Correlation between Protonation of Tailor-Made Polypiperazines and Endosomal Escape for Cytosolic Protein Delivery

Recent Progress in the Endosomal Escape Mechanism and Chemical Structures of Polycations for Nucleic Acid Delivery

Nucleic acid-based therapies are seeing a spiralling surge. Stimuli-responsive polymers, especially pH-responsive ones, are gaining widespread attention because of their ability to efficiently deliver nucleic acids. These polymers can be synthesized and modified according to target requirements, such as delivery sites and the nature of nucleic acids. In this regard, the endosomal escape mechanism of polymer-nucleic acid complexes (polyplexes) remains a topic of considerable interest owing to various plausible escape mechanisms. This review describes current progress in the endosomal escape mechanism of polyplexes and state-of-the-art chemical designs for pH-responsive polymers. The importance is also discussed of the acid dissociation constant (i.e., pKa) in designing the new generation of pH-responsive polymers, along with assays to monitor and quantify the endosomal escape behavior. Further, the use of machine learning is addressed in pKa prediction and polymer design to find novel chemical structures for pH responsiveness. This review will facilitate the design of new pH-responsive polymers for advanced and efficient nucleic acid delivery.

Lipid Nanoparticles Optimized for Targeting and Release of Nucleic Acid

Lipid nanoparticles (LNPs) are currently the most promising clinical nucleic acids drug delivery vehicles. LNPs prevent the degradation of cargo nucleic acids during blood circulation. Upon entry into the cell, specific components of the lipid nanoparticles can promote the endosomal escape of nucleic acids. These are the basic properties of lipid nanoparticles as nucleic acid carriers. As LNPs exhibit hepatic aggregation characteristics, enhancing targeting out of the liver is a crucial way to improve LNPs administrated in vivo. Meanwhile, endosomal escape of nucleic acids loaded in LNPs is often considered inadequate, and therefore, much effort is devoted to enhancing the intracellular release efficiency of nucleic acids. Here, different strategies to efficiently deliver nucleic acid delivery from LNPs are concluded and their mechanisms are investigated. In addition, based on the information on LNPs that are in clinical trials or have completed clinical trials, the issues that are necessary to be approached in the clinical translation of LNPs are discussed, which it is hoped will shed light on the development of LNP nucleic acid drugs.

A piperazine-substituted phthalocyanine with rapid cellular uptake and dual organelle-targeting for in vitro photodynamic therapy

The rational design of photosensitizers with rapid cellular uptake and dual-organelle targeting ability is essential for enhancing the efficacy of photodynamic therapy (PDT). However, achieving this goal is a great challenge. In this paper, a novel axial piperazine substituted (PIP) silicon phthalocyanine (PIP-SiPc) has been synthesized. The PIP substitution significantly improved the cellular uptake of PIP-SiPc in MCF-7 breast cancer cells, as demonstrated by two-photon fluorescence imaging combined with fluorescence correlation spectroscopy. Additionally, PIP-SiPc was able to target both mitochondria and lysosomes simultaneously. Notably, PIP-SiPc exhibited remarkable singlet oxygen generation ability, leading to apoptosis in cancer cells upon irradiation, with an IC50 value of only 0.2 µM. These findings highlight the effectiveness of PIP-SiPc as a multifunctional photosensitizer for PDT.

Understanding How Cationic Polymers' Properties Inform Toxic or Immunogenic Responses via Parametric Analysis

Cationic polymers are widely used materials in diverse biotechnologies. Subtle variations in these polymers' properties can change them from exceptional delivery agents to toxic inflammatory hazards. Conventional screening strategies optimize for function in a specific application rather than observing how underlying polymer-cell interactions emerge from polymers' properties. An alternative approach is to map basic underlying responses, such as immunogenicity or toxicity, as a function of basic physicochemical parameters to inform the design of materials for a breadth of applications. To demonstrate the potential of this approach, we synthesized 107 polymers varied in charge, hydrophobicity, and molecular weight. We then screened this library for cytotoxic behavior and immunogenic responses to map how these physicochemical properties inform polymer-cell interactions. We identify three compositional regions of interest and use confocal microscopy to uncover the mechanisms behind the observed responses. Finally, immunogenic activity is confirmed in vivo. Highly cationic polymers disrupted the cellular plasma membrane to induce a toxic phenotype, while high molecular weight, hydrophobic polymers were uptaken by active transport to induce NLRP3 inflammasome activation, an immunogenic phenotype. Tertiary amine- and triethylene glycol-containing polymers did not invoke immunogenic or toxic responses. The framework described herein allows for the systematic characterization of new cationic materials with different physicochemical properties for applications ranging from drug and gene delivery to antimicrobial coatings and tissue scaffolds.

Polyheterocyclic peptidomimetics: Parallel solid phase synthesis of oligo cyclic guanidines and their inhibition activity against Mycobacterium tuberculosis DNA gyrase

Polyheterocycles are one of the most desired synthetic targets due to their numerous and valuable applications in various fields. We report the design and the parallel synthesis of novel linear oligocyclic guanidine peptidomimetics from predesigned reduced polyamides. A screening of these compounds identified active Mycobacterium tuberculosis DNA gyrase inhibitors which do not inhibit human DNA topoisomerase IIα and topoisomerase I.

Piperazine-modified dendrimer achieves efficient intracellular protein delivery via caveolar endocytosis bypassing the endo-lysosomal pathway

Intracellular protein delivery has been a major challenge due to various physiological barriers including low proteolytic stability and poor membrane permeability of the biologics. Nanoparticles were widely proposed to deliver cargo proteins into cells by endocytosis, however, the materials and complexes with proteins are often entrapped in endosomes and subject to lysosome degradation. In this study, we report a piperazine modified dendrimer for stabilizing the complexes via a combination of electrostatic interaction and hydrophobic interactions. The complexes show rapid cell internalization and the loaded proteins are released into the cytosols as early as half an hour post incubation. Mechanism study suggests that the complexes are endocytosed into cells via caveolae-based pathways, which could be inhibited by inhibitors such as genistein, filipin III, brefeldin A and nystatin. The phenylpiperazine-modified polymer enables the delivery of cargo proteins with reserved bioactivity and show high permeability in three-dimensional cell spheroids. The results prove the beneficial roles of phenylpiperazine ligands in polymer-mediated cytosolic protein delivery systems. STATEMENT OF SIGNIFICANCE: We synthesized a list of piperazine and derivatives modified dendrimers as cytosolic protein delivery vectors via facile reactions. Phenylpiperazine modification enables the efficient protein binding through the combination of electrostatic, hydrogen bonding and hydrophobic interactions. Phenylpiperazine modified dendrimers were internalized into the cells via a caveolae-based endo/lysosome-independent path and could release the cargo proteins into the cytosols as early as half an hour post incubation. Phenylpiperazine modified dendrimers delivered cargo proteins with reserved bioactivity and showed high permeability in three-dimensional cell spheroids.

Efficient Transfection via an Unexpected Mechanism by Near Neutral Polypiperazines with Tailored Response to Endosomal pH

Cationic pH-responsive polymers promise to overcome critical challenges in cellular delivery. Ideally, the polymers become selectively charged along the endosomal pathway disturbing only the local membrane and avoiding unintended interactions or cytotoxic side effects at physiological conditions. Polypiperazines represent a novel, hydrophilic class of pH-responsive polymers whose response can be tuned within the relevant pH range (5-7.4). The authors discovered that the polypiperazines are effectively binding plasmid DNA (pDNA) and demonstrate high efficiency in transfection. By design of experiments (DoE), a wide parameter space (pDNA and polymer concentration) is screened to identify the range of effective concentrations for transfection. An isopropyl modified polypiperazine is highly efficient over a wide range of concentrations outperforming linear polyethylenimine (l-PEI, 25 kDa) in regions of low N*/P ratios. A quantitative polymerase chain reaction (qPCR) surprisingly revealed that the pDNA within the piperazine-based polyplexes can be amplified in contrast to polyplexes based on l-PEI. The pDNA must therefore be more accessible and bound differently than for other known transfection polymers. Considering the various opportunities to further optimize their structure, polypiperazines represent a promising platform for designing effective soluble polymeric vectors, which are charge-neutral at physiological conditions.

Biodegradable Metal-Organic-Frameworks-Mediated Protein Delivery Enables Intracellular Cascade Biocatalysis and Pyroptosis In Vivo

Pyroptosis is a new type of regulated cell death that is of great interest for developing new strategies for treating cancers. This potential is however greatly limited by the low efficiency and selectivity of current strategies to regulate cancer cell pyroptosis. Herein, we report biodegradable metal-organic frameworks (MOFs) for intracellular delivery of glucose oxidase (GOx) that promotes cascade biocatalysis inside cells and selectively induces cancer cell pyroptosis. We show that the self-assembly of Cu²⁺ and 4,4'-azobisbenzoic acid along with GOx affords protein-encapsulated GOx@Cu MOF that efficiently delivers GOx into cells. In addition, the tumor-cell-overexpressed NAD(P)H quinone dehydrogenase 1 (NQO1) can trigger the reduction of 4,4'-azobisbenzoic acid and the degradation of GOx@Cu MOF, releasing GOx to catalyze glucose oxidation and produce excessive hydrogen peroxide (H₂O₂) intracellularly. Furthermore, released Cu²⁺ from Cu MOF could be reduced to Cu⁺ by intracellular glutathione (GSH), promoting Fenton-like reaction with H₂O₂ to continuously generate a hydroxyl radical that induces cancer cell pyroptosis and prohibits tumor cell growth. We anticipate the strategy of harnessing biodegradable MOFs for protein delivery, and intracellular biocatalysis provides a powerful approach to regulate tumor cell pyroptosis for advanced therapeutic development.

Tracking the Endosomal Escape: A Closer Look at Calcein and Related Reporters

Crossing the cellular membrane and delivering active pharmaceuticals or biologicals into the cytosol of cells is an essential step in the development of nanomedicines. One of the most important intracellular processes regarding the cellular uptake of biologicals is the endolysosomal pathway. Sophisticated nanocarriers have been developed overcoming a major hurdle, the endosomal entrapment, and delivering their cargo to the required site of action. In parallel, in vitro assays have been established analyzing the performance of these nanocarriers. Among them, the release of the membrane-impermeable dye calcein has become a popular and straightforward method. It is accessible for most researchers worldwide, allows for rapid conclusions about the release potential, and enables the study of release mechanisms. This review is intended to provide an overview and guidance for scientists applying the calcein release assay. It comprises a survey of several applications in the study of endosomal escape, considerations of potential pitfalls, challenges and limitations of the assay, and a brief summary of complementary methods. Based on this review, we hope to encourage further research groups to take advantage of the calcein release assay for their own purposes and help to create a database for more efficient cross-correlations between nanocarriers. This article is protected by copyright. All rights reserved.

Stimuli-Responsive Thiomorpholine Oxide-Derived Polymers with Tailored Hydrophilicity and Hemocompatible Properties

Thermo-responsive hydrophilic polymers, including those showing tuneable lower critical solution temperature (LCST), represent a continuous subject of exploration for a variety of applications, but particularly in nanomedicine. Since biological pH changes can inform the organism about the presence of disequilibrium or diseases, the development of dual LCST/pH-responsive hydrophilic polymers with biological potential is an attractive subject in polymer science. Here, we present a novel polymer featuring LCST/pH double responsiveness. The monomer ethylthiomorpholine oxide methacrylate (THOXMA) can be polymerised via the RAFT process to obtain well-defined polymers. Copolymers with hydroxyethyl methacrylate (HEMA) were prepared, which allowed the tuning of the LCST behaviour of the polymers. Both, the LCST behaviour and pH responsiveness of hydrophilic PTHOXMA were tested by following the evolution of particle size by dynamic light scattering (DLS). In weak and strong alkaline conditions, cloud points ranged between 40–60 °C, while in acidic medium no LCST was found due to the protonation of the amine of the THOX moieties. Additional cytotoxicity assays confirmed a high biocompatibility of PTHOXMA and haemolysis and aggregation assays proved that the thiomorpholine oxide-derived polymers did not cause aggregation or lysis of red blood cells. These preliminary results bode well for the use of PTHOXMA as smart material in biological applications.