Abstract 1795: Hypermethylation status of PDX1 has potential of diagnostic and predictive biomarker for risk stratification in colorectal cancer patients
Authors: Ichikawa Takashi , Toiyama Yuji , Okugawa Yoshinaga , Yasuda Hiromi , Fujikawa Hiroyuki , Okita Yoshiki , Yoshiyama Shigeyuki , Hiro Junichiro , Kobayashi Minako , Araki Toshimitsu , Ohi Masaki , Inoue Yasuhiro , Uchida Keiichi , Mohri Yasuhiko , Kusunoki Masato 
Published: July 2017

Background Abnormal DNA methylation is an important epigenetic mechanism that has been strongly implicated in the pathogenesis and progression of colorectal neoplasia. In contrast to other potential biomarker species such as mRNA and protein levels, measurement of DNA methylation has been shown to be stable, reproducible and consistent between individuals. Based on these standpoints, detecting aberrant methylation of cancer-related genes helps for the development of diagnostic and prognostic biomarkers in colorectal cancer (CRC). In this study, we comprehensively evaluated whole-genome methylation analysis using colorectal cancer tissues and normal colonic mucosa to discover candidate CRC-specific DNA methylation as potential diagnostic and predictive biomarkers for risk stratification in CRC patients.

Patients and Method The study design included an initial discovery phases, and followed by a subsequent clinical validation phase. In discovery phase, we performed whole-genome methylation analysis using CRC tissues and normal colonic mucosae from total fourteen patients to identify CRC-specific methylated CpG cites. Furthermore, we evaluated methylation levels of candidate methylated CpG cites by quantitative bisulfite pyrosequencing using one hundred six colorectal specimens from fifty-three CRC patients to validate the findings from discovery phase.

Result In discovery phase, we successfully identified several candidates of CRC-specific hypermethylated- and hypomethylated-CpG cites in CRC tissues compared with normal colonic mucosa. Promoter lesion of PDX1 is one of candidate methylated CpG cites in discovery phase, and we focus a specific CpG cite of PDX1 promoter lesion as a target cite to progress in validation phase. We quantified methylation status of PDX1 using 106 colonic tissues, and demonstrated that PDX1 were significantly hyper-methylated in CRC tissues compared with normal mucosa (p&lt;0.0001, Wilcoxon rank correlation test). Receiver operating characteristic (ROC) curves analysis revealed that methylation levels of PDX1 remarkably discriminated CRC tissues from normal colonic mucosa (AUC:0.9, Sensitivity:85.4%, Specificity:91.5%). Interestingly, methylation levels of PDX1 tend to increase in stage-dependent manner, and hypermethylated status of PDX1 was significantly correlated with presence of distant metastasis in validation cohort.

Conclusion Assessment of the PDX1 methylation status could be used as potential of diagnostic and predictive biomarker for risk stratification in CRC patients.

Citation Format: Takashi Ichikawa, Yuji Toiyama, Yoshinaga Okugawa, Hiromi Yasuda, Hiroyuki Fujikawa, Yoshiki Okita, Shigeyuki Yoshiyama, Junichiro Hiro, Minako Kobayashi, Toshimitsu Araki, Masaki Ohi, Yasuhiro Inoue, Keiichi Uchida, Yasuhiko Mohri, Masato Kusunoki. Hypermethylation status of PDX1 has potential of diagnostic and predictive biomarker for risk stratification in colorectal cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1795. doi:10.1158/1538-7445.AM2017-1795