Pharmacokinetic and Pharmacodynamic Modeling of siRNA Therapeutics - a Minireview

Mechanistic intracellular PK/PD modeling to inform development strategies for small interfering RNA therapeutics

Small interfering RNA (siRNA) therapeutics provide a targeted approach to silence disease-related genes, with notable success in liver-targeting applications. However, the quantitative effects of siRNA properties, such as stability and affinity, as well as biological factors like cell proliferation, mRNA turnover, and abundance, on gene silencing, particularly for extrahepatic targets, remain poorly understood. To identify determinants influencing gene knockdown extent and duration, we developed a mechanistic intracellular pharmacokinetic/pharmacodynamic (PK/PD) model for RNAiMAX-delivered siRNA, based on cytoplasmic siRNA disposition, RISC-loaded siRNA exposure, and mRNA knockdown across different targets in MCF7 and BT474 cells. The model highlighted the critical roles of cell proliferation in silencing duration and mRNA turnover rates on knockdown extent. In rapid-dividing cells, mRNA half-life drives knockdown profiles, whereas chemical siRNA stabilization extends silencing in slow-dividing cells. Targets with extremely low or high mRNA abundance pose silencing challenges. While sufficient RISC occupancy is essential, increasing RISC exposure has minimal impact on silencing extent; enhancing siRNA-mRNA target engagement is more effective. The model also defined a quantitative relationship for maximal mRNA knockdown, governed by cell proliferation, mRNA half-life, and RISC-mediated cleavage rates. This mechanistic PK/PD modeling provides insights into optimizing siRNA design and target selection in therapeutic development.

Prediction of Interspecies Translation for Targeting Delivery Coefficients of GalNAc-siRNA Silencing Apolipoprotein C-III Using a Mechanistic Minimal Physiologically Based Pharmacokinetic/Pharmacodynamic Model

BACKGROUND AND OBJECTIVE

The emerging N-acetylgalactosamine-small interfering RNA (GalNAc-siRNA) conjugates lead the way for liver-targeting delivery to exert gene-silencing therapeutic effects. To facilitate the drug development of GalNAc-siRNA, further detailed understanding of the key modality-specific mechanisms underlying the temporal discordance between pharmacokinetics and pharmacodynamics and how these processes can be extrapolated from animals to humans is needed.

METHODS

A mechanistic minimal physiologically based pharmacokinetic/pharmacodynamic (mPBPK-PD) model for an investigational new apolipoprotein C-III (APOC3)-silencing GalNAc-siRNA (RBD5044) was developed using available pharmacokinetic/pharmacodynamic (PK/PD) data. The aim was to explore hepatic-targeting delivery processes, the PK/PD relationship, and interspecies translation.

RESULTS

First, multiple PK/PD datasets from mice were satisfactorily fitted using the mPBPK-PD model. Second, we translated the mice model to the monkey model, validated it, and then extrapolated from mice and monkeys to humans to simulate the PK/PD characteristics. We then mechanistically summarized and proposed the essential in vivo delivery processes of GalNAc-siRNA after subcutaneous administration (termed "ADUEB": Absorption [into system circulation], Disposition [distribution to liver target and elimination], Uptake [into hepatocytes], Escape [from endosome and lysosome compartments], and Binding [with argonaute2 to form RNA-induced silencing complex]). The targeting delivery coefficients of these processes achieved with the model using RBD5044 and the published data of another GalNAc-siRNA (fitusiran) quantitatively reflected the delivery efficiency and rate-limiting factors in targeted hepatocytes.

CONCLUSION

This study successfully constructed the mPBPK-PD model and conducted interspecies extrapolation for a GalNAc-siRNA targeting APOC3. Promising quantitative insights into a hepatic-targeted GalNAc-siRNA delivery system are provided to characterize the unique temporal disconnection of PK/PD properties and evaluate the key in vivo delivery processes. It will promote model-informed strategies and quantitative mechanistic understanding to support efficient drug development, evaluation, and clinical application of this modality in the future.

GalNac-siRNA conjugate delivery technology promotes the treatment of typical chronic liver diseases

INTRODUCTION

Nucleic acid-based therapeutics have become a key pillar of the 'third wave' of modern medicine, following the eras of small molecule inhibitors and antibody drugs. Their rapid progress is heavily dependent on delivery technologies, with the development of N-acetylgalactosamine (GalNAc) conjugates marking a breakthrough in targeting liver diseases. This technology has gained significant attention for its role in addressing chronic conditions like chronic hepatitis B (CHB) and nonalcoholic steatohepatitis (NASH), which are challenging to treat with conventional methods.

AREAS COVERED

This review explores the origins, mechanisms, and advantages of GalNAc-siRNA delivery systems, highlighting their ability to target hepatocytes via the asialoglycoprotein receptor (ASGPR). The literature reviewed covers preclinical and clinical advancements, particularly in CHB and NASH. Key developments in stabilization chemistry and conjugation technologies are examined, emphasizing their impact on enhancing therapeutic efficacy and patient compliance.

EXPERT OPINION

GalNAc-siRNA technology represents a transformative advancement in RNA interference (RNAi) therapies, addressing unmet needs in liver-targeted diseases. While significant progress has been made, challenges remain, including restricted targeting scope and scalability concerns. Continued innovation is expected to expand applications, improve delivery efficiency, and overcome limitations, establishing GalNAc-siRNA as a cornerstone for future nucleic acid-based treatments.

Advancement of Nanomaterials- and Biomaterials-Based Technologies for Wound Healing and Tissue Regenerative Applications

Patients and healthcare systems face significant social and financial challenges due to the increasing number of individuals with chronic external and internal wounds that fail to heal. The complexity of the healing process remains a serious health concern, despite the effectiveness of conventional wound dressings in promoting healing. Recent advancements in materials science and fabrication techniques have led to the development of innovative dressings that enhance wound healing. To further expedite the healing process, novel approaches such as nanoparticles, 3D-printed wound dressings, and biomolecule-infused dressings have emerged, along with cell-based methods. Additionally, gene therapy technologies are being harnessed to generate stem cell derivatives that are more functional, selective, and responsive than their natural counterparts. This review highlights the significant potential of biomaterials, nanoparticles, 3D bioprinting, and gene- and cell-based therapies in wound healing. However, it also underscores the necessity for further research to address the existing challenges and integrate these strategies into standard clinical practice.

Model-Informed Drug Development Applications and Opportunities in mRNA-LNP Therapeutics

The utilization of lipid nanoparticles (LNP) for encapsulating mRNA has revolutionized the field of therapeutics, enabling the rapid development of COVID-19 vaccines and cancer vaccines. However, the clinical development of mRNA-LNP therapeutics faces numerous challenges due to their complex mechanisms of action and limited clinical experience. To overcome these hurdles, Model-Informed Drug Development (MIDD) emerges as a valuable tool that can be applied to mRNA-LNP therapeutics, facilitating the evaluation of their safety and efficacy through the integration of data from all stages into appropriate modeling and simulation techniques. In this review, we provide an overview of current MIDD applications in mRNA-LNP therapeutics clinical development using in vivo data. A variety of modeling methods are reviewed, including quantitative system pharmacology (QSP), physiologically based pharmacokinetics (PBPK), mechanistic pharmacokinetics/pharmacodynamics (PK/PD), population PK/PD, and model-based meta-analysis (MBMA). Additionally, we compare the differences between mRNA-based therapeutics, small interfering RNA, and adeno-associated virus-based gene therapies in terms of their clinical pharmacology, and discuss the potential for mutual sharing of MIDD knowledge between these therapeutics. Furthermore, we highlight the promising future opportunities for applying MIDD approaches in the development of mRNA-LNP drugs. By emphasizing the importance of applying MIDD knowledge throughout mRNA-LNP therapeutics development, this review aims to encourage stakeholders to recognize the value of MIDD and its potential to enhance the safety and efficacy evaluation of mRNA-LNP therapeutics.

Impact of Dapagliflozin on Hepatic Lipid Metabolism and a Dynamic Model of Ketone Body Levels

The rising prevalence of metabolic-associated steatotic liver disease emphasizes the need to understand its lipid metabolism. Dapagliflozin may improve hepatic steatosis but could also increase the risk of ketoacidosis by elevating β-hydroxybutyrate (KB) levels. This study investigates dapagliflozin's effects on hepatic lipid metabolism and quantifies KB levels in vivo. Male Sprague-Dawley rats were fed either a normal diet or a high-fat diet (HFD) for 12 weeks. The HFD rats were then divided into four subgroups to receive vehicle, 0.5 mg/kg, 1 mg/kg, and 3 mg/kg of dapagliflozin for four weeks. Free fatty acids (FFA) and KB levels were monitored, while protein and gene expression were analyzed. And a dynamic model of KB was developed for humans based on preclinical data. Dapagliflozin decreased body weight and visceral fat in HFD rats, increasing KB by upregulating CPT1a, HMGCS2, and HMGCL, and downregulating ACC. These changes correlated with reduced liver/fat index, liver pathology score, and oil-red staining area. A pharmacokinetic/pharmacodynamic (PK/PD) model was created from preclinical data to quantify KB levels in rats and validated in humans. Dapagliflozin reduces hepatic steatosis by enhancing fatty acid β-oxidation and ketogenesis and inhibiting fat synthesis. A dynamic model accurately predicts ketone body levels in treated individuals.

A journey into siRNA therapeutics development: A focus on Pharmacokinetics and Pharmacodynamics

siRNA therapeutics are emerging novel modalities targeting highly specific mRNA via RNA interference mechanism. Its unique pharmacokinetics (PKs) and pharmacodynamics (PDs) are significant challenges for clinical use. Furthermore, naked siRNA is a highly soluble macromolecule with a negative charge, making plasma membrane penetration a significant hurdle. It is also vulnerable to nuclease degradation. Therefore, advanced formulation technologies, such as lipid nanoparticles and N-acetylgalactosamine conjugation, have been developed and are now used in clinical practice to enhance target organ delivery and stability. The innate complex biological mechanisms of siRNA, along with its formulation, are major determinants of the PK/PD characteristics of siRNA products. To systematically and quantitatively understand these characteristics, it is essential to develop and utilize quantitative PK/PD models for siRNA therapeutics. In this review, the effects of formulation on the PKs and PK/PD models of approved siRNA products were presented, highlighting the importance of selecting appropriate biomarkers and understanding formulation, PKs, and PDs for quantitative interpreting the relationship between plasma concentration, organ concentration, biomarkers, and efficacy.

The absorption, distribution, metabolism and elimination characteristics of small interfering RNA therapeutics and the opportunity to predict disposition in pregnant women

Small interfering RNA (siRNA) therapeutics represent an emerging class of pharmacotherapy with the potential to address previously hard-to-treat diseases. Currently approved siRNA therapeutics include lipid nanoparticle-encapsulated siRNA and tri-N-acetylated galactosamine-conjugated siRNA. These siRNA therapeutics exhibit distinct pharmacokinetic characteristics and unique absorption, distribution, metabolism, and elimination (ADME) properties. As a new drug modality, limited clinical data are available for siRNA therapeutics in specific populations, including pediatrics, geriatrics, individuals with renal or hepatic impairment, and pregnant women, making dosing challenging. In this Minireview, a mechanistic overview of the ADME properties of the 5 currently approved siRNA therapeutics is presented. A concise overview of the clinical data available for therapeutic siRNAs in special populations, focusing on the potential impact of physiologic changes during pregnancy on siRNA disposition, is provided. The utility of physiologically based pharmacokinetic (PBPK) modeling as a tool to elucidate the characteristics and disposition of siRNA therapeutics in pregnant women is explored. Additionally, opportunities to integrate known physiologic alterations induced by pregnancy into PBPK models that incorporate siRNA ADME mechanisms to predict the effects of pregnancy on siRNA disposition are discussed. Clinical data regarding the use of therapeutic siRNA in special populations remain limited. Data for precise parameterization of maternal-fetal siRNA PBPK models are lacking presently and underscore the need for further research in this area. Addressing this gap in knowledge will not only enhance our understanding of siRNA pharmacokinetics during pregnancy but also advance the possible development of siRNA therapeutics to treat pregnancy-related conditions. SIGNIFICANCE STATEMENT: This Minireview proposes a framework on how small interfering RNA (siRNA) disposition can be predicted in pregnancy based on mechanistic absorption, distribution, metabolism, and elimination (ADME) information using physiologically-based pharmacokinetic (PBPK) modeling. The mechanistic ADME information and available clinical data in special populations of currently Food and Drug Administration-approved siRNA therapeutics are summarized. Additionally, how physiological changes during pregnancy may affect siRNA disposition is reviewed, and the opportunities to use PBPK modeling to predict siRNA disposition in pregnant women is explored.

Artificial intelligence-driven rational design of ionizable lipids for mRNA delivery

Lipid nanoparticles (LNPs) have proven effective in mRNA delivery, as evidenced by COVID-19 vaccines. Its key ingredient, ionizable lipids, is traditionally optimized by inefficient and costly experimental screening. This study leverages artificial intelligence (AI) and virtual screening to facilitate the rational design of ionizable lipids by predicting two key properties of LNPs, apparent pKa and mRNA delivery efficiency. Nearly 20 million ionizable lipids were evaluated through two iterations of AI-driven generation and screening, yielding three and six new molecules, respectively. In mouse test validation, one lipid from the initial iteration, featuring a benzene ring, demonstrated performance comparable to the control DLin-MC3-DMA (MC3). Notably, all six lipids from the second iteration equaled or outperformed MC3, with one exhibiting efficacy akin to a superior control lipid SM-102. Furthermore, the AI model is interpretable in structure-activity relationships.

Modeling on in vivo disposition and cellular transportation of RNA lipid nanoparticles via quantum mechanics/physiologically-based pharmacokinetic approaches

The lipid nanoparticle (LNP) has been so far proven as a strongly effective delivery system for mRNA and siRNA. However, the mechanisms of LNP's distribution, metabolism, and elimination are complicated, while the transportation and pharmacokinetics (PK) of LNP are just sparsely investigated and simply described. This study aimed to build a model for the transportation of RNA-LNP in Hela cells, rats, mice, and humans by physiologically based pharmacokinetic (PBPK) and quantum mechanics (QM) models with integrated multi-source data. LNPs with different ionizable lipids, particle sizes, and doses were modeled and compared by recognizing their critical parameters dominating PK. Some interesting results were found by the models. For example, the metabolism of ionizable lipids was first limited by the LNP disassembly rate instead of the hydrolyzation of ionizable lipids; the ability of RNA release from endosomes for three ionizable lipids was quantitively derived and can predict the probability of RNA release. Moreover, the biodegradability of three ionizable lipids was estimated by the QM method and the is generally consistent with the result of PBPK result. In summary, the transportation model of RNA LNP among various species for the first time was successfully constructed. Various in vitro and in vivo pieces of evidence were integrated through QM/PBPK multi-level modeling. The resulting new understandings are related to biodegradability, safety, and RNA release ability which are highly concerned issues of the formulation. This would benefit the design and research of RNA-LNP in the future.

Analysis of the pharmacokinetics and efficacy of RBD1016 - A GalNAc-siRNA targeting Hepatitis B Virus X gene using semi-mechanistic PK/PD model

Small interference RNA (siRNA) is a class of short double-stranded RNA molecules that cause mRNA degradation through an RNA interference mechanism and is a promising therapeutic modality. RBD1016 is a siRNA drug in clinical development for the treatment of chronic Hepatitis B Virus (HBV) infection, which contains a conjugated with N-acetylglucosamine moiety that can facilitate its hepatic delivery. We aimed to construct a semi-mechanistic model of RBD1016 in pre-clinical animals, to elucidate the pharmacokinetic/pharmacodynamic (PK/PD) profiles in mice and PK profiles in monkeys, which can lay the foundation for potential future translation of RBD1016 PK and PD from the pre-clinical stage to the clinic stage. The proposed semi-mechanistic PK/PD model fitted PK and PD data in HBV transgenic mice well and described plasma and liver concentrations in the monkeys well. The simulation results showed that our model has a reasonable predictive ability for Hepatitis B surface antigen (HBsAg) levels after multiple dosing in mice. Further PK and PD data for RBD1016, including clinical data, will assist in refining the model presented here. Our current effort focused on model building for RBD1016, we anticipate that the model could apply to other GalNAc-siRNA drugs.

Pulmonary siRNA Delivery with Sophisticated Amphiphilic Poly(Spermine Acrylamides) for the Treatment of Lung Fibrosis

RNA interference (RNAi) is an efficient strategy to post-transcriptionally silence gene expression. While all siRNA drugs on the market target the liver, the lung offers a variety of currently undruggable targets, which can potentially be treated with RNA therapeutics. To achieve this goal, the synthesis of poly(spermine acrylamides) (P(SpAA) is reported herein. Polymers are prepared via polymerization of N-acryloxysuccinimide (NAS) and afterward this active ester is converted into spermine-based pendant groups. Copolymerizations with decylacrylamide are employed to increase the hydrophobicity of the polymers. After deprotection, polymers show excellent siRNA encapsulation to obtain perfectly sized polyplexes at very low polymer/RNA ratios. In vitro 2D and 3D cell culture, ex vivo and in vivo experiments reveal superior properties of amphiphilic spermine-copolymers with respect to delivery of siRNA to lung cells in comparison to commonly used lipid-based transfection agents. In line with the in vitro results, siRNA delivery to human lung explants confirm more efficient gene silencing of protease-activated receptor 2 (PAR2), a G protein-coupled receptor involved in fibrosis. This study reveals the importance of the balance between efficient polyplex formation, cellular uptake, gene knockdown, and toxicity for efficient siRNA delivery in vitro, in vivo, and in fibrotic human lung tissue ex vivo.

State of Gene Therapy for Monogenic Cardiovascular Diseases

Over the past 2 decades, significant efforts have been made to advance gene therapy into clinical practice. Although successful examples exist in other fields, gene therapy for the treatment of monogenic cardiovascular diseases lags behind. In this review, we (1) highlight a brief history of gene therapy, (2) distinguish between gene silencing, gene replacement, and gene editing technologies, (3) discuss vector modalities used in the field with a special focus on adeno-associated viruses, (4) provide examples of gene therapy approaches in cardiomyopathies, channelopathies, and familial hypercholesterolemia, and (5) present current challenges and limitations in the gene therapy field.

Types of RNA therapeutics

RNA therapy is one of the new treatments using small RNA molecules to target and regulate gene expression. It involves the application of synthetic or modified RNA molecules to inhibit the expression of disease-causing genes specifically. In other words, it silences genes and suppresses the transcription process. The main theory behind RNA therapy is that RNA molecules can prevent the translation into proteins by binding to specific messenger RNA (mRNA) molecules. By targeting disease-related mRNA molecules, RNA therapy can effectively silence or reduce the development of harmful proteins. There are different types of RNA molecules used in therapy, including small interfering RNAs (siRNAs), microRNAs (miRNAs), aptamer, ribozyme, and antisense oligonucleotides (ASOs). These molecules are designed to complement specific mRNA sequences, allowing them to bind and degrade the targeted mRNA or prevent its translation into protein. Nanotechnology is also highlighted to increase the efficacy of RNA-based drugs. In this chapter, while examining various methods of RNA therapy, we discuss the advantages and challenges of each.

Mechanistic Pharmacokinetics and Pharmacodynamics of GalNAc-siRNA: Translational Model Involving Competitive Receptor-Mediated Disposition and RISC-Dependent Gene Silencing Applied to Givosiran

Triantennary N-acetyl-D galactosamine (GalNAc)3-conjugated small interfering RNA (siRNA) have majorly advanced the development of RNA-based therapeutics. Chemically stabilized GalNAc-siRNAs exhibit extensive albeit capacity-limited (nonlinear) distribution into hepatocytes with additional complexities in intracellular liver disposition and pharmacology. A mechanism-based pharmacokinetic-pharmacodynamic (PK-PD) model of GalNAc-siRNA was developed to i) quantitate ASGPR-mediated disposition and downstream RNA-induced silencing complex (RISC)-dependent pharmacology following intravenous (IV) and subcutaneous (SC) dosing, ii) assess the kinetics of formed active metabolite, iii) leverage, as an example, published experimental data for givosiran, and iv) demonstrate PK translation across two preclinical species (rat and monkey) with subsequent prediction of human plasma PK. The structural model is based on competition between parent and formed active metabolite for occupancy and uptake via ASGPR into hepatocytes, intracellular sequestration and degradation, and downstream engagement of RNA-induced silencing complex (RISC) governing target mRNA degradation. The model jointly and accurately captured available concentration-time profiles of givosiran and/or AS(N-1)3' givosiran in rat and/or monkey plasma, liver, and/or kidney following givosiran administered both IV and SC. RISC-dependent gene silencing of ALAS1 mRNA was well-characterized. The model estimated an in vivo affinity (KD) value of 27.7 nM for GalNAc-ASGPR and weight-based allometric exponents of -0.27 and -0.24 for SC absorption and intracellular (endolysosomal) degradation rate constants. The model well-predicted reported givosiran plasma PK profiles in humans. PK simulations revealed net-shifts in liver-to-kidney distribution ratios with increasing IV and SC dose. Importantly, decreases in the relative liver uptake efficiency were demonstrated following IV and, to a lesser extent, following SC dosing explained by differential ASGPR occupancy profiles over time.

Pharmacokinetics and Pharmacodynamics of GalNAc-Conjugated siRNAs

Small interfering RNAs (siRNAs) represent a new class of drugs with tremendous potential for battling previously "undruggable" diseases. After nearly 2 decades of efforts in addressing the problems of the poor drug profile of naked unmodified siRNAs, this new modality has finally come to fruition, with 5 agents (patisiran, givosiran, lumasiran, inclisiran, and vutrisiran) being approved since 2018, and with many others in the different phases of clinical development. Unlike small-molecule drugs and protein therapeutics, siRNAs have different sizes, distinct mechanisms of action, differing physicochemical and pharmacological properties, and, accordingly, a unique pharmacokinetic/pharmacodynamic (PK/PD) relationship. To support the continuous development of siRNAs, it is important to have a thorough and deep understanding of the PK/PD and clinical pharmacology related features of siRNAs. As most of the current siRNA products are conjugated by N-acetylgalactosamine (GalNAc), this review focuses on the PK/PD relationships and clinical pharmacology of GalNAc-conjugated siRNAs, including their absorption, distribution, metabolism, excretion (ADME) properties, PK/PD models, drug-drug interactions, clinical pharmacology in special populations, and safety evaluation. In addition, necessary background information related to the development of siRNAs as a therapeutic modality, including the mechanisms of action, the advantages of siRNAs, the problems of naked siRNAs, as well as the strategies used to enhance the clinical utility of siRNAs, have also been covered. The goal of this review is to serve as a "primer" on siRNA PK/PD, and I hope the readers, especially those who have a limited background on siRNA therapeutics, will have a fundamental understanding of siRNA PK/PD and clinical pharmacology after reading this review.

Plasma Pharmacokinetics of N-Acetylgalactosamine-Conjugated Small-Interfering Ribonucleic Acids (GalNAc-Conjugated siRNAs)

Small-interfering ribonucleic acids (siRNAs) with N-acetylgalactosamine (GalNAc) conjugation for improved liver uptake represent an emerging class of drugs that modulate liver-expressed therapeutic targets. The pharmacokinetics of GalNAc-siRNAs are characterized by a rapid distribution from plasma to tissue (hours) and a long terminal plasma half-life, analyzed in the form of the antisense strand, driven by redistribution from tissue (weeks). Understanding how clinical pharmacokinetics relate to the dose and type of siRNA chemical stabilizing method used is critical, e.g., to design studies, to investigate safety windows, and to predict the pharmacokinetics of new preclinical assets. To this end, we collected and analyzed pharmacokinetic data from the literature regarding nine GalNAc-siRNAs. Based on this analysis, we showed that the clinical plasma pharmacokinetics of GalNAc-siRNAs are approximately dose proportional and similar between chemical stabilizing methods. This holds for both the area under the concentration-time curve (AUC) and the maximum plasma concentration (Cmax). Corresponding rat and monkey pharmacokinetic data for a subset of the nine GalNAc-siRNAs show dose-proportional Cmax, supra-dose-proportional AUC, and similar pharmacokinetics between chemical stabilizing methods​. Together, the animal and human pharmacokinetic data indicate that plasma clearance divided by bioavailability follows allometric principles and scales between species with an exponent of 0.75. Finally, the clinical plasma concentration-time profiles can be empirically described by standard one-compartment kinetics with first-order absorption up to 24 h after subcutaneous dosing, and by three-compartment kinetics with first-order absorption in general. To describe the system more mechanistically, we report a corrected and unambiguously defined version of a previously published physiologically based pharmacokinetic model.

Two Birds with One Stone: A Novel Dithiomaleimide-Based GalNAc-siRNA Conjugate Enabling Good siRNA Delivery and Traceability

For the first time, a novel dithiomaleimides (DTM) based tetra-antennary GalNAc conjugate was developed, which enable both efficient siRNA delivery and good traceability, without incorporating extra fluorophores. This conjugate can be readily constructed by three click-type reactions, that is, amidations, thiol-dibromomaleimide addition and copper catalyzed azide-alkyne cycloaddition (CuAAC). And it also has comparable siRNA delivery efficiency, with a GalNAc L96 standard to mTTR target. Additionally, due to the internal DTMs, a highly fluorescent emission was observed, which benefited delivery tracking and reduced the cost and side effects of the extra addition of hydrophobic dye molecules. In all, the simple incorporation of DTMs to the GalNAc conjugate structure has potential in gene therapy and tracking applications.

The improving strategies and applications of nanotechnology-based drugs in hepatocellular carcinoma treatment

Hepatocellular carcinoma (HCC) is one of the leading causes of tumor-related death worldwide. Conventional treatments for HCC include drugs, radiation, and surgery. Despite the unremitting efforts of researchers, the curative effect of HCC has been greatly improved, but because HCC is often found in the middle and late stages, the curative effect is still not satisfactory, and the 5-year survival rate is still low. Nanomedicine is a potential subject, which has been applied to the treatment of HCC and has achieved promising results. Here, we summarized the factors affecting the efficacy of drugs in HCC treatment and the strategies for improving the efficacy of nanotechnology-based drugs in HCC, reviewed the recent applications' progress on nanotechnology-based drugs in HCC treatment, and discussed the future perspectives and challenges of nanotechnology-based drugs in HCC treatment.

Model-Informed Approaches and Innovative Clinical Trial Design for Adeno-Associated Viral Vector-Based Gene Therapy Product Development: A White Paper

The promise of viral vector-based gene therapy (GT) as a transformative paradigm for treating severely debilitating and life-threatening diseases is slowly coming to fruition with the recent approval of several drug products. However, they have a unique mechanism of action often necessitating a tortuous clinical development plan. Expertise in such complex therapeutic modality is still fairly limited in this emerging class of adeno-associated virus (AAV) vector-based gene therapies. Because of the irreversible mode of action and incomplete understanding of genotype-phenotype relationship and disease progression in rare diseases careful considerations should be given to GT product's benefit-risk profile. In particular, special attention needs to be paid to safe dose selection, reliable dose exposure response (including clinically relevant endpoints), or creative approaches in study design targeting small patient populations during clinical development. We believe that quantitative tools encompassed within model-informed drug development (MIDD) framework fits quite well in the development of such novel therapies, as they enable us to benefit from the totality of data approach in order to support dose selection as well as optimize clinical trial designs, end point selection, and patient enrichment. In this thought leadership paper, we provide our collective experiences, identify challenges, and suggest areas of improvement in applications of modeling and innovative trial design in development of AAV-based GT products and reflect on the challenges and opportunities for incorporating MIDD tools and more in rational development of these products.

Clinical Pharmacology and Translational Considerations in the Development of CRISPR-Based Therapies

Genome editing holds the potential for curative treatments of human disease, however, clinical realization has proven to be a challenging journey with incremental progress made up until recently. Over the last decade, advances in clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) systems have provided the necessary breakthrough for genome editing in the clinic. The progress of investigational CRISPR therapies from bench to bedside reflects the culmination of multiple advances occurring in parallel, several of which intersect with clinical pharmacology and translation. Directing the CRISPR therapy to the intended site of action has necessitated novel delivery platforms, and this has resulted in special considerations for the complete characterization of distribution, metabolism, and excretion, as well as immunogenicity. Once at the site of action, CRISPR therapies aim to make permanent alterations to the genome and achieve therapeutically relevant effects with a single dose. This fundamental aspect of the mechanism of action for CRISPR therapies results in new considerations for clinical translation and dose selection. Early advances in model-informed development of CRISPR therapies have incorporated key facets of the mechanism of action and have captured hallmark features of clinical pharmacokinetics and pharmacodynamics from phase I investigations. Given the recent emergence of CRISPR therapies in clinical development, the landscape continues to evolve rapidly with ample opportunity for continued innovation. Here, we provide a snapshot of selected topics in clinical pharmacology and translation that has supported the advance of systemically administered in vivo and ex vivo CRISPR-based investigational therapies in the clinic.

Nucleic acid-based therapeutics for the treatment of central nervous system disorders

Nucleic acid-based therapeutics (NBTs) are an emerging class of drugs with potential for the treatment of a wide range of central nervous system conditions. To date, pertaining to CNS indications, there are two commercially available NBTs and a large number of ongoing clinical trials. However, these NBTs are applied directly to the brain due to very low blood brain barrier permeability. In this review, we outline recent advances in chemical modifications of NBTs and NBT delivery techniques intended to promote brain exposure, efficacy, and possible future systemic application.

Emergence of Small Interfering RNA-Based Gene Drugs for Various Diseases

Small molecule, peptide, and protein-based drugs have been developed over decades to treat various diseases. The importance of gene therapy as an alternative to traditional drugs has increased after the discovery of gene-based drugs such as Gendicine for cancer and Neovasculgen for peripheral artery disease. Since then, the pharma sector is focusing on developing gene-based drugs for various diseases. After the discovery of the RNA interference (RNAi) mechanism, the development of siRNA-based gene therapy has been accelerated immensely. siRNA-based treatment for hereditary transthyretin-mediated amyloidosis (hATTR) using Onpattro and acute hepatic porphyria (AHP) by Givlaari and three more FDA-approved siRNA drugs has set up a milestone and further improved the confidence for the development of gene therapeutics for a spectrum of diseases. siRNA-based gene drugs have more advantages over other gene therapies and are under study to treat different types of diseases such as viral infections, cardiovascular diseases, cancer, and many more. However, there are a few bottlenecks to realizing the full potential of siRNA-based gene therapy. They include chemical instability, nontargeted biodistribution, undesirable innate immune responses, and off-target effects. This review provides a comprehensive view of siRNA-based gene drugs: challenges associated with siRNA delivery, their potential, and future prospects.

Clinical Pharmacology of RNA Interference-Based Therapeutics: A Summary Based on Food and Drug Administration-Approved Small Interfering RNAs

RNA-based oligonucleotide therapeutics are revolutionizing drug development for disease treatment. This class of therapeutics differs from small molecules and protein therapeutics in various ways, including both its mechanism of action and clinical pharmacology characteristics. These unique characteristics, along with evolving oligonucleotide-associated conjugates allowing specific tissue targeting, have fueled interest in the evaluation of RNA-based oligonucleotide therapeutics in a rapidly increasing number of therapeutic areas. With these unique attributes as well as growing therapeutic potential, oligonucleotide therapeutics have generated significant interest from a clinical pharmacology perspective. The Food and Drug Administration (FDA) previously published results of a survey that summarized clinical pharmacology studies supporting oligonucleotide therapies approved and in development between 2012 and 2018. Since the first approval of a small interfering RNA (siRNA) therapeutic in 2018, this class of modalities has gained momentum in various therapeutic areas. Hence, a comprehensive examination of the clinical pharmacology of FDA-approved siRNA therapeutics would benefit the path forward for many stakeholders. Thus, in this current review, we thoroughly examine and summarize clinical pharmacology data of the FDA-approved siRNA therapeutics approved from 2018 (year of first approval) to 2022, aimed at facilitating future drug development and regulatory decision making. SIGNIFICANCE STATEMENT: This review systematically summarizes the clinical pharmacology information of Food and Drug Administration (FDA)-approved small interfering RNAs (siRNA) therapeutics. SiRNAs are revolutionizing the drug development field. Unique clinical pharmacology characteristics represent a differentiating factor for this class of therapeutics. The FDArecently published a draft guidance for clinical pharmacology considerations for developing oligonucleotide therapeutics. As clinical development of this class of therapeutics is fast growing, this review will inform discovery and clinical-stage evaluation of upcoming siRNA-associated drug candidates.

Biodrug Delivery Systems: Do mRNA Lipid Nanoparticles Come of Age?

As an appealing alternative to treat and prevent diseases ranging from cancer to COVID-19, mRNA has demonstrated significant clinical effects. Nanotechnology facilitates the successful implementation of the systemic delivery of mRNA for safe human consumption. In this manuscript, we provide an overview of current mRNA therapeutic applications and discuss key biological barriers to delivery and recent advances in the development of nonviral systems. The relevant challenges that LNPs face in achieving cost-effective and widespread clinical implementation when delivering mRNA are likewise discussed.

The therapeutic prospects of N-acetylgalactosamine-siRNA conjugates

RNA interference has become increasingly used for genetic therapy following the rapid development of oligonucleotide drugs. Significant progress has been made in its delivery system and implementation in the treatment of target organs. After a brief introduction of RNA interference technology and siRNA, the efficiency and stability of GalNAc-siRNA conjugates are highlighted since several oligonucleotide drugs of GalNAc have been approved for clinical use in recent years. The structure and features of GalNAc-siRNA conjugates are studied and the clinical efficiency and limitations of oligonucleotide-based drugs are summarized and investigated. Furthermore, another delivery system, lipid nanoparticles, that confer many advantages, is concluded, includ-ing stability and mass production, compared with GalNAc-siRNA conjugates. Importantly, developing new approaches for the use of oligonucleotide drugs brings hope to genetic therapy.

Mathematical Modeling and Experimental Validation of Extracellular Vesicle-Mediated Tumor Suppressor MicroRNA Delivery and Propagation in Ovarian Cancer Cells

Extracellular vesicle (EV)-mediated microRNA transfer and propagation from the donor cell to the recipient cell in the tumor microenvironment have significant implications, including the development of multidrug resistance (MDR). Although miRNA-encapsulated EV have been shown to have functional effects on recipient cells, the quantitative aspects of transfer kinetics and functional effects remain poorly understood. Intracellular events such as degradation of miRNA, loading of miRNA into EVs, cellular release of EVs, and their uptake by recipient cells govern the transfer and functional effect of encapsulated miRNA. Based on these rate-limiting steps, we developed a mathematical model using ordinary differential equations (model 1). We performed coculture experiments using ID8-VEGF ovarian cancer cells to demonstrate EV-mediated propagation of tumor suppressor miRNA Let7b administered with hyaluronic acid-poly(ethyleneimine) (HA-PEI) nanoparticles. Using the experimental data and model fitting, we determined the rate constants for the kinetic events involved in the transfer from the donor cells to the recipient cells. In model 2, we performed Let7b transfection experiments in ID8-VEGF cells with HA-PEI nanoparticles to determine the concentration-effect relationship on HMGA2 mRNA levels. Lastly, in model 3, we combined model 1 and model 2 parameters to describe the kinetics and effect relationship of EV-Let7b in recipient cells to predict the minimum number of miRNA copies needed to show functional effects.

Evolution of complexity in non-viral oligonucleotide delivery systems: from gymnotic delivery through bioconjugates to biomimetic nanoparticles

From the early days of research on RNA biology and biochemistry, there was an interest to utilize this knowledge and RNA itself for therapeutic applications. Today, we have a series of oligonucleotide therapeutics on the market and many more in clinical trials. These drugs - exploit different chemistries of oligonucleotides, such as modified DNAs and RNAs, peptide nucleic acids (PNAs) or phosphorodiamidate morpholino oligomers (PMOs), and different mechanisms of action, such as RNA interference (RNAi), targeted RNA degradation, splicing modulation, gene expression and modification. Despite major successes e.g. mRNA vaccines developed against SARS-CoV-2 to control COVID-19 pandemic, development of therapies for other diseases is still limited by inefficient delivery of oligonucleotides to specific tissues and organs and often prohibitive costs for the final drug. This is even more critical when targeting multifactorial disorders and patient-specific biological variations. In this review, we will present the evolution of complexity of oligonucleotide delivery methods with focus on increasing complexity of formulations from gymnotic delivery to bioconjugates and to lipid nanoparticles in respect to developments that will enable application of therapeutic oligonucleotides as drugs in personalized therapies.