Cancer cells rewire their metabolism and rely on endogenous antioxidants to mitigate lethal oxidative damage to lipids. However, the metabolic processes that modulate the response to lipid peroxidation are poorly defined. Using genetic screens, we compared metabolic genes essential for proliferation upon inhibition of cystine uptake or glutathione peroxidase-4 (GPX4). Interestingly, very few genes were commonly required under both conditions, suggesting that cystine limitation and GPX4 inhibition may impair proliferation via distinct mechanisms. Our screens also identify tetrahydrobiopterin (BH4) biosynthesis as an essential metabolic pathway upon GPX4 inhibition. Mechanistically, BH4 is a potent radical-trapping antioxidant that protects lipid membranes from autoxidation, alone and in synergy with vitamin E. Dihydrofolate reductase catalyzes the regeneration of BH4, and its inhibition by methotrexate synergizes with GPX4 inhibition. Altogether, our work identifies the mechanism by which BH4 acts as an endogenous antioxidant and provides a compendium of metabolic modifiers of lipid peroxidation.

癌细胞重新连接其新陈代谢，并依靠内源性抗氧化剂来减轻对脂质的致命氧化损伤。然而，调节脂质过氧化反应的代谢过程尚不清楚。通过基因筛选，我们比较了抑制胱氨酸摄取或谷胱甘肽过氧化物酶 4 (GPX4) 时增殖所必需的代谢基因。有趣的是，这两种条件下通常需要很少的基因，这表明胱氨酸限制和 GPX4 抑制可能通过不同的机制损害增殖。我们的筛选还确定四氢生物蝶呤 (BH4) 生物合成是 GPX4 抑制时的重要代谢途径。从机制上讲，BH4 是一种有效的自由基捕获抗氧化剂，可单独使用或与维生素 E 协同作用，保护脂质膜免于自氧化。二氢叶酸还原酶催化 BH4 的再生，甲氨蝶呤对其的抑制与 GPX4 的抑制具有协同作用。总而言之，我们的工作确定了 BH4 作为内源性抗氧化剂的机制，并提供了脂质过氧化代谢调节剂的概要。