Circular Photocaged mRNA for Light-induced Late-stage Activation of Translation.

mRNA is a new medical modality as vaccine and raises hopes to become a protein replacement agent. Despite notable advances in manufacturing, stabilization and modification, its short half-life remains a major limitation. Circular RNA bears potential to solve this issue, as degradation of mRNA proceeds primarily from the 5' and 3' ends. However, circular RNAs normally lack a 5' cap and are less efficiently translated. We present a strategy to circularize mRNA covalently via click chemistry by modifying the 5' cap and the 3' poly(A) tail with bioorthogonal functional groups. The resulting Cyclic Click Cap-containing mRNA (CyCliCap-mRNA) is translationally muted by a photocleavable protecting group. Upon irradiation by light, the photocleavable protecting group is removed and the respective linear Cap0-mRNA released. We show that CyCliCap-mRNA can be activated for efficient translation at late timepoints (24-48 h post transfection) in HeLa cells, which is not possible with the respective linear mRNA. The light-mediated opening releases linear mRNA with a native Cap0 and thus overcomes the problem of inefficient translation of circular RNAs.