title: Effects of anti-epidermal growth factor (EGF) receptor antibodies and an anti-EGF receptor recombinant-ricin A chain immunoconjugate on growth of human cells.
abstract: The effects of antiepidermal growth factor (EGF) receptor monoclonal antibodies (MAbs) 528 and 225 and a 528-ricin A conjugate on the growth of normal and malignant human cells were tested in vitro. Malignant human cell lines with EGF receptor numbers ranging from 0 to 4 X 10(5) receptors/cell, human fetal fibroblasts, and normal marrow granulocyte/macrophage progenitors (CFU-gm) showed no effect when grown with 10(-12) M to 10(-7) M MAb 225 or 528. MAbs 225 and 528 and EGF also had no effect on the ability of marrow stromal cells to maintain CFU-gm viability in long-term marrow cultures. Reversible growth inhibition of A431 epidermoid and MDA-468 breast carcinoma cells with 2 and 3 X 10(6) EGF receptors/cell, respectively, was observed with both antibodies and with 10(-8) M EGF. In contrast, an immunoconjugate prepared with MAb 528 and recombinant ricin A chain (528-rRA) showed dose-dependent killing over a concentration range of 10(-12) M to 10(-8) M against cells with greater than or equal to 1.2 X 10(5) EGF receptors/cell [concentration that causes 50% inhibition of growth (IC50) values, approximately 10(-12) M to 10(-10) M]. Human fetal fibroblasts (5.6 X 10(4) EGF receptors/cell), melanoma cells without detectable EGF receptors, and human CFU-gm showed IC50 values of greater than 10(-8) M. Killing of KB epidermoid carcinoma cells and 547 ovarian carcinoma cells with 4 and 1.2 X 10(5) EGF receptors/cell by 10(-10) or 10(-11) M 528-rRA was time dependent, but cytotoxicity to 547 cells was not complete even with 48 hours of immunotoxin treatment. Cytotoxicity of 528-rRA was not enhanced by chloroquine or verapamil. In vitro, anti-EGF receptor MAbs cause reversible antiproliferative effects only against malignant cell lines with amplified EGF receptor expression. In contrast, 528-rRA shows potent, specific toxicity to cells with greater than 50,000 EGF receptors/cell. However, kinetics of cell killing with 528-rRA are protracted, suggesting that prolonged exposure may be required for in vivo antitumor effects.
authors.affiliation: Department of Medicine, University of California, San Diego.
authors.forename: R
authors.initials: R
authors.lastname: Taetle
authors.forename: J M
authors.initials: JM
authors.lastname: Honeysett
authors.forename: L L
authors.initials: LL
authors.lastname: Houston
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology*; D002470:Cell Survival / Q000187:drug effects; D066246:ErbB Receptors / Q000032:analysis / Q000276:immunology*; D006412:Hematopoietic Stem Cells / Q000187:drug effects; D006801:Humans; D000922:Immunotoxins / Q000494:pharmacology*; D012276:Ricin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000187:drug effects
chemical_list: D000911:Antibodies, Monoclonal; D000922:Immunotoxins; D012276:Ricin; D066246:ErbB Receptors