COMMENTARY crossm Clinical Trials of Repurposed Antivirals for SARS-CoV-2 Miguel Angel Martineza a IrsiCaixa, Hospital Universitari Germans Trias i Pujol, Universitat Autònoma de Barcelona (UAB), Badalona, Spain ABSTRACT The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has prompted the repurpos- ing of drugs on the basis of promising in vitro and therapeutic results with other hu- man coronavirus diseases, such as severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS). These repurposed drugs have mainly in- cluded remdesivir, favipiravir, lopinavir-ritonavir, ribavirin, interferons, and hydroxy- chloroquine. Unfortunately, the first open-label, randomized, controlled trials are showing poor efficacy of these repurposed drugs. These results highlight the neces- sity of identifying and characterizing specific and potent SARS-CoV-2 antivirals. KEYWORDS COVID-19, SARS-CoV-2, antivirals T he worldwide spread of severe acute respiratory syndrome coronavirus 2 (SARS- CoV-2) has, as of 20 May 2020, caused at least 5 million infections and 328,000 deaths (1). The virus is highly transmissible, and in addition to its death toll, coronavirus disease 2019 (COVID-19) has a high percentage of morbidity. This has necessitated social confinement, causing great economic losses. Therefore, preventive and thera- peutic measures are urgently needed. To this end, from the beginning of the COVID-19 pandemic, several clinical trials have been initiated to test repurposed drugs that either were effective in inhibiting SARS-CoV-2 in vitro or displayed some therapeutic utility in treating other human coronavirus infections. Here, we discuss the results obtained with some of the repurposed drugs that seemed to hold the most promise of stopping COVID-19 (2). For those who become COVID-19 symptomatic, the incubation period, i.e., the time from exposure to symptom onset, is 4 to 5 days on average (3). Current data indicate that 5 to 20% of patients with COVID-19 develop critical illness approximately 5 to 10 days after symptom onset, resulting in complications such as acute respiratory distress syndrome and other end-organ failure (4, 5). Although the antiviral host immune response is essential to eliminating invading viruses, a strong and persistent antiviral immune response might also include the massive production of inflammatory cytokines and related host tissue damage. In symptomatic COVID-19 patients, cytokine storms are a major cause of disease progression and eventual death (6). Consequently, Citation Martinez MA. 2020. Clinical trials of repurposed antivirals for SARS-CoV-2. it has been suggested that therapeutics that modulate inflammation are the most Antimicrob Agents Chemother 64:e01101-20. effective therapeutic strategy for treating COVID-19 (6). However, the administration of https://doi.org/10.1128/AAC.01101-20. a potent and specific antiviral against SARS-CoV-2 after the onset of the first disease Copyright © 2020 American Society for Microbiology. All Rights Reserved. symptoms and prior to viral peak could actually stop or avoid the pathogenic course of Address correspondence to COVID-19. mmartinez@irsicaixa.es. As exemplified by the life cycles of other pathogenic viruses, that of SARS-CoV-2 has The views expressed in this article do not a number of targetable stages. These include the endocytic entry of the virion into host necessarily reflect the views of the journal or cells, RNA replication and transcription, translation and proteolytic processing of viral of ASM. Accepted manuscript posted online 6 July proteins, virion assembly, and release of new viruses through the exocytic systems (7). 2020 Diverse host targets essential for viral replication also can be interfered with, but few Published 20 August 2020 successful marketed drugs against viral diseases target host cell-virus cofactors. Dis- September 2020 Volume 64 Issue 9 e01101-20 Antimicrobial Agents and Chemotherapy aac.asm.org 1 Commentary Antimicrobial Agents and Chemotherapy rupting host cell targets is thought to be more toxic than disrupting virus-specific processes. Chloroquine (CQ) and its hydroxyl analogue, hydroxychloroquine (HCQ), are generic antimalarial drugs also employed to treat amoebic liver abscess and rheumatic disease. The early promising results of these two drugs, displaying antiviral activity against SARS-CoV-2 at micromolar concentrations in tissue culture (8) and in some ongoing clinical trials (9), drove their repurposing as possible therapies for COVID-19. It has been hypothesized that CQ and HCQ block virus cell entry by decreasing autophagosome- lysosome fusion and inhibiting autophagic flux (10). An early open-label, nonrandom- ized clinical trial on 20 SARS-CoV-2-infected patients revealed that HCQ treatment was significantly associated with viral load reduction/disappearance in COVID-19 patients (9). This study also concluded that azithromycin (AZ), a widely used broad-spectrum antibiotic that also blocks autophagosome clearance in human cells, reinforced the antiviral effect of HCQ. This study promoted public interest in and widespread utiliza- tion of HCQ for treatment and prophylaxis of COVID-19. Moreover, several health authorities have recommended HCQ off-label use in the treatment of COVID-19 (11). Unfortunately, more recent studies have not identified a benefit of HCQ in COVID-19 and have even raised concerns about its safety. A retrospective analysis of data from 368 patients hospitalized with confirmed SARS-CoV-2 infection in U.S. Veterans Health Administration medical centers up to April 2020 found no evidence that the use of HCQ, either with or without AZ, reduced the risk of mechanical ventilation in patients hospitalized with COVID-19. Importantly, an association of increased overall mortality was identified in patients treated with HCQ alone (12). Another observational study of HCQ, in patients hospitalized with COVID-19 in New York City, also found that HCQ administration was not associated with either a greatly lowered or increased risk of the composite endpoint of intubation or death (13). Another French observational study of 181 patients admitted to the hospital with COVID-19 found that survival at 21 days with or without acute respiratory distress syndrome did not differ between the groups treated with HCQ versus standard care, and 8 of 84 patients receiving HCQ had the drug stopped because of electrocardiogram changes (14). A multicenter, open-label, ran- domized, controlled trial with mainly mild to moderate COVID-19 in 16 government- designated COVID-19 treatment centers in China also indicated that HCQ administra- tion did not result in a significantly higher probability of negative conversion than standard of care alone in patients admitted to hospitals (15). In the safety population of this trial, adverse events were recorded in 7/80 (9%) non-HCQ-treated patients and in 21/70 (30%) HCQ recipients. The most common adverse event reported in this study in the HCQ-treated group was diarrhea, reported in 7/70 (10%) patients; 2 HCQ recipients experienced serious adverse events. The toxicity displayed by HCQ also may preclude the use of this drug as a prophylactic against SARS-CoV-2. Lastly, a random- ized, double-blind, placebo-controlled trial of HCQ as postexposure prophylaxis for COVID-19 showed that after a high-risk or moderate-risk exposure, HCQ did not prevent illness or confirmed infection (16). This trial, which included 821 asymptomatic partic- ipants that received HCQ within 4 days after SARS-CoV-2 exposure, did not demonstrate a significant benefit of HCQ as postexposure prophylaxis for COVID-19. Available, successfully marketed drugs targeting such diverse viruses as human immunodeficiency virus (HIV), hepatitis C virus (HCV), hepatitis B virus, influenza virus herpes simplex virus, varicella zoster virus, and human cytomegalovirus demonstrate the utility of nucleoside/nucleotide analogues in inhibiting viral RNA/DNA polymerases and stopping virus replication and spread (17). From the beginning of the SARS-CoV-2 pandemic, the most promising antiviral for fighting COVID-19 has been remdesivir. Remdesivir is an adenosine nucleotide analogue prodrug, developed by Gilead Sci- ences, with broad-spectrum antiviral activity against filoviruses, paramyxoviruses, pneu- moviruses, and pathogenic coronaviruses, including SARS-CoV and Middle East respi- ratory syndrome (MERS)-CoV (18). Initially developed to treat filoviruses, remdesivir has been shown to be safe in clinical trials against Ebola virus (19). Although nucleotide analogues may show low efficacy against coronaviruses due to the presence of the viral September 2020 Volume 64 Issue 9 e01101-20 aac.asm.org 2 Commentary Antimicrobial Agents and Chemotherapy exonuclease proofreading enzyme, remdesivir was found to be effective against SARS- CoV, MERS-CoV, and bat CoV strains, with tissue culture effective concentrations (EC50s) in the low micromolar range (18). The specificity of remdesivir in targeting coronavirus RNA-dependent RNA polymerase (RdRp) was further demonstrated by propagating the virus in tissue culture. After 23 passages in the presence of the drug, two mutations (F276L and V553L) were identified in the SARS-CoV viral RdRp gene that conferred viral resistance to remdesivir (20). In addition to cell culture experiments, remdesivir signif- icantly reduced lung viral loads in mouse models of SARS-CoV (18) and MERS-CoV (21). The prophylactic and therapeutic efficacy of remdesivir treatment was also tested in a nonhuman primate (rhesus macaque) model of MERS-CoV infection (22). In light of these previous results with other human coronaviruses, remdesivir was repurposed as a possibly effective COVID-19 treatment. One of the first studies testing the efficacy of remdesivir on COVID-19 described the compassionate use of this drug in 61 patients with severe disease (23). In this cohort of hospitalized patients, clinical improvement in oxygen support status was observed in 36 of 53 patients (68%), and overall mortality was 13% over a median follow-up of 18 days. This study was criticized for its lack of a control patient group, which made it difficult to estimate the efficacy of remdesivir in this group of advanced-disease patients. A more controlled trial with remdesivir was recently published (24). In this randomized, double-blind, placebo-controlled, multicenter trial performed in China, 237 hospitalized adult patients were enrolled and randomly assigned to two 10-day treatment groups (158 to remdesivir and 79 to placebo). Although the difference was not statistically significant, patients receiving remdesivir had a faster time to clinical improvement than those receiving placebo among patients with symptom duration of 10 days or less (18 versus 23 days). Mortality at 28 days was similar between the two groups (14% versus 13%). It is important to mention that adverse events were reported in 102 (66%) of 155 remdesivir recipients versus 50 (64%) of 78 placebo recipients, and that remdesivir was stopped early because of adverse events in 18 (12%) patients versus 4 (5%) patients who stopped placebo early. The authors of this study concluded that remdesivir was not associated with statistically significant clinical benefits; how- ever, they also suggested that the reduction in time to clinical improvement in patients treated earlier begged confirmation in larger studies. A larger randomized, controlled clinical trial sponsored by the U.S. National Institute of Allergy and Infectious Diseases (NIAID) and others noted that remdesivir was better than placebo from the perspective of the primary endpoint, i.e., time to recovery, a metric often used in influenza trials (25). This study was carried out with 1,063 hospitalized patients with advanced COVID-19 and lung involvement in the United States and 21 European countries and Asia. Those who received a 10-day course of remdesivir had a median recovery time of 11 days, compared with 15 days in those who received placebo (P ⬍ 0.001). Although these results also suggested a survival benefit, with a 14-day mortality rate of 7.1% for the group receiving remdesivir versus 11.9% for the placebo group, this difference was not significant. The comprehensive data that we have so far suggest that remdesivir is a useful drug but not the one that is going to cure and stop the spread of COVID-19. Indeed, the authors of the former study recommended the combination of different antiviral agents to continue to improve COVID-19 patient outcomes. They also sug- gested that antiviral treatment should start before the pulmonary disease progresses to the point of requiring mechanical ventilation. However, the intravenous administration of remdesivir makes this drug difficult to prescribe following the first mild or moderate symptoms observed after the first few days of SARS-CoV-2 infection. Favipiravir triphosphate is a purine nucleoside analogue that functions as a com- petitive inhibitor of RdRp (26). Favipiravir has been found to have in vitro antiviral activity against influenza A and B viruses as well as many other RNA viruses, including SARS-CoV-2 (26). Nevertheless, the tissue culture EC50 for SARS-CoV-2 is within the high micromolar range (27). This poor in vitro inhibitory capacity of favipiravir against SARS-CoV-2 has not prevented it being tested as an experimental treatment for COVID-19. An open-label, nonrandomized trial of 80 patients with COVID-19 in China September 2020 Volume 64 Issue 9 e01101-20 aac.asm.org 3 Commentary Antimicrobial Agents and Chemotherapy identified a significant reduction in the time to SARS-CoV-2 viral clearance in patients treated with favipiravir compared with historical controls treated with lopinavir- ritonavir (28). In this trial, a significant reduction in the median time to viral clearance with favipiravir compared with that for lopinavir-ritonavir (P ⬍ 0.001) was observed. There was also a significantly lower rate of adverse events in patients receiving favipiravir (11.4% versus 55.6%; P ⬍ 0.01). Again, no control patient group was included. Moreover, patients were cotreated with interferon-␣1b (IFN-␣1b) until viral clearance, which makes it difficult to estimate the antiviral activity of favipiravir. Further trials will be necessary to evaluate the efficacy of favipiravir against COVID-19. Previous work with SARS-CoV found that lopinavir combined with ritonavir had antiviral activity in tissue culture and in infected patients (29). Lopinavir is an HIV-1 protease inhibitor used, in combination with ritonavir (another HIV-1 protease inhibitor) to increase its half-life, in HIV clinics. The combination of lopinavir and ritonavir also reduced weight loss, clinical scores, viral titers, and disease progression in marmosets infected with MERS-CoV (30). Targeting viral proteases has been essential in developing successful therapies for HIV and HCV. Most RNA viruses generate viral polyproteins that have to be processed to complete the corresponding viral cycle. To evaluate the efficacy and safety of oral lopinavir-ritonavir treatment for SARS-CoV-2 infection, a randomized, controlled, open-label clinical trial was performed in China in adult patients hospitalized with COVID-19 (31). Patients (199) were randomly assigned in a 1:1 ratio to receive either lopinavir-ritonavir for 14 days (99), in addition to standard care, or standard care alone (100). Regrettably, treatment with lopinavir-ritonavir was not associated with a difference in outcome compared with standard care. Mortality at 28 days was similar in the lopinavir-ritonavir group and the standard-care group (19.2% versus 25.0%). Similarly, the percentages of patients with detectable viral RNA at various time points were similar. Although no serious adverse events were associated with lopinavir-ritonavir treatment, gastrointestinal adverse events were more common in the treated group of patients. Overall, this study showed an absence of benefit of lopinavir-ritonavir treatment in COVID-19 patients. Other HIV-1 protease inhibitors, such as darunavir, are also being tested in SARS-CoV-2-infected patients, with no positive results reported so far (32). A triple combination containing lopinavir-ritonavir and IFN-␤1b plus ribavirin has been explored in an open-label, randomized phase 2 trial in patients admitted to the hospital with COVID-19 (33). Here, 127 patients were recruited; 86 were randomly assigned to the combination group, and 41 were assigned to the control group (lopinavir-ritonavir alone). The combination group had a significantly shorter median time from start of study treatment to negative nasopharyngeal swab (7 versus 12 days; P ⫽ 0.0010). No differences in adverse events were reported. Assuming that lopinavir- ritonavir has poor antiviral activity, IFN-ribavirin might be responsible for the efficacy of the abovementioned triple combination. Different IFNs have been employed to combat diverse viral infections. Some success has been achieved, mainly in the treatment of HCV and in combination with ribavirin. Work in tissue culture has demonstrated that treatment with IFN-␣ or IFN-␤ at a concentration of 50 international units (IU) per milliliter reduces SARS-CoV-2 titers by 3.4 logs or over 4 logs, respectively, in Vero cells, with EC50s of IFN-␣ and IFN-␤ treatment of 1.35 IU/ml and 0.76 IU/ml, respectively (34). The success of IFN as an antiviral has been obtained mainly by administering it for long periods of time in chronic viral infections (e.g., HCV). The effectivity of IFNs in short, nonchronic virus infections remains to be elucidated. In addition, it is necessary to know whether IFNs administered to SARS-CoV-2-infected patients are acting as coad- juvants in generating the cytokine storm observed in some COVID-19 patients. Notably, the ACE2 gene encoding the SARS-CoV-2 cell receptor is stimulated by IFN, suggesting that SARS-CoV-2 could exploit species-specific IFN-driven upregulation of ACE2, a tissue-protective mediator during lung injury, to enhance infection (35). The proportion and magnitude of the COVID-19 pandemic have made necessary the repurposing of several drugs to quickly stop the morbidity, mortality, and spread of this new disease. While many clinical trials have been completed and many more are still September 2020 Volume 64 Issue 9 e01101-20 aac.asm.org 4 Commentary Antimicrobial Agents and Chemotherapy running, no repurposed drug has been found that could significantly impact the course of this pandemic. Remdesivir has shown the most promising results and might now be an important tool with which to try to reduce the mortality of COVID-19, but more specific and potent antivirals against SARS-CoV-2 will be necessary to curb present and/or future coronavirus pandemics. Apart from an effective vaccine, the way to stop SARS-CoV-2 in the first days of the infection, when virus transmission is greatest, is through a competent antiviral. The magnitude of the present viral pandemic requires the use of different strategies in concert, including an effective vaccine and antivirals. The crystal structures of the three likely most relevant SARS-CoV-2 targetable proteins, spike, RdRp, and main protease, have been resolved (36–38). It is not difficult to guess that first-generation SARS-CoV-2-specific antivirals have already been identified. Efforts should be made to move first-generation specific and potent antivirals to the clinic. ACKNOWLEDGMENTS This work was supported by the Spanish Ministry of Science and Innovation (PID2019-103955RB-100). The author has no conflict of interest to declare. REFERENCES 1. John Hopkins University Center for Systems Science and Engineering. sheet. U.S. Food and Drug Administration, Washington, DC. https://www 2020. COVID-19 dashboard. https://gisanddata.maps.arcgis.com/apps/ .fda.gov/media/136534/download. opsdashboard/index.html#/bda7594740fd40299423467b48e9ecf6. Ac- 12. Magagnoli J, Narendran S, Pereira F, Cummings T, Hardin JW, Sutton SS, cessed 20 May 2020. Ambati J. 2020. Outcomes of hydroxychloroquine usage in United States 2. Martinez MA. 2020. Compounds with therapeutic potential against veterans hospitalized with Covid-19. medRxiv 2020.04.16.20065920. novel respiratory 2019 coronavirus. Antimicrob Agents Chemother https://doi.org/10.1016/j.medj.2020.06.001. 64:e00399-20. https://doi.org/10.1128/AAC.00399-20. 13. Geleris J, Sun Y, Platt J, Zucker J, Baldwin M, Hripcsak G, Labella A, 3. Li Q, Guan X, Wu P, Wang X, Zhou L, Tong Y, Ren R, Leung KSM, Lau Manson DK, Kubin C, Barr RG, Sobieszczyk ME, Schluger NW. 2020. EHY, Wong JY, Xing X, Xiang N, Wu Y, Li C, Chen Q, Li D, Liu T, Zhao Observational study of hydroxychloroquine in hospitalized patients J, Liu M, Tu W, Chen C, Jin L, Yang R, Wang Q, Zhou S, Wang R, Liu with Covid-19. N Engl J Med 382:2411–2418. https://doi.org/10.1056/ H, Luo Y, Liu Y, Shao G, Li H, Tao Z, Yang Y, Deng Z, Liu B, Ma Z, Zhang NEJMoa2012410. Y, Shi G, Lam TTY, Wu JT, Gao GF, Cowling BJ, Yang B, Leung GM, 14. Mahévas M, Tran V-T, Roumier M, Chabrol A, Paule R, Guillaud C, Fois E, Feng Z. 2020. Early transmission dynamics in Wuhan, China, of novel Lepeule R, Szwebel T-A, Lescure F-X, Schlemmer F, Matignon M, Khellaf coronavirus–infected pneumonia. N Engl J Med 382:1199 –1207. M, Crickx E, Terrier B, Morbieu C, Legendre P, Dang J, Schoindre Y, https://doi.org/10.1056/NEJMoa2001316. Pawlotsky J-M, Michel M, Perrodeau E, Carlier N, Roche N, de Lastours V, 4. Cummings MJ, Baldwin MR, Abrams D, Jacobson SD, Meyer BJ, Balough Ourghanlian C, Kerneis S, Ménager P, Mouthon L, Audureau E, Ravaud P, EM, Aaron JG, Claassen J, Rabbani LE, Hastie J, Hochman BR, Salazar- Godeau B, Gallien S, Costedoat-Chalumeau N. 2020. Clinical efficacy of Schicchi J, Yip NH, Brodie D, O’Donnell MR. 2020. Epidemiology, clinical hydroxychloroquine in patients with covid-19 pneumonia who require course, and outcomes of critically ill adults with COVID-19 in New York oxygen: observational comparative study using routine care data. BMJ City: a prospective cohort study. Lancet 395:31189 –31182. https://doi 369:m1844. https://doi.org/10.1136/bmj.m1844. .org/10.1016/S0140-6736(20)31189-2. 15. Tang W, Cao Z, Han M, Wang Z, Chen J, Sun W, Wu Y, Xiao W, Liu S, Chen 5. Zhou F, Yu T, Du R, Fan G, Liu Y, Liu Z, Xiang J, Wang Y, Song B, Gu X, E, Chen W, Wang X, Yang J, Lin J, Zhao Q, Yan Y, Xie Z, Li D, Yang Y, Liu Guan L, Wei Y, Li H, Wu X, Xu J, Tu S, Zhang Y, Chen H, Cao B. 2020. L, Qu J, Ning G, Shi G, Xie Q. 2020. Hydroxychloroquine in patients with Clinical course and risk factors for mortality of adult inpatients with mainly mild to moderate coronavirus disease 2019: open label, ran- COVID-19 in Wuhan, China: a retrospective cohort study. Lancet 395: domised controlled trial. BMJ 369:m1849. https://doi.org/10.1136/bmj 1054 –1062. https://doi.org/10.1016/S0140-6736(20)30566-3. .m1849. 6. Manjili RH, Zarei M, Habibi M, Manjili MH. 2020. COVID-19 as an acute 16. Boulware DR, Pullen MF, Bangdiwala AS, Pastick KA, Lofgren SM, inflammatory disease. J Immunol 205:12–19. https://doi.org/10.4049/ jimmunol.2000413. Okafor EC, Skipper CP, Nascene AA, Nicol MR, Abassi M, Engen NW, 7. Li G, De Clercq E. 2020. Therapeutic options for the 2019 novel corona- Cheng MP, LaBar D, Lother SA, MacKenzie LJ, Drobot G, Marten N, virus (2019-nCoV). Nat Rev Drug Discov 19:149 –150. https://doi.org/10 Zarychanski R, Kelly LE, Schwartz IS, McDonald EG, Rajasingham R, .1038/d41573-020-00016-0. Lee TC, Hullsiek KH. 3 June 2020. A randomized trial of hydroxychlo- 8. Liu J, Cao R, Xu M, Wang X, Zhang H, Hu H, Li Y, Hu Z, Zhong W, Wang roquine as postexposure prophylaxis for Covid-19. N Engl J Med M. 2020. Hydroxychloroquine, a less toxic derivative of chloroquine, is https://doi.org/10.1056/NEJMoa2016638. effective in inhibiting SARS-CoV-2 infection in vitro. Cell Discov 6:16. 17. De Clercq E, Li G. 2016. Approved antiviral drugs over the past 50 years. https://doi.org/10.1038/s41421-020-0156-0. Clin Microbiol Rev 29:695–747. https://doi.org/10.1128/CMR.00102-15. 9. Gautret P, Lagier J-C, Parola P, Hoang VT, Meddeb L, Mailhe M, Doudier 18. Sheahan TP, Sims AC, Graham RL, Menachery VD, Gralinski LE, Case JB, B, Courjon J, Giordanengo V, Vieira VE, Dupont HT, Honoré S, Colson P, Leist SR, Pyrc K, Feng JY, Trantcheva I, Bannister R, Park Y, Babusis D, Chabrière E, La Scola B, Rolain J-M, Brouqui P, Raoult D. 2020. Hydroxy- Clarke MO, MacKman RL, Spahn JE, Palmiotti CA, Siegel D, Ray AS, Cihlar chloroquine and azithromycin as a treatment of COVID-19: results of an T, Jordan R, Denison MR, Baric RS. 2017. Broad-spectrum antiviral GS- open-label non-randomized clinical trial. Int J Antimicrob Agents 5734 inhibits both epidemic and zoonotic coronaviruses. Sci Transl Med :105949. https://doi.org/10.1016/j.ijantimicag.2020.105949. 9:eaal3653. https://doi.org/10.1126/scitranslmed.aal3653. 10. Mauthe M, Orhon I, Rocchi C, Zhou X, Luhr M, Hijlkema KJ, Coppes RP, 19. Mulangu S, Dodd LE, Davey RT, Tshiani Mbaya O, Proschan M, Mukadi D, Engedal N, Mari M, Reggiori F. 2018. Chloroquine inhibits autophagic Lusakibanza Manzo M, Nzolo D, Tshomba Oloma A, Ibanda A, Ali R, flux by decreasing autophagosome-lysosome fusion. Autophagy 14: Coulibaly S, Levine AC, Grais R, Diaz J, Lane HC, Muyembe-Tamfum J-J, 1435–1455. https://doi.org/10.1080/15548627.2018.1474314. Sivahera B, Camara M, Kojan R, Walker R, Dighero-Kemp B, Cao H, 11. US Food and Drug Administration. 28 March 2020. Emergency use Mukumbayi P, Mbala-Kingebeni P, Ahuka S, Albert S, Bonnett T, Crozier authorization, hydroxychloroquine sulfate health care provider fact I, Duvenhage M, Proffitt C, Teitelbaum M, Moench T, Aboulhab J, Barrett September 2020 Volume 64 Issue 9 e01101-20 aac.asm.org 5 Commentary Antimicrobial Agents and Chemotherapy K, Cahill K, Cone K, Eckes R, Hensley L, Herpin B, Higgs E, Ledgerwood J, with lopinavir/ritonavir or interferon-␤1b improves outcome of MERS- Pierson J, Smolskis M, Sow Y, Tierney J, Sivapalasingam S, Holman W, CoV infection in a nonhuman primate model of common marmoset. J Gettinger N, Vallée D, Nordwall J, the PALM Writing Group. 2019. A Infect Dis 212:1904 –1913. https://doi.org/10.1093/infdis/jiv392. randomized, controlled trial of Ebola virus disease therapeutics. N Engl 31. Cao B, Wang Y, Wen D, Liu W, Wang J, Fan G, Ruan L, Song B, Cai Y, Wei J Med 381:2293–2303. https://doi.org/10.1056/NEJMoa1910993. M, Li X, Xia J, Chen N, Xiang J, Yu T, Bai T, Xie X, Zhang L, Li C, Yuan Y, 20. Agostini ML, Andres EL, Sims AC, Graham RL, Sheahan TP, Lu X, Smith EC, Chen H, Li H, Huang H, Tu S, Gong F, Liu Y, Wei Y, Dong C, Zhou F, Gu Case JB, Feng JY, Jordan R, Ray AS, Cihlar T, Siegel D, Mackman RL, Clarke X, Xu J, Liu Z, Zhang Y, Li H, Shang L, Wang K, Li K, Zhou X, Dong X, Qu MO, Baric RS, Denison MR. 2018. Coronavirus susceptibility to the anti- Z, Lu S, Hu X, Ruan S, Luo S, Wu J, Peng L, Cheng F, Pan L, Zou J, Jia C, viral remdesivir (GS-5734) is mediated by the viral polymerase and the Wang J, Liu X, Wang S, Wu X, Ge Q, He J, Zhan H, Qiu F, Guo L, Huang proofreading exoribonuclease. mBio 9:e00221-18. https://doi.org/10 C, Jaki T, Hayden FG, Horby PW, Zhang D, Wang C. 2020. A Trial of .1128/mBio.00221-18. lopinavir–ritonavir in adults hospitalized with severe Covid-19. N Engl J 21. Sheahan TP, Sims AC, Leist SR, Schäfer A, Won J, Brown AJ, Montgomery Med 382:1787–1799. https://doi.org/10.1056/NEJMoa2001282. SA, Hogg A, Babusis D, Clarke MO, Spahn JE, Bauer L, Sellers S, Porter D, 32. Riva A, Conti F, Bernacchia D, Pezzati L, Sollima S, Merli S, Siano M, Lupo Feng JY, Cihlar T, Jordan R, Denison MR, Baric RS. 2020. Comparative A, Rusconi S, Cattaneo D, Gervasoni C. 2020. Darunavir does not prevent therapeutic efficacy of remdesivir and combination lopinavir, ritonavir, SARS-CoV-2 infection in HIV patients. Pharmacol Res 157:104826. https:// and interferon beta against MERS-CoV. Nat Commun 11:1–14. https:// doi.org/10.1016/j.phrs.2020.104826. doi.org/10.1038/s41467-019-13940-6. 33. Fan-Ngai Hung I, Lung K-C, Yuk-Keung Tso E, Liu R, Wai-Hin Chung T, 22. de Wit E, Feldmann F, Cronin J, Jordan R, Okumura A, Thomas T, Scott D, Chu M-Y, Ng Y-Y, Lo J, Chan J, Raymond Tam A, Shum H-P, Chan V, Cihlar T, Feldmann H. 2020. Prophylactic and therapeutic remdesivir Ka-Lun Wu A, Sin K-M, Leung W-S, Law W-L, Christopher Lung D, Sin S, (GS-5734) treatment in the rhesus macaque model of MERS-CoV infec- Yeung P, Chik-Yan Yip C, Ruiqi Zhang R, Yim-Fong Fung A, Yuen-Wing tion. Proc Natl Acad Sci U S A 117:6771– 6776. https://doi.org/10.1073/ Yan E, Leung K-H, Daniel Ip J, Wing-Ho Chu A, Chan W-M, Chin-Ki Ng A, pnas.1922083117. Lee R, Fung K, Yeung A, Wu T-C, Wai-Man Chan J, Yan W-W, Chan W-M, 23. Grein J, Ohmagari N, Shin D, Diaz G, Asperges E, Castagna A, Feldt T, Fuk-Woo Chan J, Kwok-Wai Lie A, Tak-Yin Tsang O, Chi-Chung Cheng V, Green G, Green ML, Lescure F-X, Nicastri E, Oda R, Yo K, Quiros-Roldan E, Que T-L, Lau C-S, Chan K-H, Kai-Wang To K, Yuen K-Y. 2020. Articles Studemeister A, Redinski J, Ahmed S, Bernett J, Chelliah D, Chen D, Triple combination of interferon beta-1b, lopinavir-ritonavir, and ribavi- Chihara S, Cohen SH, Cunningham J, D’Arminio Monforte A, Ismail S, rin in the treatment of patients admitted to hospital with COVID-19: an Kato H, Lapadula G, L’Her E, Maeno T, Majumder S, Massari M, Mora-Rillo open-label, randomised, phase 2 trial. Lancet 395:1695–1704. https://doi M, Mutoh Y, Nguyen D, Verweij E, Zoufaly A, Osinusi AO, DeZure A, Zhao .org/10.1016/S0140-6736(20)31042-4. Y, Zhong L, Chokkalingam A, Elboudwarej E, Telep L, Timbs L, Henne I, 34. Mantlo E, Bukreyeva N, Maruyama J, Paessler S, Huang C. 2020. Antiviral Sellers S, Cao H, Tan SK, Winterbourne L, Desai P, Mera R, Gaggar A, activities of type I interferons to SARS-CoV-2 infection. Antiviral Res Myers RP, Brainard DM, Childs R, Flanigan T. 2020. Compassionate use of 179:104811. https://doi.org/10.1016/j.antiviral.2020.104811. remdesivir for patients with severe Covid-19. N Engl J Med 382: 35. Ziegler CGK, Allon SJ, Nyquist SK, Mbano IM, Miao VN, Tzouanas CN, Cao 2327–2336. https://doi.org/10.1056/NEJMoa2007016. Y, Yousif AS, Bals J, Hauser BM, Feldman J, Muus C, Wadsworth MH, Kazer 24. Wang Y, Zhang D, Du G, Du R, Zhao J, Jin Y, Fu S, Gao L, Cheng Z, Lu Q, SW, Hughes TK, Doran B, Gatter GJ, Vukovic M, Taliaferro F, Mead BE, Hu Y, Luo G, Wang K, Lu Y, Li H, Wang S, Ruan S, Yang C, Mei C, Wang Guo Z, Wang JP, Gras D, Plaisant M, Ansari M, Angelidis I, Adler H, Sucre Y, Ding D, Wu F, Tang X, Ye X, Ye Y, Liu B, Yang J, Yin W, Wang A, Fan JMS, Taylor CJ, Lin B, Waghray A, Mitsialis V, Dwyer DF, Buchheit KM, G, Zhou F, Liu Z, Gu X, Xu J, Shang L, Zhang Y, Cao L, Guo T, Wan Y, Qin Boyce JA, Barrett NA, Laidlaw TM, Carroll SL, Colonna L, Tkachev V, H, Jiang Y, Jaki T, Hayden FG, Horby PW, Cao B, Wang C. 2020. Remde- Peterson CW, Yu A, Zheng HB, Gideon HP, Winchell CG, Lin PL, Bingle CD, sivir in adults with severe COVID-19: a randomised, double-blind, Snapper SB, Kropski JA, Theis FJ, Schiller HB, Zaragosi L-E, Barbry P, Leslie placebo-controlled, multicentre trial. Lancet 395:1569 –1578. https://doi .org/10.1016/S0140-6736(20)31022-9. A, Kiem H-P, Flynn JL, Fortune SM, Berger B, Finberg RW, Kean LS, Garber 25. Beigel JH, Tomashek KM, Dodd LE, Mehta AK, Zingman BS, Kalil AC, M, Schmidt AG, Lingwood D, Shalek AK, Ordovas-Montanes J, Banovich Hohmann E, Chu HY, Luetkemeyer A, Kline S, Lopez de Castilla D, N, Barbry P, Brazma A, Desai T, Duong TE, Eickelberg O, Falk C, Farzan M, Finberg RW, Dierberg K, Tapson V, Hsieh L, Patterson TF, Paredes R, Glass I, Haniffa M, Horvath P, Hung D, Kaminski N, Krasnow M, Kropski JA, Sweeney DA, Short WR, Touloumi G, Lye DC, Ohmagari N, Oh M, Kuhnemund M, Lafyatis R, Lee H, Leroy S, Linnarson S, Lundeberg J, Ruiz-Palacios GM, Benfield T, Fätkenheuer G, Kortepeter MG, Atmar RL, Meyer K, Misharin A, Nawijn M, Nikolic MZ, Ordovas-Montanes J, Pe’er D, Creech CB, Lundgren J, Babiker AG, Pett S, Neaton JD, Burgess TH, Powell J, Quake S, Rajagopal J, Tata PR, Rawlins EL, Regev A, Reyfman PA, Bonnett T, Green M, Makowski M, Osinusi A, Nayak S, Lane HC. 22 May Rojas M, Rosen O, Saeb-Parsy K, Samakovlis C, Schiller H, Schultze JL, 2020. Remdesivir for the treatment of Covid-19 —preliminary report. N Seibold MA, Shalek AK, Shepherd D, Spence J, Spira A, Sun X, Teichmann Engl J Med https://doi.org/10.1056/NEJMoa2007764. S, Theis F, Tsankov A, van den Berge M, von Papen M, Whitsett J, Xavier 26. Furuta Y, Gowen BB, Takahashi K, Shiraki K, Smee DF, Barnard DL. 2013. R, Xu Y, Zaragosi L-E, Zhang K. 2020. SARS-CoV-2 receptor ACE2 is an Favipiravir (T-705), a novel viral RNA polymerase inhibitor. Antiviral Res interferon-stimulated gene in human airway epithelial cells and is de- 100:446 – 454. https://doi.org/10.1016/j.antiviral.2013.09.015. tected in specific cell subsets across tissues. Cell 181:1016 –1035. https:// 27. Wang M, Cao R, Zhang L, Yang X, Liu J, Xu M, Shi Z, Hu Z, Zhong W, Xiao doi.org/10.1016/j.cell.2020.04.035. G. 2020. Remdesivir and chloroquine effectively inhibit the recently 36. Zhang L, Lin D, Sun X, Curth U, Drosten C, Sauerhering L, Becker S, Rox emerged novel coronavirus (2019-nCoV) in vitro. Cell Res 30:269 –271. K, Hilgenfeld R. 2020. Crystal structure of SARS-CoV-2 main protease https://doi.org/10.1038/s41422-020-0282-0. provides a basis for design of improved ␣-ketoamide inhibitors. Science 28. Cai Q, Yang M, Liu D, Chen J, Shu D, Xia J, Liao X, Gu Y, Cai Q, Yang Y, 368:409 – 412. https://doi.org/10.1126/science.abb3405. Shen C, Li X, Peng L, Huang D, Zhang J, Zhang S, Wang F, Liu J, Chen L, 37. Lan J, Ge J, Yu J, Shan S, Zhou H, Fan S, Zhang Q, Shi X, Wang Q, Zhang Chen S, Wang Z, Zhang Z, Cao R, Zhong W, Liu Y, Liu L. 18 March 2020. L, Wang X. 2020. Structure of the SARS-CoV-2 spike receptor-binding Experimental treatment with favipiravir for COVID-19: an open-label domain bound to the ACE2 receptor. Nature 581:215–220. https://doi control study. Engineering https://doi.org/10.1016/j.eng.2020.03.007. .org/10.1038/s41586-020-2180-5. 29. Chu CM, Cheng VCC, Hung IFN, Wong MML, Chan KH, Chan KS, Kao RYT, 38. Gao Y, Yan L, Huang Y, Liu F, Zhao Y, Cao L, Wang T, Sun Q, Ming Z, Poon LLM, Wong CLP, Guan Y, Peiris JSM, Yuen KY. 2004. Role of lopinavir/ Zhang L, Ge J, Zheng L, Zhang Y, Wang H, Zhu Y, Zhu C, Hu T, Hua T, ritonavir in the treatment of SARS: Initial virological and clinical findings. Zhang B, Yang X, Li J, Yang H, Liu Z, Xu W, Guddat LW, Wang Q, Lou Z, Thorax 59:252–256. https://doi.org/10.1136/thorax.2003.012658. Rao Z. 2020. Structure of the RNA-dependent RNA polymerase from 30. Fuk-Woo Chan J, Yao Y, Yeung M-L, Deng W, Bao L, Jia L, Li F, Xiao C, Gao COVID-19 virus. Science 368:eabb7498. https://doi.org/10.1126/science H, Yu P, Cai J-P, Chu H, Zhou J, Chen H, Qin C, Yuen K-Y. 2015. Treatment .abb7498. September 2020 Volume 64 Issue 9 e01101-20 aac.asm.org 6