Acquisition of bortezomib (BTZ) resistant JY cells and proteasome inhibitor cross-resistance profile. (A) Dose–response curve for BTZ-induced growth inhibition of JY/WT and BTZ-resistant variants JY/35BTZ and JY/100BTZ following 72 hours exposure to BTZ. Results represent the mean ± SD of 6 separate experiments. (B) Resistance factor for BTZ and cross- resistance factors to ONX 0914 (immunoproteasome inhibitor), MG-132, and carfilzomib. Cell growth inhibition was assessed after 72 hours incubation with PIs. (Cross) resistance factor represents the ratio of drug concentration required to inhibit cell growth of BTZ-resistant JY cells by 50% over JY/WT cells. Results are the mean ± SD of 3–5 separate experiments.