Nucleotides as nontoxic endogenous endosomolytic agents in drug delivery

Cordyceps militaris Grown on Germinated Rhynchosia nulubilis (GRC) Encapsulated in Chitosan Nanoparticle (GCN) Suppresses Particulate Matter (PM)-Induced Lung Inflammation in Mice

Cordyceps militaris grown on germinated Rhynchosia nulubilis (GRC) exerts various biological effects, including anti-allergic, anti-inflammatory, and immune-regulatory effects. In this study, we investigated the anti-inflammatory effects of GRC encapsulated in chitosan nanoparticles (CN) against particulate matter (PM)-induced lung inflammation. Optimal CN (CN6) (CHI: TPP w/w ratio of 4:1; TPP pH 2) exhibited a zeta potential of +22.77 mV, suitable for GRC encapsulation. At different GRC concentrations, higher levels (60 and 120 mg/mL) led to increased negative zeta potential, enhancing stability. The optimal GRC concentration for maximum entrapment (31.4 ± 1.35%) and loading efficiency (7.6 ± 0.33%) of GRC encapsulated in CN (GCN) was 8 mg/mL with a diameter of 146.1 ± 54 nm and zeta potential of +30.68. In vivo studies revealed that administering 300 mg/kg of GCN significantly decreased the infiltration of macrophages and T cells in the lung tissues of PM-treated mice, as shown by immunohistochemical analysis of CD4 and F4/80 markers. Additionally, GCN ameliorated PM-induced lung tissue damage, inflammatory cell infiltration, and alveolar septal hypertrophy. GCN also decreased total cells and neutrophils, showing notable anti-inflammatory effects in the bronchoalveolar lavage fluid (BALF) from PM-exposed mice, compared to GRC. Next the anti-inflammatory properties of GCN were further explored in PM- and LPS-exposed RAW264.7 cells; it significantly reduced PM- and LPS-induced cell death, NO production, and levels of inflammatory cytokine mRNAs (IL-1β, IL-6, and COX-2). GCN also suppressed NF-κB/MAPK signaling pathways by reducing levels of p-NF-κB, p-ERK, and p-c-Jun proteins, indicating its potential in managing PM-related inflammatory lung disease. Furthermore, GCN significantly reduced PM- and LPS-induced ROS production. The enhanced bioavailability of GRC components was demonstrated by an increase in fluorescence intensity in the intestinal absorption study using FITC-GCN. Our data indicated that GCN exhibited enhanced bioavailability and potent anti-inflammatory and antioxidant effects in cells and in vivo, making it a promising candidate for mitigating PM-induced lung inflammation and oxidative stress.

Selective delivery of imaging probes and therapeutics to the endoplasmic reticulum or Golgi apparatus: Current strategies and beyond

To maximize therapeutic effects and minimize unwanted effects, the interest in drug targeting to the endoplasmic reticulum (ER) or Golgi apparatus (GA) has been recently growing because two organelles are distributing hubs of cellular building/signaling components (e.g., proteins, lipids, Ca2+) to other organelles and the plasma membrane. Their structural or functional damages induce organelle stress (i.e., ER or GA stress), and their aggravation is strongly related to diseases (e.g., cancers, liver diseases, brain diseases). Many efforts have been developed to image (patho)physiological functions (e.g., oxidative stress, protein/lipid-related processing) and characteristics (e.g., pH, temperature, biothiols, reactive oxygen species) in the target organelles and to deliver drugs for organelle disruption using organelle-targeting moieties. Therefore, this review will overview the structure, (patho)physiological functions/characteristics, and related diseases of the organelles of interest. Future direction on ER or GA targeting will be discussed by understanding current strategies and investigations on targeting, imaging/sensing, and therapeutic systems.

Protein-based nanoparticles for therapeutic nucleic acid delivery

To realize the full potential of emerging nucleic acid therapies, there is a need for effective delivery agents to transport cargo to cells of interest. Protein materials exhibit several unique properties, including biodegradability, biocompatibility, ease of functionalization via recombinant and chemical modifications, among other features, which establish a promising basis for therapeutic nucleic acid delivery systems. In this review, we highlight progress made in the use of non-viral protein-based nanoparticles for nucleic acid delivery in vitro and in vivo, while elaborating on key physicochemical properties that have enabled the use of these materials for nanoparticle formulation and drug delivery. To conclude, we comment on the prospects and unresolved challenges associated with the translation of protein-based nucleic acid delivery systems for therapeutic applications.

Mg.ATP-decorated ultrafine magnetic nanofibers: A bone scaffold with high osteogenic and antibacterial properties in the presence of an electromagnetic field

In this study, ultrafine magnetic nanofibers were developed for bone regeneration purposes. Nanofibers were acquired by electrospinning using a two-component nanofiber matrix (CP: chitosan (Cs) and polyvinyl alcohol (PVA)) containing different concentrations of succinate conjugated-magnetic hydroxyapatite nanocomposites (SMHA). Hybrid nanofibers (CP&SMHA) containing 5 mg ml^-1 of SMHA nanocomposite showed well-defined properties in terms of physicochemical properties and cell behavior. Then, they were modified with adenosine 5'-triphosphate (ATP) and Mg²⁺ ions. The initial adhesion of mesenchymal stem cells and their proliferation rate on the surface of modified nanofibers (Mg.ATP.CP&SMHA) were significantly increased as compared to those of bare nanofibers. Analysis of common osteogenic markers such as alkaline phosphatase activity and the expression of Runt-related transcription factor 2 and osteocalcin confirmed the osteogenic efficacy enhancement of CP&SMHA nanofibers when they were functionalized with ATP and Mg²⁺. The utilization of the antagonist of purine receptor, P2X7, revealed that this receptor has a major role in the osteogenesis process induced by Mg.ATP.CP&SMHA. Moreover, the results showed that cell adhesion, proliferation, and differentiation improved as nanofibers were under the influence of the electromagnetic field (EMF), displaying synergistic effects in the process of bone formation. Mg.ATP.CP&SMHA also showed an antibacterial effect against gram-negative and gram-positive bacteria, Escherichia coli and Staphylococcus aureus, respectively. Considering the high osteogenic potential and antibacterial activity of Mg.ATP.CP&SMHA nanofibers particularly in combination with EMF, it can serve as a great candidate for use in bone tissue engineering applications.

Combating Antibiotic Tolerance Through Activating Bacterial Metabolism

The emergence of antibiotic tolerance enables genetically susceptible bacteria to withstand the killing by clinically relevant antibiotics. As is reported, an increasing body of evidence sheds light on the critical and underappreciated role of antibiotic tolerance in the disease burden of bacterial infections. Considering this tense situation, new therapeutic strategies are urgently required for combating antibiotic tolerance. Herein, we provide an insightful illustration to distinguish between antibiotic resistance and tolerance, and highlight its clinical significance and complexities of drug-tolerant bacteria. Then, we discuss the close relationship between antibiotic tolerance and bacterial metabolism. As such, a bacterial metabolism-based approach was proposed to counter antibiotic tolerance. These exogenous metabolites including amino acids, tricarboxylic acid cycle (TCA cycle) metabolites, and nucleotides effectively activate bacterial metabolism and convert the tolerant cells to sensitive cells, and eventually restore antibiotic efficacy. A better understanding of molecular mechanisms of antibiotic tolerance particularly in vivo would substantially drive the development of novel strategies targeting bacterial metabolism.

Controlling complexation/decomplexation and sizes of polymer-based electrostatic pDNA polyplexes is one of the key factors in effective transfection

The delivery of plasmid DNA (pDNA) using polycations has been investigated for several decades; however, obstacles that limit efficient gene delivery still hinder the clinical application of gene therapy. One of the major limiting factors is controlling pDNA binding affinity with polymers to control the complexation and decomplexation of polyplexes. To address this challenge, polycations of α-poly(_L-lysine) (APL) and ε-poly(_L-lysine) (EPL) were used to prepare variable complexation/decomplexation polyplexes with binding affinities ranging from too tight to too loose and sizes ranging from small to large. APL-EPL/ATP-pDNA polyplexes were also prepared to compare the effects of endosomolytic ATP on complexation/decomplexation and the sizes of polyplexes. The results showed that smaller and tighter polyplexes delivered more pDNA into the cells and into the nucleus than the larger and looser polyplexes. Larger polyplexes exhibited slower cytosolic transport and consequently less nuclear delivery of pDNA than smaller polyplexes. Tighter polyplexes exhibited poor pDNA release in the nucleus, leading to no improvement in transfection efficiency. Thus, polyplexes should maintain a balance between complexation and decomplexation and should have optimal sizes for effective cellular uptake, cytosolic transport, nuclear import, and gene expression. Understanding the effects of complexation/decomplexation and size is important when designing effective polymer-based electrostatic gene carriers.

The Endosomal Escape of Nanoparticles: Toward More Efficient Cellular Delivery

Many emerging therapies rely on the delivery of biological cargo into the cytosol. Nanoparticle delivery systems hold great potential to deliver these therapeutics but are hindered by entrapment and subsequent degradation in acidic compartments of the endo/lysosomal pathway. Engineering polymeric delivery systems that are able to escape the endosome has significant potential to address this issue. However, the development of safe and effective delivery systems that can reliably deliver cargo to the cytosol is still a challenge. Greater understanding of the properties that govern endosomal escape and how it can be quantified is important for the development of more efficient nanoparticle delivery systems. This Topical Review highlights the current understanding of the mechanisms by which nanoparticles escape the endosome, and the emerging techniques to improve the quantification of endosomal escape.

Charge and Assembly Reversible Micelles Fueled by Intracellular ATP for Improved siRNA Transfection

Hydrophobic modification on polycations were commonly used to improve the stability and transfection efficiency of polyplexes. However, the improved stability often means undesired release of the encapsulated siRNA, limiting the application of cationic micelles for siRNA delivery. The current strategy of preparing bioresponsive micelles based on the cleavage of sensitive linkages between polycation and hydrophobic part was far from sufficient, owing to the siRNA binding of the separated polycations from micelles leading to the incomplete release of siRNA. In this study, we propose a new strategy by the combination of micelles disassembly and separated polycations charge reversal. FPBA (3-fluoro-4-carboxyphenylboronic acid) grafted PEI 1.8 k (polyethylenimine) as the polycations of PEI-FPBA and dopamine (with diol-containing moiety) conjugated with cholesterol as the hydrophobic part (Chol-Dopa). The PFCDM micelles was assembled by PEI-FPBA and Chol-Dopa, based on the FPBA-Dopa conjugation. The prepared PFCDM showed strong siRNA loading ability and superior stability in the presence of PBS or serum. Besides, the PFCDM exhibited excellent ATP sensibility. The intracellular ATP could effectively trigger the disassembly of micelles and charge reversal of PEI-FPBA, resulting in the burst release of siRNA in the cytosol. With the property of extracellular stability and intracellular instability, PFCDM displayed good performance on in vitro and in vivo luciferase silencing on 4T1 cells. It should also be noted that the assembly of low molecular weight PEI was relatively safe to cells compared with 25 k PEI. To sum up, the ATP-fueled assembly and charge reversible micelles gave examples for polyplexes to achieve better stability and on demand cargo release at the same time and shows potential to be used for in vitro and in vivo siRNA transfection.

ATP-activated decrosslinking and charge-reversal vectors for siRNA delivery and cancer therapy

Stimuli-responsive polycations have been developed for improved nucleic acid transfection and enhanced therapeutic efficacy. The most reported mechanisms for controlled release of siRNA are based on polyelectrolyte exchange reactions in the cytoplasm and the degradation of polycations initiated by specific triggers. However, the degradation strategy has not always been sufficient due to unsatisfactory kinetics and binding of cationic fragments to siRNA, which limits the gene silencing effect. In this study, a new strategy that combines degradation and charge reversal is proposed.

Methods: We prepared a polycation (CrossPPA) by crosslinking of phenylboronic acid (PBA)-grafted 1.8k PEI with alginate. It was compared with 25k PEI, 1.8k PEI and 1.8k PEI-PBA on siRNA encapsulation, ATP-responsive behavior and mechanism, cytotoxicity, cell uptake, siRNA transfection, in vivo biodistribution and in vivo anti-tumor efficacy. The in vitro and in vivo experiments were performed on 4T1 murine breast cancer cells and 4T1 tumor model separately.

Results: The crosslinking strategy obviously improve the siRNA loading ability of 1.8k PEI. We validated that intracellular levels of ATP could trigger CrossPPA disassembly and charge reversal, which resulted in efficient and rapid siRNA release due to electrostatic repulsion. Besides, CrossPPA/siRNA showed strong cell uptake in 4T1 cells compared with 1.8k PEI/siRNA. Notably, the cytotoxicity of CrossPPA was pretty low, which was owing to its biodegradability. Furthermore, the crosslinked polyplexes significantly enhanced siRNA transfection and improved tumor accumulation. The high gene silencing ability of CrossPPA polyplex led to strong anti-tumor efficacy when using Bcl2-targeted siRNA.

Conclusion: These results indicated that the ATP-triggered disassembly and charge reversal strategy provided a new way for developing stimuli-responsive siRNA carriers and showed potential for nucleic acid delivery in the treatment of cancer.

Reversible Covalent Cross-Linked Polycations with Enhanced Stability and ATP-Responsive Behavior for Improved siRNA Delivery

Cationic polyplex as commonly used nucleic acid carriers faced several shortcomings, such as high cytotoxicity, low serum stability, and slow cargo release at the target site. The traditional solution is covering a negative charged layer (e.g., hyaluronic acid, HA) via electrostatic interaction. However, it was far from satisfactory for the deshielding by physiological anions in circulation (e.g., serum proteins, phosphate). In this study, we proposed a new strategy of reversible covalent cross-linking to enhance stability in circulation and enable stimuli-disassembly of polyplexes in tumor cells. Here, 25k polyethylenimine (PEI) was chosen as model polycations for veriying the hypothesis. HA-PEI conjugation was formed by the cross-linking of adenosine triphosphate grafted HA (HA-ATP) with phenylboronic acid grafted PEI (PEI-PBA) via the chemical reaction between PBA and ATP. Compared with noncovalent polyplex by electrostatic interaction (HA/PEI), HA-PEI exhibited much better colloidal stability and serum stability. The covered HA-ATP layer on PEI-PBA could maintain stable in the absence of physiological anions, while HA layer on PEI in HA/PEI group showed obvious detachment after anion's competition. More importantly, the covalent cross-linking polyplex could selectively release siRNA in the ATP rich environment of cytosol and significantly improve siRNA silence. Besides, the covalent cross-linking with HA-ATP could effectively reduce the cytotoxicity of cationic polyplex, improve the uptake by B61F10 cells and promote the endosomal escape. Consequently, this strategy of HA-PEI conjugation significantly enhanced the siRNA transfection in the absence or presence of FBS (fetal bovine serum) on B16F10 cells and CHO cells. Taken together, the reversible covalent cross-linking approach shows obvious superiority compared with the noncovalent absorption strategy. It held great potential to be developed to polish up the performance of cationic polyplex on reducing the toxicity, enhancing the serum tolerance and achieving controlled release of siRNA at target site.

Enhanced cell survival of pH-sensitive bioenergetic nucleotide nanoparticles in energy/oxygen-depleted cells and their intranasal delivery for reduced brain infarction

Nucleotides (NTs) (e.g., adenosine triphosphate) are very important molecules in the body. They generate bioenergy through phosphate group release, are involved in various biological processes, and are used to treat various diseases that involve energy depletion. However, their highly anionic characteristics might limit delivery of exogenous NTs into the cell, which is required to realize their functions as bioenergy sources. In this study, ionic complexation between Ca(2+) and NT phosphates was used to form Ca(2+)/NT nanocomplexes (NCs), and branched polyethyleneimine (bPEI1.8kDa) was coated on the surface of Ca(2+)/NT NCs via a simple electrostatic coating. The resultant Ca(2+)/NT/bPEI1.8kDa NCs were approximately 10-25nm in size and had positive zeta-potentials, and their NT loading efficiency and content were approximately 60-75% and 10-20 wt%, respectively. Faster NT release from Ca(2+)/NT/bPEI1.8kDa NCs was induced by lower pH and by NTs with fewer phosphates. Reductions in cell viability in response to low temperature, serum deprivation, or hypoxia were recovered by NT delivery in Ca(2+)/NT/bPEI1.8kDa NCs. In a middle cerebral artery occlusion (MCAO)-induced post-ischemic rat model, the BBB (blood brain barrier)-detoured intranasal administration of Ca(2+)/ATP/bPEI1.8kDa NCs induced a better reduction in infarct volume and neurological deficits than did free ATP. In conclusion, intracellular NT delivery using Ca(2+)/NT/bPEI1.8kDa NCs might potentially enhance cell survival and reduce infarction in energy-/oxygen-depleted environments.

STATEMENT OF SIGNIFICANCE

This study describes bioenergetic nucleotide delivery systems and their preparation, physicochemical characterization, and biological characterization both in vitro and in vivo. Nucleotides, such as adenosine triphosphate (ATP) and guanosine triphosphate (GTP), are very important signaling and energy molecules in the body. However, research on these nucleotides using nanosized carriers has been very limited. Liposomal ATP delivery has been reported in heart and renal ischemia studies. Notably, although this delivery system has potential in energy-depleted environments (e.g., low temperature, serum deprivation, and hypoxia) and in brain ischemia, studies are lacking regarding these systems. Thus, we designed polycation-shielded Ca(2+)/nucleotide nanocomplexes using simple mixing, which produced 10- to 25-nm-sized particles. The nanocomplexes released nucleotides in response to acidic pH, and they enhanced cell survival rates under conditions of low temperature, serum deprivation, or hypoxia. Importantly, the nanocomplexes reduced cerebral infarct volumes in a post-ischemic rat model. Thus, our study demonstrates that a novel nucleotide nanocomplex could have potential for preventing or treating diseases that involve energy depletion, such as cardiac, cerebral, and retinal ischemia, and liver failure.

Current preclinical small interfering RNA (siRNA)-based conjugate systems for RNA therapeutics

Recent promising clinical results of RNA therapeutics have drawn big attention of academia and industries to RNA therapeutics and their carrier systems. To improve their feasibility in clinics, systemic evaluations of currently available carrier systems under clinical trials and preclinical studies are needed. In this review, we focus on recent noticeable preclinical studies and clinical results regarding siRNA-based conjugates for clinical translations. Advantages and drawbacks of siRNA-based conjugates are discussed, compared to particle-based delivery systems. Then, representative siRNA-based conjugates with aptamers, peptides, carbohydrates, lipids, polymers, and nanostructured materials are introduced. To improve feasibility of siRNA conjugates in preclinical studies, several considerations for the rational design of siRNA conjugates in terms of cleavability, immune responses, multivalent conjugations, and mechanism of action are also presented. Lastly, we discuss lessons from previous preclinical and clinical studies related to siRNA conjugates and perspectives of their clinical applications.

Intracellular thiol-responsive nanosized drug carriers self-assembled by poly(ethylene glycol)-b-poly(ε-caprolactone)-b-poly(ethylene glycol) having multiple bioreducible disulfide linkages in hydrophobic blocks

Intracellular thiol can trigger effective drug release from polymeric nanoparticles having multiple disulfide linkages in the hydrophobic domain.

Synthetic polynucleotides as endosomolytic agents and bioenergy sources

Nucleotides (NTs), such as adenosine triphosphate (ATP) and guanosine triphosphate (GTP), are signaling and bioenergy molecules to mediate a range of cellular pathways. We recently reported their significant endosomolytic activity. To evaluate whether polymeric NTs keep endosomolytic and bioenergetic functions of NTs in drug delivery and cell survival, NTs were polymerized by a coupling reaction to form polynucleotides (pNTs: pATP and pGTP) with their molecular weights around 500kDa. The cellular toxicity, indicated by IC50, of pNT was as low as that of corresponding monomeric NT. pNTs were degraded by an intracellular enzyme, alkaline phosphatase. Introduction of pNTs in a polycation-gene complex (polyplex) enhanced the extent of gene expression in cancerous, non-cancerous, and stem cells, up to 1500-fold higher than that of pNT-free polyplex. In addition, cells stored in a pATP solution resulted in a significantly higher survival rate (e.g., up to 20% increase) when exposed to low temperatures than pATP-free solution. The presence of pNT in polyplexes prevented the reduction of transfection efficiency induced by a low temperature. The findings in this study suggest that endosomolytic and bioenergetic pNTs serve as a non-toxic gene carrier component and protect cells from a cold shock or energy depletion.

Novel lysosome targeted molecular transporter built on a guanidinium-poly-(propylene imine) hybrid dendron for efficient delivery of doxorubicin into cancer cells

A new dendron-based octa-guanidine appended molecular transporter with a lysosomal targeted peptide–doxorubicin conjugate. The transporter is found non-toxic, lysosomal selectivity while the conjugate showed significant cytotoxicity.