Size-dependent intracellular immunotargeting of therapeutic cargoes into endothelial cells

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.

Nucleic Acid Delivery to the Vascular Endothelium

This Review examines the state-of-the-art in the delivery of nucleic acid therapies that are directed to the vascular endothelium. First, we review the most important homeostatic functions and properties of the vascular endothelium and summarize the nucleic acid tools that are currently available for gene therapy and nucleic acid delivery. Second, we consider the opportunities available with the endothelium as a therapeutic target and the experimental models that exist to evaluate the potential of those opportunities. Finally, we review the progress to date from investigations that are directly targeting the vascular endothelium: for vascular disease, for peri-transplant therapy, for angiogenic therapies, for pulmonary endothelial disease, and for the blood-brain barrier, ending with a summary of the future outlook in this field.

Polymeric Delivery of Therapeutic Nucleic Acids

The advent of genome editing has transformed the therapeutic landscape for several debilitating diseases, and the clinical outlook for gene therapeutics has never been more promising. The therapeutic potential of nucleic acids has been limited by a reliance on engineered viral vectors for delivery. Chemically defined polymers can remediate technological, regulatory, and clinical challenges associated with viral modes of gene delivery. Because of their scalability, versatility, and exquisite tunability, polymers are ideal biomaterial platforms for delivering nucleic acid payloads efficiently while minimizing immune response and cellular toxicity. While polymeric gene delivery has progressed significantly in the past four decades, clinical translation of polymeric vehicles faces several formidable challenges. The aim of our Account is to illustrate diverse concepts in designing polymeric vectors towards meeting therapeutic goals of in vivo and ex vivo gene therapy. Here, we highlight several classes of polymers employed in gene delivery and summarize the recent work on understanding the contributions of chemical and architectural design parameters. We touch upon characterization methods used to visualize and understand events transpiring at the interfaces between polymer, nucleic acids, and the physiological environment. We conclude that interdisciplinary approaches and methodologies motivated by fundamental questions are key to designing high-performing polymeric vehicles for gene therapy.

Temporally distinct myeloid cell responses mediate damage and repair after cerebrovascular injury

Cerebrovascular injuries can cause severe edema and inflammation that adversely affect human health. Here, we observed that recanalization after successful endovascular thrombectomy for acute large vessel occlusion was associated with cerebral edema and poor clinical outcomes in patients who experienced hemorrhagic transformation. To understand this process, we developed a cerebrovascular injury model using transcranial ultrasound that enabled spatiotemporal evaluation of resident and peripheral myeloid cells. We discovered that injurious and reparative responses diverged based on time and cellular origin. Resident microglia initially stabilized damaged vessels in a purinergic receptor-dependent manner, which was followed by an influx of myelomonocytic cells that caused severe edema. Prolonged blockade of myeloid cell recruitment with anti-adhesion molecule therapy prevented severe edema but also promoted neuronal destruction and fibrosis by interfering with vascular repair subsequently orchestrated by proinflammatory monocytes and proangiogenic repair-associated microglia (RAM). These data demonstrate how temporally distinct myeloid cell responses can contain, exacerbate and ultimately repair a cerebrovascular injury.

Spherical Gold Nanoparticles: Small Interfering RNA Delivery in Regulation of the Tumor Necrosis Factor-Alpha Gene Expression

Proinflammatory cytokines are signaling molecules that are expelled from immune cells like macrophages and other types of cells. Tumor necrosis factor-alpha (TNF-α) is overexpressed during inflammation caused by inflammatory diseases. Therefore, the regulation of TNF-α has a key role in inflammation. The use and target delivery of small interfering RNAs (siRNAs) provide many effectual treatment benefits in the regulation of gene expression in cells. In this study, we used siRNA nanoparticle conjugates in the regulation of gene expression and inflammation. We first prepared safe fusion ribonucleic acid interference carrier, spherical nucleic acid nanoparticle conjugates (SNA-NCs), to enhance the perforation of siRNA into the macrophages and their ability to target TNF-α gene regulation. Furthermore, the suppression of the TNF-α gene was monitored after curing macrophages by SNA-NCs. Gene expression was carried out by real-time polymerase chain reaction in cells and the levels of TNF-α were investigated by the enzyme-linked immunosorbent assay (ELISA) method. This study indicated that the SNA-NCs were safe and very stable. TNF-α siRNA could significantly regulate gene expression in cells to form SNA-NCs. The results indicated that TNF-α gene expression downregulated to 93.40% ± 1.45%, 66.06% ± 0.95%, and 35.76% ± 1.09% in the presence of 0.1, 1, and 10 nM siRNA, respectively. The proliferation of macrophages and subsequently expression of TNF-α were significant for the formation of inflammation. These findings showed that the use of SNA-NC siRNA might ameliorate the inflammatory disease by suppression of gene expression and functional activity of macrophage generation.

Application of advances in endocytosis and membrane trafficking to drug delivery

Multidisciplinary research efforts in the field of drug delivery have led to the development of a variety of drug delivery systems (DDS) designed for site-specific delivery of diagnostic and therapeutic agents. Since efficient uptake of drug carriers into target cells is central to effective drug delivery, a comprehensive understanding of the biological pathways for cellular internalization of DDS can facilitate the development of DDS capable of precise tissue targeting and enhanced therapeutic outcomes. Diverse methods have been applied to study the internalization mechanisms responsible for endocytotic uptake of extracellular materials, which are also the principal pathways exploited by many DDS. Chemical inhibitors remain the most commonly used method to explore endocytotic internalization mechanisms, although genetic methods are increasingly accessible and may constitute more specific approaches. This review highlights the molecular basis of internalization pathways most relevant to internalization of DDS, and the principal methods used to study each route. This review also showcases examples of DDS that are internalized by each route, and reviews the general effects of biophysical properties of DDS on the internalization efficiency. Finally, options for intracellular trafficking and targeting of internalized DDS are briefly reviewed, representing an additional opportunity for multi-level targeting to achieve further specificity and therapeutic efficacy.

Conventional and Nanotechnology Based Approaches to Combat Chronic Obstructive Pulmonary Disease: Implications for Chronic Airway Diseases

Chronic obstructive pulmonary disease (COPD) is the most prevalent obstructive lung disease worldwide characterized by decline in lung function. It is associated with airway obstruction, oxidative stress, chronic inflammation, mucus hypersecretion, and enhanced autophagy and cellular senescence. Cigarette smoke being the major risk factor, other secondary risk factors such as the exposure to air pollutants, occupational exposure to gases and fumes in developing countries, also contribute to the pathogenesis of COPD. Conventional therapeutic strategies of COPD are based on anti-oxidant and anti-inflammatory drugs. However, traditional anti-oxidant pharmacological therapies are commonly used to alleviate the impact of COPD as they have many associated repercussions such as low diffusion rate and inappropriate drug pharmacokinetics. Recent advances in nanotechnology and stem cell research have shed new light on the current treatment of chronic airway disease. This review is focused on some of the anti-oxidant therapies currently used in the treatment and management of COPD with more emphasis on the recent advances in nanotechnology-based therapeutics including stem cell and gene therapy approaches for the treatment of chronic airway disease such as COPD and asthma.

Sticking to the Problem: Engineering Adhesion in Molecular Endoscopic Imaging

Cancers of the digestive tract cause nearly one quarter of the cancer deaths worldwide, and nearly half of these are due to cancers of the esophagus and colon. Early detection of cancer significantly increases the rate of survival, and thus it is critical that cancer within these organs is detected early. In this regard, endoscopy is routinely used to screen for transforming/cancerous (i.e. dysplastic to fully cancerous) tissue. Numerous studies have revealed that the biochemistry of the luminal surface of such tissue within the colon and esophagus becomes altered throughout disease progression. Molecular endoscopic imaging (MEI), an emerging technology, seeks to exploit these changes for the early detection of cancer. The general approach for MEI is as follows: the luminal surface of an organ is exposed to molecular ligands, or particulate probes bearing a ligand, cognate to biochemistry unique to pre-cancerous/cancerous tissue. After a wash, the tissue is imaged to determine the presence of the probes. Detection of the probes post-washing suggests pathologic tissue. In the current review we provide a succinct, but extensive, review of ligands and target moieties that could be, or are currently being investigated, as possible cognate chemistries for MEI. This is followed by a review of the biophysics that determines, in large part, the success of a particular MEI design. The work draws an analogy between MEI and the well-advanced field of cell adhesion and provides a road map for engineering MEI to achieve assays that yield highly selective recognition of transforming/cancerous tissue in situ.

Spatially controlled assembly of affinity ligand and enzyme cargo enables targeting ferritin nanocarriers to caveolae

One of the goals of nanomedicine is targeted delivery of therapeutic enzymes to the sub-cellular compartments where their action is needed. Endothelial caveolae-derived endosomes represent an important yet challenging destination for targeting, in part due to smaller size of the entry aperture of caveolae (ca. 30-50 nm). Here, we designed modular, multi-molecular, ferritin-based nanocarriers with uniform size (20 nm diameter) for easy drug-loading and targeted delivery of enzymatic cargo to these specific vesicles. These nanocarriers targeted to caveolar Plasmalemmal Vesicle-Associated Protein (Plvap) deliver superoxide dismutase (SOD) into endosomes in endothelial cells, the specific site of influx of superoxide mediating by such pro-inflammatory signaling as some cytokines and lipopolysaccharide (LPS). Cell studies showed efficient internalization of Plvap-targeted SOD-loaded nanocarriers followed by dissociation from caveolin-containing vesicles and intracellular transport to endosomes. The nanocarriers had a profound protective anti-inflammatory effect in an animal model of LPS-induced inflammation, in agreement with the characteristics of their endothelial uptake and intracellular transport, indicating that these novel, targeted nanocarriers provide an advantageous platform for caveolae-dependent delivery of biotherapeutics.

Unintended effects of drug carriers: Big issues of small particles

Humoral and cellular host defense mechanisms including diverse phagocytes, leukocytes, and immune cells have evolved over millions of years to protect the body from microbes and other external and internal threats. These policing forces recognize engineered sub-micron drug delivery systems (DDS) as such a threat, and react accordingly. This leads to impediment of the therapeutic action, extensively studied and discussed in the literature. Here, we focus on side effects of DDS interactions with host defenses. We argue that for nanomedicine to reach its clinical potential, the field must redouble its efforts in understanding the interaction between drug delivery systems and the host defenses, so that we can engineer safer interventions with the greatest potential for clinical success.

Targeting superoxide dismutase to endothelial caveolae profoundly alleviates inflammation caused by endotoxin

Inflammatory mediators binding to Toll-Like receptors (TLR) induce an influx of superoxide anion in the ensuing endosomes. In endothelial cells, endosomal surplus of superoxide causes pro-inflammatory activation and TLR4 agonists act preferentially via caveolae-derived endosomes. To test the hypothesis that SOD delivery to caveolae may specifically inhibit this pathological pathway, we conjugated SOD with antibodies (Ab/SOD, size ~10nm) to plasmalemmal vesicle-associated protein (Plvap) that is specifically localized to endothelial caveolae in vivo and compared its effects to non-caveolar target CD31/PECAM-1. Plvap Ab/SOD bound to endothelial cells in culture with much lower efficacy than CD31 Ab/SOD, yet blocked the effects of LPS signaling with higher efficiency than CD31 Ab/SOD. Disruption of cholesterol-rich membrane domains by filipin inhibits Plvap Ab/SOD endocytosis and LPS signaling, implicating the caveolae-dependent pathway(s) in both processes. Both Ab/SOD conjugates targeted to Plvap and CD31 accumulated in the lungs after IV injection in mice, but the former more profoundly inhibited LPS-induced pulmonary inflammation and elevation of plasma level of interferon-beta and -gamma and interleukin-27. Taken together, these results indicate that targeted delivery of SOD to specific cellular compartments may offer effective, mechanistically precise interception of pro-inflammatory signaling mediated by reactive oxygen species.

Removal of ligand-bound liposomes from cell surfaces by microbubbles exposed to ultrasound

Gas-filled microbubbles attached to cell surfaces can interact with focused ultrasound to create microstreaming of nearby fluid. We directly observed the ultrasound/microbubble interaction and documented that under certain conditions fluorescent particles that were attached to the surface of live cells could be removed. Fluorescently labeled liposomes that were larger than 500 nm in diameter were attached to the surface of endothelial cells using cRGD targeting to αvβ3 integrin. Microbubbles were attached to the surface of the cells through electrostatic interactions. Images taken before and after the ultrasound exposure were compared to document the effects on the liposomes. When exposed to ultrasound with peak negative pressure of 0.8 MPa, single microbubbles and groups of isolated microbubbles were observed to remove targeted liposomes from the cell surface. Liposomes were removed from a region on the cell surface that averaged 33.1 μm in diameter. The maximum distance between a single microbubble and a detached liposome was 34.5 μm. Single microbubbles were shown to be able to remove liposomes from over half the surface of a cell. The distance over which liposomes were removed was significantly dependent on the resting diameter of the microbubble. Clusters of adjoining microbubbles were not seen to remove liposomes. These observations demonstrate that the fluid shear forces generated by the ultrasound/microbubble interaction can remove liposomes from the surfaces of cells over distances that are greater than the diameter of the microbubble.

Influence of PECAM-1 ligand interactions on PECAM-1-dependent cell motility and filopodia extension

Platelet endothelial cell adhesion molecule (PECAM‐1) has been implicated in angiogenesis through processes that involve stimulation of endothelial cell motility. Previous studies suggest that PECAM‐1 tyrosine phosphorylation mediates the recruitment and then activation of the tyrosine phosphatase SHP‐2, which in turn promotes the turnover of focal adhesions and the extension of filopodia, processes critical to cell motility. While these studies have implicated PECAM‐1‐dependent signaling in PECAM‐1‐mediated cell motility, the involvement of PECAM‐1 ligand binding in cell migration is undefined. Therefore to investigate the role of PECAM‐1 binding interactions in cell motility, mutants of PECAM‐1 were generated in which either homophilic or heparin/glycosaminoglycan (GAG)‐mediated heterophilic binding had been disabled and then expressed in an endothelial cell surrogate. We found that the ability of PECAM‐1 to stimulate cell migration, promote filopodia formation and trigger Cdc42 activation were lost if PECAM‐1‐dependent homophilic or heparin/GAG‐dependent heterophilic ligand binding was disabled. We further observed that PECAM‐1 concentrated at the tips of extended filopodia, an activity that was diminished if homophilic, but not heparin/GAG‐mediated heterophilic binding had been disrupted. Similar patterns of activities were seen in mouse endothelial cells treated with antibodies that specifically block PECAM‐1‐dependent homophilic or heterophilic adhesion. Together these data provide evidence for the differential involvement of PECAM‐1‐ligand interactions in PECAM‐1‐dependent motility and the extension of filopodia.

Biophysically inspired model for functionalized nanocarrier adhesion to cell surface: roles of protein expression and mechanical factors

In order to achieve selective targeting of affinity-ligand coated nanoparticles to the target tissue, it is essential to understand the key mechanisms that govern their capture by the target cell. Next-generation pharmacokinetic (PK) models that systematically account for proteomic and mechanical factors can accelerate the design, validation and translation of targeted nanocarriers (NCs) in the clinic. Towards this objective, we have developed a computational model to delineate the roles played by target protein expression and mechanical factors of the target cell membrane in determining the avidity of functionalized NCs to live cells. Model results show quantitative agreement with in vivo experiments when specific and non-specific contributions to NC binding are taken into account. The specific contributions are accounted for through extensive simulations of multivalent receptor-ligand interactions, membrane mechanics and entropic factors such as membrane undulations and receptor translation. The computed NC avidity is strongly dependent on ligand density, receptor expression, bending mechanics of the target cell membrane, as well as entropic factors associated with the membrane and the receptor motion. Our computational model can predict the in vivo targeting levels of the intracellular adhesion molecule-1 (ICAM1)-coated NCs targeted to the lung, heart, kidney, liver and spleen of mouse, when the contributions due to endothelial capture are accounted for. The effect of other cells (such as monocytes, etc.) do not improve the model predictions at steady state. We demonstrate the predictive utility of our model by predicting partitioning coefficients of functionalized NCs in mice and human tissues and report the statistical accuracy of our model predictions under different scenarios.

Size and targeting to PECAM vs ICAM control endothelial delivery, internalization and protective effect of multimolecular SOD conjugates

Controlled endothelial delivery of SOD may alleviate abnormal local surplus of superoxide involved in ischemia-reperfusion, inflammation and other disease conditions. Targeting SOD to endothelial surface vs. intracellular compartments is desirable to prevent pathological effects of external vs. endogenous superoxide, respectively. Thus, SOD conjugated with antibodies to cell adhesion molecule PECAM (Ab/SOD) inhibits pro-inflammatory signaling mediated by endogenous superoxide produced in the endothelial endosomes in response to cytokines. Here we defined control of surface vs. endosomal delivery and effect of Ab/SOD, focusing on conjugate size and targeting to PECAM vs. ICAM. Ab/SOD enlargement from about 100 to 300nm enhanced amount of cell-bound SOD and protection against extracellular superoxide. In contrast, enlargement inhibited endocytosis of Ab/SOD and diminished mitigation of inflammatory signaling of endothelial superoxide. In addition to size, shape is important: endocytosis of antibody-coated spheres was more effective than that of polymorphous antibody conjugates. Further, targeting to ICAM provides higher endocytic efficacy than targeting to PECAM. ICAM-targeted Ab/SOD more effectively mitigated inflammatory signaling by intracellular superoxide in vitro and in animal models, although total uptake was inferior to that of PECAM-targeted Ab/SOD. Therefore, both geometry and targeting features of Ab/SOD conjugates control delivery to cell surface vs. endosomes for optimal protection against extracellular vs. endosomal oxidative stress, respectively.

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.

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.

Influence of molecular weight of PEG chain on interaction between streptavidin and biotin-PEG-conjugated phospholipids studied with QCM-D

Poly(ethylene glycol)-conjugated phospholipid (PEG-lipid) derivatives spontaneously incorporate into lipid bilayer membranes, thus, they are useful for immobilizing bioactive substances onto cell surfaces. Here, we investigated how the density and molecular weight of PEG molecules influenced immobilization and cellular uptake of a bioactive substance. We analyzed how three biotin-PEG-lipids (1k, 5k, and 40k, with PEG molecular weights: 1kD, 5kD, and 40kD, respectively) interacted with streptavidin on a surface attached to a quartz crystal microbalance with dissipation (QCM-D). We found that the volume excluded by 1k PEG could not effectively prevent adsorption of bovine serum albumin (BSA). In contrast, 5k PEG chains could completely prevent protein adsorption. However, due to strong static repulsion, 40k PEG chains could not be packed at high density. Thus, BSA migrated between PEG chains, and adsorption was not effectively prevented. When streptavidin was added, it bound to multiple neighboring sites on 1k and 5k biotin-PEG-lipids, which reduced chain viscoelasticity. In contrast, streptavidins bound at a one-to-one stoichiometry with the 40k biotin-PEG-lipids, which increased chain viscoelasticity. However, differences in PEG viscoelasticity and PEG molecular weights did not influence cellular uptake of immobilized streptavidin. Therefore, these are not important factors in designing polymers that prevent cellular endocytosis.

STATEMENT OF SIGNIFICANCE

Poly(ethylene glycol)-conjugated phospholipid (PEG-lipid) derivatives have been widely used to modify not only liposome surface, but also the surfaces of cells and pancreatic islets for cell transplantation. Since the entire cell surface can be modified with PEG-lipid through hydrophobic interactions, it is a promising approach for improving graft survival in clinical settings. Although the surface modification is protective in the early stages of transplantation, it is important to understand the factors that influence on the cellular uptake. In this study, we examined the influence of the surface density and molecular weights of PEG-lipids on the cellular uptake by QCM-D and cellular experiments. It was found that the differences in viscoelasticity of PEG chain did not affect on the cellular uptake.

Flow shear stress differentially regulates endothelial uptake of nanocarriers targeted to distinct epitopes of PECAM-1

Targeting nanocarriers (NC) to endothelial cell adhesion molecules including Platelet-Endothelial Cell Adhesion Molecule-1 (PECAM-1 or CD31) improves drug delivery and pharmacotherapy of inflammation, oxidative stress, thrombosis and ischemia in animal models. Recent studies unveiled that hydrodynamic conditions modulate endothelial endocytosis of NC targeted to PECAM-1, but the specificity and mechanism of effects of flow remain unknown. Here we studied the effect of flow on endocytosis by human endothelial cells of NC targeted by monoclonal antibodies Ab62 and Ab37 to distinct epitopes on the distal extracellular domain of PECAM. Flow in the range of 1-8dyn/cm(2), typical for venous vasculature, stimulated the uptake of spherical Ab/NC (~180nm diameter) carrying ~50 vs 200 Ab62 and Ab37 per NC, respectively. Effect of flow was inhibited by disruption of cholesterol-rich plasmalemma domains and deletion of PECAM-1 cytosolic tail. Flow stimulated endocytosis of Ab62/NC and Ab37/NC via eliciting distinct signaling pathways mediated by RhoA/ROCK and Src Family Kinases, respectively. Therefore, flow stimulates endothelial endocytosis of Ab/NC in a PECAM-1 epitope specific manner. Using ligands of binding to distinct epitopes on the same target molecule may enable fine-tuning of intracellular delivery based on the hemodynamic conditions in the vascular area of interest.

The behavior of lipid debris left on cell surfaces from microbubble based ultrasound molecular imaging

Lipid monolayer coated microbubbles are currently being developed to identify vascular regions that express certain surface proteins as part of the new technique of ultrasound molecular imaging. The microbubbles are functionalized with targeting ligands which bind to the desired cells holding the microbubbles in place as the remaining unbound microbubbles are eliminated from circulation. Subsequent scanning with ultrasound can detect the highly reflectant microbubbles that are left behind. The ultrasound scanning and detection process results in the destruction of the microbubble, creating lipid fragments from the monolayer. Here we demonstrate that microbubbles targeted to 4T1 murine breast cancer cells and human umbilical cord endothelial cells leave behind adhered fragments of the lipid monolayer after exposure to ultrasound with peak negative pressures of 0.18 and 0.8MPa. Most of the observed fragments were large enough to be resistant to receptor mediated endocytosis. The fragments were not observed to incorporate into the lipid membrane of the cell over a period of 96min. They were not observed to break into smaller pieces or significantly change shape but they were observed to undergo translation and rotation across the cell surface as the cells migrated over the substrate. These large fragments will apparently remain on the surface of the targeted cells for significant periods of time and need to be considered for their potential effects on blood flow through the microcapillaries and potential for immune system recognition.

Recent advancements in the cardiovascular drug carriers

Cardiovascular disease is the disease that affects the cardiovascular system, vascular diseases of the brain and kidney, and peripheral arterial disease. Despite of all advances in pharmacological and clinical treatment, heart failure is a leading cause of morbidness and mortality worldwide. Many new therapeutic advance strategies, including cell transplantation, gene delivery or therapy, and cytokines or other small molecules, have been research to treat heart failure. The main aim of this review article is to focus on nano carriers advancement and addressing the problems associated with old and modern therapeutics such as nonspecific effects and poor stability.

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.

Nanomedicine as an innovative therapeutic strategy for pediatric lung diseases

Nanomedicine is a rapidly emerging technology and represents an innovative field for therapy. Nanomaterials have intrinsically defined features for biomedical applications due to the high specific surface area, the amazing diversity, versatility in structure and function and the possibility of surface charge. In particular, the functionalization of targeting or stimuli-responsive unit on the surface of these materials gives them specific targeted therapeutic properties. There are many pediatric lung diseases that could potentially benefit from nanomedicine. Herein, we aim to review various drug carrier systems and release systems specifically targeting pediatric lung diseases. The injection of nanomedicine into in vivo models and their elimination will also be discussed. Finally, the potential toxicity of nanomaterials will be addressed.

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.

Nanoparticle geometry and surface orientation influence mode of cellular uptake

In order to engineer safer nanomaterials, there is a need to understand, systematically evaluate, and develop constructs with appropriate cellular uptake and intracellular fates. The overall goal of this project is to determine the uptake patterns of silica nanoparticle geometries in model cells, in order to aid in the identification of the role of geometry on cellular uptake and transport. In our experiments we observed a significant difference in the viability of two phenotypes of primary macrophages; immortalized macrophages exhibited similar patterns. However, both primary and immortalized epithelial cells did not exhibit toxicity profiles. Interestingly uptake of these geometries in all cell lines exhibited very different time-dependent patterns. A screening of a series of chemical inhibitors of endocytosis was performed to isolate the uptake mechanisms of the different particles. The results show that all geometries exhibit very different uptake profiles and that this may be due to the orientation of the nanoparticles when they interact with the cell surface. Additionally, evidence suggests that these uptake patterns initialize different downstream cellular pathways, dependent on cell type and phenotype.

Chemically self-assembled antibody nanostructures as potential drug carriers

Chemically self-assembled antibody nanorings (CSANs) displaying multiple copies of single-chain variable fragments can be prepared from dihydrofolate reductase (DHFR) fusion proteins and bis-methotrexate (bisMTX). We have designed and synthesized a bisMTX chemical dimerizer (bisMTX-NH(2)) that contains a third linker arm that can be conjugated to fluorophores, radiolabels, and drugs. Monovalent, divalent, and higher-order AntiCD3 CSANs were assembled with a fluorescein isothiocyanate (FITC)-labeled bis-methotrexate ligand (bisMTX-FITC) and found to undergo rapid internalization and trafficking by HPB-MLT, a CD3+ T-leukemia cell line, to the early and late endosome and lysosome. Because the fluorescence of bisMTX-FITC when incorporated into CSANs was found to be significantly greater than that of the free ligand, the stability of the endocytosed AntiCD3 CSANs could be monitored. The internalized CSANs were found to be stable for several hours, while treatment with the nontoxic DHFR inhibitor trimethoprim resulted in a rapid loss (>80%) of cellular fluorescence within minutes, consistent with efficient intracellular disassembly of the nanorings. Over longer time periods (24 h), cellular fluorescence decreased by 75-90%, regardless of whether cells had been treated with DMSO or trimethoprim. Although bisMTX is a potent inhibitor of DHFR, it was found to be nontoxic (GI(50) > 20 μM) to HPB-MLT cells. In contrast, AntiCD3 CSANs prepared with bisMTX were found to be at least 13-fold more cytotoxic (GI(50) = 0.5-1.5 μM) than bisMTX at 72 h. Consistent with our findings from CSAN stability studies, no increase in cytotoxicity was observed upon treatment with trimethoprim. Taken together, our results suggest that cell receptor targeting CSANs prepared with trifunctional bisMTX could be used as potential tissue selective drug carriers.

Dynamic factors controlling targeting nanocarriers to vascular endothelium

Endothelium lining the luminal surface of blood vessels is the key target and barrier for vascular drug delivery. Nanocarriers coated with antibodies or affinity peptides that bind specifically to endothelial surface determinants provide targeted delivery of therapeutic cargoes to these cells. Endothelial targeting consists of several phases including circulation in the bloodstream, anchoring on the endothelial surface and, in some cases, intracellular uptake and trafficking of the internalized materials. Dynamic parameters of the vasculature including the blood hydrodynamics as well as surface density, accessibility, membrane mobility and clustering of target determinants modulate these phases of the targeting, especially anchoring to endothelium. Further, such controlled parameters of design of drug nanocarriers such as affinity, surface density and epitope specificity of targeting antibodies, carrier size and shape also modulate endothelial targeting and resultant sub-cellular addressing. This article reviews experimental and computational approaches for analysis of factors modulating targeting nanocarriers to the endothelial cells.

Nanocarriers for vascular delivery of antioxidants

Antioxidant enzymes (AOEs) catalase and superoxide dismutase (SOD) detoxify harmful reactive oxygen species, but the therapeutic utility of AOEs is hindered by inadequate delivery. AOE modification by poly-ethylene glycol (PEG) and encapsulation in PEG-coated liposomes increases the AOE bioavailability and enhances protective effects in animal models. Pluronic-based micelles formed with AOEs show even more potent protective effects. Furthermore, polymeric nanocarriers (PNCs) based on PEG-copolymers protect encapsulated AOEs from proteolysis and improve delivery to the target cells, such as the endothelium lining the vascular lumen. Antibodies to endothelial determinants conjugated to AOEs or AOE carriers provide targeting and intracellular delivery. Targeted liposomes, protein conjugates and magnetic nanoparticles deliver AOEs to sites of vascular oxidative stress in the cardiovascular, pulmonary and nervous systems. Further advances in nanodevices for AOE delivery will provide a basis for the translation of this approach in the clinical domain.

Nanomedicine for the prevention, treatment and imaging of atherosclerosis

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in developed countries, with an increasing prevalence due to an aging population. The pathology underpinning CVD is atherosclerosis, a chronic inflammatory state involving the arterial wall. Accumulation of low density lipoprotein (LDL) laden macrophages in the arterial wall and their subsequent transformation into foam cells lead to atherosclerotic plaque formation. Progression of atherosclerotic lesions may gradually lead to plaque related complications and clinically manifest as acute vascular syndromes including acute myocardial or cerebral ischemia. Nanotechnology offers emerging therapeutic strategies, which may have advantage overclassical treatments for atherosclerosis. In this review, we present the potential applications of nanotechnology toward prevention, identification and treatment of atherosclerosis.

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.

Targeted endothelial delivery of nanosized catalase immunoconjugates protects lung grafts donated after cardiac death

BACKGROUND

Donor organ shortage represents a major problem in lung transplantation. Donation after cardiac death could help to expand the pool of organs, but the additional period of warm ischemia after cardiac arrest aggravates primary graft dysfunction. The pulmonary endothelium of the graft constitutes an important source and target of reactive oxygen species generated during ischemia and reperfusion. Targeted protection of graft pulmonary endothelial cells by the antioxidant enzyme catalase, conjugated with a platelet/endothelial cell adhesion molecule-1 (PECAM-1) antibody to nanosized particles (anti-PECAM/catalase conjugates), might improve outcome in lung transplantation using donors after cardiac death and prolonged hypothermic preservation.

METHODS

Left lung transplantation was performed in 18 pigs. Before cardiac arrest, donors received anti-PECAM/catalase, unconjugated component mixture or vehicle solution. After 90-min warm and 18-hr hypothermic ischemia, lungs were transplanted, and function was assessed during 6 hr after reperfusion. Samples of bronchoalveolar lavage fluid and lung tissue were taken thereafter. Six sham-operated animals served as controls.

RESULTS

During 6-hr reperfusion, anti-PECAM/catalase significantly ameliorated graft function, evidenced by major improvements of gas exchange and reduced intrapulmonary shunt fraction. Furthermore, lipid peroxidation, alveolar leakage, and edema formation were reduced in protected grafts. Similarly moderate lung pathology was seen after transplantation.

CONCLUSIONS

Augmentation of the antioxidant capacity of graft pulmonary endothelial cells with anti-PECAM/catalase nanoparticles represents a straightforward approach to enable a safe transplantation of prolonged preserved donation after cardiac death lungs. Anti-PECAM/catalase protection alleviated oxidative stress and allowed immediate reconstitution of normal gas exchange and pulmonary microcirculation, a prerequisite for improved graft and patient outcome.

Influence of nano-carrier architecture on in vitro siRNA delivery performance and in vivo biodistribution: polyplexes vs micelleplexes

Micelle-based siRNA carriers ("micelleplexes") were prepared from the A-B-C triblock copolymer poly(ethylene glycol)-poly(n-butyl acrylate)-poly(2-(dimethylamino)ethyl methacrylate) (PEG-PnBA-PDMAEMA), and their in vitro performance and in vivo biodistribution properties were compared with the benchmark PEGylated and basic polycation systems PEG-PDMAEMA and PDMAEMA, respectively. The micelle architecture, incorporating increased PEG shielding and a larger particle size (∼50 nm) than polycation-based complexes (polyplexes; ∼10 nm), enhances siRNA delivery performance in two important aspects: in vitro gene silencing efficiency and in vivo tumor accumulation. The in vitro gene silencing efficiency of the micelleplexes (24% in HeLa cells) was significantly better than the statistically insignificant levels observed for PDMAEMA and PEG-PDMAEMA polyplexes under identical conditions. This enhancement is linked to the different mechanisms by which micelleplexes are internalized (i.e., caveolar, etc.) compared to PDMAEMA and PEG-PDMAEMA polyplexes. Folate-functionalization significantly improved micelleplex uptake but had negligible influence on gene-silencing efficiency, suggesting that this parameter is not limited by cellular internalization. In vivo biodistribution analysis revealed that siRNA delivered by micelleplexes was more effectively accumulated and retained in tumor tissues than that delivered by PEGylated polyplexes. Overall, the micelle particle size and architecture appear to improve in vitro and in vivo delivery characteristics without significantly changing other properties, such as cytotoxicity and resistance to enzymes and dissociation. The self-assembled nature of micelleplexes is expected to enable incorporation of imaging modalities inside the hydrophobic micelle core, thus combining therapeutic and diagnostic capabilities. The findings from the present study suggest that the micelleplex-type carrier architecture is a useful platform for potential theranostic and tumor-targeting applications.

Formulation and characterization of catalase in albumin microspheres

Catalase in albumin microspheres were formulated for intravenous administration to antagonize the effects of over-production of reactive oxygenated species (ROS) such as hydrogen peroxide (H(2)O(2)) in septic shock. The aim was to increase effective half-life of catalase and take advantage of the phagocytic uptake of the encapsulated catalase by the vascular endothelium. Catalase microspheres were prepared by spray-drying. The microspheres were evaluated for particle size, particle shape and surface morphology by scanning electron microscopy (SEM), drug encapsulation efficiency, chemical stability, thermal stability and in vitro drug release characteristics. The microspheres had a mean particle size of 4.7 +/- 2 microm, optimal for phagocytic uptake, as demonstrated by Makino et al. SEM revealed that microspheres were spherical with smooth surface morphology. An encapsulation efficiency of 91.5 +/- 3% was achieved and the encapsulated catalase was chemically and thermally stable. Application of in vitro drug release data to the Higuchi kinetic equation indicated matrix diffusion-controlled catalase release from albumin microspheres.

Optimizing endothelial targeting by modulating the antibody density and particle concentration of anti-ICAM coated carriers

Targeting of drug carriers to cell adhesion molecules expressed on endothelial cells (ECs) may improve treatment of diseases involving the vascular endothelium. This is the case for carriers targeted to intercellular adhesion molecule 1 (ICAM-1), an endothelial surface protein overexpressed in many pathologies. In order to optimize our design of anti-ICAM carriers, we have explored in this study the influence of two carrier design parameters on specific and efficient endothelial targeting in vitro and in vivo: carrier dose and density of targeting molecules (antibodies-Ab) on the carrier surface. Using radioisotope tracing we assessed the role of these parameters on the biodistribution of model polymer carriers targeted to ICAM-1 ((125)I-anti-ICAM carriers) in mice. Increasing the carrier dose enhanced specific accumulation in the lung vasculature (a preferential endothelial target) and decreased non-specific hepatic and splenic uptake. Increasing the Ab density enhanced lung accumulation with minimally reduced liver and spleen uptake. These studies account for the influence of blood hydrodynamic forces on carrier binding to endothelium, relevant to arterioles, venules and larger vessels. Yet, carriers may rather bind to the extensive capillary bed where shear stress is minimal. We used fluorescence microscopy to determine binding kinetics of FITC-labeled anti-ICAM carriers in static conditions, at the threshold found in vivo and conditions mimicking low vs high ICAM-1 expression on quiescent vs activated ECs. Binding to activated ECs reached similar saturation with all tested Ab densities and carrier concentrations. In quiescent cells, carriers reached ~3-fold lower binding saturation, even at high carrier concentration and Ab density, and carriers with low Ab density did not reach saturation, reflecting avidity below threshold. Binding kinetics was positively regulated by anti-ICAM carrier concentration and Ab density. Counterintuitively, binding was faster in quiescent ECs (except for carriers with high Ab density and concentration), likely due to fast saturation of fewer binding sites on these cells. These results will guide optimization of ICAM-1-targeted carriers, e.g., in the context of targeting healthy vs diseased endothelium for prophylactic vs therapeutic interventions.

Modulation of endothelial targeting by size of antibody-antioxidant enzyme conjugates

Endothelial targeting of antioxidant enzymes attenuates acute vascular oxidative stress in animal studies. Superoxide dismutase (SOD) and catalase conjugated with antibodies to Platelet-Endothelial Cell Adhesion Molecule-1 (anti-PECAM/SOD and anti-PECAM/catalase) bind to endothelium, accumulate in the pulmonary vasculature, and detoxify reactive oxygen species. In order to define the role of conjugate size in the efficacy and specificity of endothelial targeting, we synthesized anti-PECAM/enzyme conjugates of controlled size (40nm-10,000nm). Binding of anti-PECAM/enzymes to endothelial cells increased with conjugate size from 300nm to 2μm (from 2.5 to 8.5% of bound fraction), and was specific, as conjugates did not bind to PECAM-negative cells. Pulmonary uptake of anti-PECAM/enzyme conjugates injected intravenously in mice also increased from 4.5 to 16% of injected dose for particles from 200 to 800nm. However, control conjugates larger than 300nm showed elevated non-specific pulmonary uptake, indicating that the targeting specificity of anti-PECAM/enzyme conjugates in vivo has a bell-shaped curve with a maximum close to 300-nm diameter. These results show that: i) the size of an antibody/enzyme conjugate modulates efficacy and specificity of targeting, and ii) a size optimum should be defined in vivo to account for parameters that are difficult to model in cell culture.

SHP-2 phosphatase activity is required for PECAM-1-dependent cell motility

Platelet endothelial cell adhesion molecule-1 (PECAM-1) has been implicated in endothelial cell motility during angiogenesis. Although there is evidence that SHP-2 plays a role in PECAM-1-dependent cell motility, the molecular basis of the activity of SHP-2 in this process has not been defined. To investigate the requirement of SHP-2 in PECAM-1-dependent cell motility, studies were done in which various constructs of SHP-2 were expressed in cell transfectants expressing PECAM-1. We observed that the levels of PECAM-1 tyrosine phosphorylation and SHP-2 association with PECAM-1 were significantly increased in cells expressing a phosphatase-inactive SHP-2 mutant, suggesting that the level of PECAM-1 tyrosine phosphorylation, and thus SHP-2 binding are regulated in part by bound, catalytically active SHP-2. We subsequently found that expression of PECAM-1 stimulated wound-induced migration and the formation of filopodia (a morphological feature of motile cells). These activities were associated with increased mitogen-activated protein kinase (MAPK) activation and the dephosphorylation of paxillin (an event implicated in the activation of MAPK). The phosphatase-inactive SHP-2 mutant, however, suppressed these PECAM-1-dependent phenomena, whereas the activity of PECAM-1 expressing cells was not altered by expression of wild-type SHP-2 or SHP-2 in which the scaffold/adaptor function had been disabled. Pharmacological inhibition of SHP-2 phosphatase activity also suppressed PECAM-1-dependent motility. Furthermore, PECAM-1 expression also stimulates tube formation, but none of the SHP-2 constructs affected this process. These findings therefore suggest a model for the involvement of SHP-2 in PECAM-1-dependent motility in which SHP-2, recruited by its interaction with PECAM-1, targets paxillin to ultimately activate the MAPK pathway and downstream events required for cell motility.

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.

Targeting antioxidant and antithrombotic biotherapeutics to endothelium

The endothelium is one of the key targets for pharmacological interventions in oxidative stress and thrombosis, two conditions that are notoriously difficult to treat due to limited efficacy and precision of action of current drugs. Design of molecular and nano-devices that deliver potent antioxidant and antithrombotic therapeutic enzymes to the endothelium holds promise to improve the potency, localization, timing, specificity, safety, and mechanistic precision of these interventions. In particular, cell adhesion molecules expressed on the surface of resting and pathologically altered endothelial cells can be used for drug delivery to the endothelial surface (preferable for thrombolytics) and into intracellular compartments (preferable for antioxidants). Drug delivery platforms including protein conjugates, recombinant fusion constructs, and stealth polymer carriers designed to target these drugs to endothelium are reviewed in this article.

Flow dynamics, binding and detachment of spherical carriers targeted to ICAM-1 on endothelial cells

Vascular drug delivery by administration of carriers targeted to endothelial surface determinants, such as intercellular adhesion molecule (ICAM-1), holds considerable promise to improve disease treatment. As a model to define elusive factors controlling the interplay between carrier motion in the bloodstream and its interactions with molecular targets in the endothelial wall, we used 1 mum beads coated with ICAM-1 monoclonal antibody (Ab) at 370, 1100 or 4100 Ab/microm2. Carriers were perfused at two shear rates over resting or activated endothelial cells, expressing minimum vs. maximum ICAM-1 levels, to determine carrier rolling, binding and detachment. Even at 0.1 Pa and 4100 Ab/microm2, carriers attached only to activated cells (21 fold increase over resting cells), ideal for specific drug targeting to sites of pathology. Binding was increased by raising the Ab surface density on the carrier, e.g., 59.4+/-11.1% increase for carriers having 4100 vs. 1100 Ab/microm2, as a consequence of decreased rolling velocity. Carrier binding was stable even under a high shear stress: carriers with 1100 and 4100 Ab/microm2 withstand shear stress over 3 Pa without detaching from the cells. This is further supported by theoretical modeling. These results will guide vascular targeting of drug carriers via rational design of experimentally tunable parameters.

Nonviral gene vector formation in monodispersed picolitre incubator for consistent gene delivery

A novel picolitre incubator based microfluidic system for consistent nonviral gene carrier formulation is presented. A cationic lipid-based carrier is the most attractive nonviral solution for delivering plasmid DNA, shRNA, or drugs for pharmaceutical research and RNAi applications. The size of the cationic lipid and DNA complex (CL-DNA), or the lipoplex, is one of the important variations for consistency of gene transfection. CL-DNA size, in turn, may be controlled by factors such as the cationic lipid and DNA mixing order, mixing rate, and mixture incubation time. The Picolitre Microfluidic Reactor and Incubator (PMRI) system described here is able to control these parameters in order to create homogeneous CL-DNA. Compared with conventional CL-DNA preparation techniques involving hand-shaking or vortexing, the PMRI system demonstrates a greater ability to constantly and uniformly mix cationic lipids and DNA simultaneously. After mixing in the picolitre droplet reactors, the cationic lipid and DNA is incubated within the picolitre incubator to form CL-DNA. The PMRI generates a narrower size distribution band, while also turning the sample loading, mixing and incubation steps into an integrated process enabling the consistent formation of CL-DNA. The coefficient of variation (CV) of transfection efficiency is 0.05 and 0.30 for PMRI-based and conventional methods, respectively. In addition, this paper demonstrates that the gene transfection efficiency of lipoplex created in the PMRI is more reproducible.

Nanodelivery in airway diseases: challenges and therapeutic applications

This review describes the challenges and therapeutic applications of nanodelivery systems for treatment of airway diseases. Therapeutic applications of nanodelivery in airway diseases involve targeted delivery of DNA, short interfering RNA, drugs, or peptides to hematopoietic progenitor cells and pulmonary epithelium to control chronic pathophysiology of obstructive and conformational disorders. The major challenges to nanodelivery involve physiologic barriers such as mucus and alveolar fluid. It is necessary for the nanoparticles to be biodegradable and capable of providing sustained drug delivery to the selected cell type. Once inside the cell, the nanoparticle should be capable of escaping the endocytic degradation machinery. In addition, for effective gene delivery, nuclear entry and chromosomal integration are critical. The strategies to overcome these pathophysiologic barriers are discussed as an attempt to synchronize the efforts of pulmonary biologists, chemists, and clinicians to develop novel nanodelivery therapeutics for airway diseases.

FROM THE CLINICAL EDITOR

Therapeutic applications of nano-delivery in airway diseases involve targeted delivery of DNA, siRNA, drugs or peptides to hematopoietic progenitor cells and pulmonary epithelium. These nano-particles must be biodegradable, capable of providing sustained drug delivery to specific cells, and should escape the endocytic degradation machinery. For effective gene-delivery they should also provide nuclear entry and chromosomal integration.

Studies of the cellular uptake of hydrogel nanospheres and microspheres by phagocytes, vascular endothelial cells, and smooth muscle cells

Intensive research efforts have been placed on the development of nanospheres for targeted drug delivery for treating a variety of diseases, including coronary restenosis, cancer, and inflammatory reactions. Although most of these drug-bearing spheres are delivered via intravenous administration, little is known about the effect of sphere physical characteristics on the responses of vascular and blood cells. To find the answer, this work was aimed to investigate the cellular uptake of nanosized (100 nm) and microsized hydrogel spheres (1 microm) made of poly(N-isopropylacrylamide) by vascular cells and phagocytes under various flow conditions in vitro. We found that the cellular uptake of nanospheres depended on incubation times and sphere concentrations as well as on the introduced shear stress levels of the medium. Measurements of the intracellular-released fluorescence and confocal fluorescence microscopy revealed that nanospheres were internalized by endothelial cells and smooth muscle cells more than microspheres, whereas microspheres were rapidly taken up by phagocytes, especially at high concentration. Our results strongly suggest that hydrogel nanospheres are more effective as an intravascular delivery system compared to microspheres in the terms of vascular cellular uptake and biocompatibility.