Microsatellite instability in thorotrast‐induced human intrahepatic cholangiocarcinoma

Abstract

Thorotrast, a colloidal suspension of radioactive 232 ThO 2 that emits ␣ particles, was used as a radiographic contrast during World War II. It is known to induce liver cancers, most frequently ICC, decades after injection. Since radiation induces genomic instability, we analyzed MSI in Thorotrastinduced ICC. The frequency of MSI ؉ cases was 62.5% in Thorotrast ICC, whereas it was 22.7% in non-Thorotrast ICC. However, frameshift mutations of mononucleotide repeats were not observed in Thorotrast ICC. In addition, the MSI ؉ phenotype was not associated with the quantity of Thorotrast deposited or the latency period of ICC induction. Promoter regions of both the hMLH1 and the hMSH2 MMR genes tended to be hypermethylated in the tumor part compared to the adjacent nontumor part in Thorotrast ICC. Methylation of the hMLH1 promoter was associated with the MSI ؉ phenotype in Thorotrast ICC. In contrast, methylation status of these promoter regions was not related to MSI in nonThorotrast ICC cases. These findings suggest that MSI induced by exposure to Thorotrast mainly reflects clonal expansion of cancer cells and is partly due to inactivation of hMLH1 by hypermethylation. © 2002 Wiley-Liss, Inc. Key words: Thorotrast; microsatellite instability; cholangiocellular carcinomaIdentification of genetic changes in radiation-induced cancer can contribute to risk assessment and prevention. Thorotrast is the trade name for a 25% colloidal suspension of radioactive 232 ThO 2 that naturally emits ␣ particles (90%), ␤ particles and ␥-rays (10%). It was used as a radiographic contrast agent from the 1930s to the 1950s. 1 Intravascularly injected, Thorotrast remains in the reticuloendothelial system for life, and those organs are chronically irradiated by ␣-particles. In particular, Ͼ60% of total Thorotrast is located in the liver. 2 Several decades after injection, Thorotrast has been known to induce liver cancers, of which ICC is the most frequent type. The development of cancer is thought to be a consequence of multiple carcinogenic steps, including genetic changes such as activation of proto-oncogenes and inactivation of tumor-suppressor genes. 3 It has become evident that cancer cells exhibit a mutator phenotype. Mutator phenotype or genomic instability results from aberrations of genes that normally function in the maintenance of genetic stability.There is now considerable evidence that cells that have survived irradiation may produce descendants that manifest various biologic consequences induced by genomic instability other than irreversible damage at the time of irradiation. 4,5 A higher frequency of nonclonal chromosomal aberrations appears in clonal descendants of mouse hematopoietic stem cells more than 12 generations after ␥-irradiation. 6 A persistently increased rate of gene mutation is observed in cell populations many generations after exposure to X-rays and ␣ particles. 7 To search for genetic changes characteristic of radiation exposure, we previously analyzed p53 gene mutations in Thorotrast-laden livers. Multip...

Cholangiocarcinoma: current knowledge and future perspectives consensus statement from the European Network for the Study of Cholangiocarcinoma (ENS-CCA)

“…The DNA mismatch repair system recognizes and repairs erroneous insertion of nucleotides as well as short insertions and deletions. Downregulation of MutS (MSH2, MSH3 and MSH6) and MutLa (hMLH1 and PMS2) protein complexes involved in DNA mismatch repair results in genetic instability, poorer prognosis and higher chemoresistance in CCAs in comparison with tumours without MutS and MutLa down regulation [301][302][303] . Under the direct control of Tp53, upregulation of ribonucleo tide reductase p53R2 increases the supply of nucleotides for repairing DNA damage.…”

Aberrant DNA methylation profile in cholangiocarcinoma

“…Since alterations of the cellular epigenome usually precede morphologic changes and genetic alterations, identification of related aberrant DNA methylation profiles according to specific inflammation milieu may serve as a reasonable early diagnostic marker and an intervention target for CCA. Liver fluke infection (opisthorchis viverrini, or less frequently, clonorchis sinensis) RUNX3 (49.1%) [70] ; p14 (40.2%), p15 (48.9%), p16 (28.3%) [21] ; hMLH1 (44.6%) [71] Hepatolithiasis p16 (100% [72] , 54.6% [73] ); TFF1 (37.5%) [74] Biliary malformation (congenital choledochal cysts, caroli's disease, etc) NA Thorotrast hMLH1 (45.8%), hMSH2 (25.0%) [23] …”

“…For instance, inactivation of 9p21 gene cluster (p16 INK4a /p14 ARF /p15 Ink4b ) has been unraveled in liver fluke-related CCA [21] and primary sclerosing cholangitis-associated CCA [22] . Also, a high frequency of microsatellite instability (MSI) and inactivation of hMLH1 has been obser ved in thorotrast-related CCA [23] . Although a recent study of thyroid carcinoma has uncovered that an early genetic event is necessary and sufficient for initiating a cancerous development by promoting an inflammatory microenvironment [24] , similar instances of an intrinsic pathway have yet to be addressed in CCA.…”

Clinical implications of radiation-induced genomic instability

“…Whether this reflects selection bias as the healthy miners had, on average, a longer mining history, or a true biologic similarity between the groups is unclear. Liu et al (2002) used a different approach to attempt to elucidate the induction, and significance of, genomic instability in people following a-particle irradiation by examining archival tissues sections of human intrahepatic cholangiocarcinoma (ICC). It had been previously shown that ICC can be induced by thorotrast administration, a colloidal suspension of a-particle emitting 232 ThO 2 .…”