Role of Cell Membrane-Vector Interactions in Successful Gene Delivery

Does the herbicide napropamide exhibit enantioselective effects across genus plasmid transfer from Escherichia coli to Bacillus subtilis?

The dissemination of plasmid-borne antibiotic resistance genes (ARGs) into the environment is an urgent concern. However, the enantioselective effects of herbicides on plasmid conjugation among bacterial genera and their underlying mechanisms remain unclear. This study demonstrates for the first time that the herbicide napropamide (NAP), commonly used in vegetable fields, exhibits a concentration-dependent effect on the transfer efficiency of the pBE2R plasmid from Escherichia coli to Bacillus subtilis. Notably, at a concentration of 5 mg L-1, R-NAP increased transfer efficiency by threefold compared to the S-enantiomer. Scanning electron microscopy revealed that R-NAP caused less structural damage to bacteria than S-NAP but more effectively reduced cell wall components (lipopolysaccharides and peptidoglycan) in donor and recipient bacteria, increasing reactive oxygen species levels and membrane permeability. Transcriptomic analysis indicated that NAP enantiomers altered the expression of genes related to membrane transport activity and transposons. Cross-domain network analysis identified yieK, ygeH, and ydbL as key genes mediating conjugation transfer. Molecular docking results showed that NAP likely interacts hydrophobically with the active sites of the proteins encoded by these genes. In conclusion, herbicides like R-NAP should be carefully managed in fields irrigated with livestock manure to mitigate the risk of ARG transfer and accumulation in crops.

Delivery Aspects for Implementing siRNA Therapeutics for Blood Diseases

Hematological disorders result in significant health consequences, and traditional therapies frequently entail adverse reactions without addressing the root cause. A potential solution for hematological disorders characterized by gain-of-function mutations lies in the emergence of small interfering RNA (siRNA) molecules as a therapeutic option. siRNAs are a class of RNA molecules composed of double-stranded RNAs that can degrade specific mRNAs, thereby inhibiting the synthesis of underlying disease proteins. Therapeutic interventions utilizing siRNA can be tailored to selectively target genes implicated in diverse hematological disorders, including sickle cell anemia, β-thalassemia, and malignancies such as lymphoma, myeloma, and leukemia. The development of efficient siRNA silencers necessitates meticulous contemplation of variables such as the RNA backbone, stability, and specificity. Transportation of siRNA to specific cells poses a significant hurdle, prompting investigations of diverse delivery approaches, including chemically modified forms of siRNA and nanoparticle formulations with various biocompatible carriers. This review delves into the crucial role of siRNA technology in targeting and treating hematological malignancies and disorders. It sheds light on the latest research, development, and clinical trials, detailing how various pharmaceutical approaches leverage siRNA against blood disorders, mainly concentrating on cancers. It outlines the preferred molecular targets and physiological barriers to delivery while emphasizing the growing potential of various therapeutic delivery methods. The need for further research is articulated in the context of overcoming the shortcomings of siRNA in order to enrich discussions around siRNA's role in managing blood disorders and aiding the scientific community in advancing more targeted and effective treatments.

Zwitterionic polymer-dexamethasone conjugates penetrate and protect cartilage from inflammation

Improving the pharmacokinetics of intra-articularly injected therapeutics is a major challenge in treating joint disease. Small molecules and biologics are often cleared from the joint within hours, which greatly reduces their therapeutic efficacy. Furthermore, they are often injected at high doses, which can lead to local cytotoxicity and systemic side effects. In this study, we present modular polymer-drug conjugates of zwitterionic poly(carboxybetaine acrylamide) (pCBAA) and the anti-inflammatory glucocorticoid dexamethasone (DEX) to create cartilage-targeted carriers with slow-release kinetics. pCBAA polymers showed excellent cartilage penetration (full thickness in 1 h) and retention (>50 % after 2 weeks of washing). DEX was loaded onto the pCBAA polymer by employing two different DEX-bearing comonomers to produce pCBAA-co-DEX conjugates with different release kinetics. The slow-releasing conjugate showed zero-order release kinetics in PBS over 70 days. The conjugates elicited no oxidative stress on chondrocytes compared to dose-matched free DEX and protected bovine cartilage explants from the inflammatory response after treatment with IL-1β. By combining cartilage targeting and sustained drug release properties, the pCBAA-co-DEX conjugates solve many issues of today's intra-articular therapeutics, which could ultimately enable better long-term clinical outcomes with fewer side effects.

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.

Cinchona Alkaloid Polymers Demonstrate Highly Efficient Gene Delivery Dependent on Stereochemistry, Methoxy Substitution, and Length

Nucleic acid delivery with cationic polymers is a promising alternative to expensive viral-based methods; however, it often suffers from a lower performance. Herein, we present a highly efficient delivery system based on cinchona alkaloid natural products copolymerized with 2-hydroxyethyl acrylate. Cinchona alkaloids are an attractive monomer class for gene delivery applications, given their ability to bind to DNA via both electrostatics and intercalation. To uncover the structure-activity profile of the system, four structurally similar cinchona alkaloids were incorporated into polymers: quinine, quinidine, cinchonine, and cinchonidine. These polymers differed in the chain length, the presence or absence of a pendant methoxy group, and stereochemistry, all of which were found to alter gene delivery performance and the ways in which the polymers overcome biological barriers to transfection. Longer polymers that contained the methoxy-bearing cinchona alkaloids (i.e., quinine and quinidine) were found to have the best performance. These polymers exhibited the tightest DNA binding, largest and most abundant DNA-polymer complexes, and best endosomal escape thanks to their increased buffering capacity and closest nuclear proximity of the payload. Overall, this work highlights the remarkable efficiency of polymer systems that incorporate cinchona alkaloid natural products while demonstrating the profound impact that small structural changes can have on overcoming biological hurdles associated with gene delivery.

Advancing nucleic acid delivery through cationic polymer design: non-cationic building blocks from the toolbox

The rational integration of non-cationic building blocks into cationic polymers can be devised to enhance the performance of the resulting gene delivery vectors, improving cell targeting behavior, uptake, endosomal escape, toxicity, and transfection efficiency.

Self-Immolative Polymer Nanoparticles with Precise and Controllable pH-Dependent Degradation

Polymer nanoparticles have generated significant interest as delivery systems for therapeutic cargo. Self-immolative polymers (SIPs) are an interesting category of materials for delivery applications, as the characteristic property of end-to-end depolymerization allows for the disintegration of the delivery system, facilitating a more effective release of the cargo and clearance from the body after use. In this work, nanoparticles based on a pH-responsive polymer poly(ethylene glycol)-b-(2-diisopropyl)amino ethyl methacrylate) and a self-immolative polymer poly[N,N-(diisopropylamino)ethyl glyoxylamide-r-N,N-(dibutylamino)ethyl glyoxylamide] (P(DPAEGAm-r-DBAEGAm)) were developed. Four particles were synthesized based on P(DPAEGAm-r-DBAEGAm) polymers with varied diisopropylamino to dibutylamino ratios of 4:1, 2:1, 2:3, and 0:1, termed 4:1, 2:1, 2:3, and 0:1 PGAm particles. The pH of particle disassembly was tuned from pH 7.0 to pH 5.0 by adjusting the ratio of diisopropylamino to dibutylamino substituents on the pendant tertiary amine. The P(DPAEGAm-r-DBAEGAm) polymers were observed to depolymerize (60-80%) below the particle disassembly pH after ∼2 h, compared to <10% at pH 7.4 and maintained reasonable stability at pH 7.4 (20-50% depolymerization) after 1 week. While all particles exhibited the ability to load a peptide cargo, only the 4:1 PGAm particles had higher endosomal escape efficiency (∼4%) compared to the 2:3 or 0:1 PGAm particles (<1%). The 4:1 PGAm particle is a promising candidate for further optimization as an intracellular drug delivery system with rapid and precisely controlled degradation.

A holistic analysis of the intrinsic and delivery-mediated toxicity of siRNA therapeutics

Small interfering RNAs (siRNAs) are among the most promising therapeutic platforms in many life-threatening diseases. Owing to the significant advances in siRNA design, many challenges in the stability, specificity and delivery of siRNA have been addressed. However, safety concerns and dose-limiting toxicities still stand among the reasons for the failure of clinical trials of potent siRNA therapies, calling for a need of more comprehensive understanding of their potential mechanisms of toxicity. This review delves into the intrinsic and delivery related toxicity mechanisms of siRNA drugs and takes a holistic look at the safety failure of the clinical trials to identify the underlying causes of toxicity. In the end, the current challenges, and potential solutions for the safety assessment and high throughput screening of investigational siRNA and delivery systems as well as considerations for design strategies of safer siRNA therapeutics are outlined.

Highly stable and fast-dissolving ascorbic acid-loaded microneedles

OBJECTIVES

Ascorbic acid has many benefits to the skin. Numerous attempts to promote its topical delivery show great challenges since its chemical instability and poor skin impermeability. Microneedle delivery is a simple, safe, painless and effective means to deliver therapeutic or nourishing molecules into the skin. The purpose of this study was twofold: (a) to develop a new formulation of ascorbic acid-loaded microneedles to enhance ascorbic acid stability by investigating an optimal amount of polyethyleneimine as an additive to the dextran-based microneedle formulation and (b) to assess microneedle properties in terms of dissolving rate, skin penetration ability, biocompatibility and antimicrobial activity.

METHODS

The microneedles formulated with ascorbic acid and varied polyethyleneimine concentrations were fabricated and subsequently tested for ascorbic acid stability using 2,2-diphenyl-1-picrylhydrazyl assay. The dissolution rate and skin penetration depth were investigated in porcine skin and the reconstructed human full-thickness skin model respectively. The skin irritation tests were done according to the Organisation for Economic Co-operation and Development Test Guideline No. 439. An antimicrobial disc susceptibility test was performed against Escherichia coli, Staphylococcus aureus and Staphylococcus epidermidis.

RESULTS

Among varied amounts of 0%, 1.5%, 3.0% and 4.5% (w/v), the 3.0% polyethyleneimine showed the most desirable characteristics, including well-preserved shape integrity after demoulding, significantly improved stability of ascorbic acid (p < 0.001) from 33% to 96% antioxidant activity after 8 weeks of storage at 40°C, increased dissolving rate (p < 0.001) by being completely dissolved within 2 min after the skin insertion, passing skin penetration and biocompatibility tests as well as having a broad spectrum of antimicrobial property.

CONCLUSION

With a safety profile and enhanced properties, the new formulation of ascorbic acid-loaded microneedles shows outstanding potential as commercially available cosmetics and healthcare products.

Designing polymers for cartilage uptake: effects of architecture and molar mass

Osteoarthritis (OA) is a progressive disease, involving the progressive breakdown of cartilage, as well as changes to the synovium and bone. There are currently no disease-modifying treatments available clinically. An increasing understanding of the disease pathophysiology is leading to new potential therapeutics, but improved approaches are needed to deliver these drugs, particularly to cartilage tissue, which is avascular and contains a dense matrix of collagens and negatively charged aggrecan proteoglycans. Cationic delivery vehicles have been shown to effectively penetrate cartilage, but these studies have thus far largely focused on proteins or nanoparticles, and the effects of macromolecular architectures have not yet been explored. Described here is the synthesis of a small library of polycations composed of N-(2-hydroxypropyl)methacrylamide (HPMA) and N-(3-aminopropyl)methacrylamide (APMA) with linear, 4-arm, or 8-arm structures and varying degrees of polymerization (DP) by reversible addition fragmentation chain-transfer (RAFT) polymerization. Uptake and retention of the polycations in bovine articular cartilage was assessed. While all polycations penetrated cartilage, uptake and retention generally increased with DP before decreasing for the highest DP. In addition, uptake and retention were higher for the linear polycations compared to the 4-arm and 8-arm polycations. In general, the polycations were well tolerated by bovine chondrocytes, but the highest DP polycations imparted greater cytotoxicity. Overall, this study reveals that linear polymer architectures may be more favorable for binding to the cartilage matrix and that the DP can be tuned to maximize uptake while minimizing cytotoxicity.

Characterization of polypropyleneimine as an alternative transfection reagent

Polypropyleneimine (PPI) was examined as a transfection reagent comparing with most widely used polymer, polyethyleneimine (PEI). PPI had better responsiveness to the endosomal pH and showed more condensation ability of plasmid DNA than PEI. Although the cytotoxicity of PPI was somewhat higher than PEI, the transfection efficacy of PPI was comparable with PEI or higher than PEI in some cell line. Thus, PPI would be an alternative transfection reagent.

A new strategy for stem cells therapy for erectile dysfunction: Adipose-derived stem cells transfect Neuregulin-1 gene through superparamagnetic iron oxide nanoparticles

PURPOSE

Our previous studies showed that nanotechnology improves derived adipose-derived stem cells (ADSCs) therapy for erectile dysfunction (ED). In this study, the Neuregulin-1(NRG1) gene was transfected into ADSCs with superparamagnetic iron oxide nanoparticles (SPION) further to improve the therapeutic effect of ADSCs on ED.

MATERIALS AND METHODS

ADSCs were isolated from epididymal adipose tissue of Sprague-Dawley rats. The optimal concentration of PEI-SPION (SPION modified with polyethyleneimine) was selected to construct the gene complex. After electrostatic binding of PEI-SPION and DNA, a PEI layer was wrapped to make the PEI-SPION-NRG1-PEI gene transfection complex. Different groups were set up for transfection tests. Lipo2000 transfection reagent was used as the control. PEI-SPION-NRG1-PEI in the experimental group was transfected under an external magnetic field.

RESULTS

When the concentration of PEI-SPION was 10 µg/mL, it had little cytotoxicity, and cell activity was not significantly affected. PEI-SPION-NRG1-PEI forms positively charged nanocomposites with a particle size of 72.6±14.9 nm when N/P ≥8. The PEI-SPION-NRG1-PEI gene complex can significantly improve the transfection efficiency of ADSCs, reaching 26.74%±4.62%, under the action of the external magnetic field. PCR and Western blot showed that the expression level of the NRG1 gene increased significantly, which proved that the transfection was effective.

CONCLUSIONS

PEI-SPION can be used as a vector for NRG1 gene transfection into ADSCs. PEI-SPION-NRG1-PEI packaging has the highest transfection efficiency under the external magnetic field than the other groups. These findings may provide a new strategy for ADSCs therapy for ED.

mRNA vaccines for COVID-19 and diverse diseases

Since its outbreak in late 2019, the novel coronavirus disease 2019 (COVID-19) has spread to every continent on the planet. The global pandemic has affected human health and socioeconomic status around the world. At first, the global response to the pandemic was to isolate afflicted individuals to prevent the virus from spreading, while vaccine development was ongoing. The genome sequence was first presented in early January 2020, and the phase I clinical trial of the vaccine started in March 2020 in the United States using novel lipid-based nanoparticle (LNP), encapsulated with mRNA termed as mRNA-1273. Till now, various mRNA-based vaccines are in development, while one mRNA-based vaccine got market approval from US-FDA for the prevention of COVID-19. Previously, mRNA-based vaccines were thought to be difficult to develop, but the current development is a significant accomplishment. However, widespread production and global availability of mRNA-based vaccinations to combat the COVID-19 pandemic remains a major challenge, especially when the mutations continually occur on the virus (e.g., the recent outbreaks of Omicron variant). This review elaborately discusses the COVID-19 pandemic, the biology of SARS-CoV-2 and the progress of mRNA-based vaccines. Moreover, the review also highlighted a detailed description of mRNA delivery technologies and the application potential in controlling other life-threatening diseases. Therefore, it provides a comprehensive view and multidisciplinary insights into mRNA therapy for broader audiences.

Recent advances in poly(ionic liquid)s for biomedical application

Poly(ionic liquid)s (PILs) are polymers containing ions in their side-chain or backbone, and the designability and outstanding physicochemical properties of PILs have attracted widespread attention from researchers. PILs have specific characteristics, including negligible vapor pressure, high thermal and chemical stability, non-flammability, and self-assembly capabilities. PILs can be well combined with advanced analytical instruments and technology and have made outstanding contributions to the development of biomedicine aiding in the continuous advancement of science and technology. Here we reviewed the advances of PILs in the biomedical field in the past five years with a focus on applications in proteomics, drug delivery, and development. This paper aims to engage pharmaceutical and biomedical scientists to full understand PILs and accelerate the progress from laboratory research to industrialization.

Uniform iron oxide nanoparticles reduce the required amount of polyethylenimine in the gene delivery to mesenchymal stem cells

Cationic polyethylenimine (PEI) is regarded as the 'golden standard' of non-viral gene vectors. However, the superiority of PEI with high positive charge density also induces its major drawback of cytotoxicity, which restricts its application for an effective and safe gene delivery to stem cells. To redress this shortcoming, herein, a magnetic gene complex containing uniform iron oxide nanoparticles (UIONPs), plasmid DNA, and free PEI is prepared through electrostatic interactions for the gene delivery to bone marrow-derived mesenchymal stem cells (BM-MSCs). Results show that UIONPs dramatically promote the gene delivery to BM-MSCs using the assistance of magnetic force. In addition, decreasing the free PEI nitrogen to DNA phosphate (N/P) ratio from 10 to 6 has little adverse impact on the transgene expression levels (over 300 times than that of PEI alone at the N/P ratio of 6) and significantly reduces the cytotoxicity to BM-MSCs. Further investigations confirmed that the decrease of free PEI has little influence on the cellular uptake after applying external magnetic forces, but that the reduced positive charge density decreases the cytotoxicity. The present study demonstrates that magnetic gene delivery not only contributes to the enhanced gene expression but also helps to reduce the required amount of PEI, providing a potential strategy for an efficient and safe gene delivery to stem cells.

Effect of Cationic Charge Density on Transcytosis of Polyethylenimine

The adsorption-mediated transcytosis (AMT) induced by the electrostatic interaction between the positively charged surface of carriers and negatively charged cell membrane is a new paradigm enabling nanomedicine's tumor extravasation and infiltration. However, little is known about the correlation between the carrier's charge density and its AMT-induced tumor infiltration efficiency. Herein, we investigate the effect of the cationic polymer's charge on the AMT-induced tumor penetration ability using in vitro multilayer tumor spheroids (MTSs). A cationic polymer, polyethylenimine (PEI), is amidized with acetic anhydride to obtain acetylated PEIs (AcPEIs) with different cationic charge densities. As the amidization ratio increases, the AcPEIs' cytotoxicity, zeta potential, and cell-binding affinity significantly decrease. Notably, not only does the weak cell binding (AcPEIs with high acetylation degrees) lead to slow endocytosis and inefficient transcytosis, so does the strong cell-binding PEI. The PEI with 24% acetylation (AcPEI_24%) is found to have the highest transcytosis efficiency because its balanced cell-binding affinity triggers fast adsorption-mediated endocytosis. The subsequent Golgi apparatus/endoplasmic reticulum-mediated exocytosis via extracellular vesicles leads to highly effective transcellular delivery and tumor penetration in MTSs. Therefore, the drug carrier's surface cationic charge density critically influences its AMT-induced tumor penetration efficiency. This study provides mechanistic insights into the design of drug-delivery systems with active transcytosis for improved tumor penetration and enhanced therapeutic efficiency.

Lipids and Lipid Derivatives for RNA Delivery

RNA-based therapeutics have shown great promise in treating a broad spectrum of diseases through various mechanisms including knockdown of pathological genes, expression of therapeutic proteins, and programmed gene editing. Due to the inherent instability and negative-charges of RNA molecules, RNA-based therapeutics can make the most use of delivery systems to overcome biological barriers and to release the RNA payload into the cytosol. Among different types of delivery systems, lipid-based RNA delivery systems, particularly lipid nanoparticles (LNPs), have been extensively studied due to their unique properties, such as simple chemical synthesis of lipid components, scalable manufacturing processes of LNPs, and wide packaging capability. LNPs represent the most widely used delivery systems for RNA-based therapeutics, as evidenced by the clinical approvals of three LNP-RNA formulations, patisiran, BNT162b2, and mRNA-1273. This review covers recent advances of lipids, lipid derivatives, and lipid-derived macromolecules used in RNA delivery over the past several decades. We focus mainly on their chemical structures, synthetic routes, characterization, formulation methods, and structure-activity relationships. We also briefly describe the current status of representative preclinical studies and clinical trials and highlight future opportunities and challenges.

Self-assembled PEGylated amphiphilic polypeptides for gene transfection

In the present study, three biodegradable block copolymers composed of a poly(ethylene glycol) block and a copolypeptide block with varying compositions of cationic L-lysine (L-Lys) and hydrophobic benzyl-L-glutamate (Bzl-L-Glu) were designed for gene delivery applications. The polypeptides were synthesized by ring opening polymerization (ROP) and after orthogonal deprotection of Boc-L-Lys side chains, the polymer exhibited an amphiphilic character. To bind or encapsulate plasmid DNA (pDNA), different formulations were investigated: a nanoprecipitation and an emulsion technique using various organic solvents as well as an aqueous pH-controlled formulation method. The complex and nanoparticle (NP) formations were monitored by dynamic light scattering (DLS), and pDNA interaction was shown by gel electrophoresis and subsequent controlled release with heparin. The polypeptides were further tested for their cytotoxicity as well as biodegradability. The complexes and NPs presenting the most promising size distributions and pDNA binding ability were subsequently evaluated for their transfection efficiency in HEK293T cells. The highest transfection efficiencies were obtained with an aqueous formulation of the polypeptide containing the highest L-Lys content and lowest proportion of hydrophobic, helical structures (P1*), which is therefore a promising candidate for efficient gene delivery by biodegradable gene delivery vectors.

Polycation-Mediated Transfection: Mechanisms of Internalization and Intracellular Trafficking

Polyplex-mediated gene transfection is now in its' fourth decade of serious research, but the promise of polyplex-mediated gene therapy has yet to fully materialize. Only approximately one in a million applied plasmids actually expresses. A large part of this is due to an incomplete understanding of the mechanism of polyplex transfection. There is an assumption that internalization must follow a canonical mechanism of receptor mediated endocytosis. Herein, we present arguments that untargeted (and most targeted) polyplexes do not utilize these routes. By incorporating knowledge of syndecan-polyplex interactions, we can show that syndecans are the "target" for polyplexes. Further, it is known that free polycations (which disrupt cell-membranes by acid-catalyzed hydrolysis of phospholipid esters) are necessary for (untargeted) endocytosis. This can be incorporated into the model to produce a novel mechanism of endocytosis, which fits the observed phenomenology. After membrane translocation, polyplex containing vesicles reach the endosome after diffusing through the actin mesh below the cell membrane. From there, they are acidified and trafficked toward the lysosome. Some polyplexes are capable of escaping the endosome and unpacking, while others are not. Herein, it is argued that for some polycations, as acidification proceeds the polyplexes excluding free polycations, which disrupt the endosomal membrane by acid-catalyzed hydrolysis, allowing the polyplex to escape. The polyplex's internal charge ratio is now insufficient for stability and it releases plasmids which diffuse to the nucleus. A small proportion of these plasmids diffuse through the nuclear pore complex (NPC), with aggregation being the major cause of loss. Those plasmids that have diffused through the NPC will also aggregate, and this appears to be the reason such a small proportion of nuclear plasmids express mRNA. Thus, the structural features which promote unpacking in the endosome and allow for endosomal escape can be determined, and better polycations can be designed.

mRNA-Based Cancer Vaccines: A Therapeutic Strategy for the Treatment of Melanoma Patients

Malignant melanoma is one of the most aggressive forms of cancer and the leading cause of death from skin tumors. Given the increased incidence of melanoma diagnoses in recent years, it is essential to develop effective treatments to control this disease. In this regard, the use of cancer vaccines to enhance cell-mediated immunity is considered to be one of the most modern immunotherapy options for cancer treatment. The most recent cancer vaccine options are mRNA vaccines, with a focus on their usage as modern treatments. Advantages of mRNA cancer vaccines include their rapid production and low manufacturing costs. mRNA-based vaccines are also able to induce both humoral and cellular immune responses. In addition to the many advantages of mRNA vaccines for the treatment of cancer, their use is associated with a number of challenges. For this reason, before mRNA vaccines can be used for the treatment of cancer, comprehensive information about them is required and a large number of trials need to be conducted. Here, we reviewed the general features of mRNA vaccines, including their basis, stabilization, and delivery methods. We also covered clinical trials involving the use of mRNA vaccines in melanoma cancer and the challenges involved with this type of treatment. This review also emphasized the combination of treatment with mRNA vaccines with the use of immune-checkpoint blockers to enhance cell-mediated immunity.

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

Responsive polymers, which become protonated at decreasing pH, are considered a milestone in the development of synthetic cell entry vectors. Exact correlations between their properties and their ability to escape the endosome, however, often remain elusive due to hydrophobic interactions or limitations in the design of water-soluble materials with suitable basicity. Here, we present a series of well-defined, hydrophilic polypiperazines, where systematic variation of the amino moiety facilitates an unprecedented fine-tuning of the basicity or pK_a value within the physiologically relevant range (pH 6-7.4). Coincubation of HEK 293T cells with various probes, including small fluorophores or functioning proteins, revealed a rapid increase of endosomal release for polymers with pK_a values above 6.5 or 7 in serum-free or serum-containing media, respectively. Similarly, cytotoxic effects became severe at increased pK_a values (>7). Although the window for effective transport appears narrow, the discovered correlations offer a principal guideline for the design of effective polymers for endosomal escape.

Non-viral nanoparticles for RNA interference: Principles of design and practical guidelines

Ribonucleic acid interference (RNAi) is an innovative treatment strategy for a myriad of indications. Non-viral synthetic nanoparticles (NPs) have drawn extensive attention as vectors for RNAi due to their potential advantages, including improved safety, high delivery efficiency and economic feasibility. However, the complex natural process of RNAi and the susceptible nature of oligonucleotides render the NPs subject to particular design principles and requirements for practical fabrication. Here, we summarize the requirements and obstacles for fabricating non-viral nano-vectors for efficient RNAi. To address the delivery challenges, we discuss practical guidelines for materials selection and NP synthesis in order to maximize RNA encapsulation efficiency and protection against degradation, and to facilitate the cytosolic release of oligonucleotides. The current status of clinical translation of RNAi-based therapies and further perspectives for reducing the potential side effects are also reviewed.

Polymeric Delivery of Therapeutic Nucleic Acids

The advent of genome editing has transformed the therapeutic landscape for several debilitating diseases, and the clinical outlook for gene therapeutics has never been more promising. The therapeutic potential of nucleic acids has been limited by a reliance on engineered viral vectors for delivery. Chemically defined polymers can remediate technological, regulatory, and clinical challenges associated with viral modes of gene delivery. Because of their scalability, versatility, and exquisite tunability, polymers are ideal biomaterial platforms for delivering nucleic acid payloads efficiently while minimizing immune response and cellular toxicity. While polymeric gene delivery has progressed significantly in the past four decades, clinical translation of polymeric vehicles faces several formidable challenges. The aim of our Account is to illustrate diverse concepts in designing polymeric vectors towards meeting therapeutic goals of in vivo and ex vivo gene therapy. Here, we highlight several classes of polymers employed in gene delivery and summarize the recent work on understanding the contributions of chemical and architectural design parameters. We touch upon characterization methods used to visualize and understand events transpiring at the interfaces between polymer, nucleic acids, and the physiological environment. We conclude that interdisciplinary approaches and methodologies motivated by fundamental questions are key to designing high-performing polymeric vehicles for gene therapy.

Ionic liquids: prospects for nucleic acid handling and delivery

Operations with nucleic acids are among the main means of studying the mechanisms of gene function and developing novel methods of molecular medicine and gene therapy. These endeavours usually imply the necessity of nucleic acid storage and delivery into eukaryotic cells. In spite of diversity of the existing dedicated techniques, all of them have their limitations. Thus, a recent notion of using ionic liquids in manipulations of nucleic acids has been attracting significant attention lately. Due to their unique physicochemical properties, in particular, their micro-structuring impact and tunability, ionic liquids are currently applied as solvents and stabilizing media in chemical synthesis, electrochemistry, biotechnology, and other areas. Here, we review the current knowledge on interactions between nucleic acids and ionic liquids and discuss potential advantages of applying the latter in delivery of the former into eukaryotic cells.

mRNA vaccine: a potential therapeutic strategy

mRNA vaccines have tremendous potential to fight against cancer and viral diseases due to superiorities in safety, efficacy and industrial production. In recent decades, we have witnessed the development of different kinds of mRNAs by sequence optimization to overcome the disadvantage of excessive mRNA immunogenicity, instability and inefficiency. Based on the immunological study, mRNA vaccines are coupled with immunologic adjuvant and various delivery strategies. Except for sequence optimization, the assistance of mRNA-delivering strategies is another method to stabilize mRNAs and improve their efficacy. The understanding of increasing the antigen reactiveness gains insight into mRNA-induced innate immunity and adaptive immunity without antibody-dependent enhancement activity. Therefore, to address the problem, scientists further exploited carrier-based mRNA vaccines (lipid-based delivery, polymer-based delivery, peptide-based delivery, virus-like replicon particle and cationic nanoemulsion), naked mRNA vaccines and dendritic cells-based mRNA vaccines. The article will discuss the molecular biology of mRNA vaccines and underlying anti-virus and anti-tumor mechanisms, with an introduction of their immunological phenomena, delivery strategies, their importance on Corona Virus Disease 2019 (COVID-19) and related clinical trials against cancer and viral diseases. Finally, we will discuss the challenge of mRNA vaccines against bacterial and parasitic diseases.

Lipid Membrane Interaction of Peptide/DNA Complexes Designed for Gene Delivery

Among gene delivery systems, peptide-based gene carriers have received significant attention because of their selectivity, biocompatibility, and biodegradability. Since cellular membranes function as a barrier toward exogenous molecules, cell-penetrating peptides (CPPs), which are usually cationic and/or amphiphilic, can serve as efficient carriers to deliver cargo into the cytosol. Here, we examined the interactions of carrier peptides and their DNA complexes with lipid membranes using a quartz crystal microbalance (QCM) and high-speed atomic force microscopy (HS-AFM). The carrier peptides are a 12-residue partial presequence of yeast cytochrome c oxidase subunit IV (Cytcox) and BP100, which are a mitochondria-targeting signal peptide and a CPP, respectively. QCM data showed that BP100 has a higher binding affinity than Cytcox to both plasma membrane- and mitochondrial membrane-mimicking lipid bilayers. The DNA complexes with either Cytcox or BP100 exhibited the same tendency. Furthermore, HS-AFM data demonstrated that the DNA complexes of either peptide can disrupt the lipid membranes, forming larger pores in the case of Cytcox. Our results suggest that the binding affinity of the peptide/DNA complex to the plasma membrane is more critical than its membrane disruption ability in enhancing the cellular uptake of DNA.

Limited expression of non-integrating CpG-free plasmid is associated with increased nucleosome enrichment

CpG-free pDNA was reported to facilitate sustained transgene expression with minimal inflammation in vivo as compared to CpG-containing pDNA. However, the expression potential and impact of CpG-free pDNA in in vitro model have never been described. Hence, in this study, we analyzed the transgene expression profiles of CpG-free pDNA in vitro to determine the influence of CpG depletion from the transgene. We found that in contrast to the published in vivo studies, CpG-free pDNA expressed a significantly lower level of luciferase than CpG-rich pDNA in several human cell lines. By comparing novel CpG-free pDNA carrying CpG-free GFP (pZGFP: 0 CpG) to CpG-rich GFP (pRGFP: 60 CpGs), we further showed that the discrepancy was not influenced by external factors such as gene transfer agent, cell species, cell type, and cytotoxicity. Moreover, pZGFP exhibited reduced expression despite having equal gene dosage as pRGFP. Analysis of mRNA distribution revealed that the mRNA export of pZGFP and pRGFP was similar; however, the steady state mRNA level of pZGFP was significantly lower. Upon further investigation, we found that the CpG-free transgene in non-integrating CpG-free pDNA backbone acquired increased nucleosome enrichment as compared with CpG-rich transgene, which may explain the observed reduced level of steady state mRNA. Our findings suggest that nucleosome enrichment could regulate non-integrating CpG-free pDNA expression and has implications on pDNA design.

Design, characterization, and intracellular trafficking of biofunctionalized chitosan nanomicelles

The hydrophobically modified glycol chitosan (HGC) nanomicelle has received increasing attention as a promising platform for the delivery of chemotherapeutic drugs. To improve the tumor selectivity of HGC, here an avidin and biotin functionalization strategy was applied. The hydrodynamic diameter of the biotin-avidin-functionalized HGC (cy5.5-HGC-B4F) was observed to be 104.7 nm, and the surface charge was +3.1 mV. Confocal and structured illumination microscopy showed that at 0.1 mg/ml, cy5.5-HGC-B4F nanomicelles were distributed throughout the cytoplasm of MDA-MB-231 breast cancer cells after 2 h of exposure without significant cytotoxicity. To better understand the intracellular fate of the nanomicelles, entrapment studies were performed and demonstrated that some cy5.5-HGC-B4F nanomicelles were capable of escaping endocytic vesicles, likely via the proton sponge effect. Quantitative analysis of the movements of endosomes in living cells revealed that the addition of HGC greatly enhanced the motility of endosomal compartments, and the nanomicelles were transported by early and late endosomes from cell periphery to the perinuclear region. Our results validate the importance of using live-cell imaging to quantitatively assess the dynamics and mechanisms underlying the complex endocytic pathways of nanosized drug carriers.

Polyplexes System to Enhance the LL-37 Antimicrobial Peptide Expression in Human Skin Cells

Inefficient autologous tissue recovery in diverse skin injuries increases the susceptibility of patients to infections caused by multiresistant microorganisms, resulting in a high mortality rate. Nonviral transfection is an attractive alternative for these patients, where genetically modified cells incorporated into skin substitutes could release additional antimicrobial agents into the native skin. In this work, we have modulated the conditions of using a nonviral system for transfection of primary human keratinocytes and fibroblasts, consisting of a polymer/plasmid DNA (pDNA) complex called polyplex and its effects on the expression of LL-37 antimicrobial peptide. Linear and branched polyethylenimine (PEI) polymers in different weight concentrations were varied for evaluating the formation and colloidal characteristics of the polyplexes. The PEI/pDNA polyplexes with 19 nitrogen/phosphate ratio are nanometric particles (400 and 250 nm with linear and branched PEI, respectively) exhibiting positive surface (+30 ± 2 mV). Both kinds of polyplexes allowed the expression of a reporter gene and increased the human cathelicidin antimicrobial peptide gene expression in transfected keratinocytes and fibroblasts; however, greater cytotoxicity was observed when polyplexes formed with branched PEI were used. Moreover, cell culture supernatants from transfected cells with linear PEI/pDNA polyplexes showed enhanced antimicrobial activity (decrease of bacterial growth in 95.8%) against a Staphylococcus aureus strain in vitro. The study of the PEI/pDNA polyplexes formation allowed us to develop an improved transfection strategy of skin cells, promoting the production of LL-37 antimicrobial peptide. In the future, this strategy could be used for the construction of skin substitutes to prevent, reduce, or eliminate bacterial infections. Impact statement The results of this study contribute to the understanding of the polyplexes system in the genetic modification of skin cells and its effects on the expression of the LL-37 antimicrobial peptide. In the future, three-dimensional skin substitutes built with these cells could be an efficient way to decrease bacterial growth and prevent the infections in skin wounds.

Structural behavior of amphiphilic polyion complexes interacting with saturated lipid membranes investigated by coarse-grained molecular dynamic simulations

Neutral polyelectrolyte complexes (PECs) made from an amphiphilic multiblock copolymer of type (A_nB_n)_m and an oppositely charged polyion and interacting with a dipalmitoylphosphatidylcholine (DPPC) lipid membrane.

Rekindling RNAi Therapy: Materials Design Requirements for In Vivo siRNA Delivery

With the recent FDA approval of the first siRNA-derived therapeutic, RNA interference (RNAi)-mediated gene therapy is undergoing a transition from research to the clinical space. The primary obstacle to realization of RNAi therapy has been the delivery of oligonucleotide payloads. Therefore, the main aims is to identify and describe key design features needed for nanoscale vehicles to achieve effective delivery of siRNA-mediated gene silencing agents in vivo. The problem is broken into three elements: 1) protection of siRNA from degradation and clearance; 2) selective homing to target cell types; and 3) cytoplasmic release of the siRNA payload by escaping or bypassing endocytic uptake. The in vitro and in vivo gene silencing efficiency values that have been reported in publications over the past decade are quantitatively summarized by material type (lipid, polymer, metal, mesoporous silica, and porous silicon), and the overall trends in research publication and in clinical translation are discussed to reflect on the direction of the RNAi therapeutics field.

Echogenic PEGylated PEI-Loaded Microbubble As Efficient Gene Delivery System

BACKGROUND

Cancer stem cells (CSCs) are responsible for cancer therapeutic resistance and metastasis. To date, in addition to surgery, chemotherapy, and radiotherapy, gene delivery has emerged as a potential therapeutic modality for ovarian cancer. Efficient and safe targeted gene delivery is complicated due to the tumor heterogeneity barrier. Ultrasound (US)-stimulated microbubbles (MBs) have demonstrated a method of enabling non-invasive targeted gene delivery.

PURPOSE

The purpose of our study was to show the utility of poly(ethylene glycol)-SS-polyethylenimine-loaded microbubbles (PSP@MB) as an ultrasound theranostic and redox-responsive agent in a gene delivery system.

PATIENTS AND METHODS

PSP nanoparticles were conjugated to the MB surface through biotin-avidin linkage, increasing the gene-loading efficiency of MB. The significant increase in the release of genes from the PSP@MB complexes was achieved upon ultrasound exposure. The positive surface charge in PSP@MB can condense the plasmid through electrostatic interactions; agarose-gel electrophoresis further confirmed the ability of PSP@MB to condense plasmids. The morphology, particle sizes and zeta potential of PSP@MB were characterized by transmission electron microscopy and dynamic light scattering.

RESULTS

Laser confocal microscopy showed that the combination of ultrasound with PSP@MB could promote the cellular uptake of plasmids. Plasmids which encode enhanced green fluorescence protein (EGFP) reporter genes or luciferase reporter genes were delivered to CSCs in vitro and to subcutaneous xenografts in vivo via the combination of ultrasound with PSP@MB. Gene transfection efficiency was evaluated by fluorescence microscopy and In Vivo Imaging Systems. This study demonstrated that the combination of ultrasound with PSP@MB can remarkably promote gene delivery to solid tumors as well as diminishing the toxicity towards normal tissues in vivo. The combination of PSP@MB and the use of ultrasound can efficiently enhance accumulation, extravasation and penetration into solid tumors.

CONCLUSION

Taken together, our study showed that this novel PSP@MB and ultrasound-mediated gene delivery system could efficiently target CSCs.

Messenger RNA delivery by hydrazone-activated polymers

The intracellular delivery of DNA and RNA therapeutics requires the assistance of vectors and/or nucleotide modifications to protect the nucleic acids against host nucleases and promote cellular internalization and release. Recently, messenger RNA (mRNA) has attracted much attention due to its transient activity and lack of genome permanent recombination and persistent expression. Therefore, there is a strong interest in the development of conceptually new non-viral vectors with low toxicity that could improve mRNA transfection efficiency. We have recently introduced the potential of polyhydrazones and the importance of the degree of polymerization for the delivery of siRNA and plasmid DNA. Here, we demonstrate that this technology can be easily adapted to the more interesting complexation and delivery inside living cells of mRNA. The polyplexes resulting from the combination of the amphiphilic polyhydrazone were characterized and the transfection efficiency and cell viability were studied for a discrete collection of functionalized polyhydrazones. The results obtained demonstrated the versatility of these polymeric vectors as excellent candidates for the delivery of mRNA and validate the easy adaptability of the technology to more sensitive and therapeutically relevant nucleic acids.

Investigating the intracellular effects of hyperbranched polycation-DNA complexes on lung cancer cells using LC-MS-based metabolite profiling

Cationic polymers have emerged as a promising alternative to viral vectors in gene therapy. They are cheap to scale up, easy to functionalise and are potentially safer than viral vectors, however many are cytotoxic. The large number of polycations, designed to address the toxicity problem, raises a practical need to develop a fast and reliable method for assessing the safety of these materials. In this regard, metabolomics provides a detailed and comprehensive method that can assess the potential toxicity at the cellular and molecular level. Here, we applied metabolomics to investigate the impact of hyperbranched polylysine, hyperbranched polylysine-co-histidine and branched polyethyleneimine polyplexes at sub-toxic concentrations on the metabolic pathways of A459 and H1299 lung carcinoma cell lines. The study revealed that the polyplexes downregulated metabolites associated with glycolysis and the TCA cycle, and induced oxidative stress in both cell lines. The relative changes of the metabolites indicated that the polyplexes of polyethyleneimine and hyperbranched polylysine affected the metabolism much more than the polyplexes of hyperbranched polylysine-co-histidine. This was in line with transfection results, suggesting a correlation between the toxicity and transfection efficiency of these polyplexes. Our work highlights the importance of the metabolomics approach not just to assess the potential toxicity of polyplexes but also to understand the molecular mechanisms underlying any adverse effects, which could help in designing more efficient vectors.

Nuclear localization signal peptide enhances transfection efficiency and decreases cytotoxicity of poly(agmatine/N,N'-cystamine-bis-acrylamide)/pDNA complexes

At present, nonviral gene vectors develop rapidly, especially cationic polymers. A series of bioreducible poly(amide amine) (PAA) polymers containing guanidino groups have been synthesized by our research team. These novel polymer vectors demonstrated significantly higher transfection efficiency and lower cytotoxicity than polyethylenimine (PEI)-25kDa. However, compared with viral gene vectors, relatively low transfection efficiency, and high cytotoxicity are still critical problems confronting these polymers. In this study, poly(agmatine/N,N'-cystamine-bis-acrylamide) p(AGM-CBA) was selected as a model polymer, nuclear localization signal (NLS) peptide PV7 (PKKKRKV) with good biocompatibility and nuclear localization effect was introduced to investigate its impact on transfection efficiency and cytotoxicity. NLS peptide-mediated in vitro transfection was performed in NIH 3T3 cells by directly incorporating NLS peptide with the complexes of p(AGM-CBA)/pDNA. Meanwhile, the transfection efficiency and cytotoxicity of these complexes were evaluated. The results showed that the transfection efficiency could be increased by 5.7 times under the appropriate proportion, and the cytotoxicity brought by the polymer vector could be significantly reduced.

Hyperbranched poly(ethylenimine-co-oxazoline) by thiol–yne chemistry for non-viral gene delivery: investigating the role of polymer architecture

Synthesis of long-chain hyperbranched poly(ethylenimine-co-oxazoline)s by AB₂ thiol–yne chemistry is reported, and their application as pDNA transfection agents studied.

Different-Length Hydrazone Activated Polymers for Plasmid DNA Condensation and Cellular Transfection

The recent advances in genetic engineering demand the development of conceptually new methods to prepare and identify efficient vectors for the intracellular delivery of different nucleotide payloads ranging from short single-stranded oligonucleotides to larger plasmid double-stranded circular DNAs. Although many challenges still have to be overcome, polymers hold great potential for intracellular nucleotide delivery and gene therapy. We here develop and apply the postpolymerization modification of polyhydrazide scaffolds, with different degree of polymerization, for the preparation of amphiphilic polymeric vehicles for the intracellular delivery of a circular plasmid DNA. The hydrazone formation reactions with a mixture of cationic and hydrophobic aldehydes proceed in physiologically compatible aqueous conditions, and the resulting amphiphilic polyhydrazones are directly combined with the biological cargo without any purification step. This methodology allowed the preparation of stable polyplexes with a suitable size and zeta potential to achieve an efficient encapsulation and intracellular delivery of the DNA cargo. Simple formulations that performed with efficiencies and cell viabilities comparable to the current gold standard were identified. Furthermore, the internalization mechanism was studied via internalization experiments in the presence of endocytic inhibitors and fluorescence microscopy. The results reported here confirmed that the polyhydrazone functionalization is a suitable strategy for the screening and identification of customized polymeric vehicles for the delivery of different nucleotide cargos.

The Power of Shielding: Low Toxicity and High Transfection Performance of Cationic Graft Copolymers Containing Poly(2-oxazoline) Side Chains

We show the potential of oligo(2-ethyl-2-oxazoline) (Ox_n)-shielded graft copolymers of (2-aminoethyl)-methacrylate and N-methyl-(2-aminoethyl)-methacrylate for pDNA delivery in HEK cells. For the effect of grafting density and side chain length concerning improved transfection properties through the concept of shielding to be investigated, copolymers were synthesized via the macromonomer method using a combination of cationic ring opening polymerization and reversible addition-fragmentation chain transfer polymerization to vary the degree of grafting (DG = 10 and 30%) as well as the side chain degree of polymerization (DP = 5 and 20). Investigations of the polyplex formation, in vitro flow cytometry, and confocal laser scanning microscopy measurements on the copolymer library revealed classical shielding properties of the Ox side chains, including highly reduced cytotoxicity and a partial decrease in transfection efficiency, as also reported for polyethylene glycol shielding. In terms of the transfection efficiency, the best performing copolymers (A- g-Ox₅(10) and M- g-Ox₅(10)) revealed equal or better performances compared to those of the corresponding homopolymers. In particular, the graft copolymers with low DG and side chain DP transfected well with over 10-fold higher IC₅₀ values. In contrast, a DG of 30% resulted in a loss of transfection efficiency due to missing ability for endosomal release, and a side chain DP of 20 hampered the cellular uptake.

Antimicrobial activity of nano-sized silver colloids stabilized by nitrogen-containing polymers: the key influence of the polymer capping

Synthesis of stable silver colloids was achieved using nitrogen-containing polymers acting simultaneously as a reducing and stabilizer agent. The polymers polyethyleneimine (PEI), polyvinylpyrrolidone (PVP) and poly(2-vinyl pyridine)-b-poly(ethylene oxide) (PEO-b-P2VP) were used in the procedures. The influence of the surface chemistry and chemical nature of the stabilizer on the cytotoxicity and antimicrobial properties have been evaluated. The produced nanomaterials were found to be non-toxic up to the highest evaluated concentration (1.00 ppm). Nevertheless, at this very low concentration, the AgNPs stabilized by PVP and PEO-b-P2VP were found to be remarkable biocides against bacteria and fungus. On the other hand, we have surprisingly evidenced negligible antimicrobial activity of AgNPs stabilized by positively charged PEI although both (AgNPs and PEI) materials separately are known for their antimicrobial activity as also evidenced in the current investigation. The evidence is claimed to be related to the blocking of Ag+ kinetic release. Accordingly, the antimicrobial effect of nano-sized silver colloids largely depends on the chemical nature of the polymer coating. Possibly, the outstanding colloid stabilization provided by polyethyleneimine slows down Ag+ release thereby hampering its biological activity whereas the poorer stabilization and good ionic transport property of PVP and PEO-b-P2VP allows much faster ion release and cell damage.

Comparison of Gene Transfection and Cytotoxicity Mechanisms of Linear Poly(amidoamine) and Branched Poly(ethyleneimine) Polyplexes

PURPOSE

This study aimed to further explore the mechanisms behind the ability of certain linear polyamidoamines (PAAs) to transfect cells with minimal cytotoxicity.

METHODS

The transfection efficiency of DNA complexed with a PAA of a molecular weight over 10 kDa or 25 kDa branched polyethyleneimine (BPEI) was compared in A549 cells using a luciferase reporter gene assay. The impact of endo/lysosomal escape on transgene expression was investigated by transfecting cells in presence of bafilomycin A1 or chloroquine. Cytotoxicity caused by the vectors was evaluated by measuring cell metabolic activity, lactate dehydrogenase release, formation of reactive oxygen species and changes in mitochondrial membrane potential.

RESULTS

The luciferase activity was ~3-fold lower after transfection with PAA polyplexes than with BPEI complexes at the optimal polymer to nucleotide ratio (RU:Nt). However, in contrast to BPEI vectors, PAA polyplexes caused negligible cytotoxic effects. The transfection efficiency of PAA polyplexes was significantly reduced in presence of bafilomycin A1 while chloroquine enhanced or decreased transgene expression depending on the RU:Nt.

CONCLUSIONS

PAA polyplexes displayed a pH-dependent endo/lysosomal escape which was not associated with cytotoxic events, unlike observed with BPEI polyplexes. This is likely due to their greater interactions with biological membranes at acidic than neutral pH.

Monitoring Antimicrobial Mechanisms of Surface-Immobilized Peptides in Situ

Antimicrobial peptides (AMPs) in free solution can kill bacteria by disrupting bacterial cell membranes. Their modes of action have been extensively studied, and various models ranging from pore formation to carpet-like mechanisms were proposed. Surface-immobilized AMPs have been used as coatings to kill bacteria and as sensors to capture bacteria, but the interaction mechanisms of surface-immobilized AMPs and bacteria are not fully understood. In this research, an analytical platform, sum frequency generation (SFG) microscope, which is composed of an SFG vibrational spectrometer and a fluorescence microscope, was used to probe molecular interactions between surface-immobilized AMPs and bacteria in situ in real time at the solid/liquid interface. SFG probed the molecular structure of surface-immobilized AMPs while interacting with bacteria, and fluorescence images of dead bacteria were monitored as a function of time during the peptide-bacteria interaction. It was believed that upon bacteria contact, the surface-immobilized peptides changed their orientation and killed bacteria. This research demonstrated that the SFG microscope platform can examine the structure and function (bacterial killing) at the same time in the same sample environment, providing in-depth understanding on the structure-activity relationships of surface-immobilized AMPs.