DNA Repair Shapes Ferroptotic Susceptibility in Osteosarcoma

Abstract

Cancer cells rely on coordination of genome maintenance and redox control to survive genotoxic stress. Osteosarcoma, the most common primary bone malignancy, exhibits marked genomic instability due to defective DNA repair; to survive this impairment, osteosarcoma cells rely on coordinated genome maintenance and redox control adaptations that can contribute to therapeutic non-response. The standard-of-care chemotherapeutics for osteosarcoma patients consists of the neoadjuvant and adjuvant MAP regimen, which involves high-dose methotrexate (M), adriamycin/doxorubicin (A), and cisplatin (P). While MAP chemotherapy has been shown to induce apoptosis in osteosarcoma cells both in vitro and in vivo, its role in promoting alternative cell death pathways, especially within genomically unstable tumors, remains understudied. As osteosarcoma cells frequently evade apoptotic death, determining the extent to which MAP-associated chemotherapies can engage non-apoptotic cell pathways could reveal strategies for eliciting cell death in MAP non-responding osteosarcoma cells. I focused our studies on cisplatin, as it is a DNA-damaging chemotherapy that induces various lesions including intra- and interstrand crosslinks (ICLs) repaired by mechanisms that strictly require the endonuclease XPF. In this study, I tested the extent to which XPF-deficiency (by CRISPR/Cas9) alters how U2OS osteosarcoma cells undergo cell death in vitro with and without cisplatin treatment. I observed an expected hypersensitivity to cisplatin but also discovered that XPF-deficient compared to WT U2OS cells underwent increased cell death in response to RSL3 and ML210, but not Erastin2, and also had decreased glutathione and GPX4 protein levels. XPF-deficient compared to WT cells which were treated with cisplatin underwent synergistic cell death when treated with RSL3 and ML210, but not Erastin2, that was rescuable by Liproxstatin-1 but not by the inhibitors of other cell death pathways. These results reveal that XPF shapes cell death responses to cisplatin in U2OS cells, uncovering a new potentially targetable dependency of XPF-deficient osteosarcoma cells on ferroptotic cell death with cisplatin administration.