COVID-19: A need for new rather than repurposed antiviral drugs
Authors: Kovacs Dory , Davis Chris , Cannon Paul , McFarlane Melanie , Rainey Stephanie M , Pinto Rute , Stewart Meredith E , Szemiel Agnieszka M , Taggart Aislynn , Kohl Alain , Marra Fiona , Thomson Emma C , Scott Janet T 
Published: March 2021

AbstractBackgroundSARS-CoV-2 infection, the causative agent of COVID-19, has resulted in over 2,500,000 deaths to date1. Although vaccines are becoming available, treatment options remain limited. Repurposing of compounds could reduce the time, cost, and risks associated with the development of new drugs and has been the focus of many clinical studies.Here, we summarise available evidence on 29 FDA-approved compounds, from in vitro results to clinical trials, focussing on remdesivir, galidesivir and favipiravir, and test 29 antiviral compounds’ activityin vitro.MethodsA comprehensive search strategy was used to retrieve trials and publications related to antiviral compounds with potential efficacy to treat coronaviruses. These data were used to prioritise testing of a panel of antiviral drugs in vitro against patient isolates of SARS-CoV-2. An in vitro screen was carried out to determine the activity of 29 FDA-approved compounds.Results625 clinical trials investigated 16 repurposed antiviral candidate compounds for the treatment of COVID-19. In vitro studies identified ten drug candidates with demonstrable anti-SARS-CoV-2 activity, including favipiravir, remdesivir, and galidesivir. To validate these findings, a drug screen was conducted using two cell lines and wildtype isolates of SARS-CoV-2 isolated from patients in the UK. While eight drugs with anti-SARS-CoV-2 activity were identified in vitro, activity in clinical trials has, as yet failed to demonstrate a strong effect on mortality.ConclusionsSo far, no repurposed antiviral has shown a strong effect on mortality in clinical studies. The urgent need for novel antivirals in this pandemic is clear, despite the costs and time associated with their development.Research in ContextEvidence before this studyRepurposing of existing compounds for the treatment of COVID-19 has been the focus of manyin vitrostudies and clinical trials, saving time, costs and risks associated with the research and development of new compounds.Added value of this studyWe reviewed the literature for 29 FDA-approved compounds with previously reported (or suspected) anti-SARS-CoV-2 activity and found 625 clinical trials that have been undertaken on 16 different drugs. We determined if repurposed antivirals are suitable for clinical trials based on previously published data, and conducted an additionalin vitroscreen using locally circulating strains in the UK (PHE2 and GLA1). We report the difference in IC50from published data using Wuhan1/Wash1 strains with PHE2 and GLA1, including IC50values below 100μM for galidesivir in wild-type virus. Given the limited success of repurposed compounds in the treatment of COVID-19, we comment on the urgent need for new antivirals specifically targeting SARS-CoV-2.Implications of all the available evidenceOur data show that most prospective compounds for repurposing show no anti-SARS-CoV-2 activity, and antiviral activityin vitrodoes not always translate to clinical benefit. So far, no repurposed compound has shown a strong effect on mortality in clinical studies. Drugs, including monoclonal antibody therapies, that have been developed to target SARS-CoV-2 virus itself have shown most promise.