a, Cells were treated with vehicle or 50 μM BSO for 48 h prior to treatment with cisplatin (CDDP) for 48 h, in the presence or absence of 50 μM EUK-134 or 1 mM N-acetyl cysteine (NAC). Cell viability was measured using a propidium iodide-based plate reader assay (n = 3 biologically independent replicates (Supplementary Table 1)). b, c, T47D (b) or MDA-MB-231 (c) xenografts were grown in nude mice treated with vehicle (T47D: n = 5, MDA-MB-231: n = 5), BSO (T47D: n = 4, MDA-MB-231: n = 4), CDDP (T47D: n = 4, MDA-MB-231: n = 4), or a combination of one week of BSO pre-treatment followed by CDDP (T47D: n = 5, MDA-MB-231: n = 7) (n represents number of biologically independent tumors (Supplementary Table 1)). All error bars represent s.e.m. *P<0.05, **P<0.01, ***P < 0.001 by a two-sided Student’s t-test.