Structure-activity relationship (SAR) studies of the copper mixtures with 8-OHQ analogs #11, #12 and #13. (A) MDA-MB-231 cells were treated with 10 μM of the copper mixtures of 8-OHQ analogs #11, #12 or #13 for 24 h, followed by MTT assay. The copper mixtures with 8-OHQ and its analogs #10 and #14 were used as controls. DMSO was used as a solvent control. (B) MDA-MB-231 cells treated as indicated were harvested and lysed. Cell extracts were then used for measurement of the proteasomal chymotrypsin (CT)-like activity (B), Western blot analysis using specific antibodies to ubiquitin, IκB-α, Bax, PARP and ß-actin (C), and assessment of apoptotic morphological changes in the MDA-MB-231 cells, visualized by phase-contrast imaging (D).