Clonogenic assay and inhibitory effect of CNF1 on GL261 cells proliferation. (A) Representative images of a colony assay of cells treated with vehicle (control) and increasing concentrations of CNF1. (B) Quantification of the number of colonies in the clonogenic assay for each CNF1 concentration. IC50 of the CNF1 toxin is 0.47 nM. All data represent means ± SEM (n = 3).