A new method for generating CRISPR mouse models of pancreatic cancer

The use of genetically engineered mouse (GEM) models of pancreatic cancer allows tumours with precise and known mutations to be generated in the background of a fully competent immune system [1]. This allows one to screen for effects of drugs in a defined genetic model. This is technically possible in human pancreatic cancer cell line xenograft models of pancreatic cancer, however pancreatic cancer cell lines are genetically unstable which makes unambiguous interpretation of results difficult and the xenografts require a compromised immune system which is highly functionally important in tumour biology. GEMs are highly suitable for initial identification of potential synthetic lethalities which can then be further validated in tumour xenograft models and eventually clinical trials with pre-screening for specific genetic mutations.

CRISPR/Cas9 is a molecular means to delete genes or introduce new genetic material into cell lines and primary tissues. A new study has developed a method to deliver the technology to the pancreas of mice [2]. A simplification of the steps involved is as follows a surgical incision is made and the pancreas is shifted in position so that it is more accessible for manipulation, plasmid vector DNA containing CRISPR constructs is then injected into the pancreas and finally an electric field is applied (electroporation) to the pancreas to coax the plasmid DNA into the pancreatic cells (figure 1). Electroporation is capable of delivering more CRISPR/Cas9 constructs simultaneously than viral vectors.

fig1a
Figure 1: Steps to introduce CRISPR plasmid constructs into the mouse pancreas. A laparotomy is a technical term for a surgical procedure creating a large incision through the abdominal wall to gain access into the abdominal cavity where the pancreas is located. This figure is sourced from Figure 1a of ref [2]. No changes were made. Creative Commons Attribution 4.0 International (CC BY 4.0).

This technology can be used to screen for mutations that are deleterious for tumour formation in the presence of specific compounds. For example the paper did not screen compounds however it was found that BRCA2 deletion was selected against in the presence of functional p53 but not in a p53 mutant background. This kind of analysis could be applied to potential therapeutics to identify synthetic lethalities before commencing clinical trials. There is quite a strong argument that in addition the efficacy and preclinical safety these types of studies should be incorporated into preclinical development as standard.

Refs

  1. Richmond, A., and Y. Su. ‘Mouse Xenograft Models vs GEM Models for Human Cancer Therapeutics’. Disease Models and Mechanisms 1, no. 2–3 (1 September 2008): 78–82. doi:10.1242/dmm.000976.
  2. Maresch, Roman, Sebastian Mueller, Christian Veltkamp, Rupert Öllinger, Mathias Friedrich, Irina Heid, Katja Steiger, et al. ‘Multiplexed Pancreatic Genome Engineering and Cancer Induction by Transfection-Based CRISPR/Cas9 Delivery in Mice’. Nature Communications 7 (26 February 2016): 10770. doi:10.1038/ncomms10770.
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