Glutathione conjugation of busulfan produces a hydroxyl radical-trapping dehydroalanine metabolite.
The Phase 2 drug metabolism of busulfan yields a glutathione conjugate that undergoes a β-elimination reaction. The elimination product is an electrophilic metabolite that is a dehydroalanine-containing tripeptide, γ-glutamyldehydroalanylglycine (EdAG). In the process, glutathione lacks thiol-related redox properties and gains a radical scavenging dehydroalanine group.        EdAG scavenged hydroxyl radical generated in the Fenton reaction in a concentration-dependent manner was monitored by electron paramagnetic resonance (EPR) spectroscopy. The apparent rate of hydroxyl radical scavenging was in the same range as published values for known antioxidants, including N-acyl dehydroalanines.        A captodatively stabilized carbon-centered radical intermediate was spin trapped in the reaction of EdAG with hydroxyl radical. The proposed structure of a stable product in the Fenton reaction with EdAG was consistent with that of a γ-glutamylserylglycyl dimer.        Observation of the hydroxyl trapping properties of EdAG suggests that the busulfan metabolite EdAG may contribute to or mitigate redox-related cytotoxicity associated with the therapeutic use of busulfan, and reaffirms indicators that support a role in free radical biology for dehydroalanine-containing peptides and proteins.
Department of Basic Pharmaceutical Sciences and Mary Babb Randolph Cancer Center, West Virginia University, Morgantown, WV 26506, USA.
Cody J
CJ
Peer
Islam R
IR
Younis
Stephen S
SS
Leonard
Peter M
PM
Gannett
Valerie C
VC
Minarchick
Allison J
AJ
Kenyon
Yon
Y
Rojanasakul
Patrick S
PS
Callery
D000409:Alanine / Q000031:analogs & derivatives* / Q000378:metabolism; D000975:Antioxidants / Q000378:metabolism; D055162:Biocatalysis; D002066:Busulfan / Q000737:chemistry / Q000378:metabolism*; D002853:Chromatography, Liquid; D003497:Cyclic N-Oxides / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D005978:Glutathione / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000737:chemistry; D017665:Hydroxyl Radical / Q000737:chemistry / Q000378:metabolism*; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D010084:Oxidation-Reduction; D011725:Pyridines / Q000378:metabolism; D053719:Tandem Mass Spectrometry
D000975:Antioxidants; D003497:Cyclic N-Oxides; C045076:Fenton's reagent; D011725:Pyridines; C043438:alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone; D017665:Hydroxyl Radical; C015102:dehydroalanine; D006861:Hydrogen Peroxide; D007501:Iron; D005982:Glutathione Transferase; D002066:Busulfan; D005978:Glutathione; D000409:Alanine