Efficient Shielding of Polyplexes Using Heterotelechelic Polysarcosines

Degradable Poly(amino acid) Vesicles Modulate DNA-Induced Inflammation after Traumatic Brain Injury

Following brain trauma, secondary injury from molecular and cellular changes causes progressive cerebral tissue damage. Acute/chronic neuroinflammation following traumatic brain injury (TBI) is a key player in the development of secondary injury. Rapidly elevated cell-free DNAs (cfDNAs) due to cell death could lead to production of inflammatory cytokines that aggravate TBI. Herein, we designed poly(amino acid)-based cationic nanoparticles (cNPs) and applied them intravenously in a TBI mice model with the purpose of scavenging cfDNA in the brain and suppressing the acute inflammation. In turn, these cNPs could effectively eliminate endogenous cfDNA, inhibit excessive activation of inflammation, and promote neural functional recovery.

Directing the Way-Receptor and Chemical Targeting Strategies for Nucleic Acid Delivery

Nucleic acid therapeutics have shown great potential for the treatment of numerous diseases, such as genetic disorders, cancer and infections. Moreover, they have been successfully used as vaccines during the COVID-19 pandemic. In order to unfold full therapeutical potential, these nano agents have to overcome several barriers. Therefore, directed transport to specific tissues and cell types remains a central challenge to receive carrier systems with enhanced efficiency and desired biodistribution profiles. Active targeting strategies include receptor-targeting, mediating cellular uptake based on ligand-receptor interactions, and chemical targeting, enabling cell-specific delivery as a consequence of chemically and structurally modified carriers. With a focus on synthetic delivery systems including polyplexes, lipid-based systems such as lipoplexes and lipid nanoparticles, and direct conjugates optimized for various types of nucleic acids (DNA, mRNA, siRNA, miRNA, oligonucleotides), we highlight recent achievements, exemplified by several nucleic acid drugs on the market, and discuss challenges for targeted delivery to different organs such as brain, eye, liver, lung, spleen and muscle in vivo.

Engineering poly- and micelleplexes for nucleic acid delivery - A reflection on their endosomal escape

For the longest time, the field of nucleic acid delivery has remained skeptical whether or not polycationic drug carrier systems would ever make it into clinical practice. Yet, with the disclosure of patents on polyethyleneimine-based RNA carriers through leading companies in the field of nucleic acid therapeutics such as BioNTech SE and the progress in clinical studies beyond phase I trials, this aloofness seems to regress. As one of the most striking characteristics of polymer-based vectors, the extraordinary tunability can be both a blessing and a curse. Yet, knowing about the adjustment screws and how they impact the performance of the drug carrier provides the formulation scientist committed to its development with a head start. Here, we equip the reader with a toolbox - a toolbox that should advise and support the developer to conceptualize a cutting-edge poly- or micelleplex system for the delivery of therapeutic nucleic acids; to be specific, to engineer the vector towards maximum endosomal escape performance at minimum toxicity. Therefore, after briefly sketching the boundary conditions of polymeric vector design, we will dive into the topic of endosomal trafficking. We will not only discuss the most recent knowledge of the endo-lysosomal compartment but further depict different hypotheses and mechanisms that facilitate the endosomal escape of polyplex systems. Finally, we will combine the different facets introduced in the previous chapters with the fundamental building blocks of polymer vector design and evaluate the advantages and drawbacks. Throughout the article, a particular focus will be placed on cellular peculiarities, not only as an additional barrier, but also to give inspiration to how such cell-specific traits might be capitalized on.

Transferrin Receptor Targeted Polyplexes Completely Comprised of Sequence-Defined Components

Human transferrin protein (Tf) modified polyplexes have already displayed encouraging potential for receptor-mediated nucleic acid delivery into tumors. The use of a blood-derived targeting protein and polydisperse macromolecular cationic subunits however presents a practical challenge for pharmaceutical grade production. Here, Tf receptor (TfR) targeted small interfering RNA (siRNA) polyplexes are designed that are completely composed of synthetic, monodisperse, and sequence-defined subunits generated by solid-phase supported synthesis. An optimized cationizable lipo-oligoaminoamide (lipo-OAA) is used for siRNA core polyplex formation, and a retro-enantio peptide (reTfR) attached via a monodisperse polyethylene glycol (PEG) spacer via click chemistry is applied for targeting. Improved gene silencing is demonstrated in TfR-expressing KB and DU145 cells. Analogous plasmid DNA (pDNA) polyplexes are successfully used for receptor-mediated gene delivery in TfR-rich K562 cells and Neuro2a cells. Six lipo-OAAs differing in their lipidic domain and redox-sensitive attachment of lipid residues are tested in order to evaluate the impact of core polyplex stability on receptor-dependent gene transfer.

Thermostability, Tunability, and Tenacity of RNA as Rubbery Anionic Polymeric Materials in Nanotechnology and Nanomedicine-Specific Cancer Targeting with Undetectable Toxicity

RNA nanotechnology is the bottom-up self-assembly of nanometer-scale architectures, resembling LEGOs, composed mainly of RNA. The ideal building material should be (1) versatile and controllable in shape and stoichiometry, (2) spontaneously self-assemble, and (3) thermodynamically, chemically, and enzymatically stable with a long shelf life. RNA building blocks exhibit each of the above. RNA is a polynucleic acid, making it a polymer, and its negative-charge prevents nonspecific binding to negatively charged cell membranes. The thermostability makes it suitable for logic gates, resistive memory, sensor set-ups, and NEM devices. RNA can be designed and manipulated with a level of simplicity of DNA while displaying versatile structure and enzyme activity of proteins. RNA can fold into single-stranded loops or bulges to serve as mounting dovetails for intermolecular or domain interactions without external linking dowels. RNA nanoparticles display rubber- and amoeba-like properties and are stretchable and shrinkable through multiple repeats, leading to enhanced tumor targeting and fast renal excretion to reduce toxicities. It was predicted in 2014 that RNA would be the third milestone in pharmaceutical drug development. The recent approval of several RNA drugs and COVID-19 mRNA vaccines by FDA suggests that this milestone is being realized. Here, we review the unique properties of RNA nanotechnology, summarize its recent advancements, describe its distinct attributes inside or outside the body and discuss potential applications in nanotechnology, medicine, and material science.

Artificial peptides for antitumoral siRNA delivery

Intracellular delivery has been critical for the success of siRNA and related therapeutic nucleic acids. Improvement of delivery carriers will positively influence the efficacy of future nanomedicines. Our strategy for optimizing siRNA nanocarriers focuses on a bioinspired sequence-defined process including (i) identification of artificial amino acids active in specific delivery steps, (ii) assembly into defined sequences by solid phase-assisted synthesis (SPS), and (iii) screening for siRNA delivery, selection of top candidates and understanding structure-activity relations, followed by (iv) sequence variation for the next round of carrier selection. In the current review, our experience with this artificial peptide evolution in tumor-directed siRNA delivery is addressed. The medium-sized oligoaminoamides show better biological compatibility and can be functionalized to meet the requirements of siRNA delivery, such as formation of stable nanoparticles, shielding against proteins in the bloodstream, targeting into tumor tissue, and intracellular siRNA release in bioactive form.

Polymeric delivery systems for nucleic acid therapeutics: Approaching the clinic

Gene therapy using nucleic acids has many clinical applications for the treatment of diseases with a genetic origin as well as for the development of innovative vaccine formulations. Since nucleic acids in their free form are rapidly degraded by nucleases present in extracellular matrices, have poor pharmacokinetics and hardly pass cellular membranes, carrier systems are required. Suitable carriers that protect the nucleic acid payload against enzymatic attack, prolong circulation time after systemic administration and assist in cellular binding and internalization are needed to develop nucleic acid based drug products. Viral vectors have been investigated and are also clinically used as delivery vehicles. However, some major drawbacks are associated with their use. Therefore there has been substantial attention on the use of non-viral carrier systems based on cationic lipids and polymers. This review focuses on the properties of polymer-based nucleic acid formulations, also referred as polyplexes. Different polymeric systems are summarized, and the cellular barriers polyplexes encounter and ways to tackle these are discussed. Finally attention is given to the clinical status of non-viral nucleic acid formulations.

Optimizing synthetic nucleic acid and protein nanocarriers: The chemical evolution approach

Optimizing synthetic nanocarriers is like searching for a needle in a haystack. How to find the most suitable carrier for intracellular delivery of a specified macromolecular nanoagent for a given disease target location? Here, we review different synthetic 'chemical evolution' strategies that have been pursued. Libraries of nanocarriers have been generated either by unbiased combinatorial chemistry or by variation and novel combination of known functional delivery elements. As in natural evolution, definition of nanocarriers as sequences, as barcode or design principle, may fuel chemical evolution. Screening in appropriate test system may not only provide delivery candidates, but also a refined understanding of cellular delivery including novel, unpredictable mechanisms. Combined with rational design and computational algorithms, candidates can be further optimized in subsequent evolution cycles into nanocarriers with improved safety and efficacy. Optimization of nanocarriers differs for various cargos, as illustrated for plasmid DNA, siRNA, mRNA, proteins, or genome-editing nucleases.

Hyaluronate siRNA nanoparticles with positive charge display rapid attachment to tumor endothelium and penetration into tumors

A cationizable sequence-defined lipo-oligoaminoamide (lipo-OAA) conferring stable assembly of siRNA into ~200 nm sized complexes contains an N-terminal azidolysine for covalent coating of formed nanoparticles with dibenzocyclooctyne-amine (DBCO)-modified hyaluronic acid (HA). Depending on the applied equivalents of DBCO-HA, stable nanoparticles with either cationic or anionic surface charge can be formed. The unmodified and two types of covalent HA-modified siRNA nanoparticles differ in their biological characteristics. Both types of HA coated siRNA complexes show an enhanced cellular uptake over uncoated complexes and facilitate efficient gene silencing, but differ in intracellular uptake pathways and distribution. Upon intravenous administration in mice, beyond our expectation and in contrast to the in vitro findings, only the cationic HA nanoparticles but neither the non-coated cationic nor the anionic HA complexes were able to target subcutaneous Huh 7 tumors and exert potent (78%) gene silencing. The favorable and very fast accumulation of cationic HA nanoparticles was confirmed in another subcutaneous tumor model. As evidenced by 3D nanoparticle distribution within Huh 7 tumors evaluated at early time points of 5 min and 45 min, only the cationic HA-based nanoparticles rapidly attach to the tumor endothelium and subsequently penetrate into tumor, in contrast to the analogous anionic HA coated or the cationic non-coated formulation.

Non-Viral Targeted Nucleic Acid Delivery: Apply Sequences for Optimization

In nature, genomes have been optimized by the evolution of their nucleic acid sequences. The design of peptide-like carriers as synthetic sequences provides a strategy for optimizing multifunctional targeted nucleic acid delivery in an iterative process. The optimization of sequence-defined nanocarriers differs for different nucleic acid cargos as well as their specific applications. Supramolecular self-assembly enriched the development of a virus-inspired non-viral nucleic acid delivery system. Incorporation of DNA barcodes presents a complementary approach of applying sequences for nanocarrier optimization. This strategy may greatly help to identify nucleic acid carriers that can overcome pharmacological barriers and facilitate targeted delivery in vivo. Barcode sequences enable simultaneous evaluation of multiple nucleic acid nanocarriers in a single test organism for in vivo biodistribution as well as in vivo bioactivity.

Synthesis and Characterization of Dendrimer-Based Polysarcosine Star Polymers: Well-Defined, Versatile Platforms Designed for Drug-Delivery Applications

This paper describes the synthesis of star polymers designed for future drug-delivery applications. A generation-5 lysine dendrimer was used as a macroinitiator for the ring-opening polymerization of the sarcosine N-carboxyanhydride monomer to produce 32-arm star polymers with narrow molar mass distributions and desirable hydrodynamic size control. Fluorescent dye-labeled polymers were dosed in mice to measure plasma pharmacokinetics. Long circulation times were observed, representing ideal properties for biophysical targeting of tumors. In vivo efficacy of one of these star polymers conjugated to the therapeutic molecule SN-38 was evaluated in mice bearing SW620 xenografted tumors to demonstrate high antitumor activity and low body weight loss compared to the SN-38 prodrug irinotecan and this shows the potential of these delivery systems. As a further build, we demonstrated that these star polymers can be easily chain-end-functionalized with useful chemical moieties, giving opportunities for future receptor-targeting strategies. Finally, we describe the synthetic advantages of these star polymers that make them attractive from a pharmaceutical manufacturing perspective and report characterization of the polymers with a variety of techniques.

Multifunctional Cationic PeptoStars as siRNA Carrier: Influence of Architecture and Histidine Modification on Knockdown Potential

RNA interference provides enormous potential for the treatment of several diseases, including cancer. Nevertheless, successful therapies based on siRNA require overcoming various challenges, such as poor pharmacokinetic characteristics of the small RNA molecule and inefficient cytosolic accumulation. In this respect, the development of functional siRNA carrier systems is a major task in biomedical research. To provide such a desired system, the synthesis of 3-arm and 6-arm PeptoStars is aimed for. The different branched polypept(o)idic architectures share a stealth-like polysarcosine corona for efficient shielding and a multifunctional polylysine core, which can be independently varied in size and functionality for siRNA complexation-, transport and intra cellular release. The special feature of star-like polypept(o)ides is in their uniform small size (<20 nm) and a core-shell structure, which implies a high stability and stealth-like properties and thus, they may combine long circulation times and a deep penetration of cancerous tissue. Initial toxicity and complement studies demonstrate well tolerated cationic PeptoStars with high complexation capability toward siRNA (N/P ratio up to 3:1), which can lead to potent RNAi for optimized systems. Here, the synthetic development of 3-arm and 6-arm polypept(o)idic star polymers, their modification with endosomolytic moieties, and first in vitro insights on RNA interference are reported on.

Coordinative Binding of Polymers to Metal-Organic Framework Nanoparticles for Control of Interactions at the Biointerface

Metal-organic framework nanoparticles (MOF NPs) are of growing interest in diagnostic and therapeutic applications, and due to their hybrid nature, they display enhanced properties compared to more established nanomaterials. The effective application of MOF NPs, however, is often hampered by limited control of their surface chemistry and understanding of their interactions at the biointerface. Using a surface coating approach, we found that coordinative polymer binding to Zr- fum NPs is a convenient way for peripheral surface functionalization. Different polymers with biomedical relevance were assessed for the ability to bind to the MOF surface. Carboxylic acid and amine containing polymers turned out to be potent surface coatings and a modulator replacement reaction was identified as the underlying mechanism. The strong binding of polycarboxylates was then used to shield the MOF surface with a double amphiphilic polyglutamate-polysarcosine block copolymer, which resulted in an exceptional high colloidal stability of the nanoparticles. The effect of polymer coating on interactions at the biointerface was tested with regard to cellular association and protein binding, which has, to the best of our knowledge, never been discussed in literature for functionalized MOF NPs. We conclude that the applied approach enables a high degree of chemical surface confinement, which could be used as a universal strategy for MOF NP functionalization. In this way, the physicochemical properties of MOF NPs could be tuned, which allows for control over their behavior in biological systems.

Click-Shielded and Targeted Lipopolyplexes

Lipopolyplexes present well-established nucleic acid carriers assembled from sequence-defined cationic lipo-oligomers and DNA or RNA. They can be equipped with additional surface functionality, like shielding and targeting, in a stepwise assembly method using click chemistry. Here, we describe the synthesis of the required compounds, an azide-bearing lipo-oligomer structure and dibenzocyclooctyne (DBCO) click agents as well as the assembly of the compounds with siRNA into a surface-functionalized formulation. Both the lipo-oligomer and the DBCO-equipped shielding and targeting agents are produced by solid-phase synthesis (SPS). This enables for precise variation of all functional units, like variation in the amount of DBCO attachment sites or polyethylene glycol (PEG) length. Special cleavage conditions with only 5% trifluoroacetic acid (TFA) must be applied for the synthesis of the shielding and targeting agents due to acid lability of the DBCO unit. The two-step lipopolyplex assembly technique allows for separate optimization of the core and the shell of the formulation.

Poly-sarcosine and Poly(Ethylene-Glycol) Interactions with Proteins Investigated Using Molecular Dynamics Simulations

Nanoparticles coated with hydrophilic polymers often show a reduction in unspecific interactions with the biological environment, which improves their biocompatibility. The molecular determinants of this reduction are not very well understood yet, and their knowledge may help improving nanoparticle design. Here we address, using molecular dynamics simulations, the interactions of human serum albumin, the most abundant serum protein, with two promising hydrophilic polymers used for the coating of therapeutic nanoparticles, poly(ethylene-glycol) and poly-sarcosine. By simulating the protein immersed in a polymer-water mixture, we show that the two polymers have a very similar affinity for the protein surface, both in terms of the amount of polymer adsorbed and also in terms of the type of amino acids mainly involved in the interactions. We further analyze the kinetics of adsorption and how it affects the polymer conformations. Minor differences between the polymers are observed in the thickness of the adsorption layer, that are related to the different degree of flexibility of the two molecules. In comparison poly-alanine, an isomer of poly-sarcosine known to self-aggregate and induce protein aggregation, shows a significantly larger affinity for the protein surface than PEG and PSar, which we show to be related not to a different patterns of interactions with the protein surface, but to the different way the polymer interacts with water.