Simultaneous Inhibition of Histone Deacetylases and EZH2 Reduces SASP in Non-Small Cell Lung Cancer

Background: Cellular senescence, a common outcome of treatments like chemotherapy and radiotherapy, often acts as a therapeutic hurdle. Our prior investigations revealed that this senescent state is accompanied by the secretion of the senescence-associated secretory phenotype (SASP), a potent driver of chronic inflammation and a factor that can paradoxically facilitate tumor progression. Methods: We investigated the effects of SAHA, alone or combined with the EZH2 inhibitor EPZ-6438, on NSCLC cell lines. Senescence induction was confirmed via SA-β-galactosidase staining, while cell growth was evaluated using MTT and colony formation assays. Mechanistic studies, including Western blotting, qPCR for SASP factors, and immunofluorescence for Cytoplasmic Chromatin Fragments (CCF), were performed to assess the underlying pathway. Results: SAHA effectively induced senescence-mediated growth inhibition in A549 and H1299 cells but simultaneously triggered the SASP. This SAHA-induced SASP was linked to the generation of CCFs, thereby activating the cGAS–STING pathway. Importantly, the combined administration of SAHA and EPZ-6438 significantly reduced the expression of inflammatory mediators, such as IL6 and IL8. This co-treatment not only provided superior anti-proliferative activity compared to SAHA alone but also enhanced the suppression by attenuating the SASP. Conclusion: Collectively, our data demonstrate that SAHA-induced senescence in NSCLC cells is critically linked to detrimental SASP production mediated by CCF formation. Crucially, combining SAHA with EZH2 inhibition successfully suppressed the SASP, leading to enhanced growth inhibition, thereby providing a robust rationale for this combination therapy in NSCLC treatment.