Purpose: To assess the inhibition and induction potential of tanespimycin and its major metabolite, 17-amino-17-demethoxygeldanamycin (17-AG) on cytochrome P450 (CYP) enzymes.
Methods: The inhibitory effect of tanespimycin and 17-AG on various CYP enzymes was determined in human liver microsomes. The inductive effects of tanespimycin and 17-AG on CYP1A2, CYP2B6, and CYP3A4/5 were determined in cultured primary human hepatocytes.
Results: Tanespimycin did not inhibit the activities of CYP1A2, 2A6, 2B6, and 2E1 up to a concentration of 60 μM, while it moderately inhibited CYP3A4/5 and 2C19, and weakly inhibited CYP2C8, 2C9, and 2D6. In addition, its inhibition on CYP3A4/5 was time-dependent. 17-AG moderately inhibited the activities of CYP3A4/5 and CYP2C19, but did not inhibit other CYPs up to a concentration of 30 μM. The inhibition of CYP3A4/5 by 17-AG was not time-dependent. Tanespimycin and 17-AG did not significantly induce the activities of CYP1A2, CYP2B6, or CYP3A4/5 in cultured human hepatocytes at concentrations up to 40 and 20 μM for tanespimycin and 17-AG, respectively.
Conclusions: Tanespimycin together with its active metabolite, 17-AG are moderate inhibitors of CYP3A4/5 and CYP2C19, but not inducers of CYPs. Therefore, co-administration of tanespimycin has the potential to increase the exposure of substrates of CYP2C19 and CYP3A4/5.