GPX4-IN-3 (26a) is a potent glutathione peroxidase 4 (GPX4) inhibitor as a selective ferroptosis inducer. GPX4-IN-3 (26a) exhibits 71.7% inhibition for GPX4 with 1 μM. In Vitro GPX4-IN-3 (26a) exhibits IC 50 values of 0.78 μM, 6.9 μM, 0.15 μM and 4.73 μM in 4T1, MCF-7, HT1080 and HT1080 (with Fer-1) cells, respectively. ?\nGPX4-IN-3 (26a) exhibits outstanding GPX4 inhibitory activity with a percent inhibition up to 71.7% at 1.0 μM compared to 45.9% of RSL-3. ?\nGPX4-IN-3 (26a) could significantly induce lipid peroxide (LPO) increase and effectively induce ferroptosis with satisfactory selectivity. ?\nGPX4-IN-3 (26a) is more likely to induce ferroptosis through the accumulation of intracellular peroxides via inhibiting GPX4 activity. ?\nGPX4-IN-3 (26a) significantly increased the level of ROS in 4T1 cells, which could also be reversed by Ferrostatin-1 (fer-1). MCE has not independently confirmed the accuracy of these methods. They are for reference only. In Vivo GPX4-IN-3 (26a) exertes antitumor activity and good biological safety in vivo . MCE has not independently confirmed the accuracy of these methods. They are for reference only. Animal Model: Mouse 4T1 xenograft model . Dosage: 15 and 30 mg/kg. Administration: Intravenous injection, every two days for a total of five times. Result: Significantly suppress tumor growth with a tumor growth inhibition (TGI) value of 33.2 and 55.1% at 15 and 30 mg/kg, respectively. Form:Solid