Targeting the Hippo/YAP-TAZ pathway increases X-ray sensitivity in chondrosarcoma spheroids and is associated with autophagic disruption.

BACKGROUND: Chondrosarcomas are malignant cartilage-forming bone tumors with limited therapeutic options, as surgical resection remains the only curative treatment, while chemo- and radiotherapy show limited efficacy due to intrinsic resistance mechanisms. Dysregulation of the Hippo signaling pathway been associated with tumor progression and therapy resistance and has emerged as a promising experimental target across several cancer entities. However, its relevance in chondrosarcoma remains unclear, particularly with regard to potential radiosensitizing effects.

METHODS: Human chondrosarcoma (SW-1353 and Cal78) and healthy chondrocyte (HC) spheroids were treated with Verteporfin (VP) alone or in combination with X-ray irradiation. Cell viability, Hippo/YAP-TAZ signaling, autophagy-associated markers, DNA damage, apoptosis, ultrastructural alterations, and gene expression were analyzed using ATP assays, immunoblotting, RT-qPCR, immunohistochemistry, and transmission electron microscopy.

RESULTS: VP treatment caused a dose-dependent decline in cell proliferation and suppressed key YAP/TAZ target genes, both in chondrosarcoma cells and HC, alongside downregulation of Hippo pathway components and proliferative markers like cMyc and PCNA. Combined with X-ray irradiation, these effects were amplified, supporting a potential radiosensitizing activity of VP in this preclinical model. Ultrastructural and molecular data showed that VP disrupted autophagic balance in all cell types, leading to mitochondrial damage, lipid accumulation, and nuclear fragmentation. Despite the higher basal autophagy in HC cells, VP led to cell death involving autophagy, apoptosis, and DNA damage, evidenced by increased LC3B-II, Beclin, γH2AX, and PARP cleavage. Enhanced DNA damage markers and altered p53-MDM2 signaling after treatment reflect the genotoxic stress induced.

CONCLUSION: Our data suggest that VP, particularly in combination with irradiation, is associated with disruption of multiple survival pathways in chondrosarcoma cells, offering a promising avenue for therapeutic intervention. Future studies should investigate the interplay between autophagy, apoptosis, and Hippo signaling to enable their therapeutic targeting in cancer.