June 11, 2018

expert reaction to using CRISPR/Cas9 and potential cancer risk in cells

A new study, published in Nature Medicine, investigates whether using the CRISPR/Cas9 genome editing tool may – in some instances –  increase cancer risk in cells.

Dr Alena Pance, Senior staff scientist at the Wellcome Trust Sanger Institute, said:

“The findings are very relevant to the latest gene editing technologies and will certainly inform these methodologies leading to improvements and better understanding of the mechanisms involved. However, the results are preliminary, mainly showing the effect of p53 in 1 particular cell line and it is difficult to assess whether the phenomenon described is exclusive of this cell type or whether it applies to primary cells in general.

“A more in depth examination of p53 will be needed in order to understand how its role in DNA repair can interfere with gene editing and whether other pathways are also involved. This means examining expression levels activity and integrity of the gene and protein in the different cells under the experimental circumstances used. Finally, a comprehensive discussion must follow on the potential manipulation of DNA repair and the cell cycle in the production of corrected cells, particularly for clinical applications.”

Prof Robin Lovell-Badge FMedSci FRS, Group Leader, The Francis Crick Institute, said:

“It has been known for a long time that too many double-strand breaks in DNA trigger cells to die (through apoptosis) and that this mechanism depends on the activity of p53. It is therefore of no surprise that mutations that inactivate the gene encoding p53 are more likely to survive processes that can lead to DNA damage as reported in these two papers. Indeed, p53 is a tumour suppressor gene whose loss is associated with the ability of cells to give rise to cancers where chromosome rearrangements and DNA breaks are very common. Many cell types can tolerate a few double strand breaks and some may without triggering cell death, especially if they are grown in optimal conditions. Indeed there are many papers published using genome editing methods like CRISPR/Cas9 in cells or in early embryos from mice, other animals, and humans, including making whole animals with highly efficient rates of genome editing – sometimes approaching 100%. Such high rates would not be apparent if p53 had to be mutated to allow cells to survive. It would be fairly obvious, especially in animals, if p53 or one of its critical downstream target genes had been mutated – they would be prone to developing tumours. It has also been possible to “multiplex”, i.e. to make genome edits in several genes at the same time.

“The need to reduce p53 activity in order to mutate many genes at once was also known previously. As an example, Niu et al^± the authors were attempting to eliminate all the endogenous porcine endogenous retroviruses (PERVs) from a pig cell line. They could mutate many but not all, unless they used an inhibitor of p53 (called pifithrin alpha or PFTα).

“Perhaps, however, some cell lines are more prone to p53-mediated apoptosis than others, or perhaps specific culture conditions can lead to this, especially if they are sub-optimal or somehow lead to cellular stress. Culture conditions for human ES cells are often suboptimal, moreover retinal pigmented cells seem difficult to grow unless, as in one of these papers, they have been modified. This suggests that they are indeed likely to be suffering cellular stress. It is therefore not apparent that the problems identified by these two papers, and certainly the scary press releases, are entirely justified – they may be relatively specific to the two studies themselves. I would also hope that any assessment of the clinical use of genome editing methods would include an analysis of genes such as p53 before the resulting cells were deemed safe enough to use.”

^± https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5813284/ (Science 357 1303-7, 2017)

Prof Darren Griffin, Professor of Genetics, University of Kent, said:

“CRISPR-Cas9 has, since its inception, been an incredibly promising technique, particularly given its potential for highly specific targeting and minimal “off target” effects compared to previous approaches of gene manipulation. As such, rigorous assessment of its safety is essential.  This paper provides reason for caution, but not necessarily alarm.  In this excellent study, the group have established that editing cancerous cells is easier by this approach than in normal cells. It is very elegant in that it has identified the p53 pathway as the place for further study.  Almost any treatment that has the power to do good, has the power to do harm and this finding should be considered in this broader context.  As we learn more about the CRISPR-Cas9 system and how it can be used, this study will inevitably be considered a significant finding.”

* ‘CRISPR–Cas9 genome editing induces a p53-mediated DNA damage response’ by name of first author et al. published in Nature Medicine on Monday 11th June.

All our previous output on this subject can be seen at this weblink: http://www.sciencemediacentre.org/tag/genome-editing/

Declared interests

Prof Darren Griffin: No COI

None others recieved.