Ss (-) RNA; 19 kbDENV, ZIKV, YFV, WNVMukhopadhyay et al. (2005); Barrows et al. (2018) –FiloviridaeEBOV, MARVArenaviridaess (-) RNA; segmentedLASV, JUNVJae et al. (2014); Pontremoli et al. (2019)Nairoviridaess (-) RNA; segmentedCCHFVSimon et al. (2009); Zivcec et al. (2016)Orthomyxoviridaess (-) RNA; segmentedIAV (H1N1, H2N2, H5N1, H3N2, H7N9, … )Ramos and Fernandez-Sesma (2012)TABLE two | Compound library for drug repurposing. Library Library scale 1,520 three,500 12,000 Introduction RefsPrestwick chemical library NCATS pharmaceutical collection (or NCGC pharmaceutical Collection) ReFRAME compound library99 approved drugs (FDA, EMA and other agencies) 2,500 approved molecules, plus about 1,000 investigational compounds Containing nearly all small molecules that have reached clinical SIRT2 MedChemExpress development or undergone important preclinical profiling, 38 of which are authorized drugs Biologically annotated collection of inhibitors, receptor ligands, pharmadeveloped tools, and authorized drugs All have a history of use in human clinical trials and recognized security profilesUlferts et al. (2016) Huang et al. (2011) Janes et al. (2018); Riva et al. (2020) Hu et al. (2014) van Cleef et al. (2013)Library of pharmacologically active compounds (LOPAC), sigma NIH clinical collection1,280that the pathogens that need to be confronted may possibly display higher genetic variability (e.g., HIV) or an identity hardly predicted ahead of time (e.g., SARS-CoV-2 or ZIKV). Therefore, unprecedented demands have emerged on MGMT review antivirals which can be rapidly available in clinical practices. Within the absence of a vaccine available to utilize, hepatitis C virus (HCV) is supposed to be eliminated within the use on the direct-acting antivirals, which almost certainly represents the initial virus to be cured by antivirals. That strengthens the promising potential of antivirals when it comes to virus therapy. Drug repurposing (also referred to as drug repositioning) is a strategy for identifying new utilizes for authorized or investigational drugs that beyond the original indicative scope to facilitate antiviral development. Normally, antiviral discovery improvement is time and resource-consuming, which includes 3 significant stages including drug discovery (3 years), preclinical studies inexperimental animal models (about 3 years), clinical trials in humans from phase I to III (about 5 years). Finally, if a therapeutic succeeds to pass all the processes, it demands to get approved by the suitable agency. It’s estimated that only 5 of the candidate molecules are lastly approved and as much as three billion dollars are consumed. Offered that the repurposed drugs have been verified to be safe in humans, drug repurposing most likely can skip phase I and possibly the phase II clinical trials. Therefore, the attrition rate to be a novel antiviral is reduced, though the phase III trial continues to be necessary. Remdesivir, an adenosine analog to inhibit EBOV RNA-dependent RNA polymerase (RdRp) (Tchesnokov et al., 2019), would be the most up-to-date example. While remdesvir did not show therapeutic activity against EBOV infection inside a real-world phase III clinical trial (Nakkazi, 2018), remdesivir shows potent antiviral activity against SARS-CoV-2, SARS-CoV, and MERSCoV in vitro or in vivo in preclinical animal models (de Wit et al.,Frontiers in Pharmacology | www.frontiersin.orgMay 2021 | Volume 12 | ArticleLi and PengDrug Repurposing for Antiviral DiscoveryFIGURE 1 | Drug repurposing development procedure. DAA, direct-acting antivirals; HTA, host-targeting antivirals; FDA, Food and Dru.