Inhibition of signaling from Type 1 receptor tyrosine kinases via intracellular expression of single-chain antibodies.

Members of the Type I/epidermal growth factor receptor (EGFR)-related family of receptor tyrosine kinases have been implicated in the development of human cancer. We have taken a novel approach using the intracellular expression of single chain antibodies (scFv) to specifically inhibit the in vivo action of these receptors. A scFv is a recombinant protein analogous to an Fv domain which is the smallest high affinity binding portion of an antibody. We report here on the expression in mammalian cells of cDNAs encoding scFv-225 and scFv-FRP5 directed against the extracellular domain of, respectively, human EGFR and human ErbB-2. The scFvs were provided with a signal peptide which directs them to the secretory pathway of the cell. scFv-225, which competes with EGF for binding, functions in an autocrine fashion to inhibit EGF-dependent cell growth. scFv-FRP5 was also provided with an endoplasmic reticulum (ER) retention signal and inactivates ErbB-2 in an intracrine fashion, by preventing its appearance on the cell surface.