Treating flaviviruses with mRNA-encoded Cas13

Project Summary Flaviviruses are vector-borne, positive-stranded RNA viruses that emerge unexpectedly and cause a spectrum of potentially severe diseases including hepatitis, vascular shock syndrome, encephalitis, paralysis, and congenital abnormalities. During the last 70 years, Dengue (DENV), West Nile virus (WNV), and Zika virus (ZIKV) epidemics have occurred globally, and flaviviruses infect over 400 million people annually. Despite extensive research, there are currently no FDA approved antivirals available for any flavivirus infection. Vaccines exist for Japanese encephalitis virus (JEV), Yellow Fever virus (YFV), and tick-borne encephalitis virus (TBEV); for Dengue, Dengvaxia is for those previously infected, and Qdenga has received EU approval for all populations. However, due to poor efficacy, low vaccination rates and sequence variability, cases due to flaviviruses still remain high, justifying the need for antiviral development. Current antiviral drug development is focused on small molecules and neutralizing antibodies, which require high doses or frequent re-dosing to obtain functional outcomes; their efficacy has been challenged by virus sequence variations. Thus, it is crucial to address the need for higher efficiency and broader spectrum antivirals. To address this need we are proposing a new paradigm for antiviral development, a mRNA-encoded activatable RNase, Cas13, as a platform for flavivirus treatment. Cas13 represents a programmable RNase that can directly target and degrade multiple viral RNAs. Synthetic mRNA and lipid nanoparticles are being used to deliver the RNase, as it allows for transient, non-viral delivery, with an improved safety profile over other gene therapy vectors. To date, our team was the first to demonstrate efficacy of mRNA-encoded Cas13 in vivo against influenza and SARS-CoV-2 in our recent publication in Nature Biotechnology. We also have preliminary data demonstrating single-dose efficacy using mRNA-encoded Cas13 with DENV-2 via systemic LNP-based delivery. Our long-term goal is to generate a suite of mRNA-encoded Cas13 drugs against pathogenic flaviviruses. Our short-term goal is to demonstrate targeting of multiple flaviviruses, including DENV, WNV, ZIKV, Powassan and YFV, further investigate the mechanism of action of Cas13, and demonstrate in vivo efficacy against DENV 1-4 and WNV.