Cationic cross-linked polymers containing labile disulfide and boronic ester linkages for effective triple responsive DNA release

Stimulus-Responsive Nanodelivery and Release Systems for Cancer Gene Therapy: Efficacy Improvement Strategies

Introduction of exogenous genes into target cells to overcome various tumor diseases caused by genetic defects or abnormalities and gene therapy, a new treatment method, provides a promising strategy for tumor treatment. Over the past decade, gene therapy has made exciting progress; however, it still faces the challenge of low nucleic acid delivery and release efficiencies. The emergence of nonviral vectors, primarily nanodelivery and release systems (NDRS), has resulted in a historic breakthrough in the application of gene therapy. NDRS, especially stimulus-responsive NDRS that can respond in a timely manner to changes in the internal and external microenvironment (eg, low pH, high concentration of glutathione/reactive oxygen species, overexpressed enzymes, temperature, light, ultrasound, and magnetic field), has shown excellent loading and release advantages in the precision and efficiency of tumor gene therapy and has been widely applied. The only disadvantage is that poor transfection efficiency limits the in-depth application of gene therapy in clinical practice, owing to the presence of biological barriers in the body. Therefore, this review first introduces the development history of gene therapy, the current obstacles faced by gene delivery, strategies to overcome these obstacles, and conventional vectors, and then focuses on the latest research progress in various stimulus-responsive NDRS for improving gene delivery efficiency. Finally, the future challenges and prospects that stimulus-responsive NDRS may face in clinical application and transformation are discussed to provide references for enhancing in-depth research on tumor gene therapy.

ATP-Responsive Multifunctional Supramolecular Polymer as a Nonviral Vector for Boosting Cholesterol Removal from Lipid-Laden Macrophages

Specific delivery of NCEH1 plasmid is a promising approach to boost the cholesterol removal from lipid-laden macrophages for antiatherosclerosis. Polyethylenimine (PEI) is one of the most efficient gene carriers among nonviral vectors. However, the high transfection activity of PEI is always accompanied by profound cytotoxicity. To tackle the paradox between transfection efficiency and safety, we constructed a novel ATP-responsive multifunctional supramolecular polymer by cross-linking functionalized low-molecular-weight PEI via a boronic ester bond for NCEH1 plasmid delivery. The supramolecular polymer could condense NCEH1 plasmids to form stable nanosized polyplexes when the w/w ratios of the polymer and gene were higher than 2. ATP-triggered degradation of the polymer and pDNA release were characterized by a series of studies, including ¹H NMR, ³¹P NMR, XPS, agarose gel electrophoresis, and ethidium bromide exclusion tests. In addition, the changes in particle size and morphology were observed in the presence of ATP. Interestingly, the supramolecular polymer showed broad spectrum antioxidant activities by measuring the elimination rates of different reactive oxygen species. In addition, the supramolecular polymer displayed a high buffering capability and good cytocompatibility as demonstrated by the results of the buffering capacity, a hemolysis assay, and a cytotoxicity test. Importantly, it was revealed that the supramolecular polymer/NCEH1 plasmid polyplex formulated at a w/w ratio of 20 was most effective in enhancing cholesterol removal from lipid-laden macrophages and reducing the accumulation of lipid droplets as evidenced by transfection study, cholesterol efflux assay, and oil red O staining studies. Collectively, the ATP-responsive multifunctional supramolecular polymer holds great potential for safe and efficient gene delivery for antiatherosclerosis.

Histidine-Based Reduction-Sensitive Star-Polymer Inclusion Complex as a Potential DNA Carrier: Biophysical Studies Using Time-Resolved Fluorescence as an Important Tool

An ideal DNA carrier is one that is capable of effectively condensing DNA into complexes of optimum size and shape, preventing premature decomplexation in the bloodstream and efficiently releasing the DNA into affected cells. In this context, we have developed a novel β-cyclodextrin (β-CD)-based four-arm star-shaped polymer inclusion complex (IC) with arms made of a poly(l-histidine)-based cationic polymer. The polymer was well characterized by gel permeation chromatography, NMR, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. We have also investigated its DNA complexation and release properties. Bisadamantane containing a disulfide bond was synthesized that linked two such poly(l-histidine)-containing β-CD units via guest-host interactions to prepare the presented IC. Besides using the conventional steady-state fluorescence spectroscopy, the ability of this IC to condense DNA to form polyplexes and their release behavior have been established by using the time-resolved fluorescence spectroscopy technique. Thiazole orange (TO) was used for the first time as a DNA-intercalating dye in the time-resolved fluorescence spectroscopic study. The superior DNA-condensing ability of the IC as compared to that of the precursor two-arm β-CD and linear poly(l-histidine) of a comparable molecular weight, as confirmed by dynamic light scattering, zeta potential, atomic force microscopy, and gel electrophoresis studies, could be attributed to a higher charge density. The IC-DNA polyplexes were found to be stable in a medium similar to an extracellular fluid but could efficiently release DNA in the presence of 10 mM glutathione, a concentration prevalent in the intracellular fluid of cancer cells. Hence, here, we have successfully demonstrated the synthesis of a novel biocompatible star-shaped IC with the potential to carry and release DNA in cancer cells and also established the feasibility of using the time-resolved fluorescence spectroscopic technique to study the complexation behavior of the polycation and DNA using TO as a DNA-intercalating dye.