Hydrotropic polymer micelles containing acrylic acid moieties for oral delivery of paclitaxel

Stimulus-sensitive polymeric nanoparticles and their applications as drug and gene carriers

Polymeric nanoparticles are promising candidates as drug and gene carriers. Among polymeric nanoparticles, those that are responsive to internal or external stimuli are of greater interest because they allow more efficient delivery of therapeutics to pathological regions. Stimulus-sensitive polymeric nanoparticles have been fabricated based on numerous nanostructures, including micelles, vesicles, crosslinked nanoparticles, and hybrid nanoparticles. The changes in chemical or physical properties of polymeric nanoparticles that occur in response to single, dual, or multiple stimuli endow these nanoparticles with the ability to retain cargoes during circulation, target the pathological region, and release their cargoes after cell internalization. This Review focuses on the most recent developments in the preparation of stimulus-sensitive polymeric nanoparticles and their applications in drug and gene delivery.

Enhancement on oral absorption of paclitaxel by multifunctional pluronic micelles

The aim of the present study is to synthesize Pluronic F127-polyethylenimine-folate (PF127-PEI-FA) copolymer, construct a mixed micelle system with PF127-PEI-FA copolymer and Pluronic P123 (PP123) and to evaluate the potential of these mixed micelles as an oral drug delivery system for paclitaxel (PTX). The results of intestinal absorption revealed that the PTX-loaded micelles displayed superior permeability across intestinal barrier than free drug and PF127-PEI-FA/PP123 mixed micelles exhibited the strongest permeability across intestinal barrier. These results were also proved by the studies on cytotoxicity and cell uptake tests. The mechanism was demonstrated in connection with inhibition of the efflux mediated by intestinal P-glycoprotein (P-gp) and enhancement of the electrostatic interaction of positive micelles with the negative intestinal epithelial cells, thereby promoting the permeation across the intestinal wall. The presence of verapamil and Pluronic both improved the intestinal absorption of PTX, which further certified the effect of Pluronic on P-gp inhibition. Pharmacokinetic study demonstrated that the area under the plasma concentration-time curve (AUC(0→36 h)) of PTX-loaded micelles was three times greater than the PTX solution (dissolved in a 50/50 (vol/vol) mixture of Cremophore EL/dehydrated ethanol) (p < 0.05). In general PF127-PEI-FA/PP123 mixed micelles were proved to be potential oral drug delivery system for PTX.

Hydrotropic polymeric mixed micelles based on functional hyperbranched polyglycerol copolymers as hepatoma-targeting drug delivery system

Mixed copolymer nanoparticles (NPs) self-assembled from β-cyclodextrin-grafted hyperbranched polyglycerol (HPG-g-CD) and lactobionic acid (LA)-grafted hyperbranched polyglycerol (HPG-g-LA) were applied as carriers for a hydrophobic antitumor drug, paclitaxel (PTX), achieving hepatocellular carcinoma-targeted delivery. The resulting NPs exhibited high drug loading capacity and substantial stability in aqueous solution. In vitro drug release studies demonstrated a controlled drug release profile with increased release at acidic pH. Remarkably, tumor proliferation assays showed that PTX-loaded mixed copolymer NPs inhibited asialoglycoprotein (ASGP) receptor positive HepG2 cell proliferation in a concentration-dependent manner in comparison with ASGP receptor negative BGC-823 cells. Moreover, the competition assay demonstrated that the small molecular LA inhibited the cellular uptake of the PTX-loaded mixed copolymer NPs, indicating the ASGP receptor-mediated endocytosis in HepG2 cells. In addition, the intracellular uptake tests by confocal laser scanning microscopy showed that the mixed copolymer NPs were more efficiently taken up by HepG2 cells compared with HPG-g-CD NPs. These results suggest a feasible application of the mixed copolymer NPs as nanocarriers for hepatoma-targeted delivery of potent antitumor drugs.

pH-sensitive vesicles, polymeric micelles, and nanospheres prepared with polycarboxylates

Titratable polyanions, and more particularly polymers bearing carboxylate groups, have been used in recent years to produce a variety of pH-sensitive colloids. These polymers undergo a coil-to-globule conformational change upon a variation in pH of the surrounding environment. This conformational change can be exploited to trigger the release of a drug from a drug delivery system in a pH-dependent fashion. This review describes the current status of pH-sensitive vesicles, polymeric micelles, and nanospheres prepared with polycarboxylates and their performance as nano-scale drug delivery systems, with emphasis on our recent contribution to this field.

Enhanced oral bioavailability of paclitaxel in pluronic/LHR mixed polymeric micelles: preparation, in vitro and in vivo evaluation

In order to enhance paclitaxel oral bioavailability, mixed polymeric micelles that comprised of pluronic copolymers and low molecular weight heparin-all-trans-retinoid acid (LHR) conjugate were developed. PTX-loaded mixed polymeric micelles (MPMs) were prepared by dialysis method with high drug loading 26.92 ± 2.08% and 25.82 ± 1.9% for F127/LHR and P188/LHR MPMs respectively, and were found to be spherical in shape with an average size of around 140 nm and a narrow size distribution. In vitro release study showed that pluronic/LHR MPMs exhibited delayed release characteristics compared to Taxol and faster drug release profile compared to LHR plain polymeric micelles (PPMs). The cytotoxic activity of PTX-loaded pluronic/LHR MPMs was slightly higher than LHR PPMs in MCF-7 cells (p<0.01). In situ effective permeability of PTX through rat small intestine was 5- to 6-fold higher with mixed micelles than that of Taxol. Moreover, pluronic/LHR MPMs achieved significantly higher AUC and C(max) level than both of LHR PPMs and Taxol. This enhancement might be due to the inhibition of both P-glycoprotein efflux system and cytochrome P450 metabolism by pluronic copolymers. The current results encourage further development of paclitaxel mixed polymeric micelles as an oral drug delivery system.

Development of oxaliplatin encapsulated in magnetic nanocarriers of pectin as a potential targeted drug delivery for cancer therapy

Superparamagnetic iron oxide nanoparticles (SPIONs) and oxaliplatin (OHP) were in-situ encapsulated in pectin cross-linked with Ca(2+) forming 100-200 nm sized magnetically functionalized pectin nanocarriers, referred here as MP-OHP nanocarriers. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies revealed formation of spherical nanostructures. The magnetic measurements by vibration sample magnetometer (VSM) revealed high saturation magnetization (M s=45.65 emu/g). The superparamagnetic property of MP-OHP was confirmed from the blocking temperature (T B) determined from field cooled and zero field cooled magnetization, measured by superconducting quantum unit interference device (SQUID) magnetometry. The stability of the aqueous dispersion of MP-OHP nanocarriers was confirmed from its high zeta potential (-30.5 mV). The drug encapsulation efficiency (55.2±4.8% w/w) and the drug loading content (0.10±0.04 wt%) in MP-OHP nanocarriers were determined from corresponding platinum contents in OHP and MP-OHP batches measured by inductively coupled plasma mass spectrometry (ICPMS). These nanocarriers exhibited a sustained release of OHP in phosphate buffer solution maintained at pH 5.5 and 7.4, where the drug release profile satisfied a combination of diffusion and swelling controlled mechanism. The cytotoxicity effect of MP-OHP nanocarriers was studied on MIA-PaCa-2 (pancreas) cancer cell line, where the GI50 values were more than 5 mg/mL and it exhibited 10 folds higher cytoxicity than the equivalent concentration of free drug.

Optimization of self-assembling properties of fatty acids grafted to methoxy poly(ethylene glycol) as nanocarriers for etoposide

The objective of this work was to study the effect of fatty acid chain length grafted to methoxy poly(ethylene glycol) (mPEG) on self assembling properties of micelles for etoposide delivery. Three amphiphilic copolymers were synthesized using mPEG, myristic acid, stearic acid and behenic acid through an esteric linkage. The particle size and zeta potential of the micelles were determined by the dynamic light scattering method. Etoposide was loaded into micelles by film casting using various drug/polymer ratios. Drug release was studied by the dialysis method. The structure of copolymers was confirmed by (1)H NMR and FTIR. Central micellar concentration (CMC) measurements showed that the longer hydrophobic chains formed more thermodynamically stable micelles. Among the prepared copolymers, etoposide showed the highest solubility in the mPEG-behenic copolymer. Drug loading efficiency depended on the hydrophobic chain length and drug/polymer ratio. The highest drug loading efficiency was found in mPEG-myristic micelles with 1:20 drug/polymer ratio. Micelles released 80 % of loaded drug within about 5 h.

Architectural layer-by-layer assembly of drug nanocapsules with PEGylated polyelectrolytes

150-200 nm diameter capsules containing 60-70 wt % of poorly soluble drugs, paclitaxel and camptothecin, were produced by layer-by-layer (LbL) assembly on drug nanocores in a solution containing uncharged stabilizers. Optimization of capsule shell architecture and thickness allowed for concentrated (3-5 mg/mL) colloids that are stable in isotonic salt buffers. Nanoparticle aggregation during the washless LbL-assembly was prevented by using low molecular weight block-copolymers of poly(amino acids) (poly-L-lysine and poly-L-glutamic acid) with polyethylene glycol (PEG) in combination with heparin and bovine serum albumin at every bilayer building step. Minimal amounts of the polyelectrolytes were used to recharge the surface of nanoparticles in this non-washing LbL process. Such PEGylated shells resulted in drug nanocapsules with high colloidal stability in PBS buffer and increased protein adhesion resistance. The washless LbL polyelectrolyte nanocapsule assembly process, colloidal stability and nanoparticle morphology were monitored by dynamic light scattering and electrophoretic mobility measurements, UV-vis spectroscopy, TEM, SEM and laser confocal microscopy imaging.

Nanoparticle-based biocompatible and targeted drug delivery: characterization and in vitro studies

Paclitaxel nanoparticles (PAX NPs) prepared with the size of 110 ± 10 nm and ζ potential of -40 ± 3 mV were encapsulated in synthetic/biomacromolecule shell chitosan, dextran-sulfate using a layer-by-layer self-assembly technique. Zeta potential measurements, analysis of X-ray photoelectron spectroscopy, and scanning electron microscopy confirmed the successful adsorption of each layer. Surface modifications of these core-shell NPs were performed by covalently conjugating with poly(ethylene glycol) (H(2)N-PEG-carboxymethyl, M(w) 3400) and fluorescence labeled wheat germ agglutinin (F-WGA) to build a biocompatible and targeted drug delivery system. 32% of PAX was released from four bilayers of biomacromolecule assembled NPs within 8 h as compared with >85% of the drug released from the bare NPs. Moreover, high cell viability with PEG conjugation and high binding capacity of WGA-modified NPs with Caco-2 cells were observed. This biocompatible and targeted NP-based drug delivery system, therefore, may be considered as a potential candidate for the treatment of colonic cancer and other diseases.

Mesoscopic simulations on the aggregation behavior of pH-responsive polymeric micelles for drug delivery

Computer simulations, dissipative particle dynamics (DPD) and mesoscopic dynamics (MesoDyn), are performed to study the aggregation behavior of pH-sensitive micelles self-assembled from amphiphilic polymer poly(methyl methacrylate-co-methacrylic acid)-b-poly(poly-(ethylene glycol) methyl ether monomethacrylate), P(MMA-co-MAA)-b-PPEGMA. Ibuprofen (IBU) is selected as the model drug. It can be seen from DPD simulations that P(MMA-co-MAA)-b-PPEGMA and IBU form spherical core-shell micelles at certain compositions, and IBU molecules distribute inside the core formed by hydrophobic MMA. The polymer molecules aggregate first, and then IBU diffuses into the aggregate, forming drug-loaded nanoparticles. With different compositions of polymer and IBU, aggregate morphologies in water are observed as sphere, column and lamella. From MesoDyn results, with less hydrophobic MMA beads, the polymer chains are more difficult to form ordered aggregates, and the order parameters get equilibrated in a longer time. The pH value also affects the aggregate process. At pH<5, the polymer could form traditional core-shell micelles. But at pH>5, the morphology of micelles is found to be anomalous and loose for releasing drug. MAA aggregates on the surface, instead of the inside. The simulation results are qualitatively consistent with the experimental results.

Development of lipid-based nanoparticles for enhancing the oral bioavailability of paclitaxel

The current research work investigates the potential of solid lipid nanoparticles (SLNs) in improving the oral bioavailability of paclitaxel. Paclitaxel-loaded SLNs (PTX-SLNs) were prepared by modified solvent injection method using stearylamine as lipid, soya lecithin and poloxamer 188 as emulsifiers. SLNs were characterized in terms of surface morphology, size and size distribution, surface chemistry and encapsulation efficiency. Pharmacokinetics and bioavailability studies were conducted in male Swiss albino mice after oral administration of PTX-SLNs. SLNs exhibited spherical shape with smooth surface as analyzed by transmission electron microscopy (TEM). The mean particle size of SLNs was 96 ± 4.4 nm with a low polydispersity index of 0.162 ± 0.04 and zeta potential of 39.1 ± 0.8 mV. The drug entrapment efficiency was found to be 75.42 ± 1.5% with a loading capacity of 31.5 ± 2.1% (w/w). Paclitaxel showed a slow and sustained in vitro release profile and followed Higuchi kinetic equations. After oral administration of the PTX-SLNs, drug exposure in plasma and tissues was ten- and twofold higher, respectively, when compared with free paclitaxel solution. PTX-SLNs produced a high mean C (max) (10,274 ng/ml) compared with that of free paclitaxel solution (3,087 ng/ml). The absorbed drug was found to be distributed in liver, lungs, kidneys, spleen, and brain. The results suggested that PTX-SLNs dispersed in an aqueous environment are promising novel formulations that enhanced the oral bioavailability of hydrophobic drugs, like paclitaxel and were quite safe for oral delivery of paclitaxel as observed by in vivo toxicity studies.

Hydrotropic polymer micelles as versatile vehicles for delivery of poorly water-soluble drugs

Polymer micelles have been used widely for delivery of poorly water-soluble drugs. Such drug delivery, however, has been based primarily on hydrophobic interactions. For better drug loading and improved stability, hydrotropic polymer micelles were used. To develop a versatile polymer micelle for solubilizing various poorly soluble drugs, two different hydrotropic agents were examined. The solubilizing properties of two hydrotropic agents, N,N-diethylnicotinamide (DENA) and N,N-dimethylbenzamide (DMBA), in polymeric form were investigated for their ability to solubilize five drugs with low aqueous solubility covering a wide range of hydrophobicity and molecular structures. The hydrotropes were covalently linked to the hydrophobic block of a block copolymer that also had a hydrophilic poly(ethylene glycol) (PEG) block. The solubilizing capacity of the polymeric hydrotropes was compared with that of the non polymeric hydrotropes, as well as of two conventional (non hydrotropic) copolymer systems. The solubilizing capacity of polymeric hydrotropes reflects combined effects of the micellar solubilization by the hydrophobic micelle core and hydrotropic solubilization. Because of the highly localized configuration, hydrotropes in the polymeric form are more powerful solubilizers than in the monomeric (non-polymeric) solution. It is possible to produce 1~3 orders of magnitude increase in solubility with polymeric hydrotropes at the 1% (w/v) level. Of the two hydrotropic polymeric systems in this study, the DENA-based system is highly specific, whereas the DMBA-based system is a general solubilizer of hydrophobic drugs. An additional advantage of polymeric hydrotropes over the non-polymeric form is absence of high concentrations of free hydrotropes in the formulation. Solubilization vehicles based on polymeric hydrotropes are expected to provide a new and versatile means of preparing formulations for various poorly soluble drugs and drug candidates without using organic solvents. This advantage is accompanied with the inherent controlled release property of the hydrotropic polymer micelles, making them ideal for pharmaceutical formulations used in drug candidate screening and toxicology studies.

Novel pH-sensitive polyacetal-based block copolymers for controlled drug delivery

The principal aim of this study was to synthesize and characterize pH-sensitive biodegradable triblock copolymers containing a hydrophobic polyacetal segment for controlled drug delivery. Poly(ethylene glycol)-poly(ethyl glyoxylate)-poly(ethylene glycol) (PEG-PEtG-PEG) triblock copolymers with PEG molecular weights 500 (PEtG-PEG(500)) and 750 (PEtG-PEG(750)) were synthesized by PEtG end-capping with methoxy PEG via a carbamate linkage. Synthesized amphiphilic PEG-PEtG-PEG was characterized by (1)H NMR spectroscopy. Molecular weights of PEtG-PEG(500) and PEtG-PEG(750) were determined to be 2823 and 3387, respectively, by gel permeation chromatography. The polymers with a biodegradable polyacetal block underwent pH-dependent degradation via an acid-catalyzed hydrolysis. Paclitaxel (PTX)-loaded polymeric micelles were prepared by a dialysis method and the amount of PTX incorporated into the polymeric micelle formulations was 45,000 times greater than the water solubility of PTX at room temperature. The polymeric micelles prepared from the amphiphilic PEG-PEtG-PEG triblock copolymers have released the loaded PTX in a pH-dependent manner. The novel PEtG-based amphiphilic block copolymers can find applications for targeted and controlled drug delivery to the acidic environments found in tumors and intracellular compartments.

Chitosan-poly(ε-caprolactone)-poly(ethylene glycol) graft copolymers: synthesis, self-assembly, and drug release behavior

Biodegradable tri-component graft copolymers, chitosan-poly(ε-caprolactone)-poly(ethylene glycol) (CPP), were synthesized via a mild route, using sodium dodecyl sulfate-chitosan complex (SCC) as a precursor. Both PCL and PEG could be conveniently conjugated to the hydroxyl sites of chitosan without the need of tedious chemical protection/deprotection processes, thereby leaving the amino groups of chitosan intact. The self-assembly and release behavior of the copolymer micelles were investigated. Paclitaxel and rutin were used as model drugs. Spherical micelles could be formed through self-assembly of CPP in aqueous media. The micelle diameter increased with PEGylation degree and ranged from 30 to 45 nm. The incorporation of drugs into the micelles significantly raised the micelle diameter and diversified the micelle morphologies. The micelles were further subjected to glutaraldehyde treatment to prolong the release of the incorporated drugs. It was found that the crosslinking process shrunk the drug-loaded micelles. In addition, the micelles were endowed with self-luminescent properties after crosslinked with glutaraldehyde. By increasing crosslinking density, the release duration of the model drugs could be prolonged.

Biopharmaceutical parameters to consider in order to alter the fate of nanocarriers after oral delivery

Oral route is the most common route for the delivery of drugs because it is simple to implement and improves patient compliance and quality of life. However, oral absorption is limited by various physiological barriers and remains a scientific challenge. Nanometric-sized drug delivery systems are being extensively studied and provide promising potential for oral drug delivery. Many different technological solutions have been proposed to enhance the bioavailability or the targeting of drug after oral administration. To reach these goals, it is important to analyze the biopharmaceutical parameters to consider in order to alter the fate of nanocarriers after oral delivery. In the present review, the gastrointestinal barrier and physiological stress factors with regard to nanocarriers' performance or integrity issues are first described. Second, the different characteristics offered by the nanocarriers (size, surface composition and properties mediated by external factors such as ligands) and their effect on the optimal transport of drug into the bloodstream are discussed. Finally, the integrity issue is discussed in function of the expected role of the nanocarriers: bioavailability enhancement or pharmacological targeting.

Hydrophobic pharmaceuticals mediated self-assembly of beta-cyclodextrin containing hydrophilic copolymers: novel chemical responsive nano-vehicles for drug delivery

Double hydrophilic copolymers with one polyethylene glycol (PEG) block and one beta-cyclodextrin (beta-CD) flanking block (PEG-b-PCDs) were synthesized through the post-modification of macromolecules. The self-assembly of PEG-b-PCDs in aqueous solutions was initially studied by a fluorescence technique. This measurement together with AFM and TEM characterizations demonstrated the formation of nanoparticles in the presence of lipophilic small molecules. The host-guest interaction between the beta-CD unit of a host copolymer and the hydrophobic group of a guest molecule was found to be the driving force for the observed self-assembly. This spontaneous assembly upon loading of guest molecules was also observed for hydrophobic drugs with various chemical structures. Relatively high drug loading was achieved by this approach. Desirable encapsulation was also achieved for the hydrophobic drugs that cannot efficiently interact with free beta-CD. In vitro release studies suggested that the payload in nano-assemblies could be released in a sustained manner. In addition, both the fluorescence measurement and the in vitro drug release studies suggested that these nano-assemblies mediated by the inclusion complexation exhibited a chemical sensitivity. The release of payload can be accelerated upon the triggering by hydrophobic guest molecules or free beta-CD molecules. These results support the potential applications of the synthesized copolymers for the delivery of hydrophobic drugs.

Delivery of paclitaxel from cobalt-chromium alloy surfaces without polymeric carriers

Polymer-based carriers are commonly used to deliver drugs from stents. However, adverse responses to polymer coatings have raised serious concerns. This research is focused on delivering drugs from stents without using polymers or any carriers. Paclitaxel (PAT), an anti-restenotic drug, has strong adhesion towards a variety of material surfaces. In this study, we have utilized such natural adhesion property of PAT to attach these molecules directly to cobalt-chromium (Co-Cr) alloy, an ultra-thin stent strut material. Four different groups of drug coated specimens were prepared by directly adding PAT to Co-Cr alloy surfaces: Group-A (PAT coated, unheated, and ethanol cleaned); Group-B (PAT coated, heat treated, and ethanol cleaned); Group-C (PAT coated, unheated, and not ethanol cleaned); and Group-D (PAT coated, heat treated and not ethanol cleaned). In vitro drug release of these specimens was investigated using high performance liquid chromatography. Groups A and B showed sustained PAT release for up to 56 days. A simple ethanol cleaning procedure after PAT deposition can remove the loosely bound drug crystals from the alloy surfaces and thereby allowing the remaining strongly bound drug molecules to be released at a sustained rate. The heat treatment after PAT coating further improved the stability of PAT on Co-Cr alloy and allowed the drug to be delivered at a much slower rate, especially during the initial 7 days. The specimens which were not cleaned in ethanol, Groups C and D, showed burst release. PAT coated Co-Cr alloy specimens were thoroughly characterized using scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. These techniques were collectively useful in studying the morphology, distribution, and attachment of PAT molecules on Co-Cr alloy surfaces. Thus, this study suggests the potential for delivering paclitaxel from Co-Cr alloy surfaces without using any carriers.

Overcoming the barriers in micellar drug delivery: loading efficiency, in vivo stability, and micelle-cell interaction

IMPORTANCE OF THE FIELD

Spontaneously constructed from block copolymers in aqueous media, the polymer micelle has been extensively studied as a potential carrier of poorly water-soluble drugs, but cellular uptake pathways and stability of micelles in blood have not yet been clearly understood. An in-depth insight into the physical and biological behaviors of polymer micelles is necessitated for designing next-generation micelles.

AREAS COVERED IN THIS REVIEW

This review suggests possible solutions to improve micellar drug loading capacity, scrutinizes the parameters influencing the micelle stability in blood, and also discusses the fate of micelles in cellular and in vivo environment, respectively. Direct and indirect evidences from the literatures mostly published after 90's were collected, analyzed and summarized.

WHAT THE READER WILL GAIN

A critical analysis of micelle's stability in vivo and micelle-cell interaction is provided to highlight the key issues to be addressed to affirm that micelle can properly work as a drug carrier in clinical settings.

TAKE HOME MESSAGE

With a clear understanding of its behaviors in biological environment, the polymer micelle is a promising nanocarrier for chemotherapy.

Paclitaxel-loaded poly(N-vinylpyrrolidone)-b-poly(epsilon-caprolactone) nanoparticles: preparation and antitumor activity in vivo

Paclitaxel (PTX)-loaded poly(N-vinylpyrrolidone)-b-poly(epsilon-caprolactone) (PVP-b-PCL) nanoparticles with high drug payload were successfully prepared by a modified nano-precipitation method and characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS) and zeta potential. The satisfactory drug loading content (>25%) and high encapsulation efficiency (>85%) were achieved. The in vivo real-time biodistribution of PTX-loaded nanoparticles was investigated using near-infrared fluorescence (NIRF) imaging. The antitumor effect of PTX-loaded nanoparticles was evaluated, both, in vitro on three different cancer cell lines and in vivo on hepatic H22 tumor bearing mice model via intravenous administration (i.v.). It is found that PTX-loaded nanoparticles exhibit significant superior in vivo antitumor effect than the commercially available Taxol formulation by combining the tumor volumes and survival rates measurement, intravital positron emission tomography and computed tomography (PET/CT) imaging.