Search

In situforminghydrogels were developed from4-arm poly(ethylene glycol)–methacrylate (PEG-4-MA) and −tetrazole(PEG-4-Tet) derivatives through catalyst-free and bioorthogonal “tetrazole–alkene”photo-click chemistry. PEG-4-MA and PEG-4-Tet (Mn= 10 kg/mol) were soluble at 37 °C in phosphate buffer(PB, pH 7.4, 10 mM) at total polymer concentrations ranging from 20to 60 wt % but formed fluorescent hydrogels upon 365 nm UV irradiationat an intensity of 20.6, 30.7, or 60 mW/cm2. The gelationtimes ranged from ca. 50 s to 5 min, and storage moduli varied from0.65 to 25.2 kPa depending on polymer concentrations and degrees ofTet substitution in PEG-4-Tet conjugates. The cell experiments viaan indirect contact assay demonstrated that these “tetrazole–alkene”photo-click PEG hydrogels were noncytotoxic. The high specificityof photo-click reaction renders thus obtained PEG hydrogels particularlyinteresting for controlled protein release. Notably, in vitrorelease studies showed that cytochrome c(CC),γ-globulins (Ig), and recombinant human interleukin-2 (rhIL-2)all were released from PEG hydrogels in a sustained and quantitativemanner over a period of 14–20 days. Importantly, released CCand rhIL-2 exhibited comparable biological activities to native CCand rhIL-2, respectively. These results confirm that “tetrazole–alkene”photo-click reaction is highly compatible with these loaded proteins.This photo-controlled, specific, efficient, and catalyst-free clickchemistry provides a new and versatile strategy to in situforming hydrogels that hold tremendous potentials for protein deliveryand tissue engineering. [ABSTRACT FROM AUTHOR]

A novel and versatile family of enzymaticallyand reductively degradableα-amino acid-based poly(ester amide)s (SS-PEAs) were developedfrom solution polycondensation of disulfide-containing di-p-toluenesulfonic acid salts of bis-l-phenylalaninediesters (SS-Phe-2TsOH) with di-p-nitrophenyl adipate(NA) in N,N-dimethylformamide (DMF).SS-PEAs with Mnranging from 16.6 to 23.6kg/mol were obtained, depending on NA/SS-Phe-2TsOH molar ratios. Thechemical structures of SS-PEAs were confirmed by 1H NMRand FTIR spectra. Thermal analyses showed that the obtained SS-PEAswere amorphous with a glass transition temperature (Tg) in the range of 35.2–39.5 °C. The in vitrodegradation studies of SS-PEA films revealed that SS-PEAs underwentsurface erosion in the presence of 0.1 mg/mL α-chymotrypsinand bulk degradation under a reductive environment containing 10 mMdithiothreitol (DTT). The preliminary cell culture studies displayedthat SS-PEA films could well support adhesion and proliferation ofL929 fibroblast cells, indicating that SS-PEAs have excellent cellcompatibility. The nanoparticles prepared from SS-PEA with PVA asa surfactant had an average size of 167 nm in phosphate buffer (PB,10 mM, pH 7.4). SS-PEA nanoparticles while stable under physiologicalenvironment undergo rapid disintegration under an enzymatic or reductivecondition. The in vitro drug release studies showed that DOX releasewas accelerated in the presence of 0.1 mg/mL α-chymotrypsinor 10 mM DTT. Confocal microscopy observation displayed that SS-PEAnanoparticles effectively transported DOX into both drug-sensitiveand -resistant MCF-7 cells. MTT assays revealed that DOX-loaded SS-PEAnanoparticles had a high antitumor activity approaching that of freeDOX in drug-sensitive MCF-7 cells, while more than 10 times higherthan free DOX in drug-resistant MCF-7/ADR cells. These enzymaticallyand reductively degradable α-amino acid-based poly(ester amide)shave provided an appealing platform for biomedical technology in particularcontrolled drug delivery applications. [ABSTRACT FROM AUTHOR]

Inrecent years, polymeric nanoparticles have appeared as a mostviable and versatile delivery system for targeted cancer therapy.Various in vivo studies have demonstrated that virus-sized stealthparticles are able to circulate for a prolonged time and preferentiallyaccumulate in the tumor site via the enhanced permeability and retention(EPR) effect (so-called “passive tumor-targeting”).The surface decoration of stealth nanoparticles by a specific tumor-homingligand, such as antibody, antibody fragment, peptide, aptamer, polysaccharide,saccharide, folic acid, and so on, might further lead to increasedretention and accumulation of nanoparticles in the tumor vasculatureas well as selective and efficient internalization by target tumorcells (termed as “active tumor-targeting”). Notably,these active targeting nanoparticulate drug formulations have shownimproved, though to varying degrees, therapeutic performances in differenttumor models as compared to their passive targeting counterparts.In addition to type of ligands, several other factors such as in vivostability of nanoparticles, particle shape and size, and ligand densityalso play an important role in targeted cancer chemotherapy. In thisreview, concept and recent development of polymeric nanoparticlesconjugated with specific targeting ligands, ranging from proteins(e.g., antibodies, antibody fragments, growth factors, and transferrin),peptides (e.g., cyclic RGD, octreotide, AP peptide, and tLyp-1 peptide),aptamers (e.g., A10 and AS1411), polysaccharides (e.g., hyaluronicacid), to small biomolecules (e.g., folic acid, galactose, bisphosphonates,and biotin), for active tumor-targeting drug delivery in vitro andin vivo are highlighted and discussed. With promise to maximize therapeuticefficacy while minimizing systemic side effects, ligand-mediated activetumor-targeting treatment modality has become an emerging and indispensableplatform for safe and efficient cancer therapy. [ABSTRACT FROM AUTHOR]

Reduction-sensitiveshell-sheddable glyco-nanoparticles were designedand developed based on poly(ε-caprolactone)-graft-SS-lactobionic acid (PCL-g-SS-LBA) copolymer forefficient hepatoma-targeting delivery of doxorubicin (DOX). PCL-g-SS-LBA was prepared by ring-opening copolymerization ofε-caprolactone and pyridyl disulfide carbonate followed by postpolymerizationmodification with thiolated lactobionic acid (LBA-SH) via thiol-disulfideexchange reaction. The dynamic light scattering (DLS) and transmissionelectron microscopy (TEM) showed that PCL-g-SS-LBAwas self-assembled into monodisperse nanoparticles (SS-GNs) with amean diameter of about 80 nm. SS-GNs while remaining stable underphysiological conditions (37 °C, pH 7.4) were prone to rapidshell-shedding and aggregation in the presence of 10 mM dithiothreitol(DTT). DOX was loaded into SS-GNs with a decent loading content of12.0 wt %. Notably, in vitro release studies revealed that about 80.3%DOX was released from DOX-loaded SS-GNs in 24 h under a reductivecondition while low drug release (<21%) was observed for DOX-loadedPCL-g-LBA nanoparticles (reduction-insensitive control)under otherwise the same condition and for DOX-loaded SS-GNs undera nonreductive condition. The flow cytometry and confocal microscopyobservations indicated that SS-GNs were efficiently taken up by asialoglycoproteinreceptor (ASGP-R)-overexpressing HepG2 cells likely via a receptor-mediatedendocytosis mechanism and DOX was released into the nuclei of cellsfollowing 4 h incubation. MTT assays showed that DOX-loaded SS-GNsexhibited a high antitumor activity toward HepG2 cells, which wascomparable to free DOX and about 18-fold higher than their reduction-insensitivecounterparts, while blank SS-GNs were nontoxic up to a tested concentrationof 1.0 mg/mL. These shell-sheddable glyco-nanoparticles are promisingfor hepatoma-targeting chemotherapy. [ABSTRACT FROM AUTHOR]

The therapeutic performance of biodegradablemicellar drugs isfar from optimal due to existing challenges like poor tumor cell uptakeand intracellular drug release. Here, we report on ligand-directedreduction-sensitive shell-sheddable biodegradable micelles based onpoly(ethylene glycol)-poly(ε-caprolactone) (PEG-PCL) copolymeractively delivering doxorubicin (DOX) into the nuclei of target cancercells, inducing superb in vitro antitumor effects. The micelles wereconstructed from PEG-SS-PCL and galactose-PEG-PCL (Gal-PEG-PCL) blockcopolymers, in which Gal-PEG-PCL was designed with a longer PEG thanthat in PEG-SS-PCL (6.0 vs 5.0 kDa) to fully expose Gal ligands ontothe surface of micelles for effective targeting to hepatocellularcarcinoma cells. PEG-SS-PCL combining with 10 or 20 wt % of Gal-PEG-PCLformed uniform micelles with average sizes of 56.1 and 58.2 nm (denotedas PEG-SS-PCL/Gal10 and PEG-SS-PCL/Gal20, respectively). The in vitrorelease studies showed that about 81.1 and 75.0% DOX was releasedin 12 h from PEG-SS-PCL/Gal10 and PEG-SS-PCL/Gal20 micelles undera reducing condition containing 10 mM dithiothreitol (DTT). In contrast,minimal DOX release (<12%) was observed for PEG-SS-PCL/Gal10 andPEG-SS-PCL/Gal20 micelles under nonreducing conditions as well asfor reduction-insensitive Gal-PEG-PCL and PEG-PCL/Gal20 micelles inthe presence of 10 mM DTT. MTT assays in HeLa and HepG2 cells showedthat DOX-loaded PEG-SS-PCL/Gal20 micelles exhibited apparent targetabilityand significantly enhanced antitumor efficacy toward asialoglycoproteinreceptor (ASGP-R)-overexpressing HepG2 cells with a particularly lowhalf maximal inhibitory concentration (IC50) of 1.58 μgDOX equiv/mL, which was comparable to free DOX and approximately sixtimes lower than that for nontargeting PEG-SS-PCL counterparts underotherwise the same conditions. Interestingly, confocal microscopyobservations using FITC-labeled PEG-SS-PCL/Gal20 micelles showed thatDOX was efficiently delivered and released into the nuclei of HepG2cells in 8 h. Flow cytometry revealed that cellular DOX level in HepG2cells treated with DOX-loaded PEG-SS-PCL/Gal20 micelles was much greaterthan that with reduction-insensitive PEG-PCL/Gal20 and nontargetingPEG-SS-PCL controls, signifying the importance of combining shell-sheddingand active targeting. Ligand-directed, reduction-sensitive, shell-sheddable,and biodegradable micelles have emerged as a versatile and potentplatform for targeted cancer chemotherapy. [ABSTRACT FROM AUTHOR]

Hepatoma-targetingreduction-sensitive chimaeric biodegradable polymersomes were designedand developed based on galactose–poly(ethylene glycol)–poly(ε-caprolactone)(Gal-PEG-PCL), PEG–PCL–poly(2-(diethylamino)ethyl methacrylate)(PEG-PCL-PDEA, asymmetric), and PEG-SS-PCL for facile loading andtriggered intracellular delivery of proteins. The chimaeric polymersomesformed from PEG-PCL-PDEA and PEG-SS-PCL had a monodisperse distributionwith average sizes ranging from 95.5 to 199.2 nm depending on PEG-SS-PCLcontents. Notably, these polymersomes displayed decent loading ofbovine serum albumin (BSA), ovalbumin (OVA), and cytochrome C (CC)proteins likely due to presence of electrostatic and hydrogen bondinginteractions between proteins and PDEA block located in the interiorof polymersomes. The in vitrorelease studies showedthat protein release was largely accelerated under a reductive conditioncontaining 10 mM dithiothreitol (DTT). For example, ca. 77.2 and 22.1%of FITC-BSA were released from CP(SS50) (chimaeric polymersomes containing50 wt % PEG-SS-PCL) at 37 °C in 12 h in the presence and absenceof 10 mM DTT, respectively. Confocal microscopy showed that FITC-CC-loadedGal-decorated CP(SS40) could efficiently deliver and release FITC-CCinto HepG2 cells following 24 h treatment, in contrast to little ornegligible fluorescence detected in HepG2 cells treated with FITC-CC-loadednontargeting polymersomes or free CC. MTT assays revealed that CC-loadedGal-decorated CP(SS40) exhibited apparent targetability and pronouncedantitumor activity to HepG2 cells, in which cell viabilities decreasedfrom 81.9, 60.6, 49.5, 42.2 to 31.5% with increasing Gal-PEG-PCL contentsfrom 0, 10, 20, 30 to 40 wt %. Most remarkably, granzyme B-loadedGal-decorated chimaeric polymersomes effectively caused apoptosisof HepG2 cells with a markedly low half-maximal inhibitory concentration(IC50) of 2.7 nM. These reduction-responsive chimaericbiodegradable polymersomes offer a multifunctional platform for efficientintracellular protein delivery. [ABSTRACT FROM AUTHOR]

Endosomal pH-activatable paclitaxel(PTX) prodrug micellar nanoparticleswere designed and prepared by conjugating PTX onto water-soluble poly(ethyleneglycol)-b-poly(acrylic acid) (PEG-PAA) block copolymersvia an acid-labile acetal bond to the PAA block and investigated forpotent growth inhibition of human cancer cells in vitro. PTX was readilyconjugated to PEG-PAA with high drug contents of 21.6, 27.0, and 42.8wt % (denoted as PTX prodrugs 1, 2, and 3, respectively) using ethyl glycol vinyl ether (EGVE) asa linker. The resulting PTX conjugates had defined molecular weightsand self-assembled in phosphate buffer (PB, pH 7.4, 10 mM) into monodispersemicellar nanoparticles with average sizes of 158.3–180.3 nmdepending on PTX contents. The in vitro release studies showed thatdrug release from PTX prodrug nanoparticles was highly pH-dependent,in which ca. 86.9%, 66.4% and 29.0% of PTX was released from PTX prodrug 3at 37 °C in 48 h at pH 5.0, 6.0, and pH 7.4, respectively.MTT assays showed that these pH-sensitive PTX prodrug nanoparticlesexhibited high antitumor effect to KB and HeLa cells (IC50= 0.18 and 0.9 μg PTX equiv/mL, respectively) as well as PTX-resistantA549 cells. Notably, folate-decorated PTX prodrug micellar nanoparticlesbased on PTX prodrug 3and 20 wt % folate-poly(ethyleneglycol)-b-poly(d,l-lactide) (FA-PEG-PLA)displayed apparent targetability to folate receptor-overexpressingKB cells with IC50over 12 times lower than nontargetingPTX prodrug 3under otherwise the same conditions. Furthermore,PTX prodrug nanoparticles could also load doxorubicin (DOX) to simultaneouslyrelease PTX and DOX under mildly acidic pH. These acetal-linked PTXprodrug micellar nanoparticles have appeared as a highly versatileand potent platform for cancer therapy. [ABSTRACT FROM AUTHOR]

Insitu forming reduction-sensitive degradable nanogels were designedand developed based on poly(ethylene glycol)-b-poly(2-(hydroxyethyl)methacrylate-co-acryloyl carbonate) (PEG-P(HEMA-co-AC)) block copolymers for efficient loading as well astriggered intracellular release of proteins. PEG-P(HEMA-co-AC) copolymers were prepared with controlled Mnof 9.1, 9.5, and 9.9 kg/mol and varying numbers of AC unitsper molecule of 7, 9 and 11, respectively (denoted as copolymer 1, 2, and 3) by reversible addition–fragmentationchain transfer copolymerization. These copolymers were freely solublein phosphate buffer but formed disulfide-cross-linked nanogels withdefined sizes ranging from 72.5 to 124.1 nm in the presence of cystaminevia ring-opening reaction with cyclic carbonate groups. The sizesof nanogels decreased with increasing AC units as a result of increasedcross-linking density. Dynamic light scattering studies showed thatthese nanogels though stable at physiological conditions were rapidlydissociated in response to 10 mM dithiothreitol (DTT). Interestingly,FITC-labeled cytochrome C (FITC–CC) could be readily loadedinto nanogels with remarkable loading efficiencies (up to 98.2%) andloading contents (up to 48.2 wt.%). The in vitroreleasestudies showed that release of FITC–CC was minimal under physiologicalconditions but significantly enhanced under reductive conditions inthe presence of 10 mM DTT with about 96.8% of FITC–CC releasedin 22 h from nanogel 1. In contrast, protein releasefrom 1,4-butanediamine cross-linked nanogels (reduction-insensitivecontrol) remained low under otherwise the same conditions. MTT assaysshowed that these nanogels were nontoxic to HeLa cells up to a testedconcentration of 2 mg/mL. Confocal microscopy results showed thatnanogel 1delivered and released FITC–CC intothe perinuclei region of HeLa cells following 8 h incubation. CC-loadedreductively degradable nanogels demonstrated apparently better apoptoticactivity than free CC as well as reduction-insensitive controls. Thesein situ forming, surfactant and oil-free, and reduction-sensitivedegradable nanogels are highly promising for targeted protein therapy. [ABSTRACT FROM AUTHOR]

Reduction-sensitive reversibly core-cross-linked micellesweredeveloped based on poly(ethylene glycol)-b-poly(N-2-hydroxypropyl methacrylamide)–lipoic acid (PEG-b-PHPMA-LA) conjugates and investigated for triggered doxorubicin(DOX) release. Water-soluble PEG-b-PHPMA block copolymerswere obtained with Mn,PEGof 5.0 kg/moland Mn,HPMAvarying from 1.7 and 4.1 to7.0 kg/mol by reversible addition–fragmentation chain transfer(RAFT) polymerization. The esterification of the hydroxyl groups inthe PEG-b-PHPMA copolymers with lipoic acid (LA)gave amphiphilic PEG-b-PHPMA-LA conjugates with degreesof substitution (DS) of 71–86%, which formed monodispersedmicelles with average sizes ranging from 85.3 to 142.5 nm, dependingon PHPMA molecular weights, in phosphate buffer (PB, 10 mM, pH 7.4).These micelles were readily cross-linked with a catalytic amount ofdithiothreitol (DTT). Notably, PEG-b-PHPMA(7.0k)-LAmicelles displayed superior DOX loading content (21.3 wt %) and loadingefficiency (90%). The in vitro release studies showed that only about23.0% of DOX was released in 12 h from cross-linked micelles at 37°C at a low micelle concentration of 40 μg/mL, whereasabout 87.0% of DOX was released in the presence of 10 mM DTT underotherwise the same conditions. MTT assays showed that DOX-loaded core-cross-linkedPEG-b-PHPMA-LA micelles exhibited high antitumoractivity in HeLa and HepG2 cells with low IC50(half inhibitoryconcentration) of 6.7 and 12.8 μg DOX equiv/mL, respectively,following 48 h incubation, while blank micelles were practically nontoxicup to a tested concentration of 1.0 mg/mL. Confocal laser scanningmicroscope (CLSM) studies showed that DOX-loaded core-cross-linkedmicelles released DOX into the cell nuclei of HeLa cells in 12 h.These reduction-sensitive disassemblable core-cross-linked micelleswith excellent biocompatibility, superior drug loading, high extracellularstability, and triggered intracellular drug release are promisingfor tumor-targeted anticancer drug delivery. [ABSTRACT FROM AUTHOR]