  Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the strain of
coronavirus that causes coronavirus disease 2019 (COVID-19), the respiratory
illness responsible for the COVID-19 pandemic. Currently there is no known
vaccine or specific antiviral treatment for COVID-19 and so, there is an urgent
need for expedite discovery of new therapeutics to combat the disease until a
vaccine will be available worldwide. Drug repurposing is a strategy for
identifying new uses for approved drugs that has the advantage (over
conventional approaches that attempt to develop a drug from scratch) that time
frame of the overall process can be significantly reduced because of the few
number of clinical trial required. In this work, a virtual screening of
FDA-approved drugs was performed for repositioning as potential inhibitors of
the main protease Mpro of SARS-CoV-2. As a result of this study, 12 drugs are
proposed as candidates for inhibitors of the Mpro enzyme. Some of the selected
compounds are antiviral drugs that are already being tested in COVID-19
clinical trials (i.e. ribavirin) or are used to alleviate symptoms of the
disease (i.e. codeine). Surprisingly, the most promising candidate is the
naturally occurring broad spectrum antibiotic oxytetracycline. This compound
has largely outperformed the remaining selected candidates along all filtering
steps of our virtual screening protocol. If the activity of any of these drugs
is experimentally corroborated, they could be used directly in clinical trials
without the need for pre-clinical testing or safety evaluation since they are
already used as drugs for other diseases.
