Fibronectin as target for tumor therapy

Fibronectin overexpression is associated with latent membrane protein 1 expression and has independent prognostic value for nasopharyngeal carcinoma

Despite recent improvements in the diagnosis and treatment, the final outcomes in patients with nasopharyngeal carcinomas (NPC) still remain suboptimal. Through data mining from published transcriptomic database with further bioinformatic validation, fibronectin (FN1) was identified as a differentially upregulated gene in NPC tissues, which implicates the transition from epithelial to mesenchymal phenotype (EMT) and promotes metastasis. Given the roles of fibronectin in risk stratification and in the frontline therapeutics of common carcinomas, such as renal cell cancer, we explored fibronectin immunoexpression status and its associations with clinicopathological variables and survival in a well-defined cohort of NPC patients. Fibronectin immunohistochemistry was retrospectively performed and analyzed using H-score for 124 biopsy specimens from NPC patients who received standard treatment without distant metastasis at initial diagnosis. Those cases with H-score higher than the median value were regarded as fibronectin overexpression. The findings were correlated with clinicopathological variables, EBV latent membrane protein 1 (LMP1) expression, disease-specific survival (DSS), distant metastasis-free survival (DMFS), and local recurrence-free survival (LRFS). Fibronectin overexpression was significantly associated with American Joint Committee on Cancer (AJCC) stages III-IV (p = 0.019) and LMP1 expression (p = 0.004), and univariately predictive of adverse outcomes for DSS, DMFS, and LRFS (all p < 0.0001). In the multivariate comparison, fibronectin overexpression still remained prognostically independent to portend worse DSS (p < 0.01, hazard ratio = 5.958), DMFS (p < 0.01, hazard ratio = 5.728), and LRFS (p < 0.01, hazard ratio = 5.411) together with a vanced AJCC stages III-IV. Fibronectin is upregulated in a subset of NPCs, and its increased immunoexpression significantly correlated with advanced features, justifying the potentiality of fibronectin as a theragnostic biomaker of NPC.

Cetuximab attenuates its cytotoxic and radiosensitizing potential by inducing fibronectin biosynthesis

Inherent and acquired resistance to targeted therapeutics continues to emerge as a major clinical obstacle. For example, resistance to EGF receptor targeting occurs commonly, more so than was expected, on the basis of preclinical work. Given emerging evidence that cancer cell-substrate interactions are important determinants of therapeutic sensitivity, we examined the impact of cell-fibronectin interactions on the efficacy of the EGF receptor antibody cetuximab, which is used widely for lung cancer treatment. Our results revealed the potential for cell-fibronectin interactions to induce radioresistance of human non-small cell lung cancer cells. Cell adhesion to fibronectin enhanced tumor cell radioresistance and attenuated the cytotoxic and radiosensitizing effects of cetuximab. Both in vitro and in vivo, we found that cetuximab treatment led to a remarkable induction of fibronectin biosynthesis. Mechanistic analyses revealed the induction was mediated by a p38-MAPK-ATF2 signaling pathway and that RNAi-mediated inhibition of fibronectin could elevate the cytotoxic and radiosensitizing potential of cetuximab. Taken together, our findings show how cell adhesion blunts cetuximab, which, by inducing fibronectin, generates a self-attenuating mechanism of drug resistance.

The EDA-containing cellular fibronectin induces epithelial-mesenchymal transition in lung cancer cells through integrin α9β1-mediated activation of PI3-K/AKT and Erk1/2

Cellular fibronectin (cFN) is one of the main components of tissue extracellular matrices and is involved in multiple physiologic and pathologic processes such as embryogenesis, wound healing, inflammation and tumor progression. The function of fibronectin in regulating normal cell adhesion and migration is well documented, but its function in cancer progression is only partially unraveled. We have reported previously that fibronectin stimulates the proliferation and survival of non-small lung carcinoma cells through upregulation of pro-oncogenic signals related to cyclooxygenase-2/phosphatidylinositol-3-kinase/protein kinase B (COX-2/PI3-K/AKT)/mammalian target of rapamycin triggered by activation of the integrin α5β1. Here, we extend these studies by showing that fibronectin promotes epithelial-mesenchymal transition (EMT) in lung cancer cells. We found that cFN, but not plasma fibronectin or type 1 collagen, induces lung carcinoma cell scattering in vitro, promotes cell migration and invasion of Matrigel and stimulates the expression of the mesenchymal marker α-smooth muscle actin while decreasing the expression of the epithelial marker E-cadherin through PI3-K and Erk pathways. Interestingly, the extra domain A (EDA) within cFN was found to be crucial for this process, as confirmed by testing cells overexpressing EDA or cells exposed to EDA-containing matrices. We found that the integrin α9, but not α5, mediated cFN-induced EMT as silencing integrin α9 neutralized cFN-induced EMT. Overall, our findings show that the EDA domain within cFN induces EMT in lung carcinoma cells through integrin α9-mediated activation of PI3-K and Erk.

Fibronectin extra domain A (EDA) sustains CD133(+)/CD44(+) subpopulation of colorectal cancer cells

Fibronectin is a major extracellular matrix glycoprotein with several alternatively spliced variants, including extra domain A (EDA), which was demonstrated to promote tumorigenesis via stimulating angiogenesis and lymphangiogenesis. Given that CD133(+)/CD44(+) cancer cells are critical in tumorigenesis of colorectal cancer (CRC), we hypothesize that fibronectin EDA may promote tumorigenesis by sustaining the properties of CD133(+)/CD44(+) colon cancer cells. We found that tumor tissue and serum EDA levels are substantially higher in advanced versus early stage human CRC. Additionally we showed that tumor tissue EDA levels are positively correlated with differentiation status and chemoresistance, and correlated with a poor prognosis of CRC patients. We also showed that in colon cancer cells SW480, CD133(+)/CD44(+) versus CD133(-)/CD44(-) cells express significantly elevated EDA receptor integrin α9β1. Silencing EDA in SW480 cells reduces spheroid formation and cells positive for CD133 or CD44, which is associated with reduced expressions of embryonic stem cell markers and increased expressions of differentiation markers. Blocking integrin α9β1 function strongly reversed the effect of EDA overexpression. We also provided evidence suggesting that EDA sustains Wnt/β-catenin signaling activity via activating integrin/FAK/ERK pathway. In xenograft models, EDA-silenced SW480 cells exhibit reduced tumorigenic and metastatic capacity. In conclusion, EDA is essential for the maintenance of the properties of CD133(+)/CD44(+) colon cancer cells.

Suppression of mitochondrial complex I influences cell metastatic properties

Despite the fact that mitochondrial dysfunction has an important role in tumorigenesis and metastasis, the underlying mechanism remains to be elucidated. Mitochondrial Complex I (NADH:ubiquinone oxidoreductase) is the first and the largest protein complex of the mitochondrial electron-transport chain (ETC),which has an essential role in maintaining mitochondrial function and integrity. In this study, we separately knocked down two subunits of mitochondrial complex I, GRIM-19 or NDUFS3, and investigated their effects on metastatic behaviors and explored the possible mechanisms. Our data showed that stable down-modulation of GRIM-19 or NDUFS3 decreased complex I activity and reactive oxygen species (ROS) production; led to enhanced cell adhesion, migration, invasion, and spheroid formation; and influenced the expressions of extracellular matrix (ECM) molecules and its related proteins. We also observed that the expressions of GRIM-19, NDUFS3, and ECM elements were correlated with invasive capabilities of breast cancer cell lines. These results suggest that inhibition of complex I affects metastatic properties of cancer cells, and mitochondrial ROS might play a crucial role in these processes by regulating ECM.

A novel human anti-syndecan-1 antibody inhibits vascular maturation and tumour growth in melanoma

INTRODUCTION

Syndecan-1 is a cell membrane protein that, after its shedding by heparanase enzymes, is accumulated in the extracellular matrix of some tumours, e.g. myeloma and lung carcinoma, where it modulates several key processes of tumourigenesis such as cancer cell proliferation and apoptosis, angiogenesis and metastasis. Few studies have focused on syndecan-1 in malignant melanoma, a tumour for which new therapeutic targets are desperately needed. We aimed to investigate the role of syndecan-1 in melanoma and to evaluate the potential therapeutic efficacy of a novel fully human anti-syndecan-1 recombinant antibody in this deadly disease.

METHODS

The OC-46F2 recombinant antibody was generated by selecting a human antibody phage display library on human melanoma cells and by its expression in mammalian cells. The specific antigen recognised by the antibody was identified by mass spectrometry. Murine models of human melanoma and ovarian carcinoma were used in the pre-clinical in vivo experiments.

RESULTS

The fully human antibody OC-46F2, specific for the extracellular domain of syndecan-1, inhibited vascular maturation and tumour growth in an experimental human melanoma model. The therapeutic efficacy of this antibody was also demonstrated in an experimental ovarian carcinoma model. A co-distribution of syndecan-1 with vascular endothelial growth factor receptor 2 (VEGFR2) observed in the intratumour melanoma microenvironment was absent in the tumours from mice treated with OC-46F2 scFv.

CONCLUSION

These findings highlight the role of syndecan-1 as a potential therapeutic target in melanoma and ovarian carcinoma and provide a new tool able to block vessel maturation, one of the mechanisms that underpin the angiogenic process essential for solid tumour growth.

Design and characterization of a protein superagonist of IL-15 fused with IL-15Rα and a high-affinity T cell receptor

To avoid high systemic doses, strategies involving antigen-specific delivery of cytokine via linked antibodies or antibody fragments have been used. Targeting cancer-associated peptides presented by major histocompatibility complex (MHC) molecules (pepMHC) increases the number of potential target antigens and takes advantage of cross-presentation on tumor stroma and in draining lymph nodes. Here, we use a soluble, high-affinity single-chain T cell receptor Vα-Vβ (scTv), to deliver cytokines to intracellular tumor-associated antigens presented as pepMHC. As typical wild-type T cell receptors (TCRs) exhibit low affinity (K(d) = 1-100 μM or more), we used an engineered TCR, m33, that binds its antigenic peptide SIYRYYGL (SIY) bound to the murine class I major histocompatability complex protein H2-K(b) (SIY/K(b) ) with nanomolar affinity (K(d) = 30 nM). We generated constructs consisting of m33 scTv fused to murine interleukin 2 (IL-2), interleukin 15 (IL-15), or IL-15/IL-15Rα (IL-15 linked to IL-15Rα sushi domain, called "superfusion"). The fusions were purified with good yields and bound specifically to SIY/K(b) with high affinity. Proper cytokine folding and binding were confirmed, and the fusions were capable of stimulating proliferation of cytokine-dependent cells, both when added directly and when presented in trans, bound to cells with the target pepMHC. The m33 superfusion was particularly potent and stable and represents a promising design for targeted antitumor immunomodulation.

Extracellular matrix remodeling: the common denominator in connective tissue diseases. Possibilities for evaluation and current understanding of the matrix as more than a passive architecture, but a key player in tissue failure

Increased attention is paid to the structural components of tissues. These components are mostly collagens and various proteoglycans. Emerging evidence suggests that altered components and noncoded modifications of the matrix may be both initiators and drivers of disease, exemplified by excessive tissue remodeling leading to tissue stiffness, as well as by changes in the signaling potential of both intact matrix and fragments thereof. Although tissue structure until recently was viewed as a simple architecture anchoring cells and proteins, this complex grid may contain essential information enabling the maintenance of the structure and normal functioning of tissue. The aims of this review are to (1) discuss the structural components of the matrix and the relevance of their mutations to the pathology of diseases such as fibrosis and cancer, (2) introduce the possibility that post-translational modifications (PTMs), such as protease cleavage, citrullination, cross-linking, nitrosylation, glycosylation, and isomerization, generated during pathology, may be unique, disease-specific biochemical markers, (3) list and review the range of simple enzyme-linked immunosorbent assays (ELISAs) that have been developed for assessing the extracellular matrix (ECM) and detecting abnormal ECM remodeling, and (4) discuss whether some PTMs are the cause or consequence of disease. New evidence clearly suggests that the ECM at some point in the pathogenesis becomes a driver of disease. These pathological modified ECM proteins may allow insights into complicated pathologies in which the end stage is excessive tissue remodeling, and provide unique and more pathology-specific biochemical markers.

Proteomic identification of plasma protein tyrosine phosphatase alpha and fibronectin associated with liver fluke, Opisthorchis viverrini, infection

Opisthorchiasis caused by Opisthorchis viverrini induces periductal fibrosis via host immune/inflammatory responses. Plasma protein alteration during host-parasite interaction-mediated inflammation may provide potential diagnostic and/or prognostic biomarkers. To search for target protein changes in O. viverrini-infected hamsters, a 1-D PAGE gel band was trypsin-digested and analyzed by a LC-MS/MS-based proteomics approach in the plasma profile of infected hamsters, and applied to humans. Sixty seven proteins were selected for further analysis based on at least two unique tryptic peptides with protein ID score >10 and increased expression at least two times across time points. These proteins have not been previously identified in O. viverrini-associated infection. Among those, proteins involved in structural (19%), immune response (13%), cell cycle (10%) and transcription (10%) were highly expressed. Western blots revealed an expression level of protein tyrosine phosphatase alpha (PTPα) which reached a peak at 1 month and subsequently tended to decrease. Fibronectin significantly increased at 1 month and tended to increase with time, supporting proteomic analysis. PTPα was expressed in the cytoplasm of inflammatory cells, while fibronectin was observed mainly in the cytoplasm of fibroblasts and the extracellular matrix at periductal fibrosis areas. In addition, these protein levels significantly increased in the plasma of O. viverrini-infected patients compared to healthy individuals, and significantly decreased at 2-months post-treatment, indicating their potential as disease markers. In conclusion, our results suggest that plasma PTPα and fibronectin may be associated with opisthorchiasis and the hamster model provides the basis for development of novel diagnostic markers in the future.

Neuropilin-1 stimulates tumor growth by increasing fibronectin fibril assembly in the tumor microenvironment

The tumor microenvironment, including stromal myofibroblasts and associated matrix proteins, regulates cancer cell invasion and proliferation. Here, we report that neuropilin-1 (NRP-1) orchestrates communications between myofibroblasts and soluble fibronectin that promote α5β1 integrin-dependent fibronectin fibril assembly, matrix stiffness, and tumor growth. Tumor growth and fibronectin fibril assembly were reduced by genetic depletion or antibody neutralization of NRP-1 from stromal myofibroblasts in vivo. Mechanistically, the increase in fibronectin fibril assembly required glycosylation of serine 612 of the extracellular domain of NRP-1, an intact intracellular NRP-1 SEA domain, and intracellular associations between NRP-1, the scaffold protein GIPC, and the nonreceptor tyrosine kinase c-Abl that augmented α5β1 fibronectin fibril assembly activity. Analysis of human cancer specimens established an association between tumoral NRP-1 levels and clinical outcome. Our findings indicate that NRP-1 activates the tumor microenvironment, thereby promoting tumor growth. These results not only identify new molecular mechanisms of fibronectin fibril assembly but also have important implications for therapeutic targeting of the myofibroblast in the tumor microenvironment.

Matrikines and the lungs

The extracellular matrix is a complex network of fibrous and nonfibrous molecules that not only provide structure to the lung but also interact with and regulate the behaviour of the cells which it surrounds. Recently it has been recognised that components of the extracellular matrix proteins are released, often through the action of endogenous proteases, and these fragments are termed matrikines. Matrikines have biological activities, independent of their role within the extracellular matrix structure, which may play important roles in the lung in health and disease pathology. Integrins are the primary cell surface receptors, characterised to date, which are used by the matrikines to exert their effects on cells. However, evidence is emerging for the need for co-factors and other receptors for the matrikines to exert their effects on cells. The potential for matrikines, and peptides derived from these extracellular matrix protein fragments, as therapeutic agents has recently been recognised. The natural role of these matrikines (including inhibitors of angiogenesis and possibly inflammation) make them ideal targets to mimic as therapies. A number of these peptides have been taken forward into clinical trials. The focus of this review will be to summarise our current understanding of the role, and potential for highly relevant actions, of matrikines in lung health and disease.

MR molecular imaging of prostate cancer with a peptide-targeted contrast agent in a mouse orthotopic prostate cancer model

PURPOSE

To study the effectiveness of a peptide targeted nanoglobular Gd-DOTA complexes for MR molecular imaging of prostate cancer in a mouse orthotopic PC-3 prostate cancer model.

METHODS

A CLT1 (CGLIIQKNEC) peptide-targeted generation 2 nanoglobular Gd-DOTA monoamide conjugate [CLT1-G2-(Gd-DOTA)] was used for imaging fibrin-fibronectin complexes in prostate tumor using a non-specific peptide KAREC modified conjugate, KAREC-G2-(Gd-DOTA) as a control. Cy5 conjugates of CLT1 and KAREC were synthesized for binding studies. Orthotopic PC-3 prostate tumors were established in the prostate of athymic male nude mice. MRI study was performed on a Bruker 7T small animal MRI system.

RESULTS

CLT1 peptide showed specific binding in the prostate tumor with no binding in normal tissues. The control peptide had little binding in normal and tumor tissues. CLT1-G2-(Gd-DOTA) resulted in stronger contrast enhancement in tumor tissue than KAREC-G2-(Gd-DOTA). CLT1-G2-(Gd-DOTA) generated ~100% increase in contrast-to-noise ratio (CNR) in the tumor compared to precontrast CNR at 1 min post-injection, while KAREC-G2-(Gd-DOTA) resulted in 8% increase.

CONCLUSION

CLT1-G2-(Gd-DOTA) is a promising molecular MRI contrast agent for fibrin-fibronectin complexes in tumor stroma. It has potential for diagnosis and assessing prognosis of malignant tumors with MRI.

Integrin-mediated cell-matrix interaction in physiological and pathological blood vessel formation

Physiological as well as pathological blood vessel formation are fundamentally dependent on cell-matrix interaction. Integrins, a family of major cell adhesion receptors, play a pivotal role in development, maintenance, and remodeling of the vasculature. Cell migration, invasion, and remodeling of the extracellular matrix (ECM) are integrin-regulated processes, and the expression of certain integrins also correlates with tumor progression. Recent advances in the understanding of how integrins are involved in the regulation of blood vessel formation and remodeling during tumor progression are highlighted. The increasing knowledge of integrin function at the molecular level, together with the growing repertoire of integrin inhibitors which allow their selective pharmacological manipulation, makes integrins suited as potential diagnostic markers and therapeutic targets.

Post-translational modifications of the extracellular matrix are key events in cancer progression: opportunities for biochemical marker development

The aim of this review is to discuss the potential usefulness of a novel class of biochemical markers, designated neoepitopes. Neoepitopes are post-translational modifications (PTMs) of proteins and are derived by processes, such as protease cleavage, citrullination, nitrosylation, glycosylation and isomerization. Each PTM results from a specific local physiological or pathobiological process. Identification of each modification to a tissue-specific protein may reveal a unique disease-specific biochemical marker. During cancer metastasis, the host tissue is extensively degraded and replaced by cancer-associated extracellular matrix (ECM) proteins. Furthermore, severe cellular stress and inflammation, caused by cancer, results in generation of PTMs, which will be distributed throughout the ECM. This gives rise to release of protein-specific fragments to the circulation. Here we highlight the importance of remodeling of the ECM in cancer and the generation of PTMs, which may be cancer specific and reflect disease progression; thus having potential for biochemical marker development.

Different patterns of fibronectin and tenascin-C splice variants expression in primary and metastatic melanoma lesions

We have investigated the staining patterns of primary and metastatic melanoma lesions using F8, L19 and F16. These three clinical-stage antibodies are currently being studied in clinical trials for the pharmacodelivery of cytokines or therapeutic radionuclides to neoplastic sites in patients with cancer. Frozen sections of 24 primary and 29 metastatic melanoma lesions were stained, using immunofluorescence procedures, with biotinylated preparations of the F8, L19 and F16 antibodies, which are specific to the alternatively spliced extra domain A and extra domain B domains of fibronectin and A1 domain of tenascin-C, respectively. Blood vessels were costained using von Willebrand factor-specific antibodies. In primary cutaneous melanoma lesions, F16 and F8 (but not L19) strongly stained the basal lamina at the interface between epidermis and dermis, with a strikingly complementary pattern. By contrast, metastatic melanoma lesions displayed a strong and diffuse pattern of immunoreactivity with all three antibodies. It was found that the extracellular matrix in melanoma undergoes extensive remodelling during the transition from primary to metastatic lesions. The intense staining of metastatic melanoma lesions by the F8, L19 and F16 antibodies provides a strong rationale for the use of these antibodies and their derivatives for the treatment of melanoma patients and possibly for the personalized choice of the best performing antibody in individual patients.

A novel synthetic naïve human antibody library allows the isolation of antibodies against a new epitope of oncofetal fibronectin

Human monoclonal antibodies (mAbs) can routinely be isolated from phage display libraries against virtually any protein available in sufficient purity and quantity, but library design can influence epitope coverage on the target antigen. Here we describe the construction of a novel synthetic human antibody phage display library that incorporates hydrophilic or charged residues at position 52 of the CDR2 loop of the variable heavy chain domain, instead of the serine residue found in the corresponding germline gene. The novel library was used to isolate human mAbs to various antigens, including the alternatively-spliced EDA domain of fibronectin, a marker of tumor angiogenesis. In particular, the mAb 2H7 was proven to bind to a novel epitope on EDA, which does not overlap with the one recognized by the clinical-stage F8 antibody. F8 and 2H7 were used for the construction of chelating recombinant antibodies (CRAbs), whose tumor-targeting properties were assessed in vivo in biodistribution studies in mice bearing F9 teratocarcinoma, revealing a preferential accumulation at the tumor site.

Impact of PINCH expression on survival in colorectal cancer patients

Background

The adaptor protein PINCH is overexpressed in the stroma of several types of cancer, and is an independent prognostic marker in colorectal cancer. In this study we further investigate the relationship of PINCH and survival regarding the response to chemotherapy in colorectal cancer.

Results

Paraffin-embedded tissue sections from 251 primary adenocarcinomas, 149 samples of adjacent normal mucosa, 57 samples of distant normal mucosa and 75 lymph node metastases were used for immunohistochemical staining. Stromal staining for PINCH increased from normal mucosa to primary tumour to metastasis. Strong staining in adjacent normal mucosa was related to worse survival independently of sex, age, tumour location, differentiation and stage (p = 0.044, HR, 1.60, 95% CI, 1.01-2.52). PINCH staining at the invasive margin tended to be related to survival (p = 0.051). In poorly differentiated tumours PINCH staining at the invasive margin was related to survival independently of sex, age and stage (p = 0.013, HR, 1.90, 95% CI, 1.14-3.16), while in better differentiated tumours it was not. In patients with weak staining, adjuvant chemotherapy was related to survival (p = 0.010, 0.013 and 0.013 in entire tumour area, invasive margin and inner tumour area, respectively), but not in patients with strong staining. However, in the multivariate analysis no such relationship was seen.

Conclusions

PINCH staining in normal adjacent mucosa was related to survival. Further, PINCH staining at the tumour invasive margin was related to survival in poorly differentiated tumours but not in better differentiated tumours, indicating that the impact of PINCH on prognosis was dependent on differentiation status.

Engineered high-affinity affibody molecules targeting platelet-derived growth factor receptor β in vivo

Platelet-derived growth factor receptor (PDGFR) β is a marker of stromal pericytes and fibroblasts and represents an interesting target for both diagnosis and therapy of solid tumors. A receptor-specific imaging agent would be a useful tool for further understanding the prognostic role of this receptor in vivo. Affibody molecules constitute a class of very small binding proteins that are highly suited for in vivo imaging applications and that can be selected to specifically recognize a desired target protein. Here we describe the isolation of PDGFRβ-specific Affibody molecules with subnanomolar affinity. First-generation Affibody molecules were generated from a large naive library using phage display selection. Subsequently, sequences from binders having a desired selectivity profile and competing with the natural ligand for binding were used in the design of an affinity maturation library, which was created using a single partially randomized oligonucleotide. From this second-generation library, Affibody molecules with a 10-fold improvement in affinity (K(d)=0.4-0.5 nM) for human PDGFRβ and a 4-fold improvement in affinity (K(d)=6-7 nM) for murine PDGFRβ were isolated and characterized. Complete reversible folding after heating to 90 °C, as demonstrated by circular dichroism analysis, supports tolerance to labeling conditions for molecular imaging. The binders were highly specific, as verified by dot blot showing staining reactivity only with human and murine PDGFRβ, but not with human PDGFRα, or a panel of control proteins including 16 abundant human serum proteins. The final binder recognized the native conformation of PDGFRβ expressed in murine NIH-3T3 fibroblasts and human AU565 cells, and inhibited ligand-induced receptor phosphorylation in PDGFRβ-transfected porcine aortic endothelial cells. The PDGFRβ-specific Affibody molecule also accumulated around tumoral blood vessels in a model of spontaneous insulinoma, confirming a potential for in vivo targeting.

Innovative proteomics for the discovery of systemically accessible cancer biomarkers suitable for imaging and targeted therapies

The discovery of biomarkers that are readily accessible through the circulating blood and are selectively overexpressed in pathological tissues has become a major research objective, particularly in the field of oncology. Indisputably, this group of molecules has a high potential to serve as an innovative tool for effective imaging and targeted cancer therapy approaches. In this attractive therapeutic concept, specific cancer proteins are reached by intravenously administered ligands that are coupled to cytotoxic drugs. Such compounds are able to induce cancer destruction while sparing normal tissues. Owing to the performance of mass spectrometry technology, current high-throughput proteomic analysis allows for the identification of a high number of proteins that are differentially expressed in the cancerous tissues. However, such approaches provide no information regarding the effective accessibility of the >biomarkers and, therefore, the possibility for these discovered proteins to be targeted. To bypass this major limitation, which clearly slows the discovery of such biomarkers, innovative methodological strategies have been developed to enrich the clinical specimens before the mass spectrometry analysis. The focus is laid on the group of proteins that are necessarily located either at the exterior face of the plasma membrane or in the extracellular matrix. The present review addresses the current technologies meant for the discovery and analysis of accessible antigens from clinically relevant samples.

An effective targeted nanoglobular manganese(II) chelate conjugate for magnetic resonance molecular imaging of tumor extracellular matrix

Stable manganese(II) chelates are of great interest for the design and development of safe and effective non-gadolinium(III)-based targeted MRI contrast agents for MR cancer molecular imaging. In this study, a CLT1 peptide targeted G3 nanoglobular Mn(II)-DOTA monoamide conjugate was designed and synthesized as a targeted MRI contrast agent for molecular imaging of the fibrin-fibronectin complexes or oncofetal fibronectin in tumor stroma. The targeted contrast agent comprised 2 peptides and 42 Mn(II)-DOTA chelates on the surface of the G3 nanoglobule. The T(1) and T(2) relaxivities of the targeted agent at room temperature were 3.13 and 8.74 mM(-1) s(-1) per Mn(II) chelate at 3 T (tesla), respectively. It had a well-defined nanosize (5.2 nm) and could be readily excreted via renal filtration. The targeted nanoglobular contrast agent specifically bound to tumor tissue, resulting in significant tumor contrast enhancement with minimal nonspecific enhancement in the liver of tumor bearing mice as compared to a nontargeted control at a dose as low as 0.03 mmol-Mn/kg. The targeted G3 nanoglobular Mn(II)-DOTA conjugate is promising as a targeted non-gadolinium(III)-based MRI contrast agent for MR cancer molecular imaging.

Jekyll and Hyde: the role of the microenvironment on the progression of cancer

It is now recognized that the host microenvironment undergoes extensive change during the evolution and progression of cancer. This involves the generation of cancer-associated fibroblasts (CAFs), which, through release of growth factors and cytokines, lead to enhanced angiogenesis, increased tumour growth and invasion. It has also been demonstrated that CAFs may modulate the cancer stem cell (CSC) phenotype, which has therapeutic implications. The altered fibroblast phenotype also contributes to the development of an altered extracellular matrix (ECM), with synthesis of ECM isoforms rarely found in normal tissues, including tenascin-C isoforms and the fibronectin EDA isoform. There is also emerging evidence of how the tensile strength of the tumour-associated ECM may be modified and lead to altered signalling in tumour cells. The hypoxic environment of the tumour stimulates angiogenesis and also impacts on other aspects of cell signalling, including the c-met pathway and lysyl oxidase-mediated signalling, which can directly promote tumour cell invasion. The inflammatory infiltrate associated with many solid tumours also modulates tumour function, having both anti- and pro-tumour effects. All of these components of the microenvironment provide potential targets for therapeutic attack, with a number of molecules already in clinical trials. It is also becoming evident that characterizing the tumour microenvironment can provide important prognostic and predictive information about tumours, independent of the tumour cell phenotype.

Effect of multimerization of a linear Arg-Gly-Asp peptide on integrin binding affinity and specificity

Multivalent interactions are frequently used to enhance ligand-receptor binding affinity. In this study, mono-, di- and trimeric Ala-Val-Thr-Gly-Arg-Gly-Asp-Ser-Tyr (AVTGRGDSY) peptides, labeled with (125)I or Cy5.5, were compared in vitro and in vivo. Using human embryonic kidney HEK293 (naturally alpha(V)-positive and beta(3)-negative), HEK293(beta(1)) (beta(1)-transfected and alpha(V)beta(3)-negative), HEK293(beta(3)) (beta(3)-transfected and strongly alpha(V)beta(3)-positive), and human glioblastoma U87MG (naturally alpha(V)beta(3)-positive) cell lines we evaluated their binding affinity and specificity. In vitro, the monomeric AVTGRGDSY showed specific binding to both HEK293(beta(1)) and HEK293(beta(3)) cells. Multimerization resulted in no change toward HEK293 cells, diminished binding with HEK293(beta(1)) cells, but substantially enhanced binding with alpha(V)beta(3)-positive HEK293(beta(3)) and U87MG cells. Moreover, multimeric AVTGRGDSY peptides were found to be nearly comparable to the same molar concentration of a well-known alpha(V)beta(3)-specific cyclo(RGDfV) (c(RGDfV)) peptide in specificity and affinity for targeting alpha(V)beta(3) integrin. Non-invasive in vivo optical imaging demonstrated that as compared to its monomeric analogue, the Cy5.5-labeled dimeric AVTGRGDSY peptide produced markedly enhanced tumor-to-background contrast in HEK293(beta(3)) tumor-bearing mice than in HEK293(beta(1)) tumor-bearing mice. In conclusion, the present study showed the difference of monomeric and multimeric linear Arg-Gly-Asp (RGD)-containing compound in integrin selectivity and affinity. Our data provide useful information for the design of novel RGD peptides.

STAT3alpha is oncogenic for endometrial carcinoma cells and mediates the oncogenic effects of autocrine human growth hormone

We herein demonstrate an oncogenic role for signal transducer and activator of transcription (STAT)-3alpha (the full length STAT3 isoform), which also mediates autocrine human GH (hGH)-stimulated oncogenicity, in human endometrial carcinoma (EC) cells. Autocrine hGH stimulated Y705 phosphorylation of STAT3 and STAT3-mediated transcriptional activity in a SRC and Janus-2 Kinase dependent manner in human EC cell lines. Forced expression of a constitutively active variant of STAT3alpha increased proliferation, anchorage-independent, three-dimensional (3D) Matrigel, and xenograft growth and promoted epithelial-mesenchymal transition, migration, and invasion of EC cells. Conversely, the oncogenic capacity of EC cells was significantly impaired by treatment with JSI-124, an inhibitor of STAT3 phosphorylation and activity, small interfering RNA-mediated depletion of STAT3alpha, or a dominant-negative variant of STAT3alpha. Furthermore, the enhanced EC cell oncogenicity stimulated by autocrine hGH, was also abrogated by functional inhibition or small interfering RNA-mediated depletion of STAT3alpha. STAT3alpha may therefore be a common mediator of oncogenic signaling pathways stimulating progression of EC.

Peptide-targeted Nanoglobular Gd-DOTA monoamide conjugates for magnetic resonance cancer molecular imaging

Effective imaging of a cancer molecular biomarker is critical for accurate cancer diagnosis and prognosis. CLT1 peptide was observed to specifically bind to the fibrin-fibronectin complexes presented in tumor extracellular matrix. In this study, we synthesized and evaluated CLT1 peptide-targeted nanoglobular Gd-DOTA monoamide conjugates for magnetic resonance (MR) imaging of the fibrin-fibronectin complexes in tumor. The targeted nanoglobular contrast agents were prepared by conjugating peptide CLT1 to G2 and G3 nanoglobule (lysine dendrimers with a cubic silsesquioxane core) Gd-DOTA monoamide conjugates via click chemistry. The T(1) relaxivities of peptide-targeted G2 and G3 nanoglobules were 7.92 and 8.20 mM(-1) s(-1) at 3T, respectively. Approximately 2 peptides and 25 Gd-DOTA chelates were conjugated onto the surface of 32 amine groups of G2 nanoglobule, and 3 peptides and 43 Gd-DOTA chelates onto the surface of 64 amine groups of G3 nanoglobule. The peptide-targeted nanoglobular contrast agents showed greater contrast enhancement than the corresponding nontargeted agents in tumor at a dose of 0.03 mmol-Gd/kg in female athymic mice bearing MDA-MB-231 human breast carcinoma xenografts. The targeted MRI contrast agents have a potential for specific cancer molecular imaging with MRI.

New strategy for the extension of the serum half-life of antibody fragments

Antibody fragments can recognize their cognate antigen with high affinity and can be produced at high yields, but generally display rapid blood clearance profiles. For pharmaceutical applications, the serum half-life of antibody fragments is often extended by chemical modification with polymers or by genetic fusion to albumin or albumin-binding polypeptides. Here, we report that the site-specific chemical modification of a C-terminal cysteine residue in scFv antibody fragments with a small organic molecule capable of high-affinity binding to serum albumin substantially extends serum half-life in rodents. The strategy was implemented using the antibody fragment F8, specific to the alternatively spliced EDA domain of fibronectin, a tumor-associated antigen. The unmodified and chemically modified scFv-F8 antibody fragments were studied by biodistribution analysis in tumor-bearing mice, exhibiting a dramatic increase in tumor uptake for the albumin-binding antibody derivative. The data presented in this paper indicate that the chemical modification of the antibody fragment with the 2-(3-maleimidopropanamido)-6-(4-(4-iodophenyl)butanamido)hexanoate albumin-binding moiety may represent a general strategy for the extension of the serum half-life of antibody fragments and for the improvement of their in vivo targeting performance.

Co-purified gelatinases alter the stability and biological activities of human plasma fibronectin preparations

BACKGROUND AND OBJECTIVE

Fibronectin (FN) is an important cell adhesion molecule that is used widely to characterize cell behavior. Preparations of FN purified from human plasma by gelatin-Sepharose affinity chromatography typically also contain gelatin-binding gelatinases that may cleave FN, reduce its stability and alter its biological activities. Available methods for separating gelatinases from FN are resource demanding. Therefore, our objective was to devise a time- and cost-efficient protocol for purification of gelatinase-free FN.

MATERIAL AND METHODS

Experiments tested the elution profiles for FN and gelatinases from gelatin-Sepharose using a concentration range (1-7%) of dimethyl sulfoxide (DMSO) and 4 m urea as eluants. Subsequently, we explored the sequential application of those eluants for differential elution of gelatinases and FN using a single affinity column. Finally, experiments characterized the stability of purified FN with or without contaminating gelatinases, as well as the effects of FN degradation on cell attachment and migration.

RESULTS

Assay optimization demonstrated that pre-elution with 3% DMSO efficiently eliminated gelatinases but not FN from gelatin-Sepharose, whereas subsequent elution with 4 m urea released FN. Sequential elutions with DMSO and urea produced gelatinase-free FN, which was more stable than FN eluted by urea only. Fibronectin degradation did not affect human gingival fibroblast attachment, but increased cell migration significantly.

CONCLUSION

The present experiments devised a time- and cost-efficient protocol for eliminating gelatinases during purification of human plasma FN. Gelatinase-free FN preparations had greater stability, which may be essential for experiments because FN fragments have altered biological activities compared with intact FN.

Impact of VEGF-dependent tumour micro-environment on EDB fibronectin expression by subcutaneous human tumour xenografts in nude mice

Fibronectin (FN) is an extracellular matrix cell-adhesive glycoprotein. The alternative spliced isoform EDB-FN (extra domain B containing FN) is highly expressed in tumour blood vessels and stroma and represents a candidate for tumour targeting. To investigate the impact of different angiogenic micro-environments on EDB-FN expression, we used a tumour model in which human endometrial adenocarcinoma Tet-FGF2 cells overexpressing fibroblast growth factor-2 (FGF2) driven by the tetracycline-responsive promoter were further transfected with a VEGF antisense cDNA, generating AS-VEGF/Tet-FGF2 cells. In this model, the expression of FGF2 plus VEGF results in fast-growing, highly vascularized Tet-FGF2 tumours. Down-regulation of FGF2 production by tetracycline administration and/or of VEGF production by AS-VEGF transduction inhibited tumour growth and vascularization, with profound changes in tumour micro-environment. Quantitative RT-PCR analysis using human EDB-FN primers shows that subcutaneous grafting in immunodeficient mice is per se sufficient to cause a dramatic up-regulation of EDB-FN expression by these cells, as well as by human oesophageal cancer KYSE 30 cells and renal carcinoma Caki-1 cells. However, in vivo down-regulation of VEGF expression, as occurs in AS-VEGF/Tet-FGF2 tumours, and to a lesser extent of FGF2 expression, as occurs in tetracycline-treated Tet-FGF2 tumour-bearing animals, causes significant inhibition of EDB-FN production in tumour grafts, as shown by immunohistochemistry and quantitative RT-PCR analysis. Accordingly, treatment of Tet-FGF2 tumour-bearing animals with the neutralizing anti-murine VEGF receptor-2 antibody DC101, or of Caki-1 tumour-bearing animals with the anti-VEGF antibody bevacizumab, inhibited EDB-FN expression in tumour grafts. EDB-FN down-regulation was paralleled by a decrease in vascularity, thus confirming EDB-FN as a marker of tumour angiogenesis. These data demonstrate that the angiogenic micro-environment, and in particular the VEGF/VEGFR-2 system, plays a key role in modulating EDB-FN expression by tumour cells in vivo. This may have implications for the design of therapeutic strategies targeting EDB-FN in combination with anti-angiogenic and/or cytotoxic drugs.

In vivo biotinylation of the vasculature in B-cell lymphoma identifies BST-2 as a target for antibody-based therapy

The discovery of accessible markers of lymphoma may facilitate the development of antibody-based therapeutic strategies. Here, we describe the results of a chemical proteomic study, based on the in vivo biotinylation of vascular proteins in lymphoma-bearing mice followed by mass spectrometric and bioinformatic analysis, to discover proteins expressed at the tissue-blood border of disseminated B-cell lymphoma. From a list of 58 proteins, which were more than 10-fold up-regulated in nodal and extranodal lymphoma lesions compared with their levels in the corresponding normal host organs, we validated BST-2 as a novel vascular marker of B-cell lymphoma, using immunochemical techniques and in vivo biodistribution studies. Furthermore, targeting BST-2 with 2 independent monoclonal antibodies delayed lymphoma growth in a syngeneic mouse model of the disease. The results of this study delineate a strategy for the treatment of systemic B-cell lymphoma in humans and suggest that anti–BST-2 antibodies may facilitate pharmacodelivery approaches that target the tumor-stroma interface.

Tenascin-W is a specific marker of glioma-associated blood vessels and stimulates angiogenesis in vitro

The microenvironment hosting a tumor actively participates in regulating tumor cell proliferation, migration, and invasion. Among the extracellular matrix proteins enriched in the stroma of carcinomas are the tenascin family members tenascin-C and tenascin-W. Whereas tenascin-C overexpression in gliomas is known to correlate with poor prognosis, the status of tenascin-W in brain tumors has not been investigated so far. In the present study, we analyzed protein levels of tenascin-W in 38 human gliomas and found expression of tenascin-W in 80% of the tumor samples, whereas no tenascin-W could be detected in control, nontumoral brain tissues. Double immunohistochemical staining of tenascin-W and von Willebrand factor revealed that tenascin-W is localized around blood vessels, exclusively in tumor samples. In vitro, the presence of tenascin-W increased the proportion of elongated human umbilical vein endothelial cells (HUVECs) and augmented the mean speed of cell migration. Furthermore, tenascin-W triggered sprouting of HUVEC spheroids to a similar extent as the proangiogenic factor tenascin-C. In conclusion, our study identifies tenascin-W as a candidate biomarker for brain tumor angiogenesis that could be used as a molecular target for therapy irrespective of the glioma subtype.—Martina, E., Degen, M., Rüegg, C., Merlo, A., Lino, M. M., Chiquet-Ehrismann, R., Brellier, F. Tenascin-W is a specific marker of glioma-associated blood vessels and stimulates angiogenesis in vitro.

Differential secreted proteome approach in murine model for candidate biomarker discovery in colon cancer

The complexity and heterogeneity of the plasma proteome have presented significant challenges in the identification of protein changes associated with tumor development. We used cell culture as a model system and identified differentially expressed, secreted proteins which may constitute serological biomarkers. A stable isotope labeling by amino acids in cell culture (SILAC) approach was used to label the entire secreted proteomes of the CT26 murine colon cancer cell line and normal young adult mouse colon (YAMC) cell line, thereby creating a stable isotope labeled proteome (SILAP) standard. This SILAP standard was added to unlabeled murine CT26 colon cancer cell or normal murine YAMC colon epithelial cell secreted proteome samples. A multidimensional approach combining isoelectric focusing (IEF), strong cation exchange (SCX) followed by reversed phase liquid chromatography was used for extensive protein and peptide separation. A total of 614 and 929 proteins were identified from the YAMC and CT26 cell lines, with 418 proteins common to both cell lines. Twenty highly abundant differentially expressed proteins from these groups were selected for liquid chromatography-multiple reaction monitoring/mass spectrometry (LC-MRM/MS) analysis in sera. Differential secretion into the serum was observed for several proteins when Apc(min) mice were compared with control mice. These findings were then confirmed by Western blot analysis.

The role of tenascin-C in tissue injury and tumorigenesis

The extracellular matrix molecule tenascin-C is highly expressed during embryonic development, tissue repair and in pathological situations such as chronic inflammation and cancer. Tenascin-C interacts with several other extracellular matrix molecules and cell-surface receptors, thus affecting tissue architecture, tissue resilience and cell responses. Tenascin-C modulates cell migration, proliferation and cellular signaling through induction of pro-inflammatory cytokines and oncogenic signaling molecules amongst other mechanisms. Given the causal role of inflammation in cancer progression, common mechanisms might be controlled by tenascin-C during both events. Drugs targeting the expression or function of tenascin-C or the tenascin-C protein itself are currently being developed and some drugs have already reached advanced clinical trials. This generates hope that increased knowledge about tenascin-C will further improve management of diseases with high tenascin-C expression such as chronic inflammation, heart failure, artheriosclerosis and cancer.

The role of tenascin-C in tissue injury and tumorigenesis

The extracellular matrix molecule tenascin-C is highly expressed during embryonic development, tissue repair and in pathological situations such as chronic inflammation and cancer. Tenascin-C interacts with several other extracellular matrix molecules and cell-surface receptors, thus affecting tissue architecture, tissue resilience and cell responses. Tenascin-C modulates cell migration, proliferation and cellular signaling through induction of pro-inflammatory cytokines and oncogenic signaling molecules amongst other mechanisms. Given the causal role of inflammation in cancer progression, common mechanisms might be controlled by tenascin-C during both events. Drugs targeting the expression or function of tenascin-C or the tenascin-C protein itself are currently being developed and some drugs have already reached advanced clinical trials. This generates hope that increased knowledge about tenascin-C will further improve management of diseases with high tenascin-C expression such as chronic inflammation, heart failure, artheriosclerosis and cancer.

Preclinical characterization of DEKAVIL (F8-IL10), a novel clinical-stage immunocytokine which inhibits the progression of collagen-induced arthritis

Introduction

In this article, we present a comparative immunohistochemical evaluation of four clinical-stage antibodies (L19, F16, G11 and F8) directed against splice isoforms of fibronectin and of tenascin-C for their ability to stain synovial tissue alterations in rheumatoid arthritis patients. Furthermore we have evaluated the therapeutic potential of the most promising antibody, F8, fused to the anti-inflammatory cytokine interleukin (IL) 10.

Methods

F8-IL10 was produced and purified to homogeneity in CHO cells and shown to comprise biological active antibody and cytokine moieties by binding assays on recombinant antigen and by MC/9 cell proliferation assays. We have also characterized the ability of F8-IL10 to inhibit arthritis progression in the collagen-induced arthritis mouse model.

Results

The human antibody F8, specific to the extra-domain A of fibronectin, exhibited the strongest and most homogenous staining pattern in synovial biopsies and was thus selected for the development of a fully human fusion protein with IL10 (F8-IL10, also named DEKAVIL). Following radioiodination, F8-IL10 was able to selectively target arthritic lesions and tumor neo-vascular structures in mice, as evidenced by autoradiographic analysis and quantitative biodistribution studies. The subcutaneous administration route led to equivalent targeting results when compared with intravenous administration and was thus selected for the clinical development of the product. F8-IL10 potently inhibited progression of established arthritis in the collagen-induced mouse model when tested alone and in combination with methotrexate. In preparation for clinical trials in patients with rheumatoid arthritis, F8-IL10 was studied in rodents and in cynomolgus monkeys, revealing an excellent safety profile at doses tenfold higher than the planned starting dose for clinical phase I trials.

Conclusions

Following the encouraging preclinical results presented in this paper, clinical trials with F8-IL10 will now elucidate the therapeutic potential of this product and whether the targeted delivery of IL10 potentiates the anti-arthritic action of the cytokine in rheumatoid arthritis patients.

[Expression pattern of invasion-related molecules in brain tumors of different origin]

Tumor cell invasion into the surrounding brain tissue is mainly responsible for the failure of radical surgical resection and successful treatment, with tumor recurrence as microdisseminated disease. Epidermal growth factor receptors (EGFRs), integrins and their ligands in the extracellular matrix (ECM) predominantly participate in the invasion process, including the cell adhesion to the surrounding microenvironment and cell migration. The extent of infiltration of the surrounding brain tissue by malignant tumors strongly depends on the tumor cell type. Malignant gliomas show much more intensive peritumoral invasion than do metastatic tumors. In this study, the mRNA expression of 29 invasion-related molecules (18 cell membrane receptors or receptor subunits (EGFRs and integrins) and 11 ECM components: collagens, laminins and fibronectin) was investigated by quantitative reverse transcriptase-polymerase chain reaction. Fresh frozen human tissue samples from glioblastoma (GBM) and intracerebral bronchial adenocarcinoma metastases (five pieces from each) were evaluated. Significant differences were established in six of the 29 molecules (ErbB1, 2, 3, integrins alpha3, 7 and beta1). To confirm our results at the protein level, immunohistochemical analysis of nine molecules was performed. The staining intensity differed definitely in the case of ErbB1, 2 and integrins alpha3 and beta1. Determining the differences in invasion-related molecules in tumors of different origin can help identify the exact molecular mechanisms that facilitate peritumoral infiltration by glioblastoma cells. These results should allow the selection of target molecules for potential chemotherapeutic agents directed against highly invasive malignant gliomas.

Early dysregulation of cell adhesion and extracellular matrix pathways in breast cancer progression

Proliferative breast lesions, such as simple ductal hyperplasia (SH) and atypical ductal hyperplasia (ADH), are candidate precursors to ductal carcinoma in situ (DCIS) and invasive cancer. To better understand the relationship of breast lesions to more advanced disease, we used microdissection and DNA microarrays to profile the gene expression of patient-matched histologically normal (HN), ADH, and DCIS from 12 patients with estrogen receptor positive sporadic breast cancer. SH were profiled from a subset of cases. We found 837 differentially expressed genes between DCIS-HN and 447 between ADH-HN, with >90% of the ADH-HN genes also present among the DCIS-HN genes. Only 61 genes were identified between ADH-DCIS. Expression differences were reproduced in an independent cohort of patient-matched lesions by quantitative real-time PCR. Many breast cancer-related genes and pathways were dysregulated in ADH and maintained in DCIS. Particularly, cell adhesion and extracellular matrix interactions were overrepresented. Focal adhesion was the top pathway in each gene set. We conclude that ADH and DCIS share highly similar gene expression and are distinct from HN. In contrast, SH appear more similar to HN. These data provide genetic evidence that ADH (but not SH) are often precursors to cancer and suggest cancer-related genetic changes, particularly adhesion and extracellular matrix pathways, are dysregulated before invasion and even before malignancy is apparent. These findings could lead to novel risk stratification, prevention, and treatment approaches.