Structural Characterization of Dendriplexes In Vacuo: A Joint Ion Mobility/Molecular Dynamics Investigation

The combination between ion mobility mass spectrometry and molecular dynamics simulations is demonstrated for the first time to afford valuable information on structural changes undergone by dendriplexes containing ds-DNA and low-generation dendrimers when transferred from the solution to the gas phase. Dendriplex ions presenting 1:1 and 2:1 stoichiometries are identified using mass spectrometry experiments, and the collision cross sections (CCS) of the 1:1 ions are measured using drift time ion mobility experiments. Structural predictions using Molecular Dynamics (MD) simulations showed that gas-phase relevant structures, i.e., with a good match between the experimental and theoretical CCS, are generated when the global electrospray process is simulated, including the solvent molecule evaporation, rather than abruptly transferring the ions from the solution to the gas phase. The progressive migration of ammonium groups (either NH₄⁺ from the buffer or protonated amines of the dendrimer) into the minor and major grooves of DNA all along the evaporation processes is shown to compact the DNA structure by electrostatic and hydrogen-bond interactions. The subsequent proton transfer from the ammonium (NH₄⁺ or protonated amino groups) to the DNA phosphate groups allows creation of protonated phosphate/phosphate hydrogen bonds within the compact structures. MD simulations showed major structural differences between the dendriplexes in solution and in the gas phase, not only due to the loss of the solvent but also due to the proton transfers and the huge difference between the solution and gas-phase charge states.

Fluorescence Lifetime Imaging Microscopy (FLIM) of Intracellular Transport by Means of Doubly Labelled siRNA Architectures

For monitoring the intracellular pathway of small interfering RNA (siRNA), both strands were labelled at internal positions by two ATTO dyes as an interstrand Förster resonance energy transfer pair. siRNA double strands show red emission and a short donor lifetime as readout, whereas siRNA antisense single strands show green emission and a long donor lifetime. This readout signals if GFP silencing can be expected (green) or not (red). We attached both dyes to three structurally different alkyne anchors by postsynthetic modifications. There is only a slight preference for the ribofuranoside anchors with the dyes at their 2'-positions. For the first time, the delivery and fate of siRNA in live HeLa cells was tracked by fluorescence lifetime imaging microscopy (FLIM), which revealed a clear relationship between intracellular transport using different transfection methods and knockdown of GFP expression, which demonstrates the potential of our siRNA architectures as a tool for future development of effective siRNA.

Self-assembling ferritin-dendrimer nanoparticles for targeted delivery of nucleic acids to myeloid leukemia cells

BACKGROUND

In recent years, the use of ferritins as nano-vehicles for drug delivery is taking center stage. Compared to other similar nanocarriers, Archaeoglobus fulgidus ferritin is particularly interesting due to its unique ability to assemble-disassemble under very mild conditions. Recently this ferritin was engineered to get a chimeric protein targeted to human CD71 receptor, typically overexpressed in cancer cells.

RESULTS

Archaeoglobus fulgidus chimeric ferritin was used to generate a self-assembling hybrid nanoparticle hosting an aminic dendrimer together with a small nucleic acid. The positively charged dendrimer can indeed establish electrostatic interactions with the chimeric ferritin internal surface, allowing the formation of a protein-dendrimer binary system. The 4 large triangular openings on the ferritin shell represent a gate for negatively charged small RNAs, which access the internal cavity attracted by the dense positive charge of the dendrimer. This ternary protein-dendrimer-RNA system is efficiently uptaken by acute myeloid leukemia cells, typically difficult to transfect. As a proof of concept, we used a microRNA whose cellular delivery and induced phenotypic effects can be easily detected. In this article we have demonstrated that this hybrid nanoparticle successfully delivers a pre-miRNA to leukemia cells. Once delivered, the nucleic acid is released into the cytosol and processed to mature miRNA, thus eliciting phenotypic effects and morphological changes similar to the initial stages of granulocyte differentiation.

CONCLUSION

The results here presented pave the way for the design of a new family of protein-based transfecting agents that can specifically target a wide range of diseased cells.

Polymeric nanoparticles for RNA delivery

As exemplified by recent clinical approval of RNA drugs including the latest COVID-19 mRNA vaccines, RNA therapy has demonstrated great promise as an emerging medicine. Central to the success of RNA therapy is the delivery of RNA molecules into the right cells at the right location. While the clinical success of nanotechnology in RNA therapy has been limited to lipid-based nanoparticles currently, polymers, due to their tunability and robustness, have also evolved as a class of promising material for the delivery of various therapeutics including RNAs. This article overviews different types of polymers used in RNA delivery and the methods for the formulation of polymeric nanoparticles and highlights recent progress of polymeric nanoparticle-based RNA therapy.

Guijarro L, García-Honduvilla N, Álvarez-Mon M, Buján J, García-Gallego S. Dendrimers and Dendritic Materials: From Laboratory to Medical Practice in Infectious Diseases

Infectious diseases are one of the main global public health risks, predominantly caused by viruses, bacteria, fungi, and parasites. The control of infections is founded on three main pillars: prevention, treatment, and diagnosis. However, the appearance of microbial resistance has challenged traditional strategies and demands new approaches. Dendrimers are a type of polymeric nanoparticles whose nanometric size, multivalency, biocompatibility, and structural perfection offer boundless possibilities in multiple biomedical applications. This review provides the reader a general overview about the uses of dendrimers and dendritic materials in the treatment, prevention, and diagnosis of highly prevalent infectious diseases, and their advantages compared to traditional approaches. Examples of dendrimers as antimicrobial agents per se, as nanocarriers of antimicrobial drugs, as well as their uses in gene transfection, in vaccines or as contrast agents in imaging assays are presented. Despite the need to address some challenges in order to be used in the clinic, dendritic materials appear as an innovative tool with a brilliant future ahead in the clinical management of infectious diseases and many other health issues.

Evolution from Covalent to Self-Assembled PAMAM-Based Dendrimers as Nanovectors for siRNA Delivery in Cancer by Coupled In Silico-Experimental Studies. Part I: Covalent siRNA Nanocarriers

Small interfering RNAs (siRNAs) represent a new approach towards the inhibition of gene expression; as such, they have rapidly emerged as promising therapeutics for a plethora of important human pathologies including cancer, cardiovascular diseases, and other disorders of a genetic etiology. However, the clinical translation of RNA interference (RNAi) requires safe and efficient vectors for siRNA delivery into cells. Dendrimers are attractive nanovectors to serve this purpose, as they present a unique, well-defined architecture and exhibit cooperative and multivalent effects at the nanoscale. This short review presents a brief introduction to RNAi-based therapeutics, the advantages offered by dendrimers as siRNA nanocarriers, and the remarkable results we achieved with bio-inspired, structurally flexible covalent dendrimers. In the companion paper, we next report our recent efforts in designing, characterizing and testing a series of self-assembled amphiphilic dendrimers and their related structural alterations to achieve unprecedented efficient siRNA delivery both in vitro and in vivo.

Nanoparticle Delivery of TWIST Small Interfering RNA and Anticancer Drugs: A Therapeutic Approach for Combating Cancer

Breast and ovarian cancer are the leading cause of cancer-related deaths in women in the United States with over 232,000 new Breast Cancer (BC) diagnoses expected in 2018 and almost 40,000 deaths and an estimated 239,000 new ovarian cancer (OC) cases and 152,000 deaths worldwide annually. OC is the most lethal gynecologic malignancy. This high mortality rate is due to tumor recurrence and metastasis, primarily caused by chemoresistant cancer stem-like cells (CSCs). Triple Negative Breast Cancer (TNBC) patients also become resistant to chemotherapy due to recurrence of CSCs. Currently, no ovarian or breast cancer therapies target CSC specifically. TWIST is overexpressed in the majority of chemoresistant cancers resulting in a low survival rate. Our long-term goal is to develop novel treatments for women with ovarian and breast cancer, specifically treatments that sensitize chemoresistant tumors. Despite successful initial surgery and chemotherapy, over 70% of advanced EOC will recur, and only 15-30% of recurrent disease will respond to chemotherapy (Cortez et al., 2017; Berezhnaya, 2010; Jackson et al., 2015). Moreover, drug resistance causes treatment failure in over 90% of patients with metastatic disease (Solmaz et al., 2015). Thus, recurrent metastatic disease is a major clinical challenge without effective therapy. One of the major challenges in the treatment of breast cancer is the presence of a subpopulation of cancer cells that are chemoresistant (CRC) and metastatic. Given that metastasis is the driving force behind mortality for breast and ovarian cancer patients, it is essential to identify the characteristics of these aberrant cancer cells that allow them to spread to distant sites in the body and develop into metastatic tumors. Understanding the metastatic mechanisms driving cancer cell dispersal will open the door to developing novel therapies that prevent metastasis and improve long-term outcomes for patients. In this chapter we assess the feasibility of targeting the Twist and EMT signaling pathways in breast and ovarian cancer. Additional discussions of the pathways that mediate epithelial-mesenchymal transition (EMT), a process that can give rise to chemoresistance. We review potential treatment strategies for targeting EMT and drug resistance as well as the problems that may arise with these targeted delivery therapeutic approaches. Finally, we examine recent advances in the field, including cancer stem cell targeted nanoparticle delivery and small interference RNA (siRNA) technology, and discuss the impact that these approaches may have on translating much needed therapeutic approaches into the clinic, for the benefit of patients battling this devastating disease.

Use of Polyamidoamine Dendrimers in Brain Diseases

Polyamidoamine (PAMAM) dendrimers are one of the smallest and most precise nanomolecules available today, which have promising applications for the treatment of brain diseases. Each aspect of the dendrimer (core, size or generation, size of cavities, and surface functional groups) can be precisely modulated to yield a variety of nanocarriers for delivery of drugs and genes to brain cells in vitro or in vivo. Two of the most important criteria to consider when using PAMAM dendrimers for neuroscience applications is their safety profile and their potential to be prepared in a reproducible manner. Based on these criteria, features of PAMAM dendrimers are described to help the neuroscience researcher to judiciously choose the right type of dendrimer and the appropriate method for loading the drug to form a safe and effective delivery system to the brain.

Novel PAMAM-PEG-Peptide Conjugates for siRNA Delivery Targeted to the Transferrin and Epidermal Growth Factor Receptors

The transferrin (TfR) and epidermal growth factor receptors (EGFR) are known to be overexpressed on the surface of a wide variety of tumor cells. Therefore, the peptides B6 (TfR specific) and GE11 (targeted to the EGFR) were linked to the PAMAM (polyamidoamine) structure via a polyethylenglycol (PEG) 2 kDa chain with the aim of improving the silencing capacity of the PAMAM-based dendriplexes. The complexes showed an excellent binding capacity to the siRNA with a maximal condensation at nitrogen/phosphate (N/P) 2. The nanoparticles formed exhibited hydrodynamic diameters below 200 nm. The zeta potential was always positive, despite the complexes containing the PEG chain in the structure showing a drop of the values due to the shielding effect. The gene silencing capacity was assayed in HeLa and LS174T cells stably transfected with the eGFPLuc cassette. The dendriplexes containing a specific anti luciferase siRNA, assayed at different N/P ratios, were able to mediate a mean decrease of the luciferase expression values of 14% for HeLa and 20% in LS174T cells, compared to an unspecific siRNA-control. (p < 0.05). In all the conditions assayed, dendriplexes resulted to be non-toxic and viability was always above 75%.

Interfacial analysis of siRNA complexes with poly-ethylenimine (PEI) or PAMAM dendrimers in gene delivery

Solution and interfacial analysis has been employed to gain insight into the complexation of siRNA using either G4 PAMAM dendrimers or 25kDa branched poly-ethylenimine (bPEI). The size, charge and shape/structure of the complexing agents were probed using atomic force microscopy (AFM), circular dichroism spectrometry (CD), dynamic light scattering (DLS), and gel electrophoresis (GE). The binding capability of these cationic polymers to the siRNA molecule, subsequently controls the surface/adsorption behaviour of the complexes to a negatively charged surface. G4 PAMAM dendrimers bind to the major groove of the siRNA structure, while bPEI binds to both major and minor groove. PAMAM-siRNA complexes form a thin uniform surface film with adsorption of monomeric particles, whilst bPEI-siRNA complexes adsorb as particles in random orientations at low bPEI concentration and form network structures across the surface at high charge ratio. This is due to their ability to bind to both regions within siRNA. This new understanding of the interfacial behaviour of siRNA complexes correlates with observations of cellular transfection and can be used in the design of optimal transfection agents.

In vitro studies of phospholipid-modified PAMAM-siMDR1 complexes for the reversal of multidrug resistance in human breast cancer cells

The application of RNAi therapeutics is promising in combating several major human diseases including malignant tumors. However, this approach is limited due to its delivery barriers. In this study, we designed a new carrier system loaded with a functional siRNA targeting MDR1 gene to reverse multi-drug resistance (MDR) in human breast cancer MCF-7/ADR cells. Phospholipid-modified PAMAM-siMDR1 complexes were designed on the external decoration of polyamidoamine (PAMAM) with phospholipid (PL) and the electrostatical interaction between PAMAM and siMDR1 to form hybrid nanocomplexes (PL-dendriplexes). Compared with siMDR1 and dendriplexes (PAMAM-siMDR1), this delivery system represented higher gene silencing efficiency, enhanced cellular uptake of siMDR1, decreased p-gp expression, raised cellular accumulation of doxorubicin (DOX) and inhibited the tumor cell migration. Moreover, the siMDR1 loaded PL-dendriplexes worked synergistically with paclitaxel (PTX) for treating MDR, leading to increased cell apoptosis and cell phase regulation. Overall, this study shows that the PL-dendriplexes hold great promise in reversing the drug-resistance in MCF-7/ADR cells.

Electrostatic theory of the assembly of PAMAM dendrimers and DNA

The electrostatic interactions mediated by counterions between a cationic PAMAM dendrimer, modelized as a sphere of radius and cationic surface charge highly increasing with generation, and a DNA, modelized as an anionic elastic line, are analytically calculated in the framework of condensation theory. Under these interactions the DNA is wrapped around the sphere. For excess phosphates relative to dendrimer primary amines, the free energy of the DNA-dendrimer complex displays an absolute minimum when the complex is weakly negatively overcharged. This overcharging opposes gene delivery. For a highly positive dendrimer and a DNA fixed by experimental conditions to a number of phosphates less than the number of dendrimer primary amines, excess amine charges, the dendrimer may at the same time bind stably DNA and interact with negative cell membranes to activate cell transfection in fair agreement with molecular simulations and experiments.

MDM2 knockdown mediated by a triazine-modified dendrimer in the treatment of non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is the most common type of lung cancer and the five-year survival rate is lower in advanced NSCLC patients. Chemotherapy is a widely used strategy in NSCLC treatment, but is usually limited by poor therapeutic efficacy and adverse effects. Therefore, a new therapeutic regimen is needed for NSCLC treatment. Gene therapy is a new strategy in the treatment of NSCLC. However, the lack of efficient and low toxic vectors remains the major obstacle. Here, we developed a biocompatible dendrimer as a non-viral vector for the delivery of mouse double minute2 (MDM2) siRNA in vitro and in vivo to treat NSCLC. The triazine-modified dendrimer efficiently stimulates the down-regulation of MDM2 gene in NSCLC PC9 cells, which induces significant cell apoptosis through the activation of apoptosis markers such as caspase-8 and poly(ADP-ribose) polymerase (PARP) cleavage. Furthermore, the dendrimer/MDM2 siRNA polyplexes showed excellent activity in the inhibition of tumor growth in a PC9 xenograft tumor model. These results suggested that inhibition the expression of MDM2 might be a potential target in NSCLC treatment.

Current progress in nanotechnology applications for diagnosis and treatment of kidney diseases

Significant progress has been made in nanomedicine, primarily in the form of nanoparticles, for theranostic applications to various diseases. A variety of materials, both organic and inorganic, have been used to develop nanoparticles with promise to achieve improved efficacy in medical applications as well as reduced systemic side effects compared to current standard of care medical practices. In particular, this article highlights the recent development and application of nanoparticles for diagnosing and treating nephropathologies.

Applications of dendrimers for brain delivery and cancer therapy

Dendrimers are emerging as potential nonviral vectors for the efficient delivery of drugs and nucleic acids to the brain and cancer cells. These polymers are highly branched, 3D macromolecules with modifiable surface functionalities and available internal cavities that make them attractive as delivery systems for drug and gene delivery applications. This article highlights the recent therapeutic advances resulting from the use of dendrimers for brain targeting and cancer treatment.

Fluorescence and Förster resonance energy transfer investigations on DNA oligonucleotide and PAMAM dendrimer packing interactions in dendriplexes

Considering the importance of short oligonucleotide packing in dendriplex-mediated gene delivery, a direct insight into the 14-mer oligonucleotide and dendrimer interactions using fluorescence and FRET techniques is the focus of this study. Fluorometric titrations of various fluorophore-tagged oligonucleotides with the first three PAMAM dendrimer generations showed a decrease in the fluorescence intensity with two break points, namely Z and Z, for each titration. The first break point for each dendrimer was identical to the neutralization point observed by basic biophysical studies for the corresponding dendrimer generations. Additionally, FRET studies on dual tagged oligonucleotide (DFT) molecules revealed a third break point at the charge ratio (Z) where there was the highest fluorescence energy transfer from the donor to the acceptor fluorophores. Altogether, dendriplex formation was considered to take place via three steps with an increase in the dendrimer concentration, where initially there was monomeric complexation at the neutralization point (Z) followed by loosely held molecular aggregation of the dendrimer (Z). In the final step, dendrimer molecular aggregates were held tightly together for the closest possible packing of the oligonucleotide molecules onto their surface. The effective molecular packing is identified by the highest FRET intensity for the dendrimer of generation 2 at a charge ratio of 0.34 (Z±).

Efficient delivery of small interfering RNA into cancer cells using dodecylated dendrimers

Dodecylated dendrimers show significantly improved gene silencing efficacy after dodecylation. Among the dendrimers, G4-23C12 shows the highest gene knockdown efficacy.

Efficient gene and siRNA delivery with cationic polyphosphoramide with amino moieties in the main chain

A novel cation polyphosphoramide with amino moieties in the main chain was synthesized, which can be used as efficient carriers for plasmid and siRNA.

Copper(II) binding to flexible triethanolamine-core PAMAM dendrimers: a combined experimental/in silico approach

The structure of copper(II) complexes formed with triethanolamine (TEA) core poly(amidoamine) (PAMAM) dendrimers from generation 0 (G0) to 4 (G4) were investigated by the electron paramagnetic resonance (EPR) technique and molecular simulations. Different square planar coordination modes were detected as a function of copper(II) concentration, whose dynamic evolution relates to the high structural flexibility peculiar to this dendrimer family. Modulated by generation and solvation effects, copper(II) complexation begins at the dendrimer core and progresses to the dendrimer periphery. Differently from the ethylenediamine (EDA) core PAMAM dendrimers, the copper complexes involving the TEA core showed high mobility and saturation of the internal sites above the 1 : 1 molar ratio between the dendrimers and the ions. Therefore, by combining EPR and molecular simulations for the first time, ultimately we obtained unique information on structure, dynamics and copper interacting ability of these dendrimers which could be successfully exploited in biomedical applications.

Targeted delivery of Dicer-substrate siRNAs using a dual targeting peptide decorated dendrimer delivery system

Small interfering RNAs (siRNA) are emerging as novel therapeutic agents, providing competent delivery systems that are available. Dendrimers, a special family of synthetic macromolecules, represent an exciting delivery platform by virtue of their well-defined dendritic structure and unique multivalency and cooperativity confined within a nanoscale volume. Here, we report a Dicer-substrate siRNA (dsiRNA) which, when delivered using a structurally flexible triethanolamine-core poly(amidoamine) dendrimer of generation 5 as the nanocarrier, gives rise to a much greater RNAi response than that produced with conventional siRNA. Further decoration of the dsiRNA/dendrimer complexes with a dual targeting peptide simultaneously promoted cancer cell targeting through interacting with integrins and cell penetration via the interaction with neuropilin-1 receptors, which led to improved gene silencing and anticancer activity. Altogether, our results disclosed here open a new avenue for therapeutic implementation of RNAi using dendrimer nanovector based targeted delivery.

FROM THE CLINICAL EDITOR

This study demonstrates superior therapeutic properties of siRNA when combined with a dendrimer-based targeted nano-delivery system. Similar approaches may eventually gain clinical utility following additional studies determining safety and efficacy.

Arginine-terminated generation 4 PAMAM dendrimer as an effective nanovector for functional siRNA delivery in vitro and in vivo

Successful therapeutic implementation of RNA interference critically depends on systems able to safely and efficiently deliver small interfering RNA (siRNA). Dendrimers are emerging as appealing nanovectors for siRNA delivery by virtue of their unique well-defined dendritic nanostructure within which is confined an intriguing cooperativity and multivalency. We have previously demonstrated that structurally flexible triethanolamine (TEA) core poly(amidoamine) (PAMAM) dendrimers of high generations are effective nanovectors for siRNA delivery in vitro and in vivo. In the present study, we have developed arginine-terminated dendrimers with the aim of combining and harnessing the unique siRNA delivery properties of the TEA-core PAMAM dendrimer and the cell-penetrating advantages of the arginine-rich motif. A generation 4 dendrimer of this family (G4Arg) formed stable dendriplexes with siRNA, leading to improved cell uptake of siRNA by comparison with its nonarginine bearing dendrimer counterpart. Moreover, G4Arg was demonstrated to be an excellent nanocarrier for siRNA delivery, yielding potent gene silencing and anticancer effects in prostate cancer models both in vitro and in vivo with no discernible toxicity. Consequently, importing an arginine residue on the surface of a dendrimer is an appealing option to improve delivery efficiency, and at the same time, the dendrimer G4Arg constitutes a highly promising nanovector for efficacious siRNA delivery and holds great potential for further therapeutic applications.

Nanoparticle-Based Delivery of RNAi Therapeutics: Progress and Challenges

RNA interference (RNAi) is an evolutionarily conserved, endogenous process for post-transcriptional regulation of gene expression. Although RNAi therapeutics have recently progressed through the pipeline toward clinical trials, the application of these as ideal, clinical therapeutics requires the development of safe and effective delivery systems. Inspired by the immense progress with nanotechnology in drug delivery, efforts have been dedicated to the development of nanoparticle-based RNAi delivery systems. For example, a precisely engineered, multifunctional nanocarrier with combined passive and active targeting capabilities may address the delivery challenges for the widespread use of RNAi as a therapy. Therefore, in this review, we introduce the major hurdles in achieving efficient RNAi delivery and discuss the current advances in applying nanotechnology-based delivery systems to overcome the delivery hurdles of RNAi therapeutics. In particular, some representative examples of nanoparticle-based delivery formulations for targeted RNAi therapeutics are highlighted.

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.

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.

Nanoscale drug delivery systems for enhanced drug penetration into solid tumors: current progress and opportunities

Poor penetration of anticancer drags into solid tumors significantly limits their efficacy. This phenomenon has long been observed for small-molecule chemotherapeutics, and it can be even more pronounced for nanoscale therapies. Nanoparticles have enormous potential for the treatment of cancer due to their wide applicability as drug delivery and imaging vehicles and their size-dependent accumulation into solid tumors by the enhanced permeability and retention (EPR) effect. Further, synthetic nanoparticles can be engineered to overcome barriers to drag delivery. Despite their promise for the treatment of cancer, relatively little work has been done to study and improve their ability to diffuse into solid tumors following passive accumulation in the tumor vasculature. In this review, we present the complex issues governing efficient penetration of nanoscale therapies into solid tumors. The current methods available to researchers to study nanoparticle penetration into malignant tumors are described, and the most recent works studying the penetration of nanoscale materials into solid tumors are summarized. We conclude with an overview of the important nanoparticle design parameters governing their tumor penetration, as well as by highlighting critical directions in this field.

Efficient delivery of sticky siRNA and potent gene silencing in a prostate cancer model using a generation 5 triethanolamine-core PAMAM dendrimer

Successful achievement of RNA interference in therapeutic applications requires safe and efficient vectors for siRNA delivery. In the present study, we demonstrate that a triethanolamine (TEA)-core PAMAM dendrimer of generation 5 (G(5)) is able to deliver sticky siRNAs bearing complementary A(n)/T(n) 3'-overhangs effectively to a prostate cancer model in vitro and in vivo and produce potent gene silencing of the heat shock protein 27, leading to a notable anticancer effect. The complementary A(n)/T(n) (n = 5 or 7) overhangs characteristic of these sticky siRNA molecules help the siRNA molecules self-assemble into "gene-like" longer double-stranded RNAs thus endowing a low generation dendrimer such as G(5) with greater delivery capacity. In addition, the A(n)/T(n) (n = 5 or 7) overhangs act as protruding molecular arms that allow the siRNA molecule to enwrap the dendrimer and promote a better interaction and stronger binding, ultimately contributing toward the improved delivery activity of G(5). Consequently, the low generation dendrimer G(5) in combination with sticky siRNA therapeutics may constitute a promising gene silencing-based approach for combating castration-resistant prostate tumors or other cancers and diseases, for which no effective treatment currently exists.

Systemic administration of combinatorial dsiRNAs via nanoparticles efficiently suppresses HIV-1 infection in humanized mice

We evaluated the in vivo efficacy of structurally flexible, cationic PAMAM dendrimers as a small interfering RNA (siRNA) delivery system in a Rag2(-)/-γc-/- (RAG-hu) humanized mouse model for HIV-1 infection. HIV-infected humanized Rag2-/-γc-/- mice (RAG-hu) were injected intravenously (i.v.) with dendrimer-siRNA nanoparticles consisting of a cocktail of dicer substrate siRNAs (dsiRNAs) targeting both viral and cellular transcripts. We report in this study that the dendrimer-dsiRNA treatment suppressed HIV-1 infection by several orders of magnitude and protected against viral induced CD4(+) T-cell depletion. We also demonstrated that follow-up injections of the dendrimer-cocktailed dsiRNAs following viral rebound resulted in complete inhibition of HIV-1 titers. Biodistribution studies demonstrate that the dendrimer-dsiRNAs preferentially accumulate in peripheral blood mononuclear cells (PBMCs) and liver and do not exhibit any discernable toxicity. These data demonstrate for the first time efficacious combinatorial delivery of anti-host and -viral siRNAs for HIV-1 treatment in vivo. The dendrimer delivery approach therefore represents a promising method for systemic delivery of combinations of siRNAs for treatment of HIV-1 infection.

Elucidating the molecular mechanism of PAMAM-siRNA dendriplex self-assembly: effect of dendrimer charge density

Dendrimers are attractive vehicles for nucleic acid delivery due to monodispersity and ease of chemical design. The purpose of this study was to elucidate the self-assembly process between small interfering RNA (siRNA) and different generation poly(amidoamine) dendrimers and to characterize the resulting structures. The generation 4 (G4) and G7 displayed equal efficiencies for dendriplex aggregate formation, whereas G1 lacked this ability. Nanoparticle tracking analysis and dynamic light scattering showed reduced average size and increased polydispersity at higher dendrimer concentration. The nanoparticle tracking analysis indicated that electrostatic complexation results in an equilibrium between differently sized complex aggregates, where the centre of mass depends on the siRNA:dendrimer ratio. Isothermal titration calorimetric data suggested a simple binding for G1, whereas a biphasic binding was evident for G4 and G7 with an initial exothermic binding and a secondary endothermic formation of larger dendriplex aggregates, followed by agglomeration. The initial binding became increasingly exothermic as the generation increased, and the values were closely predicted by molecular dynamics simulations, which also demonstrated a generation dependent differences in the entropy of binding. The flexible G1 displayed the highest entropic penalty followed by the rigid G7, making the intermediate G4 the most suitable for dendriplex formation, showing favorable charge density for siRNA binding.

Molecular modeling and in vivo imaging can identify successful flexible triazine dendrimer-based siRNA delivery systems

This study aimed to identify suitable siRNA delivery systems based on flexible generation 2-4 triazine dendrimers by correlating physico-chemical and biological in vitro and in vivo properties of the complexes with thermodynamic parameters calculated using molecular modeling. The siRNA binding properties of the dendrimers and PEI 25 kDa were simulated, binding and stability were measured in SYBR Gold assays, and hydrodynamic diameters, zeta potentials, and cytotoxicity were quantified. These parameters were compared with cellular uptake of the complexes and their ability to mediate RNAi. Radiolabeled complexes were administered intravenously, and pharmacokinetic profiles and biodistribution of these polyplexes were assessed both invasively and non-invasively. All flexible triazine dendrimers formed thermodynamically more stable complexes than PEI. While PEI and the generation 4 dendrimer interacted more superficially with siRNA, generation 2 and 3 virtually coalesced with siRNA, forming a tightly intertwined structure. These dendriplexes were therefore more efficiently charge-neutralized than PEI complexes, reducing agglomeration. This behavior was confirmed by results of hydrodynamic diameters (72.0 nm-153.5 nm) and zeta potentials (4.9 mV-21.8 mV in 10 mM HEPES) of the dendriplexes in comparison to PEI complexes (312.8 nm-480.0 nm and 13.7 mV-17.4 mV in 10 mM HEPES). All dendrimers, even generation 3 and 4, were less toxic than PEI. All dendriplexes were efficiently endocytosed and showed significant and specific luciferase knockdown in HeLa/Luc cells. Scintillation counting confirmed that the generation 2 triazine complexes showed more than twofold prolonged circulation times as a result of their good thermodynamic stability. Conversely, generation 3 complexes dissociated in vivo, and generation 4 complexes were captured by the reticulo-endothelial system due to their increased surface charge. Molecular modeling proves very valuable for rationalizing experimental parameters based on the dendrimers' structural properties. Non-invasive molecular imaging predicted the in vivo fate of the complexes. Therefore, both techniques effectively promote the rapid development of safe and efficient siRNA formulations that are stable in vivo.

Neutral coatings for the study of polycation/multicharged anion interactions by capillary electrophoresis: application to dendrigraft poly-L-lysines with negatively multicharged molecules

The study of interactions between oppositely multicharged (macro)molecules remains a challenging issue. In frontal analysis capillary electrophoresis (FACE), it is difficult to avoid the adsorption of one of the interacting partners onto the capillary wall. In this work, we demonstrate the possibility to use FACE and affinity capillary electrophoresis (ACE) on a neutrally coated capillary for the study of interactions between a polycationic dendrigraft (or linear) poly-l-lysines, on one hand, and a multicharged anionic biomolecule (adenosine monophosphate, AMP, or adenosine triphosphate, ATP), on the other hand. A systematic comparison of four different neutral coatings (hydroxypropyl cellulose, polydimethylacrylamide, polyacrylamide, polyethylene glycol) has been performed based on the repeatability of the electrophoretic migration of the dendrigraft poly-l-lysines at pH close to neutrality. Both FACE and ACE methodogies were then used to study the interactions and to get the association constants and the stoichiometry of the complex. Multisite interactions, with two classes of independent sites, were determined. The specificity of the dendritic polylysine structure compared with linear polylysine in the interaction with ATP or AMP is also emphasized.

Structure, dynamics, and energetics of siRNA-cationic vector complexation: a molecular dynamics study

The design and synthesis of safe and efficient nonviral vectors for gene delivery has attracted significant attention in recent years. Previous experiments have revealed that the charge density of a polycation (the carrier) plays a crucial role in complexation and the release of the gene from the complex in the cytosol. In this work, we adopt an atomistic molecular dynamics simulation approach to study the complexation of short strand duplex RNA with six cationic carrier systems of varying charge and surface topology. The simulations reveal detailed molecular-level pictures of the structures and dynamics of the RNA-polycation complexes. Estimates for the binding free energy indicate that electrostatic contributions are dominant followed by van der Waals interactions. The binding free energy between the 8(+)polymers and the RNA is found to be larger than that of the 4(+)polymers, in general agreement with previously published data. Because reliable binding free energies provide an effective index of the ability of the polycationic carrier to bind the nucleic acid and also carry implications for the process of gene release within the cytosol, these novel simulations have the potential to provide us with a much better understanding of key mechanistic aspects of gene-polycation complexation and thereby advance the rational design of nonviral gene delivery systems.