Acquired radioresistance is the primary cause of treatment failure in radiotherapy, which is considered as one of the primary treatments for non-small cell lung cancer (NSCLC) (Levy et al., 2022, Gronberg et al., 2021). Radiotherapy employs ionizing radiation (IR) to induce cytotoxic effects in targeted areas, maximizing anti-cancer efficacy while minimizing side effects (Chaft et al., 2021, Iyengar et al., 2021, Miller and Hanna, 2021). However, repeated radiotherapy sessions frequently lead to the gradual development of radioresistance in tumors, resulting in an unfavorable prognosis and limited options for further treatment (Van den Bossche et al., 2022, Kaidar-Person et al., 2018, Park et al., 2018). Enhanced DNA damage repair and aberrant oxidative modulation are commonly reported mechanisms underlying radioresistance (Mudassar et al., 2020, Suwa et al., 2021), as IR causes direct DNA damage and indirect cell injury through oxidative stress (Mittal et al., 2022, Huang and Zhou, 2021). Although targeting DNA damage repair has shown promise in overcoming radioresistance in laboratory settings (Gorecki et al., 2020), available drugs and strategies for reversing radioresistance are limited in clinical practice (Huang and Zhou, 2020). Therefore, there is an urgent need for new insights to enhance overall responses to radiotherapy (Wang et al., 2018, Goncalves et al., 2021, Zhuang et al., 2014).

Ferroptosis is a distinct form of programmed cell death characterized by specific morphological and biochemical features (Jiang et al., 2021, Tang et al., 2021, Lei et al., 2022). Ferroptosis is characterized by the accumulation of cytotoxic lipid peroxides, which is often induced by radiotherapy in tumor tissues (Zhang et al., 2021, Lei et al., 2020). In the situation of overloaded lipid peroxides, cells would develop ferroptotic reductive systems to maintain cell viability (Mou et al., 2019). The solute carrier family 7 member 11 (SLC7A11) - glutathione peroxidase 4 (GPX4) axis was the first identified pathway involved in ferroptosis, with glutathione (GSH) acting as a reducing agent to neutralize hyperoxidized lipids (Chen et al., 2021, Koppula et al., 2021). Recently, ferroptosis suppressor protein 1 (FSP1) has emerged as an alternative counter-ferroptosis protein, working in parallel with GPX4 (Bersuker et al., 2019, Doll et al., 2019). FSP1 functions as a reductase of Coenzyme Q (CoQ), thereby scavenging the reactive oxygen species derived from peroxidized lipids and protecting cells from ferroptotic stress.

Previous studies have shown that inducing ferroptosis can enhance the sensitivity of tumors to radiotherapy (Ye et al., 2020, Zheng and Conrad, 2020), and targeting ferroptosis is an effective strategy to overcome radioresistance (Yang et al., 2022a, Chen et al., 2022), However, the association between ferroptosis and radioresistance remains unclear. In this study, we established three acquired radioresistant NSCLC cell lines by gradient radiation exposure. Surprisingly, FSP1 inhibition, rather than GPX4 inhibition, effectively reversed radioresistance, which is driven by enhanced CoQ synthesis and decreased GSH synthesis during radiotherapy. In addition, the inhibition of CoQ by statin provoked IR induced ferroptosis. This finding enlightens a promising therapeutic strategy of targeting FSP1-CoQ pathway to reverse radioresistance in NSCLC.