CRISPR/CAS9 TECHNOLOGY UNDER PRESSURE FOR ALLEGEDLY INCREASING RISK OF CANCER IN CELLS
In recent years, advances in the CRISPR-Cas9 technology lead to a revolution in genome engineering across the world. The easy to use components of the technique facilitate accurate and fast genomic manipulation. Successful applications have been reported in human cells as well as embryos. This technology presents modern medicine with the possibility to treat diseases previously out of reach.
However, two studies published in the journal ‘Nature Medicine’ found a link between CRISPR-Cas9 mediated genome editing in human cells and cancer. One study conducted by the Karolinska Institute and the University of Cambridge reports a DNA damage response upon Cas9 mediated genome editing in p53 expressing retinal pigment epithelium (RPE1) cells (Haapaniemi et al., 2018). The introduction of double strand breaks by the Cas9 protein resulted in growth arrest and thus decreased efficiency of genome editing. Inhibiting DNA damage signaling by disrupting the p53 pathway, however, resulted in improved genome editing efficiency but left cells vulnerable to cancerous mutations and genome instability.
Another study by Novartis came to the conclusion that DNA double strand breaks introduced by Cas9 are toxic to human pluripotent stem cells (hPSCs) and caused a p53 response (Ihry et al., 2018) thus confirming the previous results. Cells with acquired p53 mutations are more likely to be successfully manipulated by Cas9, therefore, inducing a selection towards cells without a functioning DNA damage response. This has important implications for future treatments since CRISPR-Cas9 engineered hPSCs can be used for cell replacement therapies.
The two studies point out a potentially problem with CRISPR-Cas9 mediated genome engineering. The introduction of double strand breaks leads to cell cycle arrest and subsequently to cell death in the presence of proper DNA damage response signalling. Cells lacking those control mechanisms are more likely to develop into cancerous threats.
However, it remains elusive if this is an effect generally observed in all cells or if this is specific for a subset of cells. The great success in genome manipulation in model organisms such as mice and even human embryos indicate that the CRISPR-Cas9 technology is indeed a potential tool for future medicine. The studies, on the other hand, highlight that more research is needed in order to develop this approach into a save treatment option.
Multiple solutions to those problems are possible. For instant, the currently used Cas9 protein is known to remain associated with cut sites, which could prevent proper DNA repair and intensify DNA damage signalling. The engineering of a new generation of Cas proteins could lead to more effective and faster genome repair thus minimizing toxicity in cells.
The two studies underline challenges that have to be overcome before the CRISPR-Cas9 technology is ready for commercial use in human medicine. It also highlights that further improvements of the different components of the technique such as highly specific sgRNAs with minimal off-target effects and effective Cas proteins have to be accomplished to ensure a safe use of the technology in the future.
The results from the recent studies are expected having an impact on the commercial value of existing patents and will promote search for new Cas proteins with improved performance.
By Martin Fabry, Research Fellow at St. Johns College (University of Cambridge) and Scientific Advisor to IP2.