RNA interference as a technology allows knocking down genes after transcription. RNA interference can potentially allow selective knocking down or silencing of targeted SARS-CoV-2 (COVID-19) genes. Packaging RNA interference drugs for COVID-19 using synthetic RNA as nasal sprays may offer an effective way to treat COVID-19 patients. Also, carrier molecules are known to increase half-lives, chemical stability, and prevent degradation of RNA by nucleases useful for the delivery of RNA into cells. However, for efficient gene-silencing, it is essential to select the correct double-stranded RNA molecules.
Small interfering RNA (siRNA), also known as short interfering RNA or silencing RNA, is known to regulate gene expression. This type of regulation is also known as RNA interference (RNAi).
Andrew Z. Fire and Craig C. Mello received the Nobel Prize for Physiology or Medicine in 2006 for their discovery of RNA interference – gene silencing by double-stranded RNA. Fire and Mello found that double-stranded RNA can silence genes. The two scientists showed that RNAi is specific for the gene whose code matches the injected RNA molecule.
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Figure 1: RNAi, the process in which small RNA molecules activate the cellular response to destroy specific RNA molecules such as mRNAs (Source: Wiki Commons).
siRNAs are a class of double-stranded non-coding RNA molecules, usually 20 to 25 base pairs in length. siRNA based therapeutics have already been developed and implemented as anticancer and antiviral drugs, including drugs for the treatment of genetic diseases.
The outbreak of the novel coronavirus Severe Acute Respiratory Syndrome 2 (SARS-CoV-2 – COVID-19) pandemic in December 2019, started testing many drugs for the treatment of the disease. Candidates for testing are the antiviral drugs remdesivir, favipiravir, lopinavir, ritonavir, and arbidol. Also, candidates for clinal trials are the antimalarial drug hydroxychloroquine, and anticancer agents interferon-alpha 2b. However, the efficacy of these drugs against SARS-CoV-2 has yet to be proven.
In that light, siRNA based treatments may also provide a therapeutic solution. A few studies have already demonstrated that selected siRNA candidates have the potential to be effective against the outbreak of SARS and Middle-East Respiratory Syndrome (MERS). Several siRNA-related patents already were issued: CN1548054, WO2005019410, CN101173275, CN101113158, CN1010085986, and US865352.
Earlier studies showed that siRNAs targeting sequences coding for several viral genes of various SARS viruses decreased the viral load between 50 to 95 %. siRNAs targeting the N protein gene appeared to work the best. Zhang et al., in 2004, demonstrated that the expression of SARS-CoV spike protein is silenced in cultured cells using RNA interference. For expression the spike protein in cultured cells, the research group used an expression vector with a cytomegalovirus (CMV) promoter. Tagging the spike protein with hemagglutinin allowed the monitoring of its expression. Also, Vero e6 cells allowed the propagation of the SARS-CoV strain investigated. A vector containing a U6 promotor enabled the construction of a 22 base pair hairpin siRNAs using the sequence UUCAAGAGA for the hairpin loop.
Figure 2: Diagram of predicted structure of siRNAs used by Zhang et al. in 2004.
Reference
RNA delivery; https://www.biosyn.com/tew/Nanocarriers-for-RNA-delivery.aspx
Zhang Y, et al. Silencing SARS-CoV spike protein expression in cultured cells by RNA interference. FEBS Lett. 2004;560:141–146. doi: 10.1016/S0014-5793(04)00087-0. [PMC] [PubMed]
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