Conjugation of arginine-glycine-aspartic acid peptides to poly(ethylene oxide)-b-poly(epsilon-caprolactone) micelles for enhanced intracellular drug delivery to metastatic tumor cells

An arginine-glycine-aspartic acid (RGD) containing model peptide was conjugated to the surface of poly(ethylene oxide)-block-poly(epsilon-caprolactone) (PEO-b-PCL) micelles as a ligand that can recognize adhesion molecules overexpressed on the surface of metastatic cancer cells, that is, integrins, and that can enhance the micellar delivery of encapsulated hydrophobic drug into a tumor cell. Toward this goal, PEO-b-PCL copolymers bearing acetal groups on the PEO end were synthesized, characterized, and assembled to polymeric micelles. The acetal group on the surface of the PEO-b-PCL micelles was converted to reactive aldehyde under acidic condition at room temperature. An RGD-containing linear peptide, GRGDS, was conjugated on the surface of the aldehyde-decorated PEO-b-PCL micelles by incubation at room temperature. A hydrophobic fluorescent probe, that is, DiI, was physically loaded in prepared polymeric micelles to imitate hydrophobic drugs loaded in micellar carrier. The cellular uptake of DiI loaded GRGDS-modified micelles by melanoma B16-F10 cells was investigated at 4 and 37 degrees C by fluorescent spectroscopy and confocal microscopy techniques and was compared to the uptake of DiI loaded valine-PEO-b-PCL micelles (as the irrelevant ligand decorated micelles) and free DiI. GRGDS conjugation to polymeric micelles significantly facilitated the cellular uptake of encapsulated hydrophobic DiI most probably by intergrin-mediated cell attachment and endocytosis. The results indicate that acetal-terminated PEO-b-PCL micelles are amenable for introducing targeting moieties on the surface of polymeric micelles and that RGD-peptide conjugated PEO-b-PCL micelles are promising ligand-targeted carriers for enhanced drug delivery to metastatic tumor cells.     

Folate-functionalized unimolecular micelles based on a degradable amphiphilic dendrimer-like star polymer for cancer cell-targeted drug delivery

A folate-functionalized degradable amphiphilic dendrimer-like star polymer (FA-DLSP) with a well-defined poly(L-lactide) (PLLA) star polymer core and six hydrophilic polyester dendrons based on 2,2-bis(hydroxymethyl) propionic acid was successfully synthesized to be used as a nanoscale carrier for cancer cell-targeted drug delivery. This FA-DLSP hybrid formed unimolecular micelles in the aqueous solution with a mean particle size of ca. 15 nm as determined by dynamic light scattering and transmission electron microscopy. To study the feasibility of FA-DLSP micelles as a potential nanocarrier for targeted drug delivery, we encapsulated a hydrophobic anticancer drug, doxorubicin (DOX), in the hydrophobic core, and the loading content was determined by UV-vis analysis to be 4 wt %. The DOX-loaded FA-DLSP micelles demonstrated a sustained release of DOX due to the hydrophobic interaction between the polymer core and the drug molecules. The hydrolytic degradation in vitro was monitored by weight loss and proton nuclear magnetic resonance spectroscopy to gain insight into the degradation mechanism of the FA-DLSP micelles. It was found that the degradation was pH-dependent and started from the hydrophilic shell gradually to the hydrophobic core. Flow cytometry and confocal microscope studies revealed that the cellular binding of the FA-DLSP hybrid against human KB cells with overexpressed folate-receptors was about twice that of the neat DLSP (without FA). The in vitro cellular cytotoxicity indicated that the FA-DLSP micelles (without DOX) had good biocompatibility with KB cells, whereas DOX-loaded micelles exhibited a similar degree of cytotoxicity against KB cells as that of free DOX. These results clearly showed that the FA-DLSP unimolecular micelles could be a promising nanosize anticancer drug carrier with excellent targeting property.     

Epidermal growth factor-conjugated poly(ethylene glycol)-block- poly(delta-valerolactone) copolymer micelles for targeted delivery of chemotherapeutics

Epidermal growth factor (EGF)-conjugated copolymer micelles were prepared from a mixture of diblock copolymers of methoxy poly(ethylene glycol)-block-poly(delta-valerolactone) (MePEG-b-PVL) and EGF-PEG-b-PVL for targeted delivery to EGF receptor (EGFR)-overexpressing cancers. The block copolymers and functionalized block copolymers were synthesized using PEG as the macroinitiator and HCl-diethyl ether as the catalyst. The MePEG-b-PVL and the carboxyl-terminated PEG-b-PVL (HOOC-PEG-b-PVL) copolymers were found to have molecular weights of 5940 and 5900, respectively, as determined by gel permeation chromatography (GPC) analyses. The HOOC-PEG-b-PVL copolymers were then activated by N-hydroxysuccinimide and subsequently reacted with EGF to form the EGF-PEG-b-PVL copolymers. The efficiency for the conjugation of EGF to the copolymer was found to be 60.9%. A hydrophobic fluorescent probe, CM-DiI, was loaded into both the nontargeted MePEG-b-PVL micelles and the targeted EGF-conjugated PEG-b-PVL micelles. The effective mean diameters of the CMDiI-loaded nontargeted and the CMDiI-loaded targeted micelles were found to be 32 +/- 1 nm and 45 +/- 2 nm, respectively, as determined by dynamic light scattering (DLS). The zeta potentials for the nontargeted micelles (no CM-DiI-loaded), CM-DiI-loaded nontargeted micelles, and CM-DiI-loaded targeted micelles were found to be -6.5, -8.7, and - 13.5 mV, respectively. Evaluation of the in vitro release of CM-DiI from the MePEG-b-PVL micelles in phosphate buffer saline (0.01 M, pH = 7.4) containing 10% (v/v) fetal bovine serum at 37 degrees C revealed that approximately 20% of the probe was released within the first 2 h. Confocal laser scanning microscopy (CLSM) analysis revealed that the targeted micelles containing CM-DiI accumulated intracellularly in EGFR-overexpressing MDA-MB-468 breast cancer cells following a 2 h incubation period, while no detectable cell uptake was observed for the nontargeted micelles. Results obtained from the confocal images were confirmed in an independent study by measuring the intracellular CM-DiI fluorescence in cell lysate. In addition, the presence of free EGF was found to decrease the extent of uptake of the targeted micelles. Nuclear staining of the cells with Hoechst 33258 indicated that the targeted micelles mainly localized in the perinuclear region and some of the micelles were localized in the nucleus. These results demonstrate that the EGF-conjugated copolymer micelles developed in this study have potential as vehicles for targeting hydrophobic drugs to EGFR-overexpressing cancers.     

Bioreducible micelles self-assembled from amphiphilic hyperbranched multiarm copolymer for glutathione-mediated intracellular drug delivery

A new type of biodegradable micelles for glutathione-mediated intracellular drug delivery was developed on the basis of an amphiphilic hyperbranched multiarm copolymer (H40-star-PLA-SS-PEP) with disulfide linkages between the hydrophobic polyester core and hydrophilic polyphosphate arms. The resulting copolymers were characterized by nuclear magnetic resonance (NMR), Fourier transformed infrared (FTIR), gel permeation chromatography (GPC), and differential scanning calorimeter (DSC) techniques. Benefiting from amphiphilic structure, H40-star-PLA-SS-PEP was able to self-assemble into micelles in aqueous solution with an average diameter of 70 nm. Moreover, the hydrophilic polyphosphate shell of these micelles could be detached under reduction-stimulus by in vitro evaluation, which resulted in a rapid drug release due to the destruction of micelle structure. The glutathione-mediated intracellular drug delivery was investigated against a Hela human cervical carcinoma cell line. Flow cytometry and confocal laser scanning microscopy (CLSM) measurements demonstrated that H40-star-PLA-SS-PEP micelles exhibited a faster drug release in glutathione monoester (GSH-OEt) pretreated Hela cells than that in the nonpretreated cells. Cytotoxicity assay of the doxorubicin-loaded (DOX-loaded) micelles indicated the higher cellular proliferation inhibition against 10 mM of GSH-OEt pretreated Hela cells than that of the nonpretreated ones. As expected, the DOX-loaded micelles showed lower inhibition against 0.1 mM of buthionine sulfoximine (BSO) pretreated Hela cells. These reduction-responsive and biodegradable micelles show a potential to improve the antitumor efficacy of hydrophobic chemotherapeutic drugs.     

Oxime linkage: a robust tool for the design of pH-sensitive polymeric drug carriers

Oxime bonds dispersed in the backbones of the synthetic polymers, while young in the current spectrum of the biomedical application, are rapidly extending into their own niche. In the present work, oxime linkages were confirmed to be a robust tool for the design of pH-sensitive polymeric drug delivery systems. The triblock copolymer (PEG-OPCL-PEG) consisting of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic oxime-tethered polycaprolactone (OPCL) was successfully prepared by aminooxy terminals of OPCL ligating with aldehyde-terminated PEG (PEG-CHO). Owing to its amphiphilic architecture, PEG-OPCL-PEG self-assembled into the micelles in aqueous media, validated by the measurement of critical micelle concentration (CMC). The MTT assay showed that PEG-OPCL-PEG exhibited low cytotoxicity against NIH/3T3 normal cells. Doxorubicin (DOX) as a model drug was encapsulated into the PEG-OPCL-PEG micelles. Drug release study revealed that the DOX release from micelles was significantly accelerated at mildly acid pH of 5.0 compared to physiological pH of 7.4, suggesting the pH-responsive feature of the drug delivery systems with oxime linkages. Flow cytometry and confocal laser scanning microscopy (CLSM) measurements indicated that these DOX-loaded micelles were easily internalized by living cells. MTT assay against HeLa cancer cells showed DOX-loaded PEG-OPCL-PEG micelles had a high anticancer efficacy. All of these results demonstrate that these polymeric micelles self-assembled from oxime-tethered block copolymers are promising carriers for the pH-triggered intracellular delivery of hydrophobic anticancer drugs.     

D-甘露糖修饰聚合物胶束的制备及其在靶向药物输送中的应用

聚合物胶束作为药物载体具有良好的稳定性和生物相容性,提高疏水性药物溶解性等优势,是一类很有应用潜力的药物传输系统。本研究以合成的共价键连D-甘露糖的双亲性聚合物分子(PGMA-Mannose)为药物载体,包载抗癌药物阿霉素(DOX)制备具有甘露糖受体靶向性和pH敏感药物释放特性的新型载药聚合物胶束。利用激光共聚焦显微镜和MTT细胞毒性评价方法对载药胶束的细胞内吞摄取和毒性进行评价。实验结果表明,载药胶束能特异性识别人乳腺癌细胞MDA-MB-231表面过度表达的甘露糖受体,被癌细胞大量摄取并在细胞溶酶体酸性环境内释放药物,而载药胶束在表面甘露糖受体低表达的HEK293细胞中只有少量摄取。与原药DOX相比,该载药胶束对癌细胞的毒性显著提高,而对正常细胞的毒性较低。因此,该PGMA-Mannose聚合物胶束有望成为一种新型的靶向药物输送系统应用于癌症的治疗。     

Enhanced stability of core-surface cross-linked micelles fabricated from amphiphilic brush copolymers

"Stealth" nanoparticles made from polymer micelles have been widely explored as drug carriers for targeted drug delivery. High stability (i.e., low critical micelle concentration (CMC)) is required for their intravenous applications. Herein, we present a "core-surface cross-linking" concept to greatly enhance nanoparticle's stability: amphiphilic brush copolymers form core-surface cross-linked micelles (nanoparticles) (SCNs). The amphiphilic brush copolymers consisted of hydrophobic poly(epsilon-caprolactone) (PCL) and hydrophilic poly(ethylene glycol) (PEG) or poly(2-(N,N-dimethylamino)ethyl methacrylate) (PDMA) chains were synthesized by macromonomer copolymerization method and used to demonstrate this concept. The resulting SCNs were about 100 times more stable than micelles from corresponding amphiphilic block copolymers. The size and surface properties of the SCNs could be easily tailored by the copolymer's compositions.     

Fluorescence study of the curcumin-casein micelle complexation and its application as a drug nanocarrier to cancer cells

In milk caseins exists a natural nanostructure, which can be exploited as a carrier of hydrophobic drugs. Here we investigated the complex formation of curcumin with bovine casein micelles (CMs) and its use as a vehicle for drug delivery to cancer cells. DLS studies of the CM suspension that was stable in buffer solution (pH 7.4) showed an average size distribution of <200 nm. SEM and AFM studies showed that the particles were roughly spherical in shape. Steady-state fluorescence spectroscopy of the CM-curcumin complex formation revealed that curcumin molecules formed complexes with CMs (CM-curcumin complex) through hydrophobic interactions. The binding constant for the CM-curcumin interaction was calculated to be 1.48 x 10(4) M(-1), as determined by the curcumin fluorescence. Fluorescence quenching showed that curcumin molecules quench the intrinsic fluorescence of caseins upon binding. We evaluated the utility of CMs as carriers of curcumin by using in vitro cultured HeLa cells. Cytotoxicity studies of HeLa cells revealed that the IC50 of free curcumin and the CM-curcumin complex was 14.85 and 12.69 microM, respectively.     

Exploiting the vitamin B12 pathway to enhance oral drug delivery via polymeric micelles

Vitamin B12 (VB12)-modified dextran-g-polyethyleneoxide cetyl ether (DEX-g-PEO-C16) was synthesized by linking VB12 residues to a DEX-g-PEO-C16 copolymer via a 2,2'-(ethylenedioxy)bis(ethylamine) spacer. The level of VB12 substitution on the DEX-g-PEO-C16 copolymer reached 1.68% (w/w). In aqueous solution, DEX-based copolymers form micelles that can entrap within their hydrophobic core up to 8.5% w/w of cyclosporin A (CsA), a poorly water soluble immunosuppressant. The permeability of Caco-2 cell membranes to CsA incorporated in VB12 modified and unmodified polymeric micelles was monitored in the presence and absence of intrinsic factor (IF). The apical (AP) to basolateral (BL) permeation of CsA through Caco-2 cell monolayers after 24 h of transport was significantly higher (1.8 and 2.3 times in absence and presence of IF, respectively) in the case of CsA loaded in VB12-modified polymeric micelles, compared to CsA in unmodified micelles. The results point to possible improvement in the application of polysaccharide-based polymeric micelles as targeted polymeric drug carriers for the oral delivery of poorly water soluble drugs.     

Norbornene derived doxorubicin copolymers as drug carriers with pH responsive hydrazone linker

The synthesis and complete characterization of both norbornene-derived doxorubicin (mono 1) and polyethylene glycol (mono 2) monomers are clearly described, and their copolymerization by ring-opening metathesis polymerization (ROMP) to get the block copolymer (COPY-DOX) is vividly elaborated. The careful design of these conjugates exhibits properties like well-shielded drug moieties and well-defined nanostructures; additionally, they show solubility in both water and biological medium and also have the important tendency of rendering acid-triggered drug release. The drug release profile suggests the importance of having the hydrazone linker that helps to release the drug exactly at the mild acidic conditions resembling the pH of the cancerous cells. It is also observed that the drug release from micelles of COPY-DOX is significantly accelerated at a mildly acidic pH of 5.5-6, compared to the physiological pH of 7.4, suggesting the pH-responsive feature of the drug delivery system with hydrazone linkages. Confocal laser scanning microscopy (CLSM) measurements indicate that these COPY-DOX micelles are easily internalized by living cells. MTT assays against HeLa and 4T cancer cells showing COPY-DOX micelles have a high anticancer efficacy. All of these results demonstrate that these polymeric micelles that self-assembled from COPY-DOX block copolymers have great scope in the world of medicine, and they also symbolize promising carriers for the pH-triggered intracellular delivery of hydrophobic anticancer drugs.     

Redox-responsive polyphosphate nanosized assemblies: a smart drug delivery platform for cancer therapy

Novel redox-responsive polyphosphate nanosized assemblies based on amphiphilic hyperbranched multiarm copolyphosphates (HPHSEP-star-PEP(x)) with backbone redox-responsive, good biocompatibility, and biodegradability simultaneously have been designed and prepared successfully. The hydrophobic core and hydrophilic multiarm of HPHSEP-star-PEP(x) are composed of hyperbranched and linear polyphosphates, respectively. Benefiting from the amphiphilicity, HPHSEP-star-PEP(x) can self-assemble into spherical micellar nanoparticles in aqueous media with tunable size from about 70 to 100 nm via adjusting the molecular weight of PEP multiarm. Moreover, HPHSEP-star-PEP(x) micellar structure can be destructed under reductive environment and result in a triggered drug release behavior. The glutathione-mediated intracellular drug delivery was investigated against a HeLa human cervical carcinoma cell line, and the results indicate that doxorubicin-loaded (DOX-loaded) HPHSEP-star-PEP(x) micelles show higher cellular proliferation inhibition against glutathione monoester pretreated HeLa cells than that of the nonpretreated ones. In contrast, the DOX-loaded micelles exhibit lower inhibition against buthionine sulfoximine pretreated HeLa cells. These results suggest that such redox-responsive polyphosphate micelles can rapidly deliver anticancer drugs into the nuclei of tumor cells enhancing the inhibition of cell proliferation and provide a favorable platform to construct excellent drug delivery systems for cancer therapy.     

Polymeric micelles with glycolipid-like structure and multiple hydrophobic domains for mediating molecular target delivery of paclitaxel

Herein, polymeric micelles with glycolipid-like structure and about 40 nm diameter are prepared by self-aggregation from stearate-grafted chitosan oligosaccharides in aqueous medium. The micelles, with high degree of substitution (DS), present specific spatial structure with multiple hydrophobic "minor cores", and thus obtain excellent internalization into cancer cells and accumulation in cytoplasm. Furthermore, the micelles showed pH-sensitive properties, thus favoring intracellular delivery of encapsulated drug via endocytosis. The cell cytotoxicity of paclitaxel encapsulated in micelles was improved sharply and contributed to the increased intracellular delivery of the drug. The present micelles are a promising carrier candidate for targeting therapy of antitumor drugs with a cytoplasmic molecule target.     

Galactose-decorated cross-linked biodegradable poly(ethylene glycol)-b-poly(ε-caprolactone) block copolymer micelles for enhanced hepatoma-targeting delivery of paclitaxel

The inferior in vivo stability of micellar drugs has been a prime challenge for their application in targeted drug delivery. Here we report on novel galactose-decorated covalently cross-linked biodegradable micelles based on photo-cross-linkable poly(ethylene glycol)-b-poly(acryloyl carbonate)-b-poly(ε-caprolactone) (PEG-PAC-PCL) and galactose-conjugated PEG-PCL (Gal-PEG-PCL) copolymers for enhanced hepatoma-targeting delivery of paclitaxel (PTX). The molecular weight of PEG in Gal-PEG-PCL was higher than that in PEG-PAC-PCL, thereby fully exposing Gal ligands at the micellar surface. These micelles, either with or without loading of PTX, were readily cross-linked by UV irradiation to afford micelles with small sizes (ca. 79-94 nm) and enhanced stability. The in vitro release studies confirmed that drug release from cross-linked micelles was significantly inhibited. Interestingly, MTT assays showed that Gal-decorated PTX-loaded cross-linked micelles retained a high antitumor activity in HepG2 cells, which was much more effective than PTX-loaded cross-linked micelles without Gal ligands and comparable to Gal-decorated PTX-loaded non-cross-linked micelles. Remarkably, the preliminary in vivo antitumor efficacy studies in SMMC-7721 tumor (human hepatoma)-bearing nude mice revealed that Gal-decorated PTX-loaded cross-linked micelles inhibited the growth of the human hepatoma more effectively than PTX-loaded cross-linked micelles as well as Gal-decorated PTX-loaded non-cross-linked micelles. These results indicate that Gal-decorated cross-linked PEG-PCL micelles have great potential in liver tumor-targeted chemotherapy.     

Polymeric micelles with water-insoluble drug as hydrophobic moiety for drug delivery

The hydrophobic block of polymeric micelles formed by amphiphilic copolymers has no direct therapeutical effect, and the metabolites of these hydrophobic segments might lead to some unexpected side effects. Here the hydrophobic core of polymeric micelles is replaced by highly water-insoluble drugs themselves, forming a new micellar drug delivery system. By grafting hydrophobic drugs of paclitaxel (PTX) onto the surface of hydrophilic hyperbranched poly(ether-ester) (HPEE), we constructed an amphiphilic copolymer (HPEE-PTX). HPEE-PTX could self-assemble into micellar nanoparticles in aqueous solution with tunable drug contents from 4.1 to 10.7%. Moreover, the hydrolysis of HPEE-PTX in serum resulted in the cumulative release of PTX. In vivo evaluation indicated that the dosage toleration of PTX in mice had been improved greatly and HPEE-PTX micellar nanoparticles could be used as an efficient prodrug with satisfactory therapeutical effect. We believe that most of the lipophilic drugs could improve their characters through this strategy.     

PSMA Ligand Conjugated PCL-PEG Polymeric Micelles Targeted to Prostate Cancer Cells

In this content, a small molecular ligand of prostate specific membrane antigen (SMLP) conjugated poly (caprolactone) (PCL)-b-poly (ethylene glycol) (PEG) copolymers with different block lengths were synthesized to construct a satisfactory drug delivery system. Four different docetaxel-loaded polymeric micelles (DTX-PMs) were prepared by dialysis with particle sizes less than 60 nm as characterized by dynamic light scattering (DLS) and transmission electron microscope (TEM). Optimization of the prepared micelles was conducted based on short-term stability and drug-loading content. The results showed that optimized systems were able to remain stable over 7 days. Compared with Taxotere, DTX-PMs with the same ratio of hydrophilic/hydrophobic chain length displayed similar sustained release behaviors. The cytotoxicity of the optimized targeted DTX-PCL_12K-PEG_5K-SMLP micelles (DTX-PMs2) and non-targeted DTX-PCL_12K-mPEG_5K micelles (DTX-PMs1) were evaluated by MTT assays using prostate specific membrane antigen (PSMA) positive prostate adenocarcinoma cells (LNCaP). The results showed that the targeted micelles had a much lower IC50 than their non-targeted counterparts (48 h: 0.87±0.27 vs 13.48±1.03 µg/ml; 72 h: 0.02±0.008 vs 1.35±0.54 µg/ml). In vitro cellular uptake of PMs2 showed 5-fold higher fluorescence intensity than that of PMs1 after 4 h incubation. According to these results, the novel nano-sized drug delivery system based on DTX-PCL-PEG-SMLP offers great promise for the treatment of prostatic cancer.     

Supramolecular copolymer micelles based on the complementary multiple hydrogen bonds of nucleobases for drug delivery

Novel supramolecular copolymer micelles with stimuli-responsive abilities were successfully prepared through the complementary multiple hydrogen bonds of nucleobases and then applied for rapid intracellular release of drugs. First, both adenine-terminated poly(ε-caprolactone) (PCL-A) and uracil-terminated poly(ethylene glycol) (PEG-U) were synthesized. The supramolecular amphiphilic block copolymers (PCL-A:U-PEG) were formed based on multiple hydrogen bonding interactions between PCL-A and PEG-U. The micelles self-assembled from PCL-A:U-PEG were sufficiently stable in water but prone to fast aggregation in acidic condition due to the dynamic and sensitive nature of noncovalent interactions. The low cytotoxicity of supramolecular copolymer micelles was confirmed by MTT assay against NIH/3T3 normal cells. As a hydrophobic anticancer model drug, doxorubicin (DOX) was encapsulated into these supramolecular copolymer micelles. In vitro release studies demonstrated that the release of DOX from micelles was significantly faster at mildly acid pH of 5.0 compared to physiological pH. MTT assay against HeLa cancer cells showed DOX-loaded micelles had high anticancer efficacy. Hence, these supramolecular copolymer micelles based on the complementary multiple hydrogen bonds of nucleobases are very promising candidates for rapid controlled release of drugs.     

Development of Chitosan-Based pH-Sensitive Polymeric Micelles Containing Curcumin for Colon-Targeted Drug Delivery

pH-sensitive N-naphthyl-N,O-succinyl chitosan (NSCS) and N-octyl-N,O-succinyl chitosan (OSCS) polymeric micelles carriers have been developed to incorporate curcumin (CUR) for colon-targeted drug delivery. The physical entrapment methods (dialysis, co­solvent evaporation, dropping, and O/W emulsion) were applied. The CUR-loaded micelles prepared by the dialysis method presented the highest loading capacity. Increasing initial amount of CUR from 5 to 40 wt% to polymer resulted in the increase in loading capacity of the polymeric micelles. Among the hydrophobic cores, there were no significant differences in the loading capacity of CUR-loaded micelles. The particle sizes of all CUR-loaded micelles were in the range of 120–338 nm. The morphology of the micelles changed after being contacted with medium with different pH values, confirming the pH-responsive properties of the micelles. The release characteristics of curcumin from all CUR-loaded micelles were pH-dependent. The percent cumulative release of curcumin from all CUR-loaded micelles in simulated gastric fluid (SGF) was limited to about 20%. However, the release amount was significantly increased after contacted with simulated intestinal fluid (SIF) (50–55%) and simulated colonic fluid (SCF) (60–70%). The released amount in SIF and SCF was significantly greater than the release of CUR from CUR powder. CUR-loaded NSCS exhibited the highest anti-cancer activity against HT-29 colorectal cancer cells. The stability studies indicated that all CUR-loaded micelles were stable for at least 90 days. Therefore, the colon targeted, pH-sensitive NSCS micelles may have potential to be a prospective candidate for curcumin delivery to the colon.     

Targeted albumin-based nanoparticles for delivery of amphipathic drugs

We report the preparation and physical and biological characterization of human serum albumin-based micelles of approximately 30 nm diameter for the delivery of amphipathic drugs, represented by doxorubicin. The micelles were surface conjugated with cyclic RGD peptides to guide selective delivery to cells expressing the α(v)β(3) integrin. Multiple poly(ethylene glycol)s (PEGs) with molecular weight of 3400 Da were used to form a hydrophilic outer layer, with the inner core formed by albumin conjugated with doxorubicin via disulfide bonds. Additional doxorubicin was physically adsorbed into this core to attain a high drug loading capacity, where each albumin was associated with about 50 doxorubicin molecules. The formed micelles were stable in serum but continuously released doxorubicin when incubated with free thiols at concentrations mimicking the intracellular environment. When incubated with human melanoma cells (M21+) that express the α(v)β(3) integrin, higher uptake and longer retention of doxorubicin was observed with the RGD-targeted micelles than in the case of untargeted control micelles or free doxorubicin. Consequently, the RGD-targeted micelles manifested cytotoxicity at lower doses of drug than control micelles or free drug.     

pH-sensitive unimolecular polymeric micelles: synthesis of a novel drug carrier

Novel amphiphilic star-shaped polymers showing pH-sensitivity were synthesized by atom transfer radical polymerization. These new polymers present a core-shell structure similar to polymeric micelles, but are inherently stable to dilution and are referred to as unimolecular polymeric micelles. A four-armed multifunctional initiator was used for the sequential polymerization of hydrophobic ethyl methacrylate and tert-butyl methacrylate and hydrophilic poly(ethylene glycol)methacrylate. Polymers of molecular weight ranging from 9000 to 20,000 were obtained. Results of dynamic light scattering showed micelle size ranging from 11 to 40 nm. Unimolecular micelles were also analyzed by static light scattering in aqueous environment. Star-shaped polymers which presented the highest molar ratio of hydrophobic monomers tended to form high molecular weight aggregates in water. Hydrolysis of the tert-butyl methacrylate units permitted the introduction of ionizable methacrylic acid functions. Size distributions were bimodal at both acidic and basic pH. Since, the polymers were designed as potential delivery systems for the oral administration of hydrophobic drugs, they were titrated to evaluate the degree of ionization as a function of pH. In the stomach, the carboxylic functions are expected to be fully protonated. However, in the intestine, the micelles will be more than 40% ionized. Fluorescence studies were conducted in order to evaluate the polarity of the micellar core. Results showed an increase in polarity with pH due to the ionization of the acid functions present along the polymer chains. The pH rise was associated with an increase in the in vitro release rate of progesterone, which was used as hydrophobic drug model.     

Synthesis of amphiphilic alternating polyesters with oligo(ethylene glycol) side chains and potential use for sustained release drug delivery

Novel amphiphilic alternating polyesters, poly((N-phthaloyl-l-glutamic anhydride)-co-(2-(2-(2-methoxyethoxy)ethoxy)methyl)oxirane) (P(PGA-co-ME(2)MO)), were synthesized by alternating copolymerization of PGA and ME(2)MO. The structures of the synthesized polyesters were characterized by (1)H NMR, (13)C NMR, FT-IR, and GPC analyses. Because of the presence of oligo(ethylene glycol) (OEG) side chains, the polyesters could self-assemble into thermosensitive micelles. Dynamic light scattering (DLS) showed that these micelles underwent thermoinduced size decrease without intermicellar aggregation. In vitro methyl thiazolyl tetrazolium (MTT) assay demonstrated that the polyesters were biocompatible to Henrietta Lacks (HeLa) cells, rendering their potential for drug delivery applications. Two hydrophobic drugs, rifampin and doxorubicin (DOX), were loaded into the polyester micelles and observed to be released in a zero-order sustained manner. The sustained release could be accelerated in lower pH or in the presence of proteinase K, due to the degradation of the polyester under these conditions. Remarkably, in vitro cell experiments showed that the polyester micelles accomplished fast release of DOX inside cells and higher anticancer efficacy as compared with the free DOX. With enhanced stability during circulation condition and accelerated drug release at the target sites (e.g., low pH or enzyme presence), these novel polyesters with amphiphilic structures are promising to be used in sustained release drug delivery systems.