As known previously, the common practice in modeling cancer is to reveal mutations by sequencing its genomes and then to discover the role of these mutations in the course of breeding certainly mutated mice. And now, researchers can rapidly model cancer by using CRISPR, a gene-editing system introducing cancer-causing mutations into the livers of adult mice.
In a study appearing in the Aug. 6 issue of Nature, the researchers generated liver tumors in adult mice by disrupting the tumor suppressor genes p53 and pten. They are currently working on ways to deliver the necessary CRISPR components to other organs, allowing them to investigate mutations found in other types of cancer.
The sequencing of human tumors, based on high throughput technique, has revealed hundreds of oncogenes and tumor suppressor genes in different combinations. The flexibility of CRISPR, as delivery gets better in the future, will present a way to pretty rapidly test those combinations.
CRISPR relies on cellular machinery that bacteria use to defend themselves from viral infection. Researchers have copied this bacterial system to create gene-editing complexes that include a DNA-cutting enzyme called Cas9 bound to a short RNA guide strand that is programmed to bind to a specific genome sequence, telling Cas9 where to make its cut.
Using Cas enzymes targeted to cut small fragments of p53 and pten, the researchers were able to disrupt those 2 genes in about 3 percent of liver cells, enough to produce liver tumors within 3 months.
Usage for CRISPR
The researchers also used CRISPR to create a mouse model with an oncogene called beta catenin, which makes cells more likely to become cancerous if additional mutations occur later on. To create this model, the researchers had to cut out the normal version of the gene and replace it with an overactive form, which was successful in about 0.5 % of hepatocytes.
In this study, the researchers delivered the genes necessary for CRISPR through injections into veins in the tails of the mice. While this is an effective way to get genetic material to the liver, it would not work for other organs of interest. However, nanoparticles and other delivery methods now being developed for DNA and RNA could prove more effective in targeting other organs, Sharp says.
CRISPR-mediated direct mutation of cancer genes.Nature,2014. doi:10.1038/nature13589