The plasma membrane is permeable to TfR-lytic hybrid peptide, allowing rapid killing of cancer cells: (A) T47D, SKBR3, U251, and HuCCT1 cells were treated with 10 μM of TfR-lytic hybrid peptide (black columns) or 10 μM of lytic peptide (white columns) for 0-24 hours, and the cells were analyzed for cell viability using WST-8 reagent. The results are represented as means ± SD (bars) from triplicate determinations. (B) Permeabilization of the cell membrane by TfR-lytic hybrid peptide in T47D breast cancer cells. Cells were observed in calcein solution 0, 5, 10, and 15 min after addition of TfR-lytic peptide (10 μM). Arrows indicate penetrated cells and arrowheads indicate a change in shape of the cell membrane by TfR-lytic peptide.