Synthesis, Biophysical and Biological Evaluation of Splice-Switching Oligonucleotides with Multiple LNA-Phosphothiotriester Backbones

Polyanionic antisense oligonucleotides hold great promise as RNA targeting drugs but issues with bioavailability hinder their development. Uncharged phosphorus-based backbones are promising alternatives but robust methods to produce them are limited. We report the synthesis and properties of oligonucleotides containing charge-neutral LNA alkyl phosphothiotriester backbones combined with 2'-O-methyl phosphorothioate nucleotides for therapeutic applications. The nature of the triester alkyl group dictates the success of solid-phase synthesis; tertiary alkyl groups are lost during the P(III) oxidation step, whereas primary alkyl groups are partially cleaved during deprotection. In contrast, oligonucleotides containing secondary phosphothiotriester linkages are stable, and large numbers of triesters can be incorporated. The modified oligonucleotides have excellent duplex stability with complementary RNA and exhibit strong nuclease resistance. To expand synthetic flexibility, oligonucleotides containing multiple internal alkynyl phosphothiotriesters can be conjugated to lipids, carbohydrates, or small molecules through CuAAC click chemistry. Oligonucleotides containing LNA-THP phosphothiotriesters exhibit high levels of pre-mRNA splice switching in eukaryotic cells.

Synthesis, Characterization, and Function of an RNA-Based Transfection Reagent

A synthetic 8-mer, amphipathic, trans-acting poly-2'-O-methyluridylic thiophosphate triester RNA element (2'-OMeUtaPS) can be prepared using solid-phase synthesis protocols. 2'-OMeUtaPS efficiently mediates the delivery of uncharged polyA-tailed phosphorodiamidate morpholino (PMO) sequences in HeLa pLuc 705 cells, as evidenced by flow cytometry measurements. In this cell line, 2'-OMeUtaPS-mediated transfection of an antisense polyA-tailed PMO sequence induces alternative splicing of an aberrant luciferase pre-mRNA splice site, leading to restoration of functional luciferase, as quantitatively measured using a typical luciferase assay. 2'-OMeUtaPS is also potent at delivering an uncharged antisense polyA-tailed PMO sequence in muscle cells of the mdx mouse model of muscular dystrophy; targeting the polyA-tailed PMO sequence against a splice site of the pre-mRNA encoding mutated dystrophin triggers an alternate splicing event that results in excision of the mutated exon (exon 23) from the pre-mRNA and production of functional dystrophin, as demonstrated by agarose gel electrophoresis. © 2018 by John Wiley & Sons, Inc.

Trans-acting oligodeoxythymidine phosphorothioate triester reagents for transient transfection optimized and facilitated by a high-throughput microbioreactor system

A rapid and cost-effective transient transfection method for mammalian cells is essential for screening biopharmaceuticals in early stages of development. A library of 25 amphipathic trans-acting oligodeoxythymidine phosphorothioate triester (dTtaPS) transfection reagents, carrying positively charged and lipophilic groups, has been constructed for this purpose. High-throughput screening of the library, using an imaging cytometer and an automated microbioreactor system, has led to the identification of dTtaPS¹⁰⁺ as a potent transfection reagent. This reagent efficiently delivers a plasmid encoding enhanced green fluorescent protein in adherent HeLa cells while exhibiting low cytotoxicity. The microbioreactor system has been particularly useful for assessing the ability of dTtaPS¹⁰⁺ to deliver a plasmid encoding immunoglobulin IgG1 in a fed-batch serum-free suspension CHO cell culture; dTtaPS¹⁰⁺ -mediated transfection resulted in the production of IgG1 in yields comparable to or better than those obtained with commercial lipid-based transfection reagents under similar conditions. The ability of dTtaPS¹⁰⁺ to deliver plasmids is essentially unaffected by the presence of a silicone-based antifoaming reagent, which is commonly used in bioreactor cell cultures. The transfection efficiency of lyophilized dTtaPS¹⁰⁺ -plasmid complexes has been significantly restored upon aqueous reconstitution when compared to that achieved while using commercial transfection reagent complexes under similar conditions. The results of all experiments underscore the potential of dTtaPS¹⁰⁺ for transient transfection of plasmids into adherent cells and fed-batch serum-free suspension CHO cells and rapid screening of reagents in a microbioreactor system.

An amphipathic trans-acting phosphorothioate RNA element delivers an uncharged phosphorodiamidate morpholino sequence in mdx mouse myotubes

An efficient method for the delivery of uncharged polyA-tailed phosphorodiamidate morpholino sequences (PMO) in mammalian cells consists of employing a synthetic 8-mer amphipathic trans-acting poly-2'-O-methyluridylic thiophosphate triester element (2'-OMeUtaPS) as a transfection reagent. Unlike the dTtaPS DNA-based element, this RNA element is potent at delivering polyA-tailed PMO sequences to HeLa pLuc 705 cells or to myotube muscle cells. However, much like dTtaPS, the 2'-OMeUtaPS-mediated internalization of PMO sequences occurs through an energy-dependent mechanism; macropinocytosis appears to be the predominant endocytic pathway used for cellular uptake. The transfected PMO sequences induce alternate splicing of either the pre-mRNA encoding luciferase in HeLa pLuc 705 cells or the excision of exon 23 from the pre-mRNA encoding dystrophin in myotube muscle cells of the mdx mouse model of muscular dystrophy with an efficiency comparable to that of commercial cationic lipid reagents but without detrimental cytotoxicity.

Advancing pharmaceutical quality: An overview of science and research in the U.S. FDA's Office of Pharmaceutical Quality

Failures surrounding pharmaceutical quality, particularly with respect to product manufacturing issues and facility remediation, account for the majority of drug shortages and product recalls in the United States. Major scientific advancements pressure established regulatory paradigms, especially in the areas of biosimilars, precision medicine, combination products, emerging manufacturing technologies, and the use of real-world data. Pharmaceutical manufacturing is increasingly globalized, prompting the need for more efficient surveillance systems for monitoring product quality. Furthermore, increasing scrutiny and accelerated approval pathways provide a driving force to be even more efficient with limited regulatory resources. To address these regulatory challenges, the Office of Pharmaceutical Quality (OPQ) in the Center for Drug Evaluation and Research (CDER) at the U.S. Food and Drug Administration (FDA) harbors a rigorous science and research program in core areas that support drug quality review, inspection, surveillance, standards, and policy development. Science and research is the foundation of risk-based quality assessment of new drugs, generic drugs, over-the-counter drugs, and biotechnology products including biosimilars. This is an overview of the science and research activities in OPQ that support the mission of ensuring that safe, effective, and high-quality drugs are available to the American public.

The influence of liposomal formulation on the incorporation and retention of PNA oligomers

Liposomal formulations composed of phospholipids with different unsaturation degrees, head groups and at different cholesterol content have been tested for the encapsulation of Peptide Nucleic Acid (PNA) oligomers. The best loading capability (177μg, ER%=87.2) was obtained for pure liposomes of phosphatidylglycerol (DOPG) with negatively charged head group. The insertion of a 10-20% of cholesterol in DOPG based liposomes provides a slight decrease (∼160μg) of the PNA loading. On the other hand, the cholesterol addition (20-30%) slows down the PNA's release (∼27%) in fetal bovine serum from the liposomal formulation. Based on the encapsulation and the release properties, PEGylated DOPG liposomes with a percentage of cholesterol of 10-20% are the optimal formulation for the loading of PNA-a210.

An Amphipathic trans-Acting Phosphorothioate DNA Element Delivers Uncharged PNA and PMO Nucleic Acid Sequences in Mammalian Cells

An innovative approach to the delivery of uncharged peptide nucleic acids (PNAs) and phosphorodiamidate morpholino (PMO) oligomers in mammalian cells is described and consists of extending the sequence of those oligomers with a short PNA-polyA or PMO-polyA tail. Recognition of the polyA-tailed PNA or PMO oligomers by an amphipathic trans-acting polythymidylic thiophosphate triester element (dTtaPS) results in efficient internalization of those oligomers in several cell lines. The authors' findings indicate that cellular uptake of the oligomers occurs through an energy-dependent mechanism and macropinocytosis appears to be the predominant endocytic pathway used for internalization. The functionality of the internalized oligomers is demonstrated by alternate splicing of the pre-mRNA encoding luciferase in HeLa pLuc 705 cells. Amphipathic phosphorothioate DNA elements may represent a unique class of cellular transporters for robust delivery of uncharged nucleic acid sequences in live mammalian cells. © 2016 by John Wiley & Sons, Inc.