Antitumor effects of monoclonal antibodies affecting dimerization between ErbB family members

表皮生长因子受体（EGFR）与其他ErbB家族成员ErbB 2、ErbB 3和ErbB 4形成同源二聚体和异源二聚体。ErbB家族成员在细胞生长和细胞存活中起着重要作用，并且它们是癌症的单克隆抗体（mAb）治疗的靶点，因为不适当的ErbB活性已经涉及几种人类癌细胞。然而，我们对mAb对肿瘤生长的药理学作用的理解并不充分。在这项研究中，我们研究了我们的抗EGFR的mAb（命名为B4 G7）对人非小细胞肺癌细胞系（PC-9、PC 14和A549）以及A431人表皮样癌细胞生长的影响。B4 G7，而不是EGF，对所有这些人癌细胞系表现出生长刺激作用。EGFR酪氨酸激酶特异性抑制剂AG 1478对B4 G7刺激的细胞生长没有影响。因此，B4 G7的生长刺激似乎不依赖于EGFR酪氨酸激酶的活化。与抗ErbB 3抗体的免疫沉淀显示，B4 G7，而不是EGF，刺激ErbB 2和ErbB 3之间的异源二聚化。ErbB 3在B4 G7的存在下被酪氨酸磷酸化，但在EGF的存在下不被酪氨酸磷酸化。此外，ErbB 2的特异性抑制剂AG 825抑制ErbB 3的磷酸化和B4 G7诱导的细胞生长增加，表明ErbB 2/ErbB 3二聚体在B4 G7处理的细胞中具有促进细胞生长的功能。这些研究结果表明，EGFR以外的ErbB家族成员影响EGFR导向的抗体治疗癌症的敏感性。检测癌细胞中ErbB 2和ErbB 3的表达水平对于优化EGFR家族定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.