From Dyrk1A inhibitors to a novel class of antiviral agents: Targeting Enterovirus EV-A71 with 2-aryl-substituted thiophene scaffolds

Enterovirus A71 (EV-A71) is a major causative agent of hand, foot, and mouth disease (HFMD) especially in children. The majority of EV-A71 cases are mild, however, severe cases have exhibited an array of neurological complications which often lead to death. In a screening campaign to discover hits against EV-A71, we identified six 2,4-diaryl-substituted thiophene compounds that were previously reported as Dyrk1A inhibitors. From these, compound S43 (EC₅₀ = 4.4 μM; CC₅₀ = 12.8 μM and SI = 2.9) was selected for an optimization campaign. Our SAR study revealed that the terminal pyridine could be removed without loss of the antiviral activity, which led to the new lead compound 23, maintaining anti-EV-A71 activity (EC₅₀ = 4.3 μM; CC₅₀ = 75.7 μM and SI = 17.6) while the cytotoxicity was 6-fold lower. Importantly, this modification also eliminated Dyrk1A inhibitory activity, avoiding further potential side effects related to inhibition of this kinase. Further results using harmine, a structurally distinct Dyrk1A inhibitor, ruled out Dyrk1A as a target in the observed antiviral effect against EV-A71. Mechanistically, our compounds act on the post-entry stage of the viral infection. When tested against a panel of related viruses, the compounds exhibited a broad spectrum against the enterovirus genus but could not inhibit the influenza virus. Additionally, S43 showed potent inhibition against herpes simplex virus (HSV). Altogether, we discovered 2-aryl thiophenes as a new class of antiviral compounds, which might be developed further into therapeutics against enterovirus infections.