Targeting EHMT2 overcomes 5-fluorouracil resistance in colorectal cancer by modulating cell cycle and apoptosis.

5-Fluorouracil (5-FU) is a first-line chemotherapy commonly used to treat colorectal cancer (CRC). However, the development of acquired resistance to 5-FU remains a significant clinical challenge, and the underlying epigenetic mechanisms are not fully understood. In this study, we demonstrate that euchromatic histone lysine methyltransferase 2 (EHMT2) is significantly upregulated in CRC patients with poor responses to 5-FU, directly correlating with lower overall survival rates. Using established 5-FU resistant (5-FUR) HCT116 and HT29 cell lines, RNA-sequencing confirmed robust EHMT2 overexpression compared with wild-type cells. Mechanistically, siRNA-mediated knockdown of EHMT2 restored 5-FU sensitivity by upregulating protein phosphatase 1B (PPM1B), a key downstream target. This EHMT2-PPM1B axis disruption effectively induced G1 phase cell cycle arrest and triggered apoptosis in 5-FUR cells, fundamentally impairing their proliferation. Furthermore, we validated the therapeutic potential of targeting this pathway using in vivo and ex vivo models. Combination treatment with 5-FU and the specific pharmacological EHMT2 inhibitor (BIX-01294) synergistically suppressed tumor growth in a 5-FUR cell-derived xenograft mouse model. Importantly, these therapeutic effects were faithfully recapitulated in 5-FUR patient-derived colorectal cancer organoid (PDO) models. Together, our findings elucidate a critical epigenetic mechanism where EHMT2 promotes 5-FU drug resistance. Targeting EHMT2 represents a promising and translatable therapeutic strategy for overcoming chemoresistance and improving clinical outcomes in CRC patients.