Ferroptosis Induction and YAP Inhibition as New Therapeutic Targets in Gastrointestinal Stromal Tumors (GISTs)

SIMPLE SUMMARY: Despite targeted therapy with tyrosine kinase inhibitors (TKIs), unresectable or metastatic human GISTs generally relapse under treatment. Thus, alternative therapeutic approaches are needed to overcome GIST resistance. Ferroptosis, a cell death driven by iron-dependent phospholipid peroxidation, is an emerging therapeutic approach in cancers. However, the potential of ferroptosis induction in GISTs remains largely unknown. This study shows that GIST cell lines are highly sensitive to the type II ferroptosis inducer, RSL3. We also provide evidence that inhibition of YAP by verteporfin (VP) promotes ferroptosis in GIST cells while, surprisingly, CA3 mediates ferroptosis independently of YAP inhibition. Finally, we highlight a positive correlation between the highly expressed transferrin receptor protein 1 (TFRC), GISTs with elevated mitotic counts or higher risk, and with YAP expression/activation in human GIST tissue microarrays (TMA). Taken together, our results suggest that induction of ferroptosis and/or modulation of YAP activity offer promising perspectives for GIST treatment. ABSTRACT: GISTs are sarcomas of the gastrointestinal tract often associated with gain-of-function mutations in KIT or PDGFRA receptor genes. While most GISTs initially respond to tyrosine kinase inhibitors, relapses due to acquired resistance frequently occur. The induction of ferroptosis, an iron-dependent form of non-apoptotic cell death, emerged as a novel therapeutic approach in cancers and remains poorly characterized in GISTs. We studied hallmarks of ferroptosis, i.e., lipid peroxidation, iron and glutathione content, and GPX4 protein expression in imatinib-sensitive (GIST882) and -resistant (GIST48) GIST cell lines. GIST cells were highly sensitive to the induction of ferroptosis by RSL3, which was reversed by liproxstatin and deferoxamine. Lipid peroxidation and ferroptosis were mediated by VP and CA3 in GIST cells through a significant decrease in antioxidant defenses. Moreover, VP, but surprisingly not CA3, inhibited a series of target genes downstream of YAP in GIST cells. The ferroptosis marker TFRC was also investigated by immunohistochemistry in GIST tissue arrays. TFRC expression was observed in all samples. High TFRC expression was positively correlated with high-risk GISTs, elevated mitotic count, and YAP nuclear localization, reflecting YAP activation. This study highlights ferroptosis as a novel cell death mechanism in GISTs, and a potential therapeutic target to overcome resistance to tyrosine kinase inhibitors.