Poster Presentation & Flash Talk Presentation 29th Lorne Cancer Conference 2017

Genetic editing of colonic organoids provides a molecularly distinct and orthotopic mouse model of serrated carcinogenesis. (#7)

Tamsin R Lannagan 1 , Young K Lee 1 , Tongtong Wang 1 , Roshini Somashekar 1 , Laura Vrbanac 1 , Jia Ng 1 , Miao Yang 1 , Mark L Bettington 2 3 , Tracy L Putoczki 4 5 , Nic Waddell 3 , Barbara A Leggett 3 , Vicki L Whitehall 3 , Daniel L Worthley 1 6 , Susan L Woods 1 6
  1. University of Adelaide/SAHMRI, Adelaide, SA, Australia
  2. Envoi Specialist Pathologists, Brisbane, QLD, Australia
  3. QIMR Berghofer Medical Research Institute, Brisbane, QLD, Australia
  4. Department of Medical Biology, University of Melbourne , Melbourne, VIC, Australia
  5. Walter and Eliza Hall Institute of Medical Research, Melbourne, VIC, Australia
  6. Contributed , Equally

In this age of next generation sequencing we are fast accruing more information on cancer associated genetic alterations than ever before. How do we translate this new knowledge into better outcomes for cancer patients? How do we prioritise genetic alterations for study and targeting from this wealth of data? Here we utilise the organoid culture technique pioneered by the Clevers lab, combined with CRISPR/Cas9 genome engineering, to sequentially introduce genetic alterations associated with the serrated pathway to colorectal cancer. This pathway accounts for up to 30% of colorectal cancer, including some of the most treatment resistant forms. It is characterised histologically by a distinct, serrated pattern in the epithelial layer of polyps, hence the name. At the molecular level it is most commonly associated with activating mutations in the mitogen activated kinase (MAPK) pathway gene, BRAF, and epigenetic modifications termed the CpG Island Methylator Phenotype (CIMP). As expected, introduction of the BrafV600E mutation into mouse colonic organoids activates the MAPK pathway. It also mimics the chemoresistance to EGFR inhibitors found in MAPK mutant colorectal cancer in the clinic. We have produced a series of organoids with alterations to genes in the MAPK, TGFβ, Wnt and senescence pathways that are associated with the serrated pathway using CRISPR technology. Targeted biallelic gene alterations have been verified by DNA sequencing, organoid growth under restricted media conditions and analysis of downstream pathway activity. To determine the essential “hits” required for tumour formation we have orthotopically injected organoids from this series using a mouse colonoscope. Orthotopic injection of the most complex organoid line containing 5 mutant genes quickly generates high-grade adenocarcinoma in vivo with some serrated features. The penetrance of this phenotype and effect on survival is reduced when organoids with less genetic alterations are used. In this way we are producing novel, preclinical models of serrated colorectal cancer that can be readily adapted to investigate the many leads generated by next generation sequencing.