The carcinogenesis of pancreatic ductal adenocarcinoma (PDA) progresses according to multi-step evolution, whereby the disease acquires increasingly aggressive pathological features. On the other hand, disease inception is poorly investigated. Decoding the cascade of events that leads to oncogenic transformation is crucial to design strategies for early diagnosis as well as to tackle tumor onset. Lineage-tracing experiments demonstrated that pancreatic cancerous lesions originate from acinar cells, a highly specialized cell type in the pancreatic epithelium. Primary acinar cells can survive in vitro as organoid-like 3D spheroids, which can transdifferentiate into cells with a clear ductal morphology in response to different cell- and non-cell-autonomous stimuli. This event, termed acinar-to-ductal metaplasia, recapitulates the histological and molecular features of disease initiation. Here, we will discuss the isolation and culture of primary pancreatic acinar cells, providing a historical and technical perspective. The impact of pancreatic cancer research will also be debated. In particular, we will dissect the roles of transcriptional, epigenetic, and metabolic reprogramming for tumor initiation and we will show how that can be modeled using ex vivo acinar cell cultures. Finally, mechanisms of PDA initiation described using organotypical cultures will be reviewed.

Cholesterol is a non-essential metabolite that exerts both structural and signaling functions. However, cholesterol biosynthesis is elevated, and actively supports, pancreatic carcinogenesis. Our previous work showed that statins block the reprogramming of mutant KRAS-expressing acinar cells, that spontaneously undergo a metaplastic event termed acinar-to-ductal metaplasia (ADM) to initiate carcinogenesis. Here we tested the impact of cholesterol supplementation on isolated primary wild-type acinar cells and observed enhanced ductal transdifferentiation, associated with generation of the second messenger cyclic adenosine monophosphate (cAMP) and the induction of downstream protein kinase A (PKA). Inhibition of PKA suppresses cholesterol-induced ADM ex vivo. Live imaging using fluorescent biosensors dissected the temporal and spatial dynamics of PKA activation upon cholesterol addition and showed uneven activation both in the cytosol and on the outer mitochondrial membrane of primary pancreatic acinar cells. The ability of cholesterol to activate cAMP signaling is lost in tumor cells. Qualitative examination of multiple normal and transformed cell lines supports the notion that the cAMP/PKA axis plays different roles during multi-step pancreatic carcinogenesis. Collectively, our findings describe the impact of cholesterol availability on the cyclic AMP/PKA axis and plasticity of pancreatic acinar cells.

Multi-step evolution characterizes the carcinogenesis of GI malignancies, where the disease progresses through the accrual of genetic mutations, co-option of multiple host cellular factors and the acquisition of increasingly aggressive pathological features. Ensuing cancer complexity and plasticity are challenges for therapeutic approaches. On the other hand, disease inception is often triggered by a defined oncogenic event, which leads to escalating effects on gene expression, cellular metabolism, chromatin organization and ultimately cell identity. Decoding this molecular cascade of events is crucial to design strategies for early diagnosis as well as to tackle tumor onset. To this aim, the in vitro culture of non-transformed epithelial cells represents a major technical challenge. Genetic studies, combined with lineage-tracing experiments demonstrated that pancreatic cancerous lesions originate from acinar cells, a specialized cell type in the pancreatic epithelium, following mutations of the KRAS oncogene. Ex vivo culture of pancreatic acinar cells has allowed the identification of early mutant KRAS-driven alterations. Primary acinar cells survive in vitro in organoid-like 3D spheroids, which can recapitulate histological and molecular features of disease initiation. Here, we will discuss the isolation and culture of primary mouse pancreatic acinar cells, providing and historical and technical perspective. Impact for pancreatic cancer research will also be debated; in particular we will dissect the role of KRAS signaling in driving oncogenic transformation and highlight differences with canonical 2D culture of established cancer cell lines.