Vera Skafar, Izadora de Souza, Biplab Ghosh, Ancély Ferreira dos Santos, Florêncio Porto Freitas, Zhiyi Chen, Shibo Sun, Merce Donate Castillo, Palina Nepachalovich, Lars Seufert, Sebastian Bothe, Juliane Tschuck, Apoorva Mathur, Ariane Nunes-Alves, Jannik Buhr, Camilo Andres Aponte-Santamaria, Werner Schmitz, Matthias Mack, Martin Eilers, Ralf C. Bargou, Milena Chaufan, Mayher Kaur, Mario Palma, Jessalyn M. Ubellacker, Ulrich Elling, Hellmut G. Augustin, Kamyar Hadian, Svenja Meierjohann, Bettina Proneth, Marcus Conrad, M. Fedorova, Hamed Alborzinia, José Pedro Friedmann Ângeli
Abstract Membrane protection against oxidative insults is achieved by the concerted action of glutathione peroxidase 4 (GPX4) and endogenous lipophilic antioxidants such as ubiquinone and vitamin E. More recently, ferroptosis suppressor protein 1 (FSP1) was identified as a critical ferroptosis inhibitor, acting via the regeneration of membrane-embedded antioxidants. Yet, regulators of FSP1 are largely uncharacterized, and their identification is essential for understanding the mechanisms buffering phospholipid peroxidation and ferroptosis. Here we report a focused CRISPR–Cas9 screen to uncover factors influencing FSP1 function, identifying riboflavin (vitamin B 2 ) as a modulator of ferroptosis sensitivity. We demonstrate that riboflavin supports FSP1 stability and the recycling of lipid-soluble antioxidants, thereby mitigating phospholipid peroxidation. Furthermore, we show that the riboflavin antimetabolite roseoflavin markedly impairs FSP1 function and sensitizes cancer cells to ferroptosis. Our findings provide a rational strategy to modulate the FSP1–antioxidant recycling pathway and underscore the therapeutic potential of targeting riboflavin metabolism, with implications for understanding the interaction of nutrients, as well as their contributions to a cell’s antioxidant capacity.