Tumor-derived circulating DNA can induce senescence and SASP activation in mouse embryonic fibroblasts

Circulating tumor DNA (ctDNA), the tumor-originating fraction of cell-free DNA (cfDNA), is widely used as a biomarker for cancer detection and therapeutic monitoring; however, its direct biological impact on normal cells remains insufficiently understood. Since ctDNA contains tumor-derived molecular features, we hypothesized that it could serve as a signal that induces stress responses in healthy stromal cells. In this study, ctDNA and cfDNA were isolated from the conditioned media of B16-F10 melanoma and L929 fibroblast cultures, respectively, and applied to mouse embryonic fibroblasts (MEFs) at concentrations of 100 and 500 ng/mL for 24 h. Senescence was evaluated by SA-β-Gal staining alongside quantitative PCR analysis of senescence and SASP-associated genes, including p16, p21, p53, IL-6, and IL-1β. ctDNA treatment induced a pronounced, dose-dependent increase in senescence marker expression and SASP cytokine production, accompanied by elevated SA-β-Gal staining, whereas cfDNA treatment elicited no significant change compared to controls. These results indicate that ctDNA may act as a biologically active stimulus capable of eliciting senescence-like responses in normal fibroblasts, supporting the possibility that tumor-derived extracellular nucleic acids contribute to alterations in stromal behavior within the tumor microenvironment.