5-AZA-2'-DEOXYCYTIDINE INDUCES GROWTH-INHIBITION AND UP-REGULATION OFEPIDERMAL GROWTH-FACTOR RECEPTOR ON HUMAN EPITHELIAL CANCER-CELLS

Background. The epidermal growth factor (EGF-R) receptor is an importa nt growth regulator of epithelial cancer cells, and is presently consi dered a tumor-associated antigen (TAA) which is overexpressed by sever al human cancers and barely detectable in most normal tissues. Since T AA density at the tumor cell surface is a critical factor regulating t he efficiency of immunotargeting procedures, a therapeutic advantage m ay derive from the pharmacologic enhancement of membrane expression of such antigens on tumor cells. Materials and methods: Utilizing a pane l of different human cancer cell lines of epithelial derivation, we ha ve investigated in the in vitro effects of 5-aza-2-deoxycytidine (5aza CdR), an antineoplastic agent able to induce gene activation and pheno typic modulation, on the surface expression of EGF-R by tumor cells. R esults: 5azaCdR (10-1000 nM) induced growth inhibition, in the absence of acute cell kill, on KB (human oropharyngeal carcinoma), LoVo and t he drug-resistant clone LoVo-Dx (colon carcinoma) and A549 (lung adeno carcinoma) cell lines, along with a significant enhancement of EGF-R e xpression at the tumor cell surface. A single 24 h pulse of 5azaCdR, f ollowed by 96 h of culture in drug-free medium, induced 50% growth inh ibition on KB cells at a concentration (IC50) of 500 nM, on A549 (IC50 = 490 nM), LoVo (IC50 = 400 nm) and LoVo-Dx (IC50 = 100 nM) cell line s. Under these conditions the specific binding of I-125-EGF was signif icantly upregulated at the surface of growth-inhibited cancer cells. S catchard analysis of EGF-binding data revealed no changes in the Kd of EGF-R for its ligand in 5azaCdR-treated tumor cells and demonstrated a significant increase in the number of both the high- and low-affinit y EGF-binding sites on KB cells, while only one class of EGF-binding s ite was detectable on A549, LoVo and LoVo-Dx tumor cell lines before a nd after exposure to 5azaCdR. The EGF-R upregulation induced by 5azaCd R was paralleled by the increased binding of the anti-EGF-R monoclonal antibody (MAb) 108.1 on the surface of cancer cells. Finally, the rat e of endocytosis of the anti-EGF-R MAb by KB cells was not modified by drug treatment, indicating that exposure to 5azaCdR does not hamper M Ab internalization by the tumor cells. This latter represents an essen tial process for the cytotoxic effects of immunoconjugate drugs or tox ins. Conclusions: We suggest a role for 5azaCdR in enhancing the effic acy of therapeutic approaches involving the use of anti-EGF-R immunoco njugated for the imaging and the treatment of human epithelial neoplas ias.