Drug repurposing for emerging viral infections

Abstract

Rapid urbanization and globalization have facilitated the rapid dissemination of novel infectious diseases. Zika virus (ZIKV) re-emerged in 2014/2015 to cause >5 million cases of infection in the Americas with some complicated by congenital microcephaly and other severe neurological complications. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first identified in China in December 2019 and quickly emerged to cause a pandemic with more than 70 million confirmed cases including over 1.7 million deaths globally as of 27 December 2020. As evidenced by these two emerging viruses, the de novo development of antiviral treatments would inevitably lag behind the rapid expansion of the epidemic. In this thesis, I aimed to find rapidly available treatment options for these emerging viral infections by repurposing clinically approved drugs with known pharmacological properties and side effects. In Chapter 2, a total of 11 FDA-approved drugs with broad-spectrum antiviral activities and/or anti-flaviviral activities were evaluated for their anti-ZIKV activity in vitro by a cell-based antiviral screening platform using a forward chemical genetics approach. Bromocriptine mesylate, a dopamine receptor agonist used for treating galactorrhea and Parkinson’s disease, and types I and II interferons potently inhibited ZIKV replication and ZIKV-induced cytopathic effects (CPE). Time-of-drug-addition assay showed that bromocriptine inhibited post-entry events of the ZIKV replication cycle. Molecular docking analysis predicted that bromocriptine bound to catalytic sites of the ZIKV NS2B-NS3 protease. Enzymatic inhibition assay validated the ZIKV protease inhibitory activity of bromocriptine. In Chapter 3, in silico structure-based screening was utilized to rapidly identify ZIKV NS2B-NS3 protease inhibitors among a large drug library consisting >8,000 drug compounds. Among the 100 primary hit compounds predicted to have high binding affinity, 8 clinically available drugs which could be used in pregnancy were selected for further evaluation. Five of these drugs showed inhibitory effects on ZIKV NS2B-NS3 protease and 2 of them displayed significant in vitro anti-ZIKV activity. Novobiocin, an anti-staphylococcal antibiotic, demonstrated potent in vivo anti-ZIKV activity in an established mouse model for ZIKV infection. Moreover, novobiocin also inhibited the NS2B-NS3 protease activity and replication of other medically important flaviviruses. In silico analysis showed that the ZIKV NS2B-NS3 protease had high structural homology with those of dengue virus, Japanese encephalitis virus, West Nile virus, and yellow fever virus. In Chapter 4, to rapidly identify clinically approved drugs with antiviral activity against SARS-CoV-2 infection, a two-tier drug screening platform was designed to screen an FDA-approved drug library containing 1,528 drugs. This two-tier drug screening platform included an enzyme-linked immunosorbent assay and a luciferase-based assay to identify the drugs’ activities on viral replication and cytopathic effects, respectively. Among the 17 drugs identified in primary screening, abiraterone acetate, bexarotene, cetillistat, and diiodohydroxyquinoline were validated to possess anti-SARS-CoV-2 activity in vitro. Mechanistic evaluation showed that bexarotene inhibited entry and/or fusion events, while the other three drugs interfered with the post-entry events of the SARS-CoV-2 replication cycle. Overall, the findings in this thesis provided new insights on the rapid identification of antiviral treatment options for emerging viral infections through repurposing clinically approved drugs.