Li Dong, Jang Seong H, Kim Jonghan, Wientjes M Guillaume, Au Jessie L S
College of Pharmacy, The Ohio State University, Columbus, Ohio 43210, USA.
Pharm Res. 2003 Jan;20(1):45-50. doi: 10.1023/a:1022242607418.
We have reported that overexpression of mdr1 P-glycoprotein (Pgp) is associated with a higher sensitivity to paclitaxel-induced apoptosis (1,2). The present study examined the substrate specificity of this phenomenon.
Two Pgp substrates (vincristine and doxorubicin) and three nonsubstrates (cisplatin, camptothecin. and 5-fluorouracil) were studied. Serum deprivation, known to induce apoptosis, was used as a comparison.
The Pgp nonsubstrates and serum deprivation showed similar overall cytotoxicity and apoptosis in human breast MCF7 cells (with negligible Pgp expression) and its mdr1-transfected subline BC19 cells (with nine-fold higher Pgp expression). In contrast, the overall cytotoxicity and apoptosis of the two Pgp substrates was higher in MCF7 cells. Cotreatment with a Pgp inhibitor, verapamil, abolished the difference in intracellular accumulation of doxorubicin as well as the differences in apoptosis between MCF7 and BC19 cells. This finding confirms that the lower apoptosis of doxorubicin in BC19 cells, in the absence of verapamil, was a result of lower intracellular drug accumulation secondary to high Pgp expression in BC19 cells. In contrast, abolishing the difference in intracellular vincristine concentration by verapamil cotreatment resulted in significantly higher apoptosis in BC19 cells. This finding is identical to our previous finding with paclitaxel, where equal intracellular drug concentration resulted in greater apoptosis in the Pgp-rich BC19 cells.
These data, together with the opposite effects of paclitaxel and vincristine on microtubules (i.e., polymerization versus depolymerization), indicate that the enhanced apoptosis in Pgp-rich cells is specific for antimicrotubule agents but is not related to the polymerization of microtubules.
我们曾报道过，多药耐药蛋白1（mdr1）P-糖蛋白（Pgp）的过表达与对紫杉醇诱导的细胞凋亡具有更高的敏感性相关（1,2）。本研究检测了该现象的底物特异性。
研究了两种Pgp底物（长春新碱和阿霉素）以及三种非底物（顺铂、喜树碱和5-氟尿嘧啶）。已知血清剥夺可诱导细胞凋亡，将其用作对照。
Pgp非底物和血清剥夺在人乳腺癌MCF7细胞（Pgp表达可忽略不计）及其mdr1转染亚系BC19细胞（Pgp表达高9倍）中显示出相似的总体细胞毒性和细胞凋亡。相比之下，两种Pgp底物在MCF7细胞中的总体细胞毒性和细胞凋亡更高。与Pgp抑制剂维拉帕米共同处理消除了阿霉素细胞内蓄积的差异以及MCF7细胞和BC19细胞之间细胞凋亡的差异。这一发现证实，在没有维拉帕米的情况下，BC19细胞中阿霉素较低的细胞凋亡是由于BC19细胞中Pgp高表达导致细胞内药物蓄积较低的结果。相反，维拉帕米共同处理消除长春新碱细胞内浓度的差异导致BC19细胞中细胞凋亡显著增加。这一发现与我们之前关于紫杉醇的发现一致，即细胞内药物浓度相等时，富含Pgp的BC19细胞中细胞凋亡更多。
这些数据，连同紫杉醇和长春新碱对微管的相反作用（即聚合与解聚），表明富含Pgp的细胞中增强的细胞凋亡是抗微管药物特有的，但与微管的聚合无关。
