Inhibition of Chikungunya virus by an adenosine analog targeting the SAM‐dependent nsP1 methyltransferase

Alphaviruses, including Chikungunya (CHIKV) and Venezuelan equine encephalitis virus (VEEV), are among the leading causes of recurrent epidemics all over the world. Alphaviral nonstructural protein 1 (nsP1) orchestrates the capping of nascent viral RNA via its S‐adenosyl methionine‐dependent N‐7‐methyltransferase (MTase) and guanylyltransferase activities. Here, we developed and validated a novel capillary electrophoresis (CE)‐based assay for measuring the MTase activity of purified VEEV and CHIKV nsP1. We employed the assay to assess the MTase inhibition efficiency of a few adenosine analogs and identified 5‐iodotubercidin (5‐IT) as an inhibitor of nsP1. The antiviral potency of 5‐IT was evaluated in vitro using a combination of cell‐based assays, which suggest that 5‐IT is efficacious against CHIKV in cell culture (EC 50 : 0.409 µ m ).