Targeting the METTL3/PCNA axis with STM2457 overcomes cisplatin resistance in osteosarcoma.

BACKGROUND: Cisplatin resistance represents a major clinical challenge in osteosarcoma (OS), often leading to treatment failure and poor patient prognosis. The underlying molecular mechanisms are complex and incompletely understood. This study investigates the role of the RNA methyltransferase methyltransferase-like 3 (METTL3) and its associated N6-methyladenosine (m6A) modification in driving cisplatin resistance, with a specific focus on the METTL3-m6A-proliferating cell nuclear antigen (PCNA) regulatory axis as a potential therapeutic target. METHODS: Cisplatin-resistant human OS cell lines (MG-63/DDP, U2OS/DDP) were used. The effects of the selective METTL3 inhibitor STM2457, both alone and in combination with cisplatin, on cell viability, apoptosis, and migration were evaluated using Cell Counting Kit-8 (CCK-8) assay, immunofluorescence staining for cleaved Caspase-3, and vimentin expression, respectively. Mechanistic investigations included quantification of global m6A levels, analysis of PCNA messenger RNA (mRNA) stability via actinomycin D assay, and western blot for protein expression. Functional roles were validated using small interfering RNA-mediated PCNA knockdown and plasmid-based PCNA overexpression. Drug interaction was analyzed using the combination index (CI) method. RESULTS: STM2457 monotherapy significantly and dose-dependently suppressed cell proliferation and migration in cisplatin-resistant OS cells. Furthermore, STM2457 demonstrated strong synergistic effects with cisplatin (CI <1), markedly enhancing apoptosis induction. At the molecular level, STM2457 inhibited METTL3 catalytic activity, leading to a significant reduction in global m6A RNA methylation. This resulted in the destabilization of PCNA mRNA and a consequent decrease in PCNA protein levels. Knockdown of PCNA effectively mimicked the anti-tumor effects of STM2457, whereas forced overexpression of PCNA attenuated the efficacy of STM2457 and partially restored the cisplatin-resistant phenotype. CONCLUSIONS: Our findings demonstrate that STM2457 overcomes cisplatin resistance in OS by targeting the METTL3-m6A-PCNA axis, thereby disrupting a key DNA repair and cell survival pathway. Pharmacological inhibition of METTL3 represents a novel and promising epigenetic strategy for resensitizing chemoresistant OS, supporting its potential for future clinical development.