Gene delivery of PAMAM dendrimer conjugated with the nuclear localization signal peptide originated from fibroblast growth factor 3

Small Particles, Big Potential: Polymeric Nanoparticles for Drug Delivery in Parkinson's Disease

Despite the availability of a number of efficacious treatments for Parkinson's disease, their limitations and drawbacks, particularly related to low brain bioavailability and associated side effects, emphasize the need for alternative and more effective therapeutic approaches. Nanomedicine, the application of nanotechnology in medicine, has received considerable interest in recent years as a method of effectively delivering potentially therapeutic molecules to the brain. In particular, polymeric nanoparticles, constructed from biodegradable polymer, have shown great promise in enhancing therapeutic efficacy, reducing toxicity, and ensuring targeted delivery. However, their clinical translation remains a considerable challenge. This article reviews recent in vitro and in vivo studies using polymeric nanoparticles as drug and gene delivery systems for Parkinson's disease with their challenges and future directions. We are also particularly interested in the technical properties, mechanism, drugs release patterns, and delivery strategies to overcome the blood-brain barrier. © 2024 International Parkinson and Movement Disorder Society.

Second-Generation Polyamidoamine Dendrimer Conjugated with Oligopeptides Can Enhance Plasmid DNA Delivery In Vitro

Poly(amidoamine) (PAMAM) dendrimers have attracted considerable attention in the field of gene therapy due to their flexibility in introducing different functional moieties and reduced toxicity at low generations. However, their transfection efficiency remains a limitation. Therefore, an essential approach for improving their transfection efficiency as gene carriers involves modifying the structure of PAMAM by conjugating functional groups around their surface. In this study, we successfully conjugated an RRHRH oligopeptide to the surface of PAMAM generation 2 (PAMAM G2) to create RRHRH-PAMAM G2. This construction aims to condense plasmid DNA (pDNA) and facilitate its penetration into cell membranes, leading to its promising potential for gene therapy. RRHRH-PAMAM G2/pDNA complexes were smaller than 100 nm and positively charged. Nano-polyplexes can enter the cell and show a high transfection efficiency after 24 h of transfection. The RRHRH-PAMAM G2 was non-toxic to HeLa, NIH3T3, A549, and MDA-MB-231 cell lines. These results strongly suggest that RRHRH-PAMAM G2 holds promise as a gene carrier for gene therapy owing to its biocompatibility and ability to deliver genes to the cell.

Nuclear Delivery of Nanoparticle-Based Drug Delivery Systems by Nuclear Localization Signals

Nanomedicine 2.0 refers to the next generation of nanotechnology-based medical therapies and diagnostic tools. This field focuses on the development of more sophisticated and precise nanoparticles (NPs) for targeted drug delivery, imaging, and sensing. It has been established that the nuclear delivery of NP-loaded drugs can increase their therapeutic efficacy. To effectively direct the NPs to the nucleus, the attachment of nuclear localization signals (NLSs) to NPs has been employed in many applications. In this review, we will provide an overview of the structure of nuclear pore complexes (NPCs) and the classic nuclear import mechanism. Additionally, we will explore various nanoparticles, including their synthesis, functionalization, drug loading and release mechanisms, nuclear targeting strategies, and potential applications. Finally, we will highlight the challenges associated with developing nucleus-targeted nanoparticle-based drug delivery systems (NDDSs) and provide insights into the future of NDDSs.

Biocompatible Macroion/Growth Factor Assemblies for Medical Applications

Growth factors are a class of proteins that play a role in the proliferation (the increase in the number of cells resulting from cell division) and differentiation (when a cell undergoes changes in gene expression becoming a more specific type of cell) of cells. They can have both positive (accelerating the normal healing process) and negative effects (causing cancer) on disease progression and have potential applications in gene therapy and wound healing. However, their short half-life, low stability, and susceptibility to degradation by enzymes at body temperature make them easily degradable in vivo. To improve their effectiveness and stability, growth factors require carriers for delivery that protect them from heat, pH changes, and proteolysis. These carriers should also be able to deliver the growth factors to their intended destination. This review focuses on the current scientific literature concerning the physicochemical properties (such as biocompatibility, high affinity for binding growth factors, improved bioactivity and stability of the growth factors, protection from heat, pH changes or appropriate electric charge for growth factor attachment via electrostatic interactions) of macroions, growth factors, and macroion-growth factor assemblies, as well as their potential uses in medicine (e.g., diabetic wound healing, tissue regeneration, and cancer therapy). Specific attention is given to three types of growth factors: vascular endothelial growth factors, human fibroblast growth factors, and neurotrophins, as well as selected biocompatible synthetic macroions (obtained through standard polymerization techniques) and polysaccharides (natural macroions composed of repeating monomeric units of monosaccharides). Understanding the mechanisms by which growth factors bind to potential carriers could lead to more effective delivery methods for these proteins, which are of significant interest in the diagnosis and treatment of neurodegenerative and civilization diseases, as well as in the healing of chronic wounds.

Application of Peptides in Construction of Nonviral Vectors for Gene Delivery

Gene therapy, which aims to cure diseases by knocking out, editing, correcting or compensating abnormal genes, provides new strategies for the treatment of tumors, genetic diseases and other diseases that are closely related to human gene abnormalities. In order to deliver genes efficiently to abnormal sites in vivo to achieve therapeutic effects, a variety of gene vectors have been designed. Among them, peptide-based vectors show superior advantages because of their ease of design, perfect biocompatibility and safety. Rationally designed peptides can carry nucleic acids into cells to perform therapeutic effects by overcoming a series of biological barriers including cellular uptake, endosomal escape, nuclear entrance and so on. Moreover, peptides can also be incorporated into other delivery systems as functional segments. In this review, we referred to the biological barriers for gene delivery in vivo and discussed several kinds of peptide-based nonviral gene vectors developed for overcoming these barriers. These vectors can deliver different types of genetic materials into targeted cells/tissues individually or in combination by having specific structure-function relationships. Based on the general review of peptide-based gene delivery systems, the current challenges and future perspectives in development of peptidic nonviral vectors for clinical applications were also put forward, with the aim of providing guidance towards the rational design and development of such systems.

Preparation and characterization of polyamidoamine dendrimers conjugated with cholesteryl-dipeptide as gene carriers in HeLa cells

Improving the transfection efficiency of non-viral carriers by using cationic polymers is a useful approach to addressing several challenges in gene therapy, such as cellular uptake, endosomal escape, and toxicity. Among the various cationic polymers, polyamidoamine (PAMAM) dendrimers have been widely utilized because of the abundance of terminal functional groups, thereby enabling further functionalization and enhancing DNA condensation and internalization into cells. The combination of various functional groups is required for these PAMAM dendrimer derivatives to function appropriately for gene delivery. Herein, we synthesized PAMAM G2-HRChol by conjugating dipeptide (histidine-arginine) and cholesterol at different ratios (6% or 23%) on the surface of PAMAM dendrimer generation 2 (PAMAM G2). Both PAMAM G2-HRChol 6% and PAMAM G2-HRChol 23% have buffering capacity, leading to improved endosomal escape after entering the cells. PAMAM G2-HRChol 6% and PAMAM G2-HRChol 23% dendrimers were condensed with pDNA to form nano-polyplexes at a weight ratio of 4 (polymer/pDNA). Polyplexes are positively charged, which facilitates cellular uptake. The transfection efficiency of PAMAM G2-HRChol 6% and PAMAM G2-HRChol 23% dendrimers was similar to that of PEI 25 kDa under optimum conditions, and the cytotoxicity was much lower than that of PEI 25 kDa in HeLa cells. In addition, after apoptin gene transfection was performed, cell death ratios of 34.47% and 22.47% were observed for PAMAM G2-HRChol 6% and PAMAM G2-HRChol 23%, respectively. The results show that a suitable amount of cholesterol can improve gene transfection efficiency, and the PAMAM G2-HRChol 6% dendrimer could be a potential gene carrier in HeLa cells.

Apoptin gene delivery by a PAMAM dendrimer modified with a nuclear localization signal peptide as a gene carrier for brain cancer therapy

In this study, we aimed to synthesize PAMAMG3 derivatives (PAMAMG3-KRRR and PAMAMG3-HKRRR), using KRRR peptides as a nuclear localization signal and introduced histidine residues into the KRRR-grafted PAMAMG3 for delivering a therapeutic, carcinoma cell-selective apoptosis gene, apoptin into human primary glioma (GBL-14) cells and human dermal fibroblasts. We examined their cytotoxicity and gene expression using luciferase activity and enhanced green fluorescent protein PAMAMG3 derivatives in both cell lines. We treated cells with PAMAMG3 derivative/apoptin complexes and investigated their intracellular distribution using confocal microscopy. The PAMAMG3-KRRR and PAMAMG3-HKRRR dendrimers were found to escape from endolysosomes into the cytosol. The JC-1 assay, glutathione levels, and Annexin V staining results showed that apoptin triggered cell death in GBL-14 cells. Overall, these findings indicated that the PAMAMG3-HKRRR/apoptin complex is a potential candidate for an effective nonviral gene delivery system for brain tumor therapy in vitro.

Peptide-Assisted Nucleic Acid Delivery Systems on the Rise

Concerns associated with nanocarriers' therapeutic efficacy and side effects have led to the development of strategies to advance them into targeted and responsive delivery systems. Owing to their bioactivity and biocompatibility, peptides play a key role in these strategies and, thus, have been extensively studied in nanomedicine. Peptide-based nanocarriers, in particular, have burgeoned with advances in purely peptidic structures and in combinations of peptides, both native and modified, with polymers, lipids, and inorganic nanoparticles. In this review, we summarize advances on peptides promoting gene delivery systems. The efficacy of nucleic acid therapies largely depends on cell internalization and the delivery to subcellular organelles. Hence, the review focuses on nanocarriers where peptides are pivotal in ferrying nucleic acids to their site of action, with a special emphasis on peptides that assist anionic, water-soluble nucleic acids in crossing the membrane barriers they encounter on their way to efficient function. In a second part, we address how peptides advance nanoassembly delivery tools, such that they navigate delivery barriers and release their nucleic acid cargo at specific sites in a controlled fashion.

Nonviral gene delivery using PAMAM dendrimer conjugated with the nuclear localization signal peptide derived from human papillomavirus type 11 E2 protein

Polyamidoamine (PAMAM) dendrimers are biocompatible polymers utilized in multiple biomedical applications including tissue engineering, medical diagnosis, drug and gene delivery systems, and biosensors. Normally, high-generation PAMAM dendrimers are advantageous for use in gene therapy research because they have a relatively high transfection efficiency. A high-generation PAMAM dendrimer has a high charge density, which induces greater damage to the membranous organelles than that induced by a low-generation PAMAM dendrimer. In this study, we added NLS sequences derived from the human papillomavirus (HPV) type 11 E2 protein to the low-generation PAMAM generation 2 (PAMAM G2) dendrimer and simultaneously introduced histidine residues to reduce cytotoxicity. RKRARH-PAMAM G2 showed similar and high transfection efficiencies in Neuro-2A and NIH3T3 cell lines and relatively low cytotoxicities relative to that of polyethylenimine 25 kDa (PEI 25 kDa).

Enhanced transfection efficiency of low generation PAMAM dendrimer conjugated with the nuclear localization signal peptide derived from herpesviridae

Polyamidoamine (PAMAM) dendrimer is an extensively studied polymer in the biomedical research because of its low polydispersity, distinct molecular structure, and surface functionalities. Generally, a high-generational PAMAM dendrimer is used for gene delivery because transfection efficiency is dependent on charge density; however, an increase in charge density induces disruption of the cellular membrane, and damage to the membrane results in cytotoxicity. In this study, we selected PAMAM generation 2 to reduce the cytotoxic effect and conjugated RRILH and RRLHL sequences, nuclear localization signals (NLS) derived from herpesviridae to PAMAM generation 2. The transfection efficiency of RRILH-PAMAM G2 and RRLHL-PAMAM G2 was similar to that of polyethylenimine (PEI) in Neuro2A, HT22, and HaCaT cells, whereas their transfection efficiency was much higher than that of PEI in NIH3T3 cells. RRILH-PAMAM G2 showed relatively lower cytotoxicity than did RRLHL-PAMAM G2 in all cell lines, but the transfection capacity of the two polymers was similar. Our study shows that low-generational PAMAM dendrimer conjugated with NLS sequences has potential as an alternative to PEI in gene delivery.

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.

Structure-function relationships of nonviral gene vectors: Lessons from antimicrobial polymers

In recent years, substantial advances have been achieved in the design and synthesis of nonviral gene vectors. However, lack of effective and biocompatible vectors still remains a major challenge that hinders their application in clinical settings. In the past decade, there has been a rapid expansion of cationic antimicrobial polymers, due to their potent, rapid, and broad-spectrum biocidal activity against resistant microbes, and biocompatible features. Given that antimicrobial polymers share common features with nonviral gene vectors in various aspects, such as membrane affinity, functional groups, physicochemical characteristics, and unique macromolecular architectures, these polymers may provide us with inspirations to overcome challenges in the design of novel vectors toward more safe and efficient gene delivery in clinic. Building off these observations, we provide here an overview of the structure-function relationships of polymers for both antimicrobial applications and gene delivery by elaborating some key structural parameters, including functional groups, charge density, hydrophobic/hydrophilic balance, MW, and macromolecular architectures. By borrowing a leaf from antimicrobial agents, great advancement in the development of newer nonviral gene vectors with high transfection efficiency and biocompatibility will be more promising. STATEMENT OF SIGNIFICANCE: The development of gene delivery is still in the preclinical stage for the lack of effective and biocompatible vectors. Given that antimicrobial polymers share common features with gene vectors in various aspects, such as membrane affinity, functional groups, physicochemical characteristics, and unique macromolecular architectures, these polymers may provide us with inspirations to overcome challenges in the design of novel vectors toward more safe and efficient gene delivery in clinic. In this review, we systematically summarized the structure-function relationships of antimicrobial polymers and gene vectors, with which the design of more advanced nonviral gene vectors is anticipated to be further boosted in the future.

Nanoparticle-Based Delivery of CRISPR/Cas9 Genome-Editing Therapeutics

The recent progress in harnessing the efficient and precise method of DNA editing provided by CRISPR/Cas9 is one of the most promising major advances in the field of gene therapy. However, the development of safe and optimally efficient delivery systems for CRISPR/Cas9 elements capable of achieving specific targeting of gene therapy to the location of interest without off-target effects is a primary challenge for clinical therapeutics. Nanoparticles (NPs) provide a promising means to meet such challenges. In this review, we present the most recent advances in developing innovative NP-based delivery systems that efficiently deliver CRISPR/Cas9 constructs and maximize their effectiveness.

Exploring the role of peptides in polymer-based gene delivery

Polymers are widely studied as non-viral gene vectors because of their strong DNA binding ability, capacity to carry large payload, flexibility of chemical modifications, low immunogenicity, and facile processes for manufacturing. However, high cytotoxicity and low transfection efficiency substantially restrict their application in clinical trials. Incorporating functional peptides is a promising approach to address these issues. Peptides demonstrate various functions in polymer-based gene delivery systems, such as targeting to specific cells, breaching membrane barriers, facilitating DNA condensation and release, and lowering cytotoxicity. In this review, we systematically summarize the role of peptides in polymer-based gene delivery, and elaborate how to rationally design polymer-peptide based gene delivery vectors.

STATEMENT OF SIGNIFICANCE

Polymers are widely studied as non-viral gene vectors, but suffer from high cytotoxicity and low transfection efficiency. Incorporating short, bioactive peptides into polymer-based gene delivery systems can address this issue. Peptides demonstrate various functions in polymer-based gene delivery systems, such as targeting to specific cells, breaching membrane barriers, facilitating DNA condensation and release, and lowering cytotoxicity. In this review, we highlight the peptides' roles in polymer-based gene delivery, and elaborate how to utilize various functional peptides to enhance the transfection efficiency of polymers. The optimized peptide-polymer vectors should be able to alter their structures and functions according to biological microenvironments and utilize inherent intracellular pathways of cells, and consequently overcome the barriers during gene delivery to enhance transfection efficiency.

Polyamidoamine (PAMAM) Dendrimers Modified with Cathepsin-B Cleavable Oligopeptides for Enhanced Gene Delivery

Because of the complex mechanisms mediating cancer onset, prognosis, and metastatic behavior, different therapeutic approaches targeting these mechanisms have been investigated. Recent advancements in nanocarrier-based drug and gene delivery methods have encouraged scientific groups to investigate various novel therapeutic techniques. In this study, a poly(amidoamine) (PAMAM) polymer-based gene carrier containing the cathepsin B-enzyme sensitive sequence (glycine-phenylalanine-leucine-glycine, GFLG) was evaluated to determine transfection efficiency. Following the GFLG sequence, the surface of PAMAM generation 4 (G4) was conjugated with histidine (H) and arginine (R) for improved endosomal escape and cellular uptake, respectively. The successful synthesis of G4-GLFG-H-R was confirmed by ¹H-nuclear magnetic resonance spectroscopy. The polyplex composed of G4-GLFG-H-R and pDNA was simulated by the enzyme cathepsin B and induced endosomal escape of pDNA, which was confirmed by gel electrophoresis. Compared with the G4 control, enzyme-sensitive G4-GLFG-H-R showed higher transfection efficiency and lower cytotoxicity in HeLa cells. These results demonstrated that G4-GLFG-H-R may be a highly potent and efficient carrier for gene therapy applications.

PAMAM-pullulan conjugates as targeted gene carriers for liver cell

Targeted nano-carriers are highly needed to promote nucleic acid delivery into the specific cell for therapeutic approaches. Pullulan as a linear carbohydrate has an intrinsic liver targeting property interacting with asialoglycoprotein receptor (ASGPR) found on liver cells. In the present study, we developed polyamidoamine (PAMAM)-pullulan conjugates and investigated their targeting activity in delivering gene into liver cells. The particle size, zeta potential, buffering capacity and ethidium bromide exclusion assays of the conjugates were evaluated. The cytotoxicity and transfection efficiency of new derivatives were assessed following in vitro transfection of HepG2 (receptor positive) and N2A (receptor negative) cell lines. Size of conjugated polymers ranged between 118 and 184 nanometers and their cytotoxicity were similar to PAMAM. Among six produced nanocarriers, G4PU4 and G5PU4 enhanced transfection efficiency in HepG2 cells compared to unmodified PAMAM. Therefore, the PAMAM-pullulan derivatives seem to improve delivery of nucleic acids into the liver cells expressing asialoglycoprotein receptor with minimal transfection in non-targeted cells.

Oligoamine-tethered low generation polyamidoamine dendrimers as potential nucleic acid carriers

Oligoamine-tethered low generation PAMAM dendrimers (mG2–mG4) have been synthesized, which showed significantly higher transfection efficiency with minimal cytotoxicity in vitro.