Harris L N, Yang L, Liotcheva V, Pauli S, Iglehart J D, Colvin O M, Hsieh T S
Adult Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts 02115, USA.
Clin Cancer Res. 2001 Jun;7(6):1497-504.
ErbB2 (HER-2) gene amplification and overexpression have been shown to predict a better outcome with doxorubicin-based chemotherapy as opposed to alkylator-based chemotherapy in early stage breast cancer. To understand the mechanism of differential response to these two regimens, we have evaluated the effect of signaling through the ErbB2 receptor on downstream enzymes that may affect drug response, using two different models. The first system employs breast cancer cells that have high levels of endogenous ErbB2 by gene amplification (BT-474 and SKBR3 cells). The second system allows us to isolate the effect of ErbB2 receptor-mediated intracellular signaling using an epidermal growth factor receptor-ErbB2 chimeric receptor activated by epidermal growth factor. Our experiments show that the cytotoxicity of doxorubicin is inhibited in ErbB2+ breast cancer cells by the anti-ErbB2 antibody, Herceptin. This is accompanied by a decrease in topoisomerase (topo) IIalpha protein and activity, suggesting that this is the mechanism of change in doxorubicin response. In addition, a 10-100-fold (1-2 log) decrease in the LD(50) of doxorubicin is seen after ErbB2 activation using the chimeric receptor model. Furthermore, we see a 100-fold decrease in the LD(50) of etoposide, another topo II inhibitor. This increase in doxorubicin sensitivity is associated with a 4.5-fold increase in the amount of topo IIalpha protein and an increase in topo II activity as measured by DNA decatenating and unknotting activities, as well as cleavable complex formation. In contradistinction to doxorubicin, we have observed an increased resistance to cyclophosphamide chemotherapy after chimeric receptor activation. We propose that the differential benefit seen with doxorubicin- versus alkylator-based chemotherapy in ErbB2+ breast cancer is due, in some cases, to ErbB2-mediated topo IIalpha activation. These data also suggest hypotheses for the optimal sequencing of Herceptin and chemotherapy agents in ErbB2+ breast cancer.
已表明，在早期乳腺癌中，与基于烷化剂的化疗相反，ErbB2（HER-2）基因扩增和过表达预示着基于阿霉素的化疗有更好的疗效。为了解对这两种治疗方案产生不同反应的机制，我们使用两种不同模型评估了通过ErbB2受体发出的信号对可能影响药物反应的下游酶的作用。第一个系统采用通过基因扩增具有高水平内源性ErbB2的乳腺癌细胞（BT-474和SKBR3细胞）。第二个系统使我们能够利用由表皮生长因子激活的表皮生长因子受体-ErbB2嵌合受体来分离ErbB2受体介导的细胞内信号传导的作用。我们的实验表明，抗ErbB2抗体赫赛汀可抑制阿霉素对ErbB2阳性乳腺癌细胞的细胞毒性。这伴随着拓扑异构酶（topo）IIα蛋白和活性的降低，表明这是阿霉素反应改变的机制。此外，使用嵌合受体模型激活ErbB2后，阿霉素的半数致死剂量（LD50）降低了10至100倍（1至2个对数）。此外，我们发现另一种拓扑异构酶II抑制剂依托泊苷的LD50降低了100倍。阿霉素敏感性的这种增加与拓扑异构酶IIα蛋白量增加4.5倍以及通过DNA解连环和解结活性以及可裂解复合物形成所测量的拓扑异构酶II活性增加有关。与阿霉素相反，我们观察到嵌合受体激活后对环磷酰胺化疗的耐药性增加。我们提出，在ErbB2阳性乳腺癌中，基于阿霉素与基于烷化剂的化疗所看到的不同益处，在某些情况下，是由于ErbB2介导的拓扑异构酶IIα激活。这些数据也为ErbB2阳性乳腺癌中赫赛汀和化疗药物的最佳序贯治疗提出了假设。
