Transcription and replication of the influenza A virus (IAV) RNA genome occurs in the nucleus of infected cells. We showed that the RED-SMU1 splicing complex regulates the splicing of the viral NS1 mRNA into the NS2 mRNA encoding the essential NS2/NEP protein. In cells depleted for RED or SMU1, the production of infectious IAVs is reduced by 2-logs, therefore designating the RED-SMU1 complex as a promising drug target. In a large collaborative effort, we solved the crystal structure of a minimal REDmid-SMU1Nter complex. A short alpha-helix of RED (RED211-221) lies into a hydrophobic groove at the surface of SMU1Nter. We undertook two complementary approaches to target the SMU1Nter-RED221-221 interface. Firstly, we screened in silico a set of small compounds for binding to the groove at the surface of SMU1Nter. We thereby identified compounds that disrupt the RED-SMU1 complex and specifically inhibit IAV replication whilst preserving cell viability. These compounds are now undergoing chemical optimization. Secondly, we used phage display to select RED206-221 variant peptides from large random libraries; these show high affinity for SMU1Nter and are being tested for inhibition of IAV replication. Our investigations pave the way for the development of future host-directed anti-influenza drugs with broad activity against IAV strains and with a low likelihood of resistance mutants.
