Expression of an oncogenic mutant EGF receptor markedly increases the sensitivity of cells to an EGF-receptor-specific antibody-toxin.
EGFRvIII is a ligand-independent, constitutively active variant of the epidermal growth factor receptor (EGFR) that is specifically expressed in gliomas and various other human malignancies and has been proposed as a target for directed tumor therapy. We have recently constructed a highly potent single-chain antibody-toxin, scFv(14E1)-ETA, which consists of the variable domains of the antibody 14E1 specific for human full-length EGFR genetically fused to a truncated form of Pseudomonas exotoxin A. We demonstrate here binding of 14E1 antibody to both full-length and variant EGFR. In contrast to a recombinant toxin containing transforming growth factor-alpha (TGF-alpha) as a cell targeting domain, scFv(14E1)-ETA was highly active on cells expressing EGFRvIII. Surprisingly, scFv(14E1)-ETA displayed cell killing activity on EGFRvIII-expressing cells that was up to 100-fold higher than on control cells expressing full-length EGFR. No differences in the binding affinities of scFv(14E1)-ETA to full-length EGFR or EGFRvIII were observed, suggesting that events downstream of immunotoxin binding are responsible for the increased sensitivity of EGFRvIII-expressing cells. This might have implications for the development of therapeutic reagents simultaneously targeting different forms of the EGFR.
Schmidt
M
M
Institute for Experimental Cancer Research, Tumor Biology Center, Freiburg, Germany.
Reiser
P
P
Hills
D
D
Gullick
W J
WJ
Wels
W
W
D016475:3T3 Cells; D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000276:immunology*; D000918:Antibody Specificity; D002470:Cell Survival; D066246:ErbB Receptors / Q000276:immunology*; D006801:Humans; D000922:Immunotoxins / Q000633:toxicity*; D051379:Mice; D011994:Recombinant Proteins; D014162:Transfection
D000911:Antibodies, Monoclonal; D000922:Immunotoxins; D011994:Recombinant Proteins; D066246:ErbB Receptors