Novel hybrid vesicles co-assembled from a cationic lipid and PAAc-g-mPEG with pH-triggered transmembrane channels for controlled drug release

Current paradigms in employing self-assembled structures: Drug delivery implications with improved therapeutic potential

Recent efforts have focused on developing improved drug delivery systems with enhanced therapeutic efficacy and minimal side effects. Micelles, self-assembled from amphiphilic block copolymers in aqueous solutions, have gained considerable attention for drug delivery. However, there is a need to further enhance their efficiency. These micelles offer benefits like biodegradability, biocompatibility, sustained drug release, and improved patient compliance. Yet, researchers must address stability issues and reduce toxicity. Nanoscale self-assembled structures have shown promise as efficient drug carriers, offering an alternative to conventional methods. Fine-tuning at the monomeric and molecular levels, along with structural modifications, is crucial for optimal drug release profiles. Various strategies, such as entrapping hydrophobic drugs and using polyethylene oxide diblock copolymer micelles to resist protein adsorption and cellular adhesion, protect the hydrophobic core from degradation. The polyethylene oxide corona also provides stealth properties, prolonging blood circulation for extended drug administration. Amphiphilic copolymers are attractive for drug delivery due to their adjustable properties, allowing control over micelle size and morphology. Emerging tools promise complex and multifunctional platforms. This article summarizes about the challenges as far as the use of micelles is concerned, including optimizing performance, rigorous pre-clinical and clinical research, and suggests further improvement for drug delivery efficacy.

Recent Advancements in Polymer/Liposome Assembly for Drug Delivery: From Surface Modifications to Hybrid Vesicles

Liposomes are consolidated and attractive biomimetic nanocarriers widely used in the field of drug delivery. The structural versatility of liposomes has been exploited for the development of various carriers for the topical or systemic delivery of drugs and bioactive molecules, with the possibility of increasing their bioavailability and stability, and modulating and directing their release, while limiting the side effects at the same time. Nevertheless, first-generation vesicles suffer from some limitations including physical instability, short in vivo circulation lifetime, reduced payload, uncontrolled release properties, and low targeting abilities. Therefore, liposome preparation technology soon took advantage of the possibility of improving vesicle performance using both natural and synthetic polymers. Polymers can easily be synthesized in a controlled manner over a wide range of molecular weights and in a low dispersity range. Their properties are widely tunable and therefore allow the low chemical versatility typical of lipids to be overcome. Moreover, depending on their structure, polymers can be used to create a simple covering on the liposome surface or to intercalate in the phospholipid bilayer to give rise to real hybrid structures. This review illustrates the main strategies implemented in the field of polymer/liposome assembly for drug delivery, with a look at the most recent publications without neglecting basic concepts for a simple and complete understanding by the reader.

Multifunctional GQDs-Concanavalin A@Fe3O4 nanocomposites for cancer cells detection and targeted drug delivery

Multifunctional nanocomposites containing intrinsic property for serving as the sensing elements as well as targeted nanoconjugates are highly preferred in various therapeutic applications. In this work, nanocomposites of graphene quantum dots (GQDs) and Fe₃O₄ with conjugation of lectin protein, concanavalin A, to form GQD-ConA@Fe₃O₄ nanocomposites are developed for both detection of cancer cell and release of drugs to HeLa cells. The GQD-ConA@Fe₃O₄ nanocomposites deposited on Pt electrode can detect cancerous HeLa cells over normal endothelial cells with a dynamic linear range of 5 × 10² to 1 × 10⁵ cells mL^-1 with a detection limit of 273 cell mL^-1. The GQD-ConA@Fe₃O₄ also can serve as nanocarriers for loading and delivering doxorubicin (Dox). The in vitro cell images show that the Dox concentration in HeLa cells is enhanced more than double in the presence of external magnetic field due to the incorporation of Fe₃O₄ in the nanocarrier. The cytotoxicity assay indicates that the susceptibility of cancerous HeLa cells to Dox is 13% higher than that of normal cells, confirming the selective role of ConA in nanocarriers. Results clearly indicate the GQD-ConA@Fe₃O₄ nanocomposites as a promising material for cancer cell detection and targeted Dox release toward HeLa cells which can serve as the multifunctional platform for novel cancer cell diagnostic and therapeutic applications.

Stimuli-responsive liposomes for drug delivery

The ultimate goal of drug delivery is to increase the bioavailability and reduce the toxic side effects of the active pharmaceutical ingredient (API) by releasing them at a specific site of action. In the case of antitumor therapy, association of the therapeutic agent with a carrier system can minimize damage to healthy, nontarget tissues, while limit systemic release and promoting long circulation to enhance uptake at the cancerous site due to the enhanced permeation and retention effect (EPR). Stimuli-responsive systems have become a promising way to deliver and release payloads in a site-selective manner. Potential carrier systems have been derived from a wide variety of materials, including inorganic nanoparticles, lipids, and polymers that have been imbued with stimuli-sensitive properties to accomplish triggered release based on an environmental cue. The unique features in the tumor microenvironment can serve as an endogenous stimulus (pH, redox potential, or unique enzymatic activity) or the locus of an applied external stimulus (heat or light) to trigger the controlled release of API. In liposomal carrier systems triggered release is generally based on the principle of membrane destabilization from local defects within bilayer membranes to effect release of liposome-entrapped drugs. This review focuses on the literature appearing between November 2008-February 2016 that reports new developments in stimuli-sensitive liposomal drug delivery strategies using pH change, enzyme transformation, redox reactions, and photochemical mechanisms of activation. WIREs Nanomed Nanobiotechnol 2017, 9:e1450. doi: 10.1002/wnan.1450 For further resources related to this article, please visit the WIREs website.

Acidity-triggered surface charge neutralization and aggregation of functionalized nanoparticles for promoted tumor uptake

A polymeric nanovehicle featured with histidine-rich surface was developed for tumor-targeted delivery of doxorubicin.

Dual-layered nanogel-coated hollow lipid/polypeptide conjugate assemblies for potential pH-triggered intracellular drug release

To achieve effective intracellular anticancer drug delivery, the polymeric vesicles supplemented with the pH-responsive outlayered gels as a delivery system of doxorubicin (DOX) were developed from self-assembly of the lipid/polypeptide adduct, distearin grafted poly(γ-glutamic acid) (poly(γ-GA)), followed by sequential deposition of chitosan and poly(γ-GA-co-γ-glutamyl oxysuccinimide)-g-monomethoxy poly(ethylene glycol) in combination with in situ covalent cross-linking on assembly surfaces. The resultant gel-caged polymeric vesicles (GCPVs) showed superior performance in regulating drug release in response to the external pH change. Under typical physiological conditions (pH 7.4 and 37 °C) at which the γ-GA/DOX ionic pairings remained mostly undisturbed, the dense outlayered gels of GCPVs significantly reduced the premature leakage of the uncomplexed payload. With the environmental pH being reduced from pH 7.4 to 4.7, the drug liberation was appreciably promoted by the massive disruption of the ionic γ-GA/DOX complexes along with the significant swelling of nanogel layers upon the increased protonation of chitosan chain segments. After being internalized by HeLa cells via endocytosis, GCPVs exhibited cytotoxic effect comparable to free DOX achieved by rapidly releasing the payload in intracellular acidic endosomes and lysosomes. This strongly implies the great promise of such unique GCPVs as an intracellular drug delivery carrier for potential anticancer treatment.

pH-responsive hierarchical transformation of charged lipid assemblies within polyelectrolyte gel layers with applications for controlled drug release and MR imaging contrast

Cationic DOTAP assemblies within poly(acrylic acid) gel effectively modulate drug release and MR imaging contrast by pH-induced morphological transformation.

Superparamagnetic hollow hybrid nanogels as a potential guidable vehicle system of stimuli-mediated MR imaging and multiple cancer therapeutics

Hollow hybrid nanogels were prepared first by the coassembly of the citric acid-coated superparamagnetic iron oxide nanoparticles (SPIONs, 44 wt %) with the graft copolymer (56 wt %) comprising acrylic acid and 2-methacryloylethyl acrylate units as the backbone and poly(ethylene glycol) and poly(N-isopropylacrylamide) as the grafts in the aqueous phase of pH 3.0 in the hybrid vesicle structure, followed by in situ covalent stabilization via the photoinitiated polymerization of MEA residues within vesicles. The resultant hollow nanogels, though slightly swollen, satisfactorily retain their structural integrity while the medium pH is adjusted to 7.4. Confining SPION clusters to such a high level (44 wt %) within the pH-responsive thin gel layer remarkably enhances the transverse relaxivity (r2) and renders the MR imaging highly pH-tunable. For example, with the pH being adjusted from 4.0 to 7.4, the r2 value can be dramatically increased from 138.5 to 265.5 mM(-1) s(-1). The DOX-loaded hybrid nanogels also exhibit accelerated drug release in response to both pH reduction and temperature increase as a result of the substantial disruption of the interactions between drug molecules and copolymer components. With magnetic transport guidance toward the target and subsequent exposure to an alternating magnetic field, this DOX-loaded nanogel system possessing combined capabilities of hyperthermia and stimuli-triggered drug release showed superior in vitro cytotoxicity against HeLa cells as compared to the case with only free drug or hyperthermia alone. This work demonstrates that the hollow inorganic/organic hybrid nanogels hold great potential to serve as a multimodal theranostic vehicle functionalized with such desirable features as the guidable delivery of stimuli-mediated diagnostic imaging and hyperthermia/chemotherapies.

Responsive hybrid microcapsules by the one-step interfacial thiol-ene photopolymerization

We here demonstrated a general, convenient, and robust method to fabricate the hybrid microcapsules through the one-step thiol-ene photopolymerization at the interface between toluene and water. In the presence of amphiphilic polyhedral oligomeric silsesquioxane (POSS) containing thiol groups (PTPS) as reactive surfactants and trimethylolpropane triacrylate (TMPTA) as a cross-linker, the wall of hybrid microcapsules can be photo-cross-linked. The obtained hybrid microcapsules (HMCs) were well-characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and confocal laser scanning microscopy (CLSM). The results revealed that the obtained HMCs are uniform with the tunable size in diameter (2-4 μm) and wall thickness (55-120 nm). The size of HMCs increased with the increasing content of toluene. The wall thickness of HMCs decreased with the increasing content of toluene, while the wall thickness of HMCs increased with the increasing content of cross-linker TMPTA. Furthermore, HMCs are thermoresponsive in aqueous solution, can encapsulate both hydrophobic and dydrophilic dyes, and can be used in the controlled dispersion of dyes in different mediums. It is believed that this simple, robust, and general method to fabricate the hybrid microcapsules will extend the potential application fields of microcapsules, such as in the controlled dispersion and drug delivery.

Dual stimuli-responsive polymeric hollow nanogels designed as carriers for intracellular triggered drug release

Dual stimuli-responsive hollow nanogel spheres serving as an efficient intracellular drug delivery platform were obtained from the spontaneous coassociation of two graft copolymers into the vesicle architecture in aqueous phase. Both copolymers comprise acrylic acid (AAc) and 2-methacryloylethyl acrylate (MEA) units as the backbone and either poly(N-isopropylacrylamide) (PNIPAAm) alone or both PNIPAAm and monomethoxypoly(ethylene glycol) (mPEG) chain segments as the grafts. The assemblies were then subjected to covalent stabilization within vesicle walls with ester-containing cross-links by radical polymerization of MEA moieties, thereby leading to hollow nanogel particles. Taking the advantage of retaining a low quantity of payload within polymer layer-enclosed aqueous chambers through the entire loading process, doxorubicin (DOX) in the external bulk phase can be effectively transported into the gel membrane and bound therein via electrostatic interactions with ionized AAc residues and hydrogen-bond pairings with PNIPAAm grafts at pH 7.4. With the environmental pH being reduced (e.g., from 7.4 to 5.0) at 37 °C, the extensive disruption of AAc/DOX complexes due to the reduced ionization of AAc residues within the gel layer and the pronounced shrinkage of nanogels enable the rapid release of DOX species from drug-loaded hollow nanogels. By contrast, the drug liberation at 4 °C was severally restricted, particularly at pH 7.4 at which the DOX molecules remain strongly bound with ionized AAc residues and PNIPAAm grafts. The in vitro characterizations suggest that the DOX-loaded hollow nanogel particles after being internalized by HeLa cells via endocytosis can rapidly release the payload within acidic endosomes or lysosomes. This will then lead to significant drug accumulation in nuclei (within 1 h) and a cytotoxic effect comparable to free drug. This work demonstrates that the novel DOX-loaded hollow nanogel particles show great promise of therapeutic efficacy for potential anticancer treatment.