Inhibition of cytotoxic activity of TfR-lytic hybrid peptide by anti-TfR antibody and knockdown using siRNA. (A) T47D and PE cells were incubated with increasing concentrations of anti-TfR monoclonal antibody (TfR-Ab) or non-specific mouse IgG1 (isotype control) 3 h prior to TfR-lytic peptide treatment at 5 μM and 55 μM, respectively. (B) T47D or MDA-MB-231 cells were transfected with TfR-siRNA or scramble-siRNA, and 4 days after transfection, the levels of target protein in the cells were confirmed by flow cytometry analysis (inset graph). T47D and MDA-MB-231 cells were treated with TfR-lytic at 5 μM and 7.5 μM respectively. Inhibition rate was assessed using WST-8 reagent. Data are represented by means ± SD (bars) from triplicate determinations. Significance levels compared to the respective scramble-siRNA transfection: *, P < 0.05.