Suppression of metastasis formation by a recombinant single chain antibody-toxin targeted to full-length and oncogenic variant EGF receptors

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Abstract
Cytotoxic strategies which are directed to tumor-associated antigens might be most beneficial for cancer patients with minimal tumor load such as in an adjuvant setting after initial therapy. We have recently described a highly potent single chain antibody-toxin, scFv(14E1)-ETA, which consists of the variable domains of the antibody 14E1 genetically fused to a truncated form of Pseudomonas exotoxin A. ScFv(14E1)-ETA specifically recognizes the human epidermal growth factor receptor (EGFR) and the oncogenically activated receptor variant EGFRvIII, which have been implicated in the development of various human malignancies. Here we have investigated the antimetastatic activity of bacterially expressed scFv(14E1)-ETA and its disulfide-stabilized derivative ds-scFv(14E1)-ETA in a novel model for disseminated disease which is based on murine renal carcinoma cells subsequently transfected with the E. coli β-galactosidase gene, and human full-length or variant EGFR cDNAs. Intravenous injection of these Renca-lacZ/EGFR and Renca-lacZ/EGFRvIII cells in syngenic Balb/c mice led to the formation of pulmonary metastases which were readily detectable upon excision of the lungs and X-gal staining. Systemic treatment of mice with scFv(14E1)-ETA resulted in the complete suppression of Renca-lacZ/EGFRvIII metastasis formation and drastically reduced the number of pulmonary Renca-lacZ/EGFR tumor nodules. The ds-scFv(14E1)-ETA derivative where the antibody variable regions are connected by an artificial disulfide bond displayed improved thermal stability at physiological temperature but due to reduced cytotoxic activity was less potent than the original scFv(14E1)-ETA in metastasis suppression.