Masui H, Moroyama T, Mendelsohn J
Cancer Res. 1986 Nov;46(11):5592-8.
In previous studies of monoclonal antibodies (mAbs) against the receptor for epidermal growth factor (EGF) both 528 IgG2a and 225 IgG1 were shown to inhibit growth of A431 cell xenografts in athymic mice. The antitumor activities of the two mAbs were similar and, although they differ in their isotypes, they share many properties. The two mAbs bind to EGF receptors with identical affinities, compete with EGF for binding to EGF receptors, down regulate the receptors identically, block EGF-induced activation of tyrosine protein kinase activity to a comparable degree, and block EGF-induced changes in the proliferation of cultured cells. These similarities in physiological effects permit a direct comparison of the mechanisms of action mAbs of the IgG1 and IgG2a isotypes. We examined in vitro cytotoxicity against A431 cells, using 528 IgG2a and 225 IgG1 mAbs. 528 IgG2a, but not 225 IgG1, demonstrated partial complement-mediated cytotoxicity by the 51Cr release assay and by growth inhibition of cultured A431 cells. 528 IgG2a, but not 225 IgG1, was cytotoxic to A431 cells in the presence of activated peritoneal macrophages, as demonstrated by release of incorporated [3H]thymidine. Neither mAb showed any significant cytotoxicity to A431 cells in the presence of nonadherent spleen cells which contain K-cells. The results of in vitro cytotoxicity experiments suggested that the antitumor activity of 528 IgG2a, but not 225 IgG1, could be mediated by macrophages. This was verified by in vivo experiments in which s.c. tumor cell inocula containing activated macrophages showed enhancement of antitumor effects in animals treated i.p. twice weekly for 3 weeks with suboptimal doses of 528 IgG2a. This enhancement was not observed when 225 IgG1 was used with the same procedure. The results of these experiments suggest that immune mechanisms involving activated macrophages or complement could contribute to the antitumor activity of anti-EGF receptor mAb with the IgG2a isotype, but not with the IgG1 isotype. This observation confirms the findings of others who examined the antitumor activity of IgG2a mAbs in other model systems. IgG1 mAb 225, and possibly IgG2a mAb 528, may prevent growth of human tumor xenografts by altering the physiological functions of the EGF receptor rather than by immune mechanisms.
在先前针对表皮生长因子（EGF）受体的单克隆抗体（mAb）研究中，已证明528 IgG2a和225 IgG1均能抑制无胸腺小鼠体内A431细胞异种移植瘤的生长。这两种单克隆抗体的抗肿瘤活性相似，尽管它们的亚型不同，但具有许多共同特性。这两种单克隆抗体以相同的亲和力与EGF受体结合，与EGF竞争结合EGF受体，同样地下调受体，在相当程度上阻断EGF诱导的酪氨酸蛋白激酶活性激活，并阻断EGF诱导的培养细胞增殖变化。这些生理效应的相似性使得可以直接比较IgG1和IgG2a亚型单克隆抗体的作用机制。我们使用528 IgG2a和225 IgG1单克隆抗体检测了对A431细胞的体外细胞毒性。通过51Cr释放试验和培养的A431细胞生长抑制试验表明，528 IgG2a而非225 IgG1表现出部分补体介导的细胞毒性。如通过掺入的[3H]胸腺嘧啶核苷释放所证明的，在存在活化的腹腔巨噬细胞的情况下，528 IgG2a而非225 IgG1对A431细胞具有细胞毒性。在存在含有K细胞的非贴壁脾细胞的情况下，两种单克隆抗体对A431细胞均未显示出任何显著的细胞毒性。体外细胞毒性实验结果表明，528 IgG2a而非225 IgG1的抗肿瘤活性可能由巨噬细胞介导。这在体内实验中得到了验证，在体内实验中，含有活化巨噬细胞的皮下肿瘤细胞接种物在每周两次腹腔注射亚最佳剂量的528 IgG2a共3周的动物中显示出抗肿瘤作用增强。当以相同程序使用225 IgG1时未观察到这种增强。这些实验结果表明，涉及活化巨噬细胞或补体的免疫机制可能有助于IgG2a亚型抗EGF受体单克隆抗体的抗肿瘤活性，但对IgG1亚型则不然。这一观察结果证实了其他人在其他模型系统中检测IgG2a单克隆抗体抗肿瘤活性的发现。IgG1单克隆抗体225以及可能的IgG2a单克隆抗体528可能通过改变EGF受体的生理功能而非免疫机制来阻止人肿瘤异种移植瘤的生长。
