Novel Peptide Conjugates of Modified Oligonucleotides for Inhibition of Bacterial RNase P

Evolution of antisense oligonucleotides: navigating nucleic acid chemistry and delivery challenges

INTRODUCTION

Antisense oligonucleotide (ASO) was established as a viable therapeutic option for genetic disorders. ASOs can target RNAs implicated in various diseases, including upregulated mRNA and pre-mRNA undergoing abnormal alternative splicing events. Therapeutic applications of ASOs have been proven with the Food and Drug Administration approval of several drugs in recent years. Earlier enzymatic stability and delivery remains a big challenge for ASOs. Introducing new chemical modifications and new formulations resolving the issues related to the nuclease stability and delivery of the ASOs. Excitingly, ASOs-based bioconjugates that target the hepatocyte have gained much attraction. Efforts are ongoing to increase the therapeutic application of the ASOs to the extrahepatic tissue as well.

AREA COVERED

We have briefly discussed the mechanism of ASOs, the development of new chemistries, and delivery strategies for ASO-based drug discovery and development. The discussion focuses more on the already approved ASOs and those in the clinical development stage.

EXPERT OPINION

To expand the clinical application of ASOs, continuous effort is required to develop precise delivery strategies for targeting extrahepatic tissue to minimize the off-target effects.

Targeting Ribonucleases with Small Molecules and Bifunctional Molecules

Ribonucleases (RNases) cleave and process RNAs, thereby regulating the biogenesis, metabolism, and degradation of coding and noncoding RNAs. Thus, small molecules targeting RNases have the potential to perturb RNA biology, and RNases have been studied as therapeutic targets of antibiotics, antivirals, and agents for autoimmune diseases and cancers. Additionally, the recent advances in chemically induced proximity approaches have led to the discovery of bifunctional molecules that target RNases to achieve RNA degradation or inhibit RNA processing. Here, we summarize the efforts that have been made to discover small-molecule inhibitors and activators targeting bacterial, viral, and human RNases. We also highlight the emerging examples of RNase-targeting bifunctional molecules and discuss the trends in developing such molecules for both biological and therapeutic applications.

Lipid and Peptide-Oligonucleotide Conjugates for Therapeutic Purposes: From Simple Hybrids to Complex Multifunctional Assemblies

Antisense and small interfering RNA (siRNA) oligonucleotides have been recognized as powerful therapeutic compounds for targeting mRNAs and inducing their degradation. However, a major obstacle is that unmodified oligonucleotides are not readily taken up into tissues and are susceptible to degradation by nucleases. For these reasons, the design and preparation of modified DNA/RNA derivatives with better stability and an ability to be produced at large scale with enhanced uptake properties is of vital importance to improve current limitations. In the present study, we review the conjugation of oligonucleotides with lipids and peptides in order to produce oligonucleotide conjugates for therapeutics aiming to develop novel compounds with favorable pharmacokinetics.

Structure and hybridization properties of phosphoryl guanidine oligonucleotides under crowding conditions

Phosphoryl guanidine oligonucleotides (PGOs) are promising uncharged analogs of nucleic acids and are used in a variety of applications. The importance of hydration is frequently ignored during the design of modified nucleic acid probes. Such hydrophobic modifications (phosphoryl guanidine) are expected to have a significant impact on the structure and thermal stability of the affected oligo with complementary nucleic acids. Here we aimed to investigate (by the osmotic stress method) hydration changes upon the formation of a duplex of a PGO with complementary DNA. According to our results, the presence of phosphoryl guanidines in one or both strands of a duplex only minimally affects hydration alterations under crowding conditions. The secondary structure of native and modified duplexes did not change significantly in the presence of ethanol, ethylene glycol, polyethylene glycol 200, or polyethylene glycol 1000. After the addition of a cosolvent, the thermodynamic stability of the PGO complexes changed in the same manner as that seen in a corresponding DNA duplex. The findings reported here and our previous studies form the basis for efficient use of PGOs in basic research and a variety of applications.

Optimizing Efficient RNAi-Mediated Control of Hemipteran Pests (Psyllids, Leafhoppers, Whitefly): Modified Pyrimidines in dsRNA Triggers

The advantages from exogenously applied RNAi biopesticides have yet to be realized in through commercialization due to inconsistent activity of the dsRNA trigger, and the activity level of RNAi suppression. This has prompted research on improving delivery methods for applying exogenous dsRNA into plants and insects for the management of pests and pathogens. Another aspect to improve RNAi activity is the incorporation of modified 2′-F pyrimidine nucleotides into the dsRNA trigger. Modified dsRNA incorporating 32–55% of the 2′-F- nucleotides produced improved RNAi activity that increased insect mortality by 12–35% greater than non-modified dsRNA triggers of the same sequence. These results were repeatable across multiple Hemiptera: the Asian citrus psyllid (Diaphorina citri, Liviidae); whitefly (Bemisia tabaci, Aleyroididae); and the glassy-winged sharpshooter (Homalodisca vitripennis, Cicadellidae). Studies using siRNA with modified 2′-F- pyrimidines in mammalian cells show they improved resistance to degradation from nucleases, plus result in greater RNAi activity, due to increase concentrations and improved binding affinity to the mRNA target. Successful RNAi biopesticides of the future will be able to increase RNAi repeatability in the field, by incorporating modifications of the dsRNA, such as 2′-F- pyrimidines, that will improve delivery after applied to fruit trees or crop plants, with increased activity after ingestion by insects. Costs of RNA modification have decreased significantly over the past few years such that biopesticides can now compete on pricing with commercial chemical products.