Selective intracellular delivery of dexamethasone into activated endothelial cells using an E-selectin-directed immunoconjugate

Selectin antagonists : therapeutic potential in asthma and COPD

Asthma and COPD are chronic inflammatory conditions that affect hundreds of millions of patients worldwide. New therapeutics are desperately needed, especially those that target the underlying causes and prevent disease progression. Although asthma and COPD have distinct etiologies, both are associated with reduced airflow caused by excess infiltration of inflammatory cells into healthy lung tissues. As selectin-mediated adhesion of leukocytes to the vascular endothelium is a key early event in the initiation of the inflammatory response, selectin inhibition is thought to be a good target for therapeutic intervention.

Three known selectins are expressed in distinct subsets of cells: P-selectin is presented on the surface of activated platelets and endothelial cells, L-selectin is constitutively expressed on leukocytes, and E-selectin synthesis is upregulated in activated endothelial cells. They mediate cell-cell adhesion in the shear flow of the bloodstream via specialized interactions with clusters of oligosaccharides presented on cell surface glycopeptide ligands. The role of selectin-ligand interactions in the inflammatory response has been demonstrated in various animal models, prompting considerable attention from the pharmaceutical industry.

Drug discovery efforts have yielded many different classes of selectin inhibitors, including soluble protein ligands, antibodies, oligosaccharides and small molecules. Although many selectin inhibitors have shown activity in preclinical models, clinical progress of selectin-directed therapies has been slow. Early approaches employed carbohydrate-based inhibitors to mimic the natural ligand sialyl Lewis X; however, these compounds proved challenging to develop. Cytel’s CY 1503, a complex oligosaccharide, progressed to phase II/III trials for reperfusion injury, but further development was halted when it failed to demonstrate clinical efficacy. Two protein-based selectin inhibitors have reached phase II development. These included Wyeth’s recombinant soluble P-selectin ligand, TSI (PSGL-1), which was discontinued after disappointing results in myocardial infarction trials and Protein Design Labs’ humanized anti-L-selectin monoclonal antibody, which is currently in development for trauma. Bimosiamose, discovered by Encysive Pharmaceutical and presently being developed by Revotar Biopharmaceuticals, is an 863 g/mol molecular weight dimer with minimal carbohydrate content and is, to date, the leading selectin inhibitor in clinical development. This compound has shown promise in a phase Ha ‘proof of concept’ trial in patients with asthma, reducing airway recruitment of eosinophils after intravenous administration. Further clinical development of an inhaled formulation is underway.

Despite a significant need for new therapeutics, selectin inhibitors have not yet been explored for the treatment of COPD. Bimosiamose represents an important proof of principle, and hopefully continued success will spark renewed interest in selectin-directed therapeutics for respiratory diseases.

Differential effects of NF-{kappa}B and p38 MAPK inhibitors and combinations thereof on TNF-{alpha}- and IL-1{beta}-induced proinflammatory status of endothelial cells in vitro

Endothelial cells actively participate in inflammatory events by regulating leukocyte recruitment via the expression of inflammatory genes such as E-selectin, VCAM-1, ICAM-1, IL-6, IL-8, and cyclooxygenase (COX)-2. In this study we showed by real-time RT-PCR that activation of human umbilical vein endothelial cells (HUVEC) by TNF-alpha and IL-1beta differentially affected the expression of these inflammatory genes. Combined treatment with TNF-alpha and IL-1beta resulted in nonadditive, additive, and even synergistic induction of expression of VCAM-1, IL-8, and IL-6, respectively. Overexpression of dominant-negative inhibitor kappaB protein blocking NF-kappaB signaling confirmed a major role of this pathway in controlling both TNF-alpha- and IL-1beta-induced expression of most of the genes studied. Although dexamethasone exerted limited effects at 1 muM, the thioredoxin inhibitor MOL-294, which regulates the redox state of NF-kappaB, mainly inhibited adhesion molecule expression. Its most pronounced effect was seen on VCAM-1 mRNA levels, especially in IL-1beta-activated endothelium. One micromolar RWJ-67657, an inhibitor of p38 MAPK activity, diminished TNF-alpha- and IL-1beta-induced expression of IL-6, IL-8, and E-selectin but had little effect on VCAM-1 and ICAM-1. Combined treatment of HUVEC with MOL-294 and RWJ-67657 resulted in significant blocking of the expression of E-selectin, IL-6, IL-8, and COX-2. The inhibitory effects were much stronger than those observed with single drug treatment. Application of combinations of drugs that affect multiple targets in activated endothelial cells may therefore be considered as a potential new therapeutic strategy to inhibit inflammatory disease activity.

Enhanced adhesion of ligand‐conjugated biodegradable particles to colitic venules

The expression of certain endothelial cell adhesion molecules (ECAMs) is increased in the vasculature of the inflamed bowel (e.g., colitis), thereby providing an opportunity for targeted drug delivery. We recently demonstrated that biodegradable particles conjugated with ligands to ECAMs exhibit significant selective adhesion to ECAM expressing endothelium. In the present study, we used a murine model of colitis to determine whether poly(lactic acid)-poly(ethylene glycol) particles conjugated with a VCAM-1 ligand (alpha-V) exhibit enhanced adhesion to colitic vasculature. In post-capillary venules of the colon, significantly more alpha-V particles accumulate in colitic mice relative to (i) control mice (i.e., selectivity) and (ii) particles bearing a control ligand (i.e., ligand efficiency). The selectivity and ligand efficiency of alpha-V particles were a function of the total number of particles infused. The highest selectivity observed within our test regime was 3, while ligand efficiency increased linearly with the number of particles injected to a value of 24. This work represents a significant step towards achieving a targeted drug delivery scheme for the treatment of inflammatory bowel disease and indicates that the efficiency of targeting is dependent on the dose regime.

A novel strategy to modify adenovirus tropism and enhance transgene delivery to activated vascular endothelial cells in vitro and in vivo

To assess the possibilities of retargeting adenovirus to activated endothelial cells, we conjugated bifunctional polyethylene glycol (PEG) onto the adenoviral capsid to inhibit the interaction between viral knob and coxsackie-adenovirus receptor (CAR). Subsequently, we introduced an alphav integrin-specific RGD peptide or E-selectin-specific antibody to the other functional group of the PEG molecule for the retargeting of the adenovirus to activated endothelial cells. In vitro studies showed that this approach resulted in the elimination of transgene transfer into CAR-positive cells, while at the same time specific transgene transfer to activated endothelial cells was achieved. PEGylated, retargeted adenovirus showed longer persistence in the blood circulation with area under plasma concentration-time curve (AUC) values increasing 12-fold compared to unmodified virus. Anti-E-selectin antibody-PEG-adenovirus selectively homed to inflamed skin in mice with a delayed-type hypersensitivity (DTH) inflammation, resulting in local expression of the reporter transgene luciferase. This is the first study showing the benefits of PEGylation on adenovirus behavior upon systemic administration. The approach described here can form the basis for further development of adenoviral gene therapy vectors with improved pharmacokinetics and increased efficiency and specificity of therapeutic gene transfer into endothelial cells in disease.

A survey of the year 2002 commercial optical biosensor literature

We have compiled 819 articles published in the year 2002 that involved commercial optical biosensor technology. The literature demonstrates that the technology's application continues to increase as biosensors are contributing to diverse scientific fields and are used to examine interactions ranging in size from small molecules to whole cells. Also, the variety of available commercial biosensor platforms is increasing and the expertise of users is improving. In this review, we use the literature to focus on the basic types of biosensor experiments, including kinetics, equilibrium analysis, solution competition, active concentration determination and screening. In addition, using examples of particularly well-performed analyses, we illustrate the high information content available in the primary response data and emphasize the impact of including figures in publications to support the results of biosensor analyses.

Hyaluronan microspheres for sustained gene delivery and site-specific targeting

Hyaluronan is a naturally occurring polymer that has enjoyed wide successes in biomedical and cosmetic applications as coatings, matrices, and hydrogels. For controlled delivery applications, formulating native hyaluronan into microspheres could be advantageous but has been difficult to process unless organic solvents are used or hyaluronan has been modified by etherification. Therefore, we present a novel method of preparing hyaluronan microspheres using adipic dihydrazide mediated crosslinking chemistry. To evaluate their potential for medical applications, hyaluronan microspheres are incorporated with DNA for gene delivery or conjugated with an antigen for cell-specific targeting. The results show that our method, originally developed for preparing hyaluronan hydrogels, generates robust microspheres with a size distribution of 5-20mum. The release of the encapsulated plasmid DNA can be sustained for months and is capable of transfection in vitro and in vivo. Hyaluronan microspheres, conjugated with monoclonal antibodies to E- and P-selectin, demonstrate selective binding to cells expressing these receptors. In conclusion, we have developed a novel microsphere preparation using native hyaluronan that delivers DNA at a controlled rate and adaptable for site-specific targeting.

Selectins-an emerging target for drug delivery

Selectins are multifunctional adhesion molecules that mediate the initial interactions between circulating leukocytes and cells of the endothelium. First identified over a decade ago, selectins have provided insight into areas as diverse as normal lymphocyte homing, leukocyte recruitment during inflammatory responses, carbohydrate ligand biosynthesis and adhesion-mediated signalling. Of late, selectins were introduced as targets for drug delivery in the development of new anti-inflammatory therapeutics and in anti-cancer therapy. This review will examine the selectins and their ligands with a focus on recent findings on their role in physiology and pathophysiology as well as the emerging role of selectins as targets in controlled drug delivery.

Leukocyte-inspired biodegradable particles that selectively and avidly adhere to inflamed endothelium in vitro and in vivo

We exploited leukocyte-endothelial cell adhesion chemistry to generate biodegradable particles that exhibit highly selective accumulation on inflamed endothelium in vitro and in vivo. Leukocyte-endothelial cell adhesive particles exhibit up to 15-fold higher adhesion to inflamed endothelium, relative to noninflamed endothelium, under in vitro flow conditions similar to that present in blood vessels, a 6-fold higher adhesion to cytokine inflamed endothelium relative to non-cytokine-treated endothelium in vivo, and a 10-fold enhancement in adhesion to trauma-induced inflamed endothelium in vivo due to the addition of a targeting ligand. The leukocyte-inspired particles have adhesion efficiencies similar to that of leukocytes and were shown to target each of the major inducible endothelial cell adhesion molecules (E-selectin, P-selectin, vascular cell adhesion molecule 1, and intercellular adhesion molecule 1) that are up-regulated at sites of pathological inflammation. The potential for targeted drug delivery to inflamed endothelium has significant implications for the improved treatment of an array of pathologies, including cardiovascular disease, arthritis, inflammatory bowel disease, and cancer.

A proteasome inhibitor reduces concurrent, sequential, and long-term IL-1 beta- and TNF-alpha-induced ECAM expression and adhesion

A promising approach for reducing aberrant leukocyte-endothelial adhesion during pathological inflammation is to inhibit endothelial cell adhesion molecule (ECAM) expression at the transcription level. Several compounds have been shown to decrease cytokine-induced upregulation of ECAMs primarily by modulating the activity of transcription factors [e.g., nuclear factor-kappa B (NF-kappa B)]. The majority of the in vitro studies have focused on the effect of transcription inhibitors on endothelial cells exposed to a single cytokine [primarily tumor necrosis factor-alpha (TNF-alpha)] for a relatively short period of time (primarily 4-6 h). However, in the in vivo setting, multiple cytokines [e.g., interleukin-1 beta (IL-1 beta) and TNF-alpha] may be present for extended periods of time. Thus we studied the effects of a transcription inhibitor, the proteasome inhibitor lactacystin, on ECAM expression and myeloid (HL60) cell adhesion to human umbilical vein endothelial cells (HUVEC) activated by concurrent, sequential, and long-term (24 h) treatment with IL-1 beta and TNF-alpha. We show, for the first time, that lactacystin inhibits 1) 4-h concurrent IL-1 beta- and TNF-alpha-induced expression of E-selectin, VCAM-1, ICAM-1, and HL60 cell adhesion to HUVEC; 2) 4-h TNF-alpha-induced expression of E-selectin, VCAM-1, and HL60 cell adhesion to HUVEC that have become desensitized to IL-1 beta activation; 3) 24-h TNF-alpha-induced expression of E-selectin and VCAM-1 but not ICAM-1; and 4) 24-h TNF-alpha-induced HL60 cell adhesion to HUVEC. Combined, our results demonstrate that a proteasome inhibitor can reduce concurrent, sequential, and long-term IL-1 beta- and TNF-alpha-induced ECAM expression and myeloid cell adhesion.

The role of selectins in inflammation and disease

Selectins are carbohydrate-binding molecules that bind to fucosylated and sialylated glycoprotein ligands, and are found on endothelial cells, leukocytes and platelets. They are involved in trafficking of cells of the innate immune system, T lymphocytes and platelets. An absence of selectins or selectin ligands has serious consequences in mice or humans, leading to recurrent bacterial infections and persistent disease. Selectins are involved in constitutive lymphocyte homing, and in chronic and acute inflammation processes, including post-ischemic inflammation in muscle, kidney and heart, skin inflammation, atherosclerosis, glomerulonephritis and lupus erythematosus. Selectin-neutralizing monoclonal antibodies, recombinant soluble P-selectin glycoprotein ligand 1 and small-molecule inhibitors of selectins have been tested in clinical trials on patients with multiple trauma, cardiac indications and pediatric asthma, respectively. Anti-selectin antibodies have also been successfully used in preclinical models to deliver imaging contrast agents and therapeutics to sites of inflammation. Further improvements in the efficiency, availability, specificity and pharmacokinetics of selectin inhibitors, and specialized application routes and schedules, hold promise for therapeutic indications.

Delivery of pharmacologically active dexamethasone into activated endothelial cells by dexamethasone-anti-E-selectin immunoconjugate

To deliver selectively anti-inflammatory agents into activated endothelial cells, drug-targeting conjugates were developed. Dexamethasone (Dexa) was covalently linked to a monoclonal antibody specifically recognizing E-selectin, which is strongly upregulated in endothelial cells at inflammatory sites. In the present study, the pharmacological effects of this Dexa-mouse antihuman E-selectin antibody (H18/7) (Ab(hEsel)) conjugate were investigated and compared to the effects obtained by free Dexa in human umbilical vein endothelial cells. Flow cytometry and ELISA were performed to analyze the levels of cell adhesion molecules (ICAM-1 and VCAM-1) and secreted cytokines (IL-6 and IL-8). The studies were extended by analysis of a complex gene expression pattern, using a cDNA expression array containing 268 genes encoding human cytokines/cytokine-receptors. Fifty genes and 28 genes were upregulated (ratio> or =2) upon incubation of human umbilical vein endothelial cells with TNFalpha for 6 and 24hr, respectively. This gene expression profile was markedly altered when cells were activated with TNFalpha in the presence of Dexa (100 nM) or Dexa-Ab(hEsel) conjugate (10 micro g/mL conjugate corresponding to 100 nM Dexa). Relative and competitive RT-PCR analysis verified downregulation of TNFalpha-mediated expression of CD40L and IL-8 by Dexa and Dexa-Ab(hEsel), respectively. These results indicated a successful internalization and processing of Dexa-Ab(hEsel) in activated endothelial cells, allowing the intracellularly delivered Dexa to exert its pleiotropic anti-inflammatory activity.

Endothelial cells at inflammatory sites as target for therapeutic intervention

In the course of an inflammation, vascular endothelial cells (VECs) are strongly involved in processes like leukocyte recruitment, cytokine production, and angiogenesis. Specific interference in these processes may yield great therapeutic benefit in the treatment of (chronic) inflammatory disorders. Drug targeting to VECs at inflamed sites may allow such intervention. VECs at inflamed sites represent a very well-accessible target cell population for circulating drug-targeting systems, which may also be selectively distinguished from normal VECs by the expression of several cell surface receptors involved in the inflammation. One group of specifically expressed molecules are the adhesion molecules (AMs), which have a major function in adhesion of cells to each other, to the extracellular matrix, or in the adhesion and subsequent recruitment of circulating immune cells. This review describes AMs with regard to their function in the inflammatory disease and their usefulness in functioning as a specific target receptor for drug-targeting approaches in general and with an emphasis on liposome-based drug delivery.

In vitro cellular handling and in vivo targeting of E-selectin-directed immunoconjugates and immunoliposomes used for drug delivery to inflamed endothelium

PURPOSE

Drug targeting to activated endothelial cells is now being explored as a new approach to interfere with chronic inflammation. This study compares a dexamethasone-anti-E-selectin immunoconjugate (dexa-AbEsel) with anti-E-selectin immunoliposomes (AbEsel-immunoliposomes) that contain dexamethasone, regarding in vitro binding and internalization as well as in vivo accumulation in activated endothelial cells.

METHODS

In vitro binding and internalization of dexa-AbEsel and the AbEsel-immunoliposomes into TNFalpha-activated HUVECs was studied using confocal laser scanning microscopy and radiolabeled compounds. Tissue accumulation of both compounds was studied in a murine delayed-type hypersensitivity model using immunohistochemistry.

RESULTS AND CONCLUSIONS

Both preparations were selectively internalized by activated endothelial cells. Dexa-AbEsel was internalized by activated HUVECs to a larger extent than the AbEsel-immunoliposomes, although in theory the high drug-loading capacity of the liposomes may enable a larger amount of dexamethasone to be delivered intracellularly. Both dexa-AbEsel and AbEsel-immunoliposomes accumulated in activated endothelial cells in murine inflamed skin. AbEsel-immunoliposomes, but not dexa-AbEsel, were additionally detected in control skin, though to a lesser extent, and in macrophages of the liver and the spleen. Studies on therapeutic effects and side effects in models of chronic inflammation are now necessary to establish pharmacodynamics of dexa-AbEsel and/or AbEsel-immunoliposomes in the treatment of chronic inflammation.

Analysis of in vivo endothelial cell activation applying RT-PCR following endothelial cell isolation by laser dissection microscopy

Laser dissection microscopy was applied to isolate endothelial cells from tumors obtained from mice treated with TNF-alpha. RNA integrity was demonstrated from whole sections and dissected cells after acetone fixation and hematoxylin staining. RT-PCR for GAPDH, CD31, VCAM-1, ICAM-1, and E-selectin was successfully performed on these samples. These data demonstrate the feasibility of analyzing local endothelial cell responses in diseased tissues at the level of gene expression.

Cellular handling of a dexamethasone-anti-E-selectin immunoconjugate by activated endothelial cells: comparison with free dexamethasone

PURPOSE

For selective inhibition of endothelial cell activation in chronic inflammation, we have developed a dexamethasone-anti-E-selectin immunoconjugate. The present study was performed to evaluate the cellular handling of this immunoconjugate by activated primary endothelial cells and to compare its drug delivery capacity with free dexamethasone.

METHODS

The binding, uptake, and degradation of 125I-radiolabeled dexamethasone-anti-E-selectin immunoconjugate by TNFalpha-activated endothelial cells were studied for different time periods and at different concentrations, as well as in the presence of inhibitors for E-selectin binding and lysosomal degradation. Its drug delivery capacity was compared with the uptake of unconjugated 3H-labeled dexamethasone.

RESULTS

The immunoconjugate was internalized by E-selectin expressing activated endothelial cells and degraded in the lysosomal compartment. The receptor-mediated binding and uptake was saturable, implying a maximal attainable intracellular concentration of the drug. In contrast, free dexamethasone entered both resting and activated endothelial cells by passive diffusion.

CONCLUSIONS

The dexamethasone-anti-E-selectin immunoconjugate is capable of selective delivering the coupled drug into activated endothelial cells. This targeting concept enables disease-induced drug delivery in which intracellular concentrations can be reached comparable with those obtained after incubation with 3 FM dexamethasone.

In vivo phage display and vascular heterogeneity: implications for targeted medicine

The vascular endothelium expresses differential receptors depending on the functional state and tissue localization of its cells. A method to characterize this receptor heterogeneity with phage display random peptide libraries has been developed. Using this technology, several peptide ligands have been isolated that home to tissue-specific endothelial cell receptors following intravenous administration. Such peptide ligands, or antibodies directed against specific vascular receptors, can be used to target therapeutic compounds or imaging agents to endothelial cells in vitro and in vivo. Recent advances in the field include identification of novel endothelial receptors expressed differentially in normal and pathological conditions and the isolation of peptides or antibody ligands to such receptors in in vitro assays, in animal models and in a human patient. These milestones, which extend the 'functional map' of the vasculature, should lead to clinical applications in diseases such as cancer and other conditions that exhibit distinct vascular characteristics.