Lung-targeted delivery of nsp12 siRNAs restores host type I interferon responses

The RNA-dependent RNA polymerase (RdRp) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), known as nsp12, is crucial to viral replication and spread. Being one of the most conserved proteins of SARS-CoV-2, nsp12 is also a promising therapeutic target for COVID-19. In addition, nsp12 has been reported to suppress the host type I interferon (IFN-I) responses. We used HEK293T cells exogenously expressing nsp12-luciferase to identify siRNAs against nsp12. A series of in vitro and in vivo experiments were employed to examine the effect of RBD-11b-modified cationic liposomes (CLs) on targeted delivery of siRNAs to the mouse lungs. Mice were airway-administered adenovirus to induce the exogenous expression of nsp12 in the mouse lungs, followed by nsp12 siRNAs@RBD-11b-CLs treatment. Nsp12 expression and the activity of the IRF3/IFN-I axis in the lungs were then examined. High-efficiency nsp12 siRNAs were identified and successfully delivered to the mouse lungs by the RBD-11b-modified CLs. The nsp12 siRNAs@RBD-11b-CLs efficiently inhibited the exogenous expression of nsp12 in the mouse lungs. Moreover, nsp12 siRNAs@ RBD-11b-CLs successfully restored the nucleus transport of IRF3, thereby increasing the expression of IFNβ and several IFN effector genes in alveolar cells. We establish a lung targeting system to efficiently deliver siRNAs against SARS-CoV-2 nsp12 and significantly restore host type I interferon responses. This study will provide fresh perspectives and forthcoming approaches for the treatment of COVID-19 and other RNA viruses.