Fig. 5: Pharmacological IRE1α inhibition promotes ferroptosis resistance.

A Viabilities of MDA-MB-231 cells co-treated with erastin and two widely used small molecule IRE1α inhibitors (4μ8c and MKC9989). 24 h after starting drug treatment, cell viability was measured by CCK8 assay. Values were normalized to treatment with 0 μM erastin (DMSO) which is set to be 100% viable. B Measurement of cellular GSH levels in MDA-MB-231 cells co-treated with DMSO or IRE1α inhibitor with 2.5 μM erastin for 12 h. The luminescence readings were normalized to cell numbers (/1000 cells). C Quantitative real-time PCR analysis of GCLC expression in MDA-MB-231 cells treated with different concentrations of 4μ8c for 7 h. β-actin was used as a normalization control. D Quantitative real-time PCR analysis of GCLC mRNA level in MDA-MB-231 cells overexpressing luciferase control (Luc) or IRE1α. β-actin was used as normalization control. Insert (top right corner): Western blotting analysis of IRE1α expression in these cells. Luciferase (Luc) was used as an overexpression control and β-actin as a loading control. E Viabilities of MDA-MB-231 cells overexpressing Luc or IRE1α with 2.5 μM erastin treatment. 24 h after starting erastin treatment, cell viability was measured by CCK8 assay. Viability is set as 100% with 0 μM erastin (DMSO). Data are presented as mean ± s.d. in all panels with n = 6 in (A) and (E) except n = 3 for the 30 μM 4μ8c group in (A), and n = 4 in (B, C, and D) except n = 3 for the 30 μM 4μ8c group in (C) and the +IRE1α group in (D). n indicates independent repeats. Unpaired, two-tailed Student’s t tests were performed to calculate the P values for all the statistical analyses. N.S. not significant. Source data are provided as a Source Data file.