Targeting to endothelial cells augments the protective effect of novel dual bioactive antioxidant/anti-inflammatory nanoparticles.

Oxidative stress and inflammation are intertwined contributors to numerous acute vascular pathologies. A novel dual bioactive nanoparticle with antioxidant/anti-inflammatory properties was developed based on the interactions of tocopherol phosphate and the manganese porphyrin SOD mimetic, MnTMPyP. The size and drug incorporation efficiency were shown to be dependent on the amount of MnTMPyP added as well as the choice of surfactant. MnTMPyP was shown to retain its SOD-like activity while in intact particles and to release in a slow and controlled manner. Conjugation of anti-PECAM antibody to the nanoparticles provided endothelial targeting and potentiated nanoparticle-mediated suppression of inflammatory activation of these cells manifested by expression of VCAM, E-selectin, and IL-8. This nanoparticle technology may find applicability with drug combinations relevant for other pathologies.

Nanocarriers for vascular delivery of anti-inflammatory agents.

There is a need for improved treatment of acute vascular inflammation in conditions such as ischemia-reperfusion injury, acute lung injury, sepsis, and stroke. The vascular endothelium represents an important therapeutic target in these conditions. Furthermore, some anti-inflammatory agents (AIAs) (e.g., biotherapeutics) require precise delivery into subcellular compartments. In theory, optimized delivery to the desired site of action may improve the effects and enable new mechanisms of action of these AIAs. Diverse nanocarriers (NCs) and strategies for targeting them to endothelial cells have been designed and explored for this purpose. Studies in animal models suggest that delivery of AIAs using NCs may provide potent and specific molecular interventions in inflammatory pathways. However, the industrial development and clinical translation of complex NC-AIA formulations are challenging. Rigorous analysis of therapeutic/side effect and benefit/cost ratios is necessary to identify and optimize the approaches that may find clinical utility in the management of acute inflammation.

Endothelial targeting of liposomes encapsulating SOD/catalase mimetic EUK-134 alleviates acute pulmonary inflammation.

Production of excessive levels of reactive oxygen species (ROS) in the vascular endothelium is a common pathogenic pathway in many dangerous conditions, including acute lung injury, ischemia-reperfusion, and inflammation. Ineffective delivery of antioxidants to the endothelium limits their utility for management of these conditions. In this study, we devised a novel translational antioxidant intervention targeted to the vascular endothelium using PEG-liposomes loaded with EUK-134 (EUK), a potent superoxide dismutase/catalase mimetic. EUK loaded into antibody-coated liposomes (size 197.8±4.5 nm diameter, PDI 0.179±0.066) exerted partial activity in the intact carrier, while full activity was recovered upon liposome disruption. For targeting we used antibodies (Abs) to platelet-endothelial cell adhesion molecule (PECAM-1). Both streptavidin-biotin and SATA/SMCC conjugation chemistries provided binding of 125-150 Ab molecules per liposome. Ab/EUK/liposomes, but not IgG/EUK/liposomes: i) bound to endothelial cells and inhibited cytokine-induced inflammatory activation in vitro; and, ii) accumulated in lungs after intravascular injection, providing >60% protection against pulmonary edema in endotoxin-challenged mice (vs <6% protection afforded by IgG/liposome/EUK counterpart). Since the design elements of this drug delivery system are already in clinical use (PEG-liposomes, antibodies, SATA/SMCC conjugation), it is an attractive candidate for translational interventions using antioxidant molecules such as EUK and other clinically acceptable drugs.

Advanced drug delivery systems for antithrombotic agents.

Despite continued achievements in antithrombotic pharmacotherapy, difficulties remain in managing patients at high risk for both thrombosis and hemorrhage. Utility of antithrombotic agents (ATAs) in these settings is restricted by inadequate pharmacokinetics and narrow therapeutic indices. Use of advanced drug delivery systems (ADDSs) may help to circumvent these problems. Various nanocarriers, affinity ligands, and polymer coatings provide ADDSs that have the potential to help optimize ATA pharmacokinetics, target drug delivery to sites of thrombosis, and sense pathologic changes in the vascular microenvironment, such as altered hemodynamic forces, expression of inflammatory markers, and structural differences between mature hemostatic and growing pathological clots. Delivery of ATAs using biomimetic synthetic carriers, host blood cells, and recombinant fusion proteins that are activated preferentially at sites of thrombus development has shown promising outcomes in preclinical models. Further development and translation of ADDSs that spare hemostatic fibrin clots hold promise for extending the utility of ATAs in the management of acute thrombotic disorders through rapid, transient, and targeted thromboprophylaxis. If the potential benefit of this technology is to be realized, a systematic and concerted effort is required to develop clinical trials and translate the use of ADDSs to the clinical arena.

Carboxylesterase-triggered hydrolysis of nanoparticle PEGylating agents.

Despite the importance of PEGylation in achieving long nanoparticle circulation times, many nanoparticles are coated with PEGylating agents susceptible to enzymatic degradation. In this study, solid lipid nanoparticles (SLNs) prepared with ester-containing compounds were evaluated for their stability in the presence of carboxylesterase. SLN suspensions became turbid within 30 min of enzymatic exposure, indicating possible disassociation of a portion of the nanoparticles. The particle size of SLNs incubated with the enzyme was smaller than the size of controls, although their morphologies appeared similar in transmission electron microscopy images. Although SLNs offered some protection over micelles, PEG6000 monostearate was rapidly degraded within 15 min. Hydrolysis of polysorbate 60 was much slower, reaching only 36% in 2 h. These studies reveal the importance of confirming the stability of PEG surface coatings prior to undertaking in vivo experiments in small animal models, which can have considerably higher plasma esterase activity than humans.

Optimization of the lyophilization process for long-term stability of solid-lipid nanoparticles.

OBJECTIVES: To optimize a lyophilization protocol for solid-lipid nanoparticles (SLNs) loaded with dexamethasone palmitate (Dex-P) and to compare the long-term stability of lyophilized SLNs and aqueous SLN suspensions at two storage conditions. MATERIALS AND METHODS: The effect of various parameters of the lyophilization process on SLN redispersibility was evaluated. A three month stability study was conducted to compare changes in the particle size and drug loading of lyophilized SLNs with SLNs stored as aqueous suspensions at either 4°C or 25°C/60% relative humidity (RH). RESULTS AND DISCUSSION: Of nine possible lyoprotectants tested, sucrose was shown to be the most efficient at achieving SLN redispersibility. Higher freezing temperatures, slower freezing rates, and longer secondary drying times were also shown to be beneficial. Loading of the SLNs with Dex-P led to slightly larger particle size and polydispersity index increases, but both parameters remained within an acceptable range. Drug loading and particle shape were maintained following lyophilization, and no large aggregates were detected. During the stability study, significant growth and drug loss were observed for aqueous SLN suspensions stored at 25°C/60% RH. In comparison, lyophilized SLNs stored at 4°C exhibited a consistent particle size and showed <20% drug loss. Other storage conditions led to intermediate results. CONCLUSIONS: A lyophilization protocol was developed that allowed SLNs to be reconstituted with minimal changes in their physicochemical properties. During a three month period, lyophilized SLNs stored at 4°C exhibited the greatest stability, showing no change in the particle size and a minimal reduction in drug retention.

Polymer micelles with hydrazone-ester dual linkers for tunable release of dexamethasone.

PURPOSE: To develop polymer micelles for the tunable release of Dexamethasone (DEX) in tumors. METHODS: DEX was conjugated to poly(ethylene glycol)-poly(aspartate) block copolymers using hydrazone, ester, or hydrazone-ester dual linkers. Ketonic acids containing 3, 4, and 5 methylene groups were used as spacers to separate the dual linkers. Polymer micelles from the DEX-conjugated polymers were tested for drug release at different pH values and carboxylesterase activity levels. RESULTS: DLS measurements and (1)H-NMR analysis confirmed all DEX-loaded micelles were <100 nm with core-shell structure. Single linker micelles appeared unsuitable to release DEX preferentially in acidic tumor tissues. Hydrazone linkages between DEX and polymers were non-degradable at both pH 7.4 and 5.0. Ester linkages stable at pH 5.0 were unstable at pH 7.4. Hydrazone-ester dual linkers suppressed DEX release at pH 7.4 while accelerating drug release at pH 5.0. DEX release decreased at pH 5.0 as the length of ketonic acid increased but was independent of spacer length at pH 7.4. Dual linker micelles were stable in the presence of carboxylesterases, suggesting DEX release was primarily due to pH-dependent hydrolysis. CONCLUSION: Tunable release of DEX was achieved using pH-sensitive polymer micelles with hydrazone-ester dual linkers.

Uniformity of drug payload and its effect on stability of solid lipid nanoparticles containing an ester prodrug.

Nanocarrier systems are frequently characterized by their size distribution, while drug encapsulation in nanocarriers is generally characterized in terms of an entire population, assuming that drug distribution is uniform. Careful characterization of nanocarriers and assessment of their behavior in biological environments are essential for adequate prediction of the fate of the nanoparticles in vivo. Solid lipid nanoparticles containing [(3)H]-dexamethasone palmitate (an ester prodrug) and [(14)C]-stearyl alcohol (a component of the nanoparticle matrix) were prepared using the nanotemplate engineering method for bioresponsive tumor delivery to overcome interstitial fluid pressure gradients, a physiological barrier to tumor uptake of chemotherapeutic agents. While particle size analysis indicated a uniform size distribution of 93.2 ± 0.5 nm, gel filtration chromatography (GFC) revealed two nanoparticle populations. Drug encapsulation efficiency was 97%, but it distributed differently in the two populations, with average drug/lipid ratios of 0.04 and 0.25, respectively. The difference in surface properties resulted in distinguishing protein adsorption features of the two populations. GFC and HPLC profiles of the mixture of nanoparticles and human serum albumin (HSA) showed that no HSA was adsorbed to the first population of nanoparticles, but minor amounts were adsorbed to the second population. After 24 h incubation in 50% human plasma, ≥80% of the [(3)H]-dexamethasone palmitate was associated with nanoparticles. Thus, characterization of solid lipid nanoparticles produced by this method may be challenging from a regulatory perspective, but the strong association of the drug with the nanoparticles in plasma indicates that this nanocarrier system has the potential for in vivo application.

Physicochemical characterization of nanotemplate engineered solid lipid nanoparticles.

As the physicochemical characteristics of solid lipid nanoparticles (SLNs) play a critical role in their success, it is important to understand how the materials and process used in their preparation affect these properties. In this study, two stearyl alcohol-based formulations were prepared using nanotemplate engineering technology and characterized. Both formulations were of a small particle size (<100 nm), ellipsoidal shape, and low polydispersity. (1)H NMR spectroscopy confirmed that the SLNs have the expected solid core structure and PEGylated surface. Analysis of the bulk materials indicated that a number of complex interactions are present among the SLN components, including a eutectic between stearyl alcohol and Brij 78. The decreased crystallinity resulting from these interactions may allow for enhanced drug loading. Physiological stability was identified and confirmed as a potential problem due to the low melting point of the eutectic. However, it is expected that with appropriate formulation modifications nanotemplate engineered SLNs will possess the properties necessary for a successful drug delivery system.

Nanoparticles containing anti-inflammatory agents as chemotherapy adjuvants: optimization and in vitro characterization.

The pre-administration of dexamethasone (DEX) has previously been shown to enhance the anti-tumor efficacy of chemotherapeutic agents. The delivery of anti-inflammatory agents specifically to tumors via nanoparticle carriers is expected to promote the effectiveness of chemotherapeutic agents while avoiding systemic toxicities. The process for preparing solid lipid nanoparticles containing anti-inflammatory agents using the nanotemplate engineering method was optimized. Due to the solubilization of DEX in the bulk aqueous phase, its more lipophilic palmitate ester was synthesized and incorporated in nanoparticles that included a pegylating agent, PEG6000 mono-stearate, as part of the formulation. The stealth properties of these nanoparticles were demonstrated to be enhanced compared to latex particles by measuring the adsorption of radioiodinated IgG (185 microg vs. 6.7 microg IgG/mg NP). In addition, the uptake of (14)C-labeled nanoparticles by murine macrophages was shown to decrease from 36.6% to 14.7% of the nanoparticles/mg cell protein as the amount of pegylating agent in the formulation increased from 0 to 4 mg/mL. The high loading values and low burst effect observed for these DEX palmitate-containing nanoparticles in addition to their stealth properties are expected to allow for the delivery of sufficient amounts of DEX to tumors to enhance the uptake of chemotherapeutic agents.