Givosiran: First Approval

Caveolae-Mediated Endocytosis Drives Robust siRNA Delivery of Polymeric Nanoparticles to Macrophages

Cytosolic delivery of small interfering RNA (siRNA) remains challenging, and a profound understanding of the cellular uptake and intracellular processing of siRNA delivery systems could greatly improve the development of siRNA-based therapeutics. Here, we show that caveolae-mediated endocytosis (CvME) accounts for the robust siRNA delivery of mannose-modified trimethyl chitosan-cysteine/tripolyphosphate nanoparticles (MTC/TPP NPs) to macrophages by circumventing lysosomes. We show that the Golgi complex and ER are key organelles required for the efficient delivery of siRNA to macrophages in which the siRNA accumulation positively correlates with its silencing efficiency (r = 0.94). We also identify syntaxin6 and Niemann-Pick type C1 (NPC1) as indispensable regulators for MTC/TPP NPs-delivered siRNA into macrophages both in vitro and in vivo. Syntaxin6 and NPC1 knockout substantially decrease the cellular uptake and gene silencing of the siRNA delivered in MTC/TPP NPs in macrophages, which result in poor therapeutic outcomes for mice bearing acute hepatic injury. Our results suggest that highly efficient siRNA delivery can be achieved via CvME, which would give ideas for designing optimal delivery vectors to facilitate the clinical translation of siRNA drugs.

Synthesis and validation of DOPY: A new gemini dioleylbispyridinium based amphiphile for nucleic acid transfection

Nucleic acids therapeutics provide a selective and promising alternative to traditional treatments for multiple genetic diseases. A major obstacle is the development of safe and efficient delivery systems. Here, we report the synthesis of the new cationic gemini amphiphile 1,3-bis[(4-oleyl-1-pyridinio)methyl]benzene dibromide (DOPY). Its transfection efficiency was evaluated using PolyPurine Reverse Hoogsteen hairpins (PPRHs), a nucleic acid tool for gene silencing and gene repair developed in our laboratory. The interaction of DOPY with PPRHs was confirmed by gel retardation assays, and it forms complexes of 155 nm. We also demonstrated the prominent internalization of PPRHs using DOPY compared to other chemical vehicles in SH-SY5Y, PC-3 and DF42 cells. Regarding gene silencing, a specific PPRH against the survivin gene delivered with DOPY decreased survivin protein levels and cell viability more effectively than with N-[1-(2,3-Dioleoyloxy)propyl]-N,N,N-trimethylammonium methylsulfate (DOTAP) in both SH-SY5Y and PC-3 cells. We also validated the applicability of DOPY in gene repair approaches by correcting a point mutation in the endogenous locus of the dhfr gene in DF42 cells using repair-PPRHs. All these results indicate both an efficient entry and release of PPRHs at the intracellular level. Therefore, DOPY can be considered as a new lipid-based vehicle for the delivery of therapeutic oligonucleotides.

Therapeutic RNA interference: A novel approach to the treatment of primary hyperoxaluria

RNA interference (RNAi) is a natural biological pathway that inhibits gene expression by targeted degradation or translational inhibition of cytoplasmic mRNA by the RNA induced silencing complex. RNAi has long been exploited in laboratory research to study the biological consequences of the reduced expression of a gene of interest. More recently RNAi has been demonstrated as a therapeutic avenue for rare metabolic diseases. This review presents an overview of the cellular RNAi machinery as well as therapeutic RNAi design and delivery. As a clinical example we present primary hyperoxaluria, an ultrarare inherited disease of increased hepatic oxalate production which leads to recurrent calcium oxalate kidney stones. In the most common form of the disease (Type 1), end‐stage kidney disease occurs in childhood or young adulthood, often necessitating combined kidney and liver transplantation. In this context we discuss nedosiran (Dicerna Pharmaceuticals, Inc.) and lumasiran (Alnylam Pharmaceuticals), which are both novel RNAi therapies for primary hyperoxaluria that selectively reduce hepatic expression of lactate dehydrogenase and glycolate oxidase respectively, reducing hepatic oxalate production and urinary oxalate levels. Finally, we consider future optimizations advances in RNAi therapies.

Modified Nucleosides, Nucleotides and Nucleic Acids via Click Azide-Alkyne Cycloaddition for Pharmacological Applications

The click azide = alkyne 1,3-dipolar cycloaddition (click chemistry) has become the approach of choice for bioconjugations in medicinal chemistry, providing facile reaction conditions amenable to both small and biological molecules. Many nucleoside analogs are known for their marked impact in cancer therapy and for the treatment of virus diseases and new targeted oligonucleotides have been developed for different purposes. The click chemistry allowing the tolerated union between units with a wide diversity of functional groups represents a robust means of designing new hybrid compounds with an extraordinary diversity of applications. This review provides an overview of the most recent works related to the use of click chemistry methodology in the field of nucleosides, nucleotides and nucleic acids for pharmacological applications.

Optimization of PEGylated KL4 Peptide for siRNA Delivery with Improved Pulmonary Tolerance

Pulmonary delivery of small interfering RNA (siRNA) is a promising therapeutic strategy for treating various respiratory diseases but an effective carrier for the delivery of siRNA into the cells of the lungs and a robust gene-silencing effect is still lacking. Previously, we reported that the KL4 peptide, a synthetic cationic peptide with a repeating KLLLL sequence, can mediate effective siRNA transfection in lung epithelial cells but its high hydrophobic leucine content, and hence poor water solubility, limits its application as a delivery vector. Here, we show that the covalent attachment of monodisperse poly(ethylene glycol) (PEG) improves the solubility of KL4 and the uptake of its complex with siRNA into lung epithelial cells, such that very robust silencing is produced. All PEGylated KL4 peptides, with PEG length varying between 6 and 24 monomers, could bind and form nanosized complexes with siRNA, but the interaction between siRNA and peptides became weaker as the PEG chain length increased. All PEGylated KL4 peptides exhibited satisfactory siRNA transfection efficiency on three human lung epithelial cell lines, including A549 cells, Calu-3 cells, and BEAS-2B cells. The PEG₁₂KL4 peptide, which contains 12 monomers of PEG, was optimal for siRNA delivery and also demonstrated a low risk of inflammatory response and toxicity in vivo following pulmonary administration.

Peptide-Based Nanoparticles for Therapeutic Nucleic Acid Delivery

Gene therapy offers the possibility to skip, repair, or silence faulty genes or to stimulate the immune system to fight against disease by delivering therapeutic nucleic acids (NAs) to a patient. Compared to other drugs or protein treatments, NA-based therapies have the advantage of being a more universal approach to designing therapies because of the versatility of NA design. NAs (siRNA, pDNA, or mRNA) have great potential for therapeutic applications for an immense number of indications. However, the delivery of these exogenous NAs is still challenging and requires a specific delivery system. In this context, beside other non-viral vectors, cell-penetrating peptides (CPPs) gain more and more interest as delivery systems by forming a variety of nanocomplexes depending on the formulation conditions and the properties of the used CPPs/NAs. In this review, we attempt to cover the most important biophysical and biological aspects of non-viral peptide-based nanoparticles (PBNs) for therapeutic nucleic acid formulations as a delivery system. The most relevant peptides or peptide families forming PBNs in the presence of NAs described since 2015 will be presented. All these PBNs able to deliver NAs in vitro and in vivo have common features, which are characterized by defined formulation conditions in order to obtain PBNs from 60 nm to 150 nm with a homogeneous dispersity (PdI lower than 0.3) and a positive charge between +10 mV and +40 mV.

In Vivo Follow-Up of Gene Inhibition in Solid Tumors Using Peptide-Based Nanoparticles for siRNA Delivery

Small interfering RNA (siRNA) exhibits a high degree of specificity for targeting selected genes. They are efficient on cells in vitro, but in vivo siRNA therapy remains a challenge for solid tumor treatment as siRNAs display difficulty reaching their intracellular target. The present study was designed to show the in vivo efficiency of a new peptide (WRAP5), able to form peptide-based nanoparticles (PBN) that can deliver siRNA to cancer cells in solid tumors. WRAP5:siRNA nanoparticles targeting firefly luciferase (Fluc) were formulated and assayed on Fluc-expressing U87 glioblastoma cells. The mode of action of WRAP5:siRNA by RNA interference was first confirmed in vitro and then investigated in vivo using a combination of bioluminescent reporter genes. Finally, histological analyses were performed to elucidate the cell specificity of this PBN in the context of brain tumors. In vitro and in vivo results showed efficient knock-down of Fluc expression with no toxicity. WRAP5:siFluc remained in the tumor for at least 10 days in vivo. Messenger RNA (mRNA) analyses indicated a specific decrease in Fluc mRNA without affecting tumor growth. Histological studies identified PBN accumulation in the cytoplasm of tumor cells but also in glial and neuronal cells. Through in vivo molecular imaging, our findings established the proof of concept for specific gene silencing in solid tumors. The evidence generated could be translated into therapy for any specific gene in different types of tumors without cell type specificity but with high molecular specificity.

From Antisense RNA to RNA Modification: Therapeutic Potential of RNA-Based Technologies

Therapeutic oligonucleotides interact with a target RNA via Watson-Crick complementarity, affecting RNA-processing reactions such as mRNA degradation, pre-mRNA splicing, or mRNA translation. Since they were proposed decades ago, several have been approved for clinical use to correct genetic mutations. Three types of mechanisms of action (MoA) have emerged: RNase H-dependent degradation of mRNA directed by short chimeric antisense oligonucleotides (gapmers), correction of splicing defects via splice-modulation oligonucleotides, and interference of gene expression via short interfering RNAs (siRNAs). These antisense-based mechanisms can tackle several genetic disorders in a gene-specific manner, primarily by gene downregulation (gapmers and siRNAs) or splicing defects correction (exon-skipping oligos). Still, the challenge remains for the repair at the single-nucleotide level. The emerging field of epitranscriptomics and RNA modifications shows the enormous possibilities for recoding the transcriptome and repairing genetic mutations with high specificity while harnessing endogenously expressed RNA processing machinery. Some of these techniques have been proposed as alternatives to CRISPR-based technologies, where the exogenous gene-editing machinery needs to be delivered and expressed in the human cells to generate permanent (DNA) changes with unknown consequences. Here, we review the current FDA-approved antisense MoA (emphasizing some enabling technologies that contributed to their success) and three novel modalities based on post-transcriptional RNA modifications with therapeutic potential, including ADAR (Adenosine deaminases acting on RNA)-mediated RNA editing, targeted pseudouridylation, and 2′-O-methylation.

Syntheses of Morpholine-Based Nucleotide Analogs for Hepatic siRNA Targeting and Stabilization

A morpholine-based nucleotide analog was developed as a building block for hepatic siRNA targeting and stabilization. Attachment of an asialoglycoprotein-binding GalNAc ligand at the morpholine nitrogen was realized with different linkers. The obtained morpholino GalNAc scaffolds were coupled to the sense strand of a transthyretin-targeting siRNA and tested for their knockdown potency in vitro and in vivo. A clear structure-activity relationship was developed with regard to the linker type and length as well as the attachment site of the morpholino GalNAc moieties at the siRNA sense strand. Further, simple alkylation of the morpholine nitrogen led to a nucleotide analog, which increased siRNA stability, when used as a double 3'-overhang at the sense strand sequence. Combination of the best morpholino GalNAc building blocks as targeting nucleotides with an optimized stabilizing alkyl-substituted morpholine as 3'-overhangs resulted in siRNAs without any phosphorothioate stabilization in the sense strand and clearly improved the duration of action in vivo.

Impact of Serum Proteins on the Uptake and RNAi Activity of GalNAc-Conjugated siRNAs

Serum protein interactions are evaluated during the drug development process since they determine the free drug concentration in blood and thereby can influence the drug's pharmacokinetic and pharmacodynamic properties. While the impact of serum proteins on the disposition of small molecules is well understood, it is not yet well characterized for a new modality, RNA interference therapeutics. When administered systemically, small interfering RNAs (siRNAs) conjugated to the N-acetylgalactosamine (GalNAc) ligand bind to proteins present in circulation. However, it is not known if these protein interactions may impact the GalNAc-conjugated siRNA uptake into hepatocytes mediated through the asialoglycoprotein receptor (ASGPR) and thereby influence the activity of GalNAc-conjugated siRNAs. In this study, we assess the impact of serum proteins on the uptake and activity of GalNAc-conjugated siRNAs in primary human hepatocytes. We found that a significant portion of the GalNAc-conjugated siRNAs is bound to serum proteins. However, ASGPR-mediated uptake and activity of GalNAc-conjugated siRNAs were minimally impacted by the presence of serum relative to their uptake and activity in the absence of serum. Therefore, in contrast to small molecules, serum proteins are expected to have minimal impact on pharmacokinetic and pharmacodynamic properties of GalNAc-conjugated siRNAs.

Lipid-Based Nanoparticles in the Clinic and Clinical Trials: From Cancer Nanomedicine to COVID-19 Vaccines

COVID-19 vaccines have been developed with unprecedented speed which would not have been possible without decades of fundamental research on delivery nanotechnology. Lipid-based nanoparticles have played a pivotal role in the successes of COVID-19 vaccines and many other nanomedicines, such as Doxil® and Onpattro®, and have therefore been considered as the frontrunner in nanoscale drug delivery systems. In this review, we aim to highlight the progress in the development of these lipid nanoparticles for various applications, ranging from cancer nanomedicines to COVID-19 vaccines. The lipid-based nanoparticles discussed in this review are liposomes, niosomes, transfersomes, solid lipid nanoparticles, and nanostructured lipid carriers. We particularly focus on the innovations that have obtained regulatory approval or that are in clinical trials. We also discuss the physicochemical properties required for specific applications, highlight the differences in requirements for the delivery of different cargos, and introduce current challenges that need further development. This review serves as a useful guideline for designing new lipid nanoparticles for both preventative and therapeutic vaccines including immunotherapies.

siRNA Therapeutics against Respiratory Viral Infections-What Have We Learned for Potential COVID-19 Therapies?

Acute viral respiratory tract infections (AVRIs) are a major burden on human health and global economy and amongst the top five causes of death worldwide resulting in an estimated 3.9 million lives lost every year. In addition, new emerging respiratory viruses regularly cause outbreaks such as SARS-CoV-1 in 2003, the "Swine flu" in 2009, or most importantly the ongoing SARS-CoV-2 pandemic, which intensely impact global health, social life, and economy. Despite the prevalence of AVRIs and an urgent need, no vaccines-except for influenza-or effective treatments were available at the beginning of the COVID-19 pandemic. However, the innate RNAi pathway offers the ability to develop nucleic acid-based antiviral drugs. siRNA sequences against conserved, essential regions of the viral genome can prevent viral replication. In addition, viral infection can be averted prophylactically by silencing host genes essential for host-viral interactions. Unfortunately, delivering siRNAs to their target cells and intracellular site of action remains the principle hurdle toward their therapeutic use. Currently, siRNA formulations and chemical modifications are evaluated for their delivery. This progress report discusses the selection of antiviral siRNA sequences, delivery techniques to the infection sites, and provides an overview of antiviral siRNAs against respiratory viruses.

Porphyric neuropathy

Acute hepatic porphyrias are inherited metabolic disorders that may present with polyneuropathy, which if not diagnosed early can lead to quadriparesis, respiratory weakness, and death. Porphyric neuropathy is an acute to subacute motor predominant axonal neuropathy with a predilection for the upper extremities and usually preceded by a predominantly parasympathetic autonomic neuropathy. The rapid progression and associated dysautonomia mimic Guillain-Barré syndrome but are distinguished by the absence of cerebrospinal fluid albuminocytologic dissociation, progression beyond 4 wk, and associated abdominal pain. Spot urine test to assess the porphyrin precursors delta-aminolevulinic acid and porphobilinogen can provide a timely diagnosis during an acute attack. Timely treatment with intravenous heme, carbohydrate loading, and avoidance of porphyrinogenic medications can prevent further neurological morbidity and mortality.

Candidates for Intra-Articular Administration Therapeutics and Therapies of Osteoarthritis

Osteoarthritis (OA) of the knee is a disease that significantly decreases the quality of life due to joint deformation and pain caused by degeneration of articular cartilage. Since the degeneration of cartilage is irreversible, intervention from an early stage and control throughout life is important for OA treatment. For the treatment of early OA, the development of a disease-modifying osteoarthritis drug (DMOAD) for intra-articular (IA) injection, which is attracting attention as a point-of-care therapy, is desired. In recent years, the molecular mechanisms involved in OA progression have been clarified while new types of drug development methods based on gene sequences have been established. In addition to conventional chemical compounds and protein therapeutics, the development of DMOAD from the new modalities such as gene therapy and oligonucleotide therapeutics is accelerating. In this review, we have summarized the current status and challenges of DMOAD for IA injection, especially for protein therapeutics, gene therapy, and oligonucleotide therapeutics.

Nanosac, a Noncationic and Soft Polyphenol Nanocapsule, Enables Systemic Delivery of siRNA to Solid Tumors

For systemic delivery of small interfering RNA (siRNA) to solid tumors, the carrier must circulate avoiding premature degradation, extravasate and penetrate tumors, enter target cells, traffic to the intracellular destination, and release siRNA for gene silencing. However, existing siRNA carriers, which typically exhibit positive charges, fall short of these requirements by a large margin; thus, systemic delivery of siRNA to tumors remains a significant challenge. To overcome the limitations of existing approaches, we have developed a carrier of siRNA, called "Nanosac", a noncationic soft polyphenol nanocapsule. A siRNA-loaded Nanosac is produced by sequential coating of mesoporous silica nanoparticles (MSNs) with siRNA and polydopamine, followed by removal of the sacrificial MSN core. The Nanosac recruits serum albumin, co-opts caveolae-mediated endocytosis to enter tumor cells, and efficiently silences target genes. The softness of Nanosac improves extravasation and penetration into tumors compared to its hard counterpart. As a carrier of siRNA targeting PD-L1, Nanosac induces a significant attenuation of CT26 tumor growth by immune checkpoint blockade. These results support the utility of Nanosac in the systemic delivery of siRNA for solid tumor therapy.

DNA Nanostructures: Current Challenges and Opportunities for Cellular Delivery

DNA nanotechnology has produced a wide range of self-assembled structures, offering unmatched possibilities in terms of structural design. Because of their programmable assembly and precise control of size, shape, and function, DNA particles can be used for numerous biological applications, including imaging, sensing, and drug delivery. While the biocompatibility, programmability, and ease of synthesis of nucleic acids have rapidly made them attractive building blocks, many challenges remain to be addressed before using them in biological conditions. Enzymatic hydrolysis, low cellular uptake, immune cell recognition and degradation, and unclear biodistribution profiles are yet to be solved. Rigorous methodologies are needed to study, understand, and control the fate of self-assembled DNA structures in physiological conditions. In this review, we describe the current challenges faced by the field as well as recent successes, highlighting the potential to solve biology problems or develop smart drug delivery tools. We then propose an outlook to drive the translation of DNA constructs toward preclinical design. We particularly believe that a detailed understanding of the fate of DNA nanostructures within living organisms, achieved through thorough characterization, is the next required step to reach clinical maturity.

Hydrophilic Hyperbranched Polymer-Coated siRNA/Polyamidoamine Dendron-Bearing Lipid Complexes Preparation for High Colloidal Stability and Efficient RNAi

RNA interference (RNAi) using siRNA has gained much attention for use in therapies for cancer and genetic disorders. To establish RNAi-based therapeutics, the development of efficient siRNA nanocarriers is desired. Earlier, we developed polyamidoamine dendron-bearing lipids able to form complexes with nucleic acids as gene vectors. Especially, dendron lipids with unsaturated alkyl chains (DL-G1-U2) induced efficient endosomal escape by membrane fusion, leading to efficient transfection in vitro. For this study, dendron lipids having oleyl/linoleyl groups (DL-G1-U3) were designed to increase membrane fusogenic activity further. Indeed, DL-G1-U3/siRNA complexes achieved higher membrane fusogenic activity and knockdown of the target gene more efficiently than conventional DL-G1-U2/siRNA complexes did. A hydrophilic polymer, hyperbranched polyglycidol lauryl ester (HPG-Lau), was modified further on the surface of DL-G1-U3/siRNA complexes to provide colloidal stability. Surface modification of HPG-Lau increased the colloidal stability in a physiological condition more than complexes without HPG-Lau. Importantly, HPG-Lau-coated DL/siRNA complexes showed identical RNAi effects to those of parental DL/siRNA complexes, whereas the RNAi activity of poly(ethylene glycol)-bearing lipid (PEG-PE)-modified DL/siRNA complexes was hindered completely. Introduction of unsaturated bonds into dendron lipids and selection of suitable hydrophilic polymers for nanocarrier modification are important for obtaining efficient siRNA vectors toward in vivo siRNA delivery.

Immunotherapy for breast cancer using EpCAM aptamer tumor-targeted gene knockdown

New strategies for cancer immunotherapy are needed since most solid tumors do not respond to current approaches. Here we used epithelial cell adhesion molecule EpCAM (a tumor-associated antigen highly expressed on common epithelial cancers and their tumor-initiating cells) aptamer-linked small-interfering RNA chimeras (AsiCs) to knock down genes selectively in EpCAM+ tumors with the goal of making cancers more visible to the immune system. Knockdown of genes that function in multiple steps of cancer immunity was evaluated in aggressive triple-negative and HER2+ orthotopic, metastatic, and genetically engineered mouse breast cancer models. Gene targets were chosen whose knockdown was predicted to promote tumor neoantigen expression (Upf2, Parp1, Apex1), phagocytosis, and antigen presentation (Cd47), reduce checkpoint inhibition (Cd274), or cause tumor cell death (Mcl1). Four of the six AsiC (Upf2, Parp1, Cd47, and Mcl1) potently inhibited tumor growth and boosted tumor-infiltrating immune cell functions. AsiC mixtures were more effective than individual AsiC and could synergize with anti-PD-1 checkpoint inhibition.

Synthesis and evaluation of modified siRNA molecules containing a novel glucose derivative

Chemical modifications are critical for the development of safe and effective siRNAs for downstream applications. In this study, we report the synthesis of a novel glucose phosphoramidite, a triazole-linked to uracil at position one, for incorporation into oligonucleotides. Biological testing revealed that the glucose derivative at key positions within the sense or antisense strand can lead to potent gene-silencing activity, thus highlighting its tolerance in both sense and antisense positions. Furthermore, the A-form helical formation was maintained with this modification. Overall, placing the modification at the 3' end and at key internal positions led to effective RNAi gene-silencing activity.

Healthcare Utilization and Cost Burden of Porphyria in Commercially Insured Adults in the United States

OBJECTIVES

The healthcare burden associated with porphyria remains unevaluated despite the associated increased risks of morbidity and mortality. We aimed to assess the healthcare utilization and cost burdens of porphyria in the United States (US) using real-world claims data.

METHODS

We performed a case-control analysis of adults in the Truven Health MarketScan^® Commercial Claims database (2010-2015). Using propensity scores, 2788 porphyria cases were matched 1:1 to porphyria-free controls with chronic liver disease. Total and service-specific parameters were quantified for the 12 months before porphyria diagnosis versus the 12 months after diagnosis and over the 12 months following a randomly selected date for controls. Wilcoxon signed rank tests and McNemar tests were used to examine incremental differences in burden between cases and controls. Adjusted multivariable generalized linear regression models were used to compare healthcare burdens for cases versus controls.

RESULTS

Relative to the 12 months before porphyria diagnosis, the following 12 months had more claims per patient (35.94 vs 39.67; p < 0.0001) and increased per-patient healthcare costs (US$21,308 vs US$27,270; p < 0.0001). Porphyria cases incurred US$7839 more in total unadjusted costs compared with controls in the 12 months after index date. Compared with controls, cases also had more claims (39.67 vs 34.81), primarily due to inpatient admissions (1.80 vs 0.78) and outpatient visits (21.41 vs 17.98). Cases also had higher healthcare costs for inpatient admissions (US$8882 vs US$4674) and outpatient visits (US$12,378 vs US$9801).

CONCLUSION

Porphyria is associated with significant healthcare costs and utilization burdens driven by increased inpatient admissions, outpatient visits, and pharmaceutical claims.

Harnessing molecular recognition for localized drug delivery

A grand challenge in drug delivery is providing the right dose, at the right anatomic location, for the right duration of time to maximize therapeutic efficacy while minimizing off-target toxicity and other deleterious side-effects. Two general modalities are receiving broad attention for localized drug delivery. In the first, referred to as "targeted accumulation", drugs or drug carriers are engineered to have targeting moieties that promote their accumulation at a specific tissue site from circulation. In the second, referred to as "local anchoring", drugs or drug carriers are inserted directly into the tissue site of interest where they persist for a specified duration of time. This review surveys recent advances in harnessing molecular recognition between proteins, peptides, nucleic acids, lipids, and carbohydrates to mediate targeted accumulation and local anchoring of drugs and drug carriers.

A Decade of FDA-Approved Drugs (2010-2019): Trends and Future Directions

A total of 378 novel drugs and 27 biosimilars approved by the U.S. Food and Drug Administration (FDA) between 2010 and 2019 were evaluated according to approval numbers by year, therapeutic areas, modalities, route of administration, first-in-class designation, approval times, and expedited review categories. From this review, oncology remains the top therapy area (25%), followed by infection (15%) and central nervous system disorders (11%). Regulatory incentives have been effective as evidenced by an increase in orphan drugs as well as antibacterial drugs approved under the GAIN act. Clinical development times may be increasing, perhaps as a result of the increase in orphan drug indications. Small molecules continue to mostly adhere to "Rule of 5" (Ro5) parameters, but innovation in new modalities is rapidly progressing with approvals for antisense oligonucleotides (ASO), small-interfering RNA (siRNAs), and antibody-directed conjugates (ADCs). Finally, novel targets and scientific breakthroughs that address areas of unmet clinical need are discussed in detail.

2020 FDA TIDES (Peptides and Oligonucleotides) Harvest

2020 has been an extremely difficult and challenging year as a result of the coronavirus disease 2019 (COVID-19) pandemic and one in which most efforts have been channeled into tackling the global health crisis. The US Food and Drug Administration (FDA) has approved 53 new drug entities, six of which fall in the peptides and oligonucleotides (TIDES) category. The number of authorizations for these kinds of drugs has been similar to that of previous years, thereby reflecting the consolidation of the TIDES market. Here, the TIDES approved in 2020 are analyzed in terms of chemical structure, medical target, mode of action, and adverse effects.

Pulmonary siRNA delivery for lung disease: Review of recent progress and challenges

Lung diseases are a leading cause of mortality worldwide and there exists urgent need for new therapies. Approval of the first siRNA treatments in humans has opened the door for further exploration of this therapeutic strategy for other disease states. Pulmonary delivery of siRNA-based biopharmaceuticals offers the potential to address multiple unmet medical needs in lung-related diseases because of the specific physiology of the lung and characteristic properties of siRNA. Inhalation-based siRNA delivery designed for efficient, targeted delivery to specific cells within the lung holds great promise. Efficient delivery of siRNA directly to the lung, however, is relatively complex. This review focuses on the barriers that impact pulmonary siRNA delivery and successful recent approaches to advance this field forward. We focus on the pulmonary barriers that affect siRNA delivery, the disease-dependent pathological changes and their role in pulmonary disease and impact on siRNA delivery, as well as the recent development on the pulmonary siRNA delivery systems.

Modified internucleoside linkages for nuclease-resistant oligonucleotides

In the past few years, several drugs derived from nucleic acids have been approved for commercialization and many more are in clinical trials. The sensitivity of these molecules to nuclease digestion in vivo implies the need to exploit resistant non-natural nucleotides. Among all the possible modifications, the one concerning the internucleoside linkage is of particular interest. Indeed minor changes to the natural phosphodiester may result in major modifications of the physico-chemical properties of nucleic acids. As this linkage is a key element of nucleic acids' chemical structures, its alteration can strongly modulate the plasma stability, binding properties, solubility, cell penetration and ultimately biological activity of nucleic acids. Over the past few decades, many research groups have provided knowledge about non-natural internucleoside linkage properties and participated in building biologically active nucleic acid derivatives. The recent renewing interest in nucleic acids as drugs, demonstrated by the emergence of new antisense, siRNA, aptamer and cyclic dinucleotide molecules, justifies the review of all these studies in order to provide new perspectives in this field. Thus, in this review we aim at providing the reader insights into modified internucleoside linkages that have been described over the years whose impact on annealing properties and resistance to nucleases have been evaluated in order to assess their potential for biological applications. The syntheses of modified nucleotides as well as the protocols developed for their incorporation within oligonucleotides are described. Given the intended biological applications, the modifications described in the literature that have not been tested for their resistance to nucleases are not reported.

Novel Lipid-Oligonucleotide Conjugates Containing Long-Chain Sulfonyl Phosphoramidate Groups: Synthesis and Biological Properties

New lipid conjugates of DNA and RNA incorporating one to four [(4-dodecylphenyl)sulfonyl]phosphoramidate or (hexadecylsulfonyl)phosphoramidate groups at internucleotidic positions near the 3′ or 5′-end were synthesized and characterized. Low cytotoxicity of the conjugates and their ability to be taken up into cells without transfection agents were demonstrated. Lipid-conjugated siRNAs targeting repulsive guidance molecules a (RGMa) have shown a comparable gene silencing activity in PK-59 cells to unmodified control siRNA when delivered into the cells via Lipofectamine mediated transfection.

Polymeric delivery systems for nucleic acid therapeutics: Approaching the clinic

Gene therapy using nucleic acids has many clinical applications for the treatment of diseases with a genetic origin as well as for the development of innovative vaccine formulations. Since nucleic acids in their free form are rapidly degraded by nucleases present in extracellular matrices, have poor pharmacokinetics and hardly pass cellular membranes, carrier systems are required. Suitable carriers that protect the nucleic acid payload against enzymatic attack, prolong circulation time after systemic administration and assist in cellular binding and internalization are needed to develop nucleic acid based drug products. Viral vectors have been investigated and are also clinically used as delivery vehicles. However, some major drawbacks are associated with their use. Therefore there has been substantial attention on the use of non-viral carrier systems based on cationic lipids and polymers. This review focuses on the properties of polymer-based nucleic acid formulations, also referred as polyplexes. Different polymeric systems are summarized, and the cellular barriers polyplexes encounter and ways to tackle these are discussed. Finally attention is given to the clinical status of non-viral nucleic acid formulations.

Acute Intermittent Porphyria: An Overview of Therapy Developments and Future Perspectives Focusing on Stabilisation of HMBS and Proteostasis Regulators

Acute intermittent porphyria (AIP) is an autosomal dominant inherited disease with low clinical penetrance, caused by mutations in the hydroxymethylbilane synthase (HMBS) gene, which encodes the third enzyme in the haem biosynthesis pathway. In susceptible HMBS mutation carriers, triggering factors such as hormonal changes and commonly used drugs induce an overproduction and accumulation of toxic haem precursors in the liver. Clinically, this presents as acute attacks characterised by severe abdominal pain and a wide array of neurological and psychiatric symptoms, and, in the long-term setting, the development of primary liver cancer, hypertension and kidney failure. Treatment options are few, and therapies preventing the development of symptomatic disease and long-term complications are non-existent. Here, we provide an overview of the disorder and treatments already in use in clinical practice, in addition to other therapies under development or in the pipeline. We also introduce the pathomechanistic effects of HMBS mutations, and present and discuss emerging therapeutic options based on HMBS stabilisation and the regulation of proteostasis. These are novel mechanistic therapeutic approaches with the potential of prophylactic correction of the disease by totally or partially recovering the enzyme functionality. The present scenario appears promising for upcoming patient-tailored interventions in AIP.

Antisense Drugs Make Sense for Neurological Diseases

The genetic basis for most inherited neurodegenerative diseases has been identified, yet there are limited disease-modifying therapies for these patients. A new class of drugs-antisense oligonucleotides (ASOs)-show promise as a therapeutic platform for treating neurological diseases. ASOs are designed to bind to the RNAs either by promoting degradation of the targeted RNA or by elevating expression by RNA splicing. Intrathecal injection into the cerebral spinal fluid results in broad distribution of antisense drugs and long-term effects. Approval of nusinersen in 2016 demonstrated that effective treatments for neurodegenerative diseases can be identified and that treatments not only slow disease progression but also improve some symptoms. Antisense drugs are currently in development for amyotrophic lateral sclerosis, Huntington's disease, Alzheimer's disease, Parkinson's disease, and Angelman syndrome, and several drugs are in late-stage research for additional neurological diseases. This review highlights the advances in antisense technology as potential treatments for neurological diseases.

Development of siRNA Therapeutics for the Treatment of Liver Diseases

Small interfering RNA (siRNA)-based therapeutics holds the promise to treat a wide range of human diseases that are currently incurable using conventional therapies. Most siRNA therapeutic efforts to date have focused on the treatment of liver diseases due to major breakthroughs in the development of efficient strategies for delivering siRNA drugs to the liver. Indeed, the development of lipid nanoparticle-formulated and GalNAc-conjugated siRNA therapeutics has resulted in recent FDA approvals of the first siRNA-based drugs, patisiran for the treatment of hereditary transthyretin amyloidosis and givosiran for the treatment of acute hepatic porphyria, respectively. Here, we describe the current strategies for delivering siRNA drugs to the liver and summarize recent advances in clinical development of siRNA therapeutics for the treatment of liver diseases.

Opportunities and challenges for antisense oligonucleotide therapies

Antisense oligonucleotide (AON) therapies involve short strands of modified nucleotides that target RNA in a sequence-specific manner, inducing targeted protein knockdown or restoration. Currently, 10 AON therapies have been approved in the United States and Europe. Nucleotides are chemically modified to protect AONs from degradation, enhance bioavailability and increase RNA affinity. Whereas single stranded AONs can efficiently be delivered systemically, delivery of double stranded AONs requires capsulation in lipid nanoparticles or binding to a conjugate as the uptake enhancing backbone is hidden in this conformation. With improved chemistry, delivery vehicles and conjugates, doses can be lowered, thereby reducing the risk and occurrence of side effects. AONs can be used to knockdown or restore levels of protein. Knockdown can be achieved by single stranded or double stranded AONs binding the RNA transcript and activating RNaseH-mediated and RISC-mediated degradation respectively. Transcript binding by AONs can also prevent translation, hence reducing protein levels. For protein restoration, single stranded AONs are used to modulate pre-mRNA splicing and either include or skip an exon to restore protein production. Intervening at a genetic level, AONs provide therapeutic options for inherited metabolic diseases as well. This review provides an overview of the different AON approaches, with a focus on AONs developed for inborn errors of metabolism.

Polymeric nanoparticles for RNA delivery

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

Clinical Applications of Single-Stranded Oligonucleotides: Current Landscape of Approved and In-Development Therapeutics

Single-stranded oligonucleotides have been explored as a therapeutic modality for more than 20 years. Only during the last 5 years have single-stranded oligonucleotides become a modality of choice in the fields of precision medicine and targeted therapeutics. Recently, there have been a number of development efforts involving this modality that have led to treatments for genetic diseases that were once untreatable. This review highlights key applications of single-stranded oligonucleotides that function in a sequence-dependent manner when applied to modulate precursor (pre-)mRNA splicing, gene expression, and immune pathways. These applications have been used to address diseases that range from neurological to muscular to metabolic, as well as to develop vaccines. The wide range of applications denotes the versatility of single-stranded oligonucleotides as a robust therapeutic platform. The focus of this review is centered on approved single-stranded oligonucleotide therapies and the evolution of oligonucleotide therapeutics into novel applications currently in clinical development.

Nucleic acids therapeutics using PolyPurine Reverse Hoogsteen hairpins

PolyPurine Reverse Hoogsteen hairpins (PPRHs) are DNA hairpins formed by intramolecular reverse Hoogsteen bonds which can bind to polypyrimidine stretches in dsDNA by Watson:Crick bonds, thus forming a triplex and displacing the fourth strand of the DNA complex. PPRHs were first described as a gene silencing tool in vitro for DHFR, telomerase and survivin genes. Then, the effect of PPRHs directed against the survivin gene was also determined in vivo using a xenograft model of prostate cancer cells (PC3). Since then, the ability of PPRHs to inhibit gene expression has been explored in other genes involved in cancer (BCL-2, mTOR, topoisomerase, C-MYC and MDM2), in immunotherapy (SIRPα/CD47 and PD-1/PD-L1 tandem) or in replication stress (WEE1 and CHK1). Furthermore, PPRHs have the ability to target the complementary strand of a G-quadruplex motif as a regulatory element of the TYMS gene. PPRHs have also the potential to correct point mutations in the DNA as shown in two collections of CHO cell lines bearing mutations in either the dhfr or aprt loci. Finally, based on the capability of PPRHs to form triplexes, they have been incorporated as probes in biosensors for the determination of the DNA methylation status of PAX-5 in cancer and the detection of mtLSU rRNA for the diagnosis of Pneumocystis jirovecii. Of note, PPRHs have high stability and do not present immunogenicity, hepatotoxicity or nephrotoxicity in vitro. Overall, PPRHs constitute a new economical biotechnological tool with multiple biomedical applications.

The microgravity enhanced polymer-mediated siRNA gene silence by improving cellular uptake

Graphical abstract

Abstract

Microgravity (MG) effect is a weightlessness phenomenon caused by the distance from the ground or low gravity of other planets outside the earth’s atmosphere. The various effects of MG have been corroborated in human and animal studies and modeled in cell-based analogs. However, the impact of MG on siRNA performance remains to be elucidated, which is crucial for aerospace medicine. In this study, we prepared nucleic acid nanomicelles (EAASc/siRNA) by using tri-block copolymer of PEG45-PAMA40-P(C7A36-DBA37) (EAASc) and siRNA and explored its working mechanism under simulated microgravity (SMG) condition generated by a random positioning machine (RPM). The binding ability of EAASc to siRNA and silence activity were firstly confirmed in normal gravity (NG) environment. Evaluation of PLK1 mRNA expression revealed that gene inhibition efficiencies were increased by 28.7% (HepG2) and 28.9% (A549) under SMG condition, compared with those under NG condition. In addition, mechanism exploration indicated that morphology and migration capability of cancer cells were significantly changed, the internalization of EAASc/siRNA by cells was magnified when the cells were incubated with RPM. No significant difference was observed regarding the expression profiles of genes involved in RNA interference (RNAi) pathway, including Ago2, Dicer, TRBP, and so on. Taken together, siRNA activity was elevated under SMG condition owning to increased cellular internalization. This study, for the first time to our knowledge, provides valuable theory for development and application of siRNA therapeutic in space in the future.

RNAi therapeutics: an antiviral strategy for human infections

Gene silencing induced by RNAi represents a promising antiviral development strategy. This review will summarise the current state of RNAi therapeutics for treating acute and chronic human virus infections. The gene silencing pathways exploited by RNAi therapeutics will be described and include both classic RNAi, inducing cytoplasmic mRNA degradation post-transcription and novel RNAi, mediating epigenetic modifications at the transcription level in the nucleus. Finally, the challenge of delivering gene modifications via RNAi will be discussed, along with the unique characteristics of respiratory versus systemic administration routes to highlight recent advances and future potential of RNAi antiviral treatment strategies.

Therapeutic strategies for acute intermittent porphyria

Acute intermittent porphyria (AIP) is an autosomal dominant disease caused by mutations in porphobilinogen deaminase (PBGD), the third enzyme of the heme synthesis pathway. Symptoms of AIP usually manifest as intermittent acute attacks with occasional neuropsychiatric crises. The management of AIP includes treatment of acute attacks, prevention of attacks, long-term monitoring and treatment of chronic complications. Intravenous injection of heme is the most effective method of treating acute attacks. Carbohydrate loading is used when heme is unavailable or in the event of mild attacks. Symptomatic treatment is also needed during attacks. Prevention of attacks includes eliminating precipitating factors, heme prophylaxis and liver transplantation. New treatment options include givosiran (siRNA) to down-regulate ALA synthase-1 (ALAS1) and the messenger RNA of PBGD (PBGD mRNA) delivered to the liver cells of patients with AIP. Long-term monitoring of chronic complications includes regular liver-kidney function and hepatocellular carcinoma (HCC) screening.

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.

The Effects of Single Nucleotide Polymorphisms in Cancer RNAi Therapies

Tremendous progress in RNAi delivery methods and design has allowed for the effective development of siRNA-based therapeutics that are currently under clinical investigation for various cancer treatments. This approach has the potential to revolutionize cancer therapy by providing the ability to specifically downregulate or upregulate the mRNA of any protein of interest. This exquisite specificity, unfortunately, also has a downside. Genetic variations in the human population are common because of the presence of single nucleotide polymorphisms (SNPs). SNPs lead to synonymous and non-synonymous changes and they occur once in every 300 base pairs in both coding and non-coding regions in the human genome. Much less common are the somatic mosaicism variations associated with genetically distinct populations of cells within an individual that is derived from postzygotic mutations. These heterogeneities in the population can affect the RNAi's efficacy or more problematically, which can lead to unpredictable and sometimes adverse side effects. From a more positive viewpoint, both SNPs and somatic mosaicisms have also been implicated in human diseases, including cancer, and these specific changes could offer the ability to effectively and, more importantly, selectively target the cancer cells. In this review, we discuss how SNPs in the human population can influence the development and success of novel anticancer RNAi therapies and the importance of why SNPs should be carefully considered.

Identifying Cleaved and Noncleaved Targets of Small Interfering RNAs and MicroRNAs in Mammalian Cells by SpyCLIP

Recently, the US Food and Drug Administration (FDA) approved the first small interfering RNA (siRNA) drug, marking a significant milestone in the therapeutic use of RNA interference (RNAi) technology. However, off-target gene silencing by siRNA remains one of the major obstacles in siRNA therapy. Although siRNA off-target effects caused by a mechanism known for microRNA (miRNA)-mediated gene repression have been extensively discussed, whether RNAi can cause unintended cleavage through the effector protein AGO2 at sites harboring partially complementary sequences to the siRNA remains unknown. Here, we report a strategy to establish a comprehensive picture of siRNA cleaved and noncleaved off-targets by performing SpyCLIP using wild-type and catalytically inactive AGO2 mutants in parallel. Additionally, we investigated naturally occurring cleavage events mediated by endogenous miRNAs using the same strategy. Our results demonstrated that AGO2 SpyCLIP is a powerful method to identify both the cleaved and noncleaved targets of siRNAs, providing valuable information for improving siRNA design rules.

Overcoming Barriers for siRNA Therapeutics: From Bench to Bedside

The RNA interference (RNAi) pathway possesses immense potential in silencing any gene in human cells. Small interfering RNA (siRNA) can efficiently trigger RNAi silencing of specific genes. FDA Approval of siRNA therapeutics in recent years garnered a new hope in siRNA therapeutics. However, their therapeutic use is limited by several challenges. siRNAs, being negatively charged, are membrane-impermeable and highly unstable in the systemic circulation. In this review, we have comprehensively discussed the extracellular barriers, including enzymatic degradation of siRNAs by serum endonucleases and RNAases, rapid renal clearance, membrane impermeability, and activation of the immune system. Besides, we have thoroughly described the intracellular barriers such as endosomal trap and off-target effects of siRNAs. Moreover, we have reported most of the strategies and techniques in overcoming these barriers, followed by critical comments in translating these molecules from bench to bedside.

Inhaled RNA Therapy: From Promise to Reality

RNA-based medicine is receiving growing attention for its diverse roles and potential therapeutic capacity. The largest obstacle in its clinical translation remains identifying a safe and effective delivery system. Studies investigating RNA therapeutics in pulmonary diseases have rapidly expanded and drug administration by inhalation allows the direct delivery of RNA therapeutics to the target site of action while minimizing systemic exposure. In this review, we highlight recent developments in pulmonary RNA delivery systems with the use of nonviral vectors. We also discuss the major knowledge gaps that require thorough investigation and provide insights that will help advance this exciting field towards the bedside.

RNA Drugs and RNA Targets for Small Molecules: Principles, Progress, and Challenges

RNA-based therapies, including RNA molecules as drugs and RNA-targeted small molecules, offer unique opportunities to expand the range of therapeutic targets. Various forms of RNAs may be used to selectively act on proteins, transcripts, and genes that cannot be targeted by conventional small molecules or proteins. Although development of RNA drugs faces unparalleled challenges, many strategies have been developed to improve RNA metabolic stability and intracellular delivery. A number of RNA drugs have been approved for medical use, including aptamers (e.g., pegaptanib) that mechanistically act on protein target and small interfering RNAs (e.g., patisiran and givosiran) and antisense oligonucleotides (e.g., inotersen and golodirsen) that directly interfere with RNA targets. Furthermore, guide RNAs are essential components of novel gene editing modalities, and mRNA therapeutics are under development for protein replacement therapy or vaccination, including those against unprecedented severe acute respiratory syndrome coronavirus pandemic. Moreover, functional RNAs or RNA motifs are highly structured to form binding pockets or clefts that are accessible by small molecules. Many natural, semisynthetic, or synthetic antibiotics (e.g., aminoglycosides, tetracyclines, macrolides, oxazolidinones, and phenicols) can directly bind to ribosomal RNAs to achieve the inhibition of bacterial infections. Therefore, there is growing interest in developing RNA-targeted small-molecule drugs amenable to oral administration, and some (e.g., risdiplam and branaplam) have entered clinical trials. Here, we review the pharmacology of novel RNA drugs and RNA-targeted small-molecule medications, with a focus on recent progresses and strategies. Challenges in the development of novel druggable RNA entities and identification of viable RNA targets and selective small-molecule binders are discussed. SIGNIFICANCE STATEMENT: With the understanding of RNA functions and critical roles in diseases, as well as the development of RNA-related technologies, there is growing interest in developing novel RNA-based therapeutics. This comprehensive review presents pharmacology of both RNA drugs and RNA-targeted small-molecule medications, focusing on novel mechanisms of action, the most recent progress, and existing challenges.

A critical analysis of methods used to investigate the cellular uptake and subcellular localization of RNA therapeutics

RNA therapeutics are a promising strategy to treat genetic diseases caused by the overexpression or aberrant splicing of a specific protein. The field has seen major strides in the clinical efficacy of this class of molecules, largely due to chemical modifications and delivery strategies that improve nuclease resistance and enhance cell penetration. However, a major obstacle in the development of RNA therapeutics continues to be the imprecise, difficult, and often problematic nature of most methods used to measure cell penetration. Here, we review these methods and clearly distinguish between those that measure total cellular uptake of RNA therapeutics, which includes both productive and non-productive uptake, and those that measure cytosolic/nuclear penetration, which represents only productive uptake. We critically analyze the benefits and drawbacks of each method. Finally, we use key examples to illustrate how, despite rigorous experimentation and proper controls, our understanding of the mechanism of gymnotic uptake of RNA therapeutics remains limited by the methods commonly used to analyze RNA delivery.

Non-Viral Targeted Nucleic Acid Delivery: Apply Sequences for Optimization

In nature, genomes have been optimized by the evolution of their nucleic acid sequences. The design of peptide-like carriers as synthetic sequences provides a strategy for optimizing multifunctional targeted nucleic acid delivery in an iterative process. The optimization of sequence-defined nanocarriers differs for different nucleic acid cargos as well as their specific applications. Supramolecular self-assembly enriched the development of a virus-inspired non-viral nucleic acid delivery system. Incorporation of DNA barcodes presents a complementary approach of applying sequences for nanocarrier optimization. This strategy may greatly help to identify nucleic acid carriers that can overcome pharmacological barriers and facilitate targeted delivery in vivo. Barcode sequences enable simultaneous evaluation of multiple nucleic acid nanocarriers in a single test organism for in vivo biodistribution as well as in vivo bioactivity.

In vivo and in vitro studies of antisense oligonucleotides - a review

The potential of antisense oligonucleotides in gene silencing was discovered over 40 years ago, which resulted in the growing interest in their chemistry, mechanism of action, and metabolic pathways. This review summarizes the selected mechanisms of antisense drug action, as well as therapeutics which are to date approved by the Food and Drug Administration and European Medicines Agency. Moreover, bioanalytical methods used for ASO pharmacokinetics and metabolism studies are briefly summarized. Special attention is paid to the primary pharmacokinetic properties of the different chemistry classes of antisense oligonucleotides. Moreover, in vivo and in vitro metabolic pathways of these compounds are widely described with the emphasis on the different animal models as well as in vitro models, including tissues homogenates, enzyme solutions, and human liver microsomes.

Modified nucleic acids: replication, evolution, and next-generation therapeutics

Modified nucleic acids, also called xeno nucleic acids (XNAs), offer a variety of advantages for biotechnological applications and address some of the limitations of first-generation nucleic acid therapeutics. Indeed, several therapeutics based on modified nucleic acids have recently been approved and many more are under clinical evaluation. XNAs can provide increased biostability and furthermore are now increasingly amenable to in vitro evolution, accelerating lead discovery. Here, we review the most recent discoveries in this dynamic field with a focus on progress in the enzymatic replication and functional exploration of XNAs.

Antisense antibacterial compounds

Extensive antibiotic use combined with poor historical drug stewardship practices have created a medical crisis in which once treatable bacterial infections are now increasingly unmanageable. To combat this, new antibiotics will need to be developed and safeguarded. An emerging class of antibiotics based upon nuclease-stable antisense technologies has proven valuable in preclinical testing against a variety of bacterial pathogens. This review describes the current state of development of antisense-based antibiotics, the mechanisms thus far employed by these compounds, and possible future avenues of research.