The initial studies were not proposed by people ignorant of molecular biology and biochemistry.
That said, studies so far have not demonstrated clinical effectiveness against Covid-19.
An AlphaScreen®-Based Assay for High-Throughput Screening for Specific Inhibitors of Nuclear Import
Kylie M. Wagstaff, Stephen M. Rawlinson, Anna C. Hearps, David A. JansFirst Published February 4, 2011
https://doi.org/10.1177/1087057110390360
Specific viral proteins enter the nucleus of infected cells to perform essential functions, as part of the viral life cycle. The integrase (IN) molecule of human immunodeficiency virus (HIV)–1 is of particular interest in this context due to its integral role in integrating the HIV genome into that of the infected host cell. Most IN-based antiviral compounds target the IN/DNA interaction, but since IN must first enter the nucleus before it can perform these critical functions, nuclear transport of IN is also an attractive target for therapeutic intervention. Here the authors describe a novel high-throughput screening assay for identifying inhibitors of nuclear import, particularly IN, based on amplified luminescent proximity homogeneous assay (AlphaScreen®) technology, which is high throughput, requires low amounts of material, and is efficient and cost-effective. The authors use the assay to screen for specific inhibitors of the interaction between IN and its nuclear transport receptor importin ?/?, successfully identifying several inhibitors of the IN/importin ?/? interaction. Importantly, they demonstrate that one of the identified compounds, mifepristone, is effective in preventing active nuclear transport of IN in transfected cells and hence may represent a useful anti-HIV therapeutic. The screen also identified broad-spectrum importin ?/? inhibitors such as ivermectin, which may represent useful tools for nuclear transport research in the future. The authors validate the activity and specificity of mifepristone and ivermectin in inhibiting nuclear protein import in living cells, underlining the utility of the screening approach.
Current Strategies of Antiviral Drug Discovery for COVID-19
Miao Mei1 and Xu Tan2*
REVIEW article - Front. Mol. Biosci., 13 May 2021 |
https://doi.org/10.3389/fmolb.2021.671263
SARS-CoV-2 belongs to the family of enveloped, single-strand RNA viruses known as Betacoronavirus in Coronaviridae, first reported late 2019 in China. It has since been circulating world-wide, causing the COVID-19 epidemic with high infectivity and fatality rates. As of the beginning of April 2021, pandemic SARS-CoV-2 has infected more than 130 million people and led to more than 2.84 million deaths. Given the severity of the epidemic, scientists from academia and industry are rushing to identify antiviral strategies to combat the disease. There are several strategies in antiviral drugs for coronaviruses including empirical testing of known antiviral drugs, large-scale phenotypic screening of compound libraries and target-based drug discovery. To date, an increasing number of drugs have been shown to have anti-coronavirus activities in vitro and in vivo, but only remdesivir and several neutralizing antibodies have been approved by the US FDA for treating COVID-19. However, remdesivir’s clinical effects are controversial and new antiviral drugs are still urgently needed. We will discuss the current status of the drug discovery efforts against COVID-19 and potential future directions. With the ever-increasing movability of human population and globalization of world economy, emerging and reemerging viral infectious diseases seriously threaten public health. Particularly the past and ongoing outbreaks of coronaviruses cause respiratory, enteric, hepatic and neurological diseases in infected animals and human (Woo et al., 2009). The human coronavirus (HCoV) strains (HCoV-229E, HCoV-OC43, HCoV-NL63, and HCoV-HKU1) usually cause common cold with mild, self-limiting upper respiratory tract infections. By contrast, the emergence of three deadly human betacoronaviruses, middle east respiratory syndrome coronavirus (MERS) (Zaki et al., 2012), severe acute respiratory syndrome coronavirus (SARS-CoV) (Lee et al., 2003), the SARS-CoV-2 (Jin et al., 2020a) highlight the need to identify new treatment strategies for viral infections. SARS-CoV-2 is the etiological agent of COVID-19 disease named by World Health Organization (WHO) (Zhu N. et al., 2020). This disease manifests as either an asymptomatic infection or a mild to severe pneumonia. This pandemic disease causes extent morbidity and mortality in the whole world, especially regions out of China. Similar to SARS and MERS, the SARS CoV-2 genome encodes four structural proteins, sixteen non-structural proteins (nsp) and accessory proteins. The structural proteins include spike (S), envelope (E), membrane (M), nucleoprotein (N). The spike glycoprotein directly recognizes and engages cellular receptors during viral entry. The four non-structural proteins including papain-like protease (PLpro), 3-chymotrypsin-like protease (3CLpro), helicase, and RNA-dependent RNA polymerase (RdRp) are key enzymes involved in viral transcription and replication. The spike and the four key enzymes were considered attractive targets to develop antiviral agents (Zumla et al., 2016). The catalytic sites of the four enzymes of SARS-CoV2 share high similarities with SARS CoV and MERS in genomic sequences (Morse et al., 2020). Besides, the structures of the key drug-binding pockets are highly conserved among the three coronaviruses (Morse et al., 2020). Therefore, it follows naturally that existing anti-SARS-CoV and anti-MERS drugs targeting these enzymes can be repurposed for SARS-CoV-2. Based on previous studies in SARS-CoV and MERS-CoV, it is anticipated a number of therapeutics can be used to control or prevent emerging infectious disease COVID-19 (Li and de Clercq, 2020; Wang et al., 2020c; Ita, 2021), these include small-molecule drugs, peptides, and monoclonal antibodies. Given the urgency of the SARS-CoV-2 outbreak, here we discuss the discovery and development of new therapeutics for SARS-CoV-2 infection based on the strategies from which the new drugs are derived.
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Ivermectin, an FDA-approved broad spectrum anti-parasitic agent (Gonzalez Canga et al., 2008),is a broad-spectrum antiviral agent with activities against flaviviruses, influenza virus and HIV-1 (Mastrangelo et al., 2012; Wagstaff et al., 2012; Lundberg et al., 2013; Tay et al., 2013; Gotz et al., 2016; Ketkar et al., 2019). It also demonstrated inhibitory effect on SARS CoV-2 infection in vitro (Caly et al., 2020). Ivermectin administration significantly reduced the mortality of COVID-19 patients (Rajter et al., 2021). Nitazoxanide, a commercial antiprotozoal agent with an antiviral potential against a broad range of viruses including human and animal coronaviruses, can also block SARS-CoV-2 replication at low micromolar concentration in vitro (Wang et al., 2020c). Although the mechanisms of actions of ivermectin and nitazoxanide are still unclear, their broad-spectrum activities suggest host-targeting mechanisms. Further in vivo and clinical evaluations of these drugs are warranted.
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