In vivo interrogation of the molecular display of atherosclerotic lesion surfaces

Small molecules targeting GRP78 mitigate anti-GRP78 autoantibody-mediated tissue factor procoagulant activity in cultured endothelial cells

BACKGROUND

The 78-kDa glucose-regulated protein (GRP78) expressed on the cell surface (csGRP78) has been reported to regulate tissue factor (TF) procoagulant activity (PCA) in lesion-resident endothelial cells (ECs), which is further enhanced by circulating anti-GRP78 autoantibodies that bind to the Leu98-Leu115 epitope in GRP78.

OBJECTIVES

Determine the effects of the engagement of the anti-GRP78 autoantibody to csGRP78 on ECs and the underlying mechanisms that impact TF PCA.

METHODS

Immunofluorescent staining was used to determine the presence of csGRP78 in tumor necrosis factor α-treated ECs. An established TF PCA assay was used to evaluate human ECs following treatment with anti-GRP78 autoantibodies. The Fura 2-AM assay (Abcam) was used to quantify changes in intracellular Ca2+ levels. Small molecules predicted to bind GRP78 were identified using artificial intelligence. Enzyme-linked immunosorbent assays were used to assess the ability of these GRP78 binders to mitigate TF activity and interfere with the autoantibody/csGRP78 complex.

RESULTS

In tumor necrosis factor α-treated ECs, anti-GRP78 autoantibodies increased TF PCA. This observation was further enhanced by endoplasmic reticulum stress-induced elevation of csGRP78 levels. Anti-GRP78 autoantibody treatment increased intracellular Ca2+ levels. Sequestering the anti-GRP78 autoantibody with a conformational peptide or blocking with heparin attenuated anti-GRP78 autoantibody-induced TF PCA. We identified B07∗, as a GRP78 binder that diminished anti-GRP78 autoantibody-induced TF PCA on ECs.

CONCLUSION

These findings show how anti-GRP78 autoantibodies enhance TF PCA that contributes to thrombosis and identify novel GRP78 binders that represent a potential novel therapeutic strategy for treating and managing atherothrombotic disease.

Fatal attractions that trigger inflammation and drive atherosclerotic disease

BACKGROUND

Atherosclerosis is the salient, underlying cause of cardiovascular diseases, such as arrhythmia, coronary artery disease, cardiomyopathy, pulmonary embolism and myocardial infarction. In recent years, atherosclerosis pathophysiology has evolved from a lipid-based to an inflammation-centric ideology.

METHODS

This narrative review is comprised of review and original articles that were found through the PubMed search engine. The following search terms or amalgamation of terms were used: "cardiovascular disease," "atherosclerosis," "inflammation," "GRP78," "Hsp60," "oxidative low-density lipoproteins," "aldehyde dehydrogenase," "β2-glycoprotein," "lipoprotein lipase A," "human cytomegalovirus." "SARS-CoV-2," "chlamydia pneumonia," "autophagy," "thrombosis" and "therapeutics."

RESULTS

Emerging evidence supports the concept that atherosclerosis is associated with the interaction between cell surface expression of stress response chaperones, including GRP78 and Hsp60, and their respective autoantibodies. Moreover, various other autoantigens and their autoantibodies have displayed a compelling connection with the development of atherosclerosis, including oxidative low-density lipoproteins, aldehyde dehydrogenase, β2-glycoprotein and lipoprotein lipase A. Atherosclerosis progression is also concurrent with viral and bacterial activators of various diseases. This narrative review will focus on the contributions of human cytomegalovirus as well as SARS-CoV-2 and chlamydia pneumonia in atherosclerosis development. Notably, the interaction of an autoantigen with their respective autoantibodies or the presence of a foreign antigen can enhance inflammation development, which leads to atherosclerotic lesion progression.

CONCLUSION

We will highlight and discuss the complex role of the interaction between autoantigens and autoantibodies, and the presence of foreign antigens in the development of atherosclerotic lesions in relationship to pro-inflammatory responses.

Cell surface GRP78: A potential therapeutic target for high glucose-induced endothelial injury

Endothelial cell inflammation and oxidative stress are critical to developing diabetic vascular complications. GRP78 translocation to the cell surface has been observed in different types of endothelial cells, but the potential role of cell surface GRP78 in modulating endothelial inflammation and oxidative stress remains uncertain. In this study, we investigated whether inhibiting cell surface GRP78 function using a novel anti-GRP78 monoclonal antibody (MAb159) could suppress high glucose (HG)-induced endothelial inflammation and oxidative stress. Our findings demonstrated that the expression of cell surface GRP78 was increased in HG-treated HUVECs. Inhibition of cell surface GRP78 using MAb159 attenuated HG-induced endothelial injury, inflammation and oxidative stress, while activation of GRP78 by recombinant GRP78 further amplified HG-induced endothelial damage, inflammation and oxidative stress. Additionally, we discovered that cell surface GRP78 promoted HG-induced inflammation and oxidative stress by activating the TLR4/NF-κB signalling pathway. Moreover, HG-induced GRP78 translocation to the cell surface is dependent on ER stress. Our data demonstrate that targeting cell surface GRP78 could be a promising therapeutic strategy for mitigating endothelial injury, inflammation and oxidative stress.

Advances in research of biological functions of Isthmin-1

Isthmin-1 (ISM1) was initially thought to be a brain secretory factor, but with the development of technical means of research and the refinement of animal models, numerous studies have shown that this molecule is expressed in multiple tissues, suggesting that it may have multiple biological functions. As a factor that regulates growth and development, ISM1 is expressed in different animals with spatial and temporal variability and can coordinate the normal development of multiple organs. Recent studies have found that under the dependence of a non-insulin pathway, ISM1 can lower blood glucose, inhibit insulin-regulated lipid synthesis, promote protein synthesis, and affect the body's glucolipid and protein metabolism. In addition, ISM1 plays an important role in cancer development by promoting apoptosis and anti-angiogenesis, and by regulating multiple inflammatory pathways to influence the body's immune response. The purpose of this paper is to summarize relevant research results from recent years and to describe the key features of the biological functions of ISM1. We aimed to provide a theoretical basis for the study of ISM1 related diseases, and potential therapeutic strategies. The main biological functions of ISM1. Current studies on the biological functions of ISM1 focus on growth and development, metabolism, and anticancer treatment. During embryonic development, ISM1 is dynamically expressed in the zebrafish, African clawed frog, chick, mouse, and human, is associated with craniofacial malformations, abnormal heart localization, and hematopoietic dysfunction. ISM1 plays an important role in regulating glucose metabolism, lipid metabolism, and protein metabolism in the body. ISM1 affects cancer development by regulating cellular autophagy, angiogenesis, and the immune microenvironment.

Unveiling the dark side of glucose-regulated protein 78 (GRP78) in cancers and other human pathology: a systematic review

Glucose-Regulated Protein 78 (GRP78) is a chaperone protein that is predominantly expressed in the lumen of the endoplasmic reticulum. GRP78 plays a crucial role in protein folding by assisting in the assembly of misfolded proteins. Under cellular stress conditions, GRP78 can translocate to the cell surface (csGRP78) were it interacts with different ligands to initiate various intracellular pathways. The expression of csGRP78 has been associated with tumor initiation and progression of multiple cancer types. This review provides a comprehensive analysis of the existing evidence on the roles of GRP78 in various types of cancer and other human pathology. Additionally, the review discusses the current understanding of the mechanisms underlying GRP78's involvement in tumorigenesis and cancer advancement. Furthermore, we highlight recent innovative approaches employed in downregulating GRP78 expression in cancers as a potential therapeutic target.

Scratching the Surface—An Overview of the Roles of Cell Surface GRP78 in Cancer

The 78 kDa glucose-regulated protein (GRP78) is considered an endoplasmic reticulum (ER)-resident molecular chaperone that plays a crucial role in protein folding homeostasis by regulating the unfolded protein response (UPR) and inducing numerous proapoptotic and autophagic pathways within the eukaryotic cell. However, in cancer cells, GRP78 has also been shown to migrate from the ER lumen to the cell surface, playing a role in several cellular pathways that promote tumor growth and cancer cell progression. There is another insidious consequence elicited by cell surface GRP78 (csGRP78) on cancer cells: the accumulation of csGRP78 represents a novel neoantigen leading to the production of anti-GRP78 autoantibodies that can bind csGRP78 and further amplify these cellular pathways to enhance cell growth and mitigate apoptotic cell death. This review examines the current body of literature that delineates the mechanisms by which ER-resident GRP78 localizes to the cell surface and its consequences, as well as potential therapeutics that target csGRP78 and block its interaction with anti-GRP78 autoantibodies, thereby inhibiting further amplification of cancer cell progression.

Linking cell-surface GRP78 to cancer: From basic research to clinical value of GRP78 antibodies

Glucose-related protein 78 (GRP78) is a chaperone protein localized primarily in the endoplasmic reticulum (ER) lumen, where it helps in proper protein folding by targeting misfolded proteins and facilitating protein assembly. In stressed cells, GRP78 is translocated to the cell surface (csGRP78) where it binds to various ligands and triggers different intracellular pathways. Thus, csGRP78 expression is associated with cancer, involved in the maintenance and progression of the disease. Extracellular exposition of csGRP78 leads to the production of autoantibodies as observed in patients with prostate or ovarian cancer, in which the ability to target csGRP78 affects the tumor development. Present on the surface of cancer cells and not normal cells in vivo, csGRP78 represents an interesting target for therapeutic antibody strategies. Here we give an overview of the csGRP78 function in the cell and its role in oncogenesis, thereby providing insight into the clinical value of GRP78 monoclonal antibodies for cancer prognosis and treatment.

Photoinduced reconfiguration to control the protein-binding affinity of azobenzene-cyclized peptides

The impact of next-generation biorecognition elements (ligands) will be determined by the ability to remotely control their binding activity for a target biomolecule in complex environments. Compared to conventional mechanisms for regulating binding affinity (pH, ionic strength, or chaotropic agents), light provides higher accuracy and rapidity, and is particularly suited for labile targets. In this study, we demonstrate a general method to develop azobenzene-cyclized peptide ligands with light-controlled affinity for target proteins. Light triggers a cis/trans isomerization of the azobenzene, which results in a major structural rearrangement of the cyclic peptide from a non-binding to a binding configuration. Critical to this goal are the ability to achieve efficient photo-isomerization under low light dosage and the temporal stability of both cis and trans isomers. We demonstrated our method by designing photo-switchable peptides targeting vascular cell adhesion marker 1 (VCAM1), a cell marker implicated in stem cell function. Starting from a known VCAM1-binding linear peptide, an ensemble of azobenzene-cyclized variants with selective light-controlled binding were identified by combining in silico design with experimental characterization via spectroscopy and surface plasmon resonance. Variant cycloAZOB[G-VHAKQHRN-K] featured rapid, light-controlled binding of VCAM1 (KD,trans/KD,cis ∼ 130). Biotin-cycloAZOB[G-VHAKQHRN-K] was utilized to label brain microvascular endothelial cells (BMECs), showing co-localization with anti-VCAM1 antibodies in cis configuration and negligible binding in trans configuration.

Phage nanofibers in nanomedicine: Biopanning for early diagnosis, targeted therapy, and proteomics analysis

Display of a peptide or protein of interest on the filamentous phage (also known as bacteriophage), a biological nanofiber, has opened a new route for disease diagnosis and therapy as well as proteomics. Earlier phage display was widely used in protein-protein or antigen-antibody studies. In recent years, its application in nanomedicine is becoming increasingly popular and encouraging. We aim to review the current status in this research direction. For better understanding, we start with a brief introduction of basic biology and structure of the filamentous phage. We present the principle of phage display and library construction method on the basis of the filamentous phage. We summarize the use of the phage displayed peptide library for selecting peptides with high affinity against cells or tissues. We then review the recent applications of the selected cell or tissue targeting peptides in developing new targeting probes and therapeutics to advance the early diagnosis and targeted therapy of different diseases in nanomedicine. We also discuss the integration of antibody phage display and modern proteomics in discovering new biomarkers or target proteins for disease diagnosis and therapy. Finally, we propose an outlook for further advancing the potential impact of phage display on future nanomedicine. This article is categorized under: Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Cell surface expression of 78-kDa glucose-regulated protein (GRP78) mediates diabetic nephropathy

The 78-kDa glucose-regulated protein (GRP78) is a well-established endoplasmic reticulum (ER)-resident chaperone that maintains protein homeostasis and regulates the unfolded protein response. Under conditions of ER stress, GRP78 is also expressed at the cell surface and implicated in tumorigenesis, immunity, and cellular signaling events. The role of cell surface-associated GRP78 (csGRP78) in the pathogenesis of diabetic nephropathy has not yet been defined. Here we explored the role of csGRP78 in regulating high glucose (HG)-induced profibrotic AKT Ser/Thr kinase (AKT) signaling and up-regulation of extracellular matrix proteins. Using primary kidney mesangial cells, we show that HG treatment, but not the osmotic control mannitol, induces csGRP78 expression through an ER stress-dependent mechanism. We found that csGRP78, known to be located on the outer membrane leaflet, interacts with the transmembrane protein integrin β1 and activates focal adhesion kinase and downstream PI3K/AKT signaling. Localization of GRP78 at the cell surface and its interaction with integrin β1 were also required for extracellular matrix protein synthesis in response to HG. Surprisingly, both the N and C termini of csGRP78 were necessary for this profibrotic response. Increased localization of GRP78 at the plasma membrane was also found in the glomerular mesangial area of type 1 diabetic mice in two different models (streptozotocin-induced and Akita). In freshly isolated glomeruli from Akita mice, csGRP78 co-localized with the mesangial cell surface marker α8-integrin. In conclusion, our work reveals a role for csGRP78 in HG-induced profibrotic responses in mesangial cells, informing a potential approach to treating diabetic nephropathy.

Anti-GRP78 autoantibodies induce endothelial cell activation and accelerate the development of atherosclerotic lesions

The 78-kDa glucose-regulated protein (GRP78) is an ER molecular chaperone that aids in protein folding and secretion. However, pathological conditions that cause ER stress can promote the relocalization of GRP78 to the cell surface (csGRP78), where it acts as a signaling receptor to promote cancer progression. csGRP78 also possesses antigenic properties, leading to the production of anti-GRP78 autoantibodies, which contribute to tumor growth. In contrast, the presence and role of anti-GRP78 autoantibodies in atherosclerosis is unknown. Here, we show that atherosclerotic-prone ApoE-/- mice develop circulating anti-GRP78 autoantibodies that bind to csGRP78 on lesion-resident endothelial cells. Moreover, GRP78-immunized ApoE-/- mice exhibit a marked increase in circulating anti-GRP78 autoantibody titers that correlated with accelerated lesion growth. Mechanistically, engagement of anti-GRP78 autoantibodies with csGRP78 on human endothelial cells activated NF-κB, thereby inducing the expression of ICAM-1 and VCAM-1, a process blocked by NF-κB inhibitors. Disrupting the autoantibody/csGRP78 complex with enoxaparin, a low-molecular-weight heparin, reduced the expression of adhesion molecules and attenuated lesion growth. In conclusion, anti-GRP78 autoantibodies play a crucial role in atherosclerosis development, and disruption of the interaction between anti-GRP78 autoantibodies and csGRP78 represents a therapeutic strategy.

Structure-based design for binding peptides in anti-cancer therapy

The conventional anticancer therapeutics usually lack cancer specificity, leading to damage of normal tissues that patients find hard to tolerate. Ideally, anticancer therapeutics carrying payloads of drugs equipped with cancer targeting peptides can act like "guided missiles" with the capacity of targeted delivery toward many types of cancers. Peptides are amenable for conjugation to nano drugs for functionalization, thereby improving drug delivery and cellular uptake in cancer-targeting therapies. Peptide drugs are often more difficult to design through molecular docking and in silico analysis than small molecules, because peptide structures are more flexible, possess intricate molecular conformations, and undergo complex interactions. In this review, the development and application of strategies for structure-based design of cancer-targeting peptides against GRP78 are discussed. This Review also covers topics related to peptide pharmacokinetics and targeting delivery, including molecular docking studies, features that provide advantages for in vivo use, and properties that influence the cancer-targeting ability. Some advanced technologies and special peptides that can overcome the pharmacokinetic challenges have also been included.

CTHRSSVVC Peptide as a Possible Early Molecular Imaging Target for Atherosclerosis

The purpose of our work was to select phages displaying peptides capable of binding to vascular markers present in human atheroma, and validate their capacity to target the vascular markers in vitro and in low-density lipoprotein receptor knockout (LDLr(-/-)) mouse model of atherosclerosis. By peptide fingerprinting on human atherosclerotic tissues, we selected and isolated four different peptides sequences, which bind to atherosclerotic lesions and share significant similarity to known human proteins with prominent roles in atherosclerosis. The CTHRSSVVC-phage peptide displayed the strongest reactivity with human carotid atherosclerotic lesions (p < 0.05), when compared to tissues from normal carotid arteries. This peptide sequence shares similarity to a sequence present in the fifth scavenger receptor cysteine-rich (SRCR) domain of CD163, which appeared to bind to CD163, and subsequently, was internalized by macrophages. Moreover, the CTHRSSVVC-phage targets atherosclerotic lesions of a low-density lipoprotein receptor knockout (LDLr(-/-)) mouse model of atherosclerosis in vivo to High-Fat diet group versus Control group. Tetraazacyclododecane-1,4,7,10-tetraacetic acid-CTHRSSVVC peptide (DOTA-CTHRSSVVC) was synthesized and labeled with (111)InCl₃ in >95% yield as determined by high performance liquid chromatography (HPLC), to validate the binding of the peptide in atherosclerotic plaque specimens. The results supported our hypothesis that CTHRSSVVC peptide has a remarkable sequence for the development of theranostics approaches in the treatment of atherosclerosis and other diseases.

Autoantibodies against cell surface GRP78 promote tumor growth in a murine model of melanoma

Autoantibodies that react with GRP78 expressed on the cell-surface of many tumor cell lines occur in the sera of patients with prostate cancer, melanoma, and ovarian cancer. These autoantibodies are a negative prognostic factor in prostate cancer and, when purified, stimulate tumor cell proliferation in vitro. It is unclear, however, whether these immunoglobulin Gs are merely a biomarker, or whether they actually promote the tumor growth in vivo. We immunized C57Bl/6 mice with recombinant GRP78 and then implanted the B16F1 murine melanoma cell line as flank tumors. We used the antisera from these mice for in-vitro cell signaling and proliferation assays. The immunodominant epitope in patients with cancer was well represented in the antibody repertoire of these immunized mice. We observed significantly accelerated tumor growth, and shortened survival in GRP78-immunized mice compared with controls. Furthermore, antisera from these mice, and purified anti-GRP78 immunoglobulin G from similarly immunized mice, stimulate Akt phosphorylation and proliferation in B16F1 and human DM6 melanoma cells in culture. These studies show a causal link between a humoral response to GRP78 and the progression of cancer in a murine melanoma model. They support the hypothesis that such autoantibodies are involved in the progression of human cancers and are not simply a biomarker. As GRP78 is present on the surface of many types of cancer cells, this hypothesis has broad clinical and therapeutic implications.

A murine monoclonal antibody directed against the carboxyl-terminal domain of GRP78 suppresses melanoma growth in mice

The HSP70 family member GRP78 is a selective tumor marker upregulated on the surface of many tumor cell types, including melanoma, where it acts as a growth factor receptor-like protein. Receptor-recognized forms of the proteinase inhibitor α2-macroglobulin (α2M*) are the best-characterized ligands for GRP78, but in melanoma and other cancer patients, autoantibodies arise against the NH2-terminal domain of GRP78 that react with tumor cell-surface GRP78. This causes the activation of signaling cascades that are proproliferative and antiapoptotic. Antibodies directed against the COOH-terminal domain of GRP78, however, upregulate p53-mediated proapoptotic signaling, leading to cell death. Here, we describe the binding characteristics, cell signaling properties, and downstream cellular effects of three novel murine monoclonal antibodies. The NH2-terminal domain-reactive antibody, N88, mimics α2M* as a ligand and drives PI 3-kinase-dependent activation of Akt and the subsequent stimulation of cellular proliferation in vitro. The COOH-terminal domain-reactive antibody, C38, acts as an antagonist of both α2M* and N88, whereas another, C107, directly induces apoptosis in vitro. In a murine B16F1 melanoma flank tumor model, we demonstrate the acceleration of tumor growth by treatment with N88, whereas C107 significantly slowed tumor growth whether administered before (P<0.005) or after (P<0.05) tumor implantation.

By-passing large screening experiments using sequencing as a tool to identify scFv fragments targeting atherosclerotic lesions in a novel in vivo phage display selection

Atherosclerosis is a chronic, progressive inflammatory disease that may develop into vulnerable lesions leading to thrombosis. To interrogate the molecular components involved in this process, single-chain variable fragments (scFvs) from a semi-synthetic human antibody library were selected on the lesions induced in a rabbit model of atherosclerosis after two rounds of in vivo phage display. Homing Phage-scFvs were isolated from (1) the injured endothelium, (2) the underlying lesional tissue and (3) the cells within the intima. Clones selected on the basis of their redundancy or the presence of key amino acids, as determined by comparing the distribution between the native and the selected libraries, were produced in soluble form, and seven scFvs were shown to specifically target the endothelial cell surface and inflamed intima-related regions of rabbit tissue sections by immunohistology approaches. The staining patterns differed depending on the scFv compartment of origin. This study demonstrates that large-scale scFv binding assays can be replaced by a sequence-based selection of best clones, paving the way for easier use of antibody libraries in in vivo biopanning experiments. Future investigations will be aimed at characterizing the scFv/target couples by mass spectrometry to set the stage for more accurate diagnostic of atherosclerosis and development of therapeutic strategies.

In vivo phage display to identify new human antibody fragments homing to atherosclerotic endothelial and subendothelial tissues [corrected]

In vivo phage display selection is a powerful strategy for directly identifying agents that target the vasculature of normal or diseased tissues in living animals. We describe here a new in vivo biopanning strategy in which a human phage single-chain antibody (scFv) library was injected into high-fat diet-fed ApoE(-/-) mice. Extracellular and internalized phage scFvs were selectively recovered from atherosclerotic vascular endothelium and subjacent tissues. After three successive biopanning rounds, a panel of six clones with distinct gene sequences was isolated. Four scFvs produced and purified in soluble form were shown to interact in vitro with a rabbit atheromatous protein extract by time-resolved fluorescence resonance energy transfer and to target the endothelial cell surface and inflamed intima-related regions of rabbit and human tissue sections ex vivo. These new scFvs selected in a mouse model recognized both rabbit and human tissue, underlying the interspecies similarities of the recognized epitopes. By combining immunoprecipitation and mass spectrometry, one of the selected scFvs was shown to recognize carbonic anhydrase II, an up-regulated enzyme involved in resorption of ectopic calcification. These results show that in vivo biopanning selection in hypercholesterolemic animals makes it possible to identify both scFvs homing to atherosclerotic endothelial and subendothelial tissues, and lesion-associated biomarkers. Such scFvs offer promising opportunities in the field of molecular targeting for the treatment of atherosclerosis.

Interaction of cowpea mosaic virus nanoparticles with surface vimentin and inflammatory cells in atherosclerotic lesions

AIMS

Detection of atherosclerosis has generally been limited to the late stages of development, after cardiovascular symptoms present or a clinical event occurs. One possibility for early detection is the use of functionalized nanoparticles. The aim of this study was the early imaging of atherosclerosis using nanoparticles with a natural affinity for inflammatory cells in the lesion.

MATERIALS & METHODS

We investigated uptake of cowpea mosaic virus by macrophages and foam cells in vitro and correlated this with vimentin expression. We also examined the ability of cowpea mosaic virus to interact with atherosclerotic lesions in a murine model of atherosclerosis.

RESULTS & CONCLUSION

We found that uptake of cowpea mosaic virus is increased in areas of atherosclerotic lesion. This correlated with increased surface vimentin in the lesion compared with nonlesion vasculature. In conclusion, cowpea mosaic virus and its vimentin-binding region holds potential for use as a targeting ligand for early atherosclerotic lesions, and as a probe for detecting upregulation of surface vimentin during inflammation.

Extracellular heat shock proteins, cellular export vesicles, and the Stress Observation System: a form of communication during injury, infection, and cell damage. It is never known how far a controversial finding will go! Dedicated to Ferruccio Ritossa

Heat shock proteins (hsp) have been found to play a fundamental role in the recovery from multiple stress conditions and to offer protection from subsequent insults. The function of hsp during stress goes beyond their intracellular localization and chaperone role as they have been detected outside cells activating signaling pathways. Extracellular hsp are likely to act as indicators of the stress conditions, priming other cells, particularly of the immune system, to avoid the propagation of the insult. Some extracellular hsp, for instance Hsp70, are associated with export vesicles, displaying a robust activation of macrophages. We have coined the term Stress Observation System (SOS) for the mechanism for sensing extracellular hsp, which we propose is a form of cellular communication during stress conditions. An enigmatic and still poorly understood process is the mechanism for the release of hsp, which do not contain any consensus secretory signal. The export of hsp appears to be a very complex phenomenon encompassing different alternative pathways. Moreover, extracellular hsp may not come in a single flavor, but rather in a variety of physical conditions. This review addresses some of our current knowledge about the release and function of extracellular hsp, in particular those associated with vesicles.

Specific penetration and accumulation of a homing peptide within atherosclerotic plaques of apolipoprotein E-deficient mice

The ability to selectively deliver compounds into atherosclerotic plaques would greatly benefit the detection and treatment of atherosclerotic disease. We describe such a delivery system based on a 9-amino acid cyclic peptide, LyP-1. LyP-1 was originally identified as a tumor-homing peptide that specifically recognizes tumor cells, tumor lymphatics, and tumor-associated macrophages. As the receptor for LyP-1, p32, is expressed in atherosclerotic plaques, we tested the ability of LyP-1 to home to plaques. Fluorescein-labeled LyP-1 was intravenously injected into apolipoprotein E (ApoE)-null mice that had been maintained on a high-fat diet to induce atherosclerosis. LyP-1 accumulated in the plaque interior, predominantly in macrophages. More than 60% of cells released from plaques were positive for LyP-1 fluorescence. Another plaque-homing peptide, CREKA, which binds to fibrin-fibronectin clots and accumulates at the surface of plaques, yielded fewer positive cells. Tissues that did not contain plaque yielded only traces of LyP-1(+) cells. LyP-1 was capable of delivering intravenously injected nanoparticles to plaques; we observed abundant accumulation of LyP-1-coated superparamagnetic iron oxide nanoparticles in the plaque interior, whereas CREKA-nanoworms remained at the surface of the plaques. Intravenous injection of 4-[(18)F]fluorobenzoic acid ([(18)F]FBA)-conjugated LyP-1 showed a four- to sixfold increase in peak PET activity in aortas containing plaques (0.31% ID/g) compared with aortas from normal mice injected with [(18)F]FBA-LyP-1(0.08% ID/g, P < 0.01) or aortas from atherosclerotic ApoE mice injected with [(18)F]FBA-labeled control peptide (0.05% ID/g, P < 0.001). These results indicate that LyP-1 is a promising agent for the targeting of atherosclerotic lesions.

Angiogenic peptides improve blood flow and promote capillary growth in a diabetic and ischaemic mouse model

OBJECTIVES

It is a common clinical observation that collateral vessel development is impaired in diabetic patients with ischaemic vascular diseases. Consequently, alternative revascularisation strategies in diabetic patients are needed. This study presents the effect and mechanism of new peptide therapeutic angiogenesis in an ischaemic and diabetic mouse model.

DESIGN

Streptozocin-injected mice that had undergone hind-limb ischaemia were treated with angiogenic peptides. Blood flow restoration was calculated by laser Doppler imager and corroborated by histological section. For the mechanism study, endothelial cells were exposed to hypoxia and high glucose concentrations to study the effect of the peptides on proliferation and anti-apoptosis.

RESULTS

The peptides significantly restored blood perfusion 21 days after surgery in the diabetic mice (p < 0.01) by neo-vascularisation, corroborated by an increase in capillary density. In addition, the peptides induced the proliferation of hypoxic endothelial cells (p < 0.01) and protected the cells from apoptosis in high glucose cultures.

CONCLUSIONS

This is the first approach for treatment of ischaemic vascular disease with peptides in a diabetic mouse model.

Glucose-Regulated Protein 78 and Platelet Deposition

Objective— To investigate the effect of rosuvastatin on platelet deposition under controlled shear rate conditions and to identify new platelet proteins involved in the interaction with the activating substrate.

Methods and Results— Platelet-vessel wall interaction and thrombosis take place under dynamic conditions involving the interaction of the exposed damaged vascular wall with the circulating blood cells and proteins. Blood was perfused over type I collagen at different wall shear rates, and platelet deposition was measured by confocal microscopy. Perfused effluent blood was collected, platelets were sequentially extracted based on differential protein solubility, and proteins were separated by 2D gel electrophoresis. Blockade of 3-hydroxy-3-methylglutaryl–coenzyme A reductase significantly reduced platelet deposition and modulated the expression pattern of 18 proteins in the platelet subproteome. Among them, an increase in platelet surface 78-kDa glucose-regulated protein (GRP78), a stress-inducible multifunctional endoplasmic reticulum protein, was clearly apparent. Immunoprecipitation of platelet GRP78 revealed its interaction with tissue factor. Moreover, blockade of surface GRP78 resulted in a substantial increase in platelet deposition and tissue factor procoagulant activity and in a decrease in clotting time.

Conclusion— These findings demonstrate that blockade of 3-hydroxy-3-methylglutaryl–coenzyme A reductase reduces platelet deposition and inhibits GRP78 translocation from the platelet surface after shear and collagen activation. For the first time to our knowledge, this study reports on the presence and functional role of GRP78 in platelets and indicates that GRP78 has additional functions beyond those of a molecular chaperone.

Cell surface relocalization of the endoplasmic reticulum chaperone and unfolded protein response regulator GRP78/BiP

The recent discovery that GRP78/BiP, a typical endoplasmic reticulum (ER) lumenal chaperone, can be expressed on the cell surface, interacting with an increasing repertoire of surface proteins and acting as receptor in signaling pathways, represents a paradigm shift in its biological function. However, the mechanism of GRP78 trafficking from the ER to the cell surface is not well understood. Using a combination of cellular, biochemical, and mutational approaches, we tested multiple hypotheses. Here we report that ER stress actively promotes GRP78 localization on the cell surface, whereas ectopic expression of GRP78 is also able to cause cell surface relocation in the absence of ER stress. Moreover, deletion of the C-terminal ER retention motif in GRP78 alters its cell surface presentation in a dose-dependent manner; however, mutation of the putative O-linked glycosylation site Thr(648) of human GRP78 is without effect. We also identified the exposure of multiple domains of GRP78 on the cell surface and determined that binding of extracellular GRP78 to the cell surface is unlikely. A new topology model for cell surface GRP78 is presented.

GRP78 signaling hub a receptor for targeted tumor therapy

Glucose-regulated protein 78 (GRP78) is a potential receptor for targeting therapy in cancer and chronic vascular disease due to its overexpression at the cell surface in tumor cells and in atherosclerotic lesions. Presence of the GRP78 autoantibody in cancer patient sera is generally associated with poor prognosis since it signals a prosurvival mechanism in response to cellular stress. Association of GRP78 with various binding partners involves coordination of multiple signaling pathways that result in either cell survival or cell death. Binding of activated alpha2-macroglobulin to cell-surface GRP78 activates Akt to suppress apoptotic pathways through multiple downstream effectors, and concomitantly upregulates NF-kappaBeta and induces the unfolded protein response (UPR) so that cell proliferation prevails. Interaction of GRP78 with cell-surface T-cadherin promotes endothelial cell survival. Association of oncogenic Cripto with GRP78 nullifies TGF-beta superfamily-dependent signaling through Smad2/3 to promote cell proliferation. In contrast, association of GRP78 with the plasminogen kringle 5 domain or extracellular Par-4 promotes apoptosis. Interaction of GRP78 with microplasminogen induces the UPR while association with tissue factor inhibits procoagulant activity. The diverse and multiple binding proteins of GRP78 and their equally diverse functional outcomes reflect the regulatory cellular functions that GRP78 orchestrates. Several GRP78 targeting peptides have been isolated from different tumors and they show remarkable tumor specificity. Conjugation of GRP78-targeting peptides to an apoptosis-inducing peptide suppresses tumor growth in tumor xenografts, thereby demonstrating that GRP78 is a viable target by which clinical cancer therapies can be successfully developed as well as its potential utility in treating vascular disease.

Regulation of PERK signaling and leukemic cell survival by a novel cytosolic isoform of the UPR regulator GRP78/BiP

The unfolded protein response (UPR) is an evolutionarily conserved mechanism to allow cells to adapt to stress targeting the endoplasmic reticulum (ER). Induction of ER chaperone GRP78/BiP increases protein folding capacity; as such it represents a major survival arm of UPR. Considering the central importance of the UPR in regulating cell survival and death, evidence is emerging that cells evolve feedback regulatory pathways to modulate the key UPR executors, however, the precise mechanisms remain to be elucidated. Here, we report the fortuitous discovery of GRP78va, a novel isoform of GRP78 generated by alternative splicing (retention of intron 1) and alternative translation initiation. Bioinformatic and biochemical analyses revealed that expression of GRP78va is enhanced by ER stress and is notably elevated in human leukemic cells and leukemia patients. In contrast to the canonical GRP78 which is primarily an ER lumenal protein, GRP78va is devoid of the ER signaling peptide and is cytosolic. Through specific knockdown of endogenous GRP78va by siRNA without affecting canonical GRP78, we showed that GRP78va promotes cell survival under ER stress. We further demonstrated that GRP78va has the ability to regulate PERK signaling and that GRP78va is able to interact with and antagonize PERK inhibitor P58(IPK). Our study describes the discovery of GRP78va, a novel cytosolic isoform of GRP78/BiP, and the first characterization of the modulation of UPR signaling via alternative splicing of nuclear pre-mRNA. Our study further reveals a novel survival mechanism in leukemic cells and other cell types where GRP78va is expressed.

Targeting atherosclerosis by using modular, multifunctional micelles

Subtle clotting that occurs on the luminal surface of atherosclerotic plaques presents a novel target for nanoparticle-based diagnostics and therapeutics. We have developed modular multifunctional micelles that contain a targeting element, a fluorophore, and, when desired, a drug component in the same particle. Targeting atherosclerotic plaques in ApoE-null mice fed a high-fat diet was accomplished with the pentapeptide cysteine-arginine-glutamic acid-lysine-alanine, which binds to clotted plasma proteins. The fluorescent micelles bind to the entire surface of the plaque, and notably, concentrate at the shoulders of the plaque, a location that is prone to rupture. We also show that the targeted micelles deliver an increased concentration of the anticoagulant drug hirulog to the plaque compared with untargeted micelles.

Phage display selection of peptides that home to atherosclerotic plaques: IL-4 receptor as a candidate target in atherosclerosis

Imaging or drug delivery tools for atherosclerosis based on the plaque biology are still insufficient. Here, we attempted to identify peptides that selectively home to atherosclerotic plaques using phage display. A phage library containing random peptides was ex viv screened for binding to human atheroma tissues. After three to four rounds of selection, the DNA inserts of phage clones wer sequenced. A peptide sequence, CRKRLDRNC, was the most frequently occurring one. Intravenously injected phage displaying the CRKRLDRNC peptide was observed to home to atherosclerotic aortic tissues of low-density lipoprotein receptor-deficient (Ldlr^−/–) mice at higher levels than to normal aortic tissues of wild-type mice. Moreover, a fluorescein- or radioisotope-conjugated synthetic CRKRLDRNC peptide, but not a control peptide, homed in vivo to atherosclerotic plaques in Ldlr^−/– mice, while homing of the peptide to other organs such as brain was minimal. The homing peptide co-localized with endothelial cells, macrophages and smooth muscle cells a mouse and human atherosclerotic plaques. Homology search revealed that the CRKRLDRNC peptide shares a motif of interleukin-receptor (IL-4) that is critical for binding to its receptor. The peptide indeed co-localized with IL-4 receptor (IL-4R) at atherosclerotic plaques. Moreover, the peptide bound to cultured cells expressing IL-4R on the cell surface and the binding was inhibited by the knock-down of IL-4R. These results show that the CRKRLDRNC peptide homes to atherosclerotic plaques through binding to IL-4R as its target and may be a useful tool for selective drug delivery and molecular imaging of atherosclerosis.

GRP78 upregulation by atheroprone shear stress via p38-, alpha2beta1-dependent mechanism in endothelial cells

OBJECTIVE

The initiation of atherosclerosis is in part dependent on the hemodynamic shear stress environment promoting a proinflammatory phenotype of the endothelium. Previous studies demonstrated increased expression of ER stress protein and unfolded protein response (UPR) regulator, GRP78, within all vascular cells in atherosclerotic lesions and its regulation in the endothelium by several atherosclerotic stressors; however, regulation of GRP78 by shear stress directly has not been established.

METHOD AND RESULTS

Using an in vitro model to simulate human arterial shear stress waveforms, atheroprone or atheroprotective flow was applied to human endothelial cells. GRP78 was found to be significantly upregulated (3-fold) in a sustained manner under atheroprone, but not atheroprotective flow up to 24 hours. This response was dependent on both sustained activation of p38, as well integrin alpha2beta1. Increased GRP78 correlated with the activation of the ER stress sensing element (ERSE1) promoter by atheroprone flow as a marker of the UPR. Shear stress regulated GRP78 through increased protein stability when compared to other flow regulated proteins, such as connexin-43 and vascular cell adhesion molecule (VCAM)-1. Increased endothelial expression of GRP78 was also observed in atheroprone versus atheroprotective regions of C57BL6 mice.

CONCLUSIONS

This study supports a role of the hemodynamic environment in preferentially inducing GRP78 and the UPR in atheroprone regions, before lesion development, and suggests a potential atheroprotective (ie, prosurvival), compensatory effect in response to ER stress within atherosclerotic lesions.

A new atherosclerotic lesion probe based on hydrophobically modified chitosan nanoparticles functionalized by the atherosclerotic plaque targeted peptides

We developed a new imaging probe for atherosclerotic lesion imaging by chemically conjugating an atherosclerotic plaque-homing peptide (termed the AP peptide) to hydrophobically modified glycol chitosan (HGC) nanoparticles. The AP peptide was previously discovered by using an in vivo phage display screening method. HGC nanoparticles were labeled with the near-infrared (NIR) fluorophore Cy5.5, yielding nanoparticles 314 nm in diameter. The binding characteristics of nanoparticles to cytokine (TNF-alpha)-activated bovine aortic endothelial cells (BAECs) were studied in vitro under static conditions and in a dynamic flow environment. AP-tagged HGC-Cy5.5 nanoparticles (100 microg/ml, 2 h incubation) bound more avidly to TNF-alpha-activated BAECs than to unactivated BAECs. Nanoparticles were mostly located in the membranes of BAECs, although some were taken up by the cells and were visible in the cytoplasm, suggesting that the AP peptides in HGC nanoparticles retained target selectivity for activated BAECs. Binding selectivity of AP-tagged HGC-Cy5.5 nanoparticles was also studied in vivo. NIR fluorescence imaging demonstrated that AP-tagged HGC-Cy5.5 nanoparticles bound better to atherosclerotic lesions in a low-density lipoprotein receptor-deficient (Ldlr(-/-)) atherosclerotic mouse than to such lesions in a normal mouse. These results suggest that the newly designed AP-tagged HGC-Cy5.5 nanoparticles may be useful for atherosclerotic lesion imaging, and may also be employed to elucidate pathophysiological changes, at the molecular level, on atherosclerotic endothelium.

Therapeutic angiogenesis of mouse hind limb ischemia by novel peptide activating GRP78 receptor on endothelial cells

Therapeutic angiogenesis emerged as a non-invasive mean of promoting neovascularization in ischemic tissues. We have searched for new molecules that induce angiogenesis by screening a phage display combinatory peptide library on endothelial cells. One of the selected peptides identified by binding to endothelial cells under hypoxic conditions was further studied. The aim of this study was to assess the therapeutic value of this peptide, RoY, in a mouse hind limb ischemia model and to identify it's receptor on endothelial cells. RoY, a 12 amino-acid synthetic peptide, induced in vitro angiogeneic activity under hypoxic conditions by increasing endothelial cell proliferation, migration and tube formation. In order to assess its therapeutic properties in ischemic tissues, a hind limb ischemia model was induced in C57BL mice by a femoral artery excision. A single local intramuscular injection of RoY peptide to the operated limb, significantly restored blood perfusion and alleviated hind limb ischemia as determined by a laser Doppler imager. Increased capillary density in histological sections corroborated these findings. Protein precipitation and mass spectroscopy studies identified GRP78, a heat shock protein, as the peptide-binding membrane receptor that was increased on endothelial cell membranes under hypoxic conditions. This study demonstrates the efficacy of RoY peptide in alleviation of hind limb ischemia. In addition, it provides evidence that GRP78 is an angiogenic receptor on hypoxic endothelial cells.

Factor Xa binding to annexin 2 mediates signal transduction via protease-activated receptor 1

The serine protease zymogen factor X is converted to its catalytically active form factor Xa by the binary complex of factor VIIa bound to its cell surface receptor tissue factor (TF) or by the intrinsic Xase complex, which consists of active factors VIII (VIIIa), IX (IXa), factor X, and Ca2+. Factor Xa has procoagulant activity by conversion of prothrombin to thrombin and also induces signal transduction, either alone or in the ternary TF:VIIa:factor Xa coagulation initiation complex. Factor Xa cleaves and activates protease activated receptor (PAR)1 or -2, but factor Xa signaling efficiency varies among cell types. We show here that annexin 2 acts as a receptor for factor Xa on the surface of human umbilical vein endothelial cells and that annexin 2 facilitates factor Xa activation of PAR-1 but does not enhance coagulant function of factor Xa. Overexpression of TF abolishes annexin 2 dependence on factor Xa signaling and diminishes binding to cell surface annexin 2, whereas selectively abolishing TF promotes the annexin 2/factor Xa interaction. We propose that annexin 2 serves to regulate factor Xa signaling specifically in the absence of cell surface TF and may thus play physiological or pathological roles when factor Xa is generated in a TF-depleted environment.

Engineering adeno-associated virus 2 vectors for targeted gene delivery to atherosclerotic lesions

Targeted delivery of biological agents to atherosclerotic plaques may provide a novel treatment and/or useful tool for imaging of atherosclerosis in vivo. However, there are no known viral vectors that possess the desired tropism. Two plaque-targeting peptides, CAPGPSKSC (CAP) and CNHRYMQMC (CNH) were inserted into the capsid of adeno-associated virus 2 (AAV2) to assess vector retargeting. AAV2-CNH produced significantly higher levels of transduction than unmodified AAV2 in human, murine and rat endothelial cells, whereas transduction of nontarget HeLa cells was unaltered. Transduction studies and surface plasmon resonance suggest that AAV2-CNH uses membrane type 1 matrix metalloproteinase as a surface receptor. AAV2-CAP only produced higher levels of transduction in rat endothelial cells, possibly because the virus was found to be affected by proteasomal degradation. In vivo substantially higher levels of both peptide-modified AAV2 vectors was detected in the brachiocephalic artery (site of advanced atherosclerotic plaques) and aorta, whereas reduced levels were detected in all other organs examined. These results suggest that in the AAV2 platform the peptides are exposed on the capsid surface in a way that enables efficient receptor binding and so creates effective atherosclerotic plaque targeted vectors.

Localization to atherosclerotic plaque and biodistribution of biochemically derivatized superparamagnetic iron oxide nanoparticles (SPIONs) contrast particles for magnetic resonance imaging (MRI)

Annexin V recognizes apoptotic cells by specific molecular interaction with phosphatidyl serine, a lipid that is normally sequestered in the inner leaflet of the cell membrane, but is translocated to the outer leaflet in apoptotic cells, such as foam cells of atherosclerotic plaque. Annexin V could potentially deliver carried materials (such as superparamagnetic contrast agents for magnetic resonance imaging) to sites containing apoptotic cells, such as high grade atherosclerotic lesions, so we administered biochemically-derivatized (annexin V) superparmagnetic iron oxide particles (SPIONs) parenterally to two related rabbit models of human atherosclerosis. We observe development of negative magnetic resonance imaging (MRI) contrast in atheromatous lesions and but not in healthy artery. Vascular targeting by annexin V SPIONs is atheroma-specific (i.e., does not occur in healthy control rabbits) and requires active annexin V decorating the SPION surface. Targeted SPIONs produce negative contrast at doses that are 2,000-fold lower than reported for non-specific atheroma uptake of untargeted superparamagnetic nanoparticles in plaque in the same animal model. Occlusive and mural plaques are differentiable. While most of the dose accumulates in liver, spleen, kidneys and bladder, annexin V SPIONs also partition rapidly and deeply into early apoptotic foamy macrophages in plaque. Contrast in plaque decays within 2 months, allowing MRI images to be replicated with a subsequent, identical dose of annexin V SPIONs. Thus, biologically targeted superparamagnetic contrast agents can contribute to non-invasive evaluation of cardiovascular lesions by simultaneously extracting morphological and biochemical data from them.

Targeted delivery of multifunctional magnetic nanoparticles

Magnetic nanoparticles and their magnetofluorescent analogues have become important tools for in vivo imaging using magnetic resonance imaging and fluorescent optical methods. A number of monodisperse magnetic nanoparticle preparations have been developed over the last decade for angiogenesis imaging, cancer staging, tracking of immune cells (monocyte/macrophage, T cells) and for molecular and cellular targeting. Phage display and data mining have enabled the procurement of novel tissue- or receptor-specific peptides, while high-throughput screening of diversity-oriented synthesis libraries has identified small molecules that permit or prevent uptake by specific cell types. Next-generation magnetic nanoparticles are expected to be truly multifunctional, incorporating therapeutic functionalities and further enhancing an already diverse repertoire of capabilities.

PepBank--a database of peptides based on sequence text mining and public peptide data sources

Background

Peptides are important molecules with diverse biological functions and biomedical uses. To date, there does not exist a single, searchable archive for peptide sequences or associated biological data. Rather, peptide sequences still have to be mined from abstracts and full-length articles, and/or obtained from the fragmented public sources.

Description

We have constructed a new database (PepBank), which at the time of writing contains a total of 19,792 individual peptide entries. The database has a web-based user interface with a simple, Google-like search function, advanced text search, and BLAST and Smith-Waterman search capabilities. The major source of peptide sequence data comes from text mining of MEDLINE abstracts. Another component of the database is the peptide sequence data from public sources (ASPD and UniProt). An additional, smaller part of the database is manually curated from sets of full text articles and text mining results. We show the utility of the database in different examples of affinity ligand discovery.

Conclusion

We have created and maintain a database of peptide sequences. The database has biological and medical applications, for example, to predict the binding partners of biologically interesting peptides, to develop peptide based therapeutic or diagnostic agents, or to predict molecular targets or binding specificities of peptides resulting from phage display selection. The database is freely available on , and the text mining source code (Peptide::Pubmed) is freely available above as well as on CPAN ().

Molecular changes in the vasculature of injured tissues

We have explored molecular specialization of the vasculature of regenerating wound tissue in the skin and tendons to identify a different repertoire of markers from that obtained by studying tumor vasculature. We screened a phage-displayed peptide library for peptides that home to wounds in mice and identified two peptides that selectively target phage to skin and tendon wounds: CARSKNKDC (CAR) and CRKDKC (CRK). CAR is homologous to heparin-binding sites in various proteins and binds to cell surface heparan sulfate and heparin. CRK is similar to a segment in thrombospondin type 1 repeat. Intravenously injected CAR and CRK phage, as well as fluorescein-labeled CAR and CRK peptides, selectively accumulated at wound sites, where they partially co-localized with blood vessels. The CAR peptide showed a preference for early stages of wound healing, whereas the CRK favored wounds at later stages of healing. The CAR peptide was internalized into the target cells and delivered the fluorescent label into the cell nuclei. These results identify new molecular markers in wound tissues and show that the expression of these markers in wound vasculature changes as healing progresses. The peptides recognizing these markers may be useful in delivering treatments into regenerating tissues.

Novel challenges in exploring peptide ligands and corresponding tissue-specific endothelial receptors

The structural and molecular diversity of vascular endothelium may depend on the functional state and tissue localisation of its cells. Tumour vasculature expresses a number of molecular markers that distinguish it from normal vasculature. In cancer, the determinant of specific tumour vasculature heterogeneity is, in part, dictated by dysregulated expression of tumour-derived angiogenic factors. The identification of molecular 'addresses' on the surface of tumour vasculature has significantly contributed to the selection of targets, which have been used for delivering therapeutic and imaging agents in cancer. Cytotoxic drug, pro-apoptotic peptides, protease inhibitors, and gene therapy vectors have been successfully linked to peptides and delivered to tumour sites with an improved experimental therapy. Different diagnostic and therapeutic compounds can be efficiently targeted to specific receptors on vascular endothelial cells; the development of ligand-directed vector tools may promote systemic targeted gene delivery. Here, we review the very recent advances in the identification of peptide ligands and their corresponding tissue-specific endothelial receptors through the phage display technology with emphasis on ligand-directed delivery of therapeutic agents and targeted gene therapy.

In vivo imaging of molecularly targeted phage

Rapid identification of in vivo affinity ligands would have far-reaching applications for imaging specific molecular targets, in vivo systems imaging, and medical use. We have developed a high-throughput method for identifying and optimizing ligands to map and image biologic targets of interest in vivo. We directly labeled viable phage clones with far-red fluorochromes and comparatively imaged them in vivo by multichannel fluorescence ratio imaging. Using Secreted Protein Acidic and Rich in Cysteine (osteonectin) and vascular cell adhesion molecule-1 as model targets, we show that: 1) fluorescently labeled phage retains target specificity on labeling; 2) in vivo distribution can be quantitated (detection thresholds of approximately 300 phage/mm(3) tissue) throughout the entire depth of the tumor using fluorescent tomographic imaging; and 3) fluorescently labeled phage itself can serve as a replenishable molecular imaging agent. The described method should find widespread application in the rapid in vivo discovery and validation of affinity ligands and, importantly, in the use of fluorochrome-labeled phage clones as in vivo imaging agents.

Identification of human scFvs targeting atherosclerotic lesions: selection by single round in vivo phage display

Our aim was to investigate by in vivo biopanning the lesions developed early in atherosclerosis and identify human antibodies that home to diseased regions. We have designed a two-step approach for a rapid isolation of human Monoclonal phage-display single-chain antibodies (MoPhabs) reactive with proteins found in lesions developed in an animal model of atherosclerosis. After a single round of in vivo biopanning, the MoPhabs were eluted from diseased sections of rabbit aorta identified by histology and NMR microscopy. MoPhabs expressed in situ were selected by subtractive colony filter screening for their capacity to recognize atherosclerotic but not normal aorta. MoPhabs selected by our method predominantly bind atherosclerotic lesions. Two of them, B3.3G and B3.GER, produced as scFv fragments, recognized an epitope present on the surface in early atherosclerotic lesions and within the intimal thickness in more complex plaques. These human MoPhabs homed to atherosclerotic lesions in ApoE(-/-) mice after in vivo injection. A protein of approximately 56 kDa recognized by B3.3G was affinity-purified and identified by mass spectrometry analysis as vitronectin. This is the first time that single round in vivo biopanning has been used to select human antibodies as candidates for diagnostic imaging and for obtaining insight into targets displayed in atherosclerotic plaques.

Vascular targeting: recent advances and therapeutic perspectives

The ability to deliver therapeutics site—specifically in vivo—remains a major challenge for the treatment of malignant, inflammatory, cardiovascular, and degenerative diseases. The need to target agents safely, efficiently, and selectively has become increasingly evident because of progress in vascular targeting. The vascular endothelium is a central target for intervention, given its multiple roles in the physiology (in health) and pathophysiology (in disease) and its direct accessibility to circulating ligands. In cancer, the expression of specific molecules on the surface of vascular endothelial and perivascular cells might enable direct therapeutic targeting. The use of in vivo phage display has significantly contributed to the identification of such targets, which have been successfully used for directed vascular targeting in preclinical animal models. Several animal studies have been performed by using fused molecules between tumor endothelium-directed molecules and immunomodulatory, procoagulant, or cytotoxic molecules. In addition to delivery of therapeutic agents, vascular targeted gene therapies based on both ligand-directed delivery of gene vectors to tumor endothelium and transcriptional targeting have also emerged. In this review, we discuss ligand-directed vascular targeting strategies with an emphasis on recent developments related to phage-display-based screenings.

Noninvasive vascular cell adhesion molecule-1 imaging identifies inflammatory activation of cells in atherosclerosis

BACKGROUND

Noninvasive imaging of adhesion molecules such as vascular cell adhesion molecule-1 (VCAM-1) may identify early stages of inflammation in atherosclerosis. We hypothesized that a novel, second-generation VCAM-1-targeted agent with enhanced affinity had sufficient sensitivity to enable real-time detection of VCAM-1 expression in experimental atherosclerosis in vivo, to quantify pharmacotherapy-induced reductions in VCAM-1 expression, and to identify activated cells in human plaques.

METHODS AND RESULTS

In vivo phage display in apolipoprotein E-deficient mice identified a linear peptide affinity ligand, VHPKQHR, homologous to very late antigen-4, a known ligand for VCAM-1. This peptide was developed into a multivalent agent detectable by MRI and optical imaging (denoted VINP-28 for VCAM-1 internalizing nanoparticle 28, with 20 times higher affinity than previously reported for VNP). In vitro, VINP-28 targeted all cell types expressing VCAM-1. In vivo, MRI and optical imaging in apolipoprotein E-deficient mice (n=28) after injection with VINP-28 or saline revealed signal enhancement in the aortic root of mice receiving VINP-28 (P<0.05). VINP-28 colocalized with endothelial cells and other VCAM-1-expressing cells, eg, macrophages, and was spatially distinct compared with untargeted control nanoparticles. Atheromata of atorvastatin-treated mice showed reduced VINP-28 deposition and VCAM-1 expression. VINP-28 enhanced early lesions in juvenile mice and resected human carotid artery plaques.

CONCLUSIONS

VINP-28 allows noninvasive imaging of VCAM-1-expressing endothelial cells and macrophages in atherosclerosis and spatial monitoring of anti-VCAM-1 pharmacotherapy in vivo and identifies inflammatory cells in human atheromata. This clinically translatable agent could noninvasively detect inflammation in early, subclinical atherosclerosis.

In vivo phage display selection yields atherosclerotic plaque targeted peptides for imaging

PURPOSE

Atherosclerosis is a leading cause of morbidity and mortality in the Western world, yet specific imaging agents to detect and map inflammatory plaques are still lacking.

PROCEDURES

We used in vivo phage display to interrogate early atherosclerotic lesions present in ApoE-/- mice with the goal of identifying plaque-associated endothelial cell internalized affinity ligands.

RESULTS

We identified 30 phage families with some of these families exhibiting homology to known atherosclerotic proteins, namely, leukemia inhibitory factor, transferrin, and VLA-4. VLA-4 homologous peptides [termed vascular cellular adhesion molecule-1 (VCAM-1) internalizing peptide-28 (VINP28)] bound to and were internalized by VCAM-1-expressing cells and were inhibited by soluble VCAM-1. In addition, a VINP28 modified multimodal nanoparticle showed high affinity for endothelial cells expressing VCAM-1 but low affinity for macrophages or smooth muscle cells.

CONCLUSION

The identified peptides represent a set of probes to interrogate the cell surface repertoire and potentially allow early detection of atherosclerosis.

Biomedical aspects of targeted delivery of drugs to pulmonary endothelium

Drug targeting to selected subcellular compartments of the pulmonary endothelium may optimise treatment of many diseases. This paper describes endothelial determinants that are potentially useful for such targeting, including endothelial ectopeptidases, cell adhesion molecules and novel candidates identified by high-throughput methods, as well as the means to achieve optimal subcellular targeting of drugs in the endothelium that have been explored in cell culture and animal studies. Criteria for determining the applicability for targeting include accessibility, specificity, safety and subcellular precision. The effects of endothelial delivery of therapeutic agents, including the effects mediated by the intervention in the function of the target determinants, must be characterised in the context of given pathological conditions.

Molecular profiling of heart endothelial cells

BACKGROUND

Endothelial cells that line the vascular lumen can express cell-surface proteins that are specific to the endothelium of a particular tissue. In this study, we probed the heart vasculature for heart-specific endothelial markers by phage display.

METHODS AND RESULTS

We used a novel combination of in vivo phage selection and a bacterial 2-hybridization scheme against a heart cDNA library, which allows simultaneous identification of peptides that specifically bind to the target endothelium, as well as the endothelial molecules (receptors) recognized by the peptides. We found 5 heart-targeting peptides and their receptors. We confirmed and quantified the selective expression of 4 of the proteins in heart endothelial cells by independent methods. The heart specificity of phages was as high as 300-fold greater than that of nonrecombinant control phages. The proteins selectively expressed by the heart endothelium were in most cases also expressed by cardiomyocytes and, at lower levels, in some other tissues.

CONCLUSIONS

These findings provide new markers for the endothelium of heart vessels and reveal a commonality between parenchymal and endothelial gene expression in the heart. The heart-homing peptides provide a means of targeting diagnostic and therapeutic agents to the heart, and their receptors are potential drug discovery targets.