Molecule that enhances CRISPR genome editing destroys part of the genome

A molecule that can be used to enhance CRISPR genome editing also causes unintended destruction of large sections of the genome in human cells.

The molecule, AZD7648, is not itself a part of the CRISPR/Cas9 system, but has been shown to increase its efficiency in human cells in vitro. This led to interest that AZD7648 may also enhance the strength of CRISPR/Cas9-based therapies. However, the new findings published in Nature Biotechnology, from a group based at ETH Zurich, Switzerland, make this far less likely.

'We are the first to say that everything is not wonderful,' said Professor Jacob Corn, the group leader. 'For us, this is a major setback because, like other scientists, we had hoped to use the technique to accelerate the development of gene therapies.'

Researchers have been trying for some time to find ways to enhance the efficiency of CRISPR/Cas9 for more complicated types of genome editing, which would widen the diseases that could be treated with gene therapy and potentially enhance effectiveness.

One approach that scientists have been studying to achieve this is the use of a group of molecules that AZD7648 belongs to, called protein kinase inhibitors (PKIs). PKIs influence a wide range of processes within cells, including the repair of damaged DNA.

Several studies in human cells have shown that PKIs indeed enhance CRISPR/Cas9 genome editing, with AZD7648 being the most potent. Editing was also highly precise at the targeted region of interest.

However, when Professor Corn and his colleagues looked at other areas of the genome, outside of the regions they were specifically targeting, they found that AZD7648 also induced the system to destroy large, unrelated sections, including whole regions of chromosomes.

'When we analysed the genome at the sites where it had been edited, it looked correct and precise. But when we analysed the genome more broadly, we saw massive genetic changes,' said Dr Grégoire Cullot, a postdoctoral fellow in the group.

It is possible that using a cocktail of alternative molecules to AZD7648 could be safer.

'There are many possible candidates. We now need to find out which components such a cocktail would have to consist of in order not to damage the genome' said Professor Corn.

The possibility for unintended CRISPR/Cas9 genome editing and damage is commonly raised as a concern for use in humans among other ethical considerations, and has been written about previously in BioNews (see BioNews 1255, 1217 and 1053).