5 x 10⁶ NB4 cells were subcutaneously injected into the flank of 6-7-week-old female nude mice. The tumor number, body weight, and tumor volume were measured every other day. Tumor volumes were estimated using the following formula: tumor volume = (length x width2)/2. When tumor volumes reached 100-200 mm³, the mice were randomly divided into solvent control, RSL3, GSK3368715, or RSL3 + GSK3368715 combination groups (six mice per group). Specifically, for the RSL3 group, mice received intraperitoneal injections of RSL3 at 50 mg/kg 2 days apart. In the GSK3368715 group, GSK3368715 was intraperitoneally injected into mice at a dose of 75 mg/kg for 2 consecutive days per week. For the group that received RSL3 + GSK3368715 combination treatment, GSK3368715 (75 mg/kg) was administered by intraperitoneal injection for the first 2 days. Immediately thereafter, the mice received an intraperitoneal injection of RSL3 (50 mg/kg) 2 days apart. After 1 day of rest, the cycle was repeated until the end of the study on Day 21. Tumor volumes and body weights of the mice were measured and recorded every other day.

Mice were housed in a dedicated laboratory animal facility with 12-h light:dark cycle, at 70F+/-2 degrees, and 40-70% relative humidity. Orthotopic xenografts were generated by implanting 2.5 million MDA-MB-231 cells in 100 uL phosphate-buffered saline (PBS) mixed with 100 uL growth factor-reduced Matrigel (Corning) bilaterally into the fourth inguinal fat pad of four- to six-week-old female NOD.