KRAS is the most frequently mutated oncogene in cancer.Tumor sequencing has revealed a complex spectrum of KRAS mutations across different cancer types, yet there is little understanding how specific KRAS alterations impact tumor in initiation, progression, or therapy response. Using highfidelity CRISPR-based engineering, we created an allelic series of new LSL-Kras mutant mice, reflecting codon 12 and 13 mutations that are highly prevalent in lung (KRAS G12C ), pancreas (KRAS G12R ) and colon (KRAS G13D ) cancers. Induction of each mutation in the developing mouse pancreas reveal striking quantitative and qualitative differences in the degree of ductal transformation and pre-malignant progression. Further, using organoid models we show that KRAS G13D mutants respond to EGFR inhibition, while the anti-proliferative effect of KRAS G12C -selective inhibitors can be overcome by upstream EGFR signaling. Together, these new mouse strains provide an ideal for investigating KRAS biology in vivo, and for developing pre-clinical precision oncology models of KRAS-mutant pancreas (G12R), colon (G13D), and lung (G12C) cancers.KRAS mutations in tumor development. However, these models alone do not recapitulate the spectrum of KRAS alterations in human cancer. Here we describe an efficient pipeline for engineering allelic series of conditional alleles that significantly expands repertoire of pre-clinical KRASdriven cancer models. Using high-fidelity CRISPR targeting in embryonic stem cell (ESC)-based mouse models (GEMM-ESCs) 11-14 , we engineered six new LSL-Kras mutant alleles (G12V, G12C, G13D, G12R, G12A, G12S) that represent the most frequent mutations at the G12/G13 hotspot, after G12D. Guided by clinical data, we generated conditional mice representing three tissue-selective alterations observed in colorectal (G13D), pancreatic (G12R), and lung cancer (G12C) and show that, even subtle mutational changes in the Kras oncogene, have a profound impact on tumor initiation in the pancreas.Conditional animal models, such as Lox-Stop-Lox (LSL)-Kras G12D and LSL-Kras G12Vgeo mice developed almost 20 years ago 9,10 , have been critical tools to dissect the role of . CC-BY-NC-ND 4.
