Tat-conjugated PAMAM dendrimers as delivery agents for antisense and siRNA oligonucleotides

Functionalized PAMAM constructed nanosystems for biomacromolecule delivery

Polyamidoamines (PAMAMs) are a class of dendrimer with monodispersity and controlled topology, which can deliver biologically active macromolecules (e.g., genes and proteins) to specific regions with high efficiency and minimum side effects. In detail, PAMAMs can be functionalized easily by core modification or surface amendment to encapsulate a wide range of biomacromolecules. Besides, self-assembled, cross-linked and hybrid PAMAMs with customized therapeutic purposes are developed as delivery vehicles, which makes PAMAMs promising for biomacromolecule therapy. In this review, we comprehensively summarize the application of PAMAMs in biomacromolecule delivery from the synthesis of functionalized PAMAM carriers to the development of PAMAM-based drug delivery systems. The underlying strategies for PAMAM functionalization and assembly are first systematically discussed, and then the current applications of PAMAMs for biomacromolecule delivery are reviewed. Finally, a brief perspective on the further applications of PAMAMs concludes, aiming to provide insights into developing PAMAM-based biomacromolecule delivery systems.

Development of a quaternary ammonium poly (amidoamine) dendrimer-based drug carrier for the solubility enhancement and sustained release of furosemide

Furosemide (FRSD) is a loop diuretic that has been categorized as a class IV drug according to the Biopharmaceutics Classification System (BCS). It is used in the treatment of congestive heart failure and edema. Owing to low solubility and permeability, its oral bioavailability is very poor. In this study, two types of poly (amidoamine) dendrimer-based drug carriers (generation G2 and G3) were synthesized to increase the bioavailability of FRSD through solubility enhancement and sustained release. The developed dendrimers enhanced the solubility of FRSD 58- and 109-fold, respectively, compared with pure FRSD. In vitro studies demonstrated that the maximum time taken to release 95% of the drug from G2 and G3 was 420-510 min, respectively, whereas for pure FRSD the maximum time was only 90 min. Such a delayed release is strong evidence for sustained drug release. Cytotoxicity studies using Vero and HBL 100 cell lines through an MTT assay revealed increased cell viability, indicating reduced cytotoxicity and improved bioavailability. Therefore, the present dendrimer-based drug carriers are proven to be prominent, benign, biocompatible, and efficient for poorly soluble drugs, such as FRSD. Therefore, they could be convenient choices for real-time applications of drug delivery.

Nano drug delivery systems for antisense oligonucleotides (ASO) therapeutics

Cancer, infectious diseases, and metabolic and hereditary genetic disorders are a global health burden affecting millions of people, with contemporary treatments offering limited relief. Antisense technology treats diseases by targeting their causal agents using its ability to alter or inhibit endogenous or malfunctioning genes. Nine antisense oligonucleotide (ASO) drugs that represent four different chemical classes have been approved for the treatment of rare diseases, including nusinersen, the first new oligonucleotide-based drug. Advances in medicinal chemistry, understanding the molecular pathways, and the availability of vast genetic data have resulted in enormous improvements in the therapeutic performance of ASO drugs; however, their susceptibility to degradation in the circulation, rapid renal clearance, and immunostimulatory adverse effects greatly limit their clinical applications. An increasing number of ASO-based therapeutics is being tested in clinical trials. Improvements to the delivery of ASO drugs could potentially change the therapeutic landscape for many conditions in the near future. This review describes the technological advances and developments in drug delivery systems pertaining to ASO therapeutics.

Cyclic peptides nanospheres: A '2-in-1' self-assembled delivery system for targeting nucleus and cytoplasm

Vascular endothelial growth factor (VEGF) is considered as one of the vital growth factors for angiogenesis, which is primarily responsible for the progress and maintenance of new vascular network in tumor. Numerous studies report that inhibition of VEGF-induced angiogenesis is a potent technique for cancer suppression. Recently, RNA interference, especially small interfering RNA (siRNA) signified a promising approach to suppress the gene expression. However, the clinical implementation of biological macromolecules such as siRNA is significantly limited because of stability and bioavailability issues. Herein, self-assembled peptide nanospheres have been generated from L,L-cyclic peptides using hydrophobic (Trp), positively charged (Arg) and cysteine (Cys) amino acid residues and demonstrated as vehicles for intracellular delivery of VEGF siRNA and VEGF antisense oligonucleotide. Formation of peptide nanostructures is confirmed by HR-TEM, AFM, SEM and DLS analysis. Possible mechanism of self-assembly of the cyclic peptides and their binding with macromolecules are demonstrated by in-silico analysis. Gel electrophoresis reveals that the newly generated peptide based organic materials exhibit strong binding affinity toward siRNAs / antisense oligonucleotides (ASOs) at optimum concentration. Flow cytometry and confocal microscopy results confirm the efficiency of the new biomaterials toward the intracellular delivery of fluorescent labeled siRNA / ASOs. Furthermore, VEGF expression evaluated by western blot and RT-PCR upon the delivery of functional VEGF siRNA/ASOs suggests that very low concentrations of VEGF siRNA/ASOs cause significant gene knockdown at protein and mRNA levels, respectively.

Insight into the Mechanism of Carrier-Mediated Delivery of siRNA in the Cell Membrane Using MD Simulation

The effective translocation of small interfering RNA (siRNA) across cell membranes has become one of the main challenges in gene silencing therapy. In this study, we have carried out molecular dynamics simulations to investigate a systematic procedure with different carriers that could be convenient for efficient siRNA delivery into the cell. Starting with poly-amido-amine (PAMAM) dendrimers and cholesterol molecules as carriers, we have found cholesterol as the most efficient carrier for siRNA when it is covalently attached with the siRNA terminal group. Our simulations show that binding of this complex in the lipid membrane alters the structure and dynamics of the nearby lipids to initiate the translocation process. Potential of mean force (PMF) was computed for siRNA with the carriers along the bilayer normal to understand the spontaneity of the process. Though all the PMF profiles show repulsive interaction inside the bilayer, the siRNA with cholesterol shows a comparative attractive interaction (∼27 kcal/mol) with respect to the siRNA-PAMAM complex. Altogether, our results demonstrate the binding interaction of the siRNA-carrier complex in the lipid membrane and propose a theoretical model for the efficient carrier by comparative study of the binding. The probable mechanism of the translocation process is also provided by the alteration of the lipid structure and dynamics for specifically siRNA-cholesterol binding.

Fluorescent Peptide Dendrimers for siRNA Transfection: Tracking pH Responsive Aggregation, siRNA Binding, and Cell Penetration

Transfecting nucleic acids into various cells is a key procedure in biological research also envisioned for therapeutic applications. In our effort to obtain simple reagents that would be readily accessible from commercial building blocks, we recently reported peptide dendrimers as single component siRNA transfection reagents accessible in pure form by solid-phase peptide synthesis. Here, we extend our studies of these dendrimers by identifying analogs bearing a coumarin or BODIPY fluorescent label in their core and displaying comparable siRNA transfection efficiencies, pH dependent aggregation, siRNA binding, and secondary structures. Fluorescence resonance energy transfer (FRET) studies show that the dendrimers are tightly associated with siRNA within the formed nanoparticles at pH 7.4 but are released into solution at pH 5.0 and can participate in endosome escape by destabilizing the membrane at this pH value. Colocalization studies furthermore suggest that peptide dendrimers and siRNA remain tightly associated throughout the transfection process.

Novel Blood-Brain Barrier Shuttle Peptides Discovered through the Phage Display Method

Delivery of therapeutic agents into the brain is a major challenge in central nervous system drug development. The blood–brain barrier (BBB) prevents access of biotherapeutics to their targets in the central nervous system and, therefore, prohibits the effective treatment of many neurological disorders. To find blood–brain barrier shuttle peptides that could target therapeutics to the brain, we applied a phage display technology on a primary endothelial rat cellular model. Two identified peptides from a 12 mer phage library, GLHTSATNLYLH and VAARTGEIYVPW, were selected and their permeability was validated using the in vitro BBB model. The permeability of peptides through the BBB was measured by ultra-performance liquid chromatography-tandem mass spectrometry coupled to a triple-quadrupole mass spectrometer (UHPLC-MS/MS). We showed higher permeability for both peptides compared to N–C reversed-sequence peptides through in vitro BBB: for peptide GLHTSATNLYLH 3.3 × 10⁻⁷ cm/s and for peptide VAARTGEIYVPW 1.5 × 10⁻⁶ cm/s. The results indicate that the peptides identified by the in vitro phage display technology could serve as transporters for the administration of biopharmaceuticals into the brain. Our results also demonstrated the importance of proper BBB model for the discovery of shuttle peptides through phage display libraries.

Comparison of cationic liposome and PAMAM dendrimer for delivery of anti-Plk1 siRNA in breast cancer treatment

Delivery of negatively charged, high molecular weight and unstable siRNA is difficult. The present study describes the development and comparison of cationic liposomes (CLs) and polyamidoamine (PAMAM) dendrimer generation 4 (PG4) nanocarriers of gene for cancer therapy. CLs and PG4 were complexed with anticancer siRNA (siPlk1) to form siPlk1-CLs lipoplex and siPlk1-PG4 dendriplex. siPlk1-CLs/PG4 complexes were characterized for average particle size, zeta potential, fluorescence and integrity of siPlk1 by agarose gel electrophoresis, ethidium bromide intercalation assay, circular dichroism, protection against RNase and stability in serum. The complexation of CLs/siPlk1 and PG4/siPlk1 were at a 100/1 and 2/1 charge ratio respectively. The CLs and PG4 were effective in protecting siPlk1 from RNase activity, also they enhanced the siPlk1 serum stability. Additionally, siPlk1-CLs and siPlk1-PG4 were evaluated by cell culture studies. In vitro anticancer activity study using MCF-7 cells showed that siPlk1-CLs and siPlk1-PG4 causes nearly similar cell death. Both siPlk1-CLs and siPlk1-PG4 resulted in enhanced cellular uptake of siPlk1 in MDA-MB-231 cells compared to naked siPlk1 solution. Cell cycle analysis suggested that increased cell population arrest in subG1 phase by siPlk1-CLs and siPlk1-PG4 compared to naked siPlk1 solution. These observations suggested that CLs and PG4 can be a potential carrier for siPlk1 delivery in breast cancer treatment.

Dendrimer-Enabled Therapeutic Antisense Delivery Systems as Innovation in Medicine

Antisense oligonucleotide (AON)-based therapies concern the treatment for genetic disorders or infections such as a range of neurodegenerative and neuromuscular diseases and have shown benefits in animal models and patients. Nevertheless, successes in the clinic are still strongly limited by unfavorable biodistribution and poor cellular uptake of AONs. Dendrimer macromolecules are synthetically accessible and consist of a core with repeated iterations (named branches) surrounding this core, and on the periphery functional groups which can be modified for ligand attachment. The generations of these branched nanoparticles are based on the number of branches emanating from the core with layered architectures. Dendrimers show promise in several biomedical applications based on their tunable surface modifications allowing the adjustment of their in vivo behavior related to biocompatibility and pharmacokinetic parameters. Dendrimers can be used as nanocarriers of various types of drugs including AONs or nanodrugs. As nanocarriers, polycationic dendrimers can complex multiple negatively charged DNA oligonucleotides on their surface and form stable complexes to promote internalization into the cells based on a good cell membrane affinity. These nanocarriers complexing antisense oligonucleotides must be stable enough to reach the cellular target, but with adequate in vivo global clearance, and have good pharmacokinetic (PK) and pharmacodynamic (PD) profiles. This Review was designed to analyze the development of AONs carried by polycationic and polyanionic (few example) dendrimers. This Review strongly supports the idea that dendrimers, with adequate modulation of their terminal groups, could be used to carry AONs in cells.

Dendrimer functionalized folate-targeted gold nanoparticles for luciferase gene silencing in vitro: A proof of principle study

Use of exogenous small interfering RNA (siRNA) has shown potential in gene silencing. The need for target-specific siRNA delivery vehicles is crucial to successful gene silencing. This study is aimed at developing and evaluating the safety and efficiency of siRNA delivery using unmodified and folic acid (FA) modified poly(amidoamine) generation 5 (PAMAM G5D) functionalized gold nanoparticles (Au:G5D/Au:G5D:FA) in vitro. All formulations were physico--chemically characterized and nanocomplexes were evaluated using the band shift, dye displacement, nuclease protection, MTT cell viability, and luciferase reporter gene assays. Nanocomplexes bound and protected siRNA against degrading RNases, and were well tolerated by the cells. The Au:G5D:FA nanocomplexes elicited excellent gene silencing in folate receptor expressing HeLa-Tat-Luc cells, decreasing significantly in the presence of excess FA ligand, indicating nanocomplex uptake by the mechanism of receptor mediation. These results highlight the synergistic role played by Au and the dendrimer in enhancement of transgene silencing.

Microfluidics for the Production of Nanomedicines: Considerations for Polymer and Lipid-based Systems

BACKGROUND

Microfluidics is becoming increasingly of interest as a superior technique for the synthesis of nanoparticles, particularly for their use in nanomedicine. In microfluidics, small volumes of liquid reagents are rapidly mixed in a microchannel in a highly controlled manner to form nanoparticles with tunable and reproducible structure that can be tailored for drug delivery. Both polymer and lipid-based nanoparticles are utilized in nanomedicine and both are amenable to preparation by microfluidic approaches.

AIM

Therefore, the purpose of this review is to collect the current state of knowledge on the microfluidic preparation of polymeric and lipid nanoparticles for pharmaceutical applications, including descriptions of the main synthesis modalities. Of special interest are the mechanisms involved in nanoparticle formation and the options for surface functionalisation to enhance cellular interactions.

CONCLUSION

The review will conclude with the identification of key considerations for the production of polymeric and lipid nanoparticles using microfluidic approaches.

Dendrimer as a new potential carrier for topical delivery of siRNA: A comparative study of dendriplex vs. lipoplex for delivery of TNF-α siRNA

Topical delivery of siRNA is challenging task due to complex barrier property of stratum corneum and cationic lipid based carriers have been widely explored for this purpose due to improved permeation through skin. For gene delivery application, dendrimers are considered as efficient carrier due to their cationic nature and well-defined surface groups. However, they are not well explored for topical delivery. This work compares the suitability of PAMAM dendrimer with DOTAP liposome for topical delivery of siRNA against TNF-α. The particle size, zeta potential and entrapment efficiency of dendriplex were 99.80 ± 1.80 nm, 13.40 ± 4.84 mV and 98.72 ± 2.02% whereas for lipoplex were 174.80 ± 0.80 nm, 29.96 ± 0.51 mV and 94.99 ± 5.01% respectively. Both the formulations were stable in serum and in the presence of RNAse. TNF-α is inflammatory cytokine, hence the in vivo efficacy of developed formulations was determined using psoriatic plaque model. Results suggested improved phenotypic and histopathological features and reduced levels of IL-6, TNF-α, IL-17 and IL-22 for dendriplex and lipoplex treated groups in comparison to Imiquimod treated group. These findings suggest that dendrimer can be a potential carrier for topical gene delivery.

Evaluation of Amino-Functional Polyester Dendrimers Based on Bis-MPA as Nonviral Vectors for siRNA Delivery

Herein, we present the first evaluation of cationic dendrimers based on 2,2-bis(methylol)propionic acid (bis-MPA) as nonviral vectors for transfection of short interfering RNA (siRNA) in cell cultures. The study encompassed dendrimers of generation one to four (G1⁻G4), modified to bear 6⁻48 amino end-groups, where the G2⁻G4 proved to be capable of siRNA complexation and protection against RNase-mediated degradation. The dendrimers were nontoxic to astrocytes, glioma (C6), and glioblastoma (U87), while G3 and G4 exhibited concentration dependent toxicity towards primary neurons. The G2 showed no toxicity to primary neurons at any of the tested concentrations. Fluorescence microscopy experiments suggested that the dendrimers are highly efficient at endo-lysosomal escape since fluorescently labeled dendrimers were localized specifically in mitochondria, and diffuse cytosolic distribution of fluorescent siRNA complexed by dendrimers was observed. This is a desired feature for intracellular drug delivery, since the endocytic pathway otherwise transfers the drugs into lysosomes where they can be degraded without reaching their intended target. siRNA-transfection was successful in C6 and U87 cell lines using the G3 and G4 dendrimers followed by a decrease of approximately 20% of target protein p42-MAPK expression.

Dendrimers Show Promise for siRNA and microRNA Therapeutics

The lack of an appropriate intracellular delivery system for therapeutic nucleic acids (TNAs) is a major problem in molecular biology, biotechnology, and medicine. A relatively new class of highly symmetrical hyperbranched polymers, called dendrimers, shows promise for transporting small TNAs into both cells and target tissues. Dendrimers have intrinsic advantages for this purpose: their physico-chemical and biological properties can be controlled during synthesis, and they are able to transport large numbers of TNA molecules that can specifically suppress the expression of single or multiple targeted genes. Numerous chemical modifications of dendrimers extend the biocompatibility of synthetic materials and allow targeted vectors to be designed for particular therapeutic purposes. This review summarizes the latest experimental data and trends in the medical application of various types of dendrimers and dendrimer-based nanoconstructions as delivery systems for short small interfering RNAs (siRNAs) and microRNAs at the cell and organism levels. It provides an overview of the structural features of dendrimers, indicating their advantages over other types of TNA transporters.

The Effect of Size and Shape of RNA Nanoparticles on Biodistribution

Drugs with ideal pharmacokinetic profile require long half-life but little organ accumulation. Generally, PK and organ accumulation are contradictory factors: smaller size leads to faster excretion and shorter half-lives and thus a lower tendency to reach targets; larger size leads to longer circulation but stronger organ accumulation that leads to toxicity. Organ accumulation has been reported to be size dependent due in large part to engulfing by macrophages. However, publications on the size effect are inconsistent because of complication by the effect of shape that varies from nanoparticle to nanoparticle. Unique to RNA nanotechnology, size could be tuned without a change in shape, resulting in a true size comparison. Here we investigated size effects using RNA squares of identical shape but varying size and shape effects using RNA triangles, squares, and pentagons of identical size but varying shape. We found that circulation time increased with increasing RNA nanoparticle size from 5-25 nm, which is the common size range of therapeutic RNA nanoparticles. Most particles were cleared from the body within 2 hr after systemic injection. Undetectable organ accumulation was found at any time for 5 nm particles. For 20 nm particles, weak signal was found after 24 hr, while accumulation in tumor was strongest during the entire study.

ZnO Nanoparticles Protect RNA from Degradation Better than DNA

Gene therapy and RNA delivery require a nanoparticle (NP) to stabilize these nucleic acids when administered in vivo. The presence of degradative hydrolytic enzymes within these environments limits the nucleic acids' pharmacologic activity. This study compared the effects of nanoscale ZnO and MgO in the protection afforded to DNA and RNA from degradation by DNase, serum or tumor homogenate. For double-stranded plasmid DNA degradation by DNase, our results suggest that the presence of MgO NP can protect DNA from DNase digestion at an elevated temperature (65 °C), a biochemical activity not present in ZnO NP-containing samples at any temperature. In this case, intact DNA was remarkably present for MgO NP after ethidium bromide staining and agarose gel electrophoresis where these same stained DNA bands were notably absent for ZnO NP. Anticancer RNA, polyinosinic-polycytidylic acid (poly I:C) is now considered an anti-metastatic RNA targeting agent and as such there is great interest in its delivery by NP. For it to function, the NP must protect it from degradation in serum and the tumor environment. Surprisingly, ZnO NP protected the RNA from degradation in either serum-containing media or melanoma tumor homogenate after gel electrophoretic analysis, whereas the band was much more diminished in the presence of MgO. For both MgO and ZnO NP, buffer-dependent rescue from degradation occurred. These data suggest a fundamental difference in the ability of MgO and ZnO NP to stabilize nucleic acids with implications for DNA and RNA delivery and therapy.

Graphene Quantum Dots Downregulate Multiple Multidrug-Resistant Genes via Interacting with Their C-Rich Promoters

Multidrug resistance (MDR) is the major factor in the failure of many forms of chemotherapy, mostly due to the increased efflux of anticancer drugs that mediated by ATP-binding cassette (ABC) transporters. Therefore, inhibiting ABC transporters is one of effective methods of overcoming MDR. However, high enrichment of ABC transporters in cells and their broad substrate spectra made to circumvent MDR are almost insurmountable by a single specific ABC transporter inhibitor. Here, this study demonstrates that graphene quantum dots (GQDs) could downregulate the expressions of P-glycoprotein, multidrug resistance protein MRP1, and breast cancer resistance protein genes via interacting with C-rich regions of their promoters. This is the first example that a single reagent could suppress multiple MDR genes, suggesting that it will be possible to target multiple ABC transporters simultaneously with a single reagent. The inhibitory ability of the GQDs to these drug-resistant genes is validated further by reversing the doxorubicin resistance of MCF-7/ADR cells. Notably, GQDs have superb chemical and physical properties, unique structure, low toxicity, and high biocompatibility; hence, their capability of inhibiting multiple drug-resistant genes holds great potential in cancer therapy.

PAMAM dendrimer: a pH-controlled nanosponge

Using fully atomistic molecular dynamics simulation that are several hundred nanoseconds long, we demonstrate the pH-controlled sponge action of PAMAM dendrimer. We show how at varying pH levels, the PAMAM dendrimer acts as a wet sponge; at neutral or low pH levels, the dendrimer expands noticeably and the interior of the dendrimer opens up to host several hundreds to thousands of water molecules depending on the generation number. Increasing the pH (i.e., going from low pH to high pH) leads to the collapse of the dendrimer size, thereby expelling the inner water, which mimics the ‘sponge’ action. As the dendrimer size swells up at a neutral pH or low pH due to the electrostatic repulsion between the primary and tertiary amines that are protonated at this pH, there is dramatic increase in the available solvent accessible surface area (SASA), as well as solvent accessible volume (SAV).

Dendrimers as Nanocarriers for Nucleic Acid and Drug Delivery in Cancer Therapy

Dendrimers are highly branched polymers with easily modifiable surfaces. This makes them promising structures for functionalization and also for conjugation with drugs and DNA/RNA. Their architecture, which can be controlled by different synthesis processes, allows the control of characteristics such as shape, size, charge, and solubility. Dendrimers have the ability to increase the solubility and bioavailability of hydrophobic drugs. The drugs can be entrapped in the intramolecular cavity of the dendrimers or conjugated to their functional groups at their surface. Nucleic acids usually form complexes with the positively charged surface of most cationic dendrimers and this approach has been extensively employed. The presence of functional groups in the dendrimer's exterior also permits the addition of other moieties that can actively target certain diseases and improve delivery, for instance, with folate and antibodies, now widely used as tumor targeting strategies. Dendrimers have been investigated extensively in the medical field, and cancer treatment is one of the greatest areas where they have been most used. This review will consider the main types of dendrimer currently being explored and how they can be utilized as drug and gene carriers and functionalized to improve the delivery of cancer therapy.

A novel penetratin-modified complex for noninvasive intraocular delivery of antisense oligonucleotides

Inhibition of gene expression by nucleic acids is a promising strategy in the treatment of ocular diseases. However, intraocular delivery of nucleic acids to the posterior ocular tissues remains a great challenge due to the presence of various biological barriers. To circumvent this problem, we established a novel penetratin (P) modified poly(amidoamine) dendrimer (D)/hyaluronic acid (H) complex to deliver antisense oligonucleotides (ASOs, O). Complexes (D/O, HD/O and PHD/O) were easily prepared and modification layers (hyaluronic acid and penetratin) were respectively absorbed on the surface via electrostatic interaction. Complexes with different outer layers were characterized as spherical particles with reversed charges. In vitro cellular uptake of ASOs in PHD/O complex was significantly increased than those in other formulations. In vivo studies were carried out after topical instillation of the complexes in the conjunctival sac of mice. Compared with D/O and HD/O, PHD/O exhibited much more distribution in the posterior segment of the eyes and prolonged retention time of ASOs in retina for more than 8h. Taken together, these results indicated that PHD/O complex possessed substantially improved ocular permeability and distribution in the posterior ocular tissues. This work provided a promising noninvasive intraocular delivery strategy for nucleic acids via topical administration.

Cationic cell-penetrating peptides as vehicles for siRNA delivery

RNA interference mediated gene silencing has tremendous applicability in fields ranging from basic biological research to clinical therapy. However, delivery of siRNA across the cell membrane into the cytoplasm, where the RNA silencing machinery is located, is a significant hurdle in most primary cells. Cell-penetrating peptides (CPPs), peptides that possess an intrinsic ability to translocate across cell membranes, have been explored as a means to achieve cellular delivery of siRNA. Approaches using CPPs by themselves or through incorporation into other siRNA delivery platforms have been investigated with the intent of improving cytoplasmic delivery. Here, we review the utilization of CPPs for siRNA delivery with a focus on strategies developed to enhance cellular uptake, endosomal escape and cytoplasmic localization of CPP/siRNA complexes.

Conjugates of small targeting molecules to non-viral vectors for the mediation of siRNA

To use siRNA (small interfering RNA) for gene therapy, a gene delivery system is often necessary to overcome several challenging requirements including rapid excretion, low stability in blood serum, non-specific accumulation in tissues, poor cellular uptake and inefficient intracellular release. Active and/or passive targeting should help the delivery system to reach the desired tissue or cell, to be internalized, and to deliver siRNA to the cytoplasm so that siRNA can inhibit protein synthesis. This review covers conjugates of small targeting molecules and non-viral delivery systems for the mediation of siRNA, with a focus on their transfection properties in order to help the development of new and efficient siRNA delivery systems, as the therapeutic solutions of tomorrow.

STATEMENT OF SIGNIFICANCE

The delivery of siRNA into cells or tissues remains to be a challenge for its applications, an alternative strategy for siRNA delivery systems is direct conjugation of non-viral vectors with targeting moieties for cellular delivery. In comparison to macromolecules, small targeting molecules have attracted great attention due to their many potential advantages including significant simplicity and ease of production, good repeatability and biodegradability. This review will focus on the most recent advances in the delivery of siRNA using conjugates of small targeting molecules and non-viral delivery systems. Based the editor's suggestions, we hope the revised manuscript could provide more profound understanding to the conjugates of targeting molecules to vectors for mediation of siRNA.

Cell-penetrating peptides as noninvasive transmembrane vectors for the development of novel multifunctional drug-delivery systems

Unique characteristics, such as nontoxicity and rapid cellular internalization, allow the cell-penetrating peptides (CPPs) to transport hydrophilic macromolecules into cells, thus, enabling them to execute biological functions. However, some CPPs have limitations due to nonspecificity and easy proteolysis. To overcome such defects, the CPP amino acid sequence can be modified, replaced, and reconstructed for optimization. CPPs can also be used in combination with other drug vectors, fused with their preponderances to create novel multifunctional drug-delivery systems that increase the stability during blood circulation, and also develop novel preparations capable of targeted delivery, along with sustainable and controllable release. Further improvements in CPP structure can facilitate the penetration of macromolecules into diverse biomembrane structures, such as the blood brain barrier, gastroenteric mucosa, and skin dermis. The ability of CPP to act as transmembrane vectors improves the clinical application of some biomolecules to treat central nervous system diseases, increase oral bioavailability, and develop percutaneous-delivery dosage form.

Modular degradable dendrimers enable small RNAs to extend survival in an aggressive liver cancer model

RNA-based cancer therapies are hindered by the lack of delivery vehicles that avoid cancer-induced organ dysfunction, which exacerbates carrier toxicity. We address this issue by reporting modular degradable dendrimers that achieve the required combination of high potency to tumors and low hepatotoxicity to provide a pronounced survival benefit in an aggressive genetic cancer model. More than 1,500 dendrimers were synthesized using sequential, orthogonal reactions where ester degradability was systematically integrated with chemically diversified cores, peripheries, and generations. A lead dendrimer, 5A2-SC8, provided a broad therapeutic window: identified as potent [EC50 < 0.02 mg/kg siRNA against FVII (siFVII)] in dose-response experiments, and well tolerated in separate toxicity studies in chronically ill mice bearing MYC-driven tumors (>75 mg/kg dendrimer repeated dosing). Delivery of let-7 g microRNA (miRNA) mimic inhibited tumor growth and dramatically extended survival. Efficacy stemmed from a combination of a small RNA with the dendrimer's own negligible toxicity, therefore illuminating an underappreciated complication in treating cancer with RNA-based drugs.

Gene Therapeutic Approaches to Overcome ABCB1-Mediated Drug Resistance

Multidrug resistance (MDR) to pharmaceutical active agents is a common clinical problem in patients suffering from cancer. MDR is often mediated by over expression of trans-membrane xenobiotic transport molecules belonging to the superfamily of ATP-binding cassette (ABC)-transporters. This protein family includes the classical MDR-associated transporter ABCB1 (MDR1/P-gp). Inhibition of ABC-transporters by low molecular weight compounds in cancer patients has been extensively investigated in clinical trials, but the results have been disappointing. Thus, in the last decades alternative experimental therapeutic strategies for overcoming MDR were under extensive investigation. These include gene therapeutic approaches applying antisense-, ribozyme-, RNA interference-, and CRISPR/Cas9-based techniques. Various delivery strategies were used to reverse MDR in different tumor models in vitro and in vivo. Results and conclusions of these gene therapeutic studies will be discussed.

Partially PEGylated dendrimer-entrapped gold nanoparticles: a promising nanoplatform for highly efficient DNA and siRNA delivery

Partially PEGylated dendrimer-entrapped gold nanoparticles can be used as a promising nanoplatform for highly efficient pDNA and siRNA delivery.

Oligonucleotide delivery with cell surface binding and cell penetrating Peptide amphiphile nanospheres

A drug delivery system designed specifically for oligonucleotide therapeutics can ameliorate the problems associated with the in vivo delivery of these molecules. The internalization of free oligonucleotides is challenging, and cytotoxicity is the main obstacle for current transfection vehicles. To develop nontoxic delivery vehicles for efficient transfection of oligonucleotides, we designed a self-assembling peptide amphiphile (PA) nanosphere delivery system decorated with cell penetrating peptides (CPPs) containing multiple arginine residues (R4 and R8), and a cell surface binding peptide (KRSR), and report the efficiency of this system in delivering G-3129, a Bcl-2 antisense oligonucleotide (AON). PA/AON (peptide amphiphile/antisense oligonucleotide) complexes were characterized with regards to their size and secondary structure, and their cellular internalization efficiencies were evaluated. The effect of the number of arginine residues on the cellular internalization was investigated by both flow cytometry and confocal imaging, and the results revealed that uptake efficiency improved as the number of arginines in the sequence increased. The combined effect of cell penetration and surface binding property on the cellular internalization and its uptake mechanism was also evaluated by mixing R8-PA and KRSR-PA. R8 and R8/KRSR decorated PAs were found to drastically increase the internalization of AONs compared to nonbioactive PA control. Overall, the KRSR-decorated self-assembled PA nanospheres were demonstrated to be noncytotoxic delivery vectors with high transfection rates and may serve as a promising delivery system for AONs.

Combination of microRNA therapeutics with small-molecule anticancer drugs: mechanism of action and co-delivery nanocarriers

MicroRNAs (miRNAs) regulate multiple molecular pathways vital for the hallmarks of cancer with a high degree of biochemical specificity and potency. By restoring tumor suppressive miRNAs or ablating oncomiRs, miRNA-based therapies can sensitize cancer cells to conventional cytotoxins and the molecularly targeted drugs by promoting apoptosis and autophagy, reverting epithelial-to-mesenchymal transition, suppressing tumor angiogenesis, and downregulating efflux transporters. The development of miRNA-based therapeutics in combination with small-molecule anticancer drugs provides an unprecedented opportunity to counteract chemoresistance and improve treatment outcome in a broad range of human cancers. This review summarizes the mechanisms and advantages for the combination therapies involving miRNAs and small-molecule drugs, as well as the recent advances in the co-delivery nanocarriers for these agents.

Therapeutic face of RNAi: in vivo challenges

INTRODUCTION

RNA interference is a sequence-specific gene silencing phenomenon in which small interfering RNAs (siRNAs) can trigger gene transcriptional and post-transcriptional silencing. This phenomenon represents an emerging therapeutic approach for in vivo studies by efficient delivery of specific synthetic siRNAs against diseases. Therefore, simultaneous development of synthetic siRNAs along with novel delivery techniques is considered as novel and interesting therapeutic challenges.

AREAS COVERED

This review provides a basic explanation to siRNA signaling pathways and their therapeutic challenges. Here, we provide a comprehensive explanation to failed and successful trials and their in vivo challenges.

EXPERT OPINION

Specific, efficient and targeted delivery of siRNAs is the major concern for their in vivo administrations. Also, anatomical barriers, drug stability and availability, immunoreactivity and existence of various delivery routes, different genetic backgrounds are major clinical challenges. However, successful administration of siRNA-based drugs is expected during foreseeable features. But, their systemic applications will depend on strong targeted drug delivery strategies.

gH625: a milestone in understanding the many roles of membranotropic peptides

Here, we review the current knowledge about viral derived membranotropic peptides, and we discuss how they may be used for many therapeutic applications. While they have been initially discovered in viral fusion proteins and have been involved in the mechanism of viral entry, it is now clear that their features and their mode of interaction with membrane bilayers can be exploited to design viral inhibitors as well as to favor delivery of cargos across the cell membrane and across the blood–brain barrier. The peptide gH625 has been extensively used for all these purposes and provides a significant contribution to the field. We describe the roles of this sequence in order to close the gap between the many functions that are now emerging for membranotropic peptides.

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Membranotropic peptides and their therapeutic applications

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Membrane fusion, viral inhibition, drug delivery

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gH625, a peptide derived from Herpes simplex virus type I: a case study

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gH625 in vitro and in vivo delivery across the blood–brain barrier

Targeted delivery of miRNA therapeutics for cardiovascular diseases: opportunities and challenges

Dysregulation of miRNA expression has been associated with many cardiovascular diseases in animal models, as well as in patients. In the present review, we summarize recent findings on the role of miRNAs in cardiovascular diseases and discuss the opportunities, possibilities and challenges of using miRNAs as future therapeutic targets. Furthermore, we focus on the different approaches that can be used to deliver these newly developed miRNA therapeutics to their sites of action. Since siRNAs are structurally homologous with the miRNA therapeutics, important lessons learned from siRNA delivery strategies are discussed that might be applicable to targeted delivery of miRNA therapeutics, thereby reducing costs and potential side effects, and improving efficacy.

mPEG-PAMAM-G4 nucleic acid nanocomplexes: enhanced stability, RNase protection, and activity of splice switching oligomer and poly I:C RNA

Dendrimer chemistries have virtually exploded in recent years with increasing interest in this class of polymers as gene delivery vehicles. An effective nucleic acid delivery vehicle must efficiently bind its cargo and form physically stable complexes. Most importantly, the nucleic acid must be protected in biological fluids and tissues, as RNA is extremely susceptible to nuclease degradation. Here, we characterized the association of nucleic acids with generation 4 PEGylated poly(amidoamine) dendrimer (mPEG-PAMAM-G4). We investigated the formation, size, and stability over time of the nanoplexes at various N/P ratios by gel shift and dynamic light scatter spectroscopy (DLS). Further characterization of the mPEG-PAMAM-G4/nucleic acid association was provided by atomic force microscopy (AFM) and by circular dichroism (CD). Importantly, mPEG-PAMAM-G4 complexation protected RNA from treatment with RNase A, degradation in serum, and various tissue homogenates. mPEG-PAMAM-G4 complexation also significantly enhanced the functional delivery of RNA in a novel engineered human melanoma cell line with splice-switching oligonucleotides (SSOs) targeting a recombinant luciferase transcript. mPEG-PAMAM-G4 triconjugates formed between gold nanoparticle (GNP) and particularly manganese oxide (MnO) nanorods, poly IC, an anticancer RNA, showed enhanced cancer-killing activity by an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) cell viability assay.

Dendrimers as carriers for siRNA delivery and gene silencing: a review

RNA interference (RNAi) was first literaturally reported in 1998 and has become rapidly a promising tool for therapeutic applications in gene therapy. In a typical RNAi process, small interfering RNAs (siRNA) are used to specifically downregulate the expression of the targeted gene, known as the term "gene silencing." One key point for successful gene silencing is to employ a safe and efficient siRNA delivery system. In this context, dendrimers are emerging as potential nonviral vectors to deliver siRNA for RNAi purpose. Dendrimers have attracted intense interest since their emanating research in the 1980s and are extensively studied as efficient DNA delivery vectors in gene transfer applications, due to their unique features based on the well-defined and multivalent structures. Knowing that DNA and RNA possess a similar structure in terms of nucleic acid framework and the electronegative nature, one can also use the excellent DNA delivery properties of dendrimers to develop effective siRNA delivery systems. In this review, the development of dendrimer-based siRNA delivery vectors is summarized, focusing on the vector features (siRNA delivery efficiency, cytotoxicity, etc.) of different types of dendrimers and the related investigations on structure-activity relationship to promote safe and efficient siRNA delivery system.

Acid-degradable core-shell nanoparticles for reversed tamoxifen-resistance in breast cancer by silencing manganese superoxide dismutase (MnSOD)

Drug resistance acquired by cancer cells is a significant challenge in the clinic and requires impairing the responsible pathological pathway. Administering chemotherapeutics along with silencing resistance-basis activity using RNA interference (RNAi) is expected to restore the activity of the chemotherapeutic and generate synergistic cancer eradication. This study attempted to reverse tamoxifen (TAM)-resistance in breast cancer by silencing a mitochondrial enzyme, manganese superoxide dismutase (MnSOD), which dismutates TAM-induced reactive oxygen species (ROS) (i.e., superoxide) to less harmful hydrogen peroxide and hampers therapeutic effects. Breast cancer cells were co-treated with TAM and MnSOD siRNA-delivering nanoparticles (NPs) made of a siRNA/poly(amidoamine) (PAMAM) dendriplex core and an acid-degradable polyketal (PK) shell. The (siRNA/PAMAM)-PK NPs were designed for the PK shell to shield siRNA from nucleases, minimize detrimental aggregation in serum, and facilitate cytosolic release of siRNA from endosomal compartments. This method of forming the PK shell around the siRNA/PAMAM core via surface-initiated photo-polymerization enables ease of tuning NPs' size for readily controlled siRNA release kinetics. The resulting NPs were notably homogenous in size, resistant to aggregation in serum, and invulnerable to heparan sulfate-mediated disassembly, compared to siRNA/PAMAM dendriplexes. Gel electrophoresis and confocal microscopy confirmed efficient siRNA release from the (siRNA/PAMAM)-PK NPs upon stimuli-responsive hydrolysis of the PK shell. Sensitization of TAM-resistant MCF7-BK-TR breast cancer cells with (MnSOD siRNA/PAMAM)-PK NPs restored TAM-induced cellular apoptosis in vitro and significantly suppressed tumor growth in vivo, as confirmed by biochemical assays and histological observations. This study implies that combined gene silencing and chemotherapy is a promising strategy to overcoming a significant challenge in cancer therapy.

Quantitative analysis of generation and branch defects in G5 poly(amidoamine) dendrimer

Although methods have been developed to synthesize and isolate generation 5 (G5) PAMAM dendrimers containing precise numbers of ligands per polymer particle, the presence of skeletal and generational defects in this material can substantially hamper the process. Here we provide a quantitative analysis of G5 PAMAM dendrimer defects via high performance liquid chromatography, potentiometric titration, mass spectrometry, size exclusion chromatography, and nuclear magnetic resonance. We identified, isolated, and characterized the major structural defects of G5 dendrimer, trailing generations, and dimer, trimer, and tetramer species. We determine that the G5 material present in the as-received mixture contains 93 arms on average. We have developed two model systems capable of generating the experimentally observed mass range and polydispersity at defect rates of 8-15%.

Dendrimer nanoparticles for ocular drug delivery

Eye is a unique organ of perfection and complexity, and is a microcosm of the body in many ways. It represents a great opportunity for nanomedicine, since it is readily accessible-allowing for direct drug/gene delivery to maximize the therapeutic effect and minimize side effects. The development of appropriate delivery systems that can sustain and deliver therapeutics to the target tissues is a key challenge that can be addressed by nanotechnology. Dendrimers are tree-like, nanostructured polymers that have received significant attention as ocular drug delivery systems, due to their well-defined size, tailorable structure, and potentially favorable ocular biodistribution. In this review, we highlight recent developments in dendrimer-based ocular therapies for both anterior and posterior segment diseases.

Dendrimers for siRNA Delivery

Since the discovery of the “starburst polymer”, later renamed as dendrimer, this class of polymers has gained considerable attention for numerous biomedical applications, due mainly to the unique characteristics of this macromolecule, including its monodispersity, uniformity, and the presence of numerous functionalizable terminal groups. In recent years, dendrimers have been studied extensively for their potential application as carriers for nucleic acid therapeutics, which utilize the cationic charge of the dendrimers for effective dendrimer-nucleic acid condensation. siRNA is considered a promising, versatile tool among various RNAi-based therapeutics, which can effectively regulate gene expression if delivered successfully inside the cells. This review reports on the advancements in the development of dendrimers as siRNA carriers.