ABCC1 RNA interference and induction in KMH2 cells. (A) ABCC1 mRNA is overexpressed in KMH2 compared with CD77⁺ centroblasts. (B) siRNA silencing shows effective and continuing knockdown of ABCC1 in KMH2 before treatment and after 24 hours of treatment. (C) Proliferation assay (WST-1) under doxorubicin treatment (0.5 μg/mL) shows increased toxicity in ABCC1 siRNA-silenced KMH2 cells compared with nonsilencing controls (each normalized to proliferation of cells not treated with doxorubicin). (D) Proliferation of siRNA-silenced KMH2 cells on day 3 is significantly decreased by the use of different doxorubicin doses (each normalized to proliferation of cells not treated with doxorubicin). (E) ABCC1 expression in KMH2 is early induced after 2 days of doxorubicin treatment. (F) Sublethal doxorubicin doses (0.25 μg/mL) produce resistant KMH2 clones highly overexpressing ABCC1 compared with doxorubicin untreated controls in long-term culture.