Targeting the NSUN2-DHODH axis reverses ferroptosis resistance and oxaliplatin resistance in colorectal cancer.

[BACKGROUND] Oxaliplatin (OXA) is a standard chemotherapy for advanced colorectal cancer (CRC), yet acquired resistance frequently limits its efficacy. Ferroptosis, an iron-dependent form of cell death driven by lipid peroxidation, has emerged as a promising strategy to overcome chemoresistance. The RNA 5-methylcytosine (m5C) methyltransferase NSUN2 has been implicated in tumor progression, but its role in CRC chemoresistance remains unclear.

[METHODS] We investigated the functional and mechanistic involvement of NSUN2 in CRC progression and OXA response, focusing on ferroptosis-related pathways. Integrative analyses of bulk, single-cell, and spatial transcriptomic datasets, together with multi-cohort clinical validation, were performed. Functional assays included colony formation, CCK-8 proliferation, migration, invasion, apoptosis, and xenograft experiments. Lipid ROS, malondialdehyde (MDA), and mitochondrial morphology were assessed to evaluate ferroptotic stress.

[RESULTS] NSUN2 was upregulated in CRC and associated with poor prognosis. NSUN2 depletion suppressed CRC growth and enhanced sensitivity to OXA. Knockdown of NSUN2 increased lipid ROS accumulation, elevated MDA levels, and induced mitochondrial damage, consistent with enhanced ferroptosis. In vivo, NSUN2 depletion potentiated the antitumor activity of OXA in SW480 xenografts, and combining OXA with the ferroptosis inducer imidazole ketone erastin (IKE) further reduced tumor burden compared with OXA alone, accompanied by increased tumor MDA levels. Mechanistically, NSUN2 stabilized dihydroorotate dehydrogenase (DHODH) mRNA via m5C modification, thereby increasing DHODH expression. Elevated DHODH suppressed ferroptosis independently of GPX4, whereas NSUN2 depletion disrupted this axis, promoting lipid peroxidation and ferroptosis sensitivity. DHODH restoration rescued ferroptosis and reversed the enhanced drug sensitivity induced by NSUN2 knockdown.

[CONCLUSION] These findings identify an NSUN2-DHODH epitranscriptomic axis that promotes CRC progression and OXA resistance by limiting ferroptosis, supporting NSUN2-targeting and ferroptosis-inducing strategies to improve chemotherapy response.