EGF and prostate cancer: Addition of 1 μg/ml of the endosomal escape enhancer SO1861 led to a 4- to 150-fold enhanced cytotoxicity of EGF-PE24mut (Table 2) and even to a more than 26.2- to 6,966-fold enhanced cytotoxicity of EGF-PE24mutΔREDLK in the prostate cancer cell lines (Table 2, Fig. 2A).