Gold nanoparticles with a monolayer of doxorubicin-conjugated amphiphilic block copolymer for tumor-targeted drug delivery

Gold (Au) nanoparticles (NPs) stabilized with a monolayer of folate-conjugated poly(l-aspartate-doxorubicin)-b-poly(ethylene glycol) copolymer (Au-P(LA-DOX)-b-PEG-OH/FA) was synthesized as a tumor-targeted drug delivery carrier. The Au-P(LA-DOX)-b-PEG-OH/FA NPs consist of an Au core, a hydrophobic poly(l-aspartate-doxorubicin) (P(LA-DOX)) inner shell, and a hydrophilic poly(ethylene glycol) and folate-conjugated poly(ethylene glycol) outer shell (PEG-OH/FA). The anticancer drug, doxorubicin (DOX), was covalently conjugated onto the hydrophobic inner shell by acid-cleavable hydrazone linkage. The DOX loading level was determined to be 17 wt%. The Au-P(LA-DOX)-b-PEG-OH/FA NPs formed stable unimolecular micelles in aqueous solution. The size of the Au-P(LA-DOX)-b-PEG-OH/FA micelles were determined as 24–52 and 10–25 nm by dynamic light scattering (DLS) and transmission electron microscopy (TEM), respectively. The conjugated DOX was released from the Au-P(LA-DOX)-b-PEG-OH/FA micelles much more rapidly at pH 5.3 and 6.6 than at pH 7.4, which is a desirable characteristic for tumor-targeted drug delivery. Cellular uptake of the Au-P(LA-DOX)-b-PEG-OH/FA micelles facilitated by the folate-receptor-mediated endocytosis process was higher than that of the micelles without folate. This was consistent with the higher cytotoxicity observed with the Au-P(LA-DOX)-b-PEG-OH/FA micelles against the 4T1 mouse mammary carcinoma cell line. These results suggest that Au-P(LA-DOX)-b-PEG-OH/FA NPs could be used as a carrier with pH-triggered drug releasing properties for tumor-targeted drug delivery.     

Multifunctional unimolecular micelles for cancer-targeted drug delivery and positron emission tomography imaging

A multifunctional unimolecular micelle made of a hyperbranched amphiphilic block copolymer was designed, synthesized, and characterized for cancer-targeted drug delivery and non-invasive positron emission tomography (PET) imaging in tumor-bearing mice. The hyperbranched amphiphilic block copolymer, Boltorn(?) H40-poly(L-glutamate-hydrazone-doxorubicin)-b-poly(ethylene glycol) (i.e., H40-P(LG-Hyd-DOX)-b-PEG), was conjugated with cyclo(Arg-Gly-Asp-D-Phe-Cys) peptides (cRGD, for integrin α(v)β(3) targeting) and macrocyclic chelators (1,4,7-triazacyclononane-N, N', N'-triacetic acid [NOTA], for (64)Cu-labeling and PET imaging) (i.e., H40-P(LG-Hyd-DOX)-b-PEG-OCH(3)/cRGD/NOTA, also referred to as H40-DOX-cRGD). The anti-cancer drug, doxorubicin (DOX) was covalently conjugated onto the hydrophobic segments of the amphiphilic block copolymer arms (i.e., PLG) via a pH-labile hydrazone linkage to enable pH-controlled drug release. The unimolecular micelles exhibited a uniform size distribution and pH-sensitive drug release behavior. cRGD-conjugated unimolecular micelles (i.e., H40-DOX-cRGD) exhibited a much higher cellular uptake in U87MG human glioblastoma cells due to integrin α(v)β(3)-mediated endocytosis than non-targeted unimolecular micelles (i.e., H40-DOX), thereby leading to a significantly higher cytotoxicity. In U87MG tumor-bearing mice, H40-DOX-cRGD-(64)Cu also exhibited a much higher level of tumor accumulation than H40-DOX-(64)Cu, measured by non-invasive PET imaging and confirmed by biodistribution studies and ex vivo fluorescence imaging. We believe that unimolecular micelles formed by hyperbranched amphiphilic block copolymers that synergistically integrate passive and active tumor-targeting abilities with pH-controlled drug release and PET imaging capabilities provide the basis for future cancer theranostics.     

Folate-conjugated amphiphilic hyperbranched block copolymers based on Boltorn® H40, poly(l-lactide) and poly(ethylene glycol) for tumor-targeted drug delivery

Folate-conjugated amphiphilic hyperbranched block copolymer (H40–PLA-b-MPEG/PEG–FA) with a dendritic Boltorn^® H40 core, a hydrophobic poly(l-lactide) (PLA) inner shell and a hydrophilic methoxy poly(ethylene glycol) (MPEG) and folate-conjugated poly(ethylene glycol) (PEG–FA) outer shell was synthesized as a carrier for tumor-targeted drug delivery. The block copolymer was characterized using ¹H NMR and gel permeation chromatography (GPC) analysis. Due to its core–shell structure, this block polymer forms unimolecular micelles in aqueous solutions. The micellar properties of H40–PLA-b-MPEG/PEG–FA block copolymer were extensively studied by dynamic light scattering (DLS), fluorescence spectroscopy, and transmission electron microscopy (TEM). An anticancer drug, doxorubicin in the free base form (DOX) was encapsulated into H40–PLA-b-MPEG/PEG–FA micelles. The DOX-loaded micelles provided an initial burst release (up to 4 h) followed by a sustained release of the entrapped DOX over a period of about 40 h. Cellular uptake of the DOX-loaded H40–PLA-b-MPEG/PEG–FA micelles was found to be higher than that of the DOX-loaded H40–PLA-b-MPEG micelles because of the folate-receptor-mediated endocytosis, thereby providing higher cytotoxicity against the 4T1 mouse mammary carcinoma cell line. In vitro degradation studies revealed that the H40–PLA-b-MPEG/PEG–FA block copolymer hydrolytically degraded into polymer fragments within six weeks. These results indicated that the micelles prepared from the H40–PLA-b-MPEG/PEG–FA block copolymer have great potential as tumor-targeted drug delivery nanocarriers.     

Image-guided and tumor-targeted drug delivery with radiolabeled unimolecular micelles

Unimolecular micelles formed by dendritic amphiphilic block copolymers poly(amidoamine)–poly(l-lactide)-b-poly(ethylene glycol) conjugated with anti-CD105 monoclonal antibody (TRC105) and 1,4,7-triazacyclononane-N, N′, N-triacetic acid (NOTA, a macrocyclic chelator for ⁶⁴Cu) (abbreviated as PAMAM–PLA-b-PEG–TRC105) were synthesized and characterized. Doxorubicin (DOX), a model anti-cancer drug, was loaded into the hydrophobic core of the unimolecular micelles formed by PAMAM and PLA via physical encapsulation. The unimolecular micelles exhibited a uniform size distribution and pH-sensitive drug release behavior. TRC105-conjugated unimolecular micelles showed a CD105-associated cellular uptake in human umbilical vein endothelial cells (HUVEC) compared with non-targeted unimolecular micelles, which was further validated by cellular uptake in CD105-negative MCF-7 cells. In 4T1 murine breast tumor-bearing mice, ⁶⁴Cu-labeled targeted micelles exhibited a much higher level of tumor accumulation than ⁶⁴Cu-labeled non-targeted micelles, measured by serial non-invasive positron emission tomography (PET) imaging and confirmed by biodistribution studies. These unimolecular micelles formed by dendritic amphiphilic block copolymers that synergistically integrate passive and active tumor-targeting abilities with pH-controlled drug release and PET imaging capabilities provide the basis for future cancer theranostics.     

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.     

Folate-conjugated amphiphilic star-shaped block copolymers as targeted nanocarriers

Folate (FA)-conjugated star-shaped copolymer was prepared as a targeted carrier for anticancer drug delivery by ring-opening polymerization of L-lactide using pentaerythritol (PTL) as an initiator, followed by conjugation with methoxy poly(ethylene glycol) (MPEG) and FA-poly(ethylene glycol) (FA-PEG). The resulting amphiphilic star-shaped copolymer was shaped into drug-loaded micelles, and the achieved micelles had an average size of around 146 nm in diameter. It was found that the sustained release time of model drug (indomethacin, IMC) from some selected micelles could reach around 40 h. In comparison with linear poly(L-lactic acid)-block-methoxy poly(ethylene glycol) copolymer (PLA-MPEG), the stability of the star-shaped pentaerythritol-co-poly(L-lactic acid)-block-[methoxy poly(ethylene glycol) and FA-poly(ethylene glycol)] (PTL-PLA-MPEG/PEG-FA) micelle was significantly improved because of the lower critical micelle concentration (CMC). The specificity of PTL-PLA-MPEG/PEG-FA targeting cancer cells was demonstrated by intracellular uptake of PTL-PLA-MPEG/PEG-FA and PTL-PLA-MPEG using HeLa human cervical cancer cells. After 2 h in vitro incubation, a significant intracellular uptake for PTL-PLA-MPEG/PEG-FA over PTL-PLA-MPEG was observed by using inverted fluorescence microscope and flow cytometry. These results suggested that PTL-PLA-MPEG/PEG-FA polymeric micelle could be a potentially useful carrier for delivering selected drugs to FA-receptor positive cancer cells.     

Self‐assembled UCST‐Type Micelles as Potential Drug Carriers for Cancer Therapeutics

A methoxy‐poly(ethylene glycol)‐block‐poly(acrylamide‐co‐acrylonitrile) (mPEG‐b‐P(AAm‐co‐AN)) amphiphilic copolymer exhibiting upper critical solution temperature (UCST) behavior is synthesized, and micelles from this copolymer are fabricated. It is found that the thermal responses of these micelles are tunable through balancing the hydrophobic/hydrophilic blocks in the copolymer. The size of the doxorubicin (DOX)‐loaded micelles is dependent on the hydrophobic interaction as well as hydrogen bonding between polymer and drug molecules. As a proof of concept, the drug release behavior is studied in vitro, and the cumulative release of DOX increases at temperature above the UCST of blank micelles. 3‐(4,5‐dimethyl‐thiazol‐2‐yl)‐2,5‐diphenyl tetrazolium bromide (MTT) assays indicate that these polymers are non‐toxic towards human hepatic carcinoma cells (Bel 7402 cells) as well as human embryonic hepatocytes (L02 cells). DOX‐loaded micelles could effectively enter Bel 7402 cells in 2 h, and display much lower half inhibitory concentration compared with free DOX. These micelles may be exploited as a promising drug carrier for cancer therapeutics.

     

Amphiphilic multiarm star block copolymer-based multifunctional unimolecular micelles for cancer targeted drug delivery and MR imaging

We report on the fabrication of multifunctional polymeric unimolecular micelles as an integrated platform for cancer targeted drug delivery and magnetic resonance imaging (MRI) contrast enhancement under in vitro and in vivo conditions. Starting from a fractionated fourth-generation hyperbranched polyester (Boltorn H40), the ring-opening polymerization of ?-caprolactone (CL) from the periphery of H40 and subsequent terminal group esterification with 2-bromoisobutyryl bromide afforded star copolymer-based atom transfer radical polymerization (ATRP) macroinitiator, H40-PCL-Br. Well-defined multiarm star block copolymers, H40-PCL-b-P(OEGMA-co-AzPMA), were then synthesized by the ATRP of oligo(ethylene glycol) monomethyl ether methacrylate (OEGMA) and 3-azidopropyl methacrylate (AzPMA). This was followed by the click reaction of H40-PCL-b-P(OEGMA-co-AzPMA) with alkynyl-functionalized cancer cell-targeting moieties, alkynyl-folate, and T(1)-type MRI contrast agents, alkynyl-DOTA-Gd (DOTA is 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakisacetic acid), affording H40-PCL-b-P(OEGMA-Gd-FA). In aqueous solution, the amphiphilic multiarm star block copolymer exists as structurally stable unimolecular micelles possessing a hyperbranched polyester core, a hydrophobic PCL inner layer, and a hydrophilic P(OEGMA-Gd-FA) outer corona. H40-PCL-b-P(OEGMA-Gd-FA) unimolecular micelles are capable of encapsulating paclitaxel, a well-known hydrophobic anticancer drug, with a loading content of 6.67 w/w% and exhibiting controlled release of up to 80% loaded drug over a time period of ～120 h. In vitro MRI experiments demonstrated considerably enhanced T(1) relaxivity (18.14 s(-1) mM(-1)) for unimolecular micelles compared to 3.12 s(-1) mM(-1) for that of the small molecule counterpart, alkynyl-DOTA-Gd. Further experiments of in vivo MR imaging in rats revealed good accumulation of unimolecular micelles within rat liver and kidney, prominent positive contrast enhancement, and relatively long duration of blood circulation. The reported unimolecular micelles-based structurally stable nanocarriers synergistically integrated with cancer targeted drug delivery and controlled release and MR imaging functions augur well for their potential applications as theranostic systems.     

Multi-functional self-fluorescent unimolecular micelles for tumor-targeted drug delivery and bioimaging

A novel type of self-fluorescent unimolecular micelle nanoparticle (NP) formed by multi-arm star amphiphilic block copolymer, Boltron^® H40 (H40, a 4th generation hyperbranched polymer)-biodegradable photo-luminescent polymer (BPLP)-poly(ethylene glycol) (PEG) conjugated with cRGD peptide (i.e., H40-BPLP-PEG-cRGD) was designed, synthesized, and characterized. The hydrophobic BPLP segment was self-fluorescent, thereby making the unimolecular micelle NP self-fluorescent. cRGD peptides, which can effectively target α_vβ₃ integrin-expressing tumor neovasculature and tumor cells, were selectively conjugated onto the surface of the micelles to offer active tumor-targeting ability. This unique self-fluorescent unimolecular micelle exhibited excellent photostability and low cytotoxicity, making it an attractive bioimaging probe for NP tracking for a variety of microscopy techniques including fluorescent microscopy, confocal laser scanning microscopy (CLSM), and two-photon microscopy. Moreover, this self-fluorescent unimolecular micelle NP also demonstrated excellent stability in aqueous solutions due to its covalent nature, high drug loading level, pH-controlled drug release, and passive and active tumor-targeting abilities, thereby making it a promising nanoplatform for targeted cancer theranostics.     

Folic acid conjugated glycol chitosan micelles for targeted delivery of doxorubicin: preparation and preliminary evaluation in vitro

For folate receptor (FR) targeted anticancer therapy, novel folic acid (FA) conjugated cholesterol-modified glycol chitosan (FCHGC) micelles were synthesized and characterized by ¹H NMR, dynamic light scattering, transmission electron microscopy, and fluorescence spectroscopy. The degree of substitution was 1.4 FA groups and 7.7 cholesterol groups per 100 sugar residues of glycol chitosan. The critical aggregation concentration of FCHGC micelles in aqueous solution was 0.0169?mg/ml. The doxorubicin (DOX)-loaded FCHGC (DFCHGC) micelles were prepared by an emulsion/solvent evaporation method. The DFCHGC micelles were almost spherical in shape and their size increased from 282 to 320?nm with the DOX-loading content increasing from 4.53 to 11.4%. DOX released from DOX-loaded micelles displayed sustained release behavior. The targeted micelles encapsulated DOX showed significantly greater cytotoxicity against FR-positive HeLa cells than the nontargeted DOX-loaded micelles and free DOX. These results suggested that FCHGC micelles could be a potential carrier for targeted drug delivery.     

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.     

Dual pH‐Sensitive DOX‐Conjugated Cyclodextrin‐Core Star Nano‐Copolymer Prodrugs

Herein this study reports dual pH‐sensitive doxorubicin (DOX)‐conjugated β‐cyclodextrin‐core star copolymers with tailoring properties such as direct water‐solubility and stability prior to reaching target sites. For these purposes, three kinds of novel well‐defined β‐cyclodextrin‐core poly(2‐(diethylamino)ethyl methacrylate‐co‐4‐formylphenyl methacrylate)‐b‐poly(poly(ethylene glycol) methyl ether methacrylate) star copolymers (CD‐star‐P(DEA‐co‐FPMA)‐b‐PPEGMA, SPDFP1–3) with different poly(ethylene glycol) methyl ether methacrylate contents are designed and synthesized by atom transfer radical polymerization (ATRP) strategy. 4‐Formylphenyl methacrylate is introduced into the inner arm block of the star copolymers for conjugating DOX by imine bond formation. Interestingly, the DOX‐conjugated β‐cyclodextrin‐core star copolymers not only can directly dissolve in aqueous buffer solution of pH 7.0 to form unimolecular micelles without any aid of organic solvent, but also exhibit strong pH‐dependent DOX release. At normal pH 7.4 the DOX amount released is very small, whereas at pH 5.0 DOX can be released. By selecting SPDFP2–DOX as a representative, it is found that the SPDFP2–DOX micelles show less cytotoxicity compared to carrier‐free DOX and can be internalized by HeLa cells. It is expected that the exploration can provide new strategy for preparing drug delivery system.

     

Polymeric topology and composition constrained polyether–polyester micelles for directional antitumor drug delivery

Amphiphilic linear and dumbbell-shaped poly(ethylene glycol)–poly(lactide-co-glycolide) (PEG–PLGA) copolymers were simply synthesized by the ring-opening polymerization of lactide and glycolide using PEG or tetrahydroxyl-functionalized PEG as the macroinitiator and stannous octoate as the catalyst. The copolymers spontaneously self-assembled into spherical micelles in phosphate-buffered saline at pH 7.4. The self-assembly behavior was dependent on both the polymeric topology and composition. Doxorubicin (DOX), an anthracycline antitumor drug, was loaded into micelles through nanoprecipitation. The in vitro release behavior could be adjusted by regulating the topology or composition of the copolymer, or the pH of the release medium. The effective intracellular DOX release from DOX-loaded micelles was confirmed by confocal laser scanning microscopy and flow cytometry in vitro. DOX-loaded micelles displayed great cellular proliferation inhibition efficacies after incubation for 24, 48 or 72 h. The hemolysis ratio of DOX was significantly reduced by the presence of copolymer. These properties indicated that the micelles derived from linear or dumbbell-shaped copolymers were promising candidates as smart antitumor drug carriers for malignancy therapy.     

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.     

Folate-conjugated amphiphilic block copolymer micelle for targeted and redox-responsive delivery of doxorubicin

In this paper, novel folate-conjugated and redox-responsive crosslinked block copolymer was successfully synthesized for targeted and controlled release of doxorubicin (DOX) to cancer cells. Folate-conjugated poly(ethylene glycol)-b-copolycarbonates (FA-PEG-b-P(MAC-co-DTC)) and methoxy poly(ethylene glycol)-b-copolycarbonates (mPEG-b-P(MAC-co-DTC)) were firstly synthesized by enzymatic method. FA-PEG/mPEG-b-P(MAC-co-DTC)-SS was then obtained by further crosslinking reaction with cystamine. Non-conjugated crosslinked copolymer mPEG-b-P(MAC-co-DTC)-SS- and non-conjugated uncrosslinked copolymer mPEG-b-P(MAC-co-DTC) were also synthesized for comparison. All the amphiphlic copolymers could self-assemble to form nano-sized micelles which dispersed in spherical shape before and after DOX loading. The core crosslinking structure of FA-PEG/mPEG-b-P(MAC-co-DTC)-SS could improve the micellar stability and drug loading capacity, while in vitro release studies also showed more sustained drug release behavior which could be accelerated in reductive condition. Moreover, confocal laser scanning microscopy indicated that the conjugation of FA could enhance the cellular uptake efficiency obviously via FA-receptor-mediated endocytosis, and MTT assays demonstrated highly potent cytotoxic activity of FA-PEG/mPEG-b-P(MAC-co-DTC)-SS.     

Biodegradable micelles with sheddable poly(ethylene glycol) shells for triggered intracellular release of doxorubicin

Biodegradable micelles with sheddable poly(ethylene glycol) shells were developed based on disulfide-linked poly(ethylene glycol)-b-poly(?-caprolactone) (PEG-SS-PCL) diblock copolymer and applied for rapid intracellular release of doxorubicin (DOX). PEG-SS-PCL was prepared with controlled block lengths via exchange reaction between PEG orthopyridyl disulfide and mercapto PCL. The micelles formed from PEG-SS-PCL, though sufficiently stable in water, were prone to fast aggregation in the presence of 10 mm dithiothreitol (DTT), due to shedding of the PEG shells through reductive cleavage of the intermediate disulfide bonds. Interestingly, the in vitro release studies revealed that these shell-sheddable micelles released DOX quantitatively within 12 h under a reductive environment analogous to that of the intracellular compartments such as cytosol and the cell nucleus. In contrast, minimal drug release (<20%) was observed within 24 h for the reduction insensitive PEG–PCL micelles under the same conditions as well as for PEG-SS-PCL micelles under the non-reductive conditions. Remarkably, cell experiments showed that these shell-sheddable micelles accomplished much faster release of DOX inside cells and higher anticancer efficacy as compared to the reduction insensitive control. These shell-sheddable biodegradable micelles are highly promising for the efficient intracellular delivery of various lipophilic anticancer drugs to achieve improved cancer therapy.     

A Biodegradable and Amphiphilic Linear‐Dendritic Copolymer as a Drug Carrier Platform for Intracellular Drug Delivery

In this work, a biodegradable linear‐dendritic copolymer composed of methoxypolyethylene glycols (mPEG) and a third generation glycolic acid oligomer based dendron is synthesized. The amphiphilic copolymer can self‐assemble into polymeric micelles in aqueous solution with a low critical micelle concentration (CMC). Hydrophobic doxorubicin (DOX) is incorporated into the micellar core via the dialysis method with a high drug loading content of 21.2%. The drug release result implies that the encapsulated drug can be released rapidly at pH 5.0, due to the hydrolysis of the ester bond resulting in quick disassembly of drug‐loaded micelles. Moreover, the results of fluorescence microscopy imaging and flow cytometry measurements demonstrate that the drug carriers can be internalized and DOX released rapidly from them upon endocytosis. Importantly, this drug delivery system exhibits excellent performance to inhibit cancer cell proliferation.

     

Doxorubicin-loaded amphiphilic polypeptide-based nanoparticles as an efficient drug delivery system for cancer therapy

An amphiphilic anionic copolymer, methoxy poly(ethylene glycol)-b-poly(l-glutamic acid-co-l-phenylalanine) (mPEG-b-P(Glu-co-Phe)), with three functionalized domains, was synthesized and used as a nanovehicle for cationic anticancer drug doxorubicin hydrochloride (DOX·HCl) delivery via electrostatic interactions for cancer treatment. The three domains displayed distinct functions: PEG block chain for prolonged circulation; poly(phenylalanine) domain for stabilizing the nanoparticle construct through hydrophobic/aromatic interactions; and the poly(glutamic acid) domain for providing electrostatic interactions with the cationic drug to be loaded. The copolymer could self-assemble into micellar-type nanoparticles, and DOX was successfully loaded into the interior of nanoparticles by simple mixing of DOX·HCl and the copolymer in the aqueous phase. DOX-loaded mPEG-b-P(Glu-co-Phe) nanoparticles (DOX-NP) had a superior drug-loading content (DLC) (21.7%), a high loading efficiency (almost 98%) and a pH-triggered release of DOX. The size of DOX-NP was ～140 nm, as determined by dynamic light scattering measurements and transmission electron microscopy. In vitro assays showed that DOX-NP exhibited higher cell proliferation inhibition and higher cell uptake in A549 cell lines compared with free DOX·HCl. Maximum tolerated dose (MTD) studies showed that DOX-NP demonstrated an excellent safety profile with a significantly higher MTD (15 mg DOX kg^?1) than that of free DOX·HCl (5 mg DOX kg^?1). The in vivo studies on the subcutaneous non-small cell lung cancer (A549) xenograft nude mice model confirmed that DOX-NP showed significant antitumor activity and reduced side effects, and then enhanced tumor accumulation as a result of the prolonged circulation in blood and the enhanced permeation and retention effect, compared with free DOX, indicating its great potential for cancer therapy.     

One‐Step Preparation of Reduction‐Responsive Biodegradable Polymers as Efficient Intracellular Drug Delivery Platforms

Reduction‐responsive biodegradable polymeric micelles based on functional 2‐methylene‐1,3‐dioxepane (MDO) copolymers are developed and investigated for triggered doxorubicin (DOX) release. The MDO‐based copolymers P(MDO‐co‐PEGMA‐co‐PDSMA) are synthesized via the simple one‐step radical ring‐opening copolymerization of MDO, poly(ethylene glycol) methyl ether methacrylate (PEGMA), and pyridyldisulfide ethylmethacrylate (PDSMA). The copolymers can self‐assemble to form micelles in aqueous solution. DOX, a model anticancer drug, is loaded into the micelles with the drug loading content (DLC) of 11.3%. The micelles can be disassembled under a reductive environment (10 × 10^?3m glutathione), which results in a triggered drug release behavior. The glutathione‐mediated intracellular drug release of DOX‐loaded micelles is investigated against A549 cells. Confocal laser scanning microscopy (CLSM) results demonstrated that DOX‐loaded micelles exhibits faster drug release in glutathione monoester (GSH‐OEt)‐pretreated A549 cells, compared with untreated and buthionine sulfoximine (BSO)‐pretreated A549 cells. Based on the facile synthetic strategy, the reduction‐sensitive biodegradable micelles with triggered intracellular drug release are promising for anticancer drug delivery.

     

Folate‐Conjugated Poly(N‐(2‐hydroxypropyl) methacrylamide)‐block‐Poly(benzyl methacrylate): Synthesis,Self‐Assembly,and Drug Release

Well‐defined amphiphilic diblock copolymers of poly(N‐(2‐hydroxypropyl)methacrylamide)‐block‐poly(benzyl methacrylate) (PHPMA‐b‐PBnMA) are synthesized using reversible addition–fragmentation chain transfer polymerization. The terminal dithiobenzoate groups are converted into carboxylic acids. The copolymers self‐assemble into micelles with a PBnMA core and PHPMA shell. Their mean size is <30 nm, and can be regulated by the length of the hydrophilic chain. The compatibility between the hydrophobic segment and the drug doxorubicin (DOX) affords more interaction of the cores with DOX. Fluorescence spectra are used to determine the critical micelle concentration of the folate‐conjugated amphiphilic block copolymer. Dynamic light scattering measurements reveal the stability of the micelles with or without DOX. Drug release experiments show that the DOX‐loaded micelles are stable under simulated circulation conditions and the DOX can be quickly released under acidic endosome pH.