Disulfide Cross-Linked Polyethylenimines (PEI) Prepared via Thiolation of Low Molecular Weight PEI as Highly Efficient Gene Vectors

Fluoroamphiphiles for enhancing immune response of subunit vaccine against SARS-CoV-2

In recent decades, protein-based therapy has garnered valid attention for treating infectious diseases, genetic disorders, cancer, and other clinical requirements. However, preserving protein-based drugs against degradation and denaturation during processing, storage, and delivery poses a formidable challenge. Herein, we designed a novel fluoroamphiphiles polymer to deliver protein. Two different formulations of nanoparticles, cross-linked (CNP) and micelle (MNP) polymer, were prepared rationally by disulfide cross-linked and thin-film hydration techniques, respectively. The size, zeta potential, and morphology of both formulations were characterized and the delivery efficacy of both in vitro and in vivo was also assessed. The in vitro findings demonstrated that both formulations effectively facilitated protein delivery into various cell lines. Moreover, in vivo experiments revealed that intramuscular administration of the two formulations loaded with a SARS-CoV-2 recombinant receptor-binding domain (RBD) vaccine induced robust antibody responses in mice without adding another adjuvant. These results highlight the potential use of our carrier system as a safe and effective platform for the in vivo delivery of subunit vaccines.

PEI-based functional materials: Fabrication techniques, properties, and biomedical applications

Cationic polymers have recently attracted considerable interest as research breakthroughs for various industrial and biomedical applications. They are particularly interesting due to their highly positive charges, acceptable physicochemical properties, and ability to undergo further modifications, making them attractive candidates for biomedical applications. Polyethyleneimines (PEIs), as the most extensively utilized polymers, are one of the valuable and prominent classes of polycations. Owing to their flexible polymeric chains, broad molecular weight (MW) distribution, and repetitive structural units, their customization for functional composites is more feasible. The specific beneficial attributes of PEIs could be introduced by purposeful functionalization or modification, long service life, biocompatibility, and distinct geometry. Therefore, PEIs have significant potential in biotechnology, medicine, and bioscience. In this review, we present the advances in PEI-based nanomaterials, their transfection efficiency, and their toxicity over the past few years. Furthermore, the potential and suitability of PEIs for various applications are highlighted and discussed in detail. This review aims to inspire readers to investigate innovative approaches for the design and development of next-generation PEI-based nanomaterials possessing cutting-edge functionalities and appealing characteristics.

Polymer-Based mRNA Delivery Strategies for Advanced Therapies

Messenger RNA (mRNA)-based therapies offer great promise for the treatment of a variety of diseases. In 2020, two FDA approvals of mRNA-based vaccines have elevated mRNA vaccines to global recognition. However, the therapeutic capabilities of mRNA extend far beyond vaccines against infectious diseases. They hold potential for cancer vaccines, protein replacement therapies, gene editing therapies, and immunotherapies. For realizing such advanced therapies, it is crucial to develop effective carrier systems. Recent advances in materials science have led to the development of promising nonviral mRNA delivery systems. In comparison to other carriers like lipid nanoparticles, polymer-based delivery systems often receive less attention, despite their unique ability to carefully tune their chemical features to promote mRNA protection, their favorable pharmacokinetics, and their potential for targeting delivery. In this review, the central features of polymer-based systems for mRNA delivery highlighting the molecular design criteria, stability, and biodistribution are discussed. Finally, the role of targeting ligands for the future of RNA therapies is analyzed.

A sugar modified amphiphilic cationic nano-adjuvant ceased tumor immune suppression and rejuvenated peptide vaccine induced antitumor immunity in cervical cancer

Human papilloma virus (HPV), one of the most common cancer-causing viruses, accounts for more than 90% of human anal and cervical cancers. Clinical studies have focused on adjuvant therapy with vaccines to improve therapeutic outcomes in patients with late-stage HPV-related cancers. In the present study, a mannose receptor (CD206) targeting a lithocholic acid-modified polyethylenimine (PEI) nano-adjuvant delivering the toll-like receptor 7/8 agonist, resiquimod (R848) (mLAPMi-R848), in a HPV E6- and E7-expressing TC-1 tumor murine model was developed. Peritumoral administration of mLAPMi resulted in enhanced accumulation in tumor/tumor-draining lymph nodes and significantly targeted antigen presenting cells like macrophage and dendritic cells. PEI-based nanocarriers can exploit the adjuvant potency of R848 and improve the antitumor immunity. Hence, co-administration of mLAPMi-R848 along with an E6E7 peptide in TC-1 tumor mice eradicated tumor burden and elicited splenocyte-induced cytotoxicity in TC-1 cancer cells. In a bilateral TC-1 tumor model, administration of mLAPMi-R848 and E6E7 peptide significantly suppressed both primary and secondary tumor burdens and improved the overall survival rate. Immune cell profiling revealed elevated levels of mature DCs and CD8+ T cells but reduced levels of tumor-associated immunosuppressive cells (TAICs) like myeloid derived suppressor cells (MDSCs) and regulatory T (Treg) cells in distal tumors. Overall, this study demonstrated that mLAPMi-R848 has improved the antitumor immunity of the peptide antigen against HPV-induced cancers by targeted immunodulation of antigen presenting cells (APCs) and reducing TAICs. Furthermore, this nano-adjuvant has the potential to offer a new treatment option for patients with cervical cancer and can be applied for the treatment of other HPV induced cancers.

Application of bioengineered elastin-like polypeptide-based system for targeted gene delivery in tumor cells

Successful gene delivery depends on the entry of negatively charged DNAs and oligonucleotides across the various barriers of the tumor cells and localization into the nucleus for its transcription and protein translation. Here, we have reported a thermal responsive self-assemble and highly biocompatible, targeted ELP-based gene delivery system. These systems consist of cell-penetrating peptides, Tat and single or multiple repeats of IL-4 receptor targeting peptide AP-1 along the backbone of ELP. Cell-penetrating peptides were introduced for nuclear localization of genes of interest, AP-1 for targeting IL-4R highly expressed tumor cells and ELP for stable condensation favoring protection of nucleic acids. The designed multidomain fusion ELPs referred to as Tat-ELP, Tat-A₁E₂₈ and Tat-A₄V₄₈ were employed to generate formulation with pEGFP-N1. Profound formulation of stable complexes occurred at different molar ratios owing to electrostatic interactions of positively charged amino acids in polymers with negatively charged nucleic acids. Among the complexes, Tat-A₄V₄₈ containing four copies of AP-1 showed maximum complexation with pEGFP-N1 in lower molar ratio. The polymer-pEGFP complexes were further analyzed for its transfection efficiency in different cancer cell lines. Both the targeted polymers, Tat-A₄V₄₈ and Tat-A₁E₂₈ upon transfection displayed significant EGFP-expression with low toxicity in different cancer cells. Therefore, both Tat-A₄V₄₈ and Tat-A₁E₂₈ can be considered as novel transfection system for successful gene delivery with therapeutic applications.

Toward Gene Transfer Nanoparticles as Therapeutics

Genetic medicine has great potential to treat the underlying causes of many human diseases with exquisite precision, but the field has historically been stymied by delivery as the central challenge. Nanoparticles, engineered constructs the size of natural viruses, are being designed to more closely mimic the delivery efficiency of viruses, while enabling the advantages of increased safety, cargo-carrying flexibility, specific targeting, and ease in manufacturing. The speed in which nonviral gene transfer nanoparticles are making progress in the clinic is accelerating, with clinical validation of multiple nonviral nucleic acid delivery nanoparticle formulations recently FDA approved for both expression and for silencing of genes. While much of this progress has been with lipid nanoparticle formulations, significant development is being made with other nanomaterials for gene transfer as well, with favorable attributes such as biodegradability, scalability, and cell targeting. This review highlights the state of the field, current challenges in delivery, and opportunities for engineered nanomaterials to meet these challenges, including enabling long-term therapeutic gene editing. Delivery technology utilizing different kinds of nanomaterials and varying cargos for gene transfer (DNA, mRNA, and ribonucleoproteins) are discussed. Clinical applications are presented, including for the treatment of genetic diseases such as cystic fibrosis.

Enhancing the in vivo stability of polyanion gene carriers by using PEGylated hyaluronic acid as a shielding system

To increase the in vivo stability of cationic gene carriers and avoid the adverse effects of their positive charge, we synthesized a new shielding material by conjugating low molecular weight polyethylene glycol (PEG) to a hyaluronic acid (HA) core. The HA-PEG conjugate assembled with the positively charged complex, forming a protective layer through electrostatic interactions. DNA/polyetherimide/HA-PEG (DNA/PEI/HA-PEG) nanoparticles had higher stability than both DNA/polyethyleneimine (DNA/PEI) and DNA/PEI/HA complexes. Furthermore, DNA/PEI/HA-PEG nanoparticles also showed a diminished nonspecific response toward serum proteins in vivo. The in vivo transfection efficiency was also enhanced by the low cytotoxicity and the improved stability; therefore, this material might be promising for use in gene delivery applications.

Systematic Combination of Oligonucleotides and Synthetic Polymers for Advanced Therapeutic Applications

The potential of oligonucleotides is exceptional in therapeutics because of their high safety, potency, and specificity compared to conventional therapeutic agents. However, many obstacles, such as low in vivo stability and poor cellular uptake, have hampered their clinical success. Use of polymeric carriers can be an effective approach for overcoming the biological barriers and thereby maximizing the therapeutic efficacy of the oligonucleotides due to the availability of highly tunable synthesis and functional modification of various polymers. As loaded in the polymeric carriers, the therapeutic oligonucleotides, such as antisense oligonucleotides, small interfering RNAs, microRNAs, and even messenger RNAs, become nuclease-resistant by bypassing renal filtration and can be efficiently internalized into disease cells. In this review, we introduced a variety of systematic combinations between the therapeutic oligonucleotides and the synthetic polymers, including the uses of highly functionalized polymers responding to a wide range of endogenous and exogenous stimuli for spatiotemporal control of oligonucleotide release. We also presented intriguing characteristics of oligonucleotides suitable for targeted therapy and immunotherapy, which can be fully supported by versatile polymeric carriers.

Polymeric siRNA delivery targeting integrin-β1 could reduce interactions of leukemic cells with bone marrow microenvironment

Uncontrolled proliferation of the myeloid cells due to BCR-ABL fusion has been successfully treated with tyrosine kinase inhibitors (TKIs), which improved the survival rate of Chronic Myeloid Leukemia (CML) patients. However, due to interactions of CML cells with bone marrow microenvironment, sub-populations of CML cells could become resistant to TKI treatment. Since integrins are major cell surface molecules involved in such interactions, the potential of silencing integrin-β1 on CML cell line K562 cells was explored using short interfering RNA (siRNA) delivered through lipid-modified polyethyleneimine (PEI) polymers. Reduction of integrin-β1 in K562 cells decreased cell adhesion towards human bone marrow stromal cells and to fibronectin, a major extracellular matrix protein for which integrin-β1 is a primary receptor. Interaction of K562 cells with fibronectin decreased the sensitivity of the cells to BCR-ABL siRNA treatment, but a combinational treatment with integrin-β1 and BCR-ABL siRNAs significantly reduced colony forming ability of the cells. Moreover, integrin-β1 silencing enhanced the detachment of K562 cells from hBMSC samples (2 out of 4 samples), which could make them more susceptible to TKIs. Therefore, the polymeric-siRNA delivery targeting integrin-β1 could be beneficial to reduce interactions with bone marrow microenvironment, aiding in the response of CML cells to therapeutic treatment.

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.

Polymeric nano-carriers for on-demand delivery of genes via specific responses to stimuli

Polymeric nano-carriers have been developed as a most capable and feasible technology platform for gene therapy. As vehicles, polymeric nano-carriers are obliged to possess high gene loading capability, low immunogenicity, safety, and the ability to transfer various genetic materials into specific sites of target cells to express therapeutic proteins or block a process of gene expression. To this end, various types of polymeric nano-carriers have been prepared to release genes in response to stimuli such as pH, redox, enzymes, light and temperature. These stimulus-responsive nano-carriers exhibit high gene transfection efficiency and low cytotoxicity. In particular, dual- and multi-stimulus-responsive polymeric nano-carriers can respond to a combination of signals. Markedly, these combined responses take place either simultaneously or in a sequential manner. These dual-stimulus-responsive polymeric nano-carriers can control gene delivery with high gene transfection both in vitro and in vivo. In this review paper, we highlight the recent exciting developments in stimulus-responsive polymeric nano-carriers for gene delivery applications.

The combined disulfide cross-linking and tyrosine-modification of very low molecular weight linear PEI synergistically enhances transfection efficacies and improves biocompatibility

Efficient and non-toxic DNA delivery is still a major limiting factor for non-viral gene therapy. Among the large diversity of non-viral vectors, the cationic polymer polyethylenimine (PEI) plays a prominent role in nucleic acid delivery. Since higher molecular weight of PEI is beneficial for transfection efficacy, but also leads to higher cytotoxicity, the biodegradable cross-linking of low-molecular PEIs, e.g. through disulfide-groups, has been introduced. Another promising strategy is the chemical modification of PEI, for example with amino acids like tyrosine. In the case of small RNA molecules, this PEI grafting has been found to enhance transfection efficacies and improve biocompatibility. In this paper, we report on the combination of these two strategies for improving DNA delivery: the (i) cross-linking of very small 2 kDa PEI ("P2") molecules through biodegradable disulfide-groups ("SS"), in combination with (ii) tyrosine-modification ("Y"). We demonstrate a surprisingly substantial, synergistic enhancement of transfection efficacies of these SSP2Y/DNA complexes over their non- or mono-modified polymer counterparts, accompanied by high biocompatibility as well as favorable physicochemical and biological properties. Beyond various cell lines, high biological activity of the SSP2Y-based complexes is also seen in an ex vivo tissue slice model, more closely mimicking in vivo conditions. The particularly high transfection efficacy SSP2Y/DNA complexes in 2D and 3D models, based on their optimized complex stability and DNA release, as well as their high biocompatibility thus provides the basis for their further exploration for therapeutic application.

Highly Osmotic Oxidized Sucrose-Crosslinked Polyethylenimine for Gene Delivery Systems

In this work, highly osmotic oxidized sucrose-crosslinked polyethylenimine (SP2K) polymers were developed for gene delivery systems, and the transfection mechanism is examined. First, periodate-oxidized sucrose and polyethylenimine 2K (PEI2K) were crosslinked with various feed ratios via reductive amination. The synthesis was confirmed by ¹H NMR and FTIR. The synthesized SP2K polymers could form positively charged (~40 mV zeta-potential) and nano-sized (150–200 nm) spherical polyplexes with plasmid DNA (pDNA). They showed lower cytotoxicity than PEI25K but concentration-dependent cytotoxicity. Among them, SP2K7 and SP2K10 showed higher transfection efficiency than PEI25K in both serum and serum-free conditions, revealing the good serum stability. It was found that SP2K polymers possessed high osmolality and endosome buffering capacity. The transfection experiments with cellular uptake inhibitors suggest that the transfection of SP2K polymers would progress by multiple pathways, including caveolae-mediated endocytosis. It was also thought that caveolae-mediated endocytosis of SP2K polyplexes would be facilitated through cyclooxygenase-2 (COX-2) expression induced by high osmotic pressure of SP2K polymers. Confocal microscopy results also supported that SP2K polyplexes would be internalized into cells via multiple pathways and escape endosomes efficiently via high osmolality and endosome buffering capacity. These results demonstrate the potential of SP2K polymers for gene delivery systems.

Solvent and catalyst-free modification of hyperbranched polyethyleneimines by ring-opening-addition or ring-opening-polymerization of N-sulfonyl aziridines

Ring-opening (polymerization) of N-sulfonyl aziridines with PEI under solvent/catalyst-free conditions allows the atom-economic synthesis of amphiphilic alkylated PEIs and luminescent PEI-graft-polysulfonamide.

"Double-punch" strategy for delivery of viral immunotherapy with prolonged tumor retention and enhanced transfection efficacy

Viral immunotherapy has shown clinical efficacy in treating cancers (e.g., melanoma). Given that viral immunotherapy commonly uses intratumoral injection, prolonging the duration of therapeutic virus at the tumor site can further enhance the antitumor efficacy and reduce potential off-target effects. In this work, we describe a "double-punch" strategy by combining dendrimer platform and injectable hydrogel encapsulation for delivery of an adenovirus encoding Flagrp170 (Adv-Flagrp170), which has been shown to effectively mount a cytotoxic T lymphocyte response through enhanced tumor immunogenicity and optimized antigen cross-presentation. We first complexed PAMAM generation 4 (G4) with Adv (G4/Adv) to strengthen its transfection efficiency and then loaded G4/Adv into a biocompatible and injectable supramolecular hydrogel (SH) made of α-cyclodextrin and 4-arm polyethylene glycol via host-guest interaction. When tested in a murine melanoma model, the G4/Adv complex was shown to have improved retention at the tumor site. The presence of SH facilitated the targeted gene expression in tumor-infiltrating leukocytes, including antigen-presenting dendritic cells. Delivery of Adv-Flagrp170 by both G4 coating and SH encapsulation significantly enhanced its therapeutic efficacy in controlling mouse melanoma (8-fold reduction in tumor volume), which is associated with increased immune activation in the tumor microenvironment as well as decreased adenovirus-reactive antibodies. Taken together, this new formulation may be used to improve the treatment outcome of adenovirus-based cancer immunotherapy.

Redox stimulus disulfide conjugated polyethyleneimine as a shuttle for gene transfer

Redox-responsive cationic polymers have gained considerable attention in gene delivery due to low cytotoxicity and spatio-temporal release of DNA into the cells. Here, we reported the synthesis of reducible disulfide conjugated polyethyleneimine (1.8 kDa) (denoted as SS-PEI) and its application to transfer pEGFP-ZNF580 plasmid (pZNF580) into EA.hy926 cell. This reducible SS-PEI polymer was prepared by one-step polycondensation reaction of low molecular weight PEI with bis-(p-nitrophenyl)-3,3'-dithiodipropionate. The SS-PEI successfully condensed pZNF580 into nano-sized complexes (170 ± 1.5 nm to 255 ± 1.6 nm) with zeta potentials of 3 ± 0.4 mV to 17 ± 0.9 mV. The complexes could be triggered to release pZNF580 when exposed to the reducing environment of 5 mM dithiothreitol. Besides, the SS-PEI exhibited low cytotoxicity. In vitro transfection results showed that SS-PEI exhibited good transfection efficiency comparable to PEI25kDa. Thus, the SS-PEI could act as an reducible gene carrier with good transfection efficiency and low cytotoxicity.

Bio-inspired gene carriers with low cytotoxicity constructed via the assembly of dextran nanogels and nano-coacervates

Aim: To achieve safe and biocompatible gene carriers. Materials & methods: A core/shell-structured hierarchical carrier with an internal peptide/gene coacervate 'core' and a dextran nanogel 'shell' on the surface has been designed. Results: The dextran nanogels shield coacervate (DNSC) can effectively condense genes and release them in reducing environments. The dextran nanogel-based 'shell' can effectively shield the positive charge of the peptide/gene coacervate 'core', thus reducing the side effects of cationic gene carriers. In contrast with the common nonviral gene carriers that had high cytotoxicities, the DNSC showed a high transfection efficiency while maintaining a low cytotoxicity. Conclusion: The DNSC provides an effective environmentally responsive gene carrier with potential applications in the fields of gene therapy and gene carrier development.

Influence of Cross-Linking Degree on Hydrodynamic Behavior and Stimulus-Sensitivity of Derivatives of Branched Polyethyleneimine

Cross-linked derivatives of acylated branched polyethyleneimine containing 2-isopropyl-2-oxazoline units were investigated in chloroform and aqueous solutions using methods of molecular hydrodynamics, static and dynamic light scattering, and turbidity. The studied samples differed by the cross-linker content. The solubility of the polyethyleneimines studied worsened with the increasing mole fraction of the cross-linker. Cross-linked polyethyleneimines were characterized by small dimensions in comparison with linear analogs; the increase in the cross-linker content leads to a growth of intramolecular density. At low temperatures, the aqueous solutions of investigated samples were molecularly dispersed, and the large aggregates were formed due to the dehydration of oxazoline units and the formation of intermolecular hydrogen bonds. For the cross-linked polyethyleneimines, the phase separation temperatures were lower than that for linear and star-shaped poly-2-isopropyl-2-oxazolines. The low critical solution temperature of the solutions of studied polymers decreased with the increasing cross-linker mole fraction. The time of establishment of the constant characteristics of the studied solutions after the jump-like change in temperature reaches 3000 s, which is at least two times longer than for linear polymers.

Reduction sensitive nanocarriers mPEG-g-γ-PGA/SSBPEI@siRNA for effective targeted delivery of survivin siRNA against NSCLC

Poly γ-glutamic acid (γ-PGA) is attractive due to its desirable biological properties such as nontoxicity, excellent biocompatibility, and minimal immunogenicity. Additionally, γ-PGA could be recognized by γ-glutamyl transpeptidase, which is regarded as a potential biomarker for many tumors. In this study, we have developed a new biodegradable, reduction sensitive, and tumor-specific gene nano-delivery platform consisting of a cationic carrier (SSBPEI) for siRNA condensation, mPEG shell for nanoparticle stabilization, and γ-PGA for accelerated cellular uptake. Disulfide bonds (-SS-) could be reduced specifically in the tumor environment, which is full of reductants such as glutathione reductase. Conjugating polyethylene glycol (PEG) to the γ-PGA led to the formation of mPEG-g-γ-PGA, with a decreased positive charge on the surface of SSBPEI@siRNA and substantially higher stability in an aqueous medium. As a result, mPEG-g-γ-PGA/SSBPEI@siRNA nanoparticles could protect siRNAs from RNase A degradation and release siRNAs in a reduction sensitive way. The multifunctional delivery system was shown to silence the Survivin gene and further promote chemotherapeutic drug-induced apoptosis in the A549 NSCLC cell line efficiently, thereby representing a novel promising platform for the delivery of siRNAs.

Poly(l-glutamic acid)-Based Zwitterionic Polymer in a Charge Conversional Shielding System for Gene Therapy of Malignant Tumors

Recently, pH-sensitive polymers have received extensive attention in tumor therapy. However, the rapid response to pH changes is the key to achieving efficient treatment. Here, a novel shielding system with a rapidly pH-responsive polymer (PAMT) is synthesized by click reaction between poly(γ-allyl-l-glutamate) and thioglycolic acid or 2-(Boc-amino)ethanethiol. The zwitterionic biodegradable polymer PAMT, which is negatively charged at physiological pH, can be used to shield positively charged nanoparticles. PAMT is electrostatically attached to the surface of the positively charged PEI/pDNA complex to form a ternary complex. The zwitterionic PAMT-shielded complex exhibits rapid charge conversion when the pH decreases from 7.4 to 6.8. For the in vivo tumor inhibition experiment, PAMT/PEI/shVEGF injected intravenously shows a more significant inhibitory effect on tumor growth. The excellent results are mainly attributed to introduction of the zwitterionic copolymer PAMT, which can shield the positively charged PEI/shVEGF complex in physiological conditions, while the surface potential of the shielded complexes changes to a positive charge in the acidic tumor environment.

A novel indomethacin/methotrexate/MMP-9 siRNA in situ hydrogel with dual effects of anti-inflammatory activity and reversal of cartilage disruption for the synergistic treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by inflammatory cell infiltration, and cartilage and bone disruption, which ultimately leads to loss of joint function. Current treatments for RA only focus on anti-inflammatory activity but neglect to prevent further damage to articular cartilage and bone. Here we attempted to co-deliver indomethacin (IND), methotrexate (MTX) and a small-interfering RNA targeting MMP-9 using an in situ hydrogel loaded with PEI-SS-IND-MTX-MMP-9 siRNA nanoparticles (D/siRNA-NGel) to treat RA synergistically and comprehensively. IND, MTX and MMP-9 siRNA were able to escape from the endosome and down-regulate the expression of MMP-9 and inflammatory cytokines of Raw-264.7 cells. After intra-articular injection in arthritic mice, the D/siRNA-NGel effectively relieved joint swelling and significantly reduced the expression of TNF-α, IL-6 and MMP-9 in the ankle fluid, knee joint fluid and plasma of RA mice without causing any side effects. Most importantly, the co-delivery system restored the morphological parameters of the ankle joints close to normal. The D/siRNA-NGel could achieve good anti-inflammatory activity and reverse cartilage disruption through a synergistic effect between chemical drugs and MMP-9 siRNA. This co-delivery system should have promising applications in the treatment of rheumatoid arthritis and other metabolic bone diseases which cause serious bone erosion.

Biodegradable Polymers for Gene-Delivery Applications

Gene-based therapies have emerged as a new modality for combating a myriad of currently incurable diseases. However, the fragile nature of gene therapeutics has significantly hampered their biomedical applications. Correspondingly, the development of gene-delivery vectors is of critical importance for gene-based therapies. To date, a variety of gene-delivery vectors have been created and utilized for gene delivery. In general, they can be categorized into viral- and non-viral vectors. Due to safety issues associated with viral vectors, non-viral vectors have recently attracted much more research focus. Of these non-viral vectors, polymeric vectors, which have been preferred due to their low immunogenicity, ease of production, controlled chemical composition and high chemical versatility, have constituted an ideal alternative to viral vectors. In particular, biodegradable polymers, which possess advantageous biocompatibility and biosafety, have been considered to have great potential in clinical applications. In this context, the aim of this review is to introduce the recent development and progress of biodegradable polymers for gene delivery applications, especially for their chemical structure design, gene delivery capacity and additional biological functions. Accordingly, we first define and categorize biodegradable polymers, followed by describing their corresponding degradation mechanisms. Various types of biodegradable polymers resulting from natural and synthetic polymers will be introduced and their applications in gene delivery will be examined. Finally, a future perspective regarding the development of biodegradable polymer vectors will be given.

Dextran-based coacervate nanodroplets as potential gene carriers for efficient cancer therapy

The intractable toxicity of cationic polymers limits their applicability in gene transport and controlled release. In consideration of the good biocompatibility and biofunctionality of dextran, herein we design and synthesize two types of amino group-containing cationic copolymers based on dextran by the copolymerization of cationic monomers from dextran backbones. Additionally, allyl crosslinkers containing disulfide bonds were introduced into polymerization, that made the copolymer crosslinked by disulfide. The resultant coacervates were formed from the self-assembly of cationic coplymers and anionic genes, and redox-responsive disulfide branch points endow coacervates with reducing environment responsiveness. The in vitro experiments showed that the dextran-based coacervates were sensitive to the reducing environment and underwent cleavage, which resulted in an effective release, uptake, and transfection of the genes by 293T cells. In addition, dextran-based coacervates can be used to carry siRNA into cancer cells with a high transfection efficiency, demonstrating their potential applicability in treatment against cancer.

Development of elastin-like polypeptide for targeted specific gene delivery in vivo

Background

The successful deliveries of siRNA depend on their stabilities under physiological conditions because greater in vivo stability enhances cellular uptake and enables endosomal escape. Viral-based systems appears as most efficient approaches for gene delivery but often compromised in terms of biocompatibility, patient safety and high cost scale up process. Here we describe a novel platform of gene delivery by elastin-like polypeptide (ELP) based targeting biopolymers.

Results

For better tumor targeting and membrane penetrating characteristics, we designed various chimeric ELP-based carriers containing a cell penetrating peptide (Tat), single or multiple copies of AP1 an IL-4 receptor targeting peptide along with coding sequence of ELP and referred as Tat-A₁E₂₈ or Tat-A₄V₄₈. These targeted polypeptides were further analyzed for its ability to deliver siRNA (Luciferase gene) in tumor cells in comparison with non-targeted controls (Tat-E₂₈ or E₂₈). The positively charged amino acids of these polypeptides enabled them to readily complex with negatively charged nucleic acids. The complexation of nucleic acid with respective polypeptides facilitated its transfection efficiency as well as stability. The targeted polypeptides (Tat-A₁E₂₈ or Tat-A₄V₄₈) selectively delivered siRNA into tumor cells in a receptor-specific fashion, achieved endosomal and lysosomal escape, and released gene into cytosol. The target specific delivery of siRNA by Tat-A₁E₂₈ or Tat-A₄V₄₈ was further validated in murine breast carcinoma 4T1 allograft mice model.

Conclusion

The designed delivery systems efficiently delivered siRNA to the target site of action thereby inducing significant gene silencing activity. The study shows Tat and AP1 functionalized ELPs constitute a novel gene delivery system with potential therapeutic applications.

Intra-articular injection of indomethacin-methotrexate in situ hydrogel for the synergistic treatment of rheumatoid arthritis

Rheumatoid arthritis is a chronic systemic autoimmune disease that causes joint swelling and cartilage damage. The objective of the present work was to develop a temperature-sensitive hydrogel (D-NGel) containing nanoparticles (D-NPs), which could simultaneously deliver combination indomethacin and methotrexate. D-NPs were formed by multiple non-covalent interactions between PEI-SS and the carboxyl-containing hydrophobic small molecule drugs IND and MTX, which were then loaded into a temperature-sensitive hydrogel matrix. The T_sol/gel of the temperature-sensitive hydrogel matrix composed of 27% F127 and 10% F68 was 33 °C and the gelation time was less than 15 s. The resultant D-NGel was injected into the articular cavity of collagen-induced arthritis rats and quickly transformed in situ into gels which slowly released drug in the joint fluid for up to 72 h. The D-NGel effectively reduced joint swelling, bone erosion and expression of inflammatory cytokines in the ankle fluid and knee joint fluid. In addition, liver and kidney function tests and histopathological examination indicated there was a good biological safety for D-NGel. In conclusion, this work has demonstrated the great potential of the D-NGel for sustained co-delivery of IND and MTX for the synergistic treatment of rheumatoid arthritis, treating both the symptoms and the root causes of rheumatoid arthritis.

Non-viral transfection vectors: are hybrid materials the way forward?

Transfection is a process by which oligonucleotides (DNA or RNA) are delivered into living cells. This allows the synthesis of target proteins as well as their inhibition (gene silencing). However, oligonucleotides cannot cross the plasma membrane by themselves; therefore, efficient carriers are needed for successful gene delivery. Recombinant viruses are among the earliest described vectors. Unfortunately, they have severe drawbacks such as toxicity and immunogenicity. In this regard, the development of non-viral transfection vectors has attracted increasing interests, and has become an important field of research. In the first part of this review we start with a tutorial introduction into the biological backgrounds of gene transfection followed by the classical non-viral vectors (cationic organic carriers and inorganic nanoparticles). In the second part we highlight selected recent reports, which demonstrate that hybrid vectors that combine key features of classical carriers are a remarkable strategy to address the current challenges in gene delivery.

Reduction sensitive CC9-PEG-SSBPEI/miR-148b nanoparticles: Synthesis, characterization, targeting delivery and application for anti-metastasis

miRNAs such as miR-148b play crucial regulatory role in tumor metastasis, but their applications are limited because they are easy to degrade in serum conditions and lack targeting ability. Herein, CC9-PEG-SSBPEI was synthesized and used as nano-carrier for miR-148b. DLS and gel retardation analyses indicated that CC9-PEG-SSBPEI could combine with miR-148b by charge interaction and formed into nanoparticles with the size changed from 811.6 nm to 146.4 nm. CC9-PEG-SSBPEI could protect miR-148b from RNase A degradation and showed a reduction sensitive release of miR-148b. FACS analysis and CLSM images displayed that the conjugated CC9 peptide improved the accumulation and penetration of the nanoparticles in HuH-7 liver cancer cells through binding with the target of miR-148b neuropilin-1(NRP-1) on the cell surface. The raised level of miR-148b in turn inhibited the expression of NRP-1 and suppressed the migration of HuH-7 liver cancer cells. Moreover, hemolysis and cytotoxicity assay demonstrated that the nanoparticles had good hemo- and cyto- compatibility. Hence, CC9-PEG-SSBPEI/miR-148b nanoparticles had the potential for targeting delivery of miR-148b and anti-metastasis of hepatocellular carcinoma (HCC) cells.

Synthesis of Bioreducible Polycations with Controlled Topologies

Bioreducible polycations, which possess disulfide linkages in the backbone, have emerged as promising nucleic acid delivery carriers due to their high stability in extracellular physiological condition and bioreduction-triggered release of the genetic material. Further benefits of bioreducible polycations include decreased cytotoxicity due to intracellular reducing environment in the cytoplasm that contains high levels of reducing molecules such as glutathione. Here, we describe the synthesis of bioreducible polycations with emphasis on methods to control their topology.

A PEG-b-poly(disulfide-l-lysine) based redox-responsive cationic polymer for efficient gene transfection

Gene therapy is concerned with the transfer of complement genes to functionally defective cells in a safe and directed manner for the treatment of the most challenging diseases. But safety issues and low transfection efficiency of the gene vectors are the major challenges, which need to be overcome. Recently, redox-responsive bioreducible polymers containing disulfide linkages have been considered as efficient gene vectors, owing to the selective degradation of the disulfide bond in the reducing environment of the cells. This enables spatiotemporal release of pDNA with no or minimum toxicity. Herein, we reported a bioreducible poly(ethyleneglycol)-b-poly(disulfide-l-lysine) cationic polymer (denoted as PEG-SSL) via a Michael addition reaction of poly(ethyleneglycol)tetraacrylate PEG(Ac)₄ and the terminal amine group of poly(disulfide-l-lysine). PEG-SSL efficiently condensed the plasmid ZNF580 gene (pZNF580) forming nano-sized polyplexes (155 ± 4 to 285 ± 3 nm) with zeta potentials of 1.9 ± 0.1 to 26.7 ± 0.4 mV. PEG-SSL successfully retarded pZNF580 at a small polymer/pDNA weight ratio of 10/1 and higher. When exposed to a reducing environment of 5 mM DTT, it rapidly released genes even at higher weight ratios of the PEG-SSL polymer in the PEG-SSL/pDNA complexes. The PEG-SSL/pZNF580 complexes exhibited good stability when exposed to DNase I and efficiently protected pDNA from degradation. In vitro transfection and cytotoxicity were investigated in EA.hy926 cells. The results showed that PEG-SSL successfully delivered pZNF580 into the cells with less cytotoxicity compared to PEI25kDa. The flow cytometry and confocal scanning laser microscopy results indicated that PEG-SSL polyplexes exhibited good cellular uptake and nuclear co-localization rates. All these results implied that PEG-SSL had the potential as a non-viral vector for gene transfection.

Tunable nonenzymatic degradability of N-substituted polyaspartamide main chain by amine protonation and alkyl spacer length in side chains for enhanced messenger RNA transfection efficiency

Degradability of polycations under physiological conditions is an attractive feature for their use in biomedical applications, such as the delivery of nucleic acids. This study aims to design polycations with tunable nonenzymatic degradability. A series of cationic N-substituted polyaspartamides were prepared to possess primary amine via various lengths of alkyl spacers in side chains. The degradation rate of each polyaspartamide derivative was determined by size exclusion chromatography under different pH conditions. The N-substituted polyaspartamide containing a 2-aminoethyl moiety in the side chain (PAsp(AE)) showed considerable degradability under physiological conditions (pH 7.4, 37 °C). In contrast, the N-substituted polyaspartamides bearing a longer alkyl spacer in the side chain, i.e. the 3-aminopropyl (PAsp(AP)) and 4-aminobutyl moieties (PAsp(AB)), more strongly suppressed degradation. Further, a positive correlation was observed between the degradation rate of N-substituted polyaspartamides and a deprotonation degree of primary amines in their side chains. Therefore, we conclude that the deprotonated primary amine in the side chain of N-substituted polyaspartamides can induce the degradation of the main chain through the activation of amide nitrogen in the side chain. When N-substituted polyaspartamides were utilized as a messenger RNA (mRNA) delivery vehicle via formation of polyion complexes (PICs), degradable PAsp(AE) elicited significantly higher mRNA expression efficiency in cultured cells compared to PAsp(AP) and PAsp(AB). The higher efficiency of PAsp(AE) might be due to the facilitated destabilization of PICs within the cells, directed toward mRNA release. Additionally, degradation of PAsp(AE) considerably reduced its cytotoxicity. Thus, our study highlights a useful design of well-defined cationic poly(amino acid)s with tunable nonenzymatic degradability.

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.

Modular Synthesis of Bioreducible Gene Vectors through Polyaddition of N,N'-Dimethylcystamine and Diglycidyl Ethers

Bioreducible, cationic linear poly(amino ether)s (PAEs) were designed as promising gene vectors. These polymers were synthesized by the reaction of a disulfide-functional monomer, N,N'-dimethylcystamine (DMC), and several different diglycidyl ethers. The resulting PAEs displayed a substantial buffer capacity (up to 64%) in the endosomal acidification region of pH 7.4⁻5.1. The PAEs condense plasmid DNA into 80⁻200 nm sized polyplexes, and have surface charges ranging from +20 to +40 mV. The polyplexes readily release DNA upon exposure to reducing conditions (2.5 mM DTT) due to the cleavage of the disulfide groups that is present in the main chain of the polymers, as was demonstrated by agarose gel electrophoresis. Upon exposing COS-7 cells to polyplexes that were prepared at polymer/DNA w/w ratios below 48, cell viabilities between 80⁻100% were observed, even under serum-free conditions. These polyplexes show comparable or higher transfection efficiencies (up to 38%) compared to 25 kDa branched polyethylenimine (PEI) polyplexes (12% under serum-free conditions). Moreover, the PAE-based polyplexes yield transfection efficiencies as high as 32% in serum-containing medium, which makes these polymers interesting for gene delivery applications.

A multifunctional nanoparticle constructed with a detachable albumin outer shell and a redox-sensitive inner core for efficient siRNA delivery to hepatocellular carcinoma cells

Successful delivery of small interfering RNA (siRNA) into the cytoplasm of target cells relies on biocompatible and efficient vectors. In this study, a novel multifunctional core/shell nanoparticle [CS-SS-9R/BSA-c(RGDyK)] was developed to effectively deliver siVEGF to hepatocellular carcinoma cells (Bel-7402 cells). To improve the gene payload and transfection efficiency, a positively charged inner core (CS-SS-9R) was constructed by grafting nona-arginine (9R) onto chitosan (CS) using disulphide bonds. The negatively charged outer shell [BSA-c(RGDyK)] assembled on the surface of the inner core by electrostatic forces that shielded high cationic charges and provided improved targeting. The protein outer shell gradually detached from the inner core in the acidic lysosomal environment, leaving the cationic inner core exposed in order to escape from lysosomes. The nanoparticles were capable of delivering siVEGF into Bel-7402 cells via integrin receptor-mediated endocytosis. Successful lysosomal escape of the inner core and the rapid release of siVEGF into the cytoplasm resulted in a 78.9% decrease in VEGF expression and 81.2% inhibition of tumour cell proliferation. In conclusion, this nanoparticle is responsive to the intracellular environment and accurately delivered siRNA into the cytoplasm, providing a safe and highly efficient gene delivery strategy for cancer therapy.

Programmed 'triple-mode' anti-tumor therapy: Improving peritoneal retention, tumor penetration and activatable drug release properties for effective inhibition of peritoneal carcinomatosis

Peritoneal carcinomatosis (PC) is a fatal condition arising in the gastrointestinal tract. PC patients administered drugs locally in the tumor region, such as in intraperitoneal chemotherapy (IPCh), suffer from low drug retention time and tumor penetration. Herein, we synthesized a lithocholic acid (LCA)-conjugated disulfide-linked polyethyleneimine (ssPEI) micelle (LAPMi) nanoconstruct by covalently conjugating ssPEI and LCA, thereby forming positive charged nanomicellar structures loaded with paclitaxel (PTX) (LAPMi-PTX) for IPCh. The incorporation of a positive surface charge aided in prolonging the peritoneal retention time, presumably via ascites-induced protein corona formation, and the subsequent size expansion caused resistance against undesired clearance through lymphatic openings. Furthermore, preferential tumor penetration by LAPMi-PTX is attributable to the permeation-enhancing properties of LCA, and the subsequent tumor activatable drug release was induced by the presence of disulfide linkages. By integrating these properties, LAPMi exhibited prolonged peritoneal residence time, enhanced tumor permeation and chemotherapeutic effect evidenced by in vitro, tumor spheroid and in vivo studies. Importantly, our strategy enabled significant PC inhibition and increased the overall survival rate of tumor-bearing mice. In conclusion, we provided a new paradigm of intractable PC treatment by enabling the prolonged residence time of the nanoconstruct, thereby enhancing tumor penetration and anti-tumor therapy.

Dual-stimuli-responsive albumin-polyplex nanoassembly for spatially controlled gene release in metastatic breast cancer

Stimuli-responsive polymeric nanoparticles are useful for overcoming challenges such as transfection efficiency and the specific and safe delivery of genes to cancer cells. Transfection outcomes can be improved through spatially and temporally controlled gene release. We formulated a nanoassembly comprising a disulfide-crosslinked polyethylenimine (ssPEI) conjugated with a tumor-specific cell-penetrating peptide (DS 4-3) (SPD) polyplex and bovine serum albumin (BSA)-loaded IR780 (BI) nanoparticle, thereby forming a dual-stimulus-triggered, tumor-penetrating and gene-carrying nanoassembly (BI-SPD) via electrostatic complexing. BI-SPD nanoassembly were composed of highly stable nanosized complexes with an average size of 457 ± 27.5 nm, exhibiting an up to two-fold enhanced transfection efficiency with no sign of potential cytotoxicity in breast cancer cells. Moreover, upon laser irradiation, a four-fold increase in transfection efficiency was achieved due to the rapid endosomal escape of polyplexes triggered by the local heat induced by the BI-SPD nanoassembly. Additionally, the high redox environment in tumor cells facilitated the disassembly of the SPD polyplex for efficient plasmid release in the cytosol. The BI-SPD nanoassembly also exhibited high penetration and enhanced photothermally triggered gene expression in the 4T1 spheroid model. This BI-SPD nanoassembly has the potential to enhance the expression of therapeutic genes in tumor models without causing significant toxicity to surrounding healthy tissues, since it has shown higher tumor targeting and accumulation in the 4T1 tumor in mice model.

Low molecular weight polyethylenimine-grafted soybean protein gene carriers with low cytotoxicity and greatly improved transfection in vitro

A series of gene carriers (SP-PEI) have been synthesized by acylation reaction between soybean protein and branched polyethylenimine with low molecular weight of 600, 1200 and 1800 Da, and designed as SP-PEI600, SP-PEI1200 and SP-PEI1800, respectively. SP-PEI could effectively condense plasmid DNA into nanoscale polyplexes with size range of 100-200 nm, and exhibited much lower cytotoxicity against 293T and SH-SY5Y cells than that of branched polyethylenimine (25 kDa). In vitro gene transfection demonstrated that SP-PEI/DNA complex displayed increased transfection against 293T and SH-SY5Y cells with the increase of the weight ratio of SP-PEI/DNA complex with or without 10% serum. At weight ratio of 24, SP-PEI1800/DNA polyplexes showed the highest transfection on SH-SY5Y cells, which was almost three folds higher than PEI (25 kDa). Furthermore, these SP-PEIs/DNA polyplexes could effectively transfect 293T and SH-SY5Y cells with or without 10% serum, suggesting their excellent serum tolerance.

Water-Reprocessable, Reformable, and Ecofriendly Sustainable Material Based on Disulfide-Cross-Linked Polyethyleneimine

A reformable polymer gel material has been developed based on the disulfide cross-linking of low-molecular-weight polyethylenimine (PEI) that can be synthesized through a facile thiolation method and reprocessed through an aqueous method without the use of solvents or additional chemicals. Despite being made with water-soluble PEI, the cross-linked gel shows good mechanical integrity and its properties can be controlled through the fabrication parameters, maintaining the hydrophilic nature of PEI while being sufficiently robust to form a free-standing film that does not dissolve in water. The properties of the gel have been characterized by Fourier transform infrared spectroscopy, thermogravimetry, and dynamic mechanical analyses, showing the effect of parameters such as the degree of thiolation and thermal curing. The reformability of the gel comes from the disulfide cross-links, which can be disrupted and reformed through a simple, aqueous processing method utilizing ultrasonication, creating an aqueous dispersion, which can be recast multiple times with minimal loss in physical properties.

Nonviral cancer gene therapy: Delivery cascade and vector nanoproperty integration

Gene therapy represents a promising cancer treatment featuring high efficacy and limited side effects, but it is stymied by a lack of safe and efficient gene-delivery vectors. Cationic polymers and lipid-based nonviral gene vectors have many advantages and have been extensively explored for cancer gene delivery, but their low gene-expression efficiencies relative to viral vectors limit their clinical translations. Great efforts have thus been devoted to developing new carrier materials and fabricating functional vectors aimed at improving gene expression, but the overall efficiencies are still more or less at the same level. This review analyzes the cancer gene-delivery cascade and the barriers, the needed nanoproperties and the current strategies for overcoming these barriers, and outlines PEGylation, surface-charge, size, and stability dilemmas in vector nanoproperties to efficiently accomplish the cancer gene-delivery cascade. Stability, surface, and size transitions (3S Transitions) are proposed to resolve those dilemmas and strategies to realize these transitions are comprehensively summarized. The review concludes with a discussion of the future research directions to design high-performance nonviral gene vectors.

Towards Hypoxia-responsive Drug-eluting Embolization Beads

Drug release from chemoembolization microspheres stimulated by the presence of a chemically reducing environment may provide benefits for targeting drug resistant and metastatic hypoxic tumours. A water-soluble disulfide-based bifunctional cross-linker bis(acryloyl)-(l)-cystine (BALC) was synthesised, characterised and incorporated into a modified poly(vinyl) alcohol (PVA) hydrogel beads at varying concentrations using reverse suspension polymerisation. The beads were characterised to confirm the amount of cross-linker within each formulation and its effects on the bead properties. Elemental and UV/visible spectroscopic analysis confirmed the incorporation of BALC within the beads and sizing studies showed that in the presence of a reducing agent, all bead formulations increased in mean diameter. The BALC beads could be loaded with doxorubicin hydrochloride and amounts in excess of 300mg of drug per mL of hydrated beads could be achieved but required conversion of the carboxylic acid groups of the BALC to their sodium carboxylate salt forms. Elution of doxorubicin from the beads demonstrated a controlled release via ionic exchange. Some formulations exhibited an increase in size and release of drug in the presence of a reducing agent, and therefore demonstrated the ability to respond to an in vitro reducing environment.

Investigation of the structural requirements of K-Ras(G12D) selective inhibitory peptide KRpep-2d using alanine scans and cysteine bridging

A structure-activity relationship study of a K-Ras(G12D) selective inhibitory cyclic peptide, KRpep-2d was performed. Alanine scanning of KRpep-2d focusing on the cyclic moiety showed that Leu⁷, Ile⁹, and Asp¹² are the key elements for K-Ras(G12D) selective inhibition of KRpep-2d. The cysteine bridging was also examined to identify the stable analog of KRpep-2d under reductive conditions. As a result, the KRpep-2d analog (12) including mono-methylene bridging showed potent K-Ras(G12D) selective inhibition in both the presence and the absence of dithiothreitol. This means that mono-methylene bridging is an effective strategy to obtain a reduction-resistance analog of parent disulfide cyclic peptides. Peptide 12 inhibited proliferation of K-Ras(G12D)-driven cancer cells significantly. These results gave valuable information for further optimization of KRpep-2d to provide novel anti-cancer drug candidates targeting the K-Ras(G12D) mutant.