A novel preclinical model of cholangiocarcinoma based on human aberrant FBXW7 expression.

Abstract

e15624 Background: Pre-clinical models that mimic human genetic events occurring in intrahepatic cholangiocarcinoma (iCCA) are limited. The ubiquitin ligase F-box and WD repeat domain-containing 7 (FBXW7) is recognized as a tumor suppressor in many cancer types. Methods: Firstly, we determined the FBXW7 mutation frequency (n = 120) and mRNA expression (n = 87) in a collection of human iCCA. Based on the preliminary findings in human data, we generated a mouse model by hydrodynamic tail vein injection of activated/myristylated (myr-)AKT with Fbxw7ΔF, a dominant negative form of Fbxw7. Subsequently, we investigated the role of established targets of Fbxw7, namely Notch2, Yap, and c-Myc in this novel mouse model and in human CCA cell lines. Results: FBXW7 mRNA expression is almost ubiquitously downregulated (71/82; 86.6%) in human iCCA specimens, while only 0.8% of samples showed FBXW7 somatic mutations. In vivo, co-expression of AKT and Fbxw7ΔF triggered the development of iCCA lesions and mice were euthanized by 15 weeks post-injection due to high tumor burden. At the molecular level, a strong induction of FBXW7 canonical targets, including Yap, Notch2, and c-Myc oncoproteins, was detected. However, only c-Myc was consistently confirmed as a FBXW7 target in human CCA cell lines. Interestingly, selected ablation of c-Myc completely impaired iCCA formation in AKT/Fbxw7ΔF mice, whereas deletion of either Yap or Notch2 delayed cholangiocarcinogenesis in the same model. Furthermore, in human iCCA specimens, a strong, inverse correlation between the expression levels of FBXW7 and c-Myc was observed. Conclusions: Downregulation of FBXW7 is almost ubiquitous in human iCCA and cooperates with AKT to induce cholangiocarcinogenesis in mice. This pre-clinical mouse model could be used to test novel therapeutics targeting c-Myc, Notch2, and/or Yap.