Cytotoxic properties of DAB486EGF and DAB389EGF, epidermal growth factor (EGF) receptor-targeted fusion toxins.

Abstract

Elevated expression of the receptor for epidermal growth factor (EGF) is a characteristic of several malignancies including those of the breast, bladder, prostate, lung, and neuroglia.To therapeutically target the cytotoxic action of diphtheria toxin to EGF receptorexpressing tumor cells, we have constructed a hybrid gene in which the sequences for the binding domain of diphtheria toxin have been replaced by those for human EGF.The resulting fusion toxins, DAB4saEGF and DAB~E~EGF, bind specifically to the EGF receptor and inhibit protein synthesis in a variety of EGF receptor expressing human tumor cell lines with an IC60 as low as 0.1 PM.Comparisons of DAB4ssEGF and DAB3,,EGF showed that DAB3,,EGF was consistently 10-to 100fold more cytotoxic than DAB4seEGF.Like diphtheria toxin, the cytotoxic action of DAB3,sEGF results from ADP-ribosylation of elongation factor-2 and is sensitive to the action of chloroquine.Studies of the kinetics of cellular intoxication showed that a 16-min exposure of EGF receptor-expressing A43 1 cells to DAB38sEGF results in complete protein synthesis inhibition within 4 h.Furthermore, inhibition of protein synthesis results in elimination of human tumor cell colonies.These findings show that DABsB9EGF is a potential therapeutic agent for a wide variety of EGF receptor-expressing solid tumors.Epidermal growth factor (EGF)' is a 53-amino acid single chain polypeptide which stimulates cellular proliferation upon interaction with specific receptors expressed on cells of epidermal and mesenchymal origin (1).The EGF receptor is a glycoprotein composed of an extracellular ligand binding domain, a membrane-spanning region, and an inner domain possessing intrinsic protein tyrosine kinase activity.It is encoded by the human counterpart of the avian protooncogene c-erbB and the internal and transmembrane domains share extensive homology with the v-erbB oncogene (2).Transforming growth factor-a (TGF-a), a molecule structurally related to EGF and secreted by various tumor tissues, is also a ligand for the EGF receptor (3).Tumor tissue expression of EGF receptors, EGF, and TGF-a suggests that an autocrine growth