Minderman H, Vanhoefer U, Toth K, Minderman M D, Rustum Y M
Department of Experimental Therapeutics, Roswell Park Cancer Institute, Buffalo, New York 14263, USA.
Cancer. 1996 Dec 1;78(11):2427-36.
The role of P-glycoprotein (Pgp) in multidrug resistance (MDR) is uncontested. Expression of Pgp on hematopoietic cells has been correlated with CD34 expression. For acute myeloid leukemia, the prognostic value of Pgp for clinical response is at best equivalent to that of CD34. The current study investigated whether expression of CD34 can be associated with selection for drug resistance.
Several established MDR cell lines were screened by flow cytometry for expression of CD34. Human ovarian carcinoma cells (A2780), which simultaneously expressed CD34 and Pgp, were identified. Subsequent cloning resulted in a new cell line (A2780-Dx5c) that expressed CD34 in the absence of Pgp. Involvement of non-Pgp-mediated MDR mechanisms was assessed by immunohistochemistry (MRP and LRP), enzyme activity studies (glutathione pathway), cross-resistance patterns, and Northern blot (type II alpha topoisomerase).
A2780-Dx5c was cross-resistant to doxorubicin, daunorubicin, idarubicin, and VP-16. However, unlike the Pgp-expressing cells, it was not cross-resistant to vincristine or amsacrine. The drug resistance was correlated with a decreased level of type II alpha topoisomerase in the A2780-Dx5c cell line compared with the parental cell line. No evidence was found of involvement of MRP, LRP, or the glutathione pathway with drug resistance in this cell line.
A new cell line of nonhematopoietic and nonvascular endothelial origin that expresses CD34 in association with selection for MDR was cloned. A study of MDR mechanisms in this cell line revealed that reduced type II alpha topoisomerase levels were likely responsible for the MDR observed. A study of the causal relation between the selection of drug resistance and the expression of CD34 may provide insight into why CD34 correlates with poor clinical response in patients with acute myeloid leukemia.
P-糖蛋白（Pgp）在多药耐药（MDR）中的作用是无可争议的。造血细胞上Pgp的表达与CD34表达相关。对于急性髓细胞白血病，Pgp对临床反应的预后价值充其量与CD34相当。本研究调查了CD34的表达是否与耐药性选择有关。
通过流式细胞术筛选几种已建立的多药耐药细胞系的CD34表达情况。鉴定出同时表达CD34和Pgp的人卵巢癌细胞（A2780）。随后的克隆产生了一个新的细胞系（A2780-Dx5c），该细胞系在没有Pgp的情况下表达CD34。通过免疫组织化学（MRP和LRP）、酶活性研究（谷胱甘肽途径）、交叉耐药模式和Northern印迹（II型α拓扑异构酶）评估非Pgp介导的多药耐药机制的参与情况。
A2780-Dx5c对阿霉素、柔红霉素、伊达比星和VP-16具有交叉耐药性。然而，与表达Pgp的细胞不同，它对长春新碱或安吖啶没有交叉耐药性。与亲代细胞系相比，A2780-Dx5c细胞系中的耐药性与II型α拓扑异构酶水平降低相关。在该细胞系中未发现MRP、LRP或谷胱甘肽途径参与耐药的证据。
克隆了一种非造血和非血管内皮来源的新细胞系，其表达CD34并伴有多药耐药性选择。对该细胞系中多药耐药机制的研究表明，II型α拓扑异构酶水平降低可能是观察到的多药耐药的原因。对耐药性选择与CD34表达之间因果关系的研究可能有助于深入了解为什么CD34与急性髓细胞白血病患者临床反应不佳相关。
