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

Cytotoxic strategies which are directed to tumor-associated antigens might be most beneficial for cancer patients with minimal tumor load such as in a n adjuvant setting after initial therapy, We have recently described a high ly potent single chain antibody-toxin, scFv(14E1)-ETA, which consists of th e variable domains of the antibody 14E1 genetically fused to a truncated fo rm of Pseudomonas exotoxin A. ScFv(14E1)-ETA specifically recognizes the hu man epidermal growth factor receptor (EGFR) and the oncogenically activated receptor variant EGFRvIII, which have been implicated in the development o f various human malignancies. Here we have investigated the antimetastatic activity of bacterially expressed scFv(14E1)-ETA and its disulfide-stabiliz ed derivative ds-scFv(14E1)-ETA in a novel model for disseminated disease w hich is based on murine renal carcinoma cells subsequently transfected with the E. coli P-galactosidase gene, and human full-length or variant EGFR cD NAs, 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 stainin g, Systemic treatment of mice with scFv(14E1)-ETA resulted in the complete suppression of Renca-lacZ/EGFRvIII metastasis formation and drastically red uced the number of pulmonary Renca-lacZ/EGFR tumor nodules, The ds-scFv(14E 1)-ETA derivative where the antibody variable regions are connected by an a rtificial disulfide bond displayed improved thermal stability at physiologi cal temperature but due to reduced cytotoxic activity was less potent than the original scFv(14E1)-ETA in metastasis suppression.