TARGETED INHIBITION OF TUMOR-CELL GROWTH BY RECOMBINANT HEREGULIN-TOXIN FUSION PROTEINS

Fusion of functional domains of proteins by in vitro recombination of gene fragments can be used to generate novel anti-tumor agents. The co mbination of tumor-cell-recognition functions and toxic functions resu lts in cytotoxic molecules with a high specificity for tumor cells. Hu man adenocarcinomas are frequently characterized by over-expression of members of the epidermal-growth-factor (EGF) receptor family (ErbB-1, 2, 3 and 4), when compared with normal cells. These tumors are partic ularly suited to treatment with recombinant toxins. The human hereguli ns (HRG) and their rat counterparts (neu differentiation factor, NDF) have been identified as ligands for these receptors. Two chimeric here gulin-toxin fusions consisting of the EGF-like receptor recognition do main of the heregulin isoforms HRG alpha and HRG beta(1), and the doma ins II, Ib and III of the Pseudomonas exotoxin A (ETA) were constructe d. HRG beta(1)-ETA is highly cytotoxic for the mammary carcinoma cell lines SK-BR-3 and MDA-MB-453. HRG alpha-ETA was less active than HRG b eta(1)-ETA. The killing activity of the recombinant toxins correlated with the expression levels of ErbB-3 and/or ErbB-4 in the cell lines s tudied. High expression of ErbB-2 is not sufficient to confer sensitiv ity towards the HRG-ETA. Treatment of mice with 0.4 mg/kg/day of HRG b eta(1)-ETA caused growth retardation of transplanted human breast tumo r cells. Higher levels of HRG beta(1)-ETA administration resulted in a cute hemorrhagic necrosis of the liver. (C) 1995 Wiley-Liss, Inc.