Shabbits Jennifer A, Mayer Lawrence D
Department of Advanced Therapeutics, British Columbia Cancer Research Centre, Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, British Columbia, Canada.
Mol Cancer Ther. 2002 Jan;1(3):205-13.
Alterations in metabolism of ceramide (Cer) to the noncytotoxic metabolite glucosylceramide have been implicated in the multidrug resistance (MDR) phenomenon. This observation has been made with tumor cells that also overexpress P-glycoprotein (Pgp), raising the possibility that Pgp plays a role in regulating Cer metabolism. We investigated the effect of the glucosylceramide synthase inhibitor 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) on the chemosensitivity of two wild-type and multidrug-resistant human breast tumor cell lines. Subtoxic concentrations of PDMP sensitized drug-selected MCF7/AdrR and Pgp-overexpressing MDA435/LCC6MDR1 (MDR1 gene-transfected) cell lines to Taxol and vincristine but did not alter the chemosensitivity of the wild-type cells. Evaluation of Taxol uptake indicated that the effect of PDMP was not due to membrane permeability alterations because anticancer drug accumulation was unaffected by PDMP. Whereas both multidrug-resistant cell lines overexpress Pgp, only the MCF7/AdrR cell line overexpresses the glucosylceramide synthase enzyme. This difference enabled us to distinguish between sensitization effects associated with Cer metabolism versus Pgp-mediated transport. Interestingly, when Pgp function was blocked, the PDMP effect was reduced 3-fold in MCF7/AdrR cells and was no longer observed in the MDA435/LCC6MDR1 cells. These observations imply that Cer metabolism and apoptosis effects are regulated not only by enzymes that convert Cer to nontoxic metabolites but also by Pgp-mediated transport. Given the intracellular distribution patterns of Pgp, we propose that this effect is related to glucosylceramide translocation across the Golgi bilayer. We have applied this model to the situation of Cer metabolism-based chemosensitization and demonstrate that MDR modulation strategies aimed primarily at altering drug transport mechanisms can influence other MDR mechanisms such as glycosphingolipid metabolism. This work highlights the relationship between drug transport and Cer metabolism in the context of chemosensitization and cautions against making oversimplified assumptions that these mechanisms act independently.
神经酰胺（Cer）代谢为无细胞毒性的代谢产物葡糖神经酰胺的过程发生改变，这与多药耐药（MDR）现象有关。这一观察结果是在同时过表达P-糖蛋白（Pgp）的肿瘤细胞中得出的，这增加了Pgp在调节神经酰胺代谢中发挥作用的可能性。我们研究了葡糖神经酰胺合酶抑制剂1-苯基-2-癸酰氨基-3-吗啉代-1-丙醇（PDMP）对两种野生型和多药耐药人乳腺癌细胞系化学敏感性的影响。亚毒性浓度的PDMP使药物筛选的MCF7/AdrR细胞系和过表达Pgp的MDA435/LCC6MDR1（转染MDR1基因）细胞系对紫杉醇和长春新碱敏感，但未改变野生型细胞的化学敏感性。对紫杉醇摄取的评估表明，PDMP的作用并非由于膜通透性改变，因为抗癌药物的积累不受PDMP影响。虽然两种多药耐药细胞系都过表达Pgp，但只有MCF7/AdrR细胞系过表达葡糖神经酰胺合酶。这种差异使我们能够区分与神经酰胺代谢相关的致敏作用和Pgp介导的转运作用。有趣的是，当Pgp功能被阻断时，MCF7/AdrR细胞中PDMP的作用降低了3倍，而在MDA435/LCC6MDR1细胞中则不再观察到这种作用。这些观察结果表明，神经酰胺代谢和凋亡效应不仅受将神经酰胺转化为无毒代谢产物的酶的调节，还受Pgp介导的转运的调节。鉴于Pgp的细胞内分布模式，我们提出这种作用与葡糖神经酰胺跨高尔基体双层的转运有关。我们已将此模型应用于基于神经酰胺代谢的化学致敏情况，并证明主要旨在改变药物转运机制的MDR调节策略可影响其他MDR机制，如糖鞘脂代谢。这项工作突出了化学致敏背景下药物转运与神经酰胺代谢之间的关系，并提醒不要做出这些机制独立起作用的过于简单化假设。
