Hydrophobic Effect from Conjugated Chemicals or Drugs on In Vivo Biodistribution of RNA Nanoparticles

RNA nanostructures for targeted drug delivery and imaging

The RNA molecule plays a pivotal role in many biological processes by relaying genetic information, regulating gene expression, and serving as molecular machines and catalyzers. This inherent versatility of RNA has fueled significant advancements in the field of RNA nanotechnology, driving the engineering of complex nanoscale architectures toward biomedical applications, including targeted drug delivery and bioimaging. RNA polymers, serving as building blocks, offer programmability and predictability of Watson-Crick base pairing, as well as non-canonical base pairing, for the construction of nanostructures with high precision and stoichiometry. Leveraging the ease of chemical modifications to protect the RNA from degradation, researchers have developed highly functional and biocompatible RNA architectures and integrated them into preclinical studies for the delivery of payloads and imaging agents. This review offers an educational introduction to the use of RNA as a biopolymer in the design of multifunctional nanostructures applied to targeted delivery in vivo, summarizing physical and biological barriers along with strategies to overcome them. Furthermore, we highlight the most recent progress in the development of both small and larger RNA nanostructures, with a particular focus on imaging reagents and targeted cancer therapeutics in pre-clinical models and provide insights into the prospects of this rapidly evolving field.

Addressing the in vivo delivery of nucleic-acid nanostructure therapeutics

DNA and RNA nanostructures are being investigated as therapeutics, vaccines, and drug delivery systems. These nanostructures can be functionalized with guests ranging from small molecules to proteins with precise spatial and stoichiometric control. This has enabled new strategies to manipulate drug activity and to engineer devices with novel therapeutic functionalities. Although existing studies have offered encouraging in vitro or pre-clinical proof-of-concepts, establishing mechanisms of in vivo delivery is the new frontier for nucleic-acid nanotechnologies. In this review, we first provide a summary of existing literature on the in vivo uses of DNA and RNA nanostructures. Based on their application areas, we discuss current models of nanoparticle delivery, and thereby highlight knowledge gaps on the in vivo interactions of nucleic-acid nanostructures. Finally, we describe techniques and strategies for investigating and engineering these interactions. Together, we propose a framework to establish in vivo design principles and advance the in vivo translation of nucleic-acid nanotechnologies.

Targeted delivery of RNAi to cancer cells using RNA-ligand displaying exosome

Exosome is an excellent vesicle for in vivo delivery of therapeutics, including RNAi and chemical drugs. The extremely high efficiency in cancer regression can partly be attributed to its fusion mechanism in delivering therapeutics to cytosol without endosome trapping. However, being composed of a lipid-bilayer membrane without specific recognition capacity for aimed-cells, the entry into nonspecific cells can lead to potential side-effects and toxicity. Applying engineering approaches for targeting-capacity to deliver therapeutics to specific cells is desirable. Techniques with chemical modification in vitro and genetic engineering in cells have been reported to decorate exosomes with targeting ligands. RNA nanoparticles have been used to harbor tumor-specific ligands displayed on exosome surface. The negative charge reduces nonspecific binding to vital cells with negatively charged lipid-membrane due to the electrostatic repulsion, thus lowering the side-effect and toxicity. In this review, we focus on the uniqueness of RNA nanoparticles for exosome surface display of chemical ligands, small peptides or RNA aptamers, for specific cancer targeting to deliver anticancer therapeutics, highlighting recent advances in targeted delivery of siRNA and miRNA that overcomes the previous RNAi delivery roadblocks. Proper understanding of exosome engineering with RNA nanotechnology promises efficient therapies for a wide range of cancer subtypes.

Effective, Rapid, and Small-Scale Bioconjugation and Purification of "Clicked" Small-Molecule DNA Oligonucleotide for Nucleic Acid Nanoparticle Functionalization

Nucleic acid-based therapeutics involves the conjugation of small molecule drugs to nucleic acid oligomers to surmount the challenge of solubility, and the inefficient delivery of these drug molecules into cells. "Click" chemistry has become popular conjugation approach due to its simplicity and high conjugation efficiency. However, the major drawback of the conjugation of oligonucleotides is the purification of the products, as traditionally used chromatography techniques are usually time-consuming and laborious, requiring copious quantities of materials. Herein, we introduce a simple and rapid purification methodology to separate the excess of unconjugated small molecules and toxic catalysts using a molecular weight cut-off (MWCO) centrifugation approach. As proof of concept, we deployed "click" chemistry to conjugate a Cy3-alkyne moiety to an azide-functionalized oligodeo-xynucleotide (ODN), as well as a coumarin azide to an alkyne-functionalized ODN. The calculated yields of the conjugated products were found to be 90.3 ± 0.4% and 86.0 ± 1.3% for the ODN-Cy3 and ODN-coumarin, respectively. Analysis of purified products by fluorescence spectroscopy and gel shift assays demonstrated a drastic amplitude of fluorescent intensity by multiple folds of the reporter molecules within DNA nanoparticles. This work is intended to demonstrate a small-scale, cost-effective, and robust approach to purifying ODN conjugates for nucleic acid nanotechnology applications.

The dynamic, motile and deformative properties of RNA nanoparticles facilitate the third milestone of drug development

Besides mRNA, rRNA, and tRNA, cells contain many other noncoding RNA that display critical roles in the regulation of cellular functions. Human genome sequencing revealed that the majority of non-protein-coding DNA actually codes for non-coding RNAs. The dynamic nature of RNA results in its motile and deformative behavior. These conformational transitions such as the change of base-pairing, breathing within complemented strands, and pseudoknot formation at the 2D level as well as the induced-fit and conformational capture at the 3D level are important for their biological functions including regulation, translation, and catalysis. The dynamic, motile and catalytic activity has led to a belief that RNA is the origin of life. We have recently reported that the deformative property of RNA nanoparticles enhances their penetration through the leaky blood vessel of cancers which leads to highly efficient tumor accumulation. This special deformative property also enables RNA nanoparticles to pass the glomerulus, overcoming the filtration size limit, resulting in fast renal excretion and rapid body clearance, thus low or no toxicity. The biodistribution of RNA nanoparticles can be further improved by the incorporation of ligands for cancer targeting. In addition to the favorable biodistribution profiles, RNA nanoparticles possess other properties including self-assembly, negative charge, programmability, and multivalency; making it a great material for pharmaceutical applications. The intrinsic negative charge of RNA nanoparticles decreases the toxicity of drugs by preventing nonspecific binding to the negative charged cell membrane and enhancing the solubility of hydrophobic drugs. The polyvalent property of RNA nanoparticles allows the multi-functionalization which can apply to overcome drug resistance. This review focuses on the summary of these unique properties of RNA nanoparticles, which describes the mechanism of RNA dynamic, motile and deformative properties, and elucidates and prepares to welcome the RNA therapeutics as the third milestone in pharmaceutical drug development.

Targeting vascular inflammation through emerging methods and drug carriers

Acute inflammation is a common dangerous component of pathogenesis of many prevalent conditions with high morbidity and mortality including sepsis, thrombosis, acute respiratory distress syndrome (ARDS), COVID-19, myocardial and cerebral ischemia-reperfusion, infection, and trauma. Inflammatory changes of the vasculature and blood mediate the course and outcome of the pathology in the tissue site of insult, remote organs and systemically. Endothelial cells lining the luminal surface of the vasculature play the key regulatory functions in the body, distinct under normal vs. pathological conditions. In theory, pharmacological interventions in the endothelial cells might enable therapeutic correction of the overzealous damaging pro-inflammatory and pro-thrombotic changes in the vasculature. However, current agents and drug delivery systems (DDS) have inadequate pharmacokinetics and lack the spatiotemporal precision of vascular delivery in the context of acute inflammation. To attain this level of precision, many groups design DDS targeted to specific endothelial surface determinants. These DDS are able to provide specificity for desired tissues, organs, cells, and sub-cellular compartments needed for a particular intervention. We provide a brief overview of endothelial determinants, design of DDS targeted to these molecules, their performance in experimental models with focus on animal studies and appraisal of emerging new approaches. Particular attention is paid to challenges and perspectives of targeted therapeutics and nanomedicine for advanced management of acute inflammation.

Novel Perspectives towards RNA-Based Nano-Theranostic Approaches for Cancer Management

In the fight against cancer, early diagnosis is critical for effective treatment. Traditional cancer diagnostic technologies, on the other hand, have limitations that make early detection difficult. Therefore, multi-functionalized nanoparticles (NPs) and nano-biosensors have revolutionized the era of cancer diagnosis and treatment for targeted action via attaching specified and biocompatible ligands to target the tissues, which are highly over-expressed in certain types of cancers. Advancements in multi-functionalized NPs can be achieved via modifying molecular genetics to develop personalized and targeted treatments based on RNA interference. Modification in RNA therapies utilized small RNA subunits in the form of small interfering RNAs (siRNA) for overexpressing the specific genes of, most commonly, breast, colon, gastric, cervical, and hepatocellular cancer. RNA-conjugated nanomaterials appear to be the gold standard for preventing various malignant tumors through focused diagnosis and delivering to a specific tissue, resulting in cancer cells going into programmed death. The latest advances in RNA nanotechnology applications for cancer diagnosis and treatment are summarized in this review.

Ratiometric Fluorescence Monitoring of Antibody-Guided Drug Delivery to Cancer Cells

Ratiometric measurements utilizing two independent fluorescence signals from a dual-dye molecular system help to improve the detection sensitivity and quantification of many analytical, bioanalytical, and pharmaceutical assays, including drug delivery monitoring. Nevertheless, these dual-dye conjugates have never been utilized for ratiometric monitoring of antibody (Ab)-guided targeted drug delivery (TDD). Here, we report for the first time on the new, dual-dye TDD system, Cy5s-Ab-Flu-Aza, comprising the switchable fluorescein-based dye (Flu) linked to the anticancer drug azatoxin (Aza), reference pentamethine cyanine dye (Cy5s), and Her2-specific humanized monoclonal Trastuzumab (Herceptin) antibody. The ability of ratiometric fluorescence monitoring of drug release was demonstrated with this model system in vitro in the example of the human breast cancer SKBR3 cell line overexpressing Her2 receptors. The proposed approach for designing ratiometric, antibody-guided TDD systems, where a "drug-switchable dye" conjugate and a reference dye are independently linked to an antibody, can be expanded to other drugs, dyes, and antibodies. Replacement of the green-emitting dye Flu, which was found not detectable in vivo, with a longer-wavelength (red or near-IR) switchable fluorophore should enable quantification of drug release in the body.

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

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

Non-Small-Cell Lung Cancer Regression by siRNA Delivered Through Exosomes That Display EGFR RNA Aptamer

Lung cancer is the second most common cancer in both men and women and is the leading cause of cancer death in the United States. The development of drug resistance to commonly used chemotherapeutics in non-small-cell lung cancer (NSCLC) poses significant health risks and there is a dire need to improve patient outcomes. In this study, we report the use of RNA nanotechnology to display ligand on exosome that was loaded with small interfering RNA (siRNA) for NSCLC regression in animal trials. Cholesterol was used to anchor the ligand targeting epidermal growth factor receptor on exosomes that were loaded with siRNA to silence the antiapoptotic factor survivin. The cytosolic delivery of siRNA overcame the problem of endosome trapping, leading to potent gene knockdown, chemotherapy sensitization, and tumor regression, thus achieving a favorable IC₅₀ of 20 nmol/kg siRNA encapsulated by exosome particles in the in vivo gene knockdown assessment.

3D RNA nanocage for encapsulation and shielding of hydrophobic biomolecules to improve the in vivo biodistribution

Ribonucleic acid (RNA) nanotechnology platforms have the potential of harboring therapeutics for in vivo delivery in disease treatment. However, the nonspecific interaction between the harbored hydrophobic drugs and cells or other components before reaching the diseased site has been an obstacle in drug delivery. Here we report an encapsulation strategy to prevent such nonspecific hydrophobic interactions in vitro and in vivo based on a self-assembled three-dimensional (3D) RNA nanocage. By placing an RNA three-way junction (3WJ) in the cavity of the nanocage, the conjugated hydrophobic molecules were specifically positioned within the nanocage, preventing their exposure to the biological environment. The assembly of the nanocages was characterized by native polyacrylamide gel electrophoresis (PAGE), atomic force microscopy (AFM), and cryogenic electron microscopy (cryo-EM) imaging. The stealth effect of the nanocage for hydrophobic molecules in vitro was evaluated by gel electrophoresis, flow cytometry, and confocal microscopy. The in vivo sheathing effect of the nanocage for hydrophobic molecules was assessed by biodistribution profiling in mice. The RNA nanocages with hydrophobic biomolecules underwent faster clearance in liver and spleen in comparison to their counterparts. Therefore, this encapsulation strategy holds promise for in vivo delivery of hydrophobic drugs for disease treatment.

Self-assembly of four generations of RNA dendrimers for drug shielding with controllable layer-by-layer release

Chemical dendrimers have been shown to be a promising drug delivery platform due to their advantageous properties such as monodispersity, multivalency and branched structure. Taking advantage of self-assembly and its intrinsic negative charge, we used RNA as the building block for dendrimer construction to eliminate complex synthesis procedures and cationic charge-related toxicity. Oligo ribonucleotides produced by solid phase chemical synthesis allow the large-scale manufacture of homologous RNA dendrimers. Employing concepts from RNA nanotechnology enabled the controllable production of dendrimers with generations from G1, G2, G3, to G4 with layer-by-layer release capability. The conjugation of functional groups into individual RNA strands and the incorporation of functionalized RNA strands into the dendrimers at different sites have been reported. Anticancer drugs loaded into RNA dendrimers showed comparable cancer cell inhibition effect to free drugs. Encapsulation of cell binding ligands and hydrophobic drugs within the dendrimer significantly reduced the efficiency of cell binding and protein binding respectively, demonstrating the shielding effect of RNA dendrimers. The results imply a potential application of RNA dendrimer for delivery, shielding and controlled release of hydrophobic drugs in vivo.

Nucleic Acid Nanoparticles at a Crossroads of Vaccines and Immunotherapies

Vaccines and immunotherapies involve a variety of technologies and act through different mechanisms to achieve a common goal, which is to optimize the immune response against an antigen. The antigen could be a molecule expressed on a pathogen (e.g., a disease-causing bacterium, a virus or another microorganism), abnormal or damaged host cells (e.g., cancer cells), environmental agent (e.g., nicotine from a tobacco smoke), or an allergen (e.g., pollen or food protein). Immunogenic vaccines and therapies optimize the immune response to improve the eradication of the pathogen or damaged cells. In contrast, tolerogenic vaccines and therapies retrain or blunt the immune response to antigens, which are recognized by the immune system as harmful to the host. To optimize the immune response to either improve the immunogenicity or induce tolerance, researchers employ different routes of administration, antigen-delivery systems, and adjuvants. Nanocarriers and adjuvants are of particular interest to the fields of vaccines and immunotherapy as they allow for targeted delivery of the antigens and direct the immune response against these antigens in desirable direction (i.e., to either enhance immunogenicity or induce tolerance). Recently, nanoparticles gained particular attention as antigen carriers and adjuvants. This review focuses on a particular subclass of nanoparticles, which are made of nucleic acids, so-called nucleic acid nanoparticles or NANPs. Immunological properties of these novel materials and considerations for their clinical translation are discussed.

Tuning the size, shape and structure of RNA nanoparticles for favorable cancer targeting and immunostimulation

The past decade has shown exponential growth in the field of RNA nanotechnology. The rapid advances of using RNA nanoparticles for biomedical applications, especially targeted cancer therapy, suggest its potential as a new generation of drug. After the first milestone of small molecule drugs and the second milestone of antibody drugs, it was predicted that RNA drugs, either RNA itself or chemicals/ligands that target RNA, will be the third milestone in drug development. Thus, a comprehensive assessment of the current therapeutic RNA nanoparticles is urgently needed to meet the drug evaluation criteria. Specifically, the pharmacological and immunological profiles of RNA nanoparticles need to be systematically studied to provide insights in rational design of RNA-based therapeutics. By virtue of its programmability and biocompatibility, RNA molecules can be designed to construct sophisticated nanoparticles with versatile functions/applications and highly tunable physicochemical properties. This intrinsic characteristic allows the systemic study of the effects of various properties of RNA nanoparticles on their in vivo behaviors such as cancer targeting and immune responses. This review will focus on the recent progress of RNA nanoparticles in cancer targeting, and summarize the effects of common physicochemical properties such as size and shape on the RNA nanoparticles' biodistribution and immunostimulation profiles. This article is categorized under: Biology-Inspired Nanomaterials > Nucleic Acid-Based Structures Diagnostic Tools > in vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Delivery of Anti-miRNA for Triple-Negative Breast Cancer Therapy Using RNA Nanoparticles Targeting Stem Cell Marker CD133

Triple-negative breast cancer (TNBC) is an aggressive disease with a short median time from relapse to death. The increased aggressiveness, drug resistance, disease relapse, and metastasis are associated with the presence of stem cells within tumors. Several stem cell markers, such as CD24, CD44, CD133, ALDH1, and ABCG2, have been reported, but their roles in breast cancer tumorigenesis remain unclear. Herein, we apply RNA nanotechnology to deliver anti-microRNA (miRNA) for TNBC therapy. The thermodynamically and chemically stable three-way junction (3WJ) motif was utilized as the scaffold to carry an RNA aptamer binding to CD133 receptor and a locked nuclei acid (LNA) sequence for miRNA21 inhibition. Binding assays revealed the specific uptake of the nanoparticles to breast cancer stem cells (BCSCs) and TNBC cells. Functional assays showed that cancer cell migration was reduced, miR21 expression was inhibited, and downstream tumor suppressor PTEN and PDCD4 expressions were upregulated. In vitro and in vivo studies revealed that these therapeutic RNA nanoparticles did not induce cytokine secretion. Systemic injection of these RNA nanoparticles in animal trial demonstrated high specificity in TNBC tumor targeting and high efficacy for tumor growth inhibition. These results revealed the clinical translation potential of these RNA nanoparticles for TNBC therapy.

RNA Micelles for the Systemic Delivery of Anti-miRNA for Cancer Targeting and Inhibition without Ligand

Displaying the advantage of nanoparticles in cancer targeting and drug delivery, micelles have shown great potential in cancer therapy. The mechanism for micelle targeting to cancer without the need for ligands is due to the size advantage of micelles within the lower end of the nanometer scale that is the optimal size for favoring the enhanced permeability and retention (EPR) effect while escaping trapping by macrophages. MicroRNAs are ubiquitous and play critical roles in regulating gene expression, cell growth, and cancer development. However, their in vivo delivery in medical applications is still challenging. Here, we report the targeted delivery of anti-miRNA to cancers via RNA micelles. The phi29 packaging RNA three-way junction (pRNA-3WJ) was used as a scaffold to construct micelles. An oligo with 8nt locked nucleic acid (LNA) complementary to the seed region of microRNA21(miR21) was included in the micelles as an interference molecule for cancer inhibition. These RNA micelles carrying anti-miR21 exhibited strong binding and internalization to cancer cells, inhibited the function of oncogenic miR21, enhanced the expression of the pro-apoptotic factor, and induced cell apoptosis. Animal trials revealed effective tumor targeting and inhibition in xenograft models. The inclusion of folate as a targeting ligand in the micelles did not show significant improvement of the therapeutic efficacy in vivo, suggesting that micelles can carry therapeutics to a target tumor and inhibit its growth without ligands.

Photo-controlled release of paclitaxel and model drugs from RNA pyramids

Stimuli-responsive release of drugs from a nanocarrier in spatial-, temporal-, and dosage-controlled fashions is of great interest in the pharmaceutical industry. Paclitaxel is one of the most effective and popular chemotherapeutic drugs against a number of cancers such as metastatic or nonmetastatic breast cancer, non-small cell lung cancer, refractory ovarian cancer, AIDS-related Kaposi's sarcoma, and head and neck cancers. Here, by taking the advantage of RNA nanotechnology in biomedical and material science, we developed a three-dimensional pyramid-shaped RNA nanocage for a photocontrolled release of cargo, using paclitaxel as a model drug. The light-triggered release of paclitaxel or fluorophore Cy5 was achieved by incorporation of photocleavable spacers into the RNA nanoparticles. Upon irradiation with ultraviolet light, cargos were rapidly released (within 5 min). In vitro treatment of breast cancer cells with the RNA nanoparticles harboring photocleavable paclitaxel showed higher cytotoxicity as compared to RNA nanoparticles without the photocleavable spacer. The methodology provides proof of concept for the application of the light-triggered controlled release of drugs from RNA nanocages.

RNA-based micelles: A novel platform for paclitaxel loading and delivery

RNA can serve as powerful building blocks for bottom-up fabrication of nanostructures for biotechnological and biomedical applications. In addition to current self-assembly strategies utilizing base pairing, motif piling and tertiary interactions, we reported for the first time the formation of RNA based micellar nanoconstruct with a cholesterol molecule conjugated onto one helical end of a branched pRNA three-way junction (3WJ) motif. The resulting amphiphilic RNA micelles consist of a hydrophilic RNA head and a covalently linked hydrophobic lipid tail that can spontaneously assemble in aqueous solution via hydrophobic interaction. Taking advantage of pRNA 3WJ branched structure, the assembled RNA micelles are capable of escorting multiple functional modules. As a proof of concept for delivery for therapeutics, Paclitaxel was loaded into the RNA micelles with significantly improved water solubility. The successful construction of the drug loaded RNA micelles was confirmed and characterized by agarose gel electrophoresis, atomic force microscopy (AFM), dynamic light scattering (DLS), and fluorescence Nile Red encapsulation assay. The estimate critical micelle formation concentration ranges from 39 nM to 78 nM. The Paclitaxel loaded RNA micelles can internalize into cancer cells and inhibit their proliferation. Further studies showed that the Paclitaxel loaded RNA micelles induced cancer cell apoptosis in a Caspase-3 dependent manner but RNA micelles alone exhibited low cytotoxicity. Finally, the Paclitaxel loaded RNA micelles targeted to tumor in vivo without accumulation in healthy tissues and organs. There is also no or very low induction of pro-inflammatory response. Therefore, multivalence, cancer cell permeability, combined with controllable assembly, low or non toxic nature, and tumor targeting are all promising features that make our pRNA micelles a suitable platform for potential drug delivery.

Methods for construction and characterization of simple or special multifunctional RNA nanoparticles based on the 3WJ of phi29 DNA packaging motor

The field of RNA nanotechnology has developed rapidly over the last decade, as more elaborate RNA nanoarchitectures and therapeutic RNA nanoparticles have been constructed, and their applications have been extensively explored. Now it is time to offer different levels of RNA construction methods for both the beginners and the experienced researchers or enterprisers. The first and second parts of this article will provide instructions on basic and simple methods for the assembly and characterization of RNA nanoparticles, mainly based on the pRNA three-way junction (pRNA-3WJ) of phi29 DNA packaging motor. The third part of this article will focus on specific methods for the construction of more sophisticated multivalent RNA nanoparticles for therapeutic applications. In these parts, some simple protocols are provided to facilitate the initiation of the RNA nanoparticle construction in labs new to the field of RNA nanotechnology. This article is intended to serve as a general reference aimed at both apprentices and senior scientists for their future design, construction and characterization of RNA nanoparticles based on the pRNA-3WJ of phi29 DNA packaging motor.

Favorable biodistribution, specific targeting and conditional endosomal escape of RNA nanoparticles in cancer therapy

The past decades have witnessed the successful transition of several nanotechnology platforms into the clinical trials. However, specific delivery of therapeutics to tumors is hindered by several barriers including cancer recognition and tissue penetration, particle heterogeneity and aggregation, and unfavorable pharmacokinetic profiles such as fast clearance and organ accumulation. With the advent of RNA nanotechnology, a series of RNA nanoparticles have been successfully constructed to overcome many of the aforementioned challenges for in vivo cancer targeting with favorable biodistribution profiles. Compared to other nanodelivery platforms, the physiochemical properties of RNA nanoparticles can be tuned with relative ease for investigating the in vivo behavior of nanoparticles upon systemic injection. The size, shape, and surface chemistry, especially hydrophobic modifications, exert significant impacts on the in vivo fate of RNA nanoparticles. Rationally designed RNA nanoparticles with defined stoichiometry and high homogeneity have been demonstrated to specifically target tumor cells while avoiding accumulation in healthy vital organs after systemic injection. RNA nanoparticles were proven to deliver therapeutics such as siRNA and anti-miRNA to block tumor growth in several animal models. Although the release of anti-miRNA from the RNA nanoparticles has achieved high efficiency of tumor regression in multiple animal models, the efficiency of endosomal escape for siRNA delivery needs further improvement. This review focuses on the advances and perspectives of this promising RNA nanotechnology platform for cancer targeting and therapy.