Triggered disassembly of hierarchically assembled onion-like micelles into the pristine core-shell micelles via a small change in pH

Formulation of pH responsive multilamellar vesicles for targeted delivery of hydrophilic antibiotics

Fight against antimicrobial resistance calls for innovative strategies that can target infection sites and enhance activity of antibiotics. Herein is a pH responsive multilamellar vesicles (MLVs) for targeting bacterial infection sites. The vancomycin (VCM) loaded MLVs had 62.25 ± 8.7 nm, 0.15 ± 0.01 and -5.55 ± 2.76 mV size, PDI and zeta potential, respectively at pH 7.4. The MLVs had a negative ZP at pH 7.4 that switched to a positive charge and faster release of the drug at acidic pH. The encapsulation efficiency was found to be 46.34 ± 3.88 %. In silico studies of the lipids, interaction suggested an energetically stable system. Studies to determine the minimum inhibitory concentration studies (MIC) showed the MLVs had 2-times and 8-times MIC against Staphylococcus aureus (SA) and Methicillin resistance SA respectively at physiological pH. While at pH 6.0 there was 8 times reduction in MICs for the formulation against SA and MRSA in comparison to the bare drug. Fluorescence-activated Cell Sorting (FACS) studies demonstrated that even with 8-times lower MIC, MLVs had a similar elimination ability of MRSA cells when compared to the bare drug. Fluorescence microscopy showed MLVs had the ability to clear biofilms while the bare drug could not. Mice skin infection models studies showed that the colony finding units (CFUs) of MRSA recovered from groups treated with MLVs was 4,050 and 525-fold lower than the untreated and bare VCM treated groups, respectively. This study demonstrated pH-responsive multilamellar vesicles as effective system for targeting and enhancing antibacterial agents.

Polymeric micelles in cancer therapy: State of the art

In recent years, polymeric micelles have been extensively utilized in pre-clinical studies for delivering poorly soluble chemotherapeutic agents in cancer. Polymeric micelles are formed via self-assembly of amphiphilic polymers in facile manners. The wide availability of hydrophobic and, to some extent, hydrophilic polymeric blocks allow researchers to explore various polymeric combinations for optimum loading, stability, systemic circulation, and delivery to the target cancer tissues. Moreover, polymeric micelles could easily be tailor-made by increasing and decreasing the number of monomers in each polymeric chain. Some of the widely accepted hydrophobic polymers are poly(lactide) (PLA), poly(caprolactone) (PCL), poly(lactide-co-glycolide) (PLGA), polyesters, poly(amino acids), lipids. The hydrophilic polymers used to wrap the hydrophobic core are poly(ethylene glycol), poly(oxazolines), chitosan, dextran, and hyaluronic acids. Drugs could be conjugated to polymers at the distal ends to prepare pharmacologically active polymeric systems that impart enhanced solubility and stability of the conjugates and provide an opportunity for combination drug delivery. Their nano-size enables them to accumulate to the tumor microenvironment via the Enhanced Permeability and Retention (EPR) effect. Moreover, the stimuli-sensitive breakdown provides the micelles an effective means to deliver the therapeutic cargo effectively. The tumor micro-environmental stimuli are pH, hypoxia, and upregulated enzymes. Externally applied stimuli to destroy micellar disassembly to release the payload include light, ultrasound, and temperature. This article delineates the current trend in developing polymeric micelles combining various block polymeric scaffolds. The development of stimuli-sensitive micelles to achieve enhanced therapeutic activity are also discussed.

Novel zwitterionic vectors: Multi-functional delivery systems for therapeutic genes and drugs

Zwitterions consist of equal molar cationic and anionic moieties and thus exhibit overall electroneutrality. Zwitterionic materials include phosphorylcholine, sulfobetaine, carboxybetaine, zwitterionic amino acids/peptides, and other mix-charged zwitterions that could form dense and stable hydration shells through the strong ion-dipole interaction among water molecules and zwitterions. As a result of their remarkable hydration capability and low interfacial energy, zwitterionic materials have become ideal choices for designing therapeutic vectors to prevent undesired biosorption especially nonspecific biomacromolecules during circulation, which was termed antifouling capability. And along with their great biocompatibility, low cytotoxicity, negligible immunogenicity, systematic stability and long circulation time, zwitterionic materials have been widely utilized for the delivery of drugs and therapeutic genes. In this review, we first summarized the possible antifouling mechanism of zwitterions briefly, and separately introduced the features and advantages of each type of zwitterionic materials. Then we highlighted their applications in stimuli-responsive "intelligent" drug delivery systems as well as tumor-targeting carriers and stressed the multifunctional role they played in therapeutic gene delivery.

Transformable nanoparticles triggered by cancer-associated fibroblasts for improving drug permeability and efficacy in desmoplastic tumors

Cancer-associated fibroblasts (CAFs) are important barriers for nanoparticles (NPs) to deeply penetrate into tumors and severely limit the antitumor efficacy of nanomedicines. Herein, we proposed a CAF-triggered transformable drug delivery system based on a cleavable peptide responsive to fibroblast activation protein-α (FAP-α) specifically overexpressed on the surface of CAFs. The NPs were composed of cationic poly(amidoamine) (PAMAM) dendrimers cross-linked by our designed peptide, a chemotherapeutical drug was incorporated onto PAMAM using disulfide bonds and finally, hyaluronic acid (HA) was conjugated to improve the tumor targetability as well as biocompatibility through electrostatic interactions. These NPs had an initial size of ∼200 nm and negative zeta potential favorable for stable blood circulation; however, after docking with CAFs, they dissociated into smaller NPs and exposed the relative positive surface charge to facilitate penetration and enter the tumor cells together with CAFs. An interesting finding was that this system intracellularly released different levels of drugs in these two kinds of cells, which was beneficial for the disruption of the stromal barrier and increasing the local drug accumulation. Our investigation confirmed that the constructed system could alleviate the biological barriers and hold promising therapeutic efficiency for desmoplastic solid tumors.

A novel disulfide bond-mediated cleavable RGD-modified PAMAM nanocomplex containing nuclear localization signal HMGB1 for enhancing gene transfection efficiency

BACKGROUND

Polyamidoamine (PAMAM) dendrimers modified by polyethylene glycol (PEG) have frequently been investigated as a delivery carrier for gene therapy. However, modification of PAMAM with PEG using covalent linkage significantly reduces the cellular uptake rate and the transfection efficiency. How to conquer these barriers becomes a burning question in gene delivery.

MATERIALS AND METHODS

The present study constructed an effective disulfide bond-mediated cleavable RGD modified gene delivery system to overcome the aforementioned limitations. The disulfide bond was introduced between PAMAM dendrimers and PEG chains to realize the cleavage of PEG from the carrier system, whereas the arginine-glycine-aspartate (RGD) peptide was expected to promote the cellular uptake rate. A high mobility group Box 1 (HMGB1) protein containing nuclear localization signal (NLS) was simultaneously introduced to further promote gene expression efficiency. A pDNA/HMGB1/PAMAM-SS-PEG-RGD (DHP) nanocomplex was prepared via electrostatic interaction and characterized.

RESULTS

The results showed that DHP generated small particles and was able to condense and protect pDNA against degradation. In addition, the RGD peptide could significantly promote the cellular uptake of a nanocomplex. Intracellular trafficking and in vitro expression study indicated that the DHP nanocomplex escaped from lysosomes and the disulfide bonds between PAMAM and PEG cleaved due to the high concentration of GSH in the cytoplasm, pDNA consequently became exclusively located in the nucleus under the guidance of HMGB1, thereby promoting the red fluorescence protein (RFP) expression. Importantly, an in vivo antitumor activity study demonstrated that the DHP nanocomplex had higher antitumor activity than any other reference preparation.

CONCLUSION

All these results confirm that DHP could be a new strategy for improving the transfection and expression efficiency in gene delivery.

Biological Stimulus-Driven Assembly/Disassembly of Functional Nanoparticles for Targeted Delivery, Controlled Activation, and Bioelimination

Nanoassembly technology has emerged as a powerful tool for targeted drug delivery and provides a basis for fabricating medical theranostic nanosystems. However, it is extremely difficult to concentrate nanoparticles at tumor sites, and the poor target-to-background ratio undoubtedly obstructs the accurate diagnosis and effective therapy of cancerous tissues. Importantly, the addition of biological stimulus-responsive groups to nanoassembly systems can enable a biological stimulus-driven assembly-disassembly mutual switch or structural composition/conformation change, thereby amplifying the imaging signal and/or enhancing the therapeutic effect. This progress report provides an overview of well-designed biological stimulus-responsive nanosystems that can realize precise assembly-disassembly switches by disrupting or rebuilding the intricate balance between the entropy and enthalpy of the nanosystems in response to stimuli (pH, redox, enzymes, etc.) in tumor tissues. The discussion encompasses different biological stimulus-responsive groups, fabrication approaches, and outstanding selective "turn-on" performance for efficient tumor imaging, therapy, and bioelimination. This progress report is expected to inspire more extensive research for the development of smart "turn-on" nanomaterials with increased signal-to-noise (S/N) ratios for diagnosis and drug delivery, which may pave the way for precise nanomedicine with site-specific theranostic features and biocompatibility.

Systematic evaluation of multifunctional paclitaxel-loaded polymeric mixed micelles as a potential anticancer remedy to overcome multidrug resistance

Multidrug resistance (MDR) of tumor cells is becoming the main reason for the failure of chemotherapy and P-glycoprotein (P-gp) mediated drug efflux has demonstrated to be the key factor for MDR. To address this issue, a novel pH-responsive mixed micelles drug delivery system composed of dextran-g-poly(lactide-co-glycolide)-g-histidine (HDP) and folate acid-D-α-tocopheryl polyethylene glycol 2000 (FA-TPGS2K) copolymers has been designed for the delivery of antitumor agent, paclitaxel (PTX) via FA-receptor mediated cell endocytosis, into PTX-resistant breast cancer MCF-7 cells (MCF-7/PTX). PTX-loaded FA-TPGS2K/HDP mixed micelles were characterized to have a small size distribution, high loading content and excellent pH-responsive drug release profiles. Compared with HDP micelles, FA-TPGS2K/HDP mixed micelles showed a higher cytotoxicity against MCF-7 and MCF-7/PTX cells due to the synergistic effect of FA-receptor mediated cell endocytosis, pH-responsive drug release and TPGS mediated P-gp inhibition. P-gp expression level, ATP content and mitochondrial membrane potential change have been measured, the results indicated blank FA-TPGS2K/HDP mixed micelles could inhibit the P-gp activity by reducing the mitochondrial membrane potential and depleting ATP content but not down-regulating the P-gp expression. In vivo antitumor activities demonstrated FA-TPGS2K/HDP mixed micelles could reach higher antitumor activity compared with HDP micelles for MCF-7/PTX tumor cells. Histological assay also indicated that FA-TPGS2K/HDP mixed micelles showed strongly apoptosis inducing effect, anti-proliferation effect and anti-angiogenesis effect. All these evidences demonstrated this pH-sensitive FA-TPGS2K/HDP micelle-based drug delivery system is a promising approach for overcoming MDR.

STATEMENT OF SIGNIFICANCE

In this work, a novel FA-TPGS2K copolymer has been synthesized and used it to construct mixed micelles with HDP copolymer to overcome MDR effect. Furthermore, a series in vitro and in vivo evaluations have been made, which supported enough evidences for the efficient delivery of antitumor drug to MDR cells.

Facile construction of near-monodisperse and dual responsive polycarbonate mixed micelles with the ability of pH-induced charge reversal for intracellular delivery of antitumor drugs

A mixed strategy was used to construct size-adjustable, pH and redox dual-responsive, near-monodisperse and charge-conversional core-shell polycarbonate carriers. First, two kinds of random polycarbonates (PC(Arss-N2CH₃)) with different ratios of hydrophobic disulfide (Arss) and hydrophilic dimethylamine functional groups (N2CH₃) (relatively hydrophobic polycarbonate (BPC) with more disulfide groups and relatively hydrophilic polycarbonate (LPC) with more dimethylamine groups) were used to construct near-monodisperse core micelles in pH 7.4 PBS. Then, a negatively charged shell polymer, poly(ethylene glycol)-b-1,2-dicarboxylic-cyclohexene anhydride modified amino polycarbonate (PEG-PCDCA), bearing acid-labile β-carboxylic amides, was added to the core micelle solution to get the desired mixed micelle. The assembly process, pH induced charge-reversal, and dual-response abilities of the resultant mixed micelles were thoroughly studied using zeta potential and dynamic light scattering (DLS). Two model drugs, Nile red (NR) and doxorubicin (DOX), were successfully loaded into the micelle and could be released in response to dithiothreitol (DTT) and acidic conditions. Confocal microscopy indicated that the micelle system could achieve effective cellular uptake and DOX release in Hela cells. Moreover, the blank micelle and the drug-loaded mixed micelle showed slight and great cytotoxicity against Hela cells, respectively, indicating their significant potential in cancer therapy.

A review of solute encapsulating nanoparticles used as delivery systems with emphasis on branched amphipathic peptide capsules

Various strategies are being developed to improve delivery and increase the biological half-lives of pharmacological agents. To address these issues, drug delivery technologies rely on different nano-sized molecules including: lipid vesicles, viral capsids and nano-particles. Peptides are a constituent of many of these nanomaterials and overcome some limitations associated with lipid-based or viral delivery systems, such as tune-ability, stability, specificity, inflammation, and antigenicity. This review focuses on the evolution of bio-based drug delivery nanomaterials that self-assemble forming vesicles/capsules. While lipid vesicles are preeminent among the structures; peptide-based constructs are emerging, in particular peptide bilayer delimited capsules. The novel biomaterial-Branched Amphiphilic Peptide Capsules (BAPCs) display many desirable properties. These nano-spheres are comprised of two branched peptides-bis(FLIVI)-K-KKKK and bis(FLIVIGSII)-K-KKKK, designed to mimic diacyl-phosphoglycerides in molecular architecture. They undergo supramolecular self-assembly and form solvent-filled, bilayer delineated capsules with sizes ranging from 20 nm to 2 μm depending on annealing temperatures and time. They are able to encapsulate different fluorescent dyes, therapeutic drugs, radionuclides and even small proteins. While sharing many properties with lipid vesicles, the BAPCs are much more robust. They have been analyzed for stability, size, cellular uptake and localization, intra-cellular retention and, bio-distribution both in culture and in vivo.

Novel polymer micelle mediated co-delivery of doxorubicin and P-glycoprotein siRNA for reversal of multidrug resistance and synergistic tumor therapy

Co-delivery of chemotherapeutics and siRNA with different mechanisms in a single system is a promising strategy for effective cancer therapy with synergistic effects. In this study, a triblock copolymer micelle was prepared based on the polymer of N-succinyl chitosan-poly-L-lysine-palmitic acid (NSC-PLL-PA) to co-deliver doxorubicin (Dox) and siRNA-P-glycoprotein (P-gp) (Dox-siRNA-micelle). Dox-siRNA-micelle was unstable in pH 5.3 medium than in pH 7.4 medium, which corresponded with the in vitro rapid release of Dox and siRNA in acidic environments. The antitumor efficacy of Dox-siRNA-micelle in vitro significantly increased, especially in HepG2/ADM cells, which was due to the downregulation of P-gp. Moreover, almost all the Dox-siRNA-micelles accumulated in the tumor region beyond 24 h post-injection, and the co-delivery system significantly inhibited tumor growth with synergistic effects in vivo. This study demonstrated the effectiveness of Dox-siRNA-micelles in tumor-targeting and MDR reversal, and provided a promising strategy to develop a co-delivery system with synergistic effects for combined cancer therapy.

cRGDyK modified pH responsive nanoparticles for specific intracellular delivery of doxorubicin

Stimuli-responsive nanocarriers attract wide attention because of the unique differences in microenvironment between solid tumors and normal tissues. Herein, we reported a novel cRGDyK peptide modified pH-sensitive nanoparticle system based on poly(ethylene glycol)-poly(2,4,6-trimethoxy benzylidene-pentaerythritol carbonate) (PEG-PTMBPEC) diblock copolymer, which was expected to destroy tumor angiogenesis and kill tumor cells simultaneously. Doxorubicin (DOX)-loaded nanoparticles (NPs) were characterized to have a uniform size distribution, high entrapment efficiency, good stability in plasma as well as a pH dependent drug release pattern. Blank NPs were non-toxic to both tumor cells and normal cells, while DOX-loaded cRGDyK peptide modified NPs (cRGDyK-NPs) exhibited the pronounced cytotoxicity against B16 cells and human umbilical vein endothelial cells (HUVEC) overexpressing αvβ3 integrin receptors. Cellular uptake studies revealed that the highly efficient uptake of cRGDyK-NPs was attributed to the receptor-mediated endocytosis and acidic-triggered drug release. Importantly, cRGDyK-NPs could dramatically reduce the systemic toxicity of DOX and exert excellent tumor killing activity in vivo. The cRGDyK modified pH-sensitive nanocarrier is a promising vehicle for intracellular drug delivery to αvβ3 integrin receptor overexpressed tumor cells and neovascular cells.

STATEMENT OF SIGNIFICANCE

Slow intracellular drug release and poor tumor targeting capacity are still the critical barriers of polymeric nanoparticles (NPs) for the treatment efficiency of chemotherapy. In the present study, we designed cRGDyK peptide modified poly(ethylene glycol)-poly(2,4,6-trimethoxybenzylidene-pentaerythritol carbonate) (cRGDyK-PEG-PTMBPEC) NPs with active targeting and fast pH-triggered drug release. Doxorubicin (DOX)-loaded cRGDyK-PEG-PTMBPEC NPs exhibited pronounced cytotoxicity and enhanced cellular uptake against B16 cells and human umbilical vein endothelial cells overexpressing αvβ3 integrin receptors. Moreover, the active targeted pH-sensitive NPs can enhance the antitumor activity and reduce the systematic toxicity of DOX in vivo.

Self-assembly of pH-responsive dextran-g-poly(lactide-co-glycolide)-g-histidine copolymer micelles for intracellular delivery of paclitaxel and its antitumor activity

Herein, dextran (DX) was conjugated with poly(lactide-co-glycolide) (PLGA) and histidine (His) to prepare a pH-responsive nanocarrier, dextran-g-poly(lactide-co-glycolide)-g-histidine (HDP) micelles, for the delivery of antitumor drugs.

Amphiphilic hyperbranched polymers with a biodegradable hyperbranched poly(ε-caprolactone) core prepared from homologous AB2 macromonomer

Amphiphilic hyperbranched polymers with biodegradable hyperbranched poly(ε-caprolactone) core were prepared from homologous AB₂ macromonomer.

Enhanced effect of pH-sensitive mixed copolymer micelles for overcoming multidrug resistance of doxorubicin

P-glycoprotein (P-gp) mediated drug efflux has been recognized as a key factor contributing to the multidrug resistance (MDR) in tumor cells. To address this issue, a new pH-sensitive mixed copolymer micelles system composed of hyaluronic acid-g-poly(l-histidine) (HA-PHis) and d-α-tocopheryl polyethylene glycol 2000 (TPGS2k) copolymers was developed to co-deliver doxorubicin (DOX) and TPGS2k into drug-resistant breast cancer MCF-7 cells (MCF-7/ADR). The DOX-loaded HA-PHis/TPGS2k mixed micelles (HPHM/TPGS2k) were characterized to have a unimodal size distribution, high DOX loading content and a pH dependent drug release profile due to the protonation of poly(l-histidine). As compared to HA-PHis micelles (HPHM), the HPHM/TPGS2k showed higher and comparable cytotoxicity against MCF-7/ADR cells and MCF-7 cells, respectively. The enhanced MDR reversal effect was attributed to the higher amount of cellular uptake of HPHM/TPGS2k in MCF-7/ADR cells than HPHM, arising from the inhibition of P-gp mediated drug efflux by TPGS2k. The measurements of P-gp expression level and mitochondrial membrane potential indicate that the blank HPHM/TPGS2k inhibited P-gp activity by reducing mitochondrial membrane potential and depletion of ATP but without inhibition of P-gp expression. In vivo study of micelles in tumor-bearing mice indicate that HPHM/TPGS2k could reach the tumor site more effectively than HPHM. The pH-sensitive mixed micelles system has been demonstrated to be a promising approach for overcoming the MDR.

Polypeptide-based "smart" micelles for dual-drug delivery: a combination study of experiments and simulations

A dual-drug-loaded micelle is designed and constructed from a mixture of poly(propylene oxide)-b-poly(γ-benzyl-l-glutamate)-b-poly(ethylene glycol) (PPO-b-PBLG-b-PEG) triblock terpolymers and two model drugs, doxorubicin (DOX) and naproxen (Nap). In the micelles, the DOX is chemically linked to the PBLG backbones through an acid-cleavable hydrazone bond, whereas the Nap is physically encapsulated in the cores. The drug loading and releasing behaviors of the dual-drug-loaded micelles as well as single drug-loaded micelles (DOX-conjugated or Nap-loaded micelles) are studied. The structures of micelles are characterized by means of microscopies and dynamic light scattering, and further examined by dissipative particle dynamics (DPD) simulations. It is revealed that the micelles possess a core-shell-corona structure in which the PPO/Nap, PBLG/DOX, and PEG aggregate to form the core, shell, and corona, respectively. In vitro studies reveal that the release of DOX and Nap is pH- and thermosensitive. Such drug releasing behaviors are also examined by DPD simulations, and more information regarding the mechanism is obtained. In addition, the bio-related properties such as cellular uptake of the micelles and biocompatibility of the deliveries are evaluated. The results show that the dual-drug-loaded micelles are biocompatible at normal physiological conditions and retain the anti-cancer efficiency.

Self-assembled pH-responsive hyaluronic acid-g-poly((L)-histidine) copolymer micelles for targeted intracellular delivery of doxorubicin

Hyaluronic acid (HA) was conjugated with hydrophobic poly(l-histidine) (PHis) to prepare a pH-responsive and tumor-targeted copolymer, hyaluronic acid-g-poly(l-histidine) (HA-PHis), for use as a carrier for anti-cancer drugs. The effect of the degree of substitution (DS) on the pH-responsive behaviour of HA-PHis copolymer micelles was confirmed by studies of particles of different sizes. In vitro drug release studies demonstrated that doxorubicin (DOX) was released from HA-PHis micelles in a pH-dependent manner. In vitro cytotoxicity assays showed that all the blank micelles were nontoxic. However, MTT assay against Michigan Cancer Foundation-7 (MCF-7) cells (overexpressed CD44 receptors) showed that DOX-loaded micelles with a low PHis DS were highly cytotoxic. Cellular uptake experiments revealed that these pH-responsive HA-PHis micelles taken up in great amounts by receptor-mediated endocytosis and DOX were efficiently delivered into cytosol. Moreover, micelles with the lowest DS exhibited the highest degree of cellular uptake, which indicated that the micelles were internalized into cells via CD44 receptor-mediated endocytosis and the carboxylic groups of HA are the active binding sites for CD44 receptors. Endocytosis inhibition experiments and confocal images demonstrated that HA-PHis micelles were internalized into cells mainly via clathrin-mediated endocytosis and delivered to lysosomes, triggering release of DOX into the cytoplasm. These results confirm that the biocompatible pH-responsive HA-PHis micelles are a promising nanosystem for the intracellular targeted delivery of DOX.

pH-sensitive micelles self-assembled from multi-arm star triblock co-polymers poly(ε-caprolactone)-b-poly(2-(diethylamino)ethyl methacrylate)-b-poly(poly(ethylene glycol) methyl ether methacrylate) for controlled anticancer drug delivery

A series of amphiphilic 4- and 6-armed star triblock co-polymers poly(ε-caprolactone)-b-poly(2-(diethylamino)ethyl methacrylate)-b-poly(poly(ethylene glycol) methyl ether methacrylate) (4/6AS-PCL-b-PDEAEMA-b-PPEGMA) were developed by a combination of ring opening polymerization and continuous activators regenerated by electron transfer atom transfer radical polymerization. The critical micelle concentration values of the star co-polymers in aqueous solution were extremely low (2.2-4.0mgl(-1)), depending on the architecture of the co-polymers. The self-assembled blank and doxorubicin (DOX)-loaded three layer micelles were spherical in shape with an average size of 60-220nm determined by scanning electron microscopy and dynamic light scattering. The in vitro release behavior of DOX from the three layer micelles exhibited pH-dependent properties. The DOX release rate was significantly accelerated by decreasing the pH from 7.4 to 5.0, due to swelling of the micelles at lower pH values caused by the protonation of tertiary amine groups in DEAEMA in the middle layer of the micelles. The in vitro cytotoxicity of DOX-loaded micelles to HepG2 cells suggested that the 4/6AS-PCL-b-PDEAEMA-b-PPEGMA micelles could provide equivalent or even enhanced anticancer activity and bioavailability of DOX and thus a lower dosage is sufficient for the same therapeutic efficacy. The results demonstrate that the pH-sensitive multilayer micelles could have great potential application in delivering hydrophobic anticancer drugs for improved cancer therapy.

Controlled drug release system based on cyclodextrin-conjugated poly(lactic acid)-b-poly(ethylene glycol) micelles

Cyclodextrin-conjugated poly(lactic acid)-b-poly(ethylene glycol) (β-CD-PLA-mPEG), a well-defined amphiphilic copolymer, was synthesized by controlled ring-open copolymerization and click coupling reaction, in order to obtain a biocompatible drug delivery system with controlled release profiles. The β-CD-PLA-mPEG copolymer could self-assemble in aqueous solution to form micelles with a mean particle size of 173.4 nm, which will decrease to 159.2 nm after loaded with a kind of hydrophobic drug (indomethacin, IND). The IND-loaded β-CD-PLA-mPEG micelles show spherical shape within the nano-size scale under TEM imaging. Compared with that formed by PLA-mPEG, the micelles formed by β-CD-PLA-mPEG copolymer present higher drug loading efficiency and controlled release profile of IND, especially in the control of its initial burst release. Meanwhile, β-CD-PLA-mPEG copolymer exhibits low toxicity to cells. The micelles formed by β-CD-PLA-mPEG copolymer could be a promising controlled release system for various hydrophobic drugs.

Targeted therapy for cancer using pH-responsive nanocarrier systems

Most of the conventional chemotherapeutic agents used against cancer have poor efficacy. An approach to improve the efficacy of cancer chemotherapy is the development of carrier systems that can be triggered to release the anticancer drug in response to extracellular or intracellular chemical stimuli. To this end, pH-responsive nanocarriers have been developed to target drugs either to the slightly acidic extracellular fluids of tumor tissue or, after endocytosis, to the endosomes or lysosomes within cancer cells. These systems can release the drug by specific processes after accumulation in tumor tissues via the enhanced permeability and retention (EPR) effect or they can release the drugs in endosomes or lysosomes by pH-controlled hydrolysis after they are taken up by the cell via the endocytic pathway. This strategy facilitates the specific delivery of the drug while reducing systemic side-effects with high potential for improving the efficacy of cancer chemotherapy.