Acriflavine and proflavine hemisulfate as potential antivirals by targeting M(pro)

The evolving SARS-CoV-2 epidemic buffets the world, and the concerted efforts are needed to explore effective drugs. M(pro) is an intriguing antiviral target for interfering with viral RNA replication and transcription. In order to get potential anti-SARS-CoV-2 agents, we established an enzymatic assay using a fluorogenic substrate to screen the inhibitors of M(pro). Fortunately, Acriflavine (ACF) and Proflavine Hemisulfate (PRF) with the same acridine scaffold were picked out for their good inhibitory activity against M(pro) with IC(50) of 5.60 ± 0.29 μM and 2.07 ± 0.01 μM, respectively. Further evaluation of MST assay and enzymatic kinetics experiment in vitro showed that they had a certain affinity to SARS-CoV-2 M(pro) and were both non-competitive inhibitors. In addition, they inhibited about 90 % HCoV-OC43 replication in BHK-21 cells at 1 μM. Both compounds showed nano-molar activities against SARS-CoV-2 virus, which were superior to GC376 for anti-HCoV-43, and equivalent to the standard molecule remdesivir. Our study demonstrated that ACF and PRF were inhibitors of M(pro), and ACF has been previously reported as a PL(pro) inhibitor. Taken together, ACF and PRF might be dual-targeted inhibitors to provide protection against infections of coronaviruses.