Vascular immunotargeting to endothelial determinant ICAM-1 enables optimal partnering of recombinant scFv-thrombomodulin fusion with endogenous cofactor

Development of endothelial-targeted CD39 as a therapy for ischemic stroke

BACKGROUND

Ischemic stroke is characterized by a necrotic lesion in the brain surrounded by an area of dying cells termed the penumbra. Salvaging the penumbra either with thrombolysis or mechanical retrieval is the cornerstone of stroke management. At-risk neuronal cells release extracellular adenosine triphosphate, triggering microglial activation and causing a thromboinflammatory response, culminating in endothelial activation and vascular disruption. This is further aggravated by ischemia-reperfusion injury that follows all reperfusion therapies. The ecto-enzyme CD39 regulates extracellular adenosine triphosphate by hydrolyzing it to adenosine, which has antithrombotic and anti-inflammatory properties and reverses ischemia-reperfusion injury.

OBJECTIVES

The objective off the study was to determine the efficacy of our therapeutic, anti-VCAM-CD39 in ischaemic stroke.

METHODS

We developed anti-VCAM-CD39 that targets the antithrombotic and anti-inflammatory properties of recombinant CD39 to the activated endothelium of the penumbra by binding to vascular cell adhesion molecule (VCAM)-1. Mice were subjected to 30 minutes of middle cerebral artery occlusion and analyzed at 24 hours. Anti-VCAM-CD39 or control agents (saline, nontargeted CD39, or anti-VCAM-inactive CD39) were given at 3 hours after middle cerebral artery occlusion.

RESULTS

Anti-VCAM-CD39 treatment reduced neurologic deficit; magnetic resonance imaging confirmed significantly smaller infarcts together with an increase in cerebrovascular perfusion. Anti-VCAM-CD39 also restored blood-brain barrier integrity and reduced microglial activation. Coadministration of anti-VCAM-CD39 with thrombolytics (tissue plasminogen activator [tPA]) further reduced infarct volumes and attenuated blood-brain barrier permeability with no associated increase in intracranial hemorrhage.

CONCLUSION

Anti-VCAM-CD39, uniquely targeted to endothelial cells, could be a new stroke therapy even when administered 3 hours postischemia and may further synergize with thrombolytic therapy to improve stroke outcomes.

Bispecific antibody shuttles targeting CD98hc mediate efficient and long-lived brain delivery of IgGs

The inability of antibodies to penetrate the blood-brain barrier (BBB) is a key limitation to their use in diverse applications. One promising strategy is to deliver IgGs using a bispecific BBB shuttle, which involves fusing an IgG to a second affinity ligand that engages a cerebrovascular endothelial target and facilitates transport across the BBB. Nearly all prior efforts have focused on shuttles that target transferrin receptor (TfR-1) despite inherent delivery and safety challenges. Here, we report bispecific antibody shuttles that engage CD98hc, the heavy chain of the large neutral amino acid transporter (LAT1), and efficiently transport IgGs into the brain. Notably, CD98hc shuttles lead to much longer-lived brain retention of IgGs than TfR-1 shuttles while enabling more specific targeting due to limited CD98hc engagement in the brain parenchyma, which we demonstrate for IgGs that either agonize a neuronal receptor (TrkB) or target other endogenous cell-surface proteins on neurons and astrocytes.

Fluorinated amphiphilic Poly(β-Amino ester) nanoparticle for highly efficient and specific delivery of nucleic acids to the Lung capillary endothelium

Endothelial cell dysfunction occurs in a variety of acute and chronic pulmonary diseases including pulmonary hypertension, viral and bacterial pneumonia, bronchopulmonary dysplasia, and congenital lung diseases such as alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV). To correct endothelial dysfunction, there is a critical need for the development of nanoparticle systems that can deliver drugs and nucleic acids to endothelial cells with high efficiency and precision. While several nanoparticle delivery systems targeting endothelial cells have been recently developed, none of them are specific to lung endothelial cells without targeting other organs in the body. In the present study, we successfully solved this problem by developing non-toxic poly(β-amino) ester (PBAE) nanoparticles with specific structure design and fluorinated modification for high efficiency and specific delivery of nucleic acids to the pulmonary endothelial cells. After intravenous administration, the PBAE nanoparticles were capable of delivering non-integrating DNA plasmids to lung microvascular endothelial cells but not to other lung cell types. IVIS whole body imaging and flow cytometry demonstrated that DNA plasmid were functional in the lung endothelial cells but not in endothelial cells of other organs. Fluorination of PBAE was required for lung endothelial cell-specific targeting. Hematologic analysis and liver and kidney metabolic panels demonstrated the lack of toxicity in experimental mice. Thus, fluorinated PBAE nanoparticles can be an ideal vehicle for gene therapy targeting lung microvascular endothelium in pulmonary vascular disorders.

Precise nanodrug delivery systems with cell-specific targeting for ALI/ARDS treatment

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are common acute and critical diseases in clinics and have no effective treatment to date. With the concept of "precision medicine", research into the precise drug delivery of therapeutic and diagnostic drugs has become a frontier in nanomedicine research and has entered the era of design of precise nanodrug delivery systems (NDDSs) with cell-specific targeting. Owing to the distinctive characteristics of ALI/ARDS, designing NDDSs for specific focal sites is an important strategy for changing drug distribution in the body and specifically increasing drug concentration at target sites while decreasing drug concentration at non-target sites. This strategy enhances drug efficacy, reduces adverse reactions, and ensures accurate nano-targeted treatment. On the basis of the characteristics of pathological ALI/ARDS microenvironments, this paper reviews NDDSs targeting vascular endothelial cells, neutrophils, alveolar macrophages, and alveolar epithelial cells to provide reference for designing accurate NDDSs for ALI/ARDS and novel insights into targeted treatments for ALI/ARDS.

Bispecific antibody shuttles targeting CD98hc mediate efficient and long-lived brain delivery of IgGs

The inability of antibodies and other biologics to penetrate the blood-brain barrier (BBB) is a key limitation to their use in diagnostic, imaging, and therapeutic applications. One promising strategy is to deliver IgGs using a bispecific BBB shuttle, which involves fusing an IgG with a second affinity ligand that engages a cerebrovascular endothelial target and facilitates transport across the BBB. Nearly all prior efforts have focused on the transferrin receptor (TfR-1) as the prototypical endothelial target despite inherent delivery and safety challenges. Here we report bispecific antibody shuttles that engage CD98hc (also known as 4F2 and SLC3A2), the heavy chain of the large neutral amino acid transporter (LAT1), and efficiently transport IgGs into the brain parenchyma. Notably, CD98hc shuttles lead to much longer-lived brain retention of IgGs than TfR-1 shuttles while enabling more specific brain targeting due to limited CD98hc engagement in the brain parenchyma. We demonstrate the broad utility of the CD98hc shuttles by reformatting three existing IgGs as CD98hc bispecific shuttles and delivering them to the mouse brain parenchyma that either agonize a neuronal receptor (TrkB) or target other endogenous antigens on specific types of brain cells (neurons and astrocytes).

Lipid Nanoparticles for Nucleic Acid Delivery to Endothelial Cells

Endothelial cells play critical roles in circulatory homeostasis and are also the gateway to the major organs of the body. Dysfunction, injury, and gene expression profiles of these cells can cause, or are caused by, prevalent chronic diseases such as diabetes, cardiovascular disease, and cancer. Modulation of gene expression within endothelial cells could therefore be therapeutically strategic in treating longstanding disease challenges. Lipid nanoparticles (LNP) have emerged as potent, scalable, and tunable carrier systems for delivering nucleic acids, making them attractive vehicles for gene delivery to endothelial cells. Here, we discuss the functions of endothelial cells and highlight some receptors that are upregulated during health and disease. Examples and applications of DNA, mRNA, circRNA, saRNA, siRNA, shRNA, miRNA, and ASO delivery to endothelial cells and their targets are reviewed, as well as LNP composition and morphology, formulation strategies, target proteins, and biomechanical factors that modulate endothelial cell targeting. Finally, we discuss FDA-approved LNPs as well as LNPs that have been tested in clinical trials and their challenges, and provide some perspectives as to how to surmount those challenges.

Reactive Oxygen Species Scavenging Nanomedicine for the Treatment of Ischemic Heart Disease

Ischemic heart disease (IHD) is the leading cause of disability and mortality worldwide. Reactive oxygen species (ROS) have been shown to play key roles in the progression of diabetes, hypertension, and hypercholesterolemia, which are independent risk factors that lead to atherosclerosis and the development of IHD. Engineered biomaterial-based nanomedicines are under extensive investigation and exploration, serving as smart and multifunctional nanocarriers for synergistic therapeutic effect. Capitalizing on cell/molecule-targeting drug delivery, nanomedicines present enhanced specificity and safety with favorable pharmacokinetics and pharmacodynamics. Herein, the roles of ROS in both IHD and its risk factors are discussed, highlighting cardiovascular medications that have antioxidant properties, and summarizing the advantages, properties, and recent achievements of nanomedicines that have ROS scavenging capacity for the treatment of diabetes, hypertension, hypercholesterolemia, atherosclerosis, ischemia/reperfusion, and myocardial infarction. Finally, the current challenges of nanomedicines for ROS-scavenging treatment of IHD and possible future directions are discussed from a clinical perspective.

Targeting pulmonary vascular endothelial cells for the treatment of respiratory diseases

Pulmonary vascular endothelial cells (VECs) are the main damaged cells in the pathogenesis of various respiratory diseases and they mediate the development and regulation of the diseases. Effective intervention targeting pulmonary VECs is of great significance for the treatment of respiratory diseases. A variety of cell markers are expressed on the surface of VECs, some of which can be specifically combined with the drugs or carriers modified by corresponding ligands such as ICAM-1, PECAM-1, and P-selectin, to achieve effective delivery of drugs in lung tissues. In addition, the great endothelial surface area of the pulmonary vessels, the “first pass effect” of venous blood in lung tissues, and the high volume and relatively slow blood perfusion rate of pulmonary capillaries further promote the drug distribution in lung tissues. This review summarizes the representative markers at the onset of respiratory diseases, drug delivery systems designed to target these markers and their therapeutic effects.

A library of Rhodamine6G-based pH-sensitive fluorescent probes with versatile in vivo and in vitro applications

Acidic pH is critical to the function of the gastrointestinal system, bone-resorbing osteoclasts, and the endolysosomal compartment of nearly every cell in the body. Non-invasive, real-time fluorescence imaging of acidic microenvironments represents a powerful tool for understanding normal cellular biology, defining mechanisms of disease, and monitoring for therapeutic response. While commercially available pH-sensitive fluorescent probes exist, several limitations hinder their widespread use and potential for biologic application. To address this need, we developed a novel library of pH-sensitive probes based on the highly photostable and water-soluble fluorescent molecule, Rhodamine 6G. We demonstrate versatility in terms of both pH sensitivity (i.e., pK a) and chemical functionality, allowing conjugation to small molecules, proteins, nanoparticles, and regenerative biomaterial scaffold matrices. Furthermore, we show preserved pH-sensitive fluorescence following a variety of forms of covalent functionalization and demonstrate three potential applications, both in vitro and in vivo, for intracellular and extracellular pH sensing. Finally, we develop a computation approach for predicting the pH sensitivity of R6G derivatives, which could be used to expand our library and generate probes with novel properties.

Targeting vascular inflammation through emerging methods and drug carriers

Acute inflammation is a common dangerous component of pathogenesis of many prevalent conditions with high morbidity and mortality including sepsis, thrombosis, acute respiratory distress syndrome (ARDS), COVID-19, myocardial and cerebral ischemia-reperfusion, infection, and trauma. Inflammatory changes of the vasculature and blood mediate the course and outcome of the pathology in the tissue site of insult, remote organs and systemically. Endothelial cells lining the luminal surface of the vasculature play the key regulatory functions in the body, distinct under normal vs. pathological conditions. In theory, pharmacological interventions in the endothelial cells might enable therapeutic correction of the overzealous damaging pro-inflammatory and pro-thrombotic changes in the vasculature. However, current agents and drug delivery systems (DDS) have inadequate pharmacokinetics and lack the spatiotemporal precision of vascular delivery in the context of acute inflammation. To attain this level of precision, many groups design DDS targeted to specific endothelial surface determinants. These DDS are able to provide specificity for desired tissues, organs, cells, and sub-cellular compartments needed for a particular intervention. We provide a brief overview of endothelial determinants, design of DDS targeted to these molecules, their performance in experimental models with focus on animal studies and appraisal of emerging new approaches. Particular attention is paid to challenges and perspectives of targeted therapeutics and nanomedicine for advanced management of acute inflammation.

Expanding the arsenal against pulmonary diseases using surface-functionalized polymeric micelles: breakthroughs and bottlenecks

Pulmonary diseases such as lung cancer, asthma and tuberculosis have remained one of the common challenges globally. Polymeric micelles (PMs) have emerged as an effective technique for achieving targeted drug delivery for a local as well as a systemic effect. These PMs encapsulate and protect hydrophobic drugs, increase pulmonary targeting, decrease side effects and enhance drug efficacy through the inhalation route. In the current review, emphasis has been placed on the different barriers encountered by the drugs given via the pulmonary route and the mechanism of PMs in achieving drug targeting. The applications of PMs in different pulmonary diseases have also been discussed in detail.

Red blood cells: The metamorphosis of a neglected carrier into the natural mothership for artificial nanocarriers

Drug delivery research pursues many types of carriers including proteins and other macromolecules, natural and synthetic polymeric structures, nanocarriers of diverse compositions and cells. In particular, liposomes and lipid nanoparticles represent arguably the most advanced and popular human-made nanocarriers, already in multiple clinical applications. On the other hand, red blood cells (RBCs) represent attractive natural carriers for the vascular route, featuring at least two distinct compartments for loading pharmacological cargoes, namely inner space enclosed by the plasma membrane and the outer surface of this membrane. Historically, studies of liposomal drug delivery systems (DDS) astronomically outnumbered and surpassed the RBC-based DDS. Nevertheless, these two types of carriers have different profile of advantages and disadvantages. Recent studies showed that RBC-based drug carriers indeed may feature unique pharmacokinetic and biodistribution characteristics favorably changing benefit/risk ratio of some cargo agents. Furthermore, RBC carriage cardinally alters behavior and effect of nanocarriers in the bloodstream, so called RBC hitchhiking (RBC-HH). This article represents an attempt for the comparative analysis of liposomal vs RBC drug delivery, culminating with design of hybrid DDSs enabling mutual collaborative advantages such as RBC-HH and camouflaging nanoparticles by RBC membrane. Finally, we discuss the key current challenges faced by these and other RBC-based DDSs including the issue of potential unintended and adverse effect and contingency measures to ameliorate this and other concerns.

A hybridoma-derived monoclonal antibody with high homology to the aberrant myeloma light chain

The identification of antibody variable regions in the heavy (V_H) and light (V_L) chains from hybridomas is necessary for the production of recombinant, sequence-defined monoclonal antibodies (mAbs) and antibody derivatives. This process has received renewed attention in light of recent reports of hybridomas having unintended specificities due to the production of non-antigen specific heavy and/or light chains for the intended antigen. Here we report a surprising finding and potential pitfall in variable domain sequencing of an anti-human CD63 hybridoma. We amplified multiple V_L genes from the hybridoma cDNA, including the well-known aberrant Sp2/0 myeloma V_K and a unique, full-length V_L. After finding that the unique V_L failed to yield a functional antibody, we discovered an additional full-length sequence with surprising similarity (~95% sequence identify) to the non-translated myeloma kappa chain but with a correction of its key frameshift mutation. Expression of the recombinant mAb confirmed that this highly homologous sequence is the antigen-specific light chain. Our results highlight the complexity of PCR-based cloning of antibody genes and strategies useful for identification of correct sequences.

Nanomedicine for acute respiratory distress syndrome: The latest application, targeting strategy, and rational design

Acute respiratory distress syndrome (ARDS) is characterized by the severe inflammation and destruction of the lung air-blood barrier, leading to irreversible and substantial respiratory function damage. Patients with coronavirus disease 2019 (COVID-19) have been encountered with a high risk of ARDS, underscoring the urgency for exploiting effective therapy. However, proper medications for ARDS are still lacking due to poor pharmacokinetics, non-specific side effects, inability to surmount pulmonary barrier, and inadequate management of heterogeneity. The increased lung permeability in the pathological environment of ARDS may contribute to nanoparticle-mediated passive targeting delivery. Nanomedicine has demonstrated unique advantages in solving the dilemma of ARDS drug therapy, which can address the shortcomings and limitations of traditional anti-inflammatory or antioxidant drug treatment. Through passive, active, or physicochemical targeting, nanocarriers can interact with lung epithelium/endothelium and inflammatory cells to reverse abnormal changes and restore homeostasis of the pulmonary environment, thereby showing good therapeutic activity and reduced toxicity. This article reviews the latest applications of nanomedicine in pre-clinical ARDS therapy, highlights the strategies for targeted treatment of lung inflammation, presents the innovative drug delivery systems, and provides inspiration for strengthening the therapeutic effect of nanomedicine-based treatment.

Red Blood Cell Hitchhiking: A Novel Approach for Vascular Delivery of Nanocarriers

Red blood cell (RBC) hitchhiking is a method of drug delivery that can increase drug concentration in target organs by orders of magnitude. In RBC hitchhiking, drug-loaded nanoparticles (NPs) are adsorbed onto red blood cells and then injected intravascularly, which causes the NPs to transfer to cells of the capillaries in the downstream organ. RBC hitchhiking has been demonstrated in multiple species and multiple organs. For example, RBC-hitchhiking NPs localized at unprecedented levels in the brain when using intra-arterial catheters, such as those in place immediately after mechanical thrombectomy for acute ischemic stroke. RBC hitchhiking has been successfully employed in numerous preclinical models of disease, ranging from pulmonary embolism to cancer metastasis. In addition to summarizing the versatility of RBC hitchhiking, we also describe studies into the surprisingly complex mechanisms of RBC hitchhiking as well as outline future studies to further improve RBC hitchhiking's clinical utility.

Mechanisms of thrombosis and research progress on targeted antithrombotic drugs

Globally, the incidence of thromboembolic diseases has increased in recent years, accompanied by an increase in patient mortality. Currently, several targeting delivery strategies have been developed to treat thromboembolic diseases. In this review, we discuss the mechanisms of thrombolysis and current anticoagulant drugs, particularly those with targeting capability, highlighting advances in the accurate treatment of thrombolysis with fewer adverse effects. Such approaches include magnetic drug-loading systems combined with molecular imaging to recanalize blood vessels and systems based on chimeric Arg-Gly-Asp (RGD) sequences that can target platelet glycoprotein receptor. With such progress in targeted antithrombotic drugs, targeted thrombolysis treatment shows significant potential benefit for patients.

Bivalent engagement of endothelial surface antigens is critical to prolonged surface targeting and protein delivery in vivo

Targeted drug delivery to the endothelium has the potential to generate localized therapeutic effects at the blood-tissue interface. For some therapeutic cargoes, it is essential to maintain contact with the bloodstream to exert protective effects. The pharmacokinetics (PK) of endothelial surface-targeted affinity ligands and biotherapeutic cargo remain a largely unexplored area, despite obvious translational implications for this strategy. To bridge this gap, we site-specifically radiolabeled mono- (scFv) and bivalent (mAb) affinity ligands specific for the endothelial cell adhesion molecules, PECAM-1 (CD31) and ICAM-1 (CD54). Radiotracing revealed similar lung biodistribution at 30 minutes post-injection (79.3% ± 4.2% vs 80.4% ± 10.6% ID/g for αICAM and 58.9% ± 3.6% ID/g vs. 47.7% ± 5.8% ID/g for αPECAM mAb vs. scFv), but marked differences in organ residence time, with antibodies demonstrating an order of magnitude greater area under the lung concentration vs. time curve (AUC_inf 1698 ± 352 vs. 53.3 ± 7.9 ID/g*hrs for αICAM and 1023 ± 507 vs. 114 ± 37 ID/g*hrs for αPECAM mAb vs scFv). A physiologically based pharmacokinetic model, fit to and validated using these data, indicated contributions from both superior binding characteristics and prolonged circulation time supporting multiple binding-detachment cycles. We tested the ability of each affinity ligand to deliver a prototypical surface cargo, thrombomodulin (TM), using one-to-one protein conjugates. Bivalent mAb-TM was superior to monovalent scFv-TM in both pulmonary targeting and lung residence time (AUC_inf 141 ± 3.2 vs 12.4 ± 4.2 ID/g*hrs for ICAM and 188 ± 90 vs 34.7 ± 19.9 ID/g*hrs for PECAM), despite having similar blood PK, indicating that binding strength is more important parameter than the kinetics of binding. To maximize bivalent target engagement, we synthesized an oriented, end-to-end anti-ICAM mAb-TM conjugate and found that this therapeutic had the best lung residence time (AUC_inf 253 ± 18 ID/g*hrs) of all TM modalities. These observations have implications not only for the delivery of TM, but also potentially all therapeutics targeted to the endothelial surface.

Targeting drug delivery in the vascular system: Focus on endothelium

The bloodstream is the main transporting pathway for drug delivery systems (DDS) from the site of administration to the intended site of action. In many cases, components of the vascular system represent therapeutic targets. Endothelial cells, which line the luminal surface of the vasculature, play a tripartite role of the key target, barrier, or victim of nanomedicines in the bloodstream. Circulating DDS may accumulate in the vascular areas of interest and in off-target areas via mechanisms bypassing specific molecular recognition, but using ligands of specific vascular determinant molecules enables a degree of precision, efficacy, and specificity of delivery unattainable by non-affinity DDS. Three decades of research efforts have focused on specific vascular targeting, which have yielded a multitude of DDS, many of which are currently undergoing a translational phase of development for biomedical applications, including interventions in the cardiovascular, pulmonary, and central nervous systems, regulation of endothelial functions, host defense, and permeation of vascular barriers. We discuss the design of endothelial-targeted nanocarriers, factors underlying their interactions with cells and tissues, and describe examples of their investigational use in models of acute vascular inflammation with an eye on translational challenges.

Selective targeting of nanomedicine to inflamed cerebral vasculature to enhance the blood-brain barrier

Drug targeting to inflammatory brain pathologies such as stroke and traumatic brain injury remains an elusive goal. Using a mouse model of acute brain inflammation induced by local tumor necrosis factor alpha (TNFα), we found that uptake of intravenously injected antibody to vascular cell adhesion molecule 1 (anti-VCAM) in the inflamed brain is >10-fold greater than antibodies to transferrin receptor-1 and intercellular adhesion molecule 1 (TfR-1 and ICAM-1). Furthermore, uptake of anti-VCAM/liposomes exceeded that of anti-TfR and anti-ICAM counterparts by ∼27- and ∼8-fold, respectively, achieving brain/blood ratio >300-fold higher than that of immunoglobulin G/liposomes. Single-photon emission computed tomography imaging affirmed specific anti-VCAM/liposome targeting to inflamed brain in mice. Intravital microscopy via cranial window and flow cytometry showed that in the inflamed brain anti-VCAM/liposomes bind to endothelium, not to leukocytes. Anti-VCAM/LNP selectively accumulated in the inflamed brain, providing de novo expression of proteins encoded by cargo messenger RNA (mRNA). Anti-VCAM/LNP-mRNA mediated expression of thrombomodulin (a natural endothelial inhibitor of thrombosis, inflammation, and vascular leakage) and alleviated TNFα-induced brain edema. Thus VCAM-directed nanocarriers provide a platform for cerebrovascular targeting to inflamed brain, with the goal of normalizing the integrity of the blood-brain barrier, thus benefiting numerous brain pathologies.

Defective fibrin deposition and thrombus stability in Bambi-/- mice are mediated by elevated anticoagulant function

BACKGROUND

Bone morphogenetic and activin membrane-bound inhibitor (BAMBI) is a transmembrane protein related to the type I transforming growth factor- β (TGF-β) receptor family that is present on both platelets and endothelial cells (ECs). Bambi-deficient mice exhibit reduced hemostatic function and thrombus stability characterized by an increased embolization.

OBJECTIVE

We aimed to delineate how BAMBI influences endothelial function and thrombus stability.

METHODS

Bambi-deficient mice were subjected to the laser-induced thrombosis model where platelet and fibrin accumulation was evaluated. Expression of thrombomodulin and tissue factor pathway inhibitor (TFPI) was also assessed in these mice.

RESULTS

Thrombus instability in Bambi-/- mice was associated with a profound defect in fibrin deposition. Injection of hirudin into Bambi+/+ mice prior to thrombus formation recapitulated the Bambi-/- thrombus instability phenotype. In contrast, hirudin had no additional effect upon thrombus formation in Bambi-/- mice. Deletion of Bambi in ECs resulted in mice with defective thrombus stability caused by decreased fibrin accumulation. Increased levels of the anticoagulant proteins TFPI and thrombomodulin were detected in Bambi-/- mouse lung homogenates. Endothelial cells isolated from Bambi-/- mouse lungs exhibited enhanced ability to activate protein C due to elevated thrombomodulin levels. Blocking thrombomodulin and TFPI in vivo fully restored fibrin accumulation and thrombus stability in Bambi-/- mice.

CONCLUSIONS

We demonstrate that endothelial BAMBI influences fibrin generation and thrombus stability by modulating thrombomodulin and TFPI anticoagulant function of the endothelium; we also highlight the importance of these anticoagulant proteins in the laser-induced thrombosis model.

Cross-linker-Modulated Nanogel Flexibility Correlates with Tunable Targeting to a Sterically Impeded Endothelial Marker

Deformability of injectable nanocarriers impacts rheological behavior, drug loading, and affinity target adhesion. Here, we present atomic force microscopy (AFM) and spectroscopy measurements of nanocarrier Young's moduli, tune the moduli of deformable nanocarriers with cross-linkers, and demonstrate vascular targeting behavior that correlates with Young's modulus. Homobifunctional cross-linkers were introduced into lysozyme-dextran nanogels (NGs). Single particle-scale AFM measurements determined NG moduli varying from ∼50-150 kPa for unmodified NGs or NGs with a short hydrophilic cross-linker (2,2'-(ethylenedioxy)bis(ethylamine), EOD) to ∼350 kPa for NGs modified with a longer hydrophilic cross-linker (4,9-dioxa-1,12-dodecanediamine, DODD) to ∼10 MPa for NGs modified with a longer hydrophobic cross-linker (1,12-diaminododecane, DAD). Cross-linked NGs were conjugated to antibodies for plasmalemma vesicle associated protein (PLVAP), a caveolar endothelial marker that cannot be accessed by rigid particles larger than ∼100 nm. In previous work, 150 nm NGs effectively targeted PLVAP, where rigid particles of similar diameter did not. EOD-modified NGs targeted PLVAP less effectively than unmodified NGs, but more effectively than DODD or DAD modified NGs, which both yielded low levels of targeting, resembling results previously obtained with polystyrene particles. Cross-linked NGs were also conjugated to antibodies against intracellular adhesion molecule-1 (ICAM-1), an endothelial marker accessible to large rigid particles. Cross-linked NGs and unmodified NGs targeted uniformly to ICAM-1. We thus demonstrate cross-linker modification of NGs, AFM determination of NG mechanical properties varying with cross-linker, and tuning of specific sterically constrained vascular targeting behavior in correlation with cross-linker-modified NG mechanical properties.

Endothelial Targeted Strategies to Combat Oxidative Stress: Improving Outcomes in Traumatic Brain Injury

The endothelium is a thin monolayer of specialized cells that lines the luminal wall of blood vessels and constitutes the critical innermost portion of the physical barrier between the blood and the brain termed the blood-brain barrier (BBB). Aberrant changes in the endothelium occur in many neuropathological states, including those with high morbidity and mortality that lack targeted therapeutic interventions, such as traumatic brain injury (TBI). Utilizing ligands of surface determinants expressed on brain endothelium to target and combat injury mechanisms at damaged endothelium offers a new approach to the study of TBI and new avenues for clinical advancement. Many factors influence the targets that are expressed on endothelium. Therefore, the optimization of binding sites and ideal design features of nanocarriers are controllable factors that permit the engineering of nanotherapeutic agents with applicability that is specific to a known disease state. Following TBI, damaged endothelial cells upregulate cell adhesion molecules, including ICAM-1, and are key sites of reactive oxygen species (ROS) generation, including hydrogen peroxide. Reactive oxygen species along with pro-inflammatory mediators are known to contribute to endothelial damage and loss of BBB integrity. The use of targeted endothelial nanomedicine, with conjugates of the antioxidant enzyme catalase linked to anti-ICAM-1 antibodies, has recently been demonstrated to minimize oxidative stress at the BBB and reduce neuropathological outcomes following TBI. Here, we discuss targeted endothelial nanomedicine and its potential to provide benefits in TBI outcomes and future directions of this approach.

Targeting therapeutics to endothelium: are we there yet?

Vascular endothelial cells represent an important therapeutic target in many pathologies, including inflammation, oxidative stress, and thrombosis; however, delivery of drugs to this site is often limited by the lack of specific affinity of therapeutics for these cells. Selective delivery of both small molecule drugs and therapeutic proteins to the endothelium has been achieved through the use of targeting ligands, such as monoclonal antibodies, directed against endothelial cell surface markers, particularly cell adhesion molecules (CAMs). Careful selection of target molecules and targeting agents allows for precise delivery to sites of inflammation, thereby maximizing therapeutic drug concentrations at the site of injury. A good understanding of the physiological and pathological determinants of drug and drug carrier pharmacokinetics and biodistribution may allow for a priori identification of optimal properties of drug carrier and targeting agent. Targeted delivery of therapeutics such as antioxidants and antithrombotic agents to the injured endothelium has shown efficacy in preclinical models, suggesting the potential for translation into clinical practice. As with all therapeutics, demonstration of both efficacy and safety are required for successful clinical implementation, which must be considered not only for the individual components (drug, targeting agent, etc.) but also for the sum of the parts (e.g., the drug delivery system), as unexpected toxicities may arise with complex delivery systems. While the use of endothelial targeting has not been translated into the clinic to date, the preclinical results summarized here suggest that there is hope for successful implementation of these agents in the years to come.

Vascular Targeting of Radiolabeled Liposomes with Bio-Orthogonally Conjugated Ligands: Single Chain Fragments Provide Higher Specificity than Antibodies

Liposomes are a proven, versatile, and clinically viable technology platform for vascular delivery of drugs and imaging probes. Although targeted liposomes have the potential to advance these applications, complex formulations and the need for optimal affinity ligands and conjugation strategies challenge their translation. Herein, we employed copper-free click chemistry functionalized liposomes to target platelet-endothelial cell adhesion molecule (PECAM-1) and intracellular adhesion molecule (ICAM-1) by conjugating clickable monoclonal antibodies (Ab) or their single chain variable fragments (scFv). For direct, quantitative tracing, liposomes were surface chelated with ¹¹¹In to a >90% radiochemical yield and purity. Particle size and distribution, stability, ligand surface density, and specific binding to target cells were characterized in vitro. Biodistribution of liposomes after IV injection was characterized in mice using isotope detection in organs and by noninvasive imaging (single-photon emission computed tomography/computed tomography, SPECT/CT). As much as 20-25% of injected dose of liposomes carrying PECAM and ICAM ligands, but not control IgG accumulated in the pulmonary vasculature. The immunospecificity of pulmonary targeting of scFv/liposomes to PECAM-1 and ICAM-1, respectively, was 10-fold and 2.5-fold higher than of Ab/liposomes. Therefore, the combination of optimal ligands, benign conjugation, and labeling yields liposomal formulations that may be used for highly effective and specific vascular targeting.

Exploring traditional and nontraditional roles for thrombomodulin

Thrombomodulin (TM) is an integral component of a multimolecular system, localized primarily to the vascular endothelium, that integrates crucial biological processes and biochemical pathways, including those related to coagulation, innate immunity, inflammation, and cell proliferation. These are designed to protect the host from injury and promote healing. The “traditional” role of TM in hemostasis was determined with its discovery in the 1980s as a ligand for thrombin and a critical cofactor for the major natural anticoagulant protein C system and subsequently for thrombin-mediated activation of the thrombin activatable fibrinolysis inhibitor (also known as procarboxypeptidase B2). Studies in the past 2 decades are redefining TM as a molecule with many properties, exhibited via its multiple domains, through its interacting partners, complex regulated expression, and synthesis by cells other than the endothelium. In this report, we review some of the recently reported diverse properties of TM and how these may impact on our understanding of the pathogenesis of several diseases.

Ferritin Nanocages with Biologically Orthogonal Conjugation for Vascular Targeting and Imaging

Genetic incorporation of biologically orthogonal functional groups into macromolecules has the potential to yield efficient, controlled, reproducible, site-specific conjugation of affinity ligands, contrast agents, or therapeutic cargoes. Here, we applied this approach to ferritin, a ubiquitous iron-storage protein that self-assembles into multimeric nanocages with remarkable stability, size uniformity (12 nm), and endogenous capacity for loading and transport of a variety of inorganic and organic cargoes. The unnatural amino acid, 4-azidophenylalanine (4-AzF), was incorporated at different sites in the human ferritin light chain (hFTL) to allow site-specific conjugation of alkyne-containing small molecules or affinity ligands to the exterior surface of the nanocage. The optimal positioning of the 4-AzF residue was evaluated by screening a library of variants for the efficiency of copper-free click conjugation. One of the engineered ferritins, hFTL-5X, was found to accommodate ∼14 small-molecule fluorophores (AlexaFluor 488) and 3-4 IgG molecules per nanocage. Intravascular injection in mice of radiolabeled hFTL-5X carrying antibody to cell adhesion molecule ICAM-1, but not control IgG, enabled specific targeting to the lung due to high basal expression of ICAM-1 (43.3 ± 6.99 vs 3.48 ± 0.14%ID/g for Ab vs IgG). Treatment of mice with endotoxin known to stimulate inflammatory ICAM-1 overexpression resulted in 2-fold enhancement of pulmonary targeting (84.4 ± 12.89 vs 43.3 ± 6.99%ID/g). Likewise, injection of fluorescent, ICAM-targeted hFTL-5X nanocages revealed the effect of endotoxin by enhancement of near-infrared signal, indicating potential utility of this approach for both vascular targeting and imaging.

Vascular endothelial effects of collaborative binding to platelet/endothelial cell adhesion molecule-1 (PECAM-1)

Targeting drugs to endothelial cells has shown the ability to improve outcomes in animal models of inflammatory, ischemic and thrombotic diseases. Previous studies have revealed that certain pairs of ligands (antibodies and antibody fragments) specific for adjacent, but distinct, epitopes on PECAM-1 enhance each other’s binding, a phenomenon dubbed Collaborative Enhancement of Paired Affinity Ligands, or CEPAL. This discovery has been leveraged to enable simultaneous delivery of multiple therapeutics to the vascular endothelium. Given the known role of PECAM-1 in promoting endothelial quiescence and cell junction integrity, we sought here to determine if CEPAL might induce unintended vascular effects. Using a combination of in vitro and in vivo techniques and employing human and mouse endothelial cells under physiologic and pathologic conditions, we found only modest or non-significant effects in response to antibodies to PECAM-1, whether given solo or in pairs. In contrast, these methods detected significant elevation of endothelial permeability, pro-inflammatory vascular activation, and systemic cytokine release following antibody binding to the related endothelial junction protein, VE-Cadherin. These studies support the notion that PECAM-1-targeted CEPAL provides relatively well-tolerated endothelial drug delivery. Additionally, the analysis herein creates a template to evaluate potential toxicities of vascular-targeted nanoparticles and protein therapeutics.

Site-Specific Modification of Single-Chain Antibody Fragments for Bioconjugation and Vascular Immunotargeting

The conjugation of antibodies to drugs and drug carriers improves delivery to target tissues. Widespread implementation and effective translation of this pharmacologic strategy awaits the development of affinity ligands capable of a defined degree of modification and highly efficient bioconjugation without loss of affinity. To date, such ligands are lacking for the targeting of therapeutics to vascular endothelial cells. To enable site-specific, click-chemistry conjugation to therapeutic cargo, we used the bacterial transpeptidase, sortase A, to attach short azidolysine containing peptides to three endothelial-specific single chain antibody fragments (scFv). While direct fusion of a recognition motif (sortag) to the scFv C-terminus generally resulted in low levels of sortase-mediated modification, improved reaction efficiency was observed for one protein, in which two amino acids had been introduced during cloning. This prompted insertion of a short, semi-rigid linker between scFv and sortag. The linker significantly enhanced modification of all three proteins, to the extent that unmodified scFv could no longer be detected. As proof of principle, purified, azide-modified scFv was conjugated to the antioxidant enzyme, catalase, resulting in robust endothelial targeting of functional cargo in vitro and in vivo.

ICAM-1-targeted thrombomodulin mitigates tissue factor-driven inflammatory thrombosis in a human endothelialized microfluidic model

Diverse human illnesses are characterized by loss or inactivation of endothelial thrombomodulin (TM), predisposing to microvascular inflammation, activation of coagulation, and tissue ischemia. Single-chain antibody fragment (scFv)/TM) fusion proteins, previously protective against end-organ injury in murine models of inflammation, are attractive candidates to treat inflammatory thrombosis. However, animal models have inherent differences in TM and coagulation biology, are limited in their ability to resolve and control endothelial biology, and do not allow in-depth testing of "humanized" scFv/TM fusion proteins, which are necessary for translation to the clinical domain. To address these challenges, we developed a human whole-blood, microfluidic model of inflammatory, tissue factor (TF)-driven coagulation that features a multichannel format for head-to-head comparison of therapeutic approaches. In this model, fibrin deposition, leukocyte adhesion, and platelet adhesion and aggregation showed a dose-dependent response to tumor necrosis factor-α activation and could be quantified via real-time microscopy. We used this model to compare hTM/R6.5, a humanized, intracellular adhesion molecule 1 (ICAM-1)-targeted scFv/TM biotherapeutic, to untargeted antithrombotic agents, including soluble human TM (shTM), anti-TF antibodies, and hirudin. The targeted hTM/R6.5 more effectively inhibited TF-driven coagulation in a protein C (PC)-dependent manner and demonstrated synergy with supplemental PC. These results support the translational prospects of ICAM-targeted scFv/TM and illustrate the utility of the microfluidic system as a platform to study humanized therapeutics at the interface of endothelium and whole blood under flow.

Dysregulation of pulmonary endothelial protein C receptor and thrombomodulin in severe falciparum malaria-associated ARDS relevant to hemozoin

To investigate the role of the protein C system, endothelial protein C receptor (EPCR) and thrombomodulin (TM) in the pathogenesis of malaria-associated acute respiratory distress syndrome (ARDS) in relation to hemozoin and proinflammatory cytokines-induced type II pneumocyte injury and -aggravated pulmonary resolution. A total of 29 left-over lung specimens that were obtained from patients who died from severe falciparum malaria were examined. Histopathological, immunohistochemical and electron microscopic analyses revealed that ARDS coexisted with pulmonary edema and systemic bleeding; the severity was dependent on the level of hemozoin deposition in the lung and internal alveolar hemorrhaging. The loss of EPCR and TM was primarily identified in ARDS patients and was related to the level of hemozoin, parasitized red blood cell (PRBC) and white blood cell accumulation in the lung. Moreover, an in vitro analysis demonstrated that interleukin-13 and -31 and hemozoin induced pneumocytic cell injury and apoptosis, as assessed by EB/AO staining, electron microscopy and the up-regulation of CARD-9 mRNA (caspase recruitment domain-9 messenger-ribonucleic acid). The dysregulation of EPCR and TM in the lung, especially in those with increased levels of hemozoin, may play an important role in the pathogenesis of malaria-associated ARDS through an apoptotic pathway.

ICAM-1 targeting, intracellular trafficking, and functional activity of polymer nanocarriers coated with a fibrinogen-derived peptide for lysosomal enzyme replacement

Enzyme replacement is a viable treatment for diseases caused by genetic deficiency of lysosomal enzymes. However, suboptimal access of enzymes to target sites limits this strategy. Polymer nanocarriers (NCs) coated with antibody against intercellular adhesion molecule 1 (ICAM-1), a protein overexpressed on most cells under disease states, enhanced biodistribution and lysosomal delivery of these therapeutics. Whether this can be achieved using more biocompatible ICAM-1-targeting moieties is unknown, since intracellular uptake via this route is sensitive to the receptor epitope being targeted. We examined this using polymer NCs coated with an ICAM-1-targeting peptide derived from the fibrinogen sequence. Scrambled-sequence peptide and anti-ICAM were used as controls. NCs carried acid sphingomyelinase (ASM), used for treatment of type B Niemann-Pick disease, and fluorescence microscopy was employed to examine cellular performance. Peptide-coated/enzyme NCs efficiently targeted ICAM-1 (22-fold over non-specific counterparts; B_max ∼180 NCs/cell; t_1/2 ∼28 min), recognised human and mouse cells (1.2- to 0.7-fold binding vs. antibody/enzyme NCs), were efficiently endocytosed (71% at 1 h chase), and trafficked to lysosomes (30--45% of internalised NCs; 2 h chase). This restored lysosomal levels of sphingomyelin and cholesterol within 5 h chase (∼95% reduction over disease levels), similar to antibody-enzyme NCs. This fibrinogen-derived ICAM-1-targeting peptide holds potential for lysosomal enzyme replacement therapy.

Red blood cells: Supercarriers for drugs, biologicals, and nanoparticles and inspiration for advanced delivery systems

Red blood cells (RBCs) constitute a unique drug delivery system as a biologic or hybrid carrier capable of greatly enhancing pharmacokinetics, altering pharmacodynamics (for example, by changing margination within the intravascular space), and modulating immune responses to appended cargoes. Strategies for RBC drug delivery systems include internal and surface loading, and the latter can be performed both ex vivo and in vivo. A relatively new avenue for RBC drug delivery is their application as a carrier for nanoparticles. Efforts are also being made to incorporate features of RBCs in nanocarriers to mimic their most useful aspects, such as long circulation and stealth features. RBCs have also recently been explored as carriers for the delivery of antigens for modulation of immune response. Therefore, RBC-based drug delivery systems represent supercarriers for a diverse array of biomedical interventions, and this is reflected by several industrial and academic efforts that are poised to enter the clinical realm.

Targeting thrombomodulin to circulating red blood cells augments its protective effects in models of endotoxemia and ischemia-reperfusion injury

Endothelial thrombomodulin (TM) regulates coagulation and inflammation via several mechanisms, including production of activated protein C (APC). Recombinant APC and soluble fragments of TM (sTM) have been tested in settings associated with insufficiency of the endogenous TM/APC pathway, such as sepsis. We previously designed a fusion protein of TM [single-chain variable fragment antibody (scFv)/TM] targeted to red blood cells (RBCs) to improve pharmacokinetics and antithrombotic effects without increasing bleeding. Here, scFv/TM was studied in mouse models of systemic inflammation and ischemia-reperfusion injury. Injected concomitantly with or before endotoxin, scFv/TM provided more potent protection against liver injury and release of pathological mediators than sTM, showing similar efficacy at up to 50-fold lower doses. scFv/TM provided protection when injected after endotoxin, whereas sTM did not, and augmented APC production by thrombin ∼50-fold more than sTM. However, scFv/TM injected after endotoxin did not reduce thrombin/antithrombin complexes; nor did antibodies that block APC anticoagulant activity suppress the prophylactic anti-inflammatory effect of scFv/TM. Therefore, similar to endogenous TM, RBC-anchored scFv/TM activates several protective pathways. Finally, scFv/TM was more effective at reducing cerebral infarct volume and alleviated neurological deficits than sTM after cerebral ischemia/reperfusion injury. These results indicate that RBC-targeted scFv/TM exerts multifaceted cytoprotective effects and may find utility in systemic and focal inflammatory and ischemic disorders.-Carnemolla, R., Villa, C. H., Greineder, C. F., Zaitseva, S., Patel, K. R., Kowalska, M. A., Atochin, D. N., Cines, D. B., Siegel, D. L., Esmon, C. T., Muzykantov, V. R. Targeting thrombomodulin to circulating red blood cells augments its protective effects in models of endotoxemia and ischemia-reperfusion injury.

Intra- and trans-cellular delivery of enzymes by direct conjugation with non-multivalent anti-ICAM molecules

Intercellular adhesion molecule 1 (ICAM-1) is a cell-surface protein overexpressed in many diseases and explored for endocytosis and transcytosis of drug delivery systems. All previous evidence demonstrating ICAM-1-mediated transport of therapeutics into or across cells was obtained using nanocarriers or conjugates coupled to multiple copies of anti-ICAM antibodies or peptides. Yet, transport of therapeutics linked to non-multivalent anti-ICAM ligands has never been shown, since multivalency was believed to be necessary to induce transport. Our goal was to explore whether non-multivalent binding to ICAM-1 could drive endocytosis and/or transcytosis of model cargo in different cell types. We found that anti-ICAM was specifically internalized by all tested ICAM-1-expressing cells, including epithelial, fibroblast and neuroblastoma cells, primary or established cell lines. Uptake was inhibited at 4°C and in the presence of an inhibitor of the ICAM-1-associated pathway, rather than inhibitors of the clathrin or caveolar routes. We observed minimal transport of anti-ICAM to lysosomes, yet prominent and specific transcytosis across epithelial monolayers. Finally, we coupled a model cargo (the enzyme horseradish peroxidase (HRP)) to anti-ICAM and separated a 1:2 antibody:enzyme conjugate for non-multivalent ICAM-1 targeting. Similar to anti-ICAM, anti-ICAM-HRP was specifically internalized and transported across cells, which rendered intra- and trans-cellular enzyme activity. Therefore, non-multivalent ICAM-1 targeting also provides transport of cargoes into and across cells, representing a new alternative for future therapeutic applications via this route.

8,9-Dehydrohispanolone-15,16-lactol diterpene prevents LPS-triggered inflammatory responses by inhibiting endothelial activation

Endothelial activation contributes to lung inflammatory disorders by inducing leucocyte recruitment to pulmonary parenchyma. Consequently, vascular-targeted therapies constitute promising strategies for the treatment of inflammatory pathologies. In the present study, we evaluated the effect of 8,9-dehydrohispanolone-15,16-lactol diterpene (DT) on lung endothelium during inflammation. Lung endothelial cells pre-treated with DT and activated with lipopolysaccharide (LPS) or tumour necrosis factor-α (TNF-α) exhibited reduced expression of the pro-inflammatory cytokines Cxcl10, Ccl5 and Cxcl1, whereas the anti-inflammatory molecules IL1r2 and IL-10 were induced. Consistent with this result, DT pre-treatment inhibited nuclear factor κB (NF-κB) nuclear translocation, by interfering with IκBα phosphorylation, and consequently NF-κB transcriptional activity in endothelium activated by LPS or TNF-α. Furthermore, DT, probably through p38 signalling, induced transcriptional activation of genes containing activator protein 1 (AP-1)-binding elements. Inhibition of p38 prevented IL1r2 mRNA expression in endothelium incubated with DT alone or in combination with LPS or TNF-α. Accordingly, conditioned medium (CM) from these cells failed to stimulate leucocytes as measured by a reduction in adhesive ability of the leucocyte cell line J774 to fibronectin (FN). Additionally, DT reduced the expression of the endothelial adhesion molecules E-selectin, vascular cell adhesion molecule 1 (VCAM-1) and intercellular adhesion molecule 1 (ICAM-1) after activation. Similarly, expression of VCAM-1 and ICAM-1 molecules on the lung endothelial layer of C57/BL6 mice pre-treated with DT and challenged with LPS were unchanged. Finally, inhibition of vascular adhesion molecule expression by DT decreased the interaction of J774 cells with lung endothelial cells in an inflammatory environment. Our findings establish DT as a novel endothelial inhibitor for the treatment of inflammatory-related diseases triggered by Gram-negative bacteria or by the associated cytokine TNF-α.

Non-affinity factors modulating vascular targeting of nano- and microcarriers

Particles capable of homing and adhering to specific vascular biomarkers have potential as fundamental tools in drug delivery for mediation of a wide variety of pathologies, including inflammation, thrombosis, and pulmonary disorders. The presentation of affinity ligands on the surface of a particle provides a means of targeting the particle to sites of therapeutic interest, but a host of other factors come into play in determining the targeting capacity of the particle. This review presents a summary of several key considerations in nano- and microparticle design that modulate targeted delivery without directly altering epitope-specific affinity. Namely, we describe the effect of factors in definition of the base carrier (including shape, size, and flexibility) on the capacity of carriers to access, adhere to, and integrate in target biological milieus. Furthermore, we present a summary of fundamental dynamics of carrier behavior in circulation, taking into account interactions with cells in circulation and the role of hemodynamics in mediating the direction of carriers to target sites. Finally, we note non-affinity aspects to uptake and intracellular trafficking of carriers in target cells. In total, recent findings presented here may offer an opportunity to capitalize on mitigating factors in the behavior of ligand-targeted carriers in order to optimize targeting.

Molecular engineering of high affinity single-chain antibody fragment for endothelial targeting of proteins and nanocarriers in rodents and humans

Endothelial cells (EC) represent an important target for pharmacologic intervention, given their central role in a wide variety of human pathophysiologic processes. Studies in lab animal species have established that conjugation of drugs and carriers with antibodies directed to surface targets like the Platelet Endothelial Cell Adhesion Molecule-1 (PECAM-1, a highly expressed endothelial transmembrane protein) help to achieve specific therapeutic interventions in ECs. To translate such "vascular immunotargeting" to clinical practice, it is necessary to replace antibodies by advanced ligands that are more amenable to use in humans. We report the molecular design of a single chain variable antibody fragment (scFv) that binds with high affinity to human PECAM-1 and cross-reacts with its counterpart in rats and other animal species, allowing parallel testing in vivo and in human endothelial cells in microfluidic model. Site-specific modification of the scFv allows conjugation of protein cargo and liposomes, enabling their endothelial targeting in these models. This study provides a template for molecular engineering of ligands, enabling studies of drug targeting in animal species and subsequent use in humans.

Vascular Accessibility of Endothelial Targeted Ferritin Nanoparticles

Targeting nanocarriers to the endothelium, using affinity ligands to cell adhesion molecules such as ICAM-1 and PECAM-1, holds promise to improve the pharmacotherapy of many disease conditions. This approach capitalizes on the observation that antibody-targeted carriers of 100 nm and above accumulate in the pulmonary vasculature more effectively than free antibodies. Targeting of prospective nanocarriers in the 10-50 nm range, however, has not been studied. To address this intriguing issue, we conjugated monoclonal antibodies (Ab) to ICAM-1 and PECAM-1 or their single chain antigen-binding fragments (scFv) to ferritin nanoparticles (FNPs, size 12 nm), thereby producing Ab/FNPs and scFv/FNPs. Targeted FNPs retained their typical symmetric core-shell structure with sizes of 20-25 nm and ∼4-5 Ab (or ∼7-9 scFv) per particle. Ab/FNPs and scFv/FNPs, but not control IgG/FNPs, bound specifically to cells expressing target molecules and accumulated in the lungs after intravenous injection, with pulmonary targeting an order of magnitude higher than free Ab. Most intriguing, the targeting of Ab/FNPs to ICAM-1, but not PECAM-1, surpassed that of larger Ab/carriers targeted by the same ligand. These results indicate that (i) FNPs may provide a platform for targeting endothelial adhesion molecules with carriers in the 20 nm size range, which has not been previously reported; and (ii) ICAM-1 and PECAM-1 (known to localize in different domains of endothelial plasmalemma) differ in their accessibility to circulating objects of this size, common for blood components and nanocarriers.

Targeted endothelial nanomedicine for common acute pathological conditions

Endothelium, a thin monolayer of specialized cells lining the lumen of blood vessels is the key regulatory interface between blood and tissues. Endothelial abnormalities are implicated in many diseases, including common acute conditions with high morbidity and mortality lacking therapy, in part because drugs and drug carriers have no natural endothelial affinity. Precise endothelial drug delivery may improve management of these conditions. Using ligands of molecules exposed to the bloodstream on the endothelial surface enables design of diverse targeted endothelial nanomedicine agents. Target molecules and binding epitopes must be accessible to drug carriers, carriers must be free of harmful effects, and targeting should provide desirable sub-cellular addressing of the drug cargo. The roster of current candidate target molecules for endothelial nanomedicine includes peptidases and other enzymes, cell adhesion molecules and integrins, localized in different domains of the endothelial plasmalemma and differentially distributed throughout the vasculature. Endowing carriers with an affinity to specific endothelial epitopes enables an unprecedented level of precision of control of drug delivery: binding to selected endothelial cell phenotypes, cellular addressing and duration of therapeutic effects. Features of nanocarrier design such as choice of epitope and ligand control delivery and effect of targeted endothelial nanomedicine agents. Pathological factors modulate endothelial targeting and uptake of nanocarriers. Selection of optimal binding sites and design features of nanocarriers are key controllable factors that can be iteratively engineered based on their performance from in vitro to pre-clinical in vivo experimental models. Targeted endothelial nanomedicine agents provide antioxidant, anti-inflammatory and other therapeutic effects unattainable by non-targeted counterparts in animal models of common acute severe human disease conditions. The results of animal studies provide the basis for the challenging translation endothelial nanomedicine into the clinical domain.

Collaborative Enhancement of Endothelial Targeting of Nanocarriers by Modulating Platelet-Endothelial Cell Adhesion Molecule-1/CD31 Epitope Engagement

Nanocarriers (NCs) coated with antibodies (Abs) to extracellular epitopes of the transmembrane glycoprotein PECAM (platelet endothelial cell adhesion molecule-1/CD31) enable targeted drug delivery to vascular endothelial cells. Recent studies revealed that paired Abs directed to adjacent, yet distinct epitopes of PECAM stimulate each other's binding to endothelial cells in vitro and in vivo ("collaborative enhancement"). This phenomenon improves targeting of therapeutic fusion proteins, yet its potential role in targeting multivalent NCs has not been addressed. Herein, we studied the effects of Ab-mediated collaborative enhancement on multivalent NC spheres coated with PECAM Abs (Ab/NC, ∼180 nm diameter). We found that PECAM Abs do mutually enhance endothelial cell binding of Ab/NC coated by paired, but not "self" Ab. In vitro, collaborative enhancement of endothelial binding of Ab/NC by paired Abs is modulated by Ab/NC avidity, epitope selection, and flow. Cell fixation, but not blocking of endocytosis, obliterated collaborative enhancement of Ab/NC binding, indicating that the effect is mediated by molecular reorganization of PECAM molecules in the endothelial plasmalemma. The collaborative enhancement of Ab/NC binding was affirmed in vivo. Intravascular injection of paired Abs enhanced targeting of Ab/NC to pulmonary vasculature in mice by an order of magnitude. This stimulatory effect greatly exceeded enhancement of Ab targeting by paired Abs, indicating that '"collaborative enhancement"' effect is even more pronounced for relatively large multivalent carriers versus free Abs, likely due to more profound consequences of positive alteration of epitope accessibility. This phenomenon provides a potential paradigm for optimizing the endothelial-targeted nanocarrier delivery of therapeutic agents.

Renal blood perfusion in GK rats using targeted contrast enhanced ultrasonography

OBJECTIVE

To explore application of targeted contrast enhanced ultrasonography in diagnosis of early stage vascular endothelial injury and diabetic nephropathy.

METHODS

Targeted SonoVue-TM microbubble was prepared by attaching anti-TM monoclonal antibody to the surface of ordinary microbubble SonoVue by biotin - avidin bridge method and ultrasonic instrument was used to evaluate the developing situation of targeted microbubble in vitro. Twenty 12-week-old male GK rats and 20 Wistar rats were enrolled in this study, and were randomly divided into targeted angiography group and ordinary angiography group. Targeted microbubbles SonoVue-TM or general microbubble SonoVue were rapidly injected to the rats via tail vein; the developing situation of the two contrast agents in rats kidneys was dynamically observed. Time-intensity curve was used to analyze rat kidney perfusion characteristics in different groups.

RESULTS

Targeted ultrasound microbubble SonoVue-TM was successfully constructed, and it could be used to develop an external image. Targeted microbubbles SonoVue-TM enabled clear development of experimental rat kidney. Time-intensity curve shapes of rat kidney of the two groups showed as single apex with steep ascending and slowly descending branch. Compared with the control group, the rising slope of the GK rat renal cortex, medulla in targeted angiography group increased (P < 0.05); the peak intensity of medulla increased (P < 0.05), and the total area under the curve of medulla increased (P < 0.05). Compared with control group, the ascending branch of the GK rat in renal cortex, medulla in ordinary angiography group increased (P < 0.05). The peak intensity of the curve increased (P < 0.05), and the total area under the curve increased (P < 0.05). Compared with the ordinary angiography group, the peak of GK rat medulla curve in targeted angiography group intensity increased (P < 0.05), and the total area under the curve increased (P < 0.05).

CONCLUSIONS

Targeted microbubbles SonoVue-TM can make a clear development of experimental rat kidney, its stable performance meet the requirement of ultrasonic observation time limit, and it can reflect early changes of blood perfusion in GK rat kindey.

Dual targeting of therapeutics to endothelial cells: collaborative enhancement of delivery and effect

Anchoring pharmacologic agents to the vascular lumen has the potential to modulate critical processes at the blood-tissue interface, avoiding many of the off-target effects of systemically circulating agents. We report a novel strategy for endothelial dual targeting of therapeutics, which both enhances drug delivery and enables targeted agents to partner enzymatically to generate enhanced biologic effect. Based on the recent discovery that paired antibodies directed to adjacent epitopes of platelet endothelial cell adhesion molecule (PECAM)-1 stimulate each other's binding, we fused single-chain fragments (scFv) of paired anti-mouse PECAM-1 antibodies to recombinant murine thrombomodulin (TM) and endothelial protein C receptor (EPCR), endothelial membrane proteins that partner in activation of protein C (PC). scFv/TM and scFv/EPCR bound to mouse endothelial PECAM-1 with high affinity (EC50 1.5 and 3.8 nM, respectively), and codelivery induced a 5-fold increase in PC activation not seen when TM and EPCR are anchored to distinct cell adhesion molecules. In a mouse model of acute lung injury, dual targeting reduces both the expression of lung inflammatory markers and trans-endothelial protein leak by as much as 40%, as compared to either agent alone. These findings provide proof of principle for endothelial dual targeting, an approach with numerous potential biomedical applications.

Endothelial nanomedicine for the treatment of pulmonary disease

INTRODUCTION

Even though pulmonary diseases are among the leading causes of morbidity and mortality in the world, exceedingly few life-prolonging therapies have been developed for these maladies. Relief may finally come from nanomedicine and targeted drug delivery.

AREAS COVERED

Here, we focus on four conditions for which the pulmonary endothelium plays a pivotal role: acute respiratory distress syndrome, primary graft dysfunction occurring immediately after lung transplantation, pulmonary arterial hypertension and pulmonary embolism. For each of these diseases, we first evaluate the targeted drug delivery approaches that have been tested in animals. Then we suggest a 'need specification' for each disease: a list of criteria (e.g., macroscale delivery method, stability, etc.) that nanomedicine agents must meet in order to warrant human clinical trials and investment from industry.

EXPERT OPINION

For the diseases profiled here, numerous nanomedicine agents have shown promise in animal models. However, to maximize the chances of creating products that reach patients, nanomedicine engineers and clinicians must work together and use each disease's need specification to guide the design of practical and effective nanomedicine agents.