While keeping an eye on the numerous ongoing projects aimed at finding a vaccine against SARS-CoV2, the identification of effective drugs to treat patients is a urgent need. However, the discovery of new drugs is a long process and drug repurposing (drug discovery strategy in which drugs approved to treat certain diseases are tested in order to be re-proposed for the treatment of a different disease) may represent a faster and more feasible approach to face this pandemic. To this aim, several drugs have been tested in the last months for the treatment of covid-19 patients, such as anti-HIV drugs (lopinavir/ritonavir), anti-hepatitis C virus drugs (danoprevir), antiviral drugs commonly used to treat the flu (favbiripavir). Moreover, remdevisir has been recently approved by the FDA (Food and Drug Administration) for the treatment of covid-19, based on clinical trial data showing efficacy in significantly reducing (by 47%) the time of recovery. However, further studies are ongoing aiming at identifying additional drugs, both to achieve a greater clinical efficacy (the goal is to reach a higher efficiency by using a “cocktail of drugs”, a strategy employed for the treatment of HIV and hepatitis C) and to be prepared in case of potential emergence of virus resistance against the drug so far identified.
Main finding. A recent study reports a large-scale screen of 12.000 known, FDA-approved drugs, either currently in clinical trial (for different diseases) or extensively characterized at pre-clinical level, in the search of effective drugs against SARS-CoV2.
Experimental details. The non-human primate kidney epithelial cells (Vero E6 cells), which have been shown to be permissive to SARS-CoV2 infection, were treated with the whole 12.000-compound collection (at 5 uM concentration) and then infected with SARS-CoV2. The analysis of viral-induced effects exerted in cells –measured 72h post infection– led to the identification of about 300 compounds active against SARS-CoV2. Next, the 300 compounds were further validated: cells were firstly treated with the compounds, at lower concentrations (1.5 and 1 uM), then infected with SARS-CoV2. Viral infection was assessed by checking viral protein expression. The validation assay enabled to identify 100 compounds that reduced viral replication by 40%. Among these, the authors were able to determine a dose-response relationship (namely greater anti-viral activity was observed at increasing doses of the compounds) of 21 compounds, demonstrating that the compounds’ antiviral effects observed in the infected cells were indeed due to the drug treatment and providing information about the optimal dosages inducing anti-viral effect, informative for therapeutic purposes. Four of these compounds, including the anti-malaria Hanfangchin (which has been also shown to antagonize entry of Ebola virus), had a synergistic effect with remdevisir,
In order to confirm these results, the 21 compounds were also tested by using two human cell lines (Hek293T and Huh-7 cells). First, ACE2 receptor –required for SARS-CoV2 virus entry– was expressed in cells; then, cells were treated with the compounds and infected with SARS-CoV2. Almost all compounds showed antiviral activity also in human cells, even stronger than that observed in non-human primate cells. Importantly, among these, 13 compounds had an anti-viral effect at concentrations low enough to be likely effective at doses compatible with in vivo administration.
Further investigation of five of the most potent compounds among those identified demonstrated that they inhibited virus entry into mammalian cells. The final five promising compounds identified are known to i) suppress herpes simplex virus replication (Z LVG CHN); ii) impair SARS-COV1 and Ebola virus infection (MDL 28170); iii) inhibit cellular proteins (cathepsins) required for processing of viral proteins during infection (ONO 5334 and VBY-825). Importantly, phase II clinical trials of ONO 5334 –for the treatment of osteoporosis– showed that the drug was well tolerated by patients; iv) lower the levels of interleukin-12 and interleukin-23 (inflammatory molecules produced by the immune system) and used as anti-cancer agent in B-cell non-Hodgkin lymphoma (apilimod).
To further strengthen the results, ONO 5334, MDL 28170, and apilimod were evaluated in primary cells, namely pneumocyte-like cells derived from human pluripotent stem cells (cells that have the potential to be differentiated in any cell type). Cells were treated with the three compounds and infected with SARS-CoV2. Viral replication resulted to be significantly reduced with all the three compounds, specifically, by 72% upon ONO 5334 treatment, by 65% upon MDL 28170 treatment, and by 85% upon apilimod treatment.
Finally, to better mirror the in vivo system and corroborate the results obtained, apilimod antiviral activity was assessed in an ex vivo system: lung tissue from donors was cultured, infected with SARS-CoV2 and treated with apilimod. Quantification of viral RNA showed a potent anti-viral activity of apilimod in a site (the lung) that represents the primary site of SARS-CoV2 replication. Importantly, Apilimod is well tolerated in humans and has been evaluated in a clinical setting for the treatment of Crohn’s disease, rheumatoid arthritis, follicular lymphoma. Interestingly, apilimod also efficiently inhibits Ebola Virus, Lassa virus and Marburg virus in human cell lines.
Conclusions. All that said, how far we are from the clinical application of these findings? How far we are from having an efficient anti-SARS-CoV2 drug cocktail? Even though in vivo efficacy test of these compounds is needed, results collected appear solid and promising and, importantly, data about pharmacology and safety in humans of these compounds are already available, supporting a rapid pre-clinical and clinical evaluation of these compounds.
Reference: Discovery of SARS-CoV-2 antiviral drugs through large-scale compound repurposing. Laura Riva, Shuofeng Yuan, […] Sumit K. Chanda. Nature 2020.