Abstract 4662: Epigenetic conversion on p53 pathway in human cancer: The clinical potential of p53 mutation status as a predictive biomarker for drug sensitivity by epigenetic treatment.

Abstract

Abstract Background: DNA methylation plays a central role in epigenetic contribution to human cancer progression. We have mentioned actual epigenetic conversion on critical molecular pathways in human cancer (Mini-symposium on AACR 2012). Such genes included PGP9.5, NMDAR2B, DAPK, and Cyclin A1, which have been all demonstrated to be involved in apoptotic process on upstream or downstream of p53 pathway. Materials and Methods: Epigenetic profiles of PGP9.5, NMDAR2B, and Cyclin A1 were examined in 163 primary gastric cancer by Q-MSP in combination with p53 mutation status (exon 4 to 8) by SSCP. Effects of epigenetic reversion by 5-aza-2’-deoxycytidine and trichostatin A, in combination with chemotherapeutic drug, CDDP, were assessed for apoptosis by flow cytometry and p53 trans-activation ability by luciferase analysis in gastric cancer cell lines with or without p53 mutation. Results: (1) SSCP identified 44 mutations (27%) of p53 gene in primary gastric cancer. Mutation status of p53 gene was not of prognostic relevance. (2) We performed epigenetic profiles for PGP9.5, NMDAR2B, DAPK, and Cyclin A1. Methylation level is higher in primary tumors with p53 wild type than in those with p53 mutant in gastric cancer (PGP9.5>NMDAR2B>Cyclin A1>DAPK).(3) Importantly, super-high methylation level of PGP9.5, NMDAR2B, and cyclin A1 was exclusively found in primary tumors with no p53 mutation, and such cut-off TaqMeth values were 50, 163, and 133, respectively. (4) Super-high methylation was found in 14 for PGP9.5, 19 for NMDAR2B, and 8 in Cyclin A1, which are not always redundant. Super-high methylation may represent functional shut-down of expression in the individual genes. (5) In NUGC4 gastric cancer cell line, harboring wild type p53, epigenetic treatment remarkably augmented apoptosis by CDDP chemotherapy, concordant with p53 transcription activity. This finding suggested that epigenetic treatment could be additional options to classical chemotherapy more efficiently to kill cancer cells with wild type p53. (6) On the other hand, in KATO III cancer cell line, harboring null p53 (mutant), epigenetic treatment alone induced robust apoptosis, with no trans-activation of p53. Conclusion: In GI cancers, several genes involved on the p53 pathway are functionally suppressed in expression by super-dense methylation of the promoter regions, and epigenetic reversion of p53 activity may be beneficial for killing cancer cells more efficiently, if p53 is not mutated. On the other hand, cancer cell with no p53 mutation is very sensitive by epigenetic treatments, and p53 status may predict sensitivity of cancer cells by chemotherapy in combination with epigenetic treatments. Citation Format: Keishi Yamashita, Mina Waraya, Hiroshi Katoh, Akira Ooki, Hiroshi Kawamata, Kazunori Nakamura, Hiroshi Nishimiya, Akira Ema, David Sidransky, Masahiko Watanabe. Epigenetic conversion on p53 pathway in human cancer: The clinical potential of p53 mutation status as a predictive biomarker for drug sensitivity by epigenetic treatment. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4662. doi:10.1158/1538-7445.AM2013-4662 Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.