Silencing of GCS by MBO-asGCS Represses MDR1 Expression and Sensitizes Drug-Resistant Cancer Cells. (A) P-gp and GCS in drug-resistant cancer cells. Cells were cultured in growth medium for 24 hr, and then treated with vehicle or MBO-asGCS (50 nM) for an additional 48 hr. Equal amounts of protein (50 μg/lane) were resolved by 4-20% gradient SDS-PAGE and immunoblotted with anti-GCS and anti-P-gp antibodies. GAPDH was used as endpoint control, and GCS/GAPDH or P-gp/GAPDH represents optical densities of the bands. -, vehicle (Lipofectamine 2000); +, MBO-asGCS (50 nM). *, p < 0.001 compared with vehicle treatment. (B) Cell response to doxorubicin. After pretreatment of MBO-asGCS (50 nM) or vehicle, cells were incubated with 5% FBS medium at the presence of doxorubicin for an additional 72 hr. *, p < 0.001 compared with vehicle.