Theaflavin-3,3'-Digallate Plays a ROS-Mediated Dual Role in Ferroptosis and Apoptosis via the MAPK Pathway in Human Osteosarcoma Cell Lines and Xenografts.

Globally, osteosarcoma (OS) is the most prevalent form of primary bone cancer in children and adolescents. Traditional neoadjuvant chemotherapy regimens have reached a bottleneck; thus, OS survivors have unsatisfactory outcomes. Theaflavin-3,3'-digallate (TF3) exhibits potent anticancer properties against many human cancers. Nevertheless, the biological effects and the underlying molecular mechanism of TF3 in human OS remain unclear. The objective of this study was to investigate the effects of TF3 on human OS cell lines and mouse xenograft models. The results showed that TF3 reduced cell viability, suppressed cell proliferation, and caused G0/G1 cell cycle arrest in both MG63 and HOS cell lines in a concentration-dependent manner. TF3 also altered the homeostatic mechanisms for iron storage in the examined cell lines, resulting in an excess of labile iron. Unsurprisingly, TF3 caused oxidative stress through reduced glutathione (GSH) exhaustion, reactive oxygen species (ROS) accumulation, and the Fenton reaction, which triggered ferroptosis and apoptosis in the cells. TF3 also induced MAPK signalling pathways, including the ERK, JNK, and p38 MAPK pathways. Furthermore, oxidative stress was shown to be the primary reason for TF3-induced proliferation inhibition, programmed cell death, and MAPK pathway activation in vitro. Moreover, TF3 exhibited markedly strong antitumour efficacy in vivo in mouse models. In summary, this study demonstrates that TF3 concomitantly plays dual roles in apoptotic and ferroptotic cell death by triggering the ROS and MAPK signalling pathways in both in vitro and in vivo models.