Histidine-rich stabilized polyplexes for cMet-directed tumor-targeted gene transfer

In Silico Screening Accelerates Nanocarrier Design for Efficient mRNA Delivery

Lipidic nanocarriers are a broad class of lipid-based vectors with proven potential for packaging and delivering emerging nucleic acid therapeutics. An important early step in the clinical development cycle is large-scale screening of diverse formulation libraries to assess particle quality and payload delivery efficiency. Due to the size of the screening space, this process can be both costly and time-consuming. To address this, computational models capable of predicting clinically relevant physio-chemical properties of dendrimer-lipid nanocarriers, along with their mRNA payload delivery efficiency in human cells are developed. The models are then deployed on a large theoretical nanocarrier pool consisting of over 4.5 million formulations. Top predictions are synthesised for validation using cell-based assays, leading to the discovery of a high quality, high performing, candidate. The methods reported here enable rapid, high-throughput, in silico pre-screening for high-quality candidates, and have great potential to reduce the cost and time required to bring mRNA therapies to the clinic.

GalNAc- or Mannose-PEG-Functionalized Polyplexes Enable Effective Lectin-Mediated DNA Delivery

A cationic, dendrimer-like oligo(aminoamide) carrier with four-arm topology based on succinoyl tetraethylene pentamine and histidines, cysteines, and N-terminal azido-lysines was screened for plasmid DNA delivery on various cell lines. The incorporated azides allow modification with various shielding agents of different polyethylene glycol (PEG) lengths and/or different ligands by copper-free click reaction, either before or after polyplex formation. Prefunctionalization was found to be advantageous over postfunctionalization in terms of nanoparticle formation, stability, and efficacy. A length of 24 ethylene oxide repetition units and prefunctionalization of ≥50% of azides per carrier promoted optimal polyplex shielding. PEG shielding resulted in drastically reduced DNA transfer, which could be successfully restored by active lectin targeting via novel GalNAc or mannose ligands, enabling enhanced receptor-mediated endocytosis of the carrier system. The involvement of the asialoglycoprotein receptor (ASGPR) in the uptake of GalNAc-functionalized polyplexes was confirmed in the ASGPR-positive hepatocarcinoma cell lines HepG2 and Huh7. Mannose-modified polyplexes showed superior cellular uptake and transfection efficacy compared to unmodified and shielded polyplexes in mannose-receptor-expressing dendritic cell-like DC2.4 cells.

Nucleic acid delivery to retinal cells using lipopeptides as a potential tool towards ocular gene therapies

We evaluated the use of lipopeptides capable to bind to nucleic acids towards plasmid DNA (pDNA) delivery. The investigations were particularly focused on arising retinal pigment epithelial cells (ARPE-19) as motivated by the considerable number of ocular disorders linked to gene aberrations. The lipopeptides comprised the artificial oligoamino acid succinyl-tetraethylene pentamine (Stp) as well as incorporated lysines, histidines, cysteines, fatty acids, and tyrosine trimers. Regardless of the structural differences, the lipopeptides demonstrated to efficiently condense pDNA at nitrogen-to-phosphate molar ratio (N/P) ≥ 6. Spheric nanoparticles were observed by cryo-TEM and dynamic light scattering determined hydrodynamic sizes ranging from 50 to 130 nm. The biological assays evidenced highly efficient pDNA delivery with a lower degree of cytotoxicity compared to the well-known transfecting agent linear polyethylenimine (LPEI). Although more efficient than LPEI, cysteine-containing carriers were demonstrated to be less efficient than the other counterparts possibly due to exceeding polyplex stabilization via disulfide cross links, which could hamper pDNA unpacking at the target site. Therefore, clearly a balance between complex stability and cargo release should be taken into account to optimize the transfection efficiency of the non-viral vectors. The gene transfer activity in ARPE-19 cells suggests the applicability of this kind of carrier for ocular treatments based on retinal gene delivery.

High-resolution bioenergetics correlates the length of continuous protonatable diaminoethane motif of four-armed oligo(ethanamino)amide transfectants to cytotoxicity

Recent clinical success with Onpattro and cationic ionizable lipid nanoparticle-based mRNA vaccines has rejuvenated research in the design and engineering of broader synthetic cationic vectors for nucleic acid compaction and transfection. However, perturbation of metabolic processes and cytotoxicity are still of concern with synthetic cationic vectors. Here, through an integrated bioenergetic and biomembrane integrity probing in three different human cell lines we reveal the dynamic effect of a library of sequence-defined four-arm oligo(ethanamino)amide transfectant on cell homeostasis, and identify metabolically safe building units over wide concentration ranges. The results show differential effects of the oligo(ethanamino)amide structure of comparable molecular weight on cell energetics. The severity of polycation effect on bioenergetic crisis follows with the length of continuous protonatable diaminoethane motif in the ascending order of glutaryl-triethylene tetramine, succinyl-tetraethylene pentamine and succinyl-pentaethylene hexamine. We further identify oligomeric structures that do not induce bioenergetic crisis even at high concentrations. Finally, transfection studies with a library of polyplexes carrying a reporter gene show no correlation between transfection efficiency and cytotoxicity. These observations demonstrate the usefulness of integrated high-resolution respirometry and plasma membrane integrity probing as a highly sensitive medium-throughput screening strategy for identification and selection of safe building units for transfectant engineering.

Harnessing Peptide-Functionalized Multivalent Gold Nanorods for Promoting Enhanced Gene Silencing and Managing Breast Cancer Metastasis

Small interfering RNA (siRNA) has become the cornerstone against undruggable targets and for managing metastatic breast cancer. However, an effective gene silencing approach is faced with a major challenge due to the delivery problem. In our present study, we have demonstrated efficient siRNA delivery, superior gene silencing, and inhibition of metastasis in triple-negative breast cancer cells (MDA-MB-231) using rod-shaped (aspect ratio: 4) multivalent peptide-functionalized gold nanoparticles and compared them to monovalent free peptide doses. Multivalency is a new concept in biology, and tuning the physical parameters of multivalent nanoparticles can enhance gene silencing and antitumor efficacy. We explored the effect of the multivalency of shape- and size-dependent peptide-functionalized gold nanoparticles in siRNA delivery. Our study demonstrates that peptide functionalization leads to reduced toxicity of the nanoparticles. Such designed peptide-functionalized nanorods also demonstrate antimetastatic efficacy in Notch1-silenced cells by preventing EMT progression in vitro. We have shown siRNA delivery in the hard-to-transfect primary cell line HUVEC and also demonstrated that the Notch1-silenced MDA-MB-231 cell line has failed to form nanobridge-mediated foci with the HUVEC in the co-culture of HUVEC and MDA-MB-231, which promote metastasis. This antimetastatic effect is further checked in a xenotransplant in vivo zebrafish model. In vivo studies also suggest that our designed nanoparticles mediated inhibition of micrometastasis due to silencing of the Notch1 gene. The outcome of our study highlights that the structure-activity relationship of multifunctional nanoparticles can be harnessed to modulate their biological activity.

Efficient Transfection via an Unexpected Mechanism by Near Neutral Polypiperazines with Tailored Response to Endosomal pH

Cationic pH-responsive polymers promise to overcome critical challenges in cellular delivery. Ideally, the polymers become selectively charged along the endosomal pathway disturbing only the local membrane and avoiding unintended interactions or cytotoxic side effects at physiological conditions. Polypiperazines represent a novel, hydrophilic class of pH-responsive polymers whose response can be tuned within the relevant pH range (5-7.4). The authors discovered that the polypiperazines are effectively binding plasmid DNA (pDNA) and demonstrate high efficiency in transfection. By design of experiments (DoE), a wide parameter space (pDNA and polymer concentration) is screened to identify the range of effective concentrations for transfection. An isopropyl modified polypiperazine is highly efficient over a wide range of concentrations outperforming linear polyethylenimine (l-PEI, 25 kDa) in regions of low N*/P ratios. A quantitative polymerase chain reaction (qPCR) surprisingly revealed that the pDNA within the piperazine-based polyplexes can be amplified in contrast to polyplexes based on l-PEI. The pDNA must therefore be more accessible and bound differently than for other known transfection polymers. Considering the various opportunities to further optimize their structure, polypiperazines represent a promising platform for designing effective soluble polymeric vectors, which are charge-neutral at physiological conditions.

The sodium iodide symporter (NIS) as theranostic gene: its emerging role in new imaging modalities and non-viral gene therapy

Cloning of the sodium iodide symporter (NIS) in 1996 has provided an opportunity to use NIS as a powerful theranostic transgene. Novel gene therapy strategies rely on image-guided selective NIS gene transfer in non-thyroidal tumors followed by application of therapeutic radionuclides. This review highlights the remarkable progress during the last two decades in the development of the NIS gene therapy concept using selective non-viral gene delivery vehicles including synthetic polyplexes and genetically engineered mesenchymal stem cells. In addition, NIS is a sensitive reporter gene and can be monitored by high resolution PET imaging using the radiotracers sodium [¹²⁴I]iodide ([¹²⁴I]NaI) or [¹⁸F]tetrafluoroborate ([¹⁸F]TFB). We performed a small preclinical PET imaging study comparing sodium [¹²⁴I]iodide and in-house synthesized [¹⁸F]TFB in an orthotopic NIS-expressing glioblastoma model. The results demonstrated an improved image quality using [¹⁸F]TFB. Building upon these results, we will be able to expand the NIS gene therapy approach using non-viral gene delivery vehicles to target orthotopic tumor models with low volume disease, such as glioblastoma.

Trial registration not applicable.

Targeting nucleic acid-based therapeutics to tumors: Challenges and strategies for polyplexes

The current medical reality of cancer gene therapy is reflected by more than ten approved products on the global market, including oncolytic and other viral vectors and CAR T-cells as ex vivo gene-modified cell therapeutics. The development of synthetic antitumoral nucleic acid therapeutics has been proceeding at a lower but steady pace, fueled by a plethora of alternative nucleic acid platforms (from various antisense oligonucleotides, siRNA, microRNA, lncRNA, sgRNA, to larger mRNA and DNA) and several classes of physical and chemical delivery technologies. This review summarizes the challenges and strategies for tumor-targeted nucleic acid delivery. Focusing primarily on polyplexes (polycation complexes) as nanocarriers, delivery options across multiple barriers into tumor cells are illustrated.

Dynamic mRNA polyplexes benefit from bioreducible cleavage sites for in vitro and in vivo transfer

Currently, messenger RNA (mRNA)-based lipid nanoparticle formulations revolutionize the clinical field. Cationic polymer-based complexes (polyplexes) represent an alternative compound class for mRNA delivery. After establishing branched polyethylenimine with a succinylation degree of 10% (succPEI) as highly effective positive mRNA transfection standard, a diverse library of PEI-like peptides termed sequence-defined oligoaminoamides (OAAs) was screened for mRNA delivery. Notably, sequences, which had previously been identified as potent plasmid DNA (pDNA) or small-interfering RNA (siRNA) carriers, displayed only moderate mRNA transfection activity. A second round of screening combined the cationizable building block succinoyl tetraethylene pentamine and histidines for endosomal buffering, tyrosine tripeptides and various fatty acids for mRNA polyplex stabilization, as well as redox-sensitive units for programmed intracellular release. For the tested OAA carriers, balancing of extracellular stability, endosomal lytic activity, and intracellular release capability was found to be of utmost importance for optimum mRNA transfection efficiency. OAAs with T-shape topology containing two oleic acids as well-stabilizing fatty acids, attached via a dynamic bioreducible building block, displayed superior activity with up to 1000-fold increased transfection efficiency compared to their non-reducible analogs. In the absence of the dynamic linkage, incorporation of shorter less stabilizing fatty acids could only partly compensate for mRNA delivery. Highest GFP expression and the largest fraction of transfected cells (96%) could be detected for the bioreducible OAA with incorporated histidines and a dioleoyl motif, outperforming all other tested carriers as well as the positive control succPEI. The good in vitro performance of the dynamic lead structure was verified in vivo upon intratracheal administration of mRNA complexes in mice.

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.

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.

Optimizing pDNA Lipo-polyplexes: A Balancing Act between Stability and Cargo Release

When optimizing nanocarriers, structural motifs that are beneficial for the respective type of cargo need to be identified. Here, succinoyl tetraethylene pentamine (Stp)-based lipo-oligoaminoamides (OAAs) were optimized for the delivery of plasmid DNA (pDNA). Structural variations comprised saturated fatty acids with chain lengths between C2 and C18 and terminal cysteines as units promoting nanoparticle stabilization, histidines for endosomal buffering, and disulfide building blocks for redox-sensitive release. Biophysical and tumor cell culture screening established clear-cut relationships between lipo-OAAs and characteristics of the formed pDNA complexes. Based on the optimized alternating Stp-histidine backbones, lipo-OAAs containing fatty acids with chain lengths around C6 to C10 displayed maximum gene transfer with around 500-fold higher gene expression than that of C18 lipo-OAA analogues. Promising lipo-OAAs, however, showed only moderate in vivo efficiency. In vitro testing in 90% full serum, revealing considerable inhibition of lytic and gene-transfer activity, was found as a new screening model predictive for intravenous applications in vivo.

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.

Peptides as a material platform for gene delivery: Emerging concepts and converging technologies

Successful gene therapies rely on methods that safely introduce DNA into target cells and enable subsequent expression of proteins. To that end, peptides are an attractive materials platform for DNA delivery, facilitating condensation into nanoparticles, delivery into cells, and subcellular release to enable protein expression. Peptides are programmable materials that can be designed to address biocompatibility, stability, and subcellular barriers that limit efficiency of non-viral gene delivery systems. This review focuses on fundamental structure-function relationships regarding peptide design and their impact on nanoparticle physical properties, biologic activity, and biocompatibility. Recent peptide technologies utilize multi-dimensional structures, non-natural chemistries, and combinations of peptides with lipids to achieve desired properties and efficient transfection. Advances in DNA cargo design are also presented to highlight further opportunities for peptide-based gene delivery. Modern DNA designs enable prolonged expression compared to traditional plasmids, providing an additional component that can be synergized with peptide carriers for improved transfection. Peptide transfection systems are poised to become a flexible and efficient platform incorporating new chemistries, functionalities, and improved DNA cargos to usher in a new era of gene therapy.

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.

The Multifaceted Histidine-Based Carriers for Nucleic Acid Delivery: Advances and Challenges

Histidines incorporated into carriers of nucleic acids may enhance the extracellular stability of the nanoparticle, yet aid in the intracellular disruption of the nanoparticle, enabling the release of the nucleic acid. Moreover, protonation of histidines in the endosomes may result in endosomal swelling with subsequent lysis. These properties of histidine are based on its five-member imidazole ring in which the two nitrogen atoms may form hydrogen bonds or act as a base in acidic environments. A wide variety of carriers have integrated histidines or histidine-rich domains, which include peptides, polyethylenimine, polysaccharides, platform delivery systems, viral phages, mesoporous silica particles, and liposomes. Histidine-rich carriers have played key roles in our understanding of the stability of nanocarriers and the escape of the nucleic acids from endosomes. These carriers show great promise and offer marked potential in delivering plasmids, siRNA, and mRNA to their intracellular targets.

Anti-vimentin, anti-TUFM, anti-NAP1L1 and anti-DPYSL2 nanobodies display cytotoxic effect and reduce glioblastoma cell migration

Background:

Glioblastoma is a particularly common and very aggressive primary brain tumour. One of the main causes of therapy failure is the presence of glioblastoma stem cells that are resistant to chemotherapy and radiotherapy, and that have the potential to form new tumours. This study focuses on validation of eight novel antigens, TRIM28, nucleolin, vimentin, nucleosome assembly protein 1-like 1 (NAP1L1), mitochondrial translation elongation factor (EF-TU) (TUFM), dihydropyrimidinase-related protein 2 (DPYSL2), collapsin response mediator protein 1 (CRMP1) and Aly/REF export factor (ALYREF), as putative glioblastoma targets, using nanobodies.

Methods:

Expression of these eight antigens was analysed at the cellular level by qPCR, ELISA and immunocytochemistry, and in tissues by immunohistochemistry. The cytotoxic effects of the nanobodies were determined using AlamarBlue and water-soluble tetrazolium tests. Annexin V/propidium iodide tests were used to determine apoptotsis/necrosis of the cells in the presence of the nanobodies. Cell migration assays were performed to determine the effects of the nanobodies on cell migration.

Results:

NAP1L1 and CRMP1 were significantly overexpressed in glioblastoma stem cells in comparison with astrocytes and glioblastoma cell lines at the mRNA and protein levels. Vimentin, DPYSL2 and ALYREF were overexpressed in glioblastoma cell lines only at the protein level. The functional part of the study examined the cytotoxic effects of the nanobodies on glioblastoma cell lines. Four of the nanobodies were selected in terms of their specificity towards glioblastoma cells and protein overexpression: anti-vimentin (Nb79), anti-NAP1L1 (Nb179), anti-TUFM (Nb225) and anti-DPYSL2 (Nb314). In further experiments to optimise the nanobody treatment schemes, to increase their effects, and to determine their impact on migration of glioblastoma cells, the anti-TUFM nanobody showed large cytotoxic effects on glioblastoma stem cells, while the anti-vimentin, anti-NAP1L1 and anti-DPYSL2 nanobodies were indicated as agents to target mature glioblastoma cells. The anti-vimentin nanobody also had significant effects on migration of mature glioblastoma cells.

Conclusion:

Nb79 (anti-vimentin), Nb179 (anti-NAP1L1), Nb225 (anti-TUFM) and Nb314 (anti-DPYSL2) nanobodies are indicated for further examination for cell targeting. The anti-TUFM nanobody, Nb225, is particularly potent for inhibition of cell growth after long-term exposure of glioblastoma stem cells, with minor effects seen for astrocytes. The anti-vimentin nanobody represents an agent for inhibition of cell migration.

Nanotechnology approaches in the current therapy of skin cancer

Skin cancer is a high burden disease with a high impact on global health. Conventional therapies have several drawbacks; thus, the development of effective therapies is required. In this context, nanotechnology approaches are an attractive strategy for cancer therapy because they enable the efficient delivery of drugs and other bioactive molecules to target tissues with low toxic effects. In this review, nanotechnological tools for skin cancer will be summarized and discussed. First, pathology and conventional therapies will be presented, followed by the challenges of skin cancer therapy. Then, the main features of developing efficient nanosystems will be discussed, and next, the most commonly used nanoparticles (NPs) described in the literature for skin cancer therapy will be presented. Subsequently, the use of NPs to deliver chemotherapeutics, immune and vaccine molecules and nucleic acids will be reviewed and discussed as will the combination of physical methods and NPs. Finally, multifunctional delivery systems to codeliver anticancer therapeutic agents containing or not surface functionalization will be summarized.

Tunable biomaterials from synthetic, sequence-controlled polymers

Polymeric biomaterials have many applications including therapeutic delivery vehicles, medical implants and devices, and tissue engineering scaffolds. Both naturally-derived and synthetic materials have successfully been used for these applications in the clinic. However, the increasing complexity of these applications requires materials with advanced properties, especially customizable or tunable materials with bioactivity. To address this issue, there have been recent efforts to better recapitulate the properties of natural materials using synthetic biomaterials composed of sequence-controlled polymers. Sequence control mimics the primary structure found in biopolymers, and in many cases, provides an extra handle for functionality in synthetic polymers. Here, we first review the advances in synthetic methods that have enabled sequence-controlled biomaterials on a relevant scale, and discuss strategies for choosing functional sequences from a biomaterials engineering context. Then, we highlight several recent studies that show strong impact of sequence control on biomaterial properties, including in vitro and in vivo behavior, in the areas of hydrogels, therapeutic materials, and novel applications such as molecular barcodes for medical devices. The role of sequence control in biomaterials properties is an emerging research area, and there remain many opportunities for investigation. Further study of this topic may significantly advance our understanding of bioactive or smart materials, as well as contribute design rules to guide the development of synthetic biomaterials for future applications in tissue engineering and regenerative medicine.

Dual-targeted NIS polyplexes-a theranostic strategy toward tumors with heterogeneous receptor expression

Tumor heterogeneity, within and between tumors, may have severe implications for tumor therapy, especially for targeted gene therapy, where single-targeted approaches often result in limited efficacy and therapy resistance. Polymer-formulated nonviral vectors provide a potent delivery platform for cancer therapy. To improve applicability for future clinical use in a broad range of patients and cancer types, a dual-targeting approach was performed. Synthetic LPEI-PEG2kDa-based polymer backbones were coupled to two tumor-specific peptide ligands GE11 (EGFR-targeting) and cMBP (cMET-targeting). The dual-targeting approach was used to deliver the theranostic sodium iodide symporter (NIS) gene to hepatocellular cancer. NIS as auspicious theranostic gene allows noninvasive imaging of functional NIS gene expression and effective anticancer radioiodide therapy. Enhanced tumor-specific transduction efficiency of dual-targeted polyplexes compared to single-targeted polyplexes was demonstrated in vitro using tumor cell lines with different EGFR and cMET expression and in vivo by 124I-PET-imaging. Therapeutic efficacy of the bispecific concept was mirrored by significantly reduced tumor growth and perfusion, which was associated with prolonged animal survival. In conclusion, the dual-targeting approach highlights the benefits of a bifunctional strategy for a future clinical translation of the bioimaging-based NIS-mediated radiotherapy allowing efficient targeting of heterogeneic tumors with variable receptor expression levels.

Peptide-grafted dextran vectors for efficient and high-loading gene delivery

Among various polymeric gene delivery systems, peptide-based vectors demonstrate great potential owing to their unique structure and properties, including flexibility; however, there is insufficient molecular understanding of the role and properties of amino acids as building blocks in gene delivery.

Histidine-Rich Cationic Cell-Penetrating Peptides for Plasmid DNA and siRNA Delivery

Amphipathic, pH-responsive, membrane-active peptides such as LAH4 and derivatives thereof have the ability to effectively deliver genes and small interfering RNA (siRNA) into mammalian cells. Their ability to bind and protect nucleic acids and then disrupt membranes when activated at low pH enables them to harness the endocytic machinery to deliver cargo efficiently and with low associated toxicity. This chapter describes protocols for the chemical synthesis of transfection peptides of the LAH4 family, complex formation with nucleic acids, and their use for the in vitro delivery of either plasmid DNA or siRNA into mammalian cell lines.

Combinatorial siRNA Polyplexes for Receptor Targeting

As synthetic small interfering RNA (siRNA) against antitumoral gene targets show promise for cancer treatment, different siRNA delivery systems have sparkled intense investigations. To develop tumor-specific carriers for cytosolic and systemic siRNA delivery, our laboratory has recently generated folate-conjugated targeted combinatorial siRNA polyplexes based on sequence-defined oligomer platform compatible with solid-phase-supported synthesis. These polyplexes presented efficient siRNA-mediated gene silencing in folate receptor-expressing tumors in vitro and in vivo. In this chapter, we provide a brief background on the formulation design and detailed protocols to evaluate polyplex formation, gene silencing efficiency, and receptor-directed cell killing in cancer cells using targeted combinatorial siRNA polyplexes.

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.

Solid-phase supported design of carriers for therapeutic nucleic acid delivery

Nucleic acid molecules are important therapeutic agents in the field of antisense oligonucleotide, RNA interference, and gene therapies. Since nucleic acids are not able to cross cell membranes and enter efficiently into cells on their own, the development of efficient, safe, and precise delivery systems is the crucial challenge for development of nucleic acid therapeutics. For the delivery of nucleic acids to their intracellular site of action, either the cytosol or the nucleus, several extracellular and intracellular barriers have to be overcome. Multifunctional carriers may handle the different special requirements of each barrier. The complexity of such macromolecules however poses a new hurdle in medical translation, which is the chemical production in reproducible and well-defined form. Solid-phase assisted synthesis (SPS) presents a solution for this challenge. The current review provides an overview on the design and SPS of precise sequence-defined synthetic carriers for nucleic acid cargos.

EGFR Targeting and Shielding of pDNA Lipopolyplexes via Bivalent Attachment of a Sequence-Defined PEG Agent

For successful nonviral gene delivery, cationic polymers are promising DNA carrier, which need to comprise several functionalities. The current work focuses on the postincorporation of epidermal growth factor receptor (EGFR) targeted PEGylation agents onto lipopolyplexes for pDNA delivery. T-shaped lipo-oligomers are previously found to be effective sequence-defined carriers for pDNA and siRNA. Here, the bis-oleoyl-oligoaminoethanamide 454 containing tyrosine trimer-cysteine ends is applied for complex formation with pDNA coding for luciferase or sodium iodide symporter (NIS). In a second step, the lipopolyplexes are modified via disulfide formation with sequence-defined monovalent or bivalent PEGylation agents containing one or two 3-nitro-2-pyridinesulfenyl (NPys)-activated cysteines, respectively. For targeting, the polyethylene glycol (PEG) agents comprise the EGFR targeting peptide GE11. In comparison of all transfection complexes, 454 lipopolyplexes modified with the bidentate PEG-GE11 agent show the best, EGFR-dependent uptake as well as luciferase and NIS gene expression into receptor-positive tumor cells.

Antitumoral Cascade-Targeting Ligand for IL-6 Receptor-Mediated Gene Delivery to Glioma

The effective treatment of glioma is largely hindered by the poor transfer of drug delivery systems across the blood-brain barrier (BBB) and the difficulty in distinguishing healthy and tumorous cells. In this work, for the first time, an interleukin-6 receptor binding I₆P₇ peptide was exploited as a cascade-targeting ligand in combination with a succinoyl tetraethylene pentamine (Stp)-histidine oligomer-based nonviral gene delivery system (I₆P₇-Stp-His/DNA). The I₆P₇ peptide provides multiple functions, including the cascade-targeting potential represented by a combined BBB-crossing and subsequent glioma-targeting ability, as well as a direct tumor-inhibiting effect. I₆P₇-Stp-His/DNA nanoparticles (NPs) mediated higher gene expression in human glioma U87 cells than in healthy human astrocytes and a deeper penetration into glioma spheroids than scrambled peptide-modified NPs. Transport of I₆P₇-modified, but not the control, NPs across the BBB was demonstrated in vitro in a transwell bEnd.3 cell model resulting in transfection of underlying U87 cells and also in vivo in glioma-bearing mice. Intravenous administration of I₆P₇-Stp-His/plasmid DNA (pDNA)-encoding inhibitor of growth 4 (pING4) significantly prolonged the survival time of orthotopic U87 glioma-bearing mice. The results denote that I₆P₇ peptide is a roborant cascade-targeting ligand, and I₆P₇-modified NPs might be exploited for efficient glioma therapy.

Influence of Defined Hydrophilic Blocks within Oligoaminoamide Copolymers: Compaction versus Shielding of pDNA Nanoparticles

Cationic polymers are promising components of the versatile platform of non-viral nucleic acid (NA) delivery agents. For a successful gene delivery system, these NA vehicles need to comprise several functionalities. This work focuses on the modification of oligoaminoamide carriers with hydrophilic oligomer blocks mediating nanoparticle shielding potential, which is necessary to prevent aggregation or dissociation of NA polyplexes in vitro, and hinder opsonization with blood components in vivo. Herein, the shielding agent polyethylene glycol (PEG) in three defined lengths (12, 24, or 48 oxyethylene repeats) is compared with two peptidic shielding blocks composed of four or eight repeats of sequential proline-alanine-serine (PAS). With both types of shielding agents, we found opposing effects of the length of hydrophilic segments on shielding and compaction of formed plasmid DNA (pDNA) nanoparticles. Two-arm oligoaminoamides with 37 cationizable nitrogens linked to 12 oxyethylene units or four PAS repeats resulted in very compact 40⁻50 nm pDNA nanoparticles, whereas longer shielding molecules destabilize the investigated polyplexes. Thus, the balance between sufficiently shielded but still compact and stable particles can be considered a critical optimization parameter for non-viral nucleic acid vehicles based on hydrophilic-cationic block oligomers.

Functionalized graphene oxide for anti-VEGF siRNA delivery: preparation, characterization and evaluation in vitro and in vivo

GO–PLL–SDGR/VEGF-siRNA inhibits tumor growth as a tumor targeting delivery system.

Important role of phosphoramido linkage in imidazole-based dioleyl helper lipids for liposome stability and primary cell transfection

BACKGROUND

To optimize synthetic gene delivery systems, there is a need to develop more efficient lipid formulations. Most cationic lipid formulations contain 'helper' neutral lipids because of their ability to increase DNA delivery, in particular by improving endosomal escape of DNA molecules via the pH-buffering effect of protonatable groups and/or fusion with the lipid bilayer of endosomes.

METHODS

We evaluated the influence of the linker structure between the two oleyl chains in the helper lipid on transfection efficiency in cell lines, as well as in primary cells (hepatocytes/cardiomyocytes). We reported the synthesis of two new pH-buffering imidazole helper lipids characterized by a polar headgroup containing one (compound 6) or two (compound 5) imidazole groups and two oleyl chains linked by an amide group. We studied their association with the aminoglycoside lipidic derivative dioleylsuccinylparomomycin (DOSP), which contains two oleyl chains linked to the aminoglycoside polar headgroup via an amide function. We compared the morphology and transfection properties of such binary liposomes of DOSP/5 and DOSP/6 with those of liposomes combining DOSP with another imidazole-based dioleyl helper lipid (MM27) in which a phosphoramido group acts as a linker between the two oleyl chains and imidazole function.

RESULTS

The phosphoramido linker in the helper lipid induces a major difference in terms of morphology and resistance to decomplexation at physical pH for DOSP/helper lipid complexes.

CONCLUSIONS

This hybrid dioleyl linker composition of DOSP/MM27 led to higher transfection efficiency in cell lines and in primary cells compared to complexes with homogeneous dioleyl linker.

How to Tackle the Challenge of siRNA Delivery with Sequence-Defined Oligoamino Amides

RNA interference (RNAi) as a mechanism of gene regulation provides exciting opportunities for medical applications. Synthetic small interfering RNA (siRNA) triggers the knockdown of complementary mRNA sequences in a catalytic fashion and has to be delivered into the cytosol of the targeted cells. The design of adequate carrier systems to overcome multiple extracellular and intracellular roadblocks within the delivery process has utmost importance. Cationic polymers form polyplexes through electrostatic interaction with negatively charged nucleic acids and present a promising class of carriers. Issues of polycations regarding toxicity, heterogeneity, and polydispersity can be overcome by solid-phase-assisted synthesis of sequence-defined cationic oligomers. These medium-sized highly versatile nucleic acid carriers display low cytotoxicity and can be modified and tailored in multiple ways to meet specific requirements of nucleic acid binding, polyplex size, shielding, targeting, and intracellular release of the cargo. In this way, sequence-defined cationic oligomers can mimic the dynamic and bioresponsive behavior of viruses.

Targeted siRNA Delivery Using a Lipo-Oligoaminoamide Nanocore with an Influenza Peptide and Transferrin Shell

Developing RNA-interference-based therapeutic approaches with efficient and targeted cytosolic delivery of small interfering RNA (siRNA) is remaining a critical challenge since two decades. Herein, a multifunctional transferrin receptor (TfR)-targeted siRNA delivery system (Tf&INF7) is designed based on siRNA complexes formed with the cationic lipo-oligoamino amide 454, sequentially surface-modified with polyethylene glycol-linked transferrin (Tf) for receptor targeting and the endosomolytic peptide INF7 for efficient cytosolic release of the siRNA. Effective Tf&INF7 polyplex internalization and target gene silencing are demonstrated for the TfR overexpressing tumor cell lines (K562, D145, and N2a). Treatment with antitumoral EG5 siRNA results in a block of tumor cell growth and triggered apoptosis. Tf-modified polyplexes are far more effective than the corresponding albumin- (Alb) or nonmodified 454 polyplexes. Competition experiments with excess of Tf demonstrate TfR target specificity. As alternative to the ligand Tf, an anti-murine TfR antibody is incorporated into the polyplexes for specific targeting and gene silencing in the murine N2a cell line. In vivo distribution studies not only demonstrate an enhanced tumor residence of siRNA in N2a tumor-bearing mice with the Tf&INF7 as compared to the 454 polyplex group but also a reduced siRNA nanoparticle stability limiting the in vivo performance.

Sequence-defined cMET/HGFR-targeted Polymers as Gene Delivery Vehicles for the Theranostic Sodium Iodide Symporter (NIS) Gene

The sodium iodide symporter (NIS) as well-characterized theranostic gene represents an outstanding tool to target different cancer types allowing noninvasive imaging of functional NIS expression and therapeutic radioiodide application. Based on its overexpression on the surface of most cancer types, the cMET/hepatocyte growth factor receptor serves as ideal target for tumor-selective gene delivery. Sequence-defined polymers as nonviral gene delivery vehicles comprising polyethylene glycol (PEG) and cationic (oligoethanoamino) amide cores coupled with a cMET-binding peptide (cMBP2) were complexed with NIS-DNA and tested for receptor-specificity, transduction efficiency, and therapeutic efficacy in hepatocellular cancer cells HuH7. In vitro iodide uptake studies demonstrated high transduction efficiency and cMET-specificity of NIS-encoding polyplexes (cMBP2-PEG-Stp/NIS) compared to polyplexes without targeting ligand (Ala-PEG-Stp/NIS) and without coding DNA (cMBP2-PEG-Stp/Antisense-NIS). Tumor recruitment and vector biodistribution were investigated in vivo in a subcutaneous xenograft mouse model showing high tumor-selective iodide accumulation in cMBP2-PEG-Stp/NIS-treated mice (6.6 ± 1.6% ID/g (123)I, biological half-life 3 hours) by (123)I-scintigraphy. Therapy studies with three cycles of polyplexes and (131)I application resulted in significant delay in tumor growth and prolonged survival. These data demonstrate the enormous potential of cMET-targeted sequence-defined polymers combined with the unique theranostic function of NIS allowing for optimized transfection efficiency while eliminating toxicity.

DNA as Tunable Adaptor for siRNA Polyplex Stabilization and Functionalization

siRNA and microRNA are promising therapeutic agents, which are engaged in a natural mechanism called RNA interference that modulates gene expression posttranscriptionally. For intracellular delivery of such nucleic acid triggers, we use sequence-defined cationic polymers manufactured through solid phase chemistry. They consist of an oligoethanamino amide core for siRNA complexation and optional domains for nanoparticle shielding and cell targeting. Due to the small size of siRNA, electrostatic complexes with polycations are less stable, and consequently intracellular delivery is less efficient. Here we use DNA oligomers as adaptors to increase size and charge of cargo siRNA, resulting in increased polyplex stability, which in turn boosts transfection efficiency. Extending a single siRNA with a 181-nucleotide DNA adaptor is sufficient to provide maximum gene silencing aided by cationic polymers. Interestingly, this simple strategy was far more effective than merging defined numbers (4–10) of siRNA units into one DNA scaffolded construct. For DNA attachment, the 3′ end of the siRNA passenger strand was beneficial over the 5′ end. The impact of the attachment site however was resolved by introducing bioreducible disulfides at the connection point. We also show that DNA adaptors provide the opportunity to readily link additional functional domains to siRNA. Exemplified by the covalent conjugation of the endosomolytic influenza peptide INF-7 to siRNA via a DNA backbone strand and complexing this construct with a targeting polymer, we could form a highly functional polyethylene glycol–shielded polyplex to downregulate a luciferase gene in folate receptor–positive cells.

From Artificial Amino Acids to Sequence-Defined Targeted Oligoaminoamides

Artificial oligoamino acids with appropriate protecting groups can be used for the sequential assembly of oligoaminoamides on solid-phase. With the help of these oligoamino acids multifunctional nucleic acid (NA) carriers can be designed and produced in highly defined topologies. Here we describe the synthesis of the artificial oligoamino acid Fmoc-Stp(Boc3)-OH, the subsequent assembly into sequence-defined oligomers and the formulation of tumor-targeted plasmid DNA (pDNA) polyplexes.

Fluorinated dendrimer for TRAIL gene therapy in cancer treatment

The transfection of tumor necrosis factor-related apoptosis-inducing ligand gene by using fluorinated dendrimer is highly efficient and low toxic, resulting in efficient killing of cancer cells in vitro and suppressing tumor growth in vivo.

Heterocyclic amine-modified polyethylenimine as gene carriers for transfection of mammalian cells

Branched polyethylenimine (PEI) is extensively used as a polycationic non-viral vector for gene delivery. Polyplexes formed with PEI are believed to be released from endocytotic vesicles by the osmotic burst mechanism in the rate-limiting step in transfection. Increasing the buffering capacity of PEI derivatives in the endosomal pH range of 4.5-7.5 should enhance transfection efficiency. In this study, PEI was derivatized by covalently attaching heterocyclic amine moieties (piperazine, pyridine and imidazole rings with pKa values from 5.23 to 6.04) through amide bonds. PEI derivatives with 50% of the primary amines on PEI exhibited increased buffering capacity, increased transfection activity and decreased cytotoxicity in murine neuroblastoma (Neuro-2a) cells. The relative effectiveness in enhancing transfection efficiency was piperazine>pyridine>histidine, but each type of amine was the most effective under a particular set of conditions. Modified vectors could significantly improve transfection efficiency in murine mesenchymal stem cells. PEI25 derivatized at 50% with histidine administered as polyplexes in the tail veins of mice resulted in remarkably enhanced luciferase gene expression in the expected organ distribution and much lower toxicity than underivatized PEI25.