In vitro characterization of leukocyte mimetic for targeting therapeutics to the endothelium using two receptors

Microbubbles: Revolutionizing Biomedical Applications with Tailored Therapeutic Precision

BACKGROUND

Over the past ten years, tremendous progress has been made in microbubble-based research for a variety of biological applications. Microbubbles emerged as a compelling and dynamic tool in modern drug delivery systems. They are employed to deliver drugs or genes to targeted regions of interest, and then ultrasound is used to burst the microbubbles, causing site-specific delivery of the bioactive materials.

OBJECTIVE

The objective of this article is to review the microbubble compositions and physiochemical characteristics in relation to the development of innovative biomedical applications, with a focus on molecular imaging and targeted drug/gene delivery.

METHODS

The microbubbles are prepared by using various methods, which include cross-linking polymerization, emulsion solvent evaporation, atomization, and reconstitution. In cross-linking polymerization, a fine foam of the polymer is formed, which serves as a bubble coating agent and colloidal stabilizer, resulting from the vigorous stirring of a polymeric solution. In the case of emulsion solvent evaporation, there are two solutions utilized in the production of microbubbles. In atomization and reconstitution, porous spheres are created by atomising a surfactant solution into a hot gas. They are encapsulated in primary modifier gas. After the addition of the second gas or gas osmotic agent, the package is placed into a vial and sealed after reconstituting with sterile saline solution.

RESULTS

Microbubble-based drug delivery is an innovative approach in the field of drug delivery that utilizes microbubbles, which are tiny gas-filled bubbles, act as carriers for therapeutic agents. These microbubbles can be loaded with drugs, imaging agents, or genes and then guided to specific target sites.

CONCLUSION

The potential utility of microbubbles in biomedical applications is continually growing as novel formulations and methods. The versatility of microbubbles allows for customization, tailoring the delivery system to various medical applications, including cancer therapy, cardiovascular treatments, and gene therapy.

Dual Affinity to RBCs and Target Cells (DART) Enhances Both Organ- and Cell Type-Targeting of Intravascular Nanocarriers

A long-standing goal of nanomedicine is to improve a drug's benefit by loading it into a nanocarrier that homes solely to a specific target cell and organ. Unfortunately, nanocarriers usually end up with only a small percentage of the injected dose (% ID) in the target organ, due largely to clearance by the liver and spleen. Further, cell-type-specific targeting is rarely achieved without reducing target organ accumulation. To solve these problems, we introduce DART (dual affinity to RBCs and target cells), in which nanocarriers are conjugated to two affinity ligands, one binding red blood cells and one binding a target cell (here, pulmonary endothelial cells). DART nanocarriers first bind red blood cells and then transfer to the target organ's endothelial cells as the bound red blood cells squeeze through capillaries. We show that within minutes after intravascular injection in mice nearly 70% ID of DART nanocarriers accumulate in the target organ (lungs), more than doubling the % ID ceiling achieved by a multitude of prior technologies, finally achieving a majority % ID in a target organ. Humanized DART nanocarriers in ex vivo perfused human lungs recapitulate this phenomenon. Furthermore, DART enhances the selectivity of delivery to target endothelial cells over local phagocytes within the target organ by 6-fold. DART's marked improvement in both organ- and cell-type targeting may thus be helpful in localizing drugs for a multitude of medical applications.

Polymeric particle-based therapies for acute inflammatory diseases

Acute inflammation is essential for initiating and coordinating the body's response to injuries and infections. However, in acute inflammatory diseases, inflammation is not resolved but propagates further, which can ultimately lead to tissue damage such as in sepsis, acute respiratory distress syndrome and deep vein thrombosis. Currently, clinical protocols are limited to systemic steroidal treatments, fluids and antibiotics that focus on eradicating inflammation rather than modulating it. Strategies based on stem cell therapeutics and selective blocking of inflammatory molecules, despite showing great promise, still lack the scalability and specificity required to treat acute inflammation. By contrast, polymeric particle systems benefit from uniform manufacturing at large scales while preserving biocompatibility and versatility, thus providing an ideal platform for immune modulation. Here, we outline design aspects of polymeric particles including material, size, shape, deformability and surface modifications, providing a strategy for optimizing the targeting of acute inflammation.

Flow topology and targeted drug delivery in cardiovascular disease

Targeted drug delivery is a promising technique to direct the drug to the specific diseased region. Nanoparticles have provided an attractive approach for this purpose. In practice, the major focus of targeted delivery has been on targeting cell receptors. However, the complex fluid mechanics in diseased biomedical flows questions if a sufficient number of nanoparticles can reach the desired region. In this paper, we propose that hidden topological structures in cardiovascular flows identified with Lagrangian coherent structures (LCS) control drug transport and provide valuable information for optimizing targeted drug delivery efficiency. We couple image-based computational fluid dynamics (CFD) with continuum transport models to study nanoparticle transport in coronary artery disease. We simulate nanoparticle transport as well as the recently proposed shear targeted drug delivery system that couples micro-carriers with nanoparticle drugs. The role of the LCS formed near the stenosed artery in controlling drug transport is discussed. Our results motivate the design of smart micro-needles guided by flow topology, which could achieve optimal drug delivery efficiency.

NIR Photodynamic Destruction of PDAC and HNSCC Nodules Using Triple-Receptor-Targeted Photoimmuno-Nanoconjugates: Targeting Heterogeneity in Cancer

Receptor heterogeneity in cancer is a major limitation of molecular targeting for cancer therapeutics. Single-receptor-targeted treatment exerts selection pressures that result in treatment escape for low-receptor-expressing tumor subpopulations. To overcome this potential for heterogeneity-driven resistance to molecular targeted photodynamic therapy (PDT), we present for the first time a triple-receptor-targeted photoimmuno-nanoconjugate (TR-PIN) platform. TR-PIN functionalization with cetuximab, holo-transferrin, and trastuzumab conferred specificity for epidermal growth factor receptor (EGFR), transferrin receptor (TfR), and human epidermal growth factor receptor 2 (HER-2), respectively. The TR-PINs exhibited up to a 24-fold improvement in cancer cell binding compared with EGFR-specific cetuximab-targeted PINs (Cet-PINs) in low-EGFR-expressing cell lines. Photodestruction using TR-PINs was significantly higher than the monotargeted Cet-PINs in heterocellular 3D in vitro models of heterogeneous pancreatic ductal adenocarcinoma (PDAC; MIA PaCa-2 cells) and heterogeneous head and neck squamous cell carcinoma (HNSCC, SCC9 cells) containing low-EGFR-expressing T47D (high TfR) or SKOV-3 (high HER-2) cells. Through their capacity for multiple tumor target recognition, TR-PINs can serve as a unique and amenable platform for the effective photodynamic eradication of diverse tumor subpopulations in heterogeneous cancers to mitigate escape for more complete and durable treatment responses.

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.

Targeting functionalized nanoparticles to activated endothelial cells under high wall shear stress

Local inflammation of the endothelium is associated with a plethora of cardiovascular diseases. Vascular-targeted carriers (VTCs) have been advocated to provide focal effective therapeutics to these disease sites. Here, we examine the design of functionalized nanoparticles (NPs) as VTCs that can specifically localize at an inflamed vessel wall under pathological levels of high shear stress, associated for example with clinical (or in vivo) conditions of vascular narrowing and arteriogenesis. To test this, carboxylated fluorescent 200 nm polystyrene particles were functionalized with ligands to activated endothelium, that is, an E-selectin binding peptide (Esbp), an anti ICAM-1 antibody, or using a combination of both. The functionalized NPs were investigated in vitro using microfluidic models lined with inflamed (TNF-α stimulated) and control endothelial cells (EC). Specifically, their adhesion was monitored under different relevant wall shear stresses (i.e., 40-300 dyne/cm2) via real-time confocal microscopy. Experiments reveal a significantly higher specific adhesion of the examined functionalized NPs to activated EC for the window of examined wall shear stresses. Moreover, particle adhesion correlated with the surface coating density whereby under high surface coating (i.e., ~10,000 molecule/particle), shear-dependent particle adhesion increased significantly. Altogether, our results show that functionalized NPs can be designed to target inflamed endothelial cells under high shear stress. Such VTCs underscore the potential for attractive avenues in targeting drugs to vasoconstriction and arteriogenesis sites.

Mechanical Model for Catch-Bond-Mediated Cell Adhesion in Shear Flow

Catch bond, whose lifetime increases with applied tensile force, can often mediate rolling adhesion of cells in a hydrodynamic environment. However, the mechanical mechanism governing the kinetics of rolling adhesion of cells through catch-bond under shear flow is not yet clear. In this study, a mechanical model is proposed for catch-bond-mediated cell adhesion in shear flow. The stochastic reaction of bond formation and dissociation is described as a Markovian process, whereas the dynamic motion of cells follows classical analytical mechanics. The steady state of cells significantly depends on the shear rate of flow. The upper and lower critical shear rates required for cell detachment and attachment are extracted, respectively. When the shear rate increases from the lower threshold to the upper threshold, cell rolling became slower and more regular, implying the flow-enhanced adhesion phenomenon. Our results suggest that this flow-enhanced stability of rolling adhesion is attributed to the competition between stochastic reactions of bonds and dynamics of cell rolling, instead of force lengthening the lifetime of catch bonds, thereby challenging the current view in understanding the mechanism behind this flow-enhanced adhesion phenomenon. Moreover, the loading history of flow defining bistability of cell adhesion in shear flow is predicted. These theoretical predictions are verified by Monte Carlo simulations and are related to the experimental observations reported in literature.

Rapid Electrostatic Capture of Rod-Shaped Particles on Planar Surfaces: Standing up to Shear

We compare the electrostatically driven capture of flowing rod-shaped and spherical silica particles from dilute solutions onto a flow chamber wall that carries the opposite electrostatic charge from the particles. Particle accumulation and orientation are measured in time at a fixed region on the wall of a shear flow chamber. Rod-shaped particle aspect ratios are 2.5-3.2 and particle lengths are 1.3 and 2.67 μm for two samples, while sphere diameters were 0.72, 0.96, and 2.0 μm for three samples. At a moderate wall shear rate of 22 s^-1, the particle accumulation for both rods and spheres is well described by diffusion-limited kinetics, demonstrating the limiting effect of particle diffusion in the near-wall boundary layer for electrostatically driven capture in this particle shape and size range. The significance of this finding is demonstrated in a calculation that shows that for delivery applications, nearly the same (within 10%) particle volume or mass is delivered to a surface at the diffusion-limited rate by rods and spheres. Therefore, in the absence of other motivating factors, the expense of developing rod-shaped microscale delivery packages to enhance capture from flow in the diffusion-limited simple shear regime is unwarranted. It is also interesting that the captured orientations of the larger rods, 2.6 μm in average length, were highly varied and insensitive to flow: a substantial fraction of rods were trapped in standing and slightly leaning orientations, touching the surface by their ends. Additionally, for particles that were substantially tipped over, there was only modest orientation in the flow direction. Taken together, these findings suggest that on the time scale of near-surface particle rotations, adhesion events are fast, trapping particles in orientations that do not necessarily maximize their favored adhesive contact or reduce hydrodynamic drag.

Dual complementary liposomes inhibit triple-negative breast tumor progression and metastasis

Distinguishing malignant cells from non-neoplastic ones is a major challenge in triple-negative breast cancer (TNBC) treatment. Here, we developed a complementary targeting strategy that uses precisely matched, multivalent ligand-receptor interactions to recognize and target TNBC tumors at the primary site and metastatic lesions. We screened a panel of cancer cell surface markers and identified intercellular adhesion molecule-1 (ICAM1) and epithelial growth factor receptor (EGFR) as optimal candidates for TNBC complementary targeting. We engineered a dual complementary liposome (DCL) that precisely complements the molecular ratio and organization of ICAM1 and EGFR specific to TNBC cell surfaces. Our in vitro mechanistic studies demonstrated that DCLs, compared to single-targeting liposomes, exhibited increased binding, enhanced internalization, and decreased receptor signaling. DCLs consistently exhibited substantially increased tumor targeting activity and antitumor efficacy in orthotopic and lung metastasis models, indicating that DCLs are a platform technology for the design of personalized nanomedicines for TNBC.

Targeted Transfection Using PEGylated Cationic Liposomes Directed Towards P-Selectin Increases siRNA Delivery into Activated Endothelial Cells

: The progress in small-interfering RNA (siRNA) therapeutics depends on the development of suitable nanocarriers to perform specific and effective delivery to dysfunctional cells. In this paper, we questioned whether P-selectin, a cell adhesion molecule specifically expressed on the surface of activated endothelial cells (EC) could be employed as a target for nanotherapeutic intervention. To this purpose, we developed and characterized P-selectin targeted PEGylated cationic liposomes able to efficiently pack siRNA and to function as efficient vectors for siRNA delivery to tumour necrosis factor-α (TNF-α) activated EC. Targeted cationic liposomes were obtained by coupling a peptide with high affinity for P-selectin to a functionalized PEGylated phospholipid inserted in the liposomes' bilayer (Psel-lipo). As control, scrambled peptide coupled cationic liposomes (Scr-lipo) were used. The lipoplexes obtained by complexation of Psel-lipo with siRNA (Psel-lipo/siRNA) were taken up specifically and at a higher extent by TNF-α activated b.End3 endothelial cells as compared to non-targeted Scr-lipo/siRNA. The Psel-lipo/siRNA delivered with high efficiency siRNA into the cells. The lipoplexes were functional as demonstrated by the down-regulation of the selected gene (GAPDH). The results demonstrate an effective targeted delivery of siRNA into cultured activated endothelial cells using P-selectin directed PEGylated cationic liposomes, which subsequently knock-down the desired gene.

A novel strategy to achieve effective drug delivery: exploit cells as carrier combined with nanoparticles

Cell-mediated drug delivery systems employ specific cells as drug vehicles to deliver drugs to targeted sites. Therapeutics or imaging agents are loaded into these cells and then released in diseased sites. These specific cells mainly include red blood cells, leukocytes, stem cells and so on. The cell acts as a Trojan horse to transfer the drug from circulating blood to the diseased tissue. In such a system, these cells keep their original properties, which allow them to mimic the migration behavior of specific cells to carry drug to the targeted site after in vivo administration. This strategy elegantly combines the advantages of both carriers, i.e. the adjustability of nanoparticles (NPs) and the natural functions of active cells, which therefore provides a new perspective to challenge current obstacles in drug delivery. This review will describe a fundamental understanding of these cell-based drug delivery systems, and discuss the great potential of combinational application of cell carrier and NPs.

How Carrier Size and Valency Modulate Receptor-Mediated Signaling: Understanding the Link between Binding and Endocytosis of ICAM-1-Targeted Carriers

Targeting of drug carriers to endocytic cell receptors facilitates intracellular drug delivery. Carrier size and number of targeting moieties (valency) influence cell binding and uptake. However, how these parameters influence receptor-mediated cell signaling (the link between binding and uptake) remains uncharacterized. We studied this using polymer carriers of different sizes and valencies, targeted to endothelial intercellular adhesion molecule-1 (ICAM-1), a marker overexpressed in many pathologies. Unexpectedly, induction of cell signals (ceramide and protein kinase C (PKC) enrichment and activation) and uptake, were independent of carrier avidity, total number of carriers bound per cell, cumulative cell surface area occupied by carriers, number of targeting antibodies at the carrier-cell contact, and cumulative receptor engagement by all bound carriers. Instead, "valency density" (number of antibodies per carrier surface area) ruled signaling, and carrier size independently influenced uptake. These results are key to understanding the interplay between carrier design parameters and receptor-mediated signaling conducive to endocytosis, paramount for intracellular drug delivery.

Engineering Factor Xa Inhibitor with Multiple Platelet-Binding Sites Facilitates its Platelet Targeting

Targeted delivery of antithrombotic drugs centralizes the effects in the thrombosis site and reduces the hemorrhage side effects in uninjured vessels. We have recently reported that the platelet-targeting factor Xa (FXa) inhibitors, constructed by engineering one Arg-Gly-Asp (RGD) motif into Ancylostoma caninum anticoagulant peptide 5 (AcAP5), can reduce the risk of systemic bleeding than non-targeted AcAP5 in mouse arterial injury model. Increasing the number of platelet-binding sites of FXa inhibitors may facilitate their adhesion to activated platelets, and further lower the bleeding risks. For this purpose, we introduced three RGD motifs into AcAP5 to generate a variant NR4 containing three platelet-binding sites. NR4 reserved its inherent anti-FXa activity. Protein-protein docking showed that all three RGD motifs were capable of binding to platelet receptor αIIbβ3. Molecular dynamics simulation demonstrated that NR4 has more opportunities to interact with αIIbβ3 than single-RGD-containing NR3. Flow cytometry analysis and rat arterial thrombosis model further confirmed that NR4 possesses enhanced platelet targeting activity. Moreover, NR4-treated mice showed a trend toward less tail bleeding time than NR3-treated mice in carotid artery endothelium injury model. Therefore, our data suggest that engineering multiple binding sites in one recombinant protein is a useful tool to improve its platelet-targeting efficiency.

Vascular-targeted nanocarriers: design considerations and strategies for successful treatment of atherosclerosis and other vascular diseases

Vascular-targeted nanocarriers are an attractive option for the treatment of a number of cardiovascular diseases, as they allow for more specific delivery and increased efficacy of many small molecule drugs. However, immune clearance, limited cellular uptake, and particle-cell dynamics in blood flow can hinder nanocarrier efficacy in many applications. This review aims to investigate successful strategies for the use of vascular-targeted nanocarriers in the treatment of cardiovascular diseases such as atherosclerosis. In particular, the review will highlight strategies employed for actively targeting the components of the atherosclerotic plaque, including endothelial cells, macrophages, and platelets and passive targeting via endothelial permeability, as well as design specifications (such as size, shape, and density) aimed at enhancing the ability of nanocarriers to reach the vascular wall. WIREs Nanomed Nanobiotechnol 2016, 8:909-926. doi: 10.1002/wnan.1414 For further resources related to this article, please visit the WIREs website.

Evaluation of Receptor-Ligand Mechanisms of Dual-Targeted Particles to an Inflamed Endothelium

Vascular-targeted carriers (VTCs) are designed as leukocyte mimics, decorated with ligands that target leukocyte adhesion molecules (LAMs) and facilitate adhesion to diseased endothelium. VTCs require different design considerations than other targeted particle therapies; adhesion of VTCs in regions with dynamic blood flow requires multiple ligand-receptor (LR) pairs that provide particle adhesion and disease specificity. Despite the ultimate goal of leukocyte mimicry, the specificity of multiple LAM-targeted VTCs remains poorly understood, especially in physiological environments. Here, we investigate particle binding to an inflamed mesentery via intravital microscopy using a series of particles with well-controlled ligand properties. We find that the total number of sites of a single ligand can drive particle adhesion to the endothelium, however, combining ligands that target multiple LR pairs provides a more effective approach. Combining sites of sialyl Lewis A (sLeA) and anti-intercellular adhesion molecule-1 (aICAM), two adhesive molecules, resulted in ~3-7-fold increase of adherent particles at the endothelium over single-ligand particles. At a constant total ligand density, a particle with a ratio of 75% sLeA: 25% aICAM resulted in more than 3-fold increase over all over other ligand ratios tested in our in vivo model. Combined with in vitro and in silico data, we find the best dual-ligand design of a particle is heavily dependent on the surface expression of the endothelial cells, producing better adhesion with more particle ligand for the lesser-expressed receptor. These results establish the importance of considering LR-kinetics in intelligent VTC ligand design for future therapeutics.

Adhesion characteristics of nano/micro-sized particles with dual ligands with different interaction distances

Dual ligand conjugated particle for targeted delivery. Rotational dislodging force on the ligand–receptor interaction. Optimal receptor and ligand ratio exist.

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.

Drug carrier interaction with blood: a critical aspect for high-efficient vascular-targeted drug delivery systems

Vascular wall endothelial cells control several physiological processes and are implicated in many diseases, making them an attractive candidate for drug targeting. Vascular-targeted drug carriers (VTCs) offer potential for reduced side effects and improved therapeutic efficacy, however, only limited therapeutic success has been achieved to date. This is perhaps due to complex interactions of VTCs with blood components, which dictate VTC transport and adhesion to endothelial cells. This review focuses on VTC interaction with blood as well as novel 'bio-inspired' designs to mimic and exploit features of blood in VTC development. Advanced approaches for enhancing VTCs are discussed along with applications in regenerative medicine, an area of massive potential growth and expansion of VTC utility in the near future.

Hierarchical biointerfaces assembled by leukocyte-inspired particles for specifically recognizing cancer cells

By mimicking certain biochemical and physical attributes of biological cells, bio-inspired particles have attracted great attention for potential biomedical applications based on cell-like biological functions. Inspired by leukocytes, hierarchical biointerfaces are designed and prepared based on specific molecules-modified leukocyte-inspired particles. These biointerfaces can efficiently recognize cancer cells from whole blood samples through the synergistic effect of molecular recognition and topographical interaction. Compared to flat, mono-micro or nano-biointerfaces, these micro/nano hierarchical biointerfaces are better able to promote specific recognition interactions, resulting in an enhanced cell-capture efficiency. It is anticipated that this study may provide promising guidance to develop new bio-inspired hierarchical biointerfaces for biomedical applications.

Plasma protein corona modulates the vascular wall interaction of drug carriers in a material and donor specific manner

The nanoscale plasma protein interaction with intravenously injected particulate carrier systems is known to modulate their organ distribution and clearance from the bloodstream. However, the role of this plasma protein interaction in prescribing the adhesion of carriers to the vascular wall remains relatively unknown. Here, we show that the adhesion of vascular-targeted poly(lactide-co-glycolic-acid) (PLGA) spheres to endothelial cells is significantly inhibited in human blood flow, with up to 90% reduction in adhesion observed relative to adhesion in simple buffer flow, depending on the particle size and the magnitude and pattern of blood flow. This reduced PLGA adhesion in blood flow is linked to the adsorption of certain high molecular weight plasma proteins on PLGA and is donor specific, where large reductions in particle adhesion in blood flow (>80% relative to buffer) is seen with ∼60% of unique donor bloods while others exhibit moderate to no reductions. The depletion of high molecular weight immunoglobulins from plasma is shown to successfully restore PLGA vascular wall adhesion. The observed plasma protein effect on PLGA is likely due to material characteristics since the effect is not replicated with polystyrene or silica spheres. These particles effectively adhere to the endothelium at a higher level in blood over buffer flow. Overall, understanding how distinct plasma proteins modulate the vascular wall interaction of vascular-targeted carriers of different material characteristics would allow for the design of highly functional delivery vehicles for the treatment of many serious human diseases.

Bioinspired microfluidic assay for in vitro modeling of leukocyte-endothelium interactions

Current in vitro models of the leukocyte adhesion cascade cannot be used for real-time studies of the entire leukocyte adhesion cascade, including rolling, adhesion, and migration in a single assay. In this study, we have developed and validated a novel bioinspired microfluidic assay (bMFA) and used it to test the hypothesis that blocking of specific steps in the adhesion/migration cascade significantly affects other steps of the cascade. The bMFA consists of an endothelialized microvascular network in communication with a tissue compartment via a 3 μm porous barrier. Human neutrophils in bMFA preferentially adhered to activated human endothelial cells near bifurcations with rolling and adhesion patterns in close agreement with in vivo observations. Treating endothelial cells with monoclonal antibodies to E-selectin or ICAM-1 or treating neutrophils with wortmannin reduced rolling, adhesion, and migration of neutrophils to 60%, 20%, and 18% of their respective control values. Antibody blocking of specific steps in the adhesion/migration cascade (e.g., mAb to E-selectin) significantly downregulated other steps of the cascade (e.g., migration). This novel in vitro assay provides a realistic human cell based model for basic science studies, identification of new treatment targets, selection of pathways to target validation, and rapid screening of candidate agents.

Leukocyte mimetic polysaccharide microparticles tracked in vivo on activated endothelium and in abdominal aortic aneurysm

We have developed injectable microparticles functionalized with fucoidan, in which sulfated groups mimic the anchor sites of P-selectin glycoprotein ligand-1 (PSGL-1), one of the principal receptors supporting leukocyte adhesion. These targeted microparticles were combined with a fluorescent dye and a T2(∗) magnetic resonance imaging (MRI) contrast agent, and then tracked in vivo with small animal imaging methods. Microparticles of 2.5μm were obtained by a water-in-oil emulsification combined with a cross-linking process of polysaccharide dextran, fluorescein isothiocyanate dextran, pullulan and fucoidan mixed with ultrasmall superparamagnetic particles of iron oxide. Fluorescent intravital microscopy observation revealed dynamic adsorption and a leukocyte-like behaviour of fucoidan-functionalized microparticles on a calcium ionophore induced an activated endothelial layer of a mouse mesentery vessel. We observed 20times more adherent microparticles on the activated endothelium area after the injection of functionalized microparticles compared to non-functionalized microparticles (197±11 vs. 10±2). This imaging tool was then applied to rats presenting an elastase perfusion model of abdominal aortic aneurysm (AAA) and 7.4T in vivo MRI was performed. Visual analysis of T2(∗)-weighted MR images showed a significant contrast enhancement on the inner wall of the aneurysm from 30min to 2h after the injection. Histological analysis of AAA cryosections revealed microparticles localized inside the aneurysm wall, in the same areas in which immunostaining shows P-selectin expression. The developed leukocyte mimetic imaging tool could therefore be relevant for molecular imaging of vascular diseases and for monitoring biologically active areas prone to rupture in AAA.

Combination-targeting to multiple endothelial cell adhesion molecules modulates binding, endocytosis, and in vivo biodistribution of drug nanocarriers and their therapeutic cargoes

Designing of drug nanocarriers to aid delivery of therapeutics is an expanding field that can improve medical treatments. Nanocarriers are often functionalized with elements that recognize cell-surface molecules involved in subcellular transport to improve targeting and endocytosis of therapeutics. Combination-targeting using several affinity elements further modulates this outcome. The most studied example is endothelial targeting via multiple cell adhesion molecules (CAMs), which mimics the strategy of leukocytes to adhere and traverse the vascular endothelium. Yet, the implications of this strategy on intracellular transport and in vivo biodistribution remain uncharacterized. We examined this using nanocarriers functionalized for dual- or triple-targeting to intercellular, platelet-endothelial, and/or vascular CAMs (ICAM-1, PECAM-1, VCAM-1). These molecules differ in expression level, location, pathological stimulation, and/or endocytic pathway. In endothelial cells, binding of PECAM-1/VCAM-1-targeted nanocarriers was intermediate to single-targeted counterparts and enhanced in disease-like conditions. ICAM-1/PECAM-1-targeted nanocarriers surpassed PECAM-1/VCAM-1 in control, but showed lower selectivity toward disease-like conditions. Triple-targeting resulted in binding similar to ICAM-1/PECAM-1 combination and displayed the highest selectivity in disease-like conditions. All combinations were effectively internalized by the cells, with slightly better performance when targeting receptors of different endocytic pathways. In vivo, ICAM-1/PECAM-1-targeted nanocarriers outperformed PECAM-1/VCAM-1 in control and disease-like conditions, and triple-targeted counterparts slightly enhanced this outcome in some organs. As a result, delivery of a model therapeutic cargo (acid sphingomyelinase, deficient in Niemann-Pick disease A-B) was enhanced to all affected organs by triple-targeted nanocarriers, particularly in disease-like conditions. Therefore, multi-CAM targeting may aid the optimization of some therapeutic nanocarriers, where the combination and multiplicity of the affinity moieties utilized allow modulation of targeting performance.

Vascular targeting of nanocarriers: perplexing aspects of the seemingly straightforward paradigm

Targeted nanomedicine holds promise to find clinical use in many medical areas. Endothelial cells that line the luminal surface of blood vessels represent a key target for treatment of inflammation, ischemia, thrombosis, stroke, and other neurological, cardiovascular, pulmonary, and oncological conditions. In other cases, the endothelium is a barrier for tissue penetration or a victim of adverse effects. Several endothelial surface markers including peptidases (e.g., ACE, APP, and APN) and adhesion molecules (e.g., ICAM-1 and PECAM) have been identified as key targets. Binding of nanocarriers to these molecules enables drug targeting and subsequent penetration into or across the endothelium, offering therapeutic effects that are unattainable by their nontargeted counterparts. We analyze diverse aspects of endothelial nanomedicine including (i) circulation and targeting of carriers with diverse geometries, (ii) multivalent interactions of carrier with endothelium, (iii) anchoring to multiple determinants, (iv) accessibility of binding sites and cellular response to their engagement, (v) role of cell phenotype and microenvironment in targeting, (vi) optimization of targeting by lowering carrier avidity, (vii) endocytosis of multivalent carriers via molecules not implicated in internalization of their ligands, and (viii) modulation of cellular uptake and trafficking by selection of specific epitopes on the target determinant, carrier geometry, and hydrodynamic factors. Refinement of these aspects and improving our understanding of vascular biology and pathology is likely to enable the clinical translation of vascular endothelial targeting of nanocarriers.

Abdominal aortic aneurysms targeted by functionalized polysaccharide microparticles: a new tool for SPECT imaging

Aneurysm diagnostic is nowadays limited by the lack of technology that enables early detection and rupture risk prediction. New non invasive tools for molecular imaging are still required. In the present study, we present an innovative SPECT diagnostic tool for abdominal aortic aneurysm (AAA) produced from injectable polysaccharide microparticles radiolabeled with technetium 99m (^99mTc) and functionalized with fucoidan, a sulfated polysaccharide with the ability to target P-Selectin. P-Selectin is a cell adhesion molecule expressed on activated endothelial cells and platelets which can be found in the thrombus of aneurysms, as well as in other vascular pathologies.

Microparticles with a maximum hydrodynamic diameter of 4 µm were obtained by crosslinking the polysaccharides dextran and pullulan. They were functionalized with fucoidan. In vitro interactions with human activated platelets were assessed by flow cytometry that demonstrated a specific affinity of fucoidan functionalized microparticles for P-Selectin expressed by activated platelets. For in vivo AAA imaging, microparticles were radiolabeled with ^99mTc and intravenously injected into healthy and AAA rats obtained by elastase perfusion through the aorta wall. Animals were scanned by SPECT imaging. A strong contrast enhancement located in the abdominal aorta of AAA rats was obtained, while no signal was obtained in healthy rats or in AAA rats after injection of non-functionalized control microparticles. Histological studies revealed that functionalized radiolabeled polysaccharide microparticles were localized in the AAA wall, in the same location where P-Selectin was expressed.

These microparticles therefore constitute a promising SPECT imaging tool for AAA and potentially for other vascular diseases characterized by P-Selectin expression. Future work will focus on validating the efficiency of the microparticles to diagnose these other pathologies and the different stages of AAA. Incorporation of a therapeutic molecule is also considered.

Heteromultivalent ligand-decoration for actively targeted nanomedicine

Active targeting has become an important component of nanomedicine design where nanovehicles are surface-decorated with cell receptor-specific or disease matrix-specific ligands to enable site-selective binding, retention and delivery of theranostic cargo. In this context, there have been numerous reports regarding surface-modification of nanovehicles with antibodies, antibody fragments, carbohydrates, aptamers and peptides as targeting ligands. However, majority of these reports have focused on using a single type of targeting moiety on the vehicle surface. In any disease development and progression, multiple receptors and proteins are often spatio-temporally upregulated simultaneously and heterogeneously. Rationalizing from this, a significant advantage can be envisioned in targeting multiple entities simultaneously using vehicle co-decoration with multiple types of ligands, to enhance binding activity and targeting specificity. To this end, we present a comprehensive up-to-date review on research endeavors in heteromultivalent ligand-modification of nanovehicles and provide a mechanistic rationale as well as an insightful discussion of this promising area, including findings from our own research.

Targeted Drug Delivery to Endothelial Adhesion Molecules

Endothelial cells represent important targets for therapeutic and diagnostic interventions in many cardiovascular, pulmonary, neurological, inflammatory, and metabolic diseases. Targeted delivery of drugs (especially potent and labile biotherapeutics that require specific subcellular addressing) and imaging probes to endothelium holds promise to improve management of these maladies. In order to achieve this goal, drug cargoes or their carriers including liposomes and polymeric nanoparticles are chemically conjugated or fused using recombinant techniques with affinity ligands of endothelial surface molecules. Cell adhesion molecules, constitutively expressed on the endothelial surface and exposed on the surface of pathologically altered endothelium—selectins, VCAM-1, PECAM-1, and ICAM-1—represent good determinants for such a delivery. In particular, PECAM-1 and ICAM-1 meet criteria of accessibility, safety, and relevance to the (patho)physiological context of treatment of inflammation, ischemia, and thrombosis and offer a unique combination of targeting options including surface anchoring as well as intra- and transcellular targeting, modulated by parameters of the design of drug delivery system and local biological factors including flow and endothelial phenotype. This review includes analysis of these factors and examples of targeting selected classes of therapeutics showing promising results in animal studies, supporting translational potential of these interventions.

The pharmacology of regenerative medicine

Regenerative medicine is a rapidly evolving multidisciplinary, translational research enterprise whose explicit purpose is to advance technologies for the repair and replacement of damaged cells, tissues, and organs. Scientific progress in the field has been steady and expectations for its robust clinical application continue to rise. The major thesis of this review is that the pharmacological sciences will contribute critically to the accelerated translational progress and clinical utility of regenerative medicine technologies. In 2007, we coined the phrase "regenerative pharmacology" to describe the enormous possibilities that could occur at the interface between pharmacology, regenerative medicine, and tissue engineering. The operational definition of regenerative pharmacology is "the application of pharmacological sciences to accelerate, optimize, and characterize (either in vitro or in vivo) the development, maturation, and function of bioengineered and regenerating tissues." As such, regenerative pharmacology seeks to cure disease through restoration of tissue/organ function. This strategy is distinct from standard pharmacotherapy, which is often limited to the amelioration of symptoms. Our goal here is to get pharmacologists more involved in this field of research by exposing them to the tools, opportunities, challenges, and interdisciplinary expertise that will be required to ensure awareness and galvanize involvement. To this end, we illustrate ways in which the pharmacological sciences can drive future innovations in regenerative medicine and tissue engineering and thus help to revolutionize the discovery of curative therapeutics. Hopefully, the broad foundational knowledge provided herein will spark sustained conversations among experts in diverse fields of scientific research to the benefit of all.

Development of quinic acid-conjugated nanoparticles as a drug carrier to solid tumors

Nanometer-sized drug carriers including polymeric nanoparticles (NPs) have been used to increase biodistribution of a drug in tumors, thereby reducing the effective dose of chemotherapy. NPs increase drug delivery to tumors to a certain extent, but the amount reaching tumors is only a small fraction of the total administered NPs because they depend on passive accumulation via the leaky vasculature surrounding tumors. In an attempt to further increase the drug delivery to tumors, we develop a polymeric NP system that interacts with an endothelial tumor marker. The NPs are decorated with quinic acid, a synthetic mimic of sialyl Lewis-x, which binds to E-selectin, overexpressed on the surface of endothelial cells surrounding solid tumors. The NPs selectively bind to endothelial cells activated with tumor necrosis factor-α, with weak affinity at a relatively high shear stress. These properties may help NPs reach tumors by increasing the encounter of NPs with the peritumoral endothelium without hindering subsequent transport of the NPs.

Adhesive interaction of functionalized particles and endothelium in idealized microvascular networks

OBJECTIVE

Leukocytes play a key role in the early response to tissue injury/infection resulting from physical, chemical or biological stimuli. This process involves the initiation of the leukocyte adhesion cascade mediated by a series of interactions between receptors and ligands on the endothelium and the leukocytes. Here, we characterize the adhesion profile of functionalized particles under physiological flow conditions in an idealized synthetic microvascular network (SMN) characterized by a bifurcation. We hypothesize that differences in the level of adhesion of functionalized particles in bifurcating SMNs are dependent on the ratio of adhesion molecules on the particles as well as geometric features of the in vitro networks.

METHODS

Functionalized particles were prepared by coating their surfaces with different ratios of antibodies against ICAM-1 and E-selectin (aICAM-1:aE-selectin=100:0, 70:30, 50:50, 30:70, and 0:100). The adhesion of functionalized particles to 4h TNF-α activated human umbilical vein endothelial cells under shear flow (0.5, 2, and 4dyn/cm(2)) in bifurcating SMNs and in a parallel plate flow chamber was then quantified.

RESULTS

The level of adhesion of 50:50 aICAM-1:aE-selectin particles was significantly higher compared to other particles in the bifurcating SMNs (~1.5-4 fold higher). However, in the parallel plate flow chamber 70:30 aICAM-1:aE-selectin particles exhibited a significantly higher level of adhesion (~1.5-2.5 fold higher). Furthermore, the adhesion of particles in junction regions was about 3-18 fold higher than that in straight sections of the SMNs. As expected, in straight sections of the SMNs and in the parallel plate flow chamber particle adhesion increased with decreasing shear. However, particle adhesion did not change significantly with decreasing shear at the junction regions of SMNs for all functionalized particles.

CONCLUSION

Adhesion efficiency of functionalized particles is significantly affected by cell-adhesion molecule ratio density as well as geometric features of the vessels. Moreover, the differential adhesion patterns of particles between straight sections of bifurcating SMNs and parallel plate flow chamber, as well as straight sections and junction regions of bifurcating SMNs, indicates that adhesion profile of particles is highly dependent on the vascular geometry of the system used.

A platelet-mimetic paradigm for metastasis-targeted nanomedicine platforms

There is compelling evidence that, beyond their traditional role in hemostasis and thrombosis, platelets play a significant role in mediating hematologic mechanisms of tumor metastasis by directly and indirectly interacting with pro-metastatic cancer cells. With this rationale, we hypothesized that platelets can be an effective paradigm to develop nanomedicine platforms that utilize platelet-mimetic interaction mechanisms for targeted diagnosis and therapy of metastatic cancer cells. Here we report on our investigation of the development of nanoconstructs that interact with metastatic cancer cells via platelet-mimetic heteromultivalent ligand-receptor pathways. For our studies, pro-metastatic human breast cancer cell line MDA-MB-231 was studied for its surface expression of platelet-interactive receptors, in comparison to another low-metastatic human breast cancer cell line, MCF-7. Certain platelet-interactive receptors were found to be significantly overexpressed on the MDA-MB-231 cells, and these cells showed significantly enhanced binding interactions with active platelets compared to MCF-7 cells. Based upon these observations, two specific receptor interactions were selected, and corresponding ligands were engineered onto the surface of liposomes as model nanoconstructs, to enable platelet-mimetic binding to the cancer cells. Our model platelet-mimetic liposomal constructs showed enhanced targeting and attachment of MDA-MB-231 cells compared to the MCF-7 cells. These results demonstrate the promise of utilizing platelet-mimetic constructs in modifying nanovehicle constructs for metastasis-targeted drug as well as modifying surfaces for ex-vivo cell enrichment diagnostic technologies.

Effects of Amyloid Beta Peptide on Neurovascular Cells

Alzheimer’s disease (AD) is a chronic neurodegenerative disorder, which is characterized by the accumulation of amyloid plaques and neurofibrillary tangles in specific regions of the brain, accompanied by impairment of the neurons, and progressive deterioration of cognition and memory of affected individuals. Although the cause and progression of AD are still not well understood, the amyloid hypothesis is dominant and widely accepted. According to this hypothesis, an increased deposition of amyloid-β peptide (Aβ) in the brain is the main cause of the AD’s onset and progression. There is increasing body of evidence that blood-brain barrier (BBB) dysfunction plays an important role in the development of AD, and may even precede neuron degeneration in AD brain. In the early stage of AD, microvasculature deficiencies, inflammatory reactions, surrounding the cerebral vasculature and endothelial dysfunctions are commonly observed. Continuous neurovascular degeneration and accumulation of Aβ on blood vessels resulting in cerebral amyloid angiopathy is associated with further progression of the disease and cognitive decline. However, little is known about molecular mechanisms that underlie Aβ induced damage of neurovascular cells. In this regards, this review is aimed to address how Aβ impacts the cerebral endothelium. Understanding the cellular pathways triggered by Aβ leading to alterations in cerebral endothelial cells structure and functions would provide insights into the mechanism of BBB dysfunction and inflammatory processes in Alzheimer’s, and may offer new approaches for prevention and treatment strategies for AD.

Towards an artificial cell

We are on the verge of producing "synthetic cells," or protocells, in which some, many or all of the tasks of a real biological cell are harnessed into a synthetic platform. Such advances are made possible through genetic engineering, microfabrication technologies, and the development of cellular membranes from new surfactants that extend beyond phospholipids in stability and chemical control, and can be used to introduce designer functionality into membranes and cells. We review some of the recent advances in the development of synthetic cells and suggest future exciting directions.

Biomimetic delivery with micro- and nanoparticles

The nascent field of biomimetic delivery with micro- and nanoparticles (MNP) has advanced considerably in recent years. Drawing inspiration from the ways that cells communicate in the body, several different modes of "delivery" (i.e., temporospatial presentation of biological signals) have been investigated in a number of therapeutic contexts. In particular, this review focuses on (1) controlled release formulations that deliver natural soluble factors with physiologically relevant temporal context, (2) presentation of surface-bound ligands to cells, with spatial organization of ligands ranging from isotropic to dynamically anisotropic, and (3) physical properties of particles, including size, shape and mechanical stiffness, which mimic those of natural cells. Importantly, the context provided by multimodal, or multifactor delivery represents a key element of most biomimetic MNP systems, a concept illustrated by an analogy to human interpersonal communication. Regulatory implications of increasingly sophisticated and "cell-like" biomimetic MNP systems are also discussed.

Targeting of ICAM-1 on vascular endothelium under static and shear stress conditions using a liposomal Gd-based MRI contrast agent

BACKGROUND

The upregulation of intercellular adhesion molecule-1 (ICAM-1) on the endothelium of blood vessels in response to pro-inflammatory stimuli is of major importance for the regulation of local inflammation in cardiovascular diseases such as atherosclerosis, myocardial infarction and stroke. In vivo molecular imaging of ICAM-1 will improve diagnosis and follow-up of patients by non-invasive monitoring of the progression of inflammation.

RESULTS

A paramagnetic liposomal contrast agent functionalized with anti-ICAM-1 antibodies for multimodal magnetic resonance imaging (MRI) and fluorescence imaging of endothelial ICAM-1 expression is presented. The ICAM-1-targeted liposomes were extensively characterized in terms of size, morphology, relaxivity and the ability for binding to ICAM-1-expressing endothelial cells in vitro. ICAM-1-targeted liposomes exhibited strong binding to endothelial cells that depended on both the ICAM-1 expression level and the concentration of liposomes. The liposomes had a high longitudinal and transversal relaxivity, which enabled differentiation between basal and upregulated levels of ICAM-1 expression by MRI. The liposome affinity for ICAM-1 was preserved in the competing presence of leukocytes and under physiological flow conditions.

CONCLUSION

This liposomal contrast agent displays great potential for in vivo MRI of inflammation-related ICAM-1 expression.

Multifactorial determinants that govern nanoparticle uptake by human endothelial cells under flow

Vascular endothelium is a potential target for therapeutic intervention in diverse pathological processes, including inflammation, atherosclerosis, and thrombosis. By virtue of their intravascular topography, endothelial cells are exposed to dynamically changing mechanical forces that are generated by blood flow. In the present study, we investigated the interactions of negatively charged 2.7 nm and 4.7 nm CdTe quantum dots and 50 nm silica particles with cultured endothelial cells under regulated shear stress (SS) conditions. Cultured cells within the engineered microfluidic channels were exposed to nanoparticles under static condition or under low, medium, and high SS rates (0.05, 0.1, and 0.5 Pa, respectively). Vascular inflammation and associated endothelial damage were simulated by treatment with tumor necrosis factor-α (TNF-α) or by compromising the cell membrane with the use of low Triton X-100 concentration. Our results demonstrate that SS is critical for nanoparticle uptake by endothelial cells. Maximal uptake was registered at the SS rate of 0.05 Pa. By contrast, endothelial exposure to mild detergents or TNF-α treatment had no significant effect on nanoparticle uptake. Atomic force microscopy demonstrated the increased formation of actin-based cytoskeletal structures, including stress fibers and membrane ruffles, which have been associated with nanoparticle endocytosis. In conclusion, the combinatorial effects of SS rates, vascular endothelial conditions, and nanoparticle physical and chemical properties must be taken into account for the successful design of nanoparticle-drug conjugates intended for parenteral delivery.

Dual functionalized PVA hydrogels that adhere endothelial cells synergistically

Cell adhesion molecules govern leukocyte-endothelial cell (EC) interactions that are essential in regulating leukocyte recruitment, adhesion, and transmigration in areas of inflammation. In this paper, we synthesized hydrogel matrices modified with antibodies against vascular cell adhesion molecule-1 (VCAM1) and endothelial leukocyte adhesion molecule-1 (E-Selectin) to mimic leukocyte-EC interactions. Adhesion of human umbilical vein ECs to polyvinyl alcohol (PVA) hydrogels was examined as a function of the relative antibody ratio (anti-VCAM1:anti-E-Selectin) and substrate elasticity. Variation of PVA backbone methacrylation was used to affect hydrogel matrix stiffness, ranging from 130 to 720 kPa. Greater EC adhesion was observed on hydrogels presenting 1:1 anti-VCAM1:anti-E-Selectin than on gels presenting either arginine-glycine-asparagine (RGD) peptide, anti-VCAM1, or anti-E-Selectin alone. Engineered cell adhesion - based on complementing the EC surface presentation - may be used to increase the strength of EC-matrix interactions. Hydrogels with tunable and synergistic adhesion may be useful in vascular remodeling.

Biodegradable nanoparticles mimicking platelet binding as a targeted and controlled drug delivery system

This research aims to develop targeted nanoparticles as drug carriers to the injured arterial wall under fluid shear stress by mimicking the natural binding ability of platelets via interactions of glycoprotein Ib-alpha (GPIbα) of platelets with P-selectin of damaged endothelial cells (ECs) and/or with von Willebrand factor (vWF) of the subendothelium. Drug-loaded poly(d,l-lactic-co-glycolic acid) (PLGA) nanoparticles were formulated using a standard emulsion method and conjugated with glycocalicin, the external fraction of platelet GPIbα, via carbodiimide chemistry. Surface-coated and cellular uptake studies in ECs showed that conjugation of PLGA nanoparticles, with GPIb, significantly increased nanoparticle adhesion to P-selectin- and vWF-coated surfaces as well as nanoparticle uptake by activated ECs under fluid shear stresses. In addition, effects of nanoparticle size and shear stress on adhesion efficiency were characterized through parallel flow chamber studies. The observed decrease in bound nanoparticle density with increased particle sizes and shear stresses is also explained through a computational model. Our results demonstrate that the GPIb-conjugated PLGA nanoparticles can be used as a targeted and controlled drug delivery system under flow conditions at the site of vascular injury.

Complementary targeting of liposomes to IL-1α and TNF-α activated endothelial cells via the transient expression of VCAM1 and E-selectin

Inflammation is in part defined by the transient upregulation of cell adhesion molecules on the surface of endothelial cells (ECs) in response to cytokines. We hypothesized that liposomes with a complementary surface presentation of antibodies to the pattern of molecules on the EC surface may enhance targeting. We quantified the expression of vascular cell adhesion molecule-1 (VCAM1) and endothelial leukocyte cell adhesion molecule-1 (E-selectin) on ECs upon exposure to either tumor necrosis factor-α (TNF-α) or interleukin-1α (IL-1α) as a function of time. Liposomes, composed of 95 mol% dioleoyl phosphatidylcholine (DOPC) and 5 mol% dodecanyl phosphatidylethanolamine (N-dod-PE), were prepared by conjugating different molar ratios of antibodies against VCAM1 (aVCAM1) and E-selectin (aE-selectin). Increased binding was observed when immunoliposomes complemented the presentation of VCAM1:E-selectin expressed on TNF-α activated ECs. The 1:1 aVCAM1:aE-selectin liposomes had maximal binding at both 6 and 24 h on IL-1α activated ECs due to differences in molecular organization. The results demonstrate that liposomes targeting to inflamed endothelium may be optimized by exploiting the dynamic expression of VCAM1 and E-selectin on the EC surface.

Targeting therapeutics to the vascular wall in atherosclerosis--carrier size matters

OBJECTIVE

Vascular-targeted imaging and drug delivery systems are promising for the treatment of atherosclerosis due to the vast involvement of endothelium in the initiation and growth of plaque. Herein, we investigated the role of particle size in dictating the ability of vascular-targeted spherical particles to interact with the vascular wall (VW) from pulsatile and recirculating human blood flow relevant in atherosclerosis.

METHODS

In vitro parallel plate flow chambers (PPFC) with straight or vertical step channel were used to examine the localization and binding efficiency of inflammation-targeted polymeric spheres sized from 0.2 to 5 μm to inflamed endothelium from disturbed reconstituted and whole blood flow. Apolipoprotein deficient mice were used to study particle localization and binding to plaque in vivo.

RESULTS

The efficiency of particle binding in disturbed reconstituted blood flow increases as spherical diameter increases from 500 nm to 5 μm. No significant difference was observed between adhesion of 200 nm and 500 nm spheres. Binding efficiency for all particle size was enhanced in disturbed whole blood flow except adhesion of 5 μm in pulsatile whole blood. The adhesion trend in the in vivo model confirmed the binding pattern observed in in vitro assays.

CONCLUSIONS

The presented data shows that the binding efficiency of vascular-targeted drug carriers in blood flow is a function of particle size, wall shear rate, flow type, blood composition and ligand characteristics. Overall, the presented results suggest that micron-sized spherical particles (2 μm), not nanospheres, are optimal for vascular-targeted drug delivery applications in medium to large vessel relevant in atherosclerosis.

Antibody-immobilized column for quick cell separation based on cell rolling

Cell separation using methodological standards that ensure high purity is a very important step in cell transplantation for regenerative medicine and for stem cell research. A separation protocol using magnetic beads has been widely used for cell separation to isolate negative and positive cells. However, not only the surface marker pattern, e.g., negative or positive, but also the density of a cell depends on its developmental stage and differentiation ability. Rapid and label-free separation procedures based on surface marker density are the focus of our interest. In this study, we have successfully developed an antiCD34 antibody-immobilized cell-rolling column, that can separate cells depending on the CD34 density of the cell surfaces. Various conditions for the cell-rolling column were optimized including graft copolymerization, and adjustment of the column tilt angle, and medium flow rate. Using CD34-positive and -negative cell lines, the cell separation potential of the column was established. We observed a difference in the rolling velocities between CD34-positive and CD34-negative cells on antibody-immobilized microfluidic device. Cell separation was achieved by tilting the surface 20 degrees and the increasing medium flow. Surface marker characteristics of the isolated cells in each fraction were analyzed using a cell-sorting system, and it was found that populations containing high density of CD34 were eluted in the delayed fractions. These results demonstrate that cells with a given surface marker density can be continuously separated using the cell rolling column.

Shear-regulated uptake of nanoparticles by endothelial cells and development of endothelial-targeting nanoparticles

The purpose of this research project was to develop nanoparticles with improved targeting, adhesion, and cellular uptake to activated or inflamed endothelial cells (ECs) under physiological flow conditions. Our hypothesis is that by mimicking platelet binding to activated ECs through the interaction between platelet glycoprotein Ibalpha (GP Ibalpha) and P-selectin on activated endothelial cells, GP Ibalpha-conjugated nanoparticles could exhibit increased targeting and higher cellular uptake in injured or activated endothelial cells under physiological flow conditions. To test this hypothesis, fluorescent-carboxylated polystyrene nanoparticles were selected for the study as a model particle because of its narrow size distribution as a "proof-of-concept." Using confocal microscopy, fluorescent measurements, and protein assays, cellular uptake properties were characterized for these polystyrene nanoparticles. The study also found that conjugation of 100-nm polystyrene nanoparticles with glycocalicin (the extracellular segment of GP Ibalpha) significantly increased the particle adhesion on P-selectin-coated surfaces and cellular uptake of nanoparticles by activated endothelial cells under physiological flow conditions. The results demonstrate that these novel endothelial-targeting nanoparticles could be the first step toward developing a targeted and sustained drug delivery system that can improve shear-regulated particle adhesion and cellular uptake.