Cholangiocarcinoma is a particularly heterogeneous cancer of the biliary tract, occurring as intrahepatic, perihilar, and distal forms. The intrahepatic form represents the second most common primary liver cancer after hepatocellular carcinoma. Its prognosis remains poor, marked by late diagnosis, a high recurrence rate, and a rising worldwide incidence, with surgery remaining the only truly effective treatment yet accessible to few patients. In this context, understanding the molecular mechanisms that govern tumor aggressiveness is of major clinical interest. Class I phosphoinositide 3-kinases (PI3Ks) are dysregulated in nearly all human cancers, but the specific role of each of their isoforms remains poorly characterized. The team had previously shown that the δ isoform (PI3Kδ) regulates the polarity and plasticity of epithelial cells, as well as its involvement in hepatocellular carcinoma. Its contribution to cholangiocarcinoma, however, remained unexplored.
Immunohistochemical analyses of human samples reveal strong PI3Kδ expression in the least differentiated tumors. To dissect its role, the authors generated, by lentiviral construction, cholangiocarcinoma cell lines stably overexpressing PI3Kδ. This overexpression is accompanied by an increase in mesenchymal markers, stem cell markers, and pluripotency transcription factors, without repression of the epithelial marker CDH1 — a signature of a hybrid phenotype combining partial epithelial-mesenchymal transition and stemness. In three-dimensional culture, these cells form a thick layer of extracellular matrix at the basement membrane and display a single large lumen. These observations are confirmed in vivo, in tumors xenografted into immunodeficient mice and following PI3Kδ overexpression via an AAV8 vector in the murine liver: the tumor tissues develop necrosis and fibrosis, accompanied by marked angiogenesis and lymphangiogenesis.
The researchers establish that these effects on cellular morphogenesis and stromal remodeling depend on the TGFβ/Src/Notch pathway. PI3Kδ overexpression increases TGFβ expression and the secretion of angiogenic factors such as VEGF and bFGF in the serum of xenografted mice. The human origin of these cytokines suggests that the cancer cells themselves contribute to the recruitment of endothelial cells, thereby describing an intrinsic role of tumor PI3Kδ in angiogenesis, distinct from the role known for PI3Kδ in endothelial cells. Finally, transcriptome analysis of 26 cell lines from the Cancer Cell Line Encyclopedia (CCLE), based on the expression levels of PIK3CD and vimentin, made it possible to stratify the cells into three groups corresponding to three stages of progression: epithelial characteristics, humoral immune response, and then tissue and matrix remodeling associated with vascular development.
This work highlights the deleterious effects of high PI3Kδ expression in cholangiocarcinoma. The combined detection of PI3Kδ and vimentin could serve as a tool for classifying tumor severity, and targeting PI3Kδ opens new directions for patient management.