Development of a liquid chromatography electrospray ionization tandem mass spectrometry method for analysis of stable 4-hydroxyequilenin-DNA adducts in human breast cancer cells.
Estrogen-DNA adducts are potential biomarkers for assessing cancer risk and progression in estrogen-dependent cancer. 4-Hydroxyequilenin (4-OHEN), the major catechol metabolite of equine estrogens present in hormone replacement therapy formulations, autoxidizes to a reactive o-quinone that subsequently causes DNA damage. The formation of stable stereoisomeric cyclic 4-OHEN-DNA adducts has been reported in vitro and in vivo, but their removal by DNA repair processes in cells has not been determined. Such studies have been hampered by low yields of cyclic adducts and poor reproducibility when treating cells in culture with 4-OHEN. These problems are attributed in part to the instability of 4-OHEN in aerobic, aqueous media. We show herein that low yields and reproducibility can be overcome by 4-OHEN diacetate as a novel, cell-permeable 4-OHEN precursor, in combination with a sensitive LC-MS/MS method developed for detecting adducts in human breast cancer cells. This method involves isolation of cellular DNA, DNA digestion to deoxynucleosides, followed by the addition of an isotope-labeled internal standard (4-OHEN-(15)N(5)-dG adduct) prior to analysis by LC-MS/MS. A concentration-dependent increase in adduct levels was observed in MCF-7 cells after exposure to 4-OHEN diacetate. The chemical stabilities of the adducts were also investigated to confirm that adducts were stable under assay conditions. In conclusion, this newly developed LC-MS/MS method allows detection and relative quantification of 4-OHEN-DNA adducts in human breast cancer cells, which could be adapted for adduct detection in human samples.
Department of Medicinal Chemistry and Pharmacognosy (M/C 781), College of Pharmacy, University of Illinois at Chicago, 833 South Wood Street, Chicago, Illinois 60612-7231, USA.
Zhican
Z
Wang
Praneeth
P
Edirisinghe
Johann
J
Sohn
Zhihui
Z
Qin
Nicholas E
NE
Geacintov
Gregory R J
GR
Thatcher
Judy L
JL
Bolton
D000818:Animals; D001943:Breast Neoplasms / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D018736:DNA Adducts / Q000032:analysis* / Q000737:chemistry; D004249:DNA Damage; D004855:Equilenin / Q000031:analogs & derivatives* / Q000737:chemistry; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D013237:Stereoisomerism; D013552:Swine; D053719:Tandem Mass Spectrometry / Q000379:methods*; D013696:Temperature; D014407:Tumor Cells, Cultured
D018736:DNA Adducts; C065250:4-hydroxy-equilenin; D004855:Equilenin