Myeloperoxidase-Catalyzed Metabolism of Etoposide to Its Quinone and Glutathione Adduct Forms in HL60 Cells
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- 作者：Yun Fan ; Emanuel M. Schreiber ; Angela Giorgianni ; Jack C. Yalowich ; and Billy W. Day
- 刊名：Chemical Research in Toxicology
- 出版年：2006
- 出版时间：July 2006
- 年：2006
- 卷：19
- 期：7
- 页码：937 - 943
- 全文大小：141K
- 年卷期：v.19,no.7(July 2006)
- ISSN：1520-5010
文摘
Etoposide is a widely used antineoplastic agent that has provided great success in the treatment ofchildhood leukemias and other malignancies. Unfortunately, its use is associated with the increased riskof development of secondary acute myelogenous leukemias involving translocations at the MLL gene inchromosome band 11q23. Previous studies showed that the phenoxyl radical of etoposide can be generatedby myeloperoxidase (MPO), an enzyme prevalent in myeloid progenitor cells that can derive myelogenousleukemias. Disproportionation of this radical leads to formation of the redox active etoposide ortho-quinone metabolite. We hypothesized that etoposide ortho-quinone could therefore form in myeloidprogenitor cells and might be a contributor to the development of treatment-related secondary leukemias.Etoposide ortho-quinone is an inherently unstable compound and readily reacts with glutathione in aqueousmedia without any requirement for catalytic assistance from glutathione S-transferase. We looked for thepresence of its glutathione adduct as an indicator of etoposide ortho-quinone in cells. MPO-expressinghuman myeloid leukemia HL60 cells were treated with etoposide for 0.5 h in the presence and absenceof the cosubstrate of MPO, hydrogen peroxide. Cell lysates and medium were analyzed by LC-ESI-iontrap-MS and MS/MS, which yielded clear evidence of the intracellular formation of the etoposide ortho-quinone-glutathione adduct. A stable isotope-labeled form of the GSH adduct was synthesized andemployed as an isotope dilution internal standard in LC-ESI-quadrupole-MS analyses. The glutathioneadduct level was dependent on the concentration of etoposide added to the cells. More importantly, theformation of the glutathione adduct was significantly suppressed by the pretreatment of HL60 cells withthe heme synthesis inhibitor succinylacetone (p < 0.001), which resulted in a decreased level and activityof MPO. These results are consistent with the idea that MPO is responsible for the conversion of etoposideto its ortho-quinone in these cells.