New platform screens for specific class of coronavirus antiviral compounds

A team at John Hopkin’s University, US, have developed a platform that can rapidly screen thousands of compounds to identify potential antiviral candidates against coronaviruses, including SARS-CoV-2. The researchers used their new high-throughput platform to screen a novel class of compounds that inhibit the macrodomain, a protein fold that plays a critical role in the coronavirus life cycle.

Prior studies suggest that some coronaviruses as well as alphaviruses largely lose their ability to replicate in cells and cause diseases in animals when their macrodomain’s enzymatic activity is disrupted. In this study, researchers targeted the macrodomain of SARS-CoV-2 called Mac1.

The new platform, detailed in ACS Chemical Biology, is thought to be the first high-throughput system that can screen for compounds that block macrodomain activity. In the study, the researchers developed a simple assay called ADPr-Glo that registers, with luminescence, the degree of enzymatic activity of a macrodomain. In the presence of compounds that inhibit the macrodomain, luminescence will be reduced. For this demonstration, they used the assay to rapidly screen two small libraries of existing drug compounds — a total of 3,233 compounds — for their ability to inhibit Mac1.

The researchers also measured those Mac1-inhibiting compounds’ ability to inhibit human MacroD2, an ADP-ribosylhydrolase enzyme that is the closest human counterpart to Mac1. MacroD2 mutation or deletion is implicated in cancer formation and neurological disorders. Since compounds that affect MacroD2 could cause unwanted side effects in patients, the aim was to demonstrate that this new method could identify compounds that inhibit Mac1 without affecting MacroD2.

The experiments uncovered one existing drug, dasatinib, that does inhibit Mac1 with moderate potency, yet does not measurably inhibit the human MacroD2. Dasatinib is a leukaemia drug that was developed to target another class of enzymes and thus hits other targets in humans beyond Mac1. It is known to be toxic to cells at the concentrations that inhibited Mac1 and would need modification to become an antiviral against coronavirus infections.

According to the team, identifying this drug demonstrates that viral Mac1’s unique structure can be targeted by small-molecule drugs without affecting their closest human counterpart. “A viral-specific macrodomain inhibitor drug could be very useful in the treatment of COVID-19, MERS, and in a possible future pandemic caused by a novel coronavirus,” commented senior author and associate professor Anthony Leung. “While developing new drugs takes time, our versatile screening platform gives us hope that we can one day find one.”