Sterically Polymer-Based Liposomal Complexes with Dual-Shell Structure for Enhancing the siRNA Delivery

A Comprehensive Review of Small Interfering RNAs (siRNAs): Mechanism, Therapeutic Targets, and Delivery Strategies for Cancer Therapy

Small interfering RNA (siRNA) delivery by nanocarriers has been identified as a promising strategy in the study and treatment of cancer. Short nucleotide sequences are synthesized exogenously to create siRNA, which triggers RNA interference (RNAi) in cells and silences target gene expression in a sequence-specific way. As a nucleic acid-based medicine that has gained popularity recently, siRNA exhibits novel potential for the treatment of cancer. However, there are still many obstacles to overcome before clinical siRNA delivery devices can be developed. In this review, we discuss prospective targets for siRNA drug design, explain siRNA drug properties and benefits, and give an overview of the current clinical siRNA therapeutics for the treatment of cancer. Additionally, we introduce the siRNA chemical modifications and delivery systems that are clinically sophisticated and classify bioresponsive materials for siRNA release in a methodical manner. This review will serve as a reference for researchers in developing more precise and efficient targeted delivery systems, promoting ongoing advances in clinical applications.

Design, strategies, and therapeutics in nanoparticle-based siRNA delivery systems for breast cancer

Utilizing small interfering RNA (siRNA) as a treatment for cancer, a disease largely driven by genetic aberrations, shows great promise. However, implementing siRNA therapy in clinical practice is challenging due to its limited bioavailability following systemic administration. An attractive approach to address this issue is the use of a nanoparticle (NP) delivery platform, which protects siRNA and delivers it to the cytoplasm of target cells. We provide an overview of design considerations for using lipid-based NPs, polymer-based NPs, and inorganic NPs to improve the efficacy and safety of siRNA delivery. We focus on the chemical structure modification of carriers and NP formulation optimization, NP surface modifications to target breast cancer cells, and the linking strategy and intracellular release of siRNA. As a practical example, recent advances in the development of siRNA therapeutics for treating breast cancer are discussed, with a focus on inhibiting cancer growth, overcoming drug resistance, inhibiting metastasis, and enhancing immunotherapy.

Emerging Approaches for Enabling RNAi Therapeutics

RNA interference (RNAi) is a primitive evolutionary mechanism developed to escape incorporation of foreign genetic material. siRNA has been instrumental in achieving the therapeutic potential of RNAi by theoretically silencing any gene of interest in a reversible and sequence-specific manner. Extrinsically administered siRNA generally needs a delivery vehicle to span across different physiological barriers and load into the RISC complex in the cytoplasm in its functional form to show its efficacy. This review discusses the designing principles and examples of different classes of delivery vehicles that have proved to be efficient in RNAi therapeutics. We also briefly discuss the role of RNAi therapeutics in genetic and rare diseases, epigenetic modifications, immunomodulation and combination modality to inch closer in creating a personalized therapy for metastatic cancer. At the end, we present, strategies and look into the opportunities to develop efficient delivery vehicles for RNAi which can be translated into clinics.

Short interfering RNA (siRNA)-Based Therapeutics for Cartilage Diseases

Articular cartilage injury, as a hallmark of arthritic diseases, is difficult to repair and causes joint pain, stiffness, and loss of mobility. Over the years, the most significant problems for the drug-based treatment of arthritis have been related to drug administration and delivery. In recent years, much research has been devoted to developing new strategies for repairing or regenerating the damaged osteoarticular tissue. The RNA interference (RNAi) has been suggested to have the potential for implementation in targeted therapy in which the faulty gene can be edited by delivering its complementary Short Interfering RNA (siRNA) at the post-transcriptional stage. The successful editing of a specific gene by the delivered siRNA might slow or halt osteoarthritic diseases without side effects caused by chemical inhibitors. However, cartilage siRNA delivery remains a challenging objective because cartilage is an avascular and very dense tissue with very low permeability. Furthermore, RNA is prone to degradation by serum nucleases (such as RNase H and RNase A) due to an extra hydroxyl group in its phosphodiester backbone. Therefore, successful delivery is the first and most crucial requirement for efficient RNAi therapy. Nanomaterials have emerged as highly advantage tools for these studies, as they can be engineered to protect siRNA from degrading, address barriers in siRNA delivery to joints, and target specific cells. This review will discuss recent breakthroughs of different siRNA delivery technologies for cartilage diseases.

Polymeric Drug Delivery Systems Bearing Cholesterol Moieties: A Review

This review aims to provide an overview of polymers comprising cholesterol moiety/ies designed to be used in drug delivery. Over the last two decades, there have been many papers published in this field, which are summarized in this review. The primary focus of this article is on the methods of synthesis of polymers bearing cholesterol in the main chain or as side chains. The data related to the composition, molecular weight, and molecular weight distribution of polymers are presented. Moreover, other aspects, such as forms of carriers, types of encapsulated drugs, encapsulation efficiency and capacity, are also included.

To Conjugate or to Package? A Look at Targeted siRNA Delivery Through Folate Receptors

RNA interference (RNAi) applications have evolved from experimental tools to study gene function to the development of a novel class of gene-silencing therapeutics. Despite decades of research, it was not until August 2018 that the US FDA approved the first-ever RNAi drug, marking a new era for RNAi therapeutics. Although there are many limitations associated with the inherent structure of RNA, delivery to target cells and tissues remains the most challenging. RNAs are unable to diffuse across cellular membranes due to their large size and polyanionic backbone and, therefore, require a delivery vector. RNAi molecules can be conjugated to a targeting ligand or packaged into a delivery vehicle. Alnylam has used both strategies in their FDA-approved formulations to achieve efficient delivery to the liver. To harness the full potential of RNAi therapeutics, however, we must be able to target additional cells and tissues. One promising target is the folate receptor α, which is overexpressed in a variety of tumors despite having limited expression and distribution in normal tissues. Folate can be conjugated directly to the RNAi molecule or used to functionalize delivery vehicles. In this review, we compare both delivery strategies and discuss the current state of research in the area of folate-mediated delivery of RNAi molecules.

Lipid and Polymer-Based Nanoparticle siRNA Delivery Systems for Cancer Therapy

RNA interference (RNAi) uses small interfering RNAs (siRNAs) to mediate gene-silencing in cells and represents an emerging strategy for cancer therapy. Successful RNAi-mediated gene silencing requires overcoming multiple physiological barriers to achieve efficient delivery of siRNAs into cells in vivo, including into tumor and/or host cells in the tumor micro-environment (TME). Consequently, lipid and polymer-based nanoparticle siRNA delivery systems have been developed to surmount these physiological barriers. In this article, we review the strategies that have been developed to facilitate siRNA survival in the circulatory system, siRNA movement from the blood into tissues and the TME, targeted siRNA delivery to the tumor or specific cell types, cellular uptake, and escape from endosomal degradation. We also discuss the use of various types of lipid and polymer-based carriers for cancer therapy, including a section on anti-tumor nanovaccines enhanced by siRNAs. Finally, we review current and recent clinical trials using NPs loaded with siRNAs for cancer therapy. The siRNA cancer therapeutics field is rapidly evolving, and it is conceivable that precision cancer therapy could, in the relatively near future, benefit from the combined use of cancer therapies, for example immune checkpoint blockade together with gene-targeting siRNAs, personalized for enhancing and fine-tuning a patient's therapeutic response.

Efficient nanocarriers of siRNA therapeutics for cancer treatment

Nanocarriers as drug delivery systems are promising and becoming popular, especially for cancer treatment. In addition to improving the pharmacokinetics of poorly soluble hydrophobic drugs by solubilizing them in a hydrophobic core, nanocarriers allow cancer-specific combination drug deliveries by inherent passive targeting phenomena and adoption of active targeting strategies. Nanoparticle-drug formulations can enhance the safety, pharmacokinetic profiles, and bioavailability of locally or systemically administered drugs, leading to improved therapeutic efficacy. Gene silencing by RNA interference (RNAi) is rapidly developing as a personalized field of cancer treatment. Small interfering RNAs (siRNAs) can be used to switch off specific cancer genes, in effect, "silence the gene, silence the cancer." siRNA can be used to silence specific genes that produce harmful or abnormal proteins. The activity of siRNA can be used to harness cellular machinery to destroy a corresponding sequence of mRNA that encodes a disease-causing protein. At present, the main barrier to implementing siRNA therapies in clinical practice is the lack of an effective delivery system that protects the siRNA from nuclease degradation, delivers to it to cancer cells, and releases it into the cytoplasm of targeted cancer cells, without creating adverse effects. This review provides an overview of various nanocarrier formulations in both research and clinical applications with a focus on combinations of siRNA and chemotherapeutic drug delivery systems for the treatment of multidrug resistant cancer. The use of various nanoparticles for siRNA-drug delivery, including liposomes, polymeric nanoparticles, dendrimers, inorganic nanoparticles, exosomes, and red blood cells for targeted drug delivery in cancer is discussed.

Lipid Nanoparticles for Delivery of Therapeutic RNA Oligonucleotides

Gene therapy is an exciting field that has the potential to address emerging scientific and therapeutic tasks. RNA-based gene therapy has made remarkable progress in recent decades. Nevertheless, efficient targeted delivery of RNA therapeutics is still a prerequisite for entering the clinics. In this review, we introduce current delivery methods for RNA gene therapeutics based on lipid nanoparticles (LNPs). We focus on the clinical appeal of recent RNA NPs and discuss existing challenges of fabrication and screening LNP candidates for effective translation into drugs of human metabolic diseases and cancer.

pH-Responsive Polyion Complex Vesicle with Polyphosphobetaine Shells

When a bioactive molecule is taken into cells by endocytosis, it is sometimes unable to escape from the lysosomes, resulting in inefficient drug release. We prepared pH-responsive polyion complex (PIC) vesicles that collapse under acidic conditions such as those inside a lysosome. Furthermore, under acidic conditions, cationic polymer was released from the PIC vesicles to break the lysosome membranes. Diblock copolymers (P₂₀M₁₆₇ and P₂₀A₁₉₀) consisting of water-soluble zwitterionic poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) block and cationic or anionic blocks were synthesized via reversible addition-fragmentation chain transfer (RAFT) radical polymerization. Poly(3-(methacrylamidopropyl) trimethylammonium chloride) (PMAPTAC) and poly(sodium 6-acrylamidohexanoate) (PAaH) were used as the cationic and anionic blocks, respectively. The pendant hexanoate groups in the PAaH block are ionized in basic water and in phosphate buffered saline (PBS), while the hexanoate groups are protonated in acidic water. In basic water, PIC vesicles were formed from a charge neutralized mixture of oppositely charged diblock copolymers. At the interface of PIC vesicle and water exists biocompatible PMPC shells. Under acidic conditions, the PIC vesicles collapsed, because the charge balance shifted due to protonation of the PAaH block. After collapse of the PIC vesicles, P₂₀A₁₉₀ formed micelles composed of protonated PAaH core and PMPC shells, while P₂₀M₁₆₇ was released as unimers. PIC vesicles can encapsulate hydrophilic nonionic guest molecules into their hollow core. Under acidic conditions, the PIC vesicles can release the guest molecules and P₂₀M₁₆₇. The cationic P₂₀M₁₆₇ can break the lysosome membrane to efficiently release the guest molecules from the lysosomes to the cytoplasm.

Targeted Delivery of siRNA Therapeutics to Malignant Tumors

Over the past 20 years, a diverse group of ligands targeting surface biomarkers or receptors has been identified with several investigated to target siRNA to tumors. Many approaches to developing tumor-homing peptides, RNA and DNA aptamers, and single-chain variable fragment antibodies by using phage display, in vitro evolution, and recombinant antibody methods could not have been imagined by researchers in the 1980s. Despite these many scientific advances, there is no reason to expect that the ligand field will not continue to evolve. From development of ligands based on novel or existing biomarkers to linking ligands to drugs and gene and antisense delivery systems, several fields have coalesced to facilitate ligand-directed siRNA therapeutics. In this review, we discuss the major categories of ligand-targeted siRNA therapeutics for tumors, as well as the different strategies to identify new ligands.

Nanoparticles for siRNA-Based Gene Silencing in Tumor Therapy

Gene silencing through RNA interference (RNAi) has emerged as a potential strategy in manipulating cancer causing genes by complementary base-pairing mechanism. Small interfering RNA (siRNA) is an important RNAi tool that has found significant application in cancer therapy. However due to lack of stability, poor cellular uptake and high probability of loss-of-function due to degradation, siRNA therapeutic strategies seek safe and efficient delivery vehicles for in vivo applications. The current review discusses various nanoparticle systems currently used for siRNA delivery for cancer therapy, with emphasis on liposome based gene delivery systems. The discussion also includes various methods availed to improve nanoparticle based-siRNA delivery with target specificity and superior efficiency. Further this review describes challenges and perspectives on the development of safe and efficient nanoparticle based-siRNA-delivery systems for cancer therapy.

Therapeutic Potentials of Noncoding RNAs: Targeted Delivery of ncRNAs in Cancer Cells

Knowledge of multiple actions of short noncoding RNAs (ncRNAs) has truly allowed for viewing DNA, RNA, and protein in novel ways. The ncRNAs are an attractive new class of therapeutics, especially against undruggable targets for the treatment of cancer and other diseases. Despite the potential of ncRNAs in cancer therapy, many challenges remain, including rapid degradation and clearance, poor cellular uptake, off-target effects, and immunogenicity. Rational design, chemical modifications, and delivery carriers offer significant opportunities to overcome these challenges. In this chapter, the development of ncRNAs as cancer therapeutics from early stages to clinical trials and strategies for ncRNA-targeted delivery to cancer cells will be introduced.

Synthesis and evaluation of the targeted binding of RGD-containing PEGylated-PEI/DNA polyplex micelles as radiotracers for a tumor-targeting imaging probe

Polyplex micelles with pEGFP and RGD-modified poly(ethylene glycol)-grafted polyethylenimine (E[c(RGDyK)]₂-PEG-g-PEI) and were labeled with ^99mTc for the in vivo study as proficient probes for molecular imaging.

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.

Enhancing endosomal escape for nanoparticle mediated siRNA delivery

Gene therapy with siRNA is a promising biotechnology to treat cancer and other diseases. To realize siRNA-based gene therapy, a safe and efficient delivery method is essential. Nanoparticle mediated siRNA delivery is of great importance to overcome biological barriers for systemic delivery in vivo. Based on recent discoveries, endosomal escape is a critical biological barrier to be overcome for siRNA delivery. This feature article focuses on endosomal escape strategies used for nanoparticle mediated siRNA delivery, including cationic polymers, pH sensitive polymers, calcium phosphate, and cell penetrating peptides. Work has been done to develop different endosomal escape strategies based on nanoparticle types, administration routes, and target organ/cell types. Also, enhancement of endosomal escape has been considered along with other aspects of siRNA delivery to ensure target specific accumulation, high cell uptake, and low toxicity. By enhancing endosomal escape and overcoming other biological barriers, great progress has been achieved in nanoparticle mediated siRNA delivery.

MicroRNAs and drug resistance in prostate cancers

Prostate cancer is the second leading cause of cancer related death in American men. Androgen deprivation therapy (ADT) is used to treat patients with aggressive prostate cancers. After androgen deprivation therapy, prostate cancers slowly progress to an androgen-independent status. Taxanes (e.g., docetaxel) are used as standard treatments for androgen-independent prostate cancers. However, these chemotherapeutic agents will eventually become ineffective due to the development of drug resistance. A microRNA (miRNA) is a small noncoding RNA molecule, which can regulate gene expression at the post-transcription level. miRNAs elicit their effects by binding to the 3'-untranslated region (3'-UTR) of their target mRNAs, leading to the inhibition of translation or the degradation of the mRNAs. miRNAs have received increasing attention as targets for cancer therapy, as they can target multiple signaling pathways related to tumor progression, metastasis, invasion, and chemoresistance. Emerging evidence suggests that aberrant expression of miRNAs can lead to the development of resistant prostate cancers. Here, we discuss the roles of miRNAs in the development of resistant prostate cancers and their involvement in various drug resistant mechanisms including androgen signaling, apoptosis avoidance, multiple drug resistance (MDR) transporters, epithelialmesenchymal transition (EMT), and cancer stem cells (CSCs). In addition, we also discuss strategies for treating resistant prostate cancers by targeting specific miRNAs. Different delivery strategies are also discussed with focus on those that have been successfully used in human clinical trials.

Delivery materials for siRNA therapeutics

RNA interference (RNAi) has broad potential as a therapeutic to reversibly silence any gene. To achieve the clinical potential of RNAi, delivery materials are required to transport short interfering RNA (siRNA) to the site of action in the cells of target tissues. This Review provides an introduction to the biological challenges that siRNA delivery materials aim to overcome, as well as a discussion of the way that the most effective and clinically advanced classes of siRNA delivery systems, including lipid nanoparticles and siRNA conjugates, are designed to surmount these challenges. The systems that we discuss are diverse in their approaches to the delivery problem, and provide valuable insight to guide the design of future siRNA delivery materials.