Ferroptosis, a form of regulated cell death that is induced by excessive lipid peroxidation, is a key tumour suppression mechanism^1,2,3,4. Glutathione peroxidase 4 (GPX4)^5,6 and ferroptosis suppressor protein 1 (FSP1)^7,8 constitute two major ferroptosis defence systems. Here we show that treatment of cancer cells with GPX4 inhibitors results in acute depletion of N-carbamoyl-l-aspartate, a pyrimidine biosynthesis intermediate, with concomitant accumulation of uridine. Supplementation with dihydroorotate or orotate—the substrate and product of dihydroorotate dehydrogenase (DHODH)—attenuates or potentiates ferroptosis induced by inhibition of GPX4, respectively, and these effects are particularly pronounced in cancer cells with low expression of GPX4 (GPX4^low). Inactivation of DHODH induces extensive mitochondrial lipid peroxidation and ferroptosis in GPX4^low cancer cells, and synergizes with ferroptosis inducers to induce these effects in GPX4^high cancer cells. Mechanistically, DHODH operates in parallel to mitochondrial GPX4 (but independently of cytosolic GPX4 or FSP1) to inhibit ferroptosis in the mitochondrial inner membrane by reducing ubiquinone to ubiquinol (a radical-trapping antioxidant with anti-ferroptosis activity). The DHODH inhibitor brequinar selectively suppresses GPX4^low tumour growth by inducing ferroptosis, whereas combined treatment with brequinar and sulfasalazine, an FDA-approved drug with ferroptosis-inducing activity, synergistically induces ferroptosis and suppresses GPX4^high tumour growth. Our results identify a DHODH-mediated ferroptosis defence mechanism in mitochondria and suggest a therapeutic strategy of targeting ferroptosis in cancer treatment.

铁死亡是一种由过度脂质过氧化诱导的受调节细胞死亡形式，是一种关键的肿瘤抑制机制^1,2,3,4。谷胱甘肽过氧化物酶 4 (GPX4) ^5,6和铁死亡抑制蛋白 1 (FSP1) ^7,8构成两个主要的铁死亡防御系统。在这里，我们表明用 GPX4 抑制剂治疗癌细胞会导致N-氨基甲酰-l的急性消耗。-天冬氨酸，一种嘧啶生物合成中间体，伴随着尿苷的积累。^{补充二氢乳清酸或乳清酸（二氢乳清酸脱氢酶 (DHODH) 的底物和产物）可分别减弱或增强抑制 GPX4 诱导的铁死亡，这些作用在 GPX4 低表达 (GPX4 low} )的癌细胞中尤其明显。^{DHODH 失活会在 GPX4低}癌细胞中诱导广泛的线粒体脂质过氧化和铁死亡，并与铁死亡诱导剂协同作用在 GPX4^{高癌细胞中诱导这些效应}癌细胞。从机制上讲，DHODH 与线粒体 GPX4 并行运作（但独立于胞质 GPX4 或 FSP1），通过将泛醌还原为泛醇（一种具有抗铁死亡活性的自由基捕获抗氧化剂）来抑制线粒体内膜的铁死亡。DHODH 抑制剂 brequinar 通过诱导铁死亡选择性抑制 GPX4^低肿瘤生长，而 brequinar 和柳氮磺吡啶（FDA 批准的具有铁死亡诱导活性的药物）联合治疗，可协同诱导铁死亡并抑制 GPX4 高肿瘤^生长。我们的结果确定了线粒体中 DHODH 介导的铁死亡防御机制，并提出了在癌症治疗中针对铁死亡的治疗策略。