Biotransformation of Geldanamycin and 17-Allylamino-17-Demethoxygeldanamycin by Human Liver Microsomes: Reductive versus Oxidative Metabolism and Implications

• Published in: Drug metabolism and disposition Vol. 35; no. 1; pp. 21 - 29
• Main Authors: Lang, Wensheng, Caldwell, Gary W, Li, Jian, Leo, Gregory C, Jones, William J, Masucci, John A
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Pharmacology and Experimental Therapeutics 01.01.2007
• Subjects: Antibiotics, Antineoplastic - metabolism; Benzoquinones - metabolism; Biological and medical sciences; Biotransformation; Cell Hypoxia; HSP90 Heat-Shock Proteins - antagonists & inhibitors; Humans; Lactams, Macrocyclic - metabolism; Medical sciences; Microsomes, Liver - metabolism; NADPH-Ferrihemoprotein Reductase - metabolism; Oxidation-Reduction; Pharmacology. Drug treatments; Human; Digestive system; Biotransformation; Liver; Geldanamycin; Pharmacokinetics; Microsome; Metabolism; In vitro; Comparative study
• ISSN: 0090-9556; 1521-009X
• DOI: 10.1124/dmd.106.009639

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°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°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.