Abstract 1626: Clonal expansion in bile duct associated with chronic inflammation
Authors: Maeda Hirona , Kakiuchi Nobuyuki , Ito Takashi , Ogawa Eri , Shiokawa Masahiro , Uza Norimitsu , Tanaka Hiroko , Nannya Yasuhito , Makishima Hideki , Kodama Yuzo , Hatano Etsuro , Miyano Satoru , Ogawa Seishi 
Published: March 2024

Abstract
Introduction: Chronic inflammation has been implicated in cancer development in many tissues and has recently been associated with promoted clonal expansion in non-cancer tissues. Primary sclerosing cholangitis (PSC) is a chronic progressive disease of unknown etiology affecting the bile ducts and has been associated with a substantially increased risk of cholangiocarcinoma. Clonal dynamics in the normal bile duct and PSC epithelium remains poorly understood because of the limited accessibility to normal/inflamed bile ducts. In this study, we established a method to detect somatic mutations accumulated in the bile duct epithelium and investigated a mutation rate in normal bile duct cells and clonal expansion in PSC epithelium.
Methods: We established single cell-derived organoids from bile, which were subjected to whole genome sequencing to measure the age-related mutation rate in normal epithelial cell in the bile ducts. We next established organoids from multiple sites in perihilar bile ducts and collected epithelial samples from intrahepatic bile ducts obtained by laser-capture microdissection (LCM) from patients with PSC who underwent total hepatectomy for liver transplantation, for which we performed whole exome sequencing to investigate clonal expansion in PSC-involved bile ducts.
Results: In total, 14 single cell-derived organoid lines were established from 2 patients with PSC and 3 control individuals. Based on the whole genome sequencing of those organoids, the number of mutations found in non-PSC bile duct epithelium increases with age at an annual mutation rate of 34.3 mutations per genome per year, which did not substantially differ from the rate in the PSC epithelium, suggesting that the inflammatory process in PSC hardly affected the mutations in PSC epithelium. To further investigate clonal expansion in the PSC epithelium, a total of 120 bulk organoid samples from perihilar bile ducts in 3 PSC patients and 111 LCM samples from intrahepatic bile ducts in 4 PSC patients were analyzed. In perihilar bile duct-derived organoids, we detected a median of 13 [1-30] somatic mutations per exome in samples derived from perihilar bile ducts and 20 [5-41] mutations per exome in those from intrahepatic LCM samples. Most mutations were detected in a single sample but some mutation clusters were shared by adjacent samples, which expanded in an area as large as 13 mm in length. Expanded clones harbored mutations in known cancer-driver genes, such as ARID1A and KRAS, which were enriched in segmental bile ducts, suggesting their role in the clonal expansion.
Conclusions: Here, we established the method to detect somatic mutations accumulated in the normal/inflamed bile duct epithelium using an organoid-based analysis of clonal somatic mutations. Our results revealed clonal expansion existing in PSC epithelium and open up a way to the better understanding of carcinogenesis in the bile duct.
Citation Format: Hirona Maeda, Nobuyuki Kakiuchi, Takashi Ito, Eri Ogawa, Masahiro Shiokawa, Norimitsu Uza, Hiroko Tanaka, Yasuhito Nannya, Hideki Makishima, Yuzo Kodama, Etsuro Hatano, Satoru Miyano, Seishi Ogawa. Clonal expansion in bile duct associated with chronic inflammation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1626.