INTRACELLULAR SINGLE-CHAIN ANTIBODY-DIRECTED AGAINST ERBB2 DOWN-REGULATES CELL-SURFACE ERBB2 AND EXHIBITS A SELECTIVE ANTIPROLIFERATIVE EFFECT IN ERBB2 OVEREXPRESSING CANCER CELL-LINES

Overexpression of the tyrosine kinease receptor erbB2 is important in the pathogenesis of a variety of neoplasms. Based on this concept, tar geted anti-cancer strategies have been designed to selectively eradica te erbB2 overexpressing tumor cells. These strategies have employed ei ther monoclonal antibodies or antibody toxin molecules with specificit y for the cell surface erbB2 protein. As an alternative strategy, anti -erbB2 single-chain immunoglobulin (sFv) genes were constructed to dir ect expression of intracellular anti-erbB2 antibodies. Expression of a n endoplasmic reticulum (ER) form of the anti-erbB2 sFv resulted in a profound down-regulation of cell surface erbB2 in an erbB2 overexpress ing ovarian carcinoma cell line. In addition, expression of the intrac ellular antibody resulted in marked inhibition of tumor cell prolifera tion. Whereas stable transfectants expressing the anti-erbB2 sFv could be derived from non-erbB2 overexpressing cancer cell lines, expressio n of the intracellular antibody was incompatible with long-term surviv al of the erbB2 overexpressing tumor cells. The ability to selectively 'knock-out' erbB2 demonstrates that cell surface localization of erbB 2 is essential to its ability to induce aberrant cellular proliferatio n in tumor cells. In addition, the ability to accomplish selective abr ogation of oncogenes by virtue of intracellular antibodies suggests a