Cell growth. The L-clone (dox+ and dox-) and HeLa cells transfected with the L-siRNA were grown in absence or presence of 0.1 mM ferric ammonium citrate (-/+FAC) for 24 hours. (A) Cell proliferation was evaluated by MTT assay (104 cells); the values of dox- cells were statistically different from those of dox+ cells (P < .001, n = 24). (B) Cell proliferation was evaluated by 3H-thymidine incorporation analysis (4 × 104 cells); the values of dox- cells were statistically different from control (P < .001, n = 12). (C) MTT assay of cells transiently transfected with H-siRNA, L-siRNA, and the 2 together. Data are the means ± SD of 3 independent experiments.