“A dearth or antivirals” Our current repertoire of U.S. Food and Drug Administration (FDA)-approved antivirals is limited to only nine out of the known 214 human-infecting RNA viruses, and almost all these antivirals target viral proteins. Unlike antivirals that target viral proteins, targeting host cell proteins can disrupt the ability of a virus to replicate, effectively shutting down the host cell “virus production facility”. An ideal host-based antiviral would selectively affect only virally infected cells, while leaving uninfected cells unscathed. But how could this work?
The key is that virally infected cells are different than the uninfected cells.
In infected cells, host cell proteins are called to action by the virus to ensure viral replication. In this process, they often leave their normal post, so their normal functions are compromised. We call this a viral-induced hypomorph, which is analogous to a loss-of-function mutation. In cancer, where cells have cancer driver loss-of-function mutations, it is possible to selectively kill cancer cells with drugs that target proteins that are redundant in function to the mutated gene/protein. This is called ‘synthetic lethality’.
Synthetic lethality is a type of genetic interaction between two nonessential genes that participate in a parallel or redundant process to carry out an essential function, where mutations in either gene alone does not affect cell viability, but mutations in both genes result in cell death. We hypothesized that synthetic lethal (SL) interactions of viral-induced hypomorphs could be targeted as host-based antiviral therapeutics – selectively disrupting the viral production facility but leaving uninfected cells unaffected.
Proof of Concept GBF1, a Golgi membrane protein is a critical host factor for many RNA viruses including poliovirus, Coxsackievirus, Dengue, Hepatitis C and E virus, and Ebola virus. GBF1 becomes a hypomorph upon interaction with the poliovirus protein 3A. We performed a genome-wide chemogenomic CRISPR screen using a specific inhibitor of GBF1 called Golgicide A (GCA) in Nalm-6 cells to identify synthetic lethal partners of GBF1 and revealed ARF1 as the top hit. We showed that disruption of ARF1, selectively kills cells that synthesize poliovirus 3A alone or in the context of a poliovirus replicon. Consistent with our hypothesis, combining 3A expression with sub-lethal amounts of GCA further exacerbated the GBF1–ARF1 SL effect.