Cystine depletion causes cell death via ferroptosis. (A) Relative cell counts at day 1 of HL60, MOLM13, and K562 cells after growth with or without cystine, or without cystine but in the presence of the ferroptosis inhibitor ferrostatin (Fer-1; 0.5-50 μM). (B) Experiment as in panel A, but the effects on viability are shown. (C) Relative cell counts at day 1 of HL60, MOLM13, and K562 cells upon exposure to the GPX4 inhibitors RSL3 or ML210. Experiment performed in the presence of cystine. (D) Experiment as in panel C, but the effects on viability are shown. (E-F) Experiments as in panels C and D on K562 cells, but the readout was at day 2. Experiments performed in the presence of cystine. Statistical analysis by ordinary 1-way ANOVA; ∗P < .05, ∗∗P < .01, ∗∗∗P < .001, ∗∗∗∗P < .0001. Ctrl, control; Rel., relative.