INTRACELLULAR EXPRESSION OF A SINGLE-CHAIN ANTIBODY-DIRECTED TO THE EGFR LEADS TO GROWTH-INHIBITION OF TUMOR-CELLS

A gene encoding a single-chain antibody (scFv) which specifically bind s the epidermal growth factor receptor (EGFR) has been constructed fro m hybridoma cells producing the R1 monoclonal antibody. The gene, desi gnated scFv-R1R, was introduced into EGFR transformed NIH3T3 cells via retroviral infection. scFv-R1R was directed to the lumen of the endop lasmic reticulum (ER) where it bound the extracellular domain of the r eceptor inhibiting its appearance on the plasma membrane. In these cel ls, EGF induced tyrosine phosphorylation of the EGFR and several subst rates was greatly reduced. Furthermore, intracellular retention of EGF R caused a partial inhibition in the transformed growth of the cells. Intracellular expression of receptor tyrosine kinase directed scFvs is a novel approach for affecting tumor cell growth. We have recently sh own that scFv-5R directed to ErbB2, another member of the ErbB family, blocks the anchorage independent growth of ErbB2 transformed cells. I n order to examine the effects of scFv-R1R and scFv-5R on the long-ter m growth of tumor cells overexpressing either EGFR or ErbB2, retroviru ses encoding the two scFvs were used to infect various human tumor cel l lines. Intracellular expression of the scFvs resulted in a marked in hibition of stable colony formation in some of the cell lines. In gene ral, inhibition was observed when overexpressed receptor was targeted. However, in some cases expression of both scFvs was incompatible with long term cell growth suggesting that heterodimers of ErbB2 and EGFR are essential for the growth of some human tumor cell lines.