DDX3 inhibitors show antiviral activity against positive-sense single-stranded RNA viruses but not against negative-sense single-stranded RNA viruses: The coxsackie B model

Picornaviridae are positive-sense single stranded RNA viruses with a similar genomic structure lacking a cap at the 5' end, but with a highly structured 5'-untranslated region (UTR) containing an internal ribosome entry site (IRES). IRES allows ribosomes to be recruited by the viral RNA and initiate translation in a cap-independent manner. Coxsackie virus type B (CV-B) belong to Picornaviridae and are widespread in human population. They usually cause subclinical infections but, occasionally, also severe diseases with various clinical manifestations. CV-B have no specific therapy. DEAD-box polypeptide 3 (DDX3) is a member of the Asp-Glu-Ala-Asp (DEAD)-box family with an ATP-dependent RNA unwinding helicase activity. Recently, several positive-sense single strand RNA viruses have been shown to need DDX3 for their translation. Here, we show that several DDX3 inhibitors reduced CV-B replication and production of viral protein, particularly when added within 12 h of infection. Based on in vitro and in silico data, we hypothesized that DDX3 inhibitors hamper interaction between DDX3 and viral IRES in a stereodynamic fashion. Accordingly, the DDX3 inhibitors tested have no activity against the Vesicular Stomatitis virus and Measles virus, which are negative-sense single stranded RNA viruses and use cap-dependent translation. This study suggests that DDX3 is required by RNA viruses lacking a cap and show that this enzyme is a valuable target to design antiviral molecules against CV-B. Thus, DDX3 is dispensable for cap-dependent translation, but required for translation of transcripts containing secondary structure in their UTRs.