FRET-based dual-emission and pH-responsive nanocarriers for enhanced delivery of protein across intestinal epithelial cell barrier

The oral route is a convenient and commonly employed way for drug delivery. However, therapeutic proteins have poor bioavailability upon oral administration due to the impermeable barrier from intestinal epithelial tight junction (TJ). Moreover, the pH of the small intestine varies among different regions of the intestinal tract where digestion and absorption occur at different levels. In this study, a tunable dual-emitting and pH-responsive nanocarrier that can alter the fluorescent color and emission intensity in response to pH changes and can trigger the opening of intestinal epithelial TJ at different levels were developed from chitosan-N-arginine and poly(γ-glutamic acid)-taurine conjugates. As pH increased from 6.0 to 8.0, the binding affinity of the oppositely charged polyions decreased, whereas the ratio of the intensity of the donor-to-acceptor emission intensity (ID/IA) increased by 27-fold. The fluorescent and pH-responsive nanocarrier was able to monitor the pH change of intestinal environment and to control the release of an anti-angiogenic protein in response to the pH gradient. The nanocarrier triggered the opening of intestinal epithelial TJ and consequently enhanced the permeation of the released protein through the intestinal epithelial barrier model (Caco-2 cell monolayer) to inhibit tube formation of human umbilical vein endothelial cells.

Engineered nanoparticles for drug delivery in cancer therapy

In medicine, nanotechnology has sparked a rapidly growing interest as it promises to solve a number of issues associated with conventional therapeutic agents, including their poor water solubility (at least, for most anticancer drugs), lack of targeting capability, nonspecific distribution, systemic toxicity, and low therapeutic index. Over the past several decades, remarkable progress has been made in the development and application of engineered nanoparticles to treat cancer more effectively. For example, therapeutic agents have been integrated with nanoparticles engineered with optimal sizes, shapes, and surface properties to increase their solubility, prolong their circulation half-life, improve their biodistribution, and reduce their immunogenicity. Nanoparticles and their payloads have also been favorably delivered into tumors by taking advantage of the pathophysiological conditions, such as the enhanced permeability and retention effect, and the spatial variations in the pH value. Additionally, targeting ligands (e.g., small organic molecules, peptides, antibodies, and nucleic acids) have been added to the surface of nanoparticles to specifically target cancerous cells through selective binding to the receptors overexpressed on their surface. Furthermore, it has been demonstrated that multiple types of therapeutic drugs and/or diagnostic agents (e.g., contrast agents) could be delivered through the same carrier to enable combination therapy with a potential to overcome multidrug resistance, and real-time readout on the treatment efficacy. It is anticipated that precisely engineered nanoparticles will emerge as the next-generation platform for cancer therapy and many other biomedical applications.

Insight into nanoparticle cellular uptake and intracellular targeting

Collaborative efforts from the fields of biology, materials science, and engineering are leading to exciting progress in the development of nanomedicines. Since the targets of many therapeutic agents are localized in subcellular compartments, modulation of nanoparticle-cell interactions for efficient cellular uptake through the plasma membrane and the development of nanomedicines for precise delivery to subcellular compartments remain formidable challenges. Cellular internalization routes determine the post-internalization fate and intracellular localization of nanoparticles. This review highlights the cellular uptake routes most relevant to the field of non-targeted nanomedicine and presents an account of ligand-targeted nanoparticles for receptor-mediated cellular internalization as a strategy for modulating the cellular uptake of nanoparticles. Ligand-targeted nanoparticles have been the main impetus behind the progress of nanomedicines towards the clinic. This strategy has already resulted in remarkable progress towards effective oral delivery of nanomedicines that can overcome the intestinal epithelial barrier. A detailed overview of the recent developments in subcellular targeting as a novel platform for next-generation organelle-specific nanomedicines is also provided. Each section of the review includes prospects, potential, and concrete expectations from the field of targeted nanomedicines and strategies to meet those expectations.

Synthesis of Acid-Labile PEG and PEG-Doxorubicin-Conjugate Nanoparticles via Brush-First ROMP

A panel of acid-labile bis-norbornene cross-linkers was synthesized and evaluated for the formation of acid-degradable brush-arm star polymers (BASPs) via the brush-first ring-opening metathesis polymerization (ROMP) method. An acetal-based cross-linker was identified that, when employed in conjunction with a poly(ethylene glycol) (PEG) macromonomer, provided highly controlled BASP formation reactions. A combination of this new cross-linker with a novel doxorubicin (DOX)-branch-PEG macromonomer provided BASPs that simultaneously degrade and release cytotoxic DOX in vitro.

Thiolated human serum albumin cross-linked dextran hydrogels as a macroscale delivery system

Hydrogels play an important role in macroscale delivery systems by enabling the transport of cells and molecules. Here we present a facile and benign method to prepare a dextran-based hydrogel (Dex-sHSA) using human serum albumin (HSA) as a simultaneous drug carrier and covalent cross-linker. Drug binding affinity of the albumin protein was conserved in the thiolation step using 2-iminothiolane and subsequently, in the in situ gelation step. Oscillation rheometry studies confirmed the formation of a three-dimensional viscoelastic network upon reaction of dextran and the HSA protein. The mechanical properties of Dex-sHSA hydrogel can be tuned by the protein concentration, and the degree of thiolation of sHSA. Sustained release of hydrophobic drugs, such as ibuprofen, paclitaxel and dexamethasone, from the Dex-sHSA network was shown over one week. Hence, this albumin-based dextran hydrogel system demonstrates its potential as a macroscale delivery system of hydrophobic therapeutics for a wide range of biomedical applications.

Acid-responsive polymeric nanocarriers for topical adapalene delivery

PURPOSE

The acne skin is characteristic of a relatively lower pH microenvironment compared to the healthy skin. The aim of this work was to utilize such pH discrepancy as a site-specific trigger for on-demand topical adapalene delivery.

METHODS

The anti-acne agent, adapalene, was encapsulated in acid-responsive polymer (Eudragit® EPO) nanocarriers via nanoprecipitation. The nanocarriers were characterized in terms of particle size, surface morphology, drug-carrier interaction, drug release and permeation.

RESULTS

Adapalene experienced a rapid release at pH 4.0 in contrast to that at pH 5.0 and 6.0. The permeation study using silicone membrane revealed a significant higher drug flux from the nanocarrier (6.5 ± 0.6 μg.cm(-2).h(-1)) in comparison to that (3.9 ± 0.4 μg.cm(-2).h(-1)) in the control vehicle (Transcutol®). The in vitro pig skin tape stripping study showed that at 24 h post dose-application the nanocarrier delivered the same amount of drug to the stratum corneum as the positive control vehicle did.

CONCLUSIONS

The acid-responsive nanocarriers hold promise for efficient adapalene delivery and thus improved acne therapy.

Tumor-preferential sustained drug release enhances antitumor activity of block copolymer micelles

Nanoparticles are widely used as drug carriers for controlled, tumor-targeted delivery of various anticancer agents that have biopharmaceutical limitations such as water solubility and tissue permeability. Growing evidence suggests that nanoparticles not only reduce toxic side effects of anticancer drugs but also improve the therapeutic efficacy as a function of their drug-release profile. The purpose of this study is to confirm such hypothetical effects of tunable drug release on improving antitumor activity of nanoparticles in vitro and in vivo, using block copolymer micelles as drug carriers. Micelles were prepared from poly(ethylene glycol)-poly(aspartate) block copolymers modified with hydrazide (HYD), aminobenzoate hydrazide (ABZ) and glycine hydrazide (GLY) linkers to achieve a pH-dependent, tunable release of doxorubicin (DOX), a model anticancer drug. Regardless of the drug-release profile, all three micelles showed similar properties in vitro, such as pH-dependent drug release, intracellular drug delivery and cancer cell growth inhibition. However, micelles releasing DOX slowly in vitro showed that the most effective antitumor activity in vivo, compared to the micelles releasing drugs faster. These results demonstrate that tumor-preferential sustained drug release can enhance the antitumor activity of the micelles.

Acid-mediated Lipinski's second rule: application to drug design and targeting in cancer

With a predicted 382.4 per 100,000 people expected to suffer from some form of malignant neoplasm by 2015, and a current death toll of 1 out of 8 deaths worldwide, improving treatment and/or drug design is an essential focus of cancer research. Multi-drug resistance is the leading cause of chemotherapeutic failure, and delivery of anticancer drugs to the inside of cancerous cells is another major challenge. Fifteen years ago, in a completely different field in which improving drug delivery is the objective, the bioavailability of oral compounds, Christopher Lipinski formulated some rules that are still used by the pharmaceutical industry as rules of thumb to improve drug delivery to their target. Although Lipinski’s rules were not formulated to improve delivery of antineoplastic drugs to the inside of cancer cells, it is interesting to note that the problems are similar. On the basis of the strong similarity between the fields, we discuss how they can be connected and how new drug targets can be defined in cancer.

Facile synthesis of photo-cleavable polymers via Passerini reaction

Passerini three-component reaction and multicomponent polymerization (MCP) were demonstrated to be facile methods for the preparation of photo-cleavable polymers, photo- and redox-dually cleavable polymers, as well as block copolymers.

Lipase-catalyzed synthesis of azido-functionalized aliphatic polyesters towards acid-degradable amphiphilic graft copolymers

A series of novel aliphatic polyesters with azido functional groups were synthesized via the direct lipase-catalyzed polycondensation of dialkyl diester, diol and 2-azido-1,3-propanediol (azido glycerol) using immobilized lipase B from Candida antarctica (CALB). The effects of polymerization conditions including reaction time, temperature, enzyme amount, substrates and monomer feed ratio on the molecular weights of the products were studied. The polyesters with pendant azido groups were characterized by (1)H NMR, (13)C NMR, 2D NMR, FTIR, GPC and DSC. Alkyne end-functionalized poly(ethylene glycol) containing a cleavable acetal group was then grafted onto the polyester backbone by copper-catalyzed azide-alkyne cycloaddition (CuAAC, click chemistry). Using fluorescence spectroscopy, dynamic light scattering (DLS) and transmission electron microscopy (TEM), these amphiphilic graft copolymers were found to readily self-assemble into nanosized micelles in aqueous solution with critical micelle concentrations between 0.70 and 1.97 mg L(-1), and micelle sizes from 20-70 nm. The degradation of these polymers under acidic conditions was investigated by GPC and (1)H NMR spectroscopy. Cell cytotoxicity tests indicated that the micelles had no apparent cytotoxicity to Bel-7402 cells, suggesting their potential as carriers for controlled drug delivery.

Polyacryloyl hydrazide: an efficient, simple, and cost effective precursor to a range of functional materials through hydrazide based click reactions

Preparation and studies of ion exchangeable epoxy resins, stimuli responsive hydrogels, and polymer-dye conjugates have been accomplished through hydrazide based click reactions using polyacryloyl hydrazide (PAH) as the precursor. A convenient synthesis of PAH with quantitative functionality was achieved by treatment of polymethyl acrylate with hydrazine hydrate in the presence of tetra-n-butyl ammonium bromide. PAH was cured with bisphenol A diglycidyl ether (BADGE) at 60 °C to form transparent resins with superior mechanical properties (tensile strength = 2-40 MPa, Young's modulus = 3.3-1043 MPa, and ultimate elongation = 9-75%) compared to the conventional resins prepared using triethylene tetramine. The resins exhibited higher ion exchange capacities (1.2-6.3 mmol/g) compared to the commercial AHA ammonium-type (Tokuyama Co., Japan) membranes. An azo dye with aldehyde functionality was covalently attached to PAH through hydrazone linkage, and the dye labeled PAH exhibited colorimetric sensing ability for base and acids up to micromolar concentration. The swelling of the PAH based hydrogel varied in the range 4-450% depending on the pH and temperature of the medium. The hydrogels gradually released 30% of the original encapsulated dye in a period of 200 h. PAH-hydroxy naphthaldehyde conjugate released 75% of the original loading in ∼11 days at 37 °C and pH 5.0 through cleavage of the -CONHN═C- linkage. The study depicts the versatility of PAH as a precursor and inspires synthesis of a range of new materials based on PAH in the future.

A nanocarrier based on a genetically engineered protein cage to deliver doxorubicin to human hepatocellular carcinoma cells

Herein, we report the preparation of genetically engineered protein cages (HspG41C-SP94), taken up selectively by human hepatocellular carcinoma (HCC) cells. An engineered protein cage-doxorubicin (DOX) conjugate was as cytotoxic as free DOX against HCC cells but much less cytotoxic against normal hepatocytes.

Redox-responsive core cross-linked micelles based on cypate and cisplatin prodrugs-conjugated block copolymers for synergistic photothermal–chemotherapy of cancer

A synergistic effect of photothermal and chemotherapy of cancers was demonstrated using redox-responsive core cross-linked micelles fabricated from cypate and cisplatin prodrugs-conjugated block copolymers.

Oxidation-responsive polymers for biomedical applications

This article summarizes recent progress in the design and synthesis of various oxidation-responsive polymers and their application in biomedical fields.

Novel poly(ethylene oxide monomethyl ether)-b-poly(ε-caprolactone) diblock copolymers containing a pH-acid labile ketal group as a block linkage

Acidic physiological conditions trigger degradation of amphiphilic block copolymers containing a ketal group as a block linkage into biocompatible degradation products.

Graft copolymer nanoparticles with pH and reduction dual-induced disassemblable property for enhanced intracellular curcumin release

Nanoparticle (NP)-assisted drug delivery systems with disassemblable behaviors in response to intracellular microenvironment are urgently demanded in systemic cancer chemotherapy for enhanced intracellular drug release. Curcumin (CUR), an effective and safe anticancer agent, was limited by its water insolubility and poor bioavailability. Herein, pH and reduction dual-induced disassemblable NPs for high loading efficiency and improved intracellular release of CUR were developed based on an acid degradable cyclic benzylidene acetal groups (CBAs)-functionalized poly(2,4,6-trimethoxybenzylidene-1,1,1-tris(hydroxymethyl)ethane methacrylate)-g-SS-poly(ethylene glycol) (PTTMA-g-SS-PEG) graft copolymer, which was readily prepared via RAFT copolymerization and coupling reaction. The NPs self-assembled from PTTMA-g-SS-PEG copolymers were stable at physiological pH, and quickly disassembled in mildly acidic and reductive environments because of the hydrolysis of CBAs in hydrophobic PTTMA core and the cleavage of disulfide-linked detachable PEG shell. PTTMA-g-SS-PEG NPs exhibited excellent CUR loading capacity with drug loading content up to 19.2% and entrapment efficiency of 96.0%. Within 20 h in vitro, less than 15.0% of CUR was released from the CUR-loaded NPs in normal physiological conditions, whereas 94.3% was released in the presence of reductive agent and mildly acidic conditions analogous to the microenvironment in endosome/lysosome and cytoplasm. Confocal fluorescence microscopies revealed that the CUR-loaded PTTMA-g-SS-PEG NPs exhibited more efficiently intracellular CUR release for EC-109 cells than that of CUR-loaded reduction-unresponsive PTTMA-g-PEG NPs and free CUR. In vitro cytotoxicity studies displayed blank PTTMA-g-SS-PEG NPs showed low toxicity at concentrations up to 1.0 mg/mL, whereas CUR-loaded PTTMA-g-SS-PEG NPs demonstrated more efficient growth inhibition toward EC-109 and HepG-2 cells than reduction-unresponsive controls and free CUR. Therefore, the above results indicated that pH and reduction dual-induced disassemblable PTTMA-g-SS-PEG NPs may have emerged as superior nanocarriers for active loading and promoted intracellular drug delivery in systemic cancer chemotherapy.

Comb-like amphiphilic copolymers bearing acetal-functionalized backbones with the ability of acid-triggered hydrophobic-to-hydrophilic transition as effective nanocarriers for intracellular release of curcumin

The pH-responsive micelles have enormous potential as nanosized drug carriers for cancer therapy due to their physicochemical changes in response to the tumor intracellular acidic microenvironment. Herein, a series of comb-like amphiphilic copolymers bearing acetal-functionalized backbone were developed based on poly[(2,4,6-trimethoxybenzylidene-1,1,1-tris(hydroxymethyl) ethane methacrylate-co-poly(ethylene glycol) methyl ether methacrylate] [P(TTMA-co-mPEGMA)] as effective nanocarriers for intracellular curcumin (CUR) release. P(TTMA-co-mPEGMA) copolymers with different hydrophobic-hydrophilic ratios were prepared by one-step reversible addition fragmentation chain transfer (RAFT) copolymerization of TTMA and mPEGMA. Their molecular structures and chemical compositions were confirmed by (1)H NMR, Fourier transform infrared spectroscopy (FT-IR) and gel permeation chromatography (GPC). P(TTMA-co-mPEGMA) copolymers could self-assemble into nanosized micelles in aqueous solution and displayed low critical micelle concentration (CMC). All P(TTMA-co-mPEGMA) micelles displayed excellent drug loading capacity, due to the strong π-π conjugate action and hydrophobic interaction between the PTTMA and CUR. Moreover, the hydrophobic PTTMA chain could be selectively hydrolyzed into a hydrophilic backbone in the mildly acidic environment, leading to significant swelling and final disassembly of the micelles. These morphological changes of P(TTMA-co-mPEGMA) micelles with time at pH 5.0 were determined by DLS and TEM. The in vitro CUR release from the micelles exhibited a pH-dependent behavior. The release rate of CUR was significantly accelerated at mildly acidic pH of 4.0 and 5.0 compared to that at pH 7.4. Toxicity test revealed that the P(TTMA-co-mPEGMA) copolymers exhibited low cytotoxicity, whereas the CUR-loaded micelles maintained high cytotoxicity for HepG-2 and EC-109 cells. The results indicated that the novel P(TTMA-co-mPEGMA) micelles with low CMC, small and tunable sizes, high drug loading, pH-responsive drug release behavior, and good biocompatibility may have potential as hydrophobic drug delivery nanocarriers for cancer therapy with intelligent delivery.

Methoxy-Poly(ethylene glycol)-block-Poly(ε-caprolactone) Bearing Pendant Aldehyde Groups as pH-Responsive Drug Delivery Carrier

A biodegradable amphiphilic block copolymer of methoxy poly(ethylene glycol)-block-poly(ϵ-caprolactone) bearing pendant aldehyde groups was synthesised by a combination of ring-opening polymerisation and thio-bromo ‘click’ chemistry. The free aldehyde groups on the copolymer were reacted with hydrophobic payloads (p-methoxylaniline as a model drug) by a benzoic–imine linker, which was responsive to pH change. NMR, FTIR, and gel permeation chromatography analysis confirmed the copolymer structures. In vitro release studies revealed that under acid stimulus, hydrolysis of the benzoic–imine bond resulted in a rapid drug release. This new amphiphilic block copolymer is expected to have promising applications in biodegradable controlled drug delivery systems.