Abstract PR02: Somatic CRISPR/Cas9-mediated tumor suppressor disruption enables versatile brain tumor modeling
Authors: Zuckermann Marc , Hovestadt Volker , Knobbe-Thomsen Christiane B. , Zapatka Marc , Northcott Paul A. , Schramm Kathrin , Belic Jelena , Jones David T.W. , Tschida Barbara , Moriarity Branden , Largaespada David , Roussel Martine F. , Korshunov Andrey , Reifenberger Guido , Pfister Stefan M. , Lichter Peter , Kawauchi Daisuke , Gronych Jan 
Published: May 2016

Abstract
Modeling cancer in mice through engineering of candidate genes in the germline has long been the gold standard for the validation of putative oncogenes or tumor suppressor genes (TSGs). For TSGs, whereby loss-of-function (LOF) mutations act as a driver for malignant transformation, this has traditionally been accomplished using constitutive or cell type-specific knockout strategies mediated by homologous recombination in embryonic stem cells. While this allows evaluation of cell type-specific susceptibility to malignant transformation, generation of genetically engineered mouse models (GEMMs) is a time consuming process. For in vivo investigation of a large number of molecular alterations, such as the many new candidates currently emerging from large-scale tumor genome sequencing efforts, a faster and more flexible method is required. We therefore sought to adapt the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9-guided endonuclease technique for the somatic disruption of candidate TSGs and thereby complement aforementioned already existing models like GEMM.
To provide a flexible and effective method for investigating somatic LOF alterations and their influence on tumorigenesis in vivo, we established in vivo somatic gene transfer of CRISPR/Cas9-encoding vectors using polyethylenimine or in utero electroporation, respectively, allowing for in vivo targeting of TSGs in the developing murine brain. We demonstrate the utility of this approach by deleting the tumor suppressor Ptch1, which resulted in the development of cerebellar tumors resembling sonic hedgehog (SHH) subgroup medulloblastoma both at the histopathological as well as the molecular level. Furthermore, we show that multiple genes can be disrupted with this approach, using in utero electroporation of guide RNAs (gRNAs) targeting Trp53, Pten and Nf1 into the forebrain of mice. This resulted in induction of glioblastoma with 100% penetrance. Using whole genome sequencing (WGS) we characterized the MB-driving Ptch1 deletions in detail and show that no off-targets were detected in these tumors.
Taken together, these approaches provide a fast and convenient way for validating the emerging wealth of novel candidate TSGs and the generation of faithful animal models of human cancer.
Citation Format: Marc Zuckermann, Volker Hovestadt, Christiane B. Knobbe-Thomsen, Marc Zapatka, Paul A. Northcott, Kathrin Schramm, Jelena Belic, David T.W. Jones, Barbara Tschida, Branden Moriarity, David Largaespada, Martine F. Roussel, Andrey Korshunov, Guido Reifenberger, Stefan M. Pfister, Peter Lichter, Daisuke Kawauchi, Jan Gronych. Somatic CRISPR/Cas9-mediated tumor suppressor disruption enables versatile brain tumor modeling. [abstract]. In: Proceedings of the AACR Special Conference: Advances in Brain Cancer Research; May 27-30, 2015; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2015;75(23 Suppl):Abstract nr PR02.