A way to model virtually any mutation associated with cancer
Researchers co-led by Ludwig MIT Co-director Tyler Jacks described in a May issue of Nature Biotechnology a new method to construct genetically engineered mouse models that overcome a major limitation of previous approaches: that such models tend to capture just a small fraction of the genetic lesions that drive human cancer. Those that employ CRISPR–Cas9 can expand this fraction, but are limited by their reliance on error-prone DNA repair. Tyler and his colleagues showed that their approach, based on a more precise variation on CRISPR gene editing called “prime editing”, enables the accurate engineering of virtually any mutation in cell lines and organoids. It involves engineering mice to conditionally express in every cell a reverse transcriptase fused to a DNA-snipping enzyme that nicks only a single strand of DNA. Expression of the fusion protein is induced by the injection of Cre recombinase into targeted tissues, while the addition of a guide RNA encoding a mutation of interest enables the precise replacement of any targeted DNA sequence. The researchers demonstrated this “somatic prime editing” in vivo using lipid nanoparticles, generating lung and pancreatic cancer models using viral delivery of prime editing guide RNAs or transplantation of prime-edited organoids. In testing their method, they showed how different types of somatic mutations in oncogenic KRAS generate distinct tumor phenotypes.