![Sample our Bioscience journals, sign in here to start your access, Latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5925/TOC-Subject-Sample-2021-Bioscience.jpg"})
Abstract
The global pandemic due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has led to ∼6.9 million deaths and affected ∼767 million people globally. The approved vaccines have contributed significantly in reducing disease severity and mortality. However, new infections post vaccination and the lack of specific antivirals have encouraged the research using multiple approaches to design novel therapeutics against COVID-19. Recent studies on the applications of RNAi against coronavirus provide substantial evidence on the prospects of this technique against SARS-CoV-2. Progress in the field of computational analysis and applications of multiple delivery methods also promises safe and effective implementation of RNAi against COVID-19. This review deals with the possible applications and challenges of RNAi against SARS-CoV-2.
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly infectious respiratory virus and the third coronavirus to have caused a pandemic in recent times.
Emergence of drug-resistant strains that can escape the vaccine-induced immune response continues to be an area of concern.
In this scenario, RNA interference (RNAi) holds great potential in designing sequence-specific, non-toxic prophylaxis.
RNAi: A novel sequence-specific therapeutic tool against viruses
Cell-culture and animal model based experiments have revealed the potency of siRNAs in reducing the viral titers.
RNAi has been studied against viruses like respiratory syncytial virus, HIV, Hepatitis C virus, SARS-CoV and MERS-CoV among several others.
RNAi-mediated inhibition of coronaviruses
Coronavirus replication can be inhibited by silencing the viral genes as well as by transient downregulation of host factors crucial for the viral life cycle.
In silico designing of siRNA sequences
For efficient inhibition of the target gene, careful designing of siRNAs and stringent in silico analysis is necessary.
ClustalW, siDirect v2.0 used for siRNA sequence prediction; MaxExpect, DuplexFold and DINAMelt used for interaction prediction between the designed sequence and the target region while HDOCK and BIOVIA Discovery Studio used for final 3D visualization of the probable interaction are important tools in siRNA designing.
In silico study allows the designing and screening of a large number of siRNAs thereby saving time and resources for further experiments.
RNAi-mediated inhibition of SARS-CoV-2 in cell-culture
siRNAs selected from computational analysis are further validated in cell-culture models.
Multiple siRNAs against SARS-CoV have been studied in cell culture.
High sequence similarity between SARS-CoV and SARS-CoV-2 enables identification of effective siRNAs from previous studies against the conserved regions.
In vivo inhibition of SARS-CoV-2
The siRNAs showing promising results in cell-culture are further examined in animal models.
BALB/C mice, Syrian hamster and Rhesus macaque models have been primarily used.
Besides validating the sequences, different delivery methods have also been evaluated.
Downregulation of SARS-CoV-2 spike and RNA dependent RNA polymerase genes showed highest viral inhibition in comparison to the other targets in the viral genome.
Delivery of siRNA
Stable and non-toxic delivery of siRNA to the host remains a major concern.
Several delivery methods have been tested for siRNAs delivery against pulmonary viruses.
Inhalational delivery appears to be the most suited method for treating respiratory infections.
Retrovirus and adeno-associated virus have also been utilized for stable transfection of siRNAs.
Non-viral carriers are examined for nebulizer-based delivery to the respiratory system.
Conditional delivery like tet on/off system awaits to be explored against viral diseases.
RNAi therapeutics & its challenges
Host nucleases often degrade the RNAi molecules before the target is reached leading to lowered efficiency.
Delivering siRNA to the respiratory system is challenging owing to the different physiological barriers.
The highly branched respiratory system along with the mucus layer pose barrier to the delivery of siRNA to the lungs.
Endosome mediated degradation of the siRNAs can be avoided by using viral vectors although immune response to such modes of delivery are an area of concern.
Chemically modified siRNAs show similar efficacy as the non-modified molecules, however, they have reduced off-target effects.
Alternative nucleic acid therapies against SARS-CoV-2
Short, single-stranded antisense oligonucleotides are also being studied as an alternate mode of therapeutics against SARS-CoV-2.
These oligonucleotides do not require a guide RNA and can be delivered in different chemically modified form for effective viral inhibition.
Peptide nucleic acids are highly stable, sequence specific modified nucleic acids that can be used as prophylactic.
However, due to the difficulties associated with solubility and delivery, peptide nucleic acids are often a weaker choice as compared with siRNAs.
Financial disclosure
The authors have no financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
Competing interests disclosure
The authors have no competing interests or relevant affiliations with any organization or entity with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
Writing disclosure
No writing assistance was utilized in the production of this manuscript.