CRISPR genome editing can be controlled with ultrasound

A novel way to control CRISPR genome editing using focused ultrasound has been discovered.

CRISPR is a genome-editing approach that employs the Cas9 enzyme to target and cut specific DNA sequences. Despite its precision and effectiveness, CRISPR faces challenges, including off-target effects where unintended DNA sections are removed and, owing to continuous uncontrolled use, potential immune responses that attack the CRISPR system itself.

'CRISPR is revolutionary,' said Professor Yingxiao Wang, from the University of California San Diego Jacobs School of Engineering and study senior author. 'You can do genome or epigenome editing right in the cell nucleus – so that essentially, you can treat genetically-related diseases. But we are pushing it one step further to make it controllable. Instead of continuously editing the genome, we can now control it to be activated at a specific location and at a specific time using a non-invasive remote-controlled ultrasound wave. That's the breakthrough.'

Previous methods to control CRISPR – such as using nanoparticles, light, or heat – have struggled with limitations, including difficulty in targeting specific regions and limited penetration depth in the body.

During this study, published in Nature Communication, a focused ultrasound beam was directed to a specific region, a tumour containing CRISPR/Cas9, causing localised heating and activation of the CRISPR system. Once the desired genome editing was complete, the ultrasound beam was removed and the tissue's temperature decreased, deactivating the system. This ensured that CRISPR is only active at the targeted site and avoids prolonged activity.

The CRISPR/Cas9 system in this study targeted and cut the telomeres of tumour cells, severing them from their chromosomes and preventing the cell from dividing and replicating. Telomeres are protective caps on the ends of the cell's chromosomes, and which dictate the maximum times a cell can divide as these caps shorten with each cell division.

Cancer cells, known for their uncontrolled growth, often bypass natural limits on cell replication by exploiting the enzyme telomerase that allows the telomeres to regrow, effectively granting them unchecked replication. As the tumour cells break down, they release cytokines, chemical signals that alert the immune system including T-cells, to the site of the tumour.

Building on their previous work in immunotherapy, Professor Wang and his team engineered T-cells featuring chimeric antigen receptors (CAR-T cells) to enhance this immune response, since CAR-T cells are better able to recognise and attack cancer cells. This synergy between CRISPR and CAR-T therapy amplified the effectiveness of the treatment.

In mouse models, the researchers demonstrated that this approach not only reduced tumour size but completely eradicated the tumours in some cases.

'The result was surprisingly good... In all the mice, the tumour was not only slowing in growth, but [was also] cleared – the tumour essentially decayed and disappeared. So, these are very encouraging results,' concluded Professor Wang.