A convergent uptake route for peptide- and polymer-based nucleotide delivery systems

Advances in peptide-based drug delivery systems

Drug delivery systems (DDSs) are designed to deliver drugs to their specific targets to minimize their toxic effects and improve their susceptibility to clearance during targeted transport. Peptides have high affinity, low immunogenicity, simple amino acid composition, and adjustable molecular size; therefore, most peptides can be coupled to drugs via linkers to form peptide-drug conjugates (PDCs) and act as active pro-drugs. PDCs are widely thought to be promising DDSs, given their ability to improve drug bio-compatibility and physiological stability. Peptide-based DDSs are often used to deliver therapeutic substances such as anti-cancer drugs and nucleic acid-based drugs, which not only slow the degradation rate of drugs in vivo but also ensure the drug concentration at the targeted site and prolong the half-life of drugs in vivo. This article provides an profile of the advancements and future development in functional peptide-based DDSs both domestically and internationally in recent years, in the expectation of achieving targeted drug delivery incorporating functional peptides and taking full advantage of synergistic effects.

Macromolecular Polymer Based Complexes: A Diverse Strategy for the Delivery of Nucleotides

This review explores the burgeoning field of macromolecular polymer-based complexes, highlighting their revolutionary potential for the delivery of nucleotides for therapeutic applications. These complexes, ingeniously crafted from a variety of polymers, offer a unique solution to the challenges of nucleotide delivery, including protection from degradation, targeted delivery, and controlled release. The focus of this report is primarily on the design principles, encapsulation strategies, and biological interactions of these complexes, with an emphasis on their biocompatibility, biodegradability, and ability to form diverse structures, such as nanoparticles and micelles. Significant attention is paid to the latest advancements in polymer science that enable the precise tailoring of these complexes for specific nucleotides, such as DNA, RNA, and siRNA. The review discusses the critical role of surface modifications and the incorporation of targeting ligands in enhancing cellular uptake and ensuring delivery to specific tissues or cells, thereby reducing off-target effects and improving therapeutic efficacy. Clinical applications of these polymer-based delivery systems are thoroughly examined with a focus on their use in treating genetic disorders, cancer, and infectious diseases. The review also addresses the challenges and limitations currently faced in this field, such as scalability, manufacturing complexities, and regulatory hurdles. Overall, this review provides a comprehensive overview of the current state and future prospects of macromolecular polymer-based complexes in nucleotide delivery. It underscores the significance of these systems in advancing the field of targeted therapeutics and their potential to reshape the landscape of medical treatment for a wide range of diseases.

Strategies for improving the safety and RNAi efficacy of noncovalent peptide/siRNA nanocomplexes

In the past decades, the striking development of cationic polypeptides and cell-penetrating peptides (CPPs) tailored for small interfering RNA (siRNA) delivery has been fuelled by the conception of nuclear acid therapy and precision medicine. Owing to their amino acid compositions, inherent secondary structures as well as diverse geometrical shapes, peptides or peptide-containing polymers exhibit good biodegradability, high flexibility, and bio-functional diversity as nonviral siRNA vectors. Also, a variety of noncovalent nanocomplexes could be built via self-assembling and electrostatic interactions between cationic peptides and siRNAs. Although the peptide/siRNA nanocomplex-based RNAi therapies, STP705 and MIR-19, are under clinical trials, a guideline addressing the current bottlenecks of peptide/siRNA nanocomplex delivery is in high demand for future research and development. In this review, we present strategies for improving the safety and RNAi efficacy of noncovalent peptide/siRNA nanocomplexes in the treatment of genetic disorders. Through thorough analysis of those RNAi formulations using different delivery strategies, we seek to shed light on the rationale of peptide design and modification in constructing robust siRNA delivery systems, including targeted and co-delivery systems. Based on this, we provide a timely and comprehensive understanding of how to engineer biocompatible and efficient peptide-based siRNA vectors.

PepFect14 Signaling and Transfection

PepFect14 is a cell-penetrating peptide (CPP) derived from stearylated transportan-10 (strearil-TP10) with which it shares the stearic acid residue on C' terminus and the amino acid sequence except for lysines that in PepFect14 are substituted with ornithines. Being non-proteinogenic amino acids, ornithines make PepFect14 less sensitive to serum proteases and due to its positive charges the CPP can form complexes with negatively charged cargos, such as splice correcting oligonucleotides (SCOs), plasmid DNA (pDNA), and proteins. It has been reported that PepFect14/SCO complexes enter the cells mainly through endocytosis, in particular: macopinocitosys and caveolae-mediated endocytosis through the interaction with two receptors of the scavenger receptors class A family (SCARAs). PepFect14 and its complexes trigger the chaperone-mediated autophagy response involving the heat shock protein family (HSP70) whose inhibition leads to an increase of PepFect14 transfection efficacy. Exploiting the interaction between HSP70 and PepFect14 and their ability to form nanoparticle. HSP70 has been delivered in Bomirsky Hamster Melanoma cells (BHM) using PepFect14 of which a protocol is described at the end of this chapter.

Peptide-Based Nanoparticles for Therapeutic Nucleic Acid Delivery

Gene therapy offers the possibility to skip, repair, or silence faulty genes or to stimulate the immune system to fight against disease by delivering therapeutic nucleic acids (NAs) to a patient. Compared to other drugs or protein treatments, NA-based therapies have the advantage of being a more universal approach to designing therapies because of the versatility of NA design. NAs (siRNA, pDNA, or mRNA) have great potential for therapeutic applications for an immense number of indications. However, the delivery of these exogenous NAs is still challenging and requires a specific delivery system. In this context, beside other non-viral vectors, cell-penetrating peptides (CPPs) gain more and more interest as delivery systems by forming a variety of nanocomplexes depending on the formulation conditions and the properties of the used CPPs/NAs. In this review, we attempt to cover the most important biophysical and biological aspects of non-viral peptide-based nanoparticles (PBNs) for therapeutic nucleic acid formulations as a delivery system. The most relevant peptides or peptide families forming PBNs in the presence of NAs described since 2015 will be presented. All these PBNs able to deliver NAs in vitro and in vivo have common features, which are characterized by defined formulation conditions in order to obtain PBNs from 60 nm to 150 nm with a homogeneous dispersity (PdI lower than 0.3) and a positive charge between +10 mV and +40 mV.

Cell-Penetrating Peptides Delivering siRNAs: An Overview

Cell-Penetrating Peptides (CPP) are valuable tools capable of crossing the plasma membrane to deliver therapeutic cargo inside cells. Small interfering RNAs (siRNA) are double-stranded RNA molecules capable of silencing the expression of a specific protein triggering the RNA interference (RNAi) pathway, but they are unable to cross the plasma membrane and have a short half-life in the bloodstream. In this overview, we assessed the many different approaches used and developed in the last two decades to deliver siRNA through the plasma membrane through different CPPs sorted according to three different loading strategies: covalent conjugation, complex formation, and CPP-decorated (functionalized) nanocomplexes. Each of these strategies has pros and cons, but it appears the latter two are the most commonly reported and emerging as the most promising strategies due to their simplicity of synthesis, use, and versatility. Recent progress with siRNA delivered by CPPs seems to focus on targeted delivery to reduce side effects and amount of drugs used, and it appears to be among the most promising use for CPPs in future clinical applications.

Effect of Mixing Ratio of Oppositely Charged Block Copolymers on Polyion Complex Micelles for In Vivo Application

Self-assembled supramolecular structures based on polyion complex (PIC) formation between oppositely charged polymers are attracting much attention for developing drug delivery systems able to endure harsh in vivo environments. As controlling polymer complexation provides an opportunity for engineering the assemblies, an improved understanding of the PIC formation will allow constructing assemblies with enhanced structural and functional capabilities. Here, we focused on the influence of the mixing charge ratio between block aniomers and catiomers on the physicochemical characteristics and in vivo biological performance of the resulting PIC micelles (PIC/m). Our results showed that by changing the mixing charge ratio, the structural state of the core was altered despite the sizes of PIC/m remaining almost the same. These structural variations greatly affected the stability of the PIC/m in the bloodstream after intravenous injection and determined their biodistribution.

Cellular Targeting of Oligonucleotides by Conjugation with Small Molecules

Drug candidates derived from oligonucleotides (ON) are receiving increased attention that is supported by the clinical approval of several ON drugs. Such therapeutic ON are designed to alter the expression levels of specific disease-related proteins, e.g., by displaying antigene, antisense, and RNA interference mechanisms. However, the high polarity of the polyanionic ON and their relatively rapid nuclease-mediated cleavage represent two major pharmacokinetic hurdles for their application in vivo. This has led to a range of non-natural modifications of ON structures that are routinely applied in the design of therapeutic ON. The polyanionic architecture of ON often hampers their penetration of target cells or tissues, and ON usually show no inherent specificity for certain cell types. These limitations can be overcome by conjugation of ON with molecular entities mediating cellular 'targeting', i.e., enhanced accumulation at and/or penetration of a specific cell type. In this context, the use of small molecules as targeting units appears particularly attractive and promising. This review provides an overview of advances in the emerging field of cellular targeting of ON via their conjugation with small-molecule targeting structures.

Deciphering the internalization mechanism of WRAP:siRNA nanoparticles

Gene silencing mediated by double-stranded small interfering RNA (siRNA) has been widely investigated as a potential therapeutic approach for a variety of diseases and, indeed, the first therapeutic siRNA was approved by the FDA in 2018. As an alternative to the traditional delivery systems for nucleic acids, peptide-based nanoparticles (PBNs) have been applied successfully for siRNA delivery. Recently, we have developed amphipathic cell-penetrating peptides (CPPs), called WRAP allowing a rapid and efficient siRNA delivery into several cell lines at low doses (20 to 50 nM). In this study, using a highly specific gene silencing system, we aimed to elucidate the cellular uptake mechanism of WRAP:siRNA nanoparticles by combining biophysical, biological, confocal and electron microscopy approaches. We demonstrated that WRAP:siRNA complexes remain fully active in the presence of chemical inhibitors of different endosomal pathways suggesting a direct cell membrane translocation mechanism. Leakage studies on lipid vesicles indicated membrane destabilization properties of the nanoparticles and this was supported by the measurement of WRAP:siRNA internalization in dynamin triple-KO cells. However, we also observed some evidences for an endocytosis-dependent cellular internalization. Indeed, nanoparticles co-localized with transferrin, siRNA silencing was inhibited by the scavenger receptor A inhibitor Poly I and nanoparticles encapsulated in vesicles were observed by electron microscopy in U87 cells. In conclusion, we demonstrate here that the efficiency of WRAP:siRNA nanoparticles is mainly based on the use of multiple internalization mechanisms including direct translocation as well as endocytosis-dependent pathways.

Designing Chimeric Molecules for Drug Discovery by Leveraging Chemical Biology

After the first seed concept introduced in the 18th century, different disciplines have attributed different names to dual-functional molecules depending on their application, including bioconjugates, bifunctional compounds, multitargeting molecules, chimeras, hybrids, engineered compounds. However, these engineered constructs share a general structure: a first component that targets a specific cell and a second component that exerts the pharmacological activity. A stable or cleavable linker connects the two modules of a chimera. Herein, we discuss the recent advances in the rapidly expanding field of chimeric molecules leveraging chemical biology concepts. This Perspective is focused on bifunctional compounds in which one component is a lead compound or a drug. In detail, we discuss chemical features of chimeric molecules and their use for targeted delivery and for target engagement studies.

Effect of small molecule signaling in PepFect14 transfection

Cell-penetrating peptides can be used to deliver oligonucleotide-based cargoes into cells. Previous studies have shown that the use of small molecule drugs could be an efficient method to increase the efficacy of delivery of oligonucleotides by cell-penetrating peptides either as targeting agents that can be used in formulation with the cell-penetrating peptide and its cargo or as cell signaling modulators that facilitates the cellular uptake of the treatment. This study presents two aims. The first aim is the identification of small molecule drugs that would induce a synergic effect on the transfection of splice correcting oligonucleotides assisted by PepFect14. The second aim is to identify the mechanisms behind the effect of small molecule drugs modulation of cell-penetrating peptide assisted transfection of oligonucleotides. Through an optimized, high-throughput luciferase assay for short oligonucleotide delivery using cell-penetrating peptides, and the simultaneous addition of a small molecule drug library, we show that three small molecule drugs (MPEP, VU0357121 and Ciproxifan) induced an increase in the transfection efficacy of PepFect14 in complex with a short single-stranded oligonucleotide in HeLa pLuc705 cells. These three drugs are described in the literature to be highly specific for their respective target receptors. However, none of those receptors are expressed in our cell line, indicating a yet non-described pathway of action for these small molecules. We show that the indicated small molecules, without interfering with the particles formed by PepFect14 and the oligonucleotide, interfere via still unidentified interactions in cell signaling, leading to an up-regulation of endocytosis and a higher efficacy in the delivery of short splice correcting oligonucleotides in complex with PepFect14.

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

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

Intracellular Trafficking and Endosomal Release of Oligonucleotides: What We Know and What We Don't

Understanding the cellular uptake and intracellular trafficking of oligonucleotides provides an important basic underpinning for the developing field of oligonucleotide-based therapeutics. Whether delivered as "free" oligonucleotides, as ligand-oligonucleotide conjugates, or in association with various nanocarriers, all forms of oligonucleotide enter cells by endocytosis and are initially ensconced within membrane-limited vesicles. Accordingly, the locus and extent of release to the cytosol and nucleus are key determinants of the pharmacological actions of oligonucleotides. A number of recent studies have explored the intracellular trafficking of various forms of oligonucleotides and their release from endomembrane compartments. These studies reveal a surprising convergence on an early-intermediate compartment in the trafficking pathway as the key locus of release for oligonucleotides administered in "free" form as well as those delivered with lipid complexes. Thus, oligonucleotide release from multivesicular bodies or from late endosomes seems to be the crucial endogenous process for attaining pharmacological effects. This intrinsic process of oligonucleotide release may be amplified by delivery agents such as lipid complexes or small molecule enhancers.

Magnetic Nanoparticle Assisted Self-assembly of Cell Penetrating Peptides-Oligonucleotides Complexes for Gene Delivery

Magnetic nanoparticles (MNPs, Fe3O4) incorporated into the complexes of cell penetrating peptides (CPPs)-oligonucleotides (ONs) promoted the cell transfection for plasmid transfection, splice correction, and gene silencing efficiencies. Six types of cell penetrating peptides (CPPs; PeptFect220 (denoted PF220), PF221, PF222, PF223, PF224 and PF14) and three types of gene therapeutic agents (plasmid (pGL3), splicing correcting oligonucleotides (SCO), and small interfering RNA (siRNA) were investigated. Magnetic nanoparticles incorporated into the complexes of CPPs-pGL3, CPPs-SCO, and CPPs-siRNA showed high cell biocompatibility and efficiently transfected the investigated cells with pGL3, SCO, and siRNA, respectively. Gene transfer vectors formed among PF14, SCO, and MNPs (PF14-SCO-MNPs) showed a superior transfection efficiency (up to 4-fold) compared to the noncovalent PF14-SCO complex, which was previously reported with a higher efficiency compared to commercial vector called Lipofectamine™2000. The high transfection efficiency of the new complexes (CPPs-SCO-MNPs) may be attributed to the morphology, low cytotoxicity, and the synergistic effect of MNPs and CPPs. PF14-pDNA-MNPs is an efficient complex for in vivo gene delivery upon systemic administration. The conjugation of CPPs-ONs with inorganic magnetic nanoparticles (Fe3O4) may open new venues for selective and efficient gene therapy.

Graphene oxide nanosheets in complex with cell penetrating peptides for oligonucleotides delivery

A new strategy for gene transfection using the nanocarrier of cell penetrating peptides (CPPs; PepFect14 (PF14) or PepFect14 (PF14) (PF221)) in complex with graphene oxide (GO) is reported. GO complexed with CPPs and plasmid (pGL3), splice correction oligonucleotides (SCO) or small interfering RNA (siRNA) are performed. Data show adsorption of CPPs and oligonucleotides on the top of the graphenic lamellar without any observed change of the particle size of GO. GO mitigates the cytotoxicity of CPPs and improves the material biocompatibility. Complexes of GO-pGL3-CPPs (CPPs; PF14 or PF221) offer 2.1-2.5 fold increase of the cell transfection compared to pGL3-CPPs (CPPs; PF14 or PF221). GO-SCO-PF14 assemblies effectively transfect the cells with an increase of >10-25 fold compared to the transfection using PF14. The concentration of GO plays a significant role in the material nanotoxicity and the transfection efficiency. The results open a new horizon in the gene treatment using CPPs and offer a simple strategy for further investigations.

A retro-inverso cell-penetrating peptide for siRNA delivery

Background

Small interfering RNAs (siRNAs) are powerful tools to control gene expression. However, due to their poor cellular permeability and stability, their therapeutic development requires a specific delivery system. Among them, cell-penetrating peptides (CPP) have been shown to transfer efficiently siRNA inside the cells. Recently we developed amphipathic peptides able to self-assemble with siRNAs as peptide-based nanoparticles and to transfect them into cells. However, despite the great potential of these drug delivery systems, most of them display a low resistance to proteases.

Results

Here, we report the development and characterization of a new CPP named RICK corresponding to the retro-inverso form of the CADY-K peptide. We show that RICK conserves the main biophysical features of its L-parental homologue and keeps the ability to associate with siRNA in stable peptide-based nanoparticles. Moreover the RICK:siRNA self-assembly prevents siRNA degradation and induces inhibition of gene expression.

Conclusions

This new approach consists in a promising strategy for future in vivo application, especially for targeted anticancer treatment (e.g. knock-down of cell cycle proteins).Graphical abstract

PEGylation rate influences peptide-based nanoparticles mediated siRNA delivery in vitro and in vivo

Small interfering RNAs (siRNAs) present a strong therapeutic potential because of their ability to inhibit the expression of any desired protein. Recently, we developed the retro-inverso amphipathic RICK peptide as novel non-covalent siRNA carrier. This peptide is able to form nanoparticles (NPs) by self-assembling with the siRNA resulting in the fully siRNA protection based on its protease resistant peptide sequence. With regard to an in vivo application, we investigated here the influence of the polyethylene glycol (PEG) grafting to RICK NPs on their in vitro and in vivo siRNA delivery properties. A detailed structural study shows that PEGylation did not alter the NP formation (only decrease in zeta potential) regardless of the used PEGylation rates. Compared to the native RICK:siRNA NPs, low PEGylation rates (≤20%) of the NPs did not influence their cellular internalization capacity as well as their knock-down specificity (over-expressed or endogenous system) in vitro. Because the behavior of PEGylated NPs could differ in their in vivo application, we analyzed the repartition of fluorescent labeled NPs injected at the one-cell stage in zebrafish embryos as well as their pharmacokinetic (PK) profile after administration to mice. After an intra-cardiac injection of the PEGylated NPs, we could clearly determine that 20% PEG-RICK NPs reduce significantly liver and kidney accumulation. NPs with 20% PEGylation constitutes a modular, easy-to-handle drug delivery system which could be adapted to other types of functional moieties to develop safe and biocompatible delivery systems for the clinical application of RNAi-based cancer therapeutics.

Peptides for nucleic acid delivery

Nucleic acids and their synthetic oligonucleotide (ON) analogs are a group of gene therapeutic compounds which hold enormous clinical potential. Despite their undoubted potential, clinical translation of these molecules, however, has been largely held back by their limited bioavailability in the target tissues/cells. To overcome this, many different drug delivery systems have been devised. Among others, short delivery peptides, called cell-penetrating peptides (CPPs), have been demonstrated to allow for efficient delivery of nucleic acids and their ON analogs, in both cell culture and animal models. In this review, we provide brief overview of the latest advances in nucleic acid delivery with CPPs, covering the two main vectorization strategies, covalent conjugation and nanoparticle formation-based approach. In conclusion, CPP-based drug delivery systems have the capacity to overcome the hurdle of delivery and thus have the potential to facilitate the clinical translation of nucleic acid-based therapeutics.

Chimeric peptide-mediated siRNA transduction to inhibit HIV-1 infection

Persistent human immunodeficiency virus 1 (HIV-1) infection provokes immune activation and depletes CD4⁺lymphocytes, leading to acquired immunodeficiency syndrome. Uninterrupted administration of combination antiretroviral therapy (cART) in HIV-infected patients suppresses viral replication to below the detectable level and partially restores the immune system. However, cART-unresponsive residual HIV-1 infection and elusive transcriptionally silent but reactivatable viral reservoirs maintain a permanent viral DNA blue print. The virus rebounds within a few weeks after interruption of suppressive therapy. Adjunct gene therapy to control viral replication by ribonucleic acid interference (RNAi) is a post-transcriptional gene silencing strategy that could suppress residual HIV-1 burden and overcome viral resistance. Small interfering ribonucleic acids (siRNAs) are efficient transcriptional inhibitors, but need delivery systems to reach inside target cells. We investigated the potential of chimeric peptide (FP-PTD) to deliver specific siRNAs to HIV-1-susceptible and permissive cells. Chimeric FP-PTD peptide was designed with an RNA binding domain (PTD) to bind siRNA and a cell fusion peptide domain (FP) to enter cells. FP-PTD-siRNA complex entered and inhibited HIV-1 replication in susceptible cells, and could be a candidate for in vivo testing.

Optimisation of vectorisation property: A comparative study for a secondary amphipathic peptide

RNA interference provides a powerful technology for specific gene silencing. Therapeutic applications of small interfering RNA (siRNA) however require efficient vehicles for stable complexation and intracellular delivery. In order to enhance their cell delivery, short amphipathic peptides called cell-penetrating peptides (CPPs) have been intensively developed for the last two decades. In this context, the secondary amphipathic peptide CADY has shown to form stable siRNA complexes and to improve their cellular uptake independent of the endosomal pathway. In the present work, we have described the parameters influencing CADY nanoparticle formation (buffers, excipients, presence of serum, etc.), and have followed in details the CPP:siRNA self-assembly. Once optimal conditions were determined, we have compared the ability of seven different CADY analogues to form siRNA-loaded nanoparticles compared to CADY:siRNA. First of all, we were able to show by biophysical methods that structural polymorphism (α-helix) is an important prerequisite for stable nanoparticle formation independently of occurring sequence mutations. Luciferase assays revealed that siRNA complexed to CADY-K (shorter version) shows better knock-down efficiency on Neuro2a-Luc(+) and B16-F10-Luc(+) cells compared to CADY:siRNA. Altogether, CADY-K is an ideal candidate for further application especially with regards to ex vivo or in vivo applications.

Cell-penetrating peptides as tools to enhance non-injectable delivery of biopharmaceuticals

Non-injectable delivery of peptide and protein drugs is hampered by their labile nature, hydrophilicity, and large molecular size; thus limiting their permeation across mucosae, which represent major biochemical and physical barriers to drugs administered via e.g. the oral, nasal, and pulmonary routes. However, in recent years cell-penetrating peptides (CPP) have emerged as promising tools to enhance mucosal delivery of co-administered or conjugated peptide and protein cargo and more advanced CPP-cargo formulations are emerging. CPPs act as transepithelial delivery vectors, but the mechanism(s) by which CPPs mediate cargo translocation across an epithelium is so far poorly understood; both due to the fact that multiple factors influence the resulting uptake and trafficking mechanisms as well as to the complicated nature of sensitive studies of this. In addition to a proper mechanistic understanding, documentation of CPP-mediated delivery in higher animal species than rodent as well as extensive toxicological studies are necessary for CPP-containing non-injectable DDSs to reach the clinic.

The delivery of therapeutic oligonucleotides

The oligonucleotide therapeutics field has seen remarkable progress over the last few years with the approval of the first antisense drug and with promising developments in late stage clinical trials using siRNA or splice switching oligonucleotides. However, effective delivery of oligonucleotides to their intracellular sites of action remains a major issue. This review will describe the biological basis of oligonucleotide delivery including the nature of various tissue barriers and the mechanisms of cellular uptake and intracellular trafficking of oligonucleotides. It will then examine a variety of current approaches for enhancing the delivery of oligonucleotides. This includes molecular scale targeted ligand-oligonucleotide conjugates, lipid- and polymer-based nanoparticles, antibody conjugates and small molecules that improve oligonucleotide delivery. The merits and liabilities of these approaches will be discussed in the context of the underlying basic biology.

pH-responsive PepFect cell-penetrating peptides

A series of cell-penetrating PepFect peptide analogues was developed by substitutions of the galanin-derived N-terminal sequence. Histidine modifications were incorporated in order to make the peptides pH-responsive. The peptides were all able to form non-covalent complexes with an oligonucleotide cargo by co-incubation in buffer. The complexes were characterized by dynamic light scattering and circular dichroism, and an assay to evaluate the peptide-cargo affinity was developed. Cellular bioactivity was studied in HeLa cells using a luciferase-based splice correction assay. In addition, the membrane interactions of the peptides in large unilammelar vesicles was studied using a calcein leakage assay. The effects of substitutions were found to be dependent of the non-modified, C-terminal sequence of the peptides; for analogues of PepFect 3 we observed an increase in membrane activity and bioactivity for histidine-containing analogues, whereas the same modifications introduced to PepFect 14 lead to a decreased bioactivity. Peptides modified with a leucine/histidine sequence were found to be pH responsive, complexes formed from these peptides were small at pH 7 and grew under acidic conditions. The most promising of the novel PepFect 3 analogues, PepFect 132 has a significantly higher bioactivity and membrane activity than the parent peptide PepFect 3.

Powering up the molecular therapy of RNA interference by novel nanoparticles

With more suitable for disease treatment due to reduced cellular toxicity, higher loading capacity, and better biocompatibility, nanoparticle-based siRNA delivery systems have proved to be more potent, higher specific and less toxic than the traditional drug therapy.

Optimized luciferase assay for cell-penetrating peptide-mediated delivery of short oligonucleotides

An improved assay for screening for the intracellular delivery efficacy of short oligonucleotides using cell-penetrating peptides is suggested. This assay is an improvement over previous assays that use luciferase reporters for cell-penetrating peptides because it has been scaled up from a 24-well format to a 96-well format and no longer relies on a luciferin reagent that has been commercially sourced. In addition, the homemade luciferin reagent is useful in multiple cell lines and in different assays that rely on altering the expression of luciferase. To establish a new protocol, the composition of the luciferin reagent was optimized for both signal strength and longevity by multiple two-factorial experiments varying the concentrations of adenosine triphosphate, luciferin, coenzyme A, and dithiothreitol. In addition, the optimal conditions with respect to cell number and time of transfection for both short interfering RNA (siRNA) and splice-correcting oligonucleotides (SCOs) are established. Optimal transfection of siRNA and SCOs was achieved using the reverse transfection method where the oligonucleotide complexes are already present in the wells before the cells are plated. Z' scores were 0.73 for the siRNA assay and 0.71 for the SCO assay, indicating that both assays are suitable for high-throughput screening.

SCARA Involvement in the Uptake of Nanoparticles Formed by Cell-Penetrating Peptides

The investigation of uptake mechanisms for cell-penetrating peptides (CPPs) is and has been an ongoing project for as long as the peptides have been known, a time period that now spans over two decades. The ultimate answer is yet to be revealed and the current understanding is that no "one" mechanism will ever be found. The reason for this is that the uptake mechanism seems to be dependent on a multitude of factors that include which CPP, what cells are used, whether or not there is cargo and what the cargo is. CPPs are capable of delivering a variety of bio-macromolecules that are by themselves unable to enter into cells. Our group has reported on many different peptides in recent years, many aimed at delivering various oligonucleotide-based cargoes. These peptides have utilized the inherent positive charge of the peptides and some rationally designed modifications to non-covalently complex oligonucleotides and bring them into cells. In this chapter, we present a brief overview of the current proposals for the uptake mechanisms of CPPs and describe methods for detecting and evaluating the role of scavenger receptor class A receptors in the uptake of non-covalent cell-penetrating peptide:oligonucleotide complexes.