Antitumor effects of monoclonal antibodies affecting dimerization between ErbB family members

表皮生长因子受体(EGFR)与ErbB家族其他成员ErbB2、ErbB3和ErbB4形成同源二聚体和异源二聚体。ErbB家族成员在细胞生长和生存中起着重要的作用，也是肿瘤单抗治疗的靶点，因为在一些人类癌细胞中发现了不适当的ErbB活性。然而，我们对单抗在肿瘤生长中的药理作用的了解还不够深入。在这项研究中，我们检测了我们的抗EGFR单抗B4G7对人非小细胞肺癌细胞系(PC-9、PC14和A549)以及对A431人表皮样癌细胞生长的影响。B4G7，而不是EGF，对所有这些人类癌细胞株都显示出促进生长的作用。EGFR酪氨酸激酶的特异性抑制剂AG1478不影响B4G7刺激的细胞生长。因此，B4G7的生长刺激作用似乎不依赖于EGFR酪氨酸激酶的激活。抗ErbB3抗体的免疫沉淀显示，B4G7刺激ErbB2和ErbB3之间的异二聚化，而不是EGF。在B4G7存在下，erbB3发生酪氨酸磷酸化，而在EGF存在下不发生酪氨酸磷酸化。此外，ErbB2的特异性抑制剂AG825可抑制ErbB3和B4G7诱导的细胞生长的磷酸化，表明ErbB2/ErbB3二聚体在B4G7处理的细胞中具有促进细胞生长的作用。这些发现表明，除EGFR外，ErbB家族成员会影响对EGFR导向的抗体治疗癌症的敏感性。检测ErbB2和ErbB3在癌细胞中的表达水平对于优化EGFR家族导向的癌症治疗具有重要意义。

Epidermal growth factor receptor (EGFR) forms homodimers and heterodimers with the other ErbB family members, ErbB2, ErbB3, and ErbB4. ErbB family members play fundamental roles in cell growth and cell survival, and they are targets for monoclonal antibody (mAb) therapy of cancer, because inappropriate ErbB activity has been implicated in several human cancer cells. However, our understanding of the pharmacological effects of mAb on tumor growth is not well developed. In this study, we examined effects of our mAb against EGFR, designated as B4G7, on growth of human non-small cell lung cancer cell lines (PC-9, PC14, and A549) as well as on that of A431 human epidermoid carcinoma cells. B4G7, but not EGF, exhibited growth-stimulatory effect upon all of these human cancer cell lines. The B4G7-stimulated cell growth was not affected by AG1478, a specific inhibitor of EGFR tyrosine kinase. Thus, the growth stimulation by B4G7 appears to be independent of the activation of EGFR tyrosine kinase. Immunoprecipitation with anti-ErbB3 antibody revealed that B4G7, but not EGF, stimulated heterodimerization between ErbB2 and ErbB3. ErbB3 was tyrosine-phosphorylated in the presence of B4G7 but not in the presence of EGF. Further, the phosphorylation of ErbB3 and B4G7-induced increase in cell growth were inhibited by AG825, a specific inhibitor of ErbB2, indicating that the ErbB2/ErbB3 dimer functions to promote cell growth in B4G7-treated cells. These findings show that ErbB family members other than EGFR affect sensitivity to EGFR-directed antibody therapies for cancer. Examination of expression levels of ErbB2 and ErbB3 in cancer cells is of importance in optimizing EGFR family-directed therapies for cancer.