Pu Y S, Hsieh T S, Tsai T C, Cheng A L, Hsieh C Y, Su I J, Lai M K
Department of Oncology and Urology, National Taiwan University Hospital, Taipei, Republic of China.
J Urol. 1995 Aug;154(2 Pt 1):601-5. doi: 10.1097/00005392-199508000-00078.
Chemosensitizers, which enhance cellular chemosensitivity and reduce chemoresistance, are expected to substantially improve response rates of systemic chemotherapy for patients with metastatic bladder cancer. Tamoxifen is a nonsteroidal antiestrogen that has been shown to reverse drug resistance in vitro in some cancer models through pathways not related to its antiestrogenic effect. In this study we tried to evaluate its possible effect on chemosensitization of bladder cancer cells.
In vitro chemosensitivity tests were done with 3 bladder cancer cell lines and 4 cytotoxic agents (methotrexate, vinblastine, doxorubicin and cisplatin) in the presence or absence of graded concentrations of tamoxifen. Verapamil was used in parallel experiments to compare the degrees of chemosensitization. The transcript and protein product [P-glycoprotein, (P-gp)] levels of the mdr-1 gene were also examined in the 3 cell lines by reverse-transcription polymerase chain reaction (RT-PCR) and flow cytometric assay, respectively.
Tamoxifen at 5 and especially 10 microM. concentrations, which were minimally toxic to the 3 bladder cancer cell lines used, enhanced the chemosensitivity of bladder cancer cells in most drug combinations in a dose-dependent manner. In some combinations 10 microM. tamoxifen did better than 5 microM. in chemosensitization. The effect of chemosensitization was more evident in cells treated with 10 microM. tamoxifen plus methotrexate and vinblastine in which 12.9 to 95.4-fold and 12.4 to 21.3-fold IC50 reduction was observed, respectively. A less prominent, but still significant, effect could be seen in doxorubicin- and cisplatin-treated cells. Verapamil, although used at concentrations up to 10 microM. which are higher than systemically tolerable, was not able to enhance chemosensitivity of the 3 bladder cancer cell lines. By flow cytometric analysis of the P-gp level and by RT-PCR assay of the mdr-1 gene transcript level, it was shown that little if any mdr-1 gene expression could be detected in the 3 cell lines. This implies that the mdr-1 gene function may play a minimal role in drug resistance mechanisms of bladder cancer cells and that tamoxifen exerts its chemosensitization effect through pathways other than mdr-1 gene function modulation.
Tamoxifen was shown to be a good chemosensitizer in a bladder cancer cell model and may well be tried in combination with systemic chemotherapy for metastatic human bladder cancers in the clinical setting.
化学增敏剂可增强细胞对化疗的敏感性并降低化疗耐药性，有望显著提高转移性膀胱癌患者全身化疗的缓解率。他莫昔芬是一种非甾体类抗雌激素药物，已证实在某些癌症模型中，它可通过与其抗雌激素作用无关的途径在体外逆转耐药性。在本研究中，我们试图评估其对膀胱癌细胞化学增敏的可能作用。
使用3种膀胱癌细胞系和4种细胞毒性药物（甲氨蝶呤、长春碱、阿霉素和顺铂）进行体外化学敏感性试验，试验中加入或不加入不同浓度梯度的他莫昔芬。在平行实验中使用维拉帕米比较化学增敏程度。分别通过逆转录聚合酶链反应（RT-PCR）和流式细胞术检测3种细胞系中mdr-1基因的转录本和蛋白产物[P-糖蛋白，（P-gp）]水平。
5μM尤其是10μM浓度的他莫昔芬对所使用的3种膀胱癌细胞系毒性极小，在大多数药物组合中以剂量依赖方式增强了膀胱癌细胞的化学敏感性。在某些组合中，10μM他莫昔芬的化学增敏效果优于5μM。在使用10μM他莫昔芬加甲氨蝶呤和长春碱处理的细胞中，化学增敏作用更明显，分别观察到IC50降低了12.9至95.4倍和12.4至21.3倍。在阿霉素和顺铂处理的细胞中也观察到不太显著但仍有统计学意义的效果。维拉帕米尽管使用浓度高达10μM，高于全身可耐受浓度，但未能增强3种膀胱癌细胞系的化学敏感性。通过对P-gp水平的流式细胞术分析和对mdr-1基因转录本水平的RT-PCR检测，结果显示在3种细胞系中几乎检测不到mdr-1基因表达。这意味着mdr-1基因功能在膀胱癌细胞的耐药机制中可能起最小作用，且他莫昔芬通过mdr-1基因功能调节以外的途径发挥其化学增敏作用。
在膀胱癌细胞模型中，他莫昔芬被证明是一种良好的化学增敏剂，在临床环境中可能值得尝试与转移性人类膀胱癌的全身化疗联合使用。
