Cytotoxicity of rGel-based fusion toxins. A. In vitro cytotoxicity of various rGel-based series fusion toxins against 2008 cells (solid upright triangle, rGel; solid up-side-down triangle, CPE-G4S-rGel; solid circle, R9-rGel; solid diamond, CPE-R9-rGel; solid sqaure, E9-G4S-R9-rGel; and ×, CPE-E9-G4S-R9-rGel). B. Enhancement of the cytotoxicity of CPE-E9-G4S-R9-rGel to 2008 cells by the endosomolytic reagent chloroquine. Cells were treated with 31.25 nM CPE-E9-G4S-R9-rGel for 6 h, washed with complete medium 3 times and subsequently incubated with 50 μM chloroquine for 16 h. Afterwards, the chloroquine-containing medium was also removed and replaced with fresh growth medium after 3 times washing. The cytotoxic effects were determined by CCK-8 assay at 72 h after exposure to CPE-E9-G4S-R9-rGel.