HDAC Inhibitors Enhance the Chemosensitivity of Osteosarcoma Cells to Etoposide by Suppressing the Hippo/YAP Signaling Pathway.

Osteosarcoma primarily occurs in children and adolescents, and is a highly aggressive bone tumor, particularly presenting challenges in metastatic or recurrent cases due to chemoresistance. Emerging evidences suggest that histone deacetylase inhibitors (HDACis) may exert anti-tumor effects by enhancing the efficacy of various therapeutic modalities. However, the combination of traditional chemotherapy with HDACi-based treatment for osteosarcoma intervention has not been thoroughly explored. This study investigates the anticancer properties of HDACis and/or etoposide (VP16) on the osteosarcoma cell lines U2OS and SJSA-1. Cell viability, morphology, growth and apoptosis were evaluated after treatments, in addition to their influence on the expression levels of proteins associated with apoptotic processes. To elucidate the underlying mechanisms, we employed RNA sequencing, RT-qPCR, and Western blot analyses. Treatment with either HDACis or VP16 alone resulted in an antiproliferative effects in U2OS and SJSA-1 cell lines. Notably, HDACis significantly increased the sensitivity of osteosarcoma cells to VP16, as evidenced by marked differences in cell viability, growth, morphology and apoptosis. Furthermore, when compared to doxorubicin treatment, this VP16/TSA/NAM combinatory regimen demonstrated a comparable ability to suppress cell viability while exhibiting a more pronounced inhibition of cell proliferation. Mechanistically, the combination of HDACis and VP16 specifically resulted in inhibition of the Hippo/YAP signaling cascade, accompanied by a reduction in total YAP1 protein expression. Collectively, our findings suggest that HDACis potentiate the capacity of VP16 to hinder cellular proliferation and trigger apoptosis via the downregulation of the Hippo/YAP pathway, thereby providing a prospective approach to overcome chemoresistance in osteosarcoma.