Design and synthesis of pH-sensitive polymeric micelles for oral delivery of poorly water-soluble drugs

pH-sensitive polymer poly (polylactide-co-methacrylic acid)–b-poly (acrylic acid) was synthesized using atom transfer radical polymerization and ring-opening polymerization and characterized by gel permeation chromatography and ¹H NMR. The polymers can self-assemble to form micelles in aqueous medium, which respond rapidly to pH change within the gastrointestinal relevant pH range. Critical micelle concentrations and pH response behavior of the polymeric micelle were investigated. Water-insoluble drug nifedipine was loaded and the drug-loading content can be controlled by tuning the composition of the polymers. The in vitro release studies indicate pH sensitivity enabled rapid drug release at the environment of simulated intestinal fluid (pH 7.36), the cumulative released amount of NFD reached more than 80% within 24 h, while only 35% in the simulated gastric fluid (pH 1.35). All the results showed that the pH-sensitive P(PLAMA-co-MAA)–b-PAA micelle may be a prospective candidate as oral drug delivery carrier for hydrophobic drugs with controlled release behavior.     

Enhanced solubility and targeted delivery of curcumin by lipopeptide micelles

A lipopeptide (LP)-containing KKGRGDS as the hydrophilic heads and lauric acid (C₁₂) as the hydrophobic tails has been designed and prepared by standard solid-phase peptide synthesis technique. LP can self-assemble into spherical micelles with the size of ~30 nm in PBS (phosphate buffer saline) (pH 7.4). Curcumin-loaded LP micelles were prepared in order to increase the water solubility, sustain the releasing rate, and improve the tumor targeted delivery of curcumin. Water solubility, cytotoxicity, in vitro release behavior, and intracellular uptake of curcumin-loaded LP micelles were investigated. The results showed that LP micelles can increase the water solubility of curcumin 1.1 × 10³ times and sustain the release of curcumin in a low rate. Curcumin-loaded LP micelles showed much higher cell inhibition than free curcumin on human cervix carcinoma (HeLa) and HepG2 cells. When incubating these curcumin-loaded micelles with HeLa and COS7 cells, due to the over-expression of integrins on cancer cells, the micelles can efficiently use the tumor-targeting function of RGD (functionalized peptide sequences: Arg-Gly-Asp) sequence to deliver the drug into HeLa cells, and better efficiency of the self-assembled LP micelles for curcumin delivery than crude curcumin was also confirmed by LCSM (laser confocal scanning microscope) assays. Combined with the enhanced solubility and higher cell inhibition, LP micelles reported in this study may be promising in clinical application for targeted curcumin delivery.     

Oligoalanine-modified Pluronic-F127 nanocarriers for the delivery of curcumin with enhanced entrapment efficiency

Curcumin is a naturally occurring compound that has been shown to have anti-oxidant, anti-inflammatory, and anti-carcinogenic activities. However, its pharmaceutical potential has been limited due to its low solubility in water. The use of amphiphilic nanocarriers is an attractive and simple method to solubilize curcumin. In this study, we modified Pluronic F-127 [poly(ethylene glycol)₁₀₀-block-poly(propylene glycol)₆₅-block-poly(ethylene glycol)₁₀₀] (PF-127) with oligomers of alanine, an amino acid, to increase the drug entrapment efficiency of curcumin through core stabilization. Alanine-modified PF-127 exhibited lower critical micelle concentration and decreased molecular motion in both the hydrophilic and hydrophobic segments (¹H NMR). Nanocarriers in the size range of 54.2–68.4?nm were observed. Entrapment efficiency of curcumin increased by at most 66% (from 25.3 to 91.3%) and the difference in solubility was clearly visualized by increased transparency of the nanocarrier solutions. Curcumin was released continuously up to 120?h from modified carriers, while drug release from unmodified carriers plateaued within 24?h. These modified nanocarriers exhibited no cytotoxicity and more efficiently delivered drugs to HeLa cells as confirmed by fluorescent microscopy. This study demonstrated that alanine modification of FDA-approved PF-127 affects copolymer nanoassembly and has a profound impact on curcumin loading and possibly on other hydrophobic drugs as well.     

The tumor accumulation and therapeutic efficacy of doxorubicin carried in calcium phosphate-reinforced polymer nanoparticles

A mineral (calcium phosphate, CaP)-reinforced core-shell-corona micelle was evaluated as a nanocarrier of doxorubicin (DOX) for cancer therapy. The polymer micelles of poly(ethylene glycol)-b-poly(L-aspartic acid)-b-poly(L-phenylalanine) (PEG-PAsp-PPhe) in the aqueous phase provided the three distinct functional domains: the hydrated PEG outer corona for prolonged circulation, the anionic PAsp middle shell for CaP mineralization, and the hydrophobic PPhe inner core for DOX loading. CaP mineralization was performed by initial electrostatic localization of calcium ions at anionic PAsp shells, and the consequent addition of phosphate anions to trigger the growth of CaP. The mineralization did not affect the micelle size or the spherical morphology. The CaP-mineralized micelles exhibited enhanced serum stability. The DOX release from the DOX-loaded mineralized micelles (DOX-CaP-PM) at physiological pH was efficiently inhibited, whereas at an endosomal pH (pH 4.5), DOX release was facilitated due to the rapid dissolution of the CaP mineral layers in the middle shell domains. The in vivo tissue distribution and tumor accumulation of the DOX-CaP-PM that were labeled with a near-infrared fluorescent (NIRF) dye, Cy5.5, were monitored in MDA-MB231 tumor-bearing mice. Non-invasive real-time optical imaging results indicated that the DOX-CaP-PM exhibited enhanced tumor specificity due to the prolonged stable circulation in the blood and an enhanced permeation and retention (EPR) effect compared with the DOX-loaded nonmineralized polymer micelles (DOX-NPM). The DOX-CaP-PM exhibited enhanced therapeutic efficacy in tumor-bearing mice compared with free DOX and DOX-NPM. The CaP mineralization on assembled nanoparticles may serve as a useful guide for enhancing the antitumor therapeutic efficacy of various polymer micelles and nano-aggregates.     

Increased Drug-Loading Enhances the Activity of Ellipticine in Poly(N-(2-hydroxypropyl) Methacrylamide) PHPMA-Based Polymeric Micelles in 2D and 3D Cancer Cell Models

Polymeric micelles are widely used as multifunctional drug carriers of poorly water-soluble drugs, but the role of drug loading content is often overlooked. The purpose of this study is to investigate the cellular uptake and penetration of polymeric micelles with different drug loading contents and their effects on biological activities. In this study, poly(N-(2-hydroxypropyl) methacrylamide-co-methacrylic acid)-block-poly methyl methacrylate P(HPMA-co-MAA)-b-PMMA micelles are used as a nanocarrier for the encapsulation of the potent anticancer agent ellipticine (EPT). The micelles are loaded with various amounts of EPT and the physicochemical characteristics such as particle size, morphology, and zeta potential of blank and EPT loaded nanoparticles are studied. Moreover, fluorescent lifetime studies confirm that hydrophobic EPT is indeed in the PMMA micelle core. In vitro cytotoxicity tests using the glioma cell line U87MG reveal lower IC₅₀ values when the cells are incubated with micelle with high drug loading content. The higher toxicity in micelles with higher drug loading content is associated with higher cellular uptake, which is monitored using laser scanning confocal microscopy and flow cytometry. Moreover, higher activity of micelles with higher drug loading is also observed in U87MG multicellular tumor spheroids although the difference is not significant.     

Constructing doxorubicin-loaded polymeric micelles through amphiphilic graft polyphosphazenes containing ethyl tryptophan and PEG segments

By changing the molar ratio of hydrophilic and hydrophobic segments, a series of novel amphiphilic graft polyphosphazenes (PEG/EtTrp-PPPs) was synthesized via thermal ring-opening polymerization and a subsequent two-step substitution reaction of hydrophilic methoxyl polyethylene glycol (MPEG) and hydrophobic ethyl tryptophan (EtTrp). ¹H-Nuclear magnetic resonance and Fourier transform infrared studies validated the expected synthesis of copolymers. The copolymer composition was also confirmed by UV–visible spectrophotometry. The molar ratio of the segment PEG to group EtTrp was 1.33:0.67, 1.01:0.99 and 0.78:1.22, respectively. Micellization behavior of PEG/EtTrp-PPPs in an aqueous phase was characterized by fluorescence technique, dynamic light scattering and transmission electron microscopy. The critical micelle concentration (CMC) of the graft copolymer in aqueous solution was 0.158, 0.033 and 0.020 g l^?1, which decreased as the hydrophobic content in amphiphilic copolymers increased. Doxorubicin (DOX) was physically loaded into micelles prepared by an O/W emulsion method with a drug loading content increasing with DOX feeding. In vitro release of DOX from micelles can be accelerated in weak acidic solution. The results of cytotoxicity study using an MTT assay method with HeLa cell showed that amphiphilic graft polyphosphazenes were biocompatible while DOX-loaded micelles achieved comparable cytotoxicity with that of free DOX. In summary, these novel amphiphilic copolymers exhibited potential to be used as injectable drug carriers for tumor treatment.     

A smart micellar system with an amine-containing polycarbonate shell

The present paper reports the design and preparation of an amphiphilic triblock co-polymer poly(ε-caprolactone) (PCL)-poly(6,14-dimethyl-1,3,9,11-tetraoxa-6,14-diaza-cyclohexadecane-2,10-dione) (PADMC)-PCL and the use of micelles composed of them as carriers for pH-sensitive drug release. The triblock co-polymers were synthesized via two-step ring-opening polymerization with catalysis by Novozym-435 lipase. By adjusting the feed ratio, three co-polymers with different PCL lengths and the same PADMC length were produced. The block structure of the co-polymers obtained was confirmed by comparative studies on PCL-PADMC-PCLs and the corresponding random poly(ε-caprolactone-random-6,14-dimethyl-1,3,9,11-tetraoxa-6,14-diaza-cyclohexadecane-2,10-dione) (poly(CL-r-ADMC)) by means of nuclear magnetic resonance and differential scanning calorimetry. Cell cytotoxicity tests showed that the co-polymer displayed no apparent cytotoxicity to 293T and HeLa cells. Transmissions electron microscopy indicates that the self-assembled micelles exhibited a well-defined spherical shape with a diameter between ～30 and 50 nm. The critical aggregation concentration was dependent on the block composition. Due to the presence of ionizable tertiary amine groups in the PADMC block, acid-induced variation in the micellar morphology was evident with respect to micelle size and size distribution. The size-pH curve was characterized by a smooth sigmoid form, and had a dramatic upward shift with decreasing pH from 6.5 to 4.5, which correlated well with the buffer range of hydrophilic PADMC. As a demonstration of the potential of PCL-PADMC-PCL micelles to control drug delivery, acid induced drug release for prednisone acetate-loaded micelles was explored. PCL-PADMC-PCL micelles show good promise as smart drug carriers, sensing the local specific pH decrease around lesion sites.     

Amphiphilic block copolymers bearing six-membered ortho ester ring in side chains as potential drug carriers: synthesis,characterization, and in vivo toxicity evaluation

A new type of amphiphilic block copolymers, poly(ethylene glycol)-block-poly(2-methyl-acrylicacid 2-methoxy-5-methyl-[1,3]dioxin-5-ylmethyl ester) (PEG-b-PMME), bearing acid-labile six-membered ortho ester rings in side chains was synthesized by reversible addition–fragmentation chain-transfer polymerization, and the influence of chain length of the hydrophobic PMME block on micelle properties was investigated. The PEG-b-PMME micelles were stable in aqueous buffer at physiological pH with a low critical micelle concentration. Nile Red as a model drug was encapsulated into the micelles to explore the release profiles. The Nile Red-loaded polymeric micelles showed rapid release of Nile Red in weakly acidic environments (pH 5) but slow release under physiological condition (pH 7.4), due to different hydrolysis rate of ortho ester side chains of PEG-b-PMME. The Paclitaxel (PTX)-loaded micelles retained potency in killing lung cancer cells (A549), compared with the free PTX. No obvious toxicity was found in vitro and in vivo after intraperitoneal injection of the micelles, which confirms that the PEG-b-PMME micelles with unique acid-labile characteristic have great potential as nano-scaled carriers for drug delivery.     

A one-pot synthesis of oleic acid end-capped temperature- and pH-sensitive amphiphilic polymers

A one-pot synthesis of an amphiphilic oleic acid-end capped random poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) (2) is reported. In aqueous media, the solubility of 2 was temperature- and pH-sensitive. Both the lower critical solution temperature and critical micelle concentration (CMC) of 2 were pH-dependent. The LCST of 2 was around 35.2 degrees C in acidic buffer solutions (pH=2.00-5.00), and it was increased significantly to around 38.4 degrees C in neutral and alkaline buffer solutions (pH 7.00-11.00). Polymer 2 exhibited a phase transition pH around 6.7, below which the polymer became significantly less water-soluble. The CMC of 2 was 40 mg/l in pH 2.0 buffer solution, and it was increased markedly to 60-67 mg/l in pH 7.0 and pH 11.0 buffer solutions. Micelle solutions of 2 in different pH conditions were prepared by a membrane-dialysis method. In aqueous solution, dynamic light scattering studies revealed that the size of micelles was 50-90 nm with the particle size being larger in acidic solutions. In solid state, transmission electron microscope studies showed that micelles were roughly spherical, their sizes were 25-90 nm and it decreased with the increase of solution pH. The pH-sensitivity of 2 was triggered by the -COOH in the hydrophobic segment. The temperature- and pH-sensitivity of the novel polymeric micelles would make an interesting drug delivery system.     

The accumulation of dual pH and temperature responsive micelles in tumors

An optimized, biodegradable, dual temperature- and pH-responsive micelle system conjugated with functional group Cy5.5 was prepared in order to enhance tumor accumulation. The Dynamic light scattering (DLS) measurements showed that these diblock copolymers form micelle in PBS buffer with a size of around 50 nm by heating of an aqueous polymer solution from below to above the cloud point (CP). Anticancer drug, doxorubicin was incorporated into the inner core of micelle by hot shock protocol. The size and stability of the micelle were controlled by the copolymer composition and is fine tuned to extracellular pH of tumor. The mechanism then caused pH change and at body temperature which induce doxorubicin release from micelles and have strong effects on the viability of HeLa, ZR-75-1, MCF-7 and H661 cancer cells. Our in vivo results revealed a clear distribution of Doxorubicin-loaded mixed micelle (Dox-micelle) and efficiency targeting tumor site with particles increasing size in the tumor interstitial space, and the particles could not diffuse throughout the tumor matrix. In vivo tumor growth inhibition showed that Dox-micelle exhibited excellent antitumor activity and a high rate of anticancer drug in cancer cells by this strategy.     

Evaluation of in vitro release and in vivo efficacy of mPEG-PLA-haloperidol conjugate micelle-like structures

Polymeric prodrugs of mPEG-PLA-haloperidol (methoxy poly(ethylene glycol)-b-poly (lactic acid)), self-assemble into nanoscale micelle-like structures in aqueous solutions. The micelles range in size from 28 to 52 nm in diameter and have been shown to be spherical in shape using cryogenic transmission electron microscopy. In this current work there is evidence shown that suggests these micelle-like structures do not dissociate below their critical micelle concentration (CMC) when the PEG weight percent is at least 68, releasing physically entrapped drug from intact micelles over a 3-day period. However, 55 wt % PEG micelles dissociate below their CMC, and release their physically entrapped drug within 8 h. Conjugate polymer micelles most closely approach a linear release profile over a 5-day period. Conjugate micelles with free drug incorporated, known as combination micelle-like structures, release drug over 4 days. However, these combination micelles have the fastest burst release indicating that free drug was potentially dominating the first 8 h of release, after which hydrolysis of covalently linked drug took over. In vivo behavioral studies can assess haloperidol bioactivity from drug loaded micelle-like structures on ketamine induced hyperlocomotion. Results are consistent with in vitro release data, showing that conjugate and combination micelles continue to release haloperidol 4 days post injection, attenuating the effects of the ketamine induced hyperlocomotion. Furthermore, results indicate that the sedative side effects of haloperidol were reduced with the micelle delivery systems as compared to the acute haloperidol injection.     

Tumor targeting by pH-sensitive,biodegradable, cross-linked N-(2-hydroxypropyl) methacrylamide copolymer micelles

Increasing the molecular weight of N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers by using micellar structures could result in more pronounced enhanced permeability and retention effect, thus increase the tumor accumulation of drug. However, most micellar formulations are relatively unstable and release their drug non-specifically. To improve on these disadvantages, we developed a micellar drug delivery system based on self-assembly of HPMA copolymers. Amphiphilic conjugates were synthesized by conjugating the hydrophobic drug doxorubicin and hydrophobic β-sitosterol to the hydrophilic HPMA polymer backbone via pH-sensitive hydrazone linkages. This linkage is quite stable at physiological pH but hydrolyzes easily at acidic pH. After conjugates self-assembly into micelles, HPMA copolymer side chains were cross-linked through the hydrazone linkages to ensure micelle stability in the blood. Using this approach, cross-linked micelles were obtained with molecular weight of 1030 KD and diameter of 10–20 nm. These micelles remained stable with undetectable doxorubicin release at pH 7.4 or mouse plasma, whereas collapsed quickly with 80% of the drug released at pH 5 which corresponds to the pH of lyso/endosome compartments of tumor cells. Both cross-linked and non-cross-linked micelles displayed similar in vitro anti-tumor activity as linear copolymer conjugates in Hep G2 and A549 cancer cell lines with internalization mechanism by caveolin, clathrin, and giant macropinocytosis. In vivo studies in an H22 mouse xenograft model of hepatocarcinoma showed the tumor accumulation (1633 μCi/L*h) and anti-tumor rate (71.8%) of cross-linked micelles were significantly higher than non-cross-linked ones (698 μCi/L*h, 64.3%). Neither type of micelle showed significant toxicity in heart, lung, liver, spleen or kidney. These results suggest that cross-linked HPMA copolymer micelles with pH-sensitivity and biodegradability show excellent potential as carriers of anti-cancer drugs.     

Mixed Hyperbranched/Triblock Copolymer Micelle Assemblies: Physicochemical Properties and Potential for Drug Encapsulation

Mixed micelles have numerous advantages while requiring little to no effort in preparation. This study aims to produce mixed micelle nanostructures from a linear triblock copolymer and a hyperbranched random copolymer, and is able to be loaded with the weakly water-soluble drugs curcumin and indomethacin. Different preparation techniques are employed to produce mixed micelles comprised of Pluronic F127 block copolymer, and hyperbranched poly[(ethylene glycol) methyl ether methacrylate-co-lauryl methacrylate], H-[P(OEGMA-co-LMA)], copolymer. Few studies have dabbled in these types of coassemblies, which provides insight into how structural differences of each copolymer can affect the formation of micelles. To determine the properties of the emerging nanostructures in aqueous environments, including their size, homogeneity, and surface charge, different physicochemical techniques are used, such as light scattering and spectroscopic methods. The results reveal that the copolymers combine, and spontaneously self-assemble into mixed micelle-like nanostructures in aqueous environments, whereas both systems of neat and drug-loaded nanostructures exhibit desirable properties such as small average micelle hydrodynamic radii and low size polydispersity indices. The nanostructures that result from the effective encapsulation of curcumin exhibit outstanding stability over 169 days. The fluorescent qualities of curcumin persist after encapsulation, making the novel nanostructures excellent candidates for bioimaging applications.     

Self-assembled pH-responsive MPEG-b-(PLA-co-PAE) block copolymer micelles for anticancer drug delivery

A series of amphiphilic pH-responsive poly (ethylene glycol) methyl ether-b-(poly lactic acid-co-poly (β-amino esters)) (MPEG-b-(PLA-co-PAE)) block copolymers with different PLA/PAE ratios were designed and synthesized via a Michael-type step polymerization. The molecular structures of the copolymers were confirmed with (1)H NMR and gel permeation chromatography (GPC). These amphiphilic copolymers were shown to self-assemble into core/shell micelles in aqueous solution at low concentrations, and their critical micelle concentrations (CMC) in water were 1.2-9.5 mg/L. The pH-responsive PAE segment was insoluble at pH 7.4, but it became positively charged and soluble via protonation of amino groups at pH lower than 6.5. The average particle size and zeta potential of micelles increased from 180 nm and 15 mV to 220 nm and 40 mV, respectively, when the pH decreased from 7.4 to 5.0. Doxorubicin (DOX) was loaded into the core of these micelles with a high drug loading of 18%. The in vitro DOX release from the micelles was significantly accelerated when solution pH decreased from 7.4 to 5.0. DOX release in the first 10 h appeared to follow Fickian diffusion mechanism. Toxicity test showed that the copolymers had low toxicity whereas the DOX-loaded micelles remained high cytotoxicity for HepG2 cells. The results indicate the pH-sensitive MPEG-b-(PLA-co-PAE) micelle may be a potential hydrophobic drug delivery carrier for cancer targeting therapy with sustained release.     

An Amphiphilic Nanocarrier Based on Guar Gum-graft-Poly(ε-caprolactone) for Potential Drug-Delivery Applications

Amphiphilic guar gum grafted with poly(ε-caprolactone) (GG-g-PCL) was fabricated as a drug-delivery carrier using microwave irradiation. The structure of the GG-g-PCL co-polymer was characterized by ¹H-NMR spectroscopy. By microwave irradiation, GG-g-PCL with high grafting percentage (>200%) was obtained in a short reaction time. The GG-g-PCL co-polymer is capable of self-assembling into nanosized spherical micelles in aqueous solution with the diameter of around 75–135 nm and 60–100 nm, as determined by DLS and TEM, respectively. The critical micelle concentration (CMC) of GG-g-PCL was found to be approx. 0.56 mg/l in a phosphate buffer solution. The drug-release profile showed that the GG-g-PCL micelles provided an initial burst release followed by a sustained release of the entrapped hydrophobic model drug, ketoprofen, over a period of 10–68 h. Under physiological conditions, the GG-g-PCL co-polymer hydrolytically degraded into lower-molecular-weight fragments within a 7-week period. These results suggest that the GG-g-PCL micelles could be used as a nanocarrier for in vitro controlled drug delivery.     

Multifunctional superparamagnetic nanocarriers with folate-mediated and pH-responsive targeting properties for anticancer drug delivery

Multifunctional nanocarriers with multilayer core-shell architecture were prepared by coating superparamagnetic Fe(3)O(4) nanoparticle cores with a mixture of the triblock copolymer methoxy poly(ethylene glycol)-b-poly(methacrylic acid-co-n-butyl methacrylate)-b-poly(glycerol monomethacrylate) and the folate-conjugated block copolymer folate-poly(ethylene glycol)-b-poly(glycerol monomethacrylate). The model anticancer agent adriamycin (ADR), containing an amine group and a hydrophobic moiety, was loaded into the nanocarrier at pH 7.4 by ionic bonding and hydrophobic interactions. The release rate of the loaded drug molecules was slow at pH 7.4 (i.e. mimicking the blood environment) but increased significantly at acidic pH (i.e. mimicking endosome/lysosome conditions). Acid-triggered drug release resulted from the polycarboxylate protonation of poly(methacrylic acid), which broke the ionic bond between the carrier and ADR. Cellular uptake by folate receptor-overexpressing HeLa cells of the folate-conjugated ADR-loaded nanoparticles was higher than that of non-folated-conjugated nanoparticles. Thus, folate conjugation significantly increased nanoparticle cytotoxicity. These findings show the potential viability of a folate-targeting, pH-responsive nanocarrier for amine-containing anticancer drugs.     

pH‐Sensitive Poly(ethylene glycol)/Poly(ethoxyethyl glycidyl ether) Block Copolymers: Synthesis,Characterization, Encapsulation,and Delivery of a Hydrophobic Drug

Curcumin is a natural polyphenolic compound known for its numerous pharmacological properties. However, its low water solubility and instability at neutral pH are serious drawbacks preventing its use as an oral drug. Well‐defined amphiphilic poly(ethylene glycol)‐block‐poly(ethoxyethyl glycidyl ether) (PEG‐b‐PEEGE) block copolymers carrying acid‐labile acetal groups are synthesized by anionic ring‐opening polymerization and investigated as potential pH‐sensitive nano‐carriers for delivery of curcumin to cancer cells. The nanoparticles, resulting from copolymer self‐assembly in aqueous media, are characterized by dynamic light scattering and cryo‐transmission electron microscopy. The nanoparticles’ stabilities are evaluated in three different phosphate buffers (pH = 7.2, 6.4, and 5.3). The stability decreases at lower pH and a complete disappearance of the nanoparticles is noticed after 4 days at pH 5.3. Curcumin is encapsulated in hydrophobic core of mPEG₄₀‐b‐PEEGE₂₅ nanoparticles allowing significant enhancements of curcumin solubility in water and lifetime at neutral pH. In vitro curcumin release is studied at different pH by UV‐spectroscopy and high‐performance liquid chromatography (HPLC). The cytotoxicity of curcumin and curcumin encapsulated in micelles is evaluated by cell viability 3‐(4,5‐Dimethyl‐2‐thiazolyl)‐2,5‐diphenyl‐2H‐tetrazolium bromide (MTT) assay on MDA‐MB‐231 human breast cancer cells.     

Self-assembled, fluorescent polymeric micelles of a graft copolymer containing carbazole for thermo-controlled drug delivery in vitro

A novel thermosensitive amphiphilic graft copolymer PNIPAAm-g-PCbzEA appending carbazole group was successfully designed and synthesized by the free radical copolymerization of N-isopropylacrylamide with hydrophobic precursor polymers of vinyl-functionalized poly(2-(N-carbazolyl)ethyl acrylate) (PCbzEA) in DMF. The PNIPAAm-g-PCbzEA copolymer was characterized by FTIR, (1)H NMR, GPC analysis, UV-vis spectroscopy and fluorescence spectroscopy. The TEM observation shows that the graft copolymer may self-assemble into polymeric micelles exhibiting a nanospheric morphology within a narrow size range of 30-60 nm in aqueous solution. From the (1)H NMR and FTIR analysis, the polymer micelles are composed of hydrophobic PCbzEA segments as the cores and the hydrophilic PNIPAAm segements as outer shells. The resulting micelles exhibited the temperature sensitivity with a lower critical solution temperature (LCST) of 31.5 degrees C and a critical micelle concentration (CMC) of 12.9 mg/L in water. In the study of drug release, an "on-off" drug release profile was found in response to stepwise temperature changes between 20 and 40 degrees C. The cytotoxicity assays for vero cells shows good biocompatibility of the graft copolymer in vitro.     

Uptake enhancement of curcumin encapsulated into phosphatidylcholine-shielding micelles by cancer cells

Internalization of drugs by cancer cells is a crucial factor to impact cancer treatment effect. Curcumin, having inhibitory effect on a variety of cancers, was encapsulated into micelles of six-arm star-shape poly(ε-caprolactone)-b-poly(2-methacryloyloxyethylphosphorylcholine) (6sPCL-PMPC) in order to enhance its concentration in blood and cellular uptake. Micelles and curcumin-loaded micelles were prepared by the solvent-evaporation method. Drug-loading content and drug-loading efficiency could be achieved as high as 18.9 and 98%. MTT results showed that these curcumin-loaded micelles displayed significant cell cytotoxicity, while these blank micelles were noncytotoxic. The curcumin-loaded 6sPCL-PMPC micelles showed higher efficiency to kill HeLa cells than that of curcumin-loaded PCL-PEG micelles. The cellular uptake study indicated that the curcumin encapsulated into 6sPCL-PMPC micelles was ingested more by HeLa cells than the curcumin encapsulated into PCL-PEG micelles. In conclusion, the micelles with phosphatidylcholine (PC) groups as their exterior can greatly enhance the uptake by HeLa cells and the cytotoxicity of curcumin due to excellent internalization by cancer cells.     

Arg-Gly-Asp (RGD) peptide conjugated poly(lactic acid)-poly(ethylene oxide) micelle for targeted drug delivery

In this study, a new poly(lactic acid)-poly (ethylene oxide)-Arg-Gly-Asp (PLA-PEO-RGD) derivative was synthesized, and paclitaxel-loaded PLA-PEO-RGD micelles were prepared by this derivative. The solubility assay showed that micelles mixed with Pluronic F-68 as surfactant could increase the solubility of this hydrophobic paclitaxel in aqueous solution. The cell-binding assay showed that PLA-PEO-RGD micelle (IC(50) = 11.13 +/- 1.38 nmol/L) had about 3.6-fold higher integrin avidity than PLA-PEO-RGD conjugates (IC(50) = 40.33 +/- 3.12 nmol/L). The avidity of micelle was also higher than RGD4C peptide (IC(50) = 24.44 +/- 1.21 nmol/L). The in vitro drug release profile of drug-loaded PLA-PEO-RGD micelles exhibited initial burst release to 37% +/- 2% (w/w) during the first 12 h, and then the release rate became steady in a controlled release manner. Furthermore, treatment of the MDA-MB-435 breast cancer cell line with paclitaxel-loaded PLA-PEO-RGD micelles yielded cytotoxicities, with EC(50) values of approximately 30 mumol/L. The paclitaxel-loaded PLA-PEO-RGD micelles treated group showed the most dramatic tumor reduction in MDA-MB-435 tumor-bearing nude mice, and the final mean tumor load was 31 +/- 16 mm(3) (mean +/- SD; n = 8). (125)I-labeled micelles administration resulted in significant (p < 0.001) higher tumor uptake (2.68% +/- 0.14%, ID/g) of PLA-PEO-RGD micelles compared to PLA-PEO micelles (0.84% +/- 0.09%, ID/g) after 2.5 h postinjection. Biodistribution study showed the best blood clearance of PLA-PEO-RGD micelles after 4.5 h postinjection. The results of this study suggest that paclitaxel-loaded PLA-PEO-RGD micelles based on the specific recognition of alpha(V)beta(3) integrin represent a potential and powerful target delivery technology.