Cimoli G, Valenti M, Noviello E, Parodi S, Mazzoni A, Rovini E, De Sessa F, Russo P
Department of Chemical Carcinogenesis, Istituto Nazionale per la Ricerca sul Cancro, Genova, Italy.
J Cancer Res Clin Oncol. 1995;121(3):155-63. doi: 10.1007/BF01198097.
Human ovarian cancer cells A2780, selected for resistance to doxorubicin (A2780-DX3), are cross-resistant to various other topoisomerase-II-targeted drugs but not to vinblastine. The parental cell line was very sensitive to doxorubicin-, mitoxantrone- or etoposide(VP16)-induced DNA single-strand breaks, under deproteinizing conditions. In contrast, little or no DNA strand breakage was seen in resistant A2780-DX3 cells, even at very high concentrations, indicating a good correlation, with cytotoxicity. No significant alterations in cellular drug uptake were observed in DX3 cells. Further studies showed that the nuclei isolated from resistant cells were also resistant to mitoxantrone- or VP16-induced single-strand breaks, indicating that nuclear modifications in resistant cells are responsible for this resistance. Catalytic activity in crude nuclear extracts from wild-type and DX3 cells was almost equal. However, an assay that specifically measures generation of 5'-protein-linked breaks in 32P-labeled 3 DNA revealed that, DNA cleavage activity in nuclear extract from the DX3 cell line is profoundly resistant to a stimulation by VP16. These data indicate that stimulation of topoisomerase-II-mediated DNA cleavage is responsible for topoisomerase-II-targeted drug-cytotoxicity rather than loss of normal topoisomerase catalytic function. These data support the hypothesis that A2780-DX3 cells display an "atypical" multidrug resistance.
人卵巢癌细胞A2780对阿霉素具有抗性（A2780 - DX3），对其他多种靶向拓扑异构酶II的药物也具有交叉抗性，但对长春碱不具有抗性。在脱蛋白条件下，亲代细胞系对阿霉素、米托蒽醌或依托泊苷（VP16）诱导的DNA单链断裂非常敏感。相比之下，即使在非常高的浓度下，抗性A2780 - DX3细胞中也几乎看不到或根本看不到DNA链断裂，这表明与细胞毒性具有良好的相关性。在DX3细胞中未观察到细胞药物摄取的显著改变。进一步的研究表明，从抗性细胞中分离出的细胞核对米托蒽醌或VP16诱导的单链断裂也具有抗性，这表明抗性细胞中的核修饰是这种抗性的原因。野生型和DX3细胞的粗核提取物中的催化活性几乎相等。然而，一项专门测量32P标记的3DNA中5'-蛋白质连接断裂生成的试验表明，DX3细胞系核提取物中的DNA切割活性对VP16的刺激具有高度抗性。这些数据表明，拓扑异构酶II介导的DNA切割的刺激是靶向拓扑异构酶II的药物细胞毒性的原因，而不是正常拓扑异构酶催化功能的丧失。这些数据支持A2780 - DX3细胞表现出“非典型”多药耐药性的假设。
