Oesophageal adenocarcinoma (OAC) develops stepwise following exposure to chronic gastric reflux: from pre-malignant Barrett’s metaplasia, through stages of low- and high-grade dysplasia, to invasive cancer. Mutation or loss of the tumour suppressor gene SMAD4 has been found to occur in the invasive disease stage of OAC, but not in pre-malignant tissue, and little is known about the significance of this. Our study aimed to delineate drivers of OAC tumourigenesis in the context of SMAD4 loss to better understand disease progression.
Our novel in vivo tumourigenesis model demonstrates progression of dysplastic Barrett’s oesophagus to OAC. In this model, SMAD4-deficient Barrett’s metaplasia cells form tumours in immunodeficient mice after a period of latency and in a dose-dependent manner. This delayed tumour growth onset suggests further drivers are required for oncogenesis. Therefore, we conducted a genome-wide CRISPR-Cas9 knockout screen to identify genes that co-operate with SMAD4 loss to promote tumourigenesis. This screen identified cross-talk between SMAD4 loss and regulation of mTOR, with specific effects on translational reprogramming. We have extended the results of this screen into a model of Barrett’s oesophagus patient-derived organoids (PDOs) and observed increased proliferative potential of our genetically modified PDOs. This work adds to our knowledge of Barrett’s tumourigenesis and gives insight into novel mechanisms of SMAD4-driven transformation.