeted the cryptic integrin binding site with monoclonal antibodies and antisera induced by peptide immunization of mice. HEK 293 cells adhered markedly stronger to truncated OPN proteins than to full length OPN. Without affecting cell binding to the full length form, the raised monoclonal antibodies specifically impeded cellular adhesion to the OPN fragments. Moreover, we show that the peptides used for immunization were able to induce antisera, which impeded adhesion either to all OPN forms, including the full-length form, or selectively to the corresponding truncated recombinant proteins. In conclusion, we developed immunological tools to selectively target functional properties of protease-cleaved OPN forms, which could find applications in treatment and prevention of various inflammatory diseases and cancers.

Osteopontin has a crucial role in osteoclast-like multinucleated giant cell formation

The osteoclast (OC) is a major player in the pathogenic bone destruction of inflammatory bone diseases such as rheumatoid arthritis and Langerhans cell histiocytosis. Recently, it was shown that immature dendritic cells (iDC) fuse faster and more efficiently than monocytes in forming OC-like multinucleated giant cells (MGCs), and that osteopontin (OPN) is involved in the pathogenesis of inflammatory bone diseases. In this study, we hypothesized that OPN is a key factor for generation of OC-like MGCs from iDCs. We used an in vitro culture system to differentiate iDCs, derived from monocytes obtained from the blood of healthy donors, into OC-like MGCs. We evaluated OPN levels and expression of OPN receptors during the course of differentiation. OPN has an arginine-glycine-aspartic acid (RGD) motif, and protease cleavage reveals a SVVYGLR motif. The concentrations of both full-length and cleaved forms of OPN increased during the course of OC-like MGC formation. Expression of OPN RGD- and SVVYGLR-recognizing receptors also increased at later stages. We analyzed whether blocking OPN binding to its receptors affected OC-like MGC formation. Monocytes treated with OPN siRNA were able to differentiate into iDCs effectively; however, differentiation of these iDCs into OC-like MGCs was significantly reduced. The formation of OC-like MGCs was not significantly reduced by RGD synthetic peptide. By contrast, SVVYGLR synthetic peptide caused a significant reduction. These data suggest that the cleaved form of OPN plays a critical role in driving iDC differentiation into OC-like MGCs in the early phase of differentiation, in an autocrine and/or paracrine fashion.

Role of osteopontin in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by joint swelling, joint tenderness, and destruction of synovial joints, leading to severe disability and premature mortality. RA is a multifactorial disease with genetic, environmental, and stochastic components related to its susceptibility. It has been demonstrated that the expression of osteopontin (OPN) is upregulated in the RA patients. Numerous studies have indicated that the full-length OPN or even OPN fragments, such as thrombin-cleaved OPN and its receptors, play the key roles in RA pathogenesis. Therapeutic application of siRNA to target OPN or neutralizing antibodies related to OPN epitopes in RA animal models are in progress, and some results are encouraging. However, there is a long way to go along with the clinical trials. This review focuses on the recent development in research associated with the OPN role in the pathogenesis of RA and provides insights concerning the OPN targeting as therapeutic approaches for patients with RA.

α9β1 integrin acts as a critical intrinsic regulator of human rheumatoid arthritis

OBJECTIVE

The role of the joint tissue microenvironment in the pathogenesis of human RA has recently attracted much attention. The present study investigated the roles of α9β1 integrin and its ligands in synovial specimens of human RA patients in generating the unique human arthritic tissue microenvironment.

METHODS

Synovial fibroblasts and macrophages were isolated from the synovial tissue of patients with RA or OA. The expression of α9β1 integrin was analysed using FACS with multicolour staining. The production of MMPs and proinflammatory cytokines was analysed in cultures of synovial fibroblasts and macrophages with α9β1 integrin ligands.

RESULTS

Synovial fibroblasts and macrophages derived from arthritic joints spontaneously secreted tenascin-C and osteopontin. Synovial fibroblasts and macrophages obtained from patients with RA expressed α9β1 integrins, a common receptor for osteopontin and tenascin-C. In the synovial fibroblasts of RA, the amount of tenascin-C protein produced was much greater than that of osteopontin in synovial fibroblasts of RA. Importantly, autocrine and paracrine interactions of α9β1 integrin and tenascin-C induced the expression of MMPs and IL-6 in synovial fibroblasts, as well as TNF-α and IL-1β in synovial macrophages.

CONCLUSION

These findings indicate that autocrine and paracrine interaction of α9β1 integrin and tenascin-C in the joint tissue microenvironment contributes to the pathogenesis of RA. Therefore α9β1 integrin may become a potential therapeutic target for RA.

Osteopontin mediates macrophage chemotaxis via α4 and α9 integrins and survival via the α4 integrin

Osteopontin (OPN) is highly expressed by macrophages and plays a key role in the pathology of several chronic inflammatory diseases including atherosclerosis and the foreign body reaction. However, the molecular mechanism behind OPN regulation of macrophage functions is not well understood. OPN is a secreted molecule and interacts with several integrins via two domains: the RGD sequence binding to α(v) -containing integrins, and the SLAYGLR sequence binding to α(4) β(1), α(4) β(7), and α(9) β(1) integrins. Here we determined the role of OPN in macrophage survival, chemotaxis, and activation state. For survival studies, OPN treated-bone marrow derived macrophages (BMDMs) were challenged with growth factor withdrawal and neutralizing integrin antibodies. We found that survival in BMDMs is mediated primarily through the α(4) integrin. In chemotaxis studies, we observed that migration to OPN was blocked by neutralizing α(4) and α(9) integrin antibodies. Further, OPN did not affect macrophage activation as measured by IL-12 production. Finally, the relative contributions of the RGD and the SLAYGLR functional domains of OPN to leukocyte recruitment were evaluated in an in vivo model. We generated chimeric mice expressing mutated forms of OPN in myeloid-derived leukocytes, and found that the SLAYGLR functional domain of OPN, but not the RGD, mediates macrophage accumulation in response to thioglycollate-elicited peritonitis. Collectively, these data indicate that α(4) and α(9) integrins interacting with OPN via the SLAYGLR domain play a key role in macrophage biology by regulating migration, survival, and accumulation.

Elevated serum osteopontin levels in chronic hepatitis C virus infection: association with autoimmune rheumatologic manifestations

Owing to the suggested role of osteopontin (OPN) in inflammation, autoimmunity and fibrosis, we investigated their serum concentrations in chronic hepatitis C virus (HCV) infected patients with and without autoimmune manifestations and correlated those levels to clinical manifestations and the histological severity of hepatic fibrosis. A total of 70 chronic HCV-infected patients (35 with and 35 without autoimmune rheumatic manifestations‏) were compared with 35 healthy volunteers matched for age and gender. Epidemiological, clinical, immunochemical and virological data were prospectively collected. OPN serum levels were assessed by an Enzyme Linked Immunosorbant Assay. The mean serum OPN levels were higher in HCV patients with autoimmune rheumatologic manifestations and in patients without; than that for the normal controls (p = 0.000). The mean OPN values progressively increased by increasing severity of liver fibrosis (p = 0.009). Multivariate analysis revealed that the presence of rheumatologic manifestations had the highest predictive value (b = 7.141, Beta = 0.414, p = 0.000) followed by liver fibrosis (b = 4.522, Beta = 0.444, p = 0.000) on the variation of OPN levels in our HCV patients. Among the group of patients with HCV and rheumatologic involvement, OPN serum levels were higher in patients with positive cryoglobulin and rheumatoid factor than in those without, and with systemic vasculitis than in those without. Correlation analysis didn't reveal any statistical significance of OPN with age, serum albumin, aminotransferases and viral load. Our data suggests OPN as a promising marker for HCV associated autoimmune rheumatologic involvement, particularly with regard to development of vasculitis and cryoglobinemia. In addition, it could serve as a biomarker to evaluate the severity of liver damages in HCV infected subjects.

Safety, tolerability, pharmacokinetics, pharmacodynamics and efficacy of the monoclonal antibody ASK8007 blocking osteopontin in patients with rheumatoid arthritis: a randomised, placebo controlled, proof-of-concept study

OBJECTIVES

Osteopontin is an extracellular matrix protein with diverse immunomodulatory functions. The authors assessed the safety, tolerability, pharmacokinetics, pharmacodynamics and initial efficacy of the humanised monoclonal antibody ASK8007, which blocks osteopontin.

METHODS

In this double-blind, multicentre, combined first-in-man, single-dose escalation (phase I, part A) and proof-of-concept, multiple-dose (phase IIA, part B) study, rheumatoid arthritis (RA) patients with active disease were randomly assigned to receive ASK8007 or placebo intravenously. Safety monitoring, pharmacokinetic and pharmacodynamic analyses and clinical assessments were performed throughout the study. The expression of phenotypic cell markers was evaluated in synovial tissue biopsy samples obtained at baseline and 43 days after initiation of treatment (part B) by immunohistochemistry and digital image analysis. Two co-primary efficacy endpoints were the change from baseline in the disease activity score evaluated in 28 joints (DAS28) and the change from baseline in the number of CD68 synovial sublining macrophages, both assessed on day 43 (part B).

RESULTS

ASK8007 was overall safe and well tolerated up to the highest studied dose (20 mg/kg). Quantifiable concentrations of ASK8007 were detected in synovial fluid. No differences were observed for changes from baseline in DAS28 and CD68 sublining macrophages between ASK8007 and placebo-treated patients. Within the ASK8007 treatment group, there were also no apparent clinical responses or changes in sublining macrophages. In addition, ASK8007 treatment did not change other assessed biomarkers.

CONCLUSIONS

Osteopontin blockade is well tolerated and not related to safety concerns. These results consistently show that osteopontin blockade is unlikely to induce robust clinical improvement in RA patients.

Crucial role of the cryptic epitope SLAYGLR within osteopontin in renal crystal formation of mice

Osteopontin plays a crucial role in the formation of renal calcium crystals, which are primarily induced by renal tubular cell injury, especially mitochondrial damage. We have previously shown that the impaired Arg-Gly-Asp (RGD) sequence of osteopontin inhibits renal crystal formation by using OPN-transgenic mice and OPN-knockout (OPN-KO) mice. Here, we investigated the effects of an antimurine osteopontin antibody (35B6-Ab) that specifically reacts with the (162) SLAYGLR(168) sequence, which is exposed by thrombin cleavage and is located adjacent to the RGD sequence, on renal crystal formation. Renal crystals induced by daily administration of glyoxylate over 9 days (from days 1 to 9) in a murine model were sporadically detected in the renal tubular cells at the corticomedullary junction, where thrombin-cleaved osteopontin expression was also coincidentally detected. On days 0, 3, 6, and 9, 35B6-Ab administration inhibited renal crystal formation and induced significant morphological changes in a dose-dependent manner (250, 500, and 1000 µg per mouse). Scanning electron microscopy showed that the crystals in 35B6-Ab-treated mice were aberrantly formed and their density was low; in contrast, the crystals in untreated mice that were not administered 35B6-Ab had a radial pattern of growth (rosette petal-like crystals), and their density was high. Microstructure analysis of renal tubular cells by transmission electron microscopy revealed that untreated mice showed collapsed mitochondria in the flattened cytoplasm of renal tubular cells, unlike the corresponding structures in 35B6-Ab-treated mice, in which renal tubular cell injury was inhibited. In vitro, 35B6-Ab was found to inhibit the attachment of (14) C-labeled crystals to renal tubular culture cells and reduce morphological damage to these cells. We conclude that thrombin-cleaved osteopontin plays an important role in formation of renal calcium crystals and that 35B6-Ab contributes to the remarkable inhibition of early-stage renal crystal formation by preventing renal tubular cell injury and crystal-cell attachment.

Plasma thrombin-cleaved osteopontin elevation after carotid artery stenting in symptomatic ischemic stroke patients

Atherothrombosis is the primary pathophysiology that underlies ischemic cerebral infarction. Osteopontin (OPN) is produced in atherosclerotic lesions and is cleaved by activated thrombin. We hypothesized that the rupture or damage of an unstable atherosclerotic plaque increases plasma levels of thrombin-cleaved OPN (trOPN). This study included 90 patients who received carotid angioplasty with stenting (CAS), 23 patients with essential hypertension (EHT) and 10 patients who were treated with carotid endarterectomy (CEA). The CAS patient group included 36 patients that had pre- and post-operative blood tests, diffusion-weighted imaging (DWI) using cerebral MRIs and estimated thrombus debris within the protection device. Immunohistochemistry of CEA specimens revealed that trOPN was detected around intra-plaque vessels. The highest tertile of plasma trOPN levels in CAS patients was higher than trOPN levels in EHT patients. Post-operative trOPN levels were significantly higher in symptomatic compared with asymptomatic patients (P=0.003). New ipsilateral DWI-positive patients revealed higher post-operative trOPN levels (P=0.003) and a higher grade of thrombi (P<0.001) than DWI-negative patients. TrOPN may be a novel biomarker that reflects the atherothrombotic status in ischemic stroke.

Aldosterone-induced osteopontin gene transcription in vascular smooth muscle cells involves glucocorticoid response element

Osteopontin (OPN) is known to be one of the cytokines that is involved in the vascular inflammation caused by aldosterone (Aldo). Previous reports have shown that Aldo increases OPN transcripts, and the mechanisms for this remain to be clarified. In this study, we investigated how Aldo increases OPN transcripts in the vascular smooth muscle cells of rats. Aldosterone increased OPN transcripts time-dependently as well as dose-dependently. This increase was diminished by eplerenone, a mineralocorticoid receptor (MR) antagonist. Luciferase promoter assays showed that the OPN promoter deleted to the -1599 site retained the same promoting ability as the full-length OPN promoter when stimulated by 10(-7) M Aldo, but the promoter deleted to the -1300 site lost the promoting ability. A glucocorticoid response element (GRE) is located in that deleted region. Luciferase assays of a mutated promoter without the GRE lost the luciferase upregulation, although mutated promoters with the deletion of other consensus sites maintained the promoter activity. The binding of the Aldo-MR complex to the GRE fragment was confirmed by an electrophoretic-mobility shift assay. This is the first report showing that Aldo regulates the transcriptional levels of OPN and inflammatory responses in the vasculature through a specific GRE site in the OPN promoter region.

Role of osteopontin, a multifunctional protein, in allergy and asthma

Osteopontin (OPN) is an extracellular matrix protein and immune modulator with a wide range of functions. OPN is recognized as a key cytokine in Th1 immune responses, yet its potential involvement in allergic/asthmatic responses has been investigated only recently. Current data from molecular and cellular studies and studies of OPN-deficient mice provide evidence that OPN plays multiple roles in the regulation of allergic responses, including regulation of IgE response, inflammatory cell migration, and the development of airway fibrosis and angiogenesis. These results suggest that OPN is a pleiotropic cytokine that functions both systemically and locally in tissue mucosa. Notably, OPN is able to exert its effects through different functional domains, and the secreted and intracellular forms of OPN may have distinct functions. Future research to elucidate all aspects of OPN function is needed to ultimately establish its role in the regulation of immune responses and various disease processes, including those critically involved in the development of allergies and asthma.

Osteopontin, intrinsic tissue regulator of intractable inflammatory diseases

Within classical extracellular matrix (ECM) proteins, there are a unique group of proteins that should be regarded as a distinct functional group of molecules. Matricellular proteins including osteopontin (OPN) and tenascin-c (TN-C) are highly expressed at the pathological foci of various inflammatory diseases. Unlike classical ECM proteins, these are soluble proteins and induce cell motility and persistent inflammation rather than providing a scaffold for stable cell adhesion. Osteopontin is a pleiotropic cytokine expressed by various cells. Two forms of OPN are present. A secreted form of OPN (sOPN) is involved in generation of T helper type 1 (Th1) and Th17 cells that are pathogenic T cells for various autoimmune diseases. An intracellular form of OPN (iOPN) is a critical regulator for Toll like receptor-9 (TLR-9) and/or TLR-7-dependent interferon-α (IFN-α) expression by plasmacytoid dendritic cells (DCs) and Th17 development. Indeed, both OPN and TN-C deficient mice are resistant to various Th1- and/or Th17-related autoimmune diseases. Interestingly, thrombin-cleaved forms of sOPN and TN-C share a common integrin receptor, α9β1, and α9β1 integrin-mediated signaling is involved in the pathogenesis of various autoimmune diseases. Thus, OPN, TN-C and its common receptor, α9β1 integrin may serve as potential therapeutic targets for various intractable inflammatory diseases.

A humanized anti-osteopontin antibody protects from Concanavalin A induced-liver injury in mice

Osteopontin has been implicated in various inflammatory diseases including rheumatoid arthritis, multiple sclerosis, Crohn's disease, and fulminant hepatitis. Increased expression of osteopontin has been detected in pathological foci of these diseases. RA and fulminant hepatitis have been successfully treated by administration of neutralizing anti-osteopontin antibody in mice. However, rodent antibodies are highly immunogenic in humans and therefore limited in their clinical application. Here, a murine monoclonal antibody 23C3 against human osteopontin, was humanized by complementarity-determining region grafting method based on computer-assisted molecular modeling. The humanized version of 23C3, denoted as Hu23C3, was shown to possess affinity comparable to that of its parental antibody. Hu23C3 could also inhibit monocyte migration in response to osteopontin in vitro. Furthermore, in vivo data showed that Hu23C3 significantly protects mice from Concanavalin A (Con A) induced-liver injury in association with the reduction of transaminase activities and improvement of liver injury. Mechanistic studies demonstrated that Hu23C3 inhibited T and NKT cell infiltration, and activation of nuclear factor κB (NF-κB) in the liver, resulting in reduction of TNF-α and IFN-γ production. Thus, our data strongly support that the humanized anti-osteopontin antibody, Hu23C3, may have a potential for the treatment of T cell mediated-hepatitis in human.

Thrombin-cleaved osteopontin levels in synovial fluid correlate with disease severity of knee osteoarthritis

OBJECTIVE

although osteoarthritis (OA) is generally assessed using standard radiographic images in clinical practice, biochemical markers can be used to detect the disease and determine its severity. Osteopontin (OPN) is an extracellular matrix glycoprotein that is a potential inflammatory cytokine. Presence of the thrombin-cleaved form of OPN is well correlated with various inflammatory diseases. We examined whether thrombin-cleaved OPN in synovial fluid (SF) and synovium could be associated with the severity of knee OA.

METHODS

SF samples were obtained from 139 knees with OA. Thrombin-cleaved OPN product was determined using Western blotting. Levels of thrombin-cleaved and full-length OPN in SF were determined by ELISA. Synovium samples were analyzed by immunohistochemistry using an antibody specific to the thrombin-cleaved form.

RESULTS

western blotting showed the presence of thrombin-cleaved OPN in SF from patients with advanced OA. Concentrations of OPN full-length in OA knees were not statistically different from those in controls (p = 0.134). In contrast, levels of OPN N-half were significantly higher in OA knees than in controls (p = 0.042). Statistically significant correlation was found between thrombin-cleaved OPN and disease severity by Kellgren-Lawrence grade 1, 2, 3, and 4 (R = 0.274, p < 0.001). Immunohistochemistry of the synovium showed stronger reactivity in samples from subjects with advanced OA.

CONCLUSION

local generation of thrombin-cleaved OPN was increased with greater OA severity.

A humanized anti-osteopontin antibody inhibits breast cancer growth and metastasis in vivo

Osteopontin (OPN) has been implicated as an important mediator of breast cancer progression and metastasis and has been investigated for use as a potential therapeutic target in the treatment of breast cancer. However, the in vivo antitumor effect of anti-OPN antibodies on breast cancer has not been reported. In this study, a mouse anti-human OPN antibody (1A12) was humanized by complementarity-determining region grafting method based on computer-assisted molecular modeling. A humanized version of 1A12, denoted as hu1A12, was shown to possess affinity comparable to that of its parental antibody. The ability of hu1A12 to inhibit cell migration, adhesion, invasion and colony formation was assessed in a highly metastatic human breast cancer cell line MDA-MB-435S. The results indicated that hu1A12 was effective in inhibiting the cell adhesion, migration, invasion and colony formation of MDA-MB-435S cells in vitro. hu1A12 also showed significant efficacy in suppressing primary tumor growth and spontaneous metastasis in a mouse lung metastasis model of human breast cancer. The specific epitope recognized by hu1A12 was identified to be (212)NAPSD(216), adjacent to the calcium binding domain of OPN. Our data strongly support that OPN is a potential target for the antibody-based therapies of breast cancer. The humanized anti-OPN antibody hu1A12 may be a promising therapeutic agent for the treatment of human breast cancer.

The role of osteopontin in inflammatory processes

Osteopontin (OPN) is a matricellular protein that mediates diverse biological functions. OPN is involved in normal physiological processes and is implicated in the pathogenesis of a variety of disease states, including atherosclerosis, glomerulonephritis, cancer, and several chronic inflammatory diseases. Through interactions with several integrins, OPN mediates cell migration, adhesion, and survival in many cell types. OPN also functions as a Th1 cytokine, promotes cell-mediated immune responses, and plays a role in chronic inflammatory and autoimmune diseases. Besides its function in inflammation, OPN is also a regulator of biomineralization and a potent inhibitor of vascular calcification.

Regulatory effects of IFN-beta on production of osteopontin and IL-17 by CD4+ T Cells in MS

IFN-beta currently serves as one of the major treatments for MS. Its anti-inflammatory mechanism has been reported as involving a shift in cytokine balance from Th1 to Th2 in the T-cell response against elements of the myelin sheath. In addition to the Th1 and Th2 groups, two other important pro-inflammatory cytokines, IL-17 and osteopontin (OPN), are believed to play important roles in CNS inflammation in the pathogenesis of MS. In this study, we examined the potential effects of IFN-beta on the regulation of OPN and IL-17 in MS patients. We found that IFN-beta used in vitro at 0.5-3 ng/mL significantly inhibited the production of OPN in primary T cells derived from PBMC. The inhibition of OPN was determined to occur at the CD4(+) T-cell level. In addition, IFN-beta inhibited the production of IL-17 and IL-21 in CD4(+) T cells. It has been described that IFN-beta suppresses IL-17 production through the inhibition of a monocytic cytokine, the intracellular translational isoform of OPN. Our further investigation demonstrated that IFN-beta also acted directly on the CD4(+) T cells to regulate OPN and IL-17 expression through the type I IFN receptor-mediated activation of STAT1 and suppression of STAT3 activity. Administration of IFN-beta to EAE mice ameliorated the disease severity. Furthermore, spinal cord infiltration of OPN(+) and IL-17(+) cells decreased in IFN-beta-treated EAE mice along with decreases in serum levels of OPN and IL-21. Importantly, decreased OPN production by IFN-beta treatment contributes to the reduced migratory activity of T cells. Taken together, the results from both in vitro and in vivo experiments indicate that IFN-beta treatment can down-regulate the OPN and IL-17 production in MS. This study provides new insights into the mechanism of action of IFN-beta in the treatment of MS.

Osteopontin is involved in migration of eosinophils in asthma

BACKGROUND

Osteopontin (OPN) is an extracellular matrix protein with a wide range of functions, and is involved in various inflammatory diseases. However, the role of OPN in eosinophilic airway inflammation is unclear.

OBJECTIVE

To elucidate the role of OPN in eosinophilic airway inflammation.

METHODS

OPN protein levels in induced sputum from asthmatic patients and healthy controls were measured. Eosinophil migration assays were performed in the presence or absence of OPN, a blocking antibody (Ab) recognizing its integrin-binding domain (2K1) and an anti-integrin alpha 4 Ab (P1H4). In the mouse asthma model, the levels of eosinophilia were examined in bronchoalveolar lavage fluids (BALFs) from ovalbumin (OVA)-sensitized and -challenged mice with or without administration of an Ab (M5) corresponding to human 2K1.

RESULTS

Levels of OPN in induced sputum were significantly higher in asthmatic patients when compared with healthy controls. In addition, levels of OPN were correlated with the percentage of sputum eosinophils. OPN induced significant migration of human eosinophils and this effect was inhibited by 2K1 and P1H4. M5 significantly attenuated OVA-induced eosinophilia in BALFs.

CONCLUSION

These results indicate that OPN plays a role in the migration of eosinophils into the airways and may be involved in the pathogenesis of asthma.

Regulation of T-helper-cell lineage development by osteopontin: the inside story

Studies of osteopontin (OPN)-dependent regulation of immune responses have focused on the cytokine activities of the secreted form of this protein. Recent evidence has revealed that an intracellular form of OPN expressed by dendritic cells regulates the expression of pro-inflammatory cytokines and the differentiation of T helper (T(H))-cell lineages. In this Opinion article, we discuss the properties of both OPN isoforms and their respective contributions to the immune response. We propose that cell-type-specific expression of secreted and intracellular OPN regulates the development of distinct effector T(H) cells, including that of T(H)1 and T(H)17 cells.

Thrombin-cleaved osteopontin in synovial fluid of subjects with rheumatoid arthritis

OBJECTIVE

Osteopontin (OPN) is an extracellular matrix glycoprotein that has been recognized as a potential inflammatory cytokine. The function of OPN is modulated by protease digestion, and a thrombin-cleaved form of OPN is involved in the pathogenesis of various inflammatory disorders. We examined thrombin-cleaved OPN products in synovial fluid from patients with rheumatoid arthritis (RA) and osteoarthritis (OA).

METHODS

Synovial fluid samples were obtained from knees of 20 patients with RA and 111 patients with OA. Thrombin-cleaved OPN product was determined using Western blotting. Levels of thrombin- cleaved and full-length OPN in synovial fluid were determined by ELISA. Synovia were analyzed by immunohistochemistry using an antibody specific to the thrombin-cleaved form.

RESULTS

Immunoblotting showed the presence of thrombin-cleaved OPN in synovial fluid from patients with RA and OA. ELISA results showed no difference between concentrations of full-length OPN in the synovial fluid of RA and OA patients; however, thrombin-cleaved OPN concentrations in RA synovial fluid samples were roughly 30-fold higher compared with OA samples (p < 0.001). Synovial fluid concentrations of thrombin-cleaved OPN in RA did not correlate with C-reactive protein levels. Immunohistochemistry of the synovium showed stronger reactivity in RA than in OA samples.

CONCLUSION

Local generation of thrombin-cleaved OPN was increased in RA joints. Thrombin-cleaved OPN may be a useful biochemical marker of RA.

Osteopontin: role in immune regulation and stress responses

Recent research has led to a better but as yet incomplete understanding of the complex roles osteopontin plays in mammalian physiology. A soluble protein found in all body fluids, it stimulates signal transduction pathways (via integrins and CD44 variants) similar to those stimulated by components of the extracellular matrix. This appears to promote the survival of cells exposed to potentially lethal insults such as ischemia/reperfusion or physical/chemical trauma. OPN is chemotactic for many cell types including macrophages, dendritic cells, and T cells; it enhances B lymphocyte immunoglobulin production and proliferation. In inflammatory situations it stimulates both pro- and anti-inflammatory processes, which on balance can be either beneficial or harmful depending on what other inputs the cell is receiving. OPN influences cell-mediated immunity and has been shown to have Th1-cytokine functions. OPN deficiency is linked to a reduced Th1 immune response in infectious diseases, autoimmunity and delayed type hypersensitivity. OPN's role in the central nervous system and in stress responses has also emerged as an important aspect related to its cytoprotective and immune functions. Evidence suggests that either OPN or anti-OPN monoclonal antibodies (depending on the circumstances) might be clinically useful in modulating OPN function. Manipulation of plasma OPN levels may be useful in the treatment of autoimmune disease, cancer metastasis, osteoporosis and some forms of stress.

Molecular basis of recognition of human osteopontin by 23C3, a potential therapeutic antibody for treatment of rheumatoid arthritis

Osteopontin plays an important role in the development and perpetuation of rheumatoid arthritis (RA). Antibodies targeting osteopontin have shown promising therapeutic benefits against this disease. We have previously reported a novel anti-RA monoclonal antibody, namely, 23C3, and shown it capable of alleviating the symptoms of RA in a murine collagen-induced arthritis model, restoring the cytokine production profile in joint tissues, and reducing T-cell recall responses to collagen type II. We describe here the crystal structure of 23C3 in complex with its epitope peptide. Analyses of the complex structure reveal the molecular mechanism of osteopontin recognition by 23C3. The peptide folds into two tandem β-turns, and two key residues of the peptide are identified to be critical for the recognition by 23C3: TrpP43 is deeply embedded into a hydrophobic pocket formed by AlaL34, TyrL36, LeuL46, TyrL49, PheL91, and MetH102 and therefore has extensive hydrophobic interactions with 23C3, while AspP47 has a network of hydrophilic interactions with residues ArgH50, ArgH52, SerH53, and AsnH56 of the antibody. Besides the complementarity-determining region loops, the framework region L2 of 23C3 is also shown to interact with the epitope peptide, which is not common in the antibody–antigen interactions and thus could be exploited in the engineering of 23C3. These results not only provide valuable information for further improvement of 23C3 such as chimerization or humanization for its therapeutic application, but also reveal the features of this specific epitope of osteopontin that may be useful for the development of new antibody drugs against RA.