Some viruses are naturally adept at evading antiviral medicines. Take enteroviruses—pathogens with RNA genomes associated with a range of illnesses including hand, foot and mouth disease (HFMD). These viruses are notorious for mutating rapidly, making them challenging targets for traditional therapies.
Wei Leong Chew, a Principal Scientist and Associate Director at A*STAR’s Genome Institute of Singapore (GIS), believes that gene editing technologies have the requisite precision and adaptability to disarm these evolving viruses once and for all.
“CRISPR-Cas13 cuts RNA and can be easily programmed towards a user-defined RNA target sequence through a guide RNA,” explained Chew, adding that this ease of programming can slash drug development timelines in the face of emerging viral strains.
Chew, along with a research team including Justin Chu and Thinesshwary Yogarajah from the National University of Singapore, as well as GIS Senior Scientist Choong Tat Keng, developed a novel CRISPR-Cas13 system to target enterovirus-A71, a common enterovirus that causes HFMD infections.
The precision of the CRISPR-Cas13 system hinges on its specific guide RNA, leading the researchers to develop a specialised bioinformatics tool for designing guide RNAs called Cas13gRNAtor. The RNA editing system was then packaged in a harmless adeno-associated viral vector (AAV) to deliver it to infected cells.
Survival outcomes for mice with HFMD up to 19 days after a lethal infection. Treatments were given 24 hours after infection with EV-A71, a known cause of HFMD epidemics. Each mouse in the treatment group was injected with AAV-CRISPR-Cas13 with EV-A71 gRNAs at either a lower dose of 1 x 1011 viral genomes (vgs) or a higher dose of 1 x 1011 vgs. Mice in the control group received 1 x 1012 vgs AAVDJ-GFPgRNA.
Results from tests on cell cultures showed that AAV-CRISPR-Cas13 treatment decreased viral replication by more than 90 percent. Data from animals with HFMD infections treated with AAV-CRISPR-Cas13 were equally exciting.
“One dose of the AAV-CRISPR-Cas13 prevented death of infected mice,” Chew commented. “From an 80 percent mortality rate to almost 0 percent mortality is stunning beyond our expectations.”
These findings underscore the unique potential of CRISPR-Cas13 antivirals to combat difficult-to-treat viral infections. “This is an antiviral mechanism that is distinct from other drug modalities such as small molecules and antibodies, which mainly target viral proteins,” Chew said.
Despite the foreseeable hurdles in getting this potential therapy to patients, Chew said the recent approval of the world’s first CRISPR-based therapeutic is highly encouraging.
Chew’s team has filed two patents on their innovation and is currently developing similar approaches to targeting pathogens with pandemic potential. “Building our pandemic preparedness will help safeguard against the next Disease X,” said Chew.
The A*STAR-affiliated researchers contributing to this research are from the Genome Institute of Singapore (GIS) and the Institute of Molecular and Cell Biology (IMCB).
