title: Biotransformation of geldanamycin and 17-allylamino-17-demethoxygeldanamycin by human liver microsomes: reductive versus oxidative metabolism and implications.
abstract: Comparative metabolite profiling of geldanamycin and 17-allylamino-17-demethoxygeldanamycin (17AAG) using human liver microsomes in normoxia and hypoxia was conducted to understand their differential metabolic fates. Geldanamycin bearing a 17-methoxy group primarily underwent reductive metabolism, generating the corresponding hydroquinone under both conditions. The formed hydroquinone resists further metabolism and serves as a reservoir. On exposure to oxygen, this hydroquinone slowly reverts to geldanamycin. In the presence of glutathione, geldanamycin was rapidly converted to 19-glutathionyl geldanamycin hydroquinone, suggesting its reactive nature. In contrast, the counterpart (17AAG) preferentially remained as its quinone form, which underwent extensive oxidative metabolism on both the 17-allylamino sidechain and the ansa ring. Only a small amount (<1%) of 19-glutathione conjugate of 17AAG was detected in the incubation of 17AAG with glutathione at 37 degrees C for 60 min. To confirm the differential nature of quinone-hydroquinone conversion between the two compounds, hypoxic incubations with human cytochrome P450 reductase at 37 degrees C and direct injection analysis were performed. Approximately 89% of hydroquinone, 5% of quinone, and 6% of 17-O-demethylgeldanamycin were observed after 1-min incubation of geldanamycin, whereas about 1% of hydroquinone and 99% of quinone were found in the 60-min incubation of 17AAG. The results provide direct evidence for understanding the 17-substituent effects of these benzoquinone ansamycins on their phase I metabolism, reactivity with glutathione, and acute hepatotoxicity.
authors.affiliation: Johnson & Johnson Pharmaceutical Research and Development, LLC, P.O. Box 776, Welsh and McKean Roads, Spring House, PA 19477, USA. wlang@prdus.jnj.com
authors.forename: Wensheng
authors.initials: W
authors.lastname: Lang
authors.forename: Gary W
authors.initials: GW
authors.lastname: Caldwell
authors.forename: Jian
authors.initials: J
authors.lastname: Li
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Leo
authors.forename: William J
authors.initials: WJ
authors.lastname: Jones
authors.forename: John A
authors.initials: JA
authors.lastname: Masucci
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000378:metabolism*; D016227:Benzoquinones / Q000378:metabolism*; D001711:Biotransformation; D015687:Cell Hypoxia; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors; D006801:Humans; D047029:Lactams, Macrocyclic / Q000378:metabolism*; D008862:Microsomes, Liver / Q000378:metabolism*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D010084:Oxidation-Reduction
chemical_list: D000903:Antibiotics, Antineoplastic; D016227:Benzoquinones; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; C112765:tanespimycin; D009251:NADPH-Ferrihemoprotein Reductase; C001277:geldanamycin