Characterization of an anti-p185HER2 monoclonal antibody that stimulates receptor function and inhibits tumor cell growth.

摘要: The HER2 protooncogene encodes a growth factor receptor-like transmembrane protein tyrosine kinase (p185HER2) whose ligand remains to be fully characterized. overexpression of p185HER2 is implicated in aggressive forms breast and ovarian cancers. role malignancy, as well its cell surface localization, makes it an attractive target for therapeutic monoclonal antibodies. In this report we have studied the modulation function with 2 antibodies, termed 4D5 6E9, which bind extracellular domain p185HER2. inhibited proliferation overexpressing SK-BR-3 human carcinoma cells (ED50 approximately 1 nM) but did not inhibit cultured MCF7 cells, low expressors Monoclonal antibody 6E9 does either line. Antibody binding studies revealed populations molecules on cells: one high abundance (approximately x 10(6) sites/cell) recognized by (Kd 6 other (2 10(4) 0.1 nM). 4D5, agonistic manner, downregulated p185HER2, was internalized, stimulated phosphorylation intact cells. Phosphoamino acid analysis derived from incubated demonstrated increased tyrosine, serine threonine phosphorylation. short term (5 min) exposure inositol lipid hydrolysis evidenced intracellular levels polyphosphates (InsP) sn-1,2-diacylglycerol (sn-1,2-DAG). On longer (24 h) appeared downregulate signalling pathway since InsP sn-1,2-DAG decreased 30 40%. proliferation, stimulate receptor phosphorylation, or second messenger pathway. Despite these properties, inhibitor at all concentrations tested (0.7 70 pM). data suggest that partial weak agonist thus may mimicking ligand-like downregulation.