Antiviral siRNA delivered using attenuated, anthrax toxin protects cells from the cytopathic effects of Zika virus

Curative drugs are needed for the treatment of viral infections. Small interfering (si)RNA offer such a prospect but require the development of safe, effective and non-hepatotropic subcellular delivery systems. Here, 5 candidate siRNA molecules targeting defined sequences within the Zika Virus (ZIKV) genome were assayed for their ability to reduce ZIKV induced cytopathic effects in vitro. The protection of Huh-7 cells from ZIKV cytopathic effects was recorded after electroporation and the siRNA Feron-Zv2, resulting in 122.7 ± 5.3% cell viability (n = 3 ± standard error of the mean (SEM), 100 nM siRNA) after exposure to ZIKV relative to a virus treated control (35.2 ± 7.1% cell viability (n = 3 ± SEM)). Protection of BHK-21 cells was recorded after transfection with an attenuated anthrax toxin containing an RNA binding domain. Treatment with Feron-Zv4 resulted in 75.1 ± 2.9% cell viability (n = 3 ± SEM, 25 nM siRNA) after exposure to ZIKV. This protection was mirrored by a system containing octameric PA where a maximum of 86.2 ± 4.4% cell viability was reported (n = 3 ± SEM, 75 nM siRNA) after treatment with Feron-Zv2. Scrambled siRNA afforded no measurable protection. Here we report for the first time that siRNA delivered by either attenuated anthrax toxin or octamer forming ATx can protect mammalian cells from ZIKV cytopathic effects.