Epigenetic Remodeling Through GSK343-induced EZH2 Inhibition Alters SMYD2/SMYD3 Expression and Promotes Antitumor Effects.
BACKGROUND Breast cancer is a heterogeneous disease in which epigenetic dysregulation plays a critical role in tumor progression, therapeutic resistance, and cellular plasticity. Among epigenetic regulators, EZH2, the catalytic subunit of the polycomb repressor complex 2 (PRC2), has emerged as a key oncogenic driver through its role in H3K27 trimethylation (H3K27me3)-mediated transcriptional repression. This study aimed to evaluate the anti-tumor effects of the EZH2 inhibitor GSK343 and to investigate its impact on the expression of additional epigenetic regulators, SMYD2 and SMYD3, in breast cancer models. MATERIAL AND METHODS Human breast cancer cell lines MDA-MB-231 (triple-negative) and MCF-7 (luminal) were treated with increasing concentrations of GSK343 (1-60 µM) for 24, 48, and 72 hours. Cell viability was assessed by MTT and Trypan Blue assays, while apoptosis was evaluated through caspase-3/7 activity. Gene expression levels of EZH2, SMYD2, and SMYD3 were quantified by RT-qPCR, and H3K27me3 levels were analyzed as a pharmacodynamic marker of EZH2 inhibition. RESULTS GSK343 induced a significant dose- and time-dependent reduction in cell viability and a corresponding increase in apoptotic activity, with more pronounced effects in MDA-MB-231 cells. Treatment also resulted in consistent downregulation of EZH2, SMYD2, and SMYD3, alongside a marked decrease in H3K27me3 levels, confirming effective epigenetic modulation. These findings demonstrate that EZH2 inhibition promotes coordinated epigenetic remodeling and disrupts key oncogenic pathways in breast cancer cells. The greater sensitivity observed in triple-negative cells highlights subtype-specific epigenetic dependencies and supports EZH2 and SMYD family members as promising therapeutic targets. CONCLUSION EZH2 inhibition reveals subtype-specific vulnerabilities and supports targeting epigenetic regulators as a promising therapeutic strategy in breast cancer. Additionally, these results suggest potential combinatorial strategies integrating EZH2 inhibition with other targeted or epigenetic therapies to enhance treatment efficacy, overcome resistance mechanisms, and improve clinical outcomes, particularly in aggressive subtypes such as triple-negative breast cancer. Further studies are warranted to validate findings.