Abstract 4430: Acute inflammation-induced abrogation of base excision repair as a potential mechanism of cancer initiation in inflammation-mediated hepatocarcinogenesis

Abstract

Abstract Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide, and chronic inflammation seems to be the most important risk factor. Since inflammation induces oxidative stress and DNA damage, base excision repair (BER) of oxidative damage in prevention of mutations and subsequent tumorigenesis in an inflammatory environment seems to be important, but a direct link between deficient DNA repair and carcinogenesis in the highly damaging environment of the inflamed liver has not been shown. Furthermore, the longstanding question about how and in which cells cancer initiation occurs and the roles that DNA damage and repair play in the process are larger problems that remain unanswered. In our study we utilize the Long Evans Cinnamon (LEC) rat, which develops spontaneous HCC after consecutive phases of acute and chronic hepatitis induced by the accumulation of copper due to a mutation in the copper transporter gene ATP7B, mimicking Wilson's disease in humans. We have previously shown that the LEC rat exhibits deficient BER during acute hepatitis, particularly in the activity of 8-oxoguanine DNA glycosylase (Ogg1), and activity returns during chronic hepatitis as preneoplastic foci begin to form. In order to study the role of BER in cancer initiation, we have generated three new cell lines from the animal. We report here that we have isolated and grown apparently spontaneously immortalized LEC hepatocytes from the acute hepatitis liver (LEC-AH) and the chronic hepatitis liver (LEC-CH) in long term culture. We have also developed a carcinoma cell line from a LEC liver tumor (LEC-T). The newly generated cell lines express albumin, and preliminary karyotyping analysis shows that the LEC-AH and LEC-CH cells are cytogenetically normal (average 42 chromosomes). As observed in the acute and chronic hepatitis tissues, LEC-AH cells exhibit decreased activity (-2.5 fold) of Ogg1 compared to LEC-CH cells. Furthermore, at 12 days post-confluency, we have observed spontaneous foci formation in the LEC-AH cells (96 foci per 106 cells) in culture while LEC-CH cells do not form foci (<1 foci per 106 cells). These preliminary results indicate a correlation between foci formation in culture and Ogg1 activity, demonstrating a potential direct link between decreased BER and preneoplastic foci formation. Additionally, the foci may represent an enriched population of initiated cells, providing a unique opportunity to study the mechanism of spontaneous cancer initiation in vitro and identify initiation markers. Experiments elucidating the specific roles of Ogg1, other BER enzymes, and oxidative damage in foci formation of LEC-AH cells are in progress, as is further molecular analysis of the foci-forming cell populations as they may reflect the biochemical and molecular characteristics of preneoplastic foci in vivo. (Supported by a grant from NIH/NCI RO1 CA113447) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4430. doi:1538-7445.AM2012-4430