Crosslinked Redox-Responsive Micelles Based on Lipoic Acid-Derived Amphiphiles for Enhanced siRNA Delivery

Improving Gene Delivery: Synergy between Alkyl Chain Length and Lipoic Acid for PDMAEMA Hydrophobic Copolymers

In the field of gene delivery, hydrophobic cationic copolymers hold great promise. They exhibit improved performance by effectively protecting genetic material from serum interactions while facilitating interactions with cellular membranes. However, managing cytotoxicity remains a significant challenge, prompting an investigation into suitable hydrophobic components. A particularly encouraging approach involves integrating nutrient components, like lipoic acid, which is known for its antioxidant properties and diverse cellular benefits such as cellular metabolism and growth. In this study, a copolymer library comprising 2-(dimethylamino)ethyl methacrylate (DMAEMA) and lipoic acid methacrylate (LAMA), combined with either n-butyl methacrylate (nBMA), ethyl methacrylate (EMA), or methyl methacrylate (MMA), is synthesized. This enables to probe the impact of lipoic acid incorporation while simultaneously exploring the influence of pendant acyclic alkyl chain length. The inclusion of lipoic acid results in a notable boost in transfection efficiency  while maintaining low cytotoxicity. Interestingly, higher levels of transfection efficiency are achieved in the presence of nBMA, EMA, or MMA. However, a positive correlation between pendant acyclic alkyl chain length and cytotoxicity is observed. Consequently, P(DMAEMA-co-LAMA-co-MMA), emerges as a promising candidate. This is attributed to the optimal combination of low cytotoxic MMA and transfection-boosting LAMA, highlighting the crucial synergy between LAMA and MMA.

Selective Perchlorate Sensing Using Electrochemical Impedance Spectroscopy with Self-Assembled Monolayers of semiaza-Bambusurils

In the last two decades, perchlorate salts have been identified as environmental pollutants and recognized as potential substances affecting human health. We describe self-assembled monolayers (SAMs) of novel semiaza-bambus[6]urils (semiaza-BUs) equipped with thioethers or disulfide (dithiolane) functionalities as surface-anchoring groups on gold electrodes. Cyclic voltammetry (CV) with Fe(CN)6 3-/4- as a redox probe, together with X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and ellipsometry, were employed to characterize the interactions at the interface between the anchoring groups and the metal substrate. Data showed that the anion receptors' packing on the gold strongly depends on the anchoring group. As a result, SAMs of BUs with lipoic amide side chains show a concentration-dependent layer thickness. The BU SAMs are extremely stable on repeated electrochemical potential scans and can selectively recognize perchlorate anions. Our electrochemical impedance spectroscopy (EIS) studies indicated that semiaza-BU equipped with the lipoic amide side chains binds perchlorate (2-100 mM) preferentially over other anions such as F- , Cl- , I- , AcO- , H2 PO4 - , HPO4 2- , SO4 2- , NO2 - , NO3 - , or CO3 2- . The resistance performance is 10 to 100 times more efficient than SAMs containing all other tested anions.

Disulfide Bridging Strategies in Viral and Nonviral Platforms for Nucleic Acid Delivery

Self-assembled nanostructures that are sensitive to environmental stimuli are promising nanomaterials for drug delivery. In this class, disulfide-containing redox-sensitive strategies have gained enormous attention because of their wide applicability and simplicity of nanoparticle design. In the context of nucleic acid delivery, numerous disulfide-based materials have been designed by relying on covalent or noncovalent interactions. In this review, we highlight major advances in the design of disulfide-containing materials for nucleic acid encapsulation, including covalent nucleic acid conjugates, viral vectors or virus-like particles, dendrimers, peptides, polymers, lipids, hydrogels, inorganic nanoparticles, and nucleic acid nanostructures. Our discussion will focus on the context of the design of materials and their impact on addressing the current shortcomings in the intracellular delivery of nucleic acids.

A reduction-responsive drug delivery with improved stability: disulfide crosslinked micelles of small amiphiphilic molecules

Micelles self-assembled from small amphiphilic molecules are unstable in biological fluids, and thus are poor drug carriers. In contrast, amphiphilic polymer micelles can encapsulate hydrophobic drugs in their core to greatly enhance their aqueous solubility and extend their retention time in blood circulation owing to their hydrophilic shell. However, the major disadvantages of conventional polymer micelles are the heterogeneity of the amphiphilic polymer structure and premature drug leakage. Thus, herein, to address these shortcomings, disulfide crosslinked micelles composed of a small amphiphilic molecule, di-lipoyl-glycerophosphorylcholine (di-LA-PC), were developed as redox-responsive drug carriers. Specifically, di-LA-PC was synthesized and self-assembled to form crosslinked micelles under catalysis by dithiothreitol. The disulfide crosslinked micelles maintained high stability in a simulated physiological environment, but rapidly disassembled under reductive conditions. Furthermore, paclitaxel (PTX), as a model drug, was encapsulated in the core of the crosslinked micelles with a high loading content of 8.13%. The in vitro release studies indicated that over 80% of PTX was released from the micelles in the reductive environment, whereas less than 20% PTX was released without reduction in the 68 h test. Benefiting from their nanoscale characteristics, the PTX-loaded micelles showed efficient cellular internalization and effectively induced the death of cancer cells, as revealed in the MTT, apoptosis and cell cycle tests. Moreover, pharmacokinetic studies demonstrated that the crosslinked micelles prolonged the circulation of the incorporated PTX in the bloodstream and increased its accumulation in the tumor tissue via the EPR effect. Finally, the PTX-loaded micelles displayed prominent in vivo anti-tumor activity in a 4T1 xenograft tumor model. In summary, the di-LA-PC crosslinked micelle platform possesses excellent stability, high loading capacity and reduction-responsive release profile, which may have applications in the delivery of PTX and other anti-cancer drugs.

Improved gene delivery to K-562 leukemia cells by lipoic acid modified block copolymer micelles

Although there has been substantial progress in the research field of gene delivery, there are some challenges remaining, e.g. there are still cell types such as primary cells and suspension cells (immune cells) known to be difficult to transfect. Cationic polymers have gained increasing attention due to their ability to bind, condense and mask genetic material, being amenable to scale up and highly variable in their composition. In addition, they can be combined with further monomers exhibiting desired biological and chemical properties, such as antioxidative, pH- and redox-responsive or biocompatible features. By introduction of hydrophobic monomers, in particular as block copolymers, cationic micelles can be formed possessing an improved chance of transfection in otherwise challenging cells. In this study, the antioxidant biomolecule lipoic acid, which can also be used as crosslinker, was incorporated into the hydrophobic block of a diblock copolymer, poly{[2-(dimethylamino)ethyl methacrylate]101-b-[n-(butyl methacrylate)124-co-(lipoic acid methacrylate)22]} (P(DMAEMA101-b-[nBMA124-co-LAMA22])), synthesized by RAFT polymerization and assembled into micelles (LAMA-mic). These micelles were investigated regarding their pDNA binding, cytotoxicity mechanisms and transfection efficiency in K-562 and HEK293T cells, the former representing a difficult to transfect, suspension leukemia cell line. The LAMA-mic exhibited low cytotoxicity at applied concentrations but demonstrated superior transfection efficiency in HEK293T and especially K-562 cells. In-depth studies on the transfection mechanism revealed that transfection efficiency in K-562 cells does not depend on the specific oncogenic fusion gene BCR-ABL alone. It is independent of the cellular uptake of polymer-pDNA complexes but correlates with the endosomal escape of the LAMA-mic. A comparison of the transfection efficiency of the LAMA-mic with structurally comparable micelles without lipoic acid showed that lipoic acid is not solely responsible for the superior transfection efficiency of the LAMA-mic. More likely, a synergistic effect of the antioxidative lipoic acid and the micellar architecture was identified. Therefore, the incorporation of lipoic acid into the core of hydrophobic-cationic micelles represents a promising tailor-made transfer strategy, which can potentially be beneficial for other difficult to transfect cell types.

Core-crosslinked nanomicelles based on crosslinkable prodrug and surfactants for reduction responsive delivery of camptothecin and improved anticancer efficacy

As an important DNA topoisomerase I inhibitor in oncotherapy, camptothecin (CPT) with traditional formulation only shows a limited clinical application mainly because of its poor solubility. In this study, a novel redox responsive nanoscaled delivery system was developed to overcome the inherent defect of CPT. Firstly, a CPT prodrug (CPT-LA) and two crosslinkable surfactants (SO-LA and MPEG-LA) was synthesized, all of which contained the same lipoic acid (LA) structure. In the preparation, highly core-crosslinked structure was formed by adding a thiol crosslinker, which can induce LA ring opening polymerization and disulfide crosslinking. The resulting CPT-LA core-crosslinked nanomicelles (CPT-LA CNM) were formulated with a highly crosslinked core and a PEG hydrophilic shell. Dynamic light scattering (DLS) characterization indicated that CPT-LA CNM possessed a narrow size distribution (184.6 ± 3.6 nm) and negatively charged zeta potential (-3.5 ± 1.2 mV). The storage and physiological stabilities showed that the size distribution of CPT-LA CNM was relatively stable in both conditions which were neutral PBS at 4 °C (1 week period) and PBS containing 10% serum at 37 °C (24 h period). Moreover, the effective CPT release behavior of CPT-LA CNM was confirmed in the reducing circumstances containing dithiothreitol (DTT). Under confocal laser scanning microscopy (CLSM), CPT-LA CNM demonstrated a rapid cellular uptake behavior against cancer cells when compared to CPT suspension. Finally, the enhanced anticancer efficacy of CPT-LA CNM was also detected by in vitro cytotoxicity and cell apoptosis assay. In summary, the core-crosslinked CPT-LA CNM could be a promising CPT delivery system because of high stability, effectively controlled release as well as improved anticancer activity.

Disulfide chemistry in responsive aggregation of amphiphilic systems

The dynamic nature of the disulfide bond has enhanced the potential for disulfide based amphiphiles in the emerging biomedical field. Disulfide containing amphiphiles have extensively been used for constructing wide ranging soft nanostructures as potential candidates for delivery of drugs, proteins and genes owing to their degradable nature in the presence of intracellular glutathione (present in a many fold excess compared to the extracellular milieu). This degradable nature of amphiphiles is not only useful to deliver therapeutics but it also eliminates the toxicity issues associated with the carrier after delivery of such therapeutics. Therefore, these bioreducible and biocompatible nano-aggregates inspired researchers to use them as vehicles for therapeutic delivery and as a result the literature of disulfide containing amphiphiles has been intensified. This review article highlights the structural diversity in disulfide containing amphiphilic small molecule and polymeric systems, structural effects on their aqueous aggregation, redox-responsive disassembly and biological applications. Furthermore, the use of disulfide chemistry towards the design of cell penetrating polymers has also been discussed. Finally a brief perspective on some future opportunities of these systems is provided.

Hyperbranched polydisulfides

Synthesis, aqueous aggregation, hydrophobic guest encapsulation, non-covalent encapsulation stability and glutathione responsive degradation of amphiphilic hyperbranched polydisulfides have been reported.

Synthesis of pH-Cleavable dPG-Amines for Gene Delivery Application

The development of effective nonviral vectors for gene therapy is still a challenge in research, due to the high toxicity of many existing polycationic nanocarriers. In this paper, the development of two pH-cleavable polyglycerol-amine-based nanocarriers is described. The benz-acetal bond represents the pH-sensitive cleavage site between dendritic polyglycerol (dPG) and glycerol-based 1,2-diamines that can complex genetic material. Due to the acid lability of the acetal moiety, the cleavable dPG-amines are less toxic in vitro. Cell-mediated degradation results in non-toxic dPG with low amine functionalization and low molecular weight cleavage products (cp). The genetic material is released because of the loss of multivalent amine groups. Interestingly, the release kinetics at the endosomal pH could be controlled by simple chemical modification of the acetals. In vitro experiments demonstrate the ability of the cleavable dPG-amine to transfect HeLa cells with GFP-DNA, which resulted in cell-compatible cleavage products.