Davis P L, Shaiu W L, Scott G L, Iglehart J D, Hsieh T S, Marks J R
Department of Surgery, Duke University Medical Center, Durham, NC 27710, USA.
Anticancer Res. 1998 Jul-Aug;18(4C):2919-32.
The topoisomerase inhibitors, camptothecin and etoposide target the activity of topoisomerase I and II respectively. These agents, or their analogues, are undergoing clinical trials for the treatment of metastatic breast cancer. In this study, we examined the response of eight breast epithelial cell lines, including six lines derived from breast cancers and two immortalized normal epithelial lines to camptothecin and etoposide. The lines varied by 700 fold in their sensitivity to the growth inhibiting effects of camptothecin and 30 fold in their response to etoposide. The BT474 line was the most resistant to both agents. The other cell lines did not have uniform sensitivity to both drugs, i.e., some lines were sensitive to one drug but relatively resistant to the other. A variety of parameters in these lines were analyzed to elucidate mechanisms of resistance including S phase, doubling time, expression and activity of topoisomerase I and II, expression of mdr-1, p53 status, cell cycle arrest, level of apoptosis, and expression of the apoptotic proteins Bcl-2 and Bax. We found that low levels of the topo I protein and its enzymatic activity were associated with increased resistance to camptothecin. This was not true for topo II activity and etoposide. Increased apoptotic responses were generally observed in cell lines that were sensitive to etoposide and this correlated with low ratios of Bcl-2/Bax protein. No single parameter was entirely predictive of response. However, the BT474 line displayed a series of characteristics including slow growth, the presence of mutant p53, low topo I activity, and a high Bcl-2/Bax ratio which together likely contributed to the resistance of this line to both etoposide and camptothecin.
拓扑异构酶抑制剂喜树碱和依托泊苷分别作用于拓扑异构酶I和II的活性。这些药物或其类似物正在进行治疗转移性乳腺癌的临床试验。在本研究中，我们检测了8种乳腺上皮细胞系对喜树碱和依托泊苷的反应，其中包括6种源自乳腺癌的细胞系和2种永生化正常上皮细胞系。这些细胞系对喜树碱生长抑制作用的敏感性相差700倍，对依托泊苷的反应相差30倍。BT474细胞系对这两种药物最具抗性。其他细胞系对这两种药物的敏感性并不一致，即有些细胞系对一种药物敏感但对另一种药物相对抗性。分析了这些细胞系中的各种参数以阐明抗性机制，包括S期、倍增时间、拓扑异构酶I和II的表达及活性、mdr-1的表达、p53状态、细胞周期阻滞、凋亡水平以及凋亡蛋白Bcl-2和Bax的表达。我们发现拓扑异构酶I蛋白水平及其酶活性较低与对喜树碱的抗性增加有关。拓扑异构酶II活性和依托泊苷的情况并非如此。在对依托泊苷敏感的细胞系中通常观察到凋亡反应增加，这与Bcl-2/Bax蛋白的低比率相关。没有单一参数能完全预测反应。然而，BT474细胞系表现出一系列特征，包括生长缓慢、存在突变型p53、拓扑异构酶I活性低以及Bcl-2/Bax比率高，这些因素共同导致了该细胞系对依托泊苷和喜树碱均具有抗性。
