Abstract 5881: Upregulation of TET2 expression by DNA methyltransferase (DNMT) inhibitors is associated with resistance in DNMT1 knockout colorectal cancer cells

Abstract Ten-eleven-translocation 2 (TET2) is a member of the TET family proteins (TET1-3) that convert 5-methylcytosine to 5-hydroxymethylcytosine (5-hmC) in DNA and causes site-specific DNA demethylation. The effects of DNMT1 on TET2 phenotype following DNMT inhibitor treatment is unclear in human cancer. In colorectal cancer HCT116 cells with DNMT1 gene intact (DNMT1+/+) and deletion (DNMT1−/−) status, we found that TET2 expression was robustly increased in DNMT1−/− cells after treatment with 0. 5 µM and 5 µM decitabine for 72 h, 96 h, and 120 h. The augmentation in TET2 expression was accompanied by a dose-dependent re-expression of p16ink4A in DNMT1−/− cells. Particularly, TET2 upregulation was associated with resistance to DNMT inhibitors, showing a lack of induction of DNA damage, cell-cycle arrest and apoptosis after drug exposure in DNMT1−/− compared to DNMT1+/+ cells. The treatment with 4’-thio-5-aza-2’-deoxycytidine (aza-T-dCyd) only up-regulated TET2 and re-expressed p16ink4A at the lower dose of 0. 5 µM, which was consistent with our previous findings that high dose of aza-T-dCyd at 5 µM predominantly eliminates the cancer cells with severe DNA damage by undergoing apoptosis and cell death (Scientific Reports, 13: 5964, 2023). Moreover, both decitabine and aza-T-dCyd had minimal effects on TET2 upregulation and p16ink4A re-expression in cells with intact DNMT1 gene. The data suggest that the absence of DNMT1 gene made the cells prone to TET2 upregulation upon DNMT inhibitor challenges. Future study is needed to investigate the interactive relationship between DNMT1 and TET2 as well as demethylation, and its impact on cancer treatment with DNMT inhibitors. Citation Format: Angelo B. Laranjeira, Dat Nguyen, Lorraine C. Pelosof, James H. Doroshow, Sherry X. Yang. Upregulation of TET2 expression by DNA methyltransferase (DNMT) inhibitors is associated with resistance in DNMT1 knockout colorectal cancer cells 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 (6Suppl): Abstract nr 5881.