Application of various nanoparticle-encapsulated siRNAs as therapeutics for SARS-CoV-2 infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) first emerged in Wuhan in 2019 and has since spread around the world. Initially, many governments were forced to adopt costly and restrictive measures to reduce disease transmission, including mandatory face masks, social distancing restrictions, and stay-at-home/stay-at-home orders. With mass vaccination programs enabling many developed countries to dismantle these restrictions, cases of the disease have increased, but deaths have fallen dramatically.

Study: Nanoparticle delivery platforms for RNAi therapeutics targeting COVID-19 disease in the airways. Image Credit: LuckyStep/Shutterstock

However, new treatments are still needed for people at risk of severe disease or those in developing countries with low vaccination rates. In a review published in the International Journal of Molecular Sciencesresearchers examined the use of siRNAs to target coronaviruses.

The article

The siRNAs begin as long double-stranded RNAs before Dicer-mediated cleavage cuts them into strands about 21 nucleotides long. These molecules can induce gene silencing in mammalian cells. This mainly occurs through post-transcriptional gene silencing (PTGS) or transcriptional gene silencing (TGS).

PTGS occurs in the cytoplasm, where the guide strand of siRNAs binds to the Argonaute-2 (Ago-2) protein of the RNA-inducing silencing complex (RISC), while the non-guide strand is cleaved and ejected by Ago-2, which then transports the guide strand to the target mRNA, causing the binding site to be degraded.

TGS is less well characterized, but it is known that siRNAs will bind to the Ago-1 protein on the RNA-induced transcriptional silencing complex (RITS), resulting in reduced methylation and acetylation of target genes to promote heterochromatin production and epigenetics. silence.

Certain siRNAs are known to be effective against different coronaviruses, including the three that cause the most severe disease in humans – severe acute respiratory syndrome coronavirus (SARS-CoV-1), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and Middle East Respiratory Syndrome Coronavirus (MERS-CoV).

The researchers identify several important factors to consider for the effectiveness of siRNAs in targeting these diseases, including the identification of highly conserved targets to prevent viral evasion. SARS-CoV-2, in particular, showed significant changes in the conformation and electrostatic charge of the spike protein, allowing evasion of both vaccine-induced and natural immunity. They also suggest targeting furin, the cellular protease responsible for cleavage of the S1 and S2 subunits of the spike (S) protein necessary for viral pathogenicity.

Many silicone experiments were performed that identified possible candidates, with in vitro followed up confirming the efficacy of four siRNAs capable of decreasing spike protein expression, four others that could decrease nucleocapsid gene expression, and three that can decrease membrane protein gene expression.

Nanoparticle-mediated delivery, or NP delivery, is often the method of choice to transport siRNAs into the body for targeted therapy. NPs form suspensions of vesicles after encapsulating siRNAs, allowing them to remain stable longer. The four currently approved siRNA drugs require a delivery system, using either the N-acetylgalactosamine or lipid NP pathway.

Lipid NPs (LNPs) have a phospholipid bilayer, with hydrophilic ends exposed both inside and outside the vesicle and hydrophobic ends facing towards the hydrophobic ends of other phospholipid molecules. They have proven effective with several drugs in the past, and studies have shown that LNP siRNAs can target tumors and deliver siRNAs to the lungs – which could be particularly effective for anti-SARS-CoV-2 drugs. Other NPs can be formed from polymers, glycogen and inorganic particles such as gold and magnetic molecules.

Delivery of siRNA NPs can be challenging. It is well known that therapeutic siRNAs can be delivered to the liver via the circulatory system. All currently approved siRNA drugs are delivered to the liver, but other organs may be more difficult to target. Long-term accumulation in non-target tissues should be avoided, as well as damage to other organs.

The lung is one of the most obvious targets, as there is already significant research on where particles of certain sizes passing through the mouth or nose will eventually settle. There are three potential methods by which NPs can be delivered into the airways – intratracheal, intranasal, and orotracheal. Inhalation devices to target them are already present and ubiquitous in the medical field. Some are even currently being used to treat SARS-CoV-2 through other methods, such as nebulizers. Inhalation is the most popular method, but more mechanical devices are sometimes needed if a patient has difficulty breathing.

The conclusion

Researchers highlight the need to optimize RNAi processing strategies and appropriate carrier platforms for SARS-CoV-2 infection. Although treatment with these strategies seems promising, it is still in the early stages of research. Other, more promising pharmaceuticals have already been tested and approved, and it seems more likely that they will continue to be the dominant choice of healthcare workers.

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