Fekete Mirela R, McBride William H, Pajonk Frank
Department of Neurology, Bürgerhospital, Tunzhofer Str. 14-16, 70191 Stuttgart, Germany.
BMC Cancer. 2005 Sep 13;5:114. doi: 10.1186/1471-2407-5-114.
P-glycoprotein is responsible for the ATP-dependent export of certain structurally unrelated compounds including many chemotherapeutic drugs. Amplification of P-glycoprotein activity can result in multi-drug resistance and is a common cause of chemotherapy treatment failure. Therefore, there is an ongoing search for inhibitors of P-glycoprotein. Observations that cyclosporin A, and certain other substances, inhibit both the proteasome and P-glycoprotein led us to investigate whether anthracyclines, well known substrates of P-gp, also inhibit the function of the proteasome.
Proteasome function was measured in cell lysates from ECV304 cells incubated with different doses of verapamil, doxorubicin, daunorubicin, idarubicin, epirubicin, topotecan, mitomycin C, and gemcitabine using a fluorogenic peptide assay. Proteasome function in living cells was monitored using ECV304 cells stably transfected with the gene for an ubiquitin/green fluorescent protein fusion protein. The ability of the proteasome inhibitor MG-132 to affect P-glycoprotein function was monitored by fluorescence due to accumulation of daunorubicin in P-glycoprotein overexpressing KB 8-5 cells.
Verapamil, daunorubicin, doxorubicin, idarubicin, and epirubicin inhibited 26S chymotrypsin-like function in ECV304 extracts in a dose-dependent fashion. With the exception of daunorubicin, 20S proteasome function was also suppressed. The proteasome inhibitor MG-132 caused a dose-dependent accumulation of daunorubicin in KB 8-5 cells that overexpress P-glycoprotein, suggesting that it blocked P-glycoprotein function.
Our data indicate that anthracyclines inhibit the 26S proteasome as well as P-glycoprotein. Use of inhibitors of either pathway in cancer therapy should take this into consideration and perhaps use it to advantage, for example during chemosensitization by proteasome inhibitors.
P-糖蛋白负责某些结构不相关化合物（包括许多化疗药物）的ATP依赖性外排。P-糖蛋白活性的增强可导致多药耐药，是化疗治疗失败的常见原因。因此，人们一直在寻找P-糖蛋白抑制剂。环孢素A和某些其他物质可同时抑制蛋白酶体和P-糖蛋白，这一发现促使我们研究P-糖蛋白的已知底物蒽环类药物是否也能抑制蛋白酶体的功能。
使用荧光肽测定法，在与不同剂量维拉帕米、阿霉素、柔红霉素、伊达比星、表柔比星、拓扑替康、丝裂霉素C和吉西他滨孵育的ECV304细胞裂解物中测量蛋白酶体功能。使用稳定转染泛素/绿色荧光蛋白融合蛋白基因的ECV304细胞监测活细胞中的蛋白酶体功能。通过柔红霉素在过表达P-糖蛋白的KB 8-5细胞中的积累所产生的荧光，监测蛋白酶体抑制剂MG-132影响P-糖蛋白功能的能力。
维拉帕米、柔红霉素、阿霉素、伊达比星和表柔比星以剂量依赖性方式抑制ECV304提取物中的26S胰凝乳蛋白酶样功能。除柔红霉素外，20S蛋白酶体功能也受到抑制。蛋白酶体抑制剂MG-132导致柔红霉素在过表达P-糖蛋白的KB 8-5细胞中呈剂量依赖性积累，表明它阻断了P-糖蛋白功能。
我们的数据表明蒽环类药物可抑制26S蛋白酶体以及P-糖蛋白。在癌症治疗中使用这两种途径的抑制剂时应考虑到这一点，并可能利用这一点，例如在蛋白酶体抑制剂进行化疗增敏期间。
