Triblock polymeric micelles as carriers for anti-inflammatory drug delivery

Abstract

This study evaluated the properties of poly(ethylene oxide)-b-poly(n-butyl acrylate)-b-poly(acrylic acid) (PEO-PnBA-PAA) polymeric micelles as carriers for anti-inflammatory drugs (prednisolone and budesonide). The micelles comprising a hydrophobic PnBA core and a PEO/PAA corona showed average diameter less than 40?nm. The size of the drug-loaded micelles did not change during eight hours into media that mimic physiological fluids indicating high colloidal stability. The calculation of Flory–Huggins parameter showed greater compatibility between budesonide and micellar core suggesting its location in the micellar core, whereas prednisolone was located also into the interface layer. This observation correlated further with slower release of budesonide, especially in acid medium (pH?=?1.2). The inclusion of budesonide into micelles showed significant protective effect against the cytotoxic damage induced by the co-cultivation of differentiated human EOL-1 and HT-29 cells. This study revealed the capacity of PEO-PnBA-PAA terpolymer as carrier of nanosized micelles suitable for oral delivery of anti-inflammatory drugs.     

Micelle formation and drug release behavior of polypeptide graft copolymer and its mixture with polypeptide block copolymer

Self-association behavior of polypeptide graft copolymer and its mixture with polypeptide block copolymer and drug carrier capability of the formed micelles was examined. The results gained through fluorescence spectroscopy, transmission electron microscopy and nuclear magnetic resonance spectroscopy revealed that both polypeptide graft copolymer and its mixture with polypeptide block copolymer can self-assemble to form polymeric micelles in aqueous media. The molecular structure of the graft copolymer and blending the graft with block copolymer exert marked effects on the critical micelle concentration and the shape of formed micelles. It was found that the hydrophobic inner core of the micelles formed either by graft copolymer or mixture of graft and block copolymers can act as an incorporation site for the hydrophobic drugs. The drug loading content of the graft copolymer micelles tends to be larger when the content of the polypeptide segments in the copolymer increases. The results obtained from the drug-release studies showed that the drug-release rates are dependent on the chemical nature of the graft copolymer, the composition of the graft and block copolymer mixture, and also the pH value of the release media.     

Micelles in anticancer drug delivery

In recent years, the development of micelle-based carriers for cancer chemotherapy has been the object of growing scientific interest, both in academia and the pharmaceutical industry. Micelles have attracted attention in drug formulation and targeting, given that they provide a set of unique features. The core/shell structure accounts for their qualities as efficient drug delivery systems. The core provides a reservoir where hydrophobic drugs can be dissolved, and the corona confers hydrophilicity to the overall system. Sequestration of anticancer drugs in the inner core can protect them from premature degradation and allow their accumulation at tumoral sites. Micelles can be subdivided into two different groups according to their molecular weights: low-molecular-weight surfactant micelles and polymeric micelles. Although surfactant micelles such as polyethoxylated castor oil (e.g. Cremophor® EL) are commonly used to solubilize hydrophobic anticancer drugs such as paclitaxel, they have often been associated with serious adverse effects. Polymeric micelles may offer several advantages over surfactant micelles in terms of drug loading, adverse effects, stability, and targeting of tumors. Indeed, polymeric micelles can increase the circulation time of cytostatics and induce substantial changes in their biodistribution, including tumor accumulation via the enhanced permeation and retention effect. In addition, some recent studies have demonstrated that amphiphilic block copolymers (e.g. poloxamers) used for the preparation of polymeric micelles could increase the activity of several cytostatics by reversing multidrug resistance. This review first describes and compares surfactant micelle and polymeric micelle systems, already commercialized or under investigation, used to administer cytostatics. Secondly, their in vitro interactions with neoplastic cells and tissues are discussed in terms of cellular uptake and pharmacologic activity. In particular, the pharmacokinetics and biodistribution of micelles, along with the factors affecting their delivery to tumoral sites, are thoroughly discussed. Finally, in vivo studies reporting the anticancer activity and toxicity of drugs associated with micelles are reviewed.     

Ketal containing amphiphilic block copolymer micelles as pH-sensitive drug carriers

pH-Responsive linkages have been widely exploited in the development of polymeric drug delivery systems, which trigger drug release selectively at tumor tissues or endosomes and lysosomes of cells. Herein we report new pH-sensitive amphiphilic poly(ketal adipate)-co-poly(ethylene glycol) block copolymers (PKA-PEG), which have acid-cleavable ketal linkages in their hydrophobic backbone. PKA-PEG copolymers self-assemble to form stable micelles with a mean diameter of ~175 nm, which can encapsulate a payload of anticancer drugs and rapidly dissociate to release drug payload at the acid environment. The micelles are biocompatible and exhibit abilities to disrupt endosomes to enhance the cytosol drug delivery. Taken together, we anticipate that the pH-sensitive PKA-PEG micelles have great potential as anticancer drug carriers.     

Investigation of thermo-sensitive amphiphilic micelles as drug carriers for chemotherapy in cholangiocarcinoma in vitro and in vivo

Cholangiocarcinoma is an epithelial cancer of the bile ducts with poor prognosis and, in recent years, a rapidly increasing incidence. In this study, nano-sized thermo-sensitive micelles were investigated as drug carriers to improve chemotherapy in cholangiocarcinoma. Thermo-sensitive amphiphilic block copolymer, P-(N,N-isopropylacrylamide-co-N-hydroxymethylacrylamide)-b-caprolactone [P-(NIPAAm-co-NHMAAm)-b-PCL] with lower critical solution temperature (LCST) at about 38 °C was synthesized. Doxorubicin (DOX)-loaded micelles were prepared by dialysis method. The micelles exhibited a sustained and temperature-dependent DOX release. Toxicity of the blank micelles for human cholangiocarcinoma (QBC939) cells was minimal both in vitro and in vivo. In contrast, the DOX-loaded micelles effectively inhibited proliferation and induced apoptosis of QBC939 cells in vitro (p < 0.05) and inhibited tumor growth in nude mice by 21.49%. These results indicated that thermo-sensitive amphiphilic micelles are a promising and effective drug carrier, and show potential for improving chemotherapy for cholangiocarcinoma.     

Micellar Nanocarriers: Pharmaceutical Perspectives

Micelles, self-assembling nanosized colloidal particles with a hydrophobic core and hydrophilic shell are currently successfully used as pharmaceutical carriers for water-insoluble drugs and demonstrate a series of attractive properties as drug carriers. Among the micelle-forming compounds, amphiphilic copolymers, i.e., polymers consisting of hydrophobic block and hydrophilic block, are gaining an increasing attention. Polymeric micelles possess high stability both in vitro and in vivo and good biocompatibility, and can solubilize a broad variety of poorly soluble pharmaceuticals many of these drug-loaded micelles are currently at different stages of preclinical and clinical trials. Among polymeric micelles, a special group is formed by lipid-core micelles, i.e., micelles formed by conjugates of soluble copolymers with lipids (such as polyethylene glycol–phosphatidyl ethanolamine conjugate, PEG–PE). Polymeric micelles, including lipid-core micelles, carrying various reporter (contrast) groups may become the imaging agents of choice in different imaging modalities. All these micelles can also be used as targeted drug delivery systems. The targeting can be achieved via the enhanced permeability and retention (EPR) effect (into the areas with the compromised vasculature), by making micelles of stimuli-responsive amphiphilic block-copolymers, or by attaching specific targeting ligand molecules to the micelle surface. Immunomicelles prepared by coupling monoclonal antibody molecules to p-nitrophenylcarbonyl groups on the water-exposed termini of the micelle corona-forming blocks demonstrate high binding specificity and targetability. This review will discuss some recent trends in using micelles as pharmaceutical carriers.     

Novel Cyclosporin A formulations using MPEG-hexyl-substituted polylactide micelles: A suitability study

The immunosuppressive agent Cyclosporin A (CsA) has very poor solubility in water and, in consequence, non-aqueous formulations have been developed for its intravenous administration to treat patients with transplant rejection. In this article, aqueous micelle solutions of novel amphiphilic copolymers based on methoxy-poly(ethylene glycol) (MPEG) and hexyl-substituted poly(lactides) (hexPLA) were studied for possible incorporation and formulation of CsA, and for their biocompatibility towards novel pharmaceutical applications. Above the critical micellar concentration (CMC), MPEG-hexPLA block-copolymers self-assemble into unimodal micelles with diameters of around 30 nm, either unloaded or drug-loaded. The best shelf-life stability of these formulations was observed when stored at 4 °C with a drug loss inferior to 7% after 1 year. The polymer and micelle toxicities were evaluated in vitro for three different cell lines and in vivo using the chick embryo chorioallantoic membrane (CAM) model. The hemolytic property was assessed using human blood samples. As the studies revealed, MPEG-hexPLAs are non-toxic and do not show hemolysis; the same was found for the comparable MPEG-PLAs, both as unimers below their CMC and as polymeric micelles up to copolymer concentrations of 20 mg/mL. At this concentration, CsA was efficiently incorporated into MPEG-hexPLA micelles up to 6 mg/mL, which corresponds to a 500-fold increase of its water solubility. The current recommended clinical concentration administered per infusion (0.5-2.5 mg/mL) can be easily achieved and requires four times less copolymer than with the often-used Cremophor®EL surfactant. In this regard, MPEG-hexPLA micelle formulations can be an applicable formulation in transplant rejection treatments as an injectable CsA carrier system.     

Block copolymer micelles for drug delivery: design, characterization and biological significance

Recently, colloidal carrier systems have been receiving much attention in the field of drug targeting because of their high loading capacity for drugs as well as their unique disposition characteristics in the body. This paper highlights the utility of polymeric micelles formed through the multimolecular assembly of block copolymers as novel core-shell typed colloidal carriers for drug and gene targeting. The process of micellization in aqueous milieu is described in detail based on differences in the driving force of core segregation, including hydrophobic interaction, electrostatic interaction, metal complexation, and hydrogen bonding of constituent block copolymers. The segregated core embedded in the hydrophilic palisade is shown to function as a reservoir for genes, enzymes, and a variety of drugs with diverse characteristics. Functionalization of the outer surface of the polymeric micelle to modify its physicochemical and biological properties is reviewed from the standpoint of designing micellar carrier systems for receptor-mediated drug delivery. Further, the distribution of polymeric micelles is described to demonstrate their long-circulating characteristics and significant tumor accumulation, emphasizing their promising utility in tumor-targeting therapy. As an important perspective on carrier systems based on polymeric micelles, their feasibility as non-viral gene vectors is also summarized in this review article.     

Block copolymer micelles for drug delivery: Design,characterization and biological significance

Recently, colloidal carrier systems have been receiving much attention in the field of drug targeting because of their high loading capacity for drugs as well as their unique disposition characteristics in the body. This paper highlights the utility of polymeric micelles formed through the multimolecular assembly of block copolymers as novel core–shell typed colloidal carriers for drug and gene targeting. The process of micellization in aqueous milieu is described in detail based on differences in the driving force of core segregation, including hydrophobic interaction, electrostatic interaction, metal complexation, and hydrogen bonding of constituent block copolymers. The segregated core embedded in the hydrophilic palisade is shown to function as a reservoir for genes, enzymes, and a variety of drugs with diverse characteristics. Functionalization of the outer surface of the polymeric micelle to modify its physicochemical and biological properties is reviewed from the standpoint of designing micellar carrier systems for receptor-mediated drug delivery. Further, the distribution of polymeric micelles is described to demonstrate their long-circulating characteristics and significant tumor accumulation, emphasizing their promising utility in tumor-targeting therapy. As an important perspective on carrier systems based on polymeric micelles, their feasibility as non-viral gene vectors is also summarized in this review article.     

PEG-b-PPS diblock copolymer aggregates for hydrophobic drug solubilization and release: cyclosporin A as an example

Micelles formed from amphiphilic block copolymers have been explored in recent years as carriers for hydrophobic drugs. In an aqueous environment, the hydrophobic blocks form the core of the micelle, which can host lipophilic drugs, while the hydrophilic blocks form the corona or outer shell and stabilize the interface between the hydrophobic core and the external medium. In the present work, mesophase behavior and drug encapsulation were explored in the AB block copolymeric amphiphile composed of poly(ethylene glycol) (PEG) as a hydrophile and poly(propylene sulfide) PPS as a hydrophobe, using the immunosuppressive drug cyclosporin A (CsA) as an example of a highly hydrophobic drug. Block copolymers with a degree of polymerization of 44 on the PEG and of 10, 20 and 40 on the PPS respectively (abbreviated as PEG44-b-PPS10, PEG44-b-PPS20, PEG44-b-PPS40) were synthesized and characterized. Drug-loaded polymeric micelles were obtained by the cosolvent displacement method as well as the remarkably simple method of dispersing the warm polymer melt, with drug dissolved therein, in warm water. Effective drug solubility up to 2 mg/mL in aqueous media was facilitated by the PEG- b-PPS micelles, with loading levels up to 19% w/w being achieved. Release was burst-free and sustained over periods of 9-12 days. These micelles demonstrate interesting solubilization characteristics, due to the low glass transition temperature, highly hydrophobic nature, and good solvent properties of the PPS block.     

Local Delivery of Indomethacin to Arthritis-Bearing Rats through Polymeric Micelles Based on Amphiphilic Polyphosphazenes

Purpose Preparation, in vitro and in vivo evaluation of indomethacin-loaded polymeric micelles based on amphiphilic polyphosphazene. Methods Amphiphilic polyphosphazenes (PNIPAAm/EAB-PPPs) with poly (N-isopropylacrylamide) (PNIPAAm) and ethyl 4-aminobenzoate (EAB) as side groups were synthesized through thermal ring-opening polymerization and subsequent substitution reactions. Indomethacin (IND) loaded polymeric micelles based on PNIPAAm/EAB-PPPs were prepared by dialysis procedure. In vitro IND release kinetics was investigated in 0.1 M PBS (pH 7.4), while in vivo pharmacokinetics was performed in Sprague–Dawley rats. In vivo pharmacodynamic study was carried out based on two animal models, i.e. carrageenan-induced acute paw edema and complete Freund’s adjuvant (CFA) induced ankle arthritis model. Results Drug loading capacity of micelles based on this type of amphiphilic copolymers was mainly determined by copolymer composition and the chemical structure of drug. In addition to the compatibility between drug and micellar core, hydrogen bonding interaction between drug and hydrophilic corona may significantly influence drug loading as well. In vitro drug release in PBS suggested that there was no significant difference in release rate between micelles based on copolymers with various EAB content. Compared with the rats administered with free IND aqueous solution, IND concentration in rats’ plasma showed a prolonged maintenance in experimental group treated with IND-loaded polymeric micelles. In vivo pharmacodynamic study indicated that sustained therapeutic efficacy could be achieved through topical injection of the aqueous solution of IND-loaded micelles. Local delivery of IND can avoid the severe gastrointestinal stimulation, which was frequently associated with oral administration as evidenced by ulceration evaluation. Conclusions The promising results of current preliminary study suggest that this type of amphiphilic copolymers could be used as injectable drug carriers for hydrophobic drugs.     

Biodegradable amphiphilic polymer–drug conjugate micelles

The coupling of drugs to macromolecular carriers received an important impetus from Ringsdorf's notion of polymer–drug conjugates. Several water-soluble polymers, poly(ethylene glycol), poly[N-(2-hydroxypropyl) methacrylamide], poly(l-glutamic acid) and dextran, are studied intensively and have been utilized successfully in clinical research. The promising results arising from clinical trials with polymer–drug conjugates (e.g., paclitaxel, doxorubicin, camptothecins) have provided a firm foundation for other synthetic polymers, especially biodegradable polymers, used as drug delivery vehicles. This review discusses biodegradable polymeric micelles as an alternative drug–conjugate system. Particular focus is on A-B or B-A-B type biodegradable amphiphilic block copolymer such as polylactide, morpholine-2,5-dione derivatives and cyclic carbonates, which can form a core–shell micellar structure, with the hydrophobic drug-binding segment forming the hydrophobic core and the hydrophilic segment as a hydrated outer shell. Polymeric micelles can be designed to avoid uptake by cells of reticuloendothelial system and thus enhance their blood lifetime via the enhanced permeability and retention effect. Active tumor-targeting may be achieved by modifying the micelle surface with specific ligands. The potential application areas are discussed and future challenges are highlighted.     

Environmental-sensitive micelles based on poly(2-ethyl-2-oxazoline)-b-poly(L-lactide) diblock copolymer for application in drug delivery

Anticancer drug doxorubicin (DOX) was physically loaded into the micelles prepared from poly(2-ethyl-2-oxazoline)-b-poly(L-lactide) diblock copolymers (PEOz-PLLA). PEOz-PLLA consists of hydrophilic segment PEOz and hydrophobic segment PLLA showed pH-sensitivity in the aqueous solution. The DOX-loaded micelle exhibited a narrow size distribution with a mean diameter around 170 nm. The micellar structure can preserve hydrophobic drug DOX under the physiological condition (pH 7.4) and selectively release DOX by sensing the intracellular pH change in late endosomes and secondary lysosomes (pH 4-5). At 37 degrees C, the cumulated released rate of DOX from micelles was about 65% at pH 5.0 in the initial 24 h. Additionally, polymeric micelles had low cytotoxicity in human normal fibroblast HFW cells for 72 h by using MTT assay. Moreover, DOX-loaded micelles could slowly and efficiency decrease cell viability of non-small-cell lung carcinoma CL3 cells. Taken together, PEOz-b-PLLA diblock polymeric micelles may act as useful drug carriers for cancer therapy.     

Amphiphilic polymeric micelles as the nanocarrier for peroral delivery of poorly soluble anticancer drugs

Introduction: Many amphiphilic copolymers have recently been synthesized as novel promising micellar carriers for the delivery of poorly water-soluble anticancer drugs. Studies on the formulation and oral delivery of such micelles have demonstrated their efficacy in enhancing drug uptake and absorption, and exhibit prolonged circulation time in vitro and in vivo.

Areas covered: In this review, literature on hydrophobic modifications of several hydrophilic polymers, including polyethylene glycol, chitosan, hyaluronic acid, pluronic and tocopheryl polyethylene glycol succinate, is summarized. Parameters influencing the properties of polymeric micelles for oral chemotherapy are discussed and strategies to overcome main barriers for polymeric micelles peroral absorption are proposed.

Expert opinion: During the design of polymeric micelles for peroral chemotherapy, selecting or synthesizing copolymers with good compatibility with the drug is an effective strategy to increase drug loading and encapsulation efficiency. Stability of the micelles can be improved in different ways. It is recommended to take permeability, mucoadhesion, sustained release, and P-glycoprotein inhibition into consideration during copolymer preparation or to consider adding some excipients in the formulation. Furthermore, both the copolymer structure and drug loading methods should be controlled in order to get micelles with appropriate particle size for better absorption.     

Solubilization of cyclosporin A in dextran-g-polyethyleneglycolalkyl ether polymeric micelles.

Solubilization of the poorly water-soluble drug, Cyclosporin A (CsA), in aqueous dispersions of dextran-grafted-polyethyleneglycolalkyl ether (DEX-g-PEG-Cn) polymeric micelles was examined as a function of copolymer structure. In aqueous solution, DEX-g-PEG-Cn form polymeric micelles of low critical association concentrations (CAC) and small micelle sizes as determined by fluorescence spectroscopy and dynamic light scattering (DLS). Copolymers with longer polysaccharide chain showed larger CAC and mean diameter. The percentage of CsA loading into micelles was determined by high performance liquid chromatography. It was significantly larger in polymeric micelles compared to unmodified dextrans. It increased with increasing number of PEG-Cn units grafted per dextran chain and decreasing dextran molecular weight. The cytotoxicity of DEX-g-PEG-C(16) polymeric micelles towards Caco-2 cells, tested by MTT cytotoxicity assay, was significantly lower than that of free PEG-C(16) molecules. It can be concluded that the length of the hydrophilic part as well as the content and chemical nature of the hydrophobic substituents have an important effect on the ability of polymeric micelles to solubilize poorly-water soluble drugs.     

Amphiphilic polysaccharide-hydrophobicized graft polymeric micelles for drug delivery nanosystems

Self-assembled amphiphilic graft copolymers in aqueous solution to form polymeric micelles, have received growing scientific attention over the years. Among the polymeric micelles, hydrophobicized polysaccharides have currently become one of the hottest researches in the field of drug delivery nanosystems. It is attributable to such appealing properties as small particle size and narrow size distribution, distinctive core-shell structure, high solubilization capacity and structural stability, tumor passive localization by enhanced permeability and retention (EPR) effect, active targeting ability via tailored targeting promoiety, long-circulation property and facile preparation. The polymeric micelles self-assembled by hydrophobicized polysaccharides can be employed as targeted drug delivery nanosystem by including thermo- or pH-sensitive components or by attaching specific targeted moieties to the outer hydrophilic surface. Beside encapsulation of water-insoluble drugs, hydrophobicized polysaccharide polymeric micelles can complex with charged proteins or peptide drugs through electrostatic force or hydrogen bond, and serve as an effective non-viral vector for gene delivery. In the latter case, polymeric micelles can not only markedly protect these macromolecules from degradation by protease or ribozymes, but also increase the gene transfection efficiency. This review will highlight the state of the art self-assembled mechanism, characterization, preparation methods and surface modification of hydrophobicized polysaccharide polymeric micelles and their recent rapid applications as drug delivery nanosystems.     

In vitro human plasma distribution of nanoparticulate paclitaxel is dependent on the physicochemical properties of poly(ethylene glycol)-block-poly(caprolactone) nanoparticles

In this study, we synthesized and characterized two methoxy poly(ethylene glycol)-block-poly(caprolactone) (MePEG-b-PCL) amphiphilic diblock copolymers, both based on MePEG with a molecular weight of 5000 g/mol (114 repeat units) and PCL block lengths of either 19 or 104 repeat units. Nanoparticles were formed from these copolymers by a nanoprecipitation and dialysis technique. The MePEG₁₁₄-b-PCL₁₉ copolymer was water soluble and formed micelles that had a hydrodynamic diameter of 40 nm at all copolymer concentrations tested, and displayed a relatively low core microviscosity. The practically water insoluble MePEG₁₁₄-b-PCL₁₀₄ copolymer formed nanoparticles with a larger hydrodynamic diameter, which was dependent on copolymer concentration, and possessed a higher core microviscosity than the MePEG₁₁₄-b-PCL₁₉ micelles, characteristic of nanospheres. The micelles solubilized a maximum of 1.6% w/w of the hydrophobic anticancer agent, paclitaxel (PTX), and released 92% of their drug payload over 7 days, as compared to the nanospheres, which solubilized a maximum of 3% w/w of PTX and released 60% over the same period of time. Both types of nanoparticles were found to be hemocompatible, causing only minimal hemolysis and no changes in plasma coagulation times as compared to control. Upon in vitro incubation in human plasma, PTX solubilized by micelles had a plasma distribution similar to free drug. The majority of PTX was associated with the lipoprotein deficient plasma (LPDP) fraction, which primarily consists of albumin and alpha-1-acid glycoprotein. In contrast, nanospheres were capable of retaining more of the encapsulated drug with significantly less PTX partitioning into the LPDP fraction.