UC San Diego

BACKGROUND & AIMS:Intraductal papillary mucinous neoplasias (IPMNs) are precancerous cystic lesions that can develop into pancreatic ductal adenocarcinomas (PDACs). These large macroscopic lesions are frequently detected during medical imaging, but it is unclear how they form or progress to PDAC. We aimed to identify cells that form IPMNs and mutations that promote IPMN development and progression. METHODS:We generated mice with disruption of Pten specifically in ductal cells (Sox9CreERT2;Ptenflox/flox;R26RYFP or PtenΔDuct/ΔDuct mice) and used PtenΔDuct/+ and Pten+/+ mice as controls. We also generated KrasG12D;PtenΔDuct/ΔDuct and KrasG12D;PtenΔDuct/+ mice. Pancreata were collected when mice were 28 weeks to 14.5 months old and analyzed by histology, immunohistochemistry, and electron microscopy. We performed multiplexed droplet digital polymerase chain reaction to detect spontaneous Kras mutations in PtenΔDuct/ΔDuct mice and study the effects of Ras pathway activation on initiation and progression of IPMNs. We obtained 2 pancreatic sections from a patient with an invasive pancreatobiliary IPMN and analyzed the regions with and without the invasive IPMN (control tissue) by immunohistochemistry. RESULTS:Mice with ductal cell-specific disruption of Pten but not control mice developed sporadic, macroscopic, intraductal papillary lesions with histologic and molecular features of human IPMNs. PtenΔDuct/ΔDuct mice developed IPMNs of several subtypes. In PtenΔDuct/ΔDuct mice, 31.5% of IPMNs became invasive; invasion was associated with spontaneous mutations in Kras. KrasG12D;PtenΔDuct/ΔDuct mice all developed invasive IPMNs within 1 month. In KrasG12D;PtenΔDuct/+ mice, 70% developed IPMN, predominately of the pancreatobiliary subtype, and 63.3% developed PDAC. In all models, IPMNs and PDAC expressed the duct-specific lineage tracing marker yellow fluorescent protein. In immunohistochemical analyses, we found that the invasive human pancreatobiliary IPMN tissue had lower levels of PTEN and increased levels of phosphorylated (activated) ERK compared with healthy pancreatic tissue. CONCLUSIONS:In analyses of mice with ductal cell-specific disruption of Pten, with or without activated Kras, we found evidence for a ductal cell origin of IPMNs. We also showed that PTEN loss and activated Kras have synergistic effects in promoting development of IPMN and progression to PDAC.