The Cytochrome P450 Enzyme Responsible for the Production of (Z)‐Norendoxifen in vitro
3
Citation
22
Reference
10
Related Paper
Citation Trend
Abstract:
Norendoxifen, an active metabolite of tamoxifen, is a potent aromatase inhibitor. Little information is available regarding production of norendoxifen in vitro. Here, we conducted a series of kinetic and inhibition studies in human liver microsomes (HLMs) and expressed P450s to study the metabolic disposition of norendoxifen. To validate that norendoxifen was the metabolite of endoxifen, metabolites in HLMs incubates of endoxifen were measured using a HPLC/MS/MS method. To further probe the specific isoforms involved in the metabolic route, endoxifen was incubated with recombinant P450s (CYP 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 3A4, 3A5 and CYP4A11). Formation rates of norendoxifen were evaluated in the absence and presence of P450 isoform specific inhibitors using HLMs. The peak of norendoxifen was found in the incubations consisting of endoxifen, HLMs, and cofactors. The retention times of norendoxifen, endoxifen, and the internal standard (diphenhydramine) were 7.81, 7.97, and 5.86 min, respectively. The Km (app) and Vmax (app) values of norendoxifen formation from endoxifen in HLM was 47.8 μm and 35.39 pmol min-1 mg-1 . The apparent hepatic intrinsic clearances of norendoxifen formation were 0.74 μl mg-1 min. CYP3A5 and CYP2D6 were the major enzymes capable of norendoxifen formation from endoxifen with the rates of 0.26 and 0.86 pmol pmol-1 P450 × min. CYP1A2, 3A2, 2C9, and 2C19 also contributed to norendoxifen formation, but the contributions were at least 6-fold lower. One micromolar ketoconazole (CYP3A inhibitor) showed an inhibitory effect on the rates of norendoxifen formation by 45%, but 1 μm quinidine (CYP2D6 inhibitor) does not show any inhibitory effect. Norendoxifen, metabolism from endoxifen by multiple P450s that including CYP3A5.Keywords:
Active metabolite
1. This study aimed to investigate the inhibitory effect of azole antifungal agents, including ketoconazole, voriconazole, fluconazole, and itraconazole, on the pharmacokinetics of bosentan (BOS) and its active metabolite hydroxy bosentan (OHBOS) in Sprague-Dawley (SD) rats.2. A total of 25 healthy male SD rats were divided into five groups and treated with various azole antifungal agents by gavage, followed by a single dose of BOS after 30 min.3. The study found that ketoconazole led to a significant increase (5.1-fold) in the AUC(0-t) of BOS, associated with a 5.8-fold elevation in the Cmax, which was greater than that for fluconazole (2.6- and 2.9-fold) and voriconazole (1.1- and 1.7-fold). Accordingly, the Vz/F and CLz/F of BOS reduced by 89.2% and 83.7%, respectively, on administering ketoconazole concomitantly. However, fluconazole caused a decrease in Vz/F and CLz/F by 77.4% and 72.2%, respectively, compared with voriconazole that exhibited a decrease in CLz/F by 51.7% with a negligible change in Vz/F. Also, obvious differences were observed in the pharmacokinetic parameters of OHBOS between the control and treated groups.4. Collectively, treatment with ketoconazole resulted in a prominent inhibitory effect on the metabolism of BOS, followed by treatment with fluconazole, voriconazole, and itraconazole. Therefore, these details of animal studies may help draw more attention to the safety of BOS while combining it with ketoconazole, voriconazole, fluconazole, or itraconazole clinically.
Azole
Active metabolite
Cite
Citations (4)
Active metabolite
Cite
Citations (9)
Tamoxifen (Tam), the major drug for estrogen receptor (ER)-positive breast cancer, is converted to its active metabolites, Z- and Z′-endoxifen and 4-OH-Tam isomers, primarily by cytochrome P450 CYP2D6. In 117 patients taking 20 mg/day of Tam, we determined CYP2D6 genotypes and measured the plasma levels of Tam metabolites. The Z-endoxifen levels increased while Z′-endoxifen levels decreased with increasing metabolizer phenotype activity (MPA) score (P ≤ 0.0004). The dosage in patients with endoxifen <40 nmol/l and/or CYP2D6 MPA scores of 0 was increased to 30 mg/day and their metabolite isomers were monitored for up to 90 days. Of the 24 patients on the increased dose, 90% showed an increase in active isomers by day 60; the rate of increase correlated with the MPA score. Notably, their antiestrogenic activity scores (AASs), which estimate total isomer biologic activity, increased from a baseline median of 17 to 26 at day 60. Further studies involving increasing/decreasing the Tam dosage based on the AAS may determine whether dose adjustment can optimize treatment and improve long-term survival. Clinical Pharmacology & Therapeutics (2011) 90 4, 605–611. doi:10.1038/clpt.2011.153
Active metabolite
Cite
Citations (73)
Active metabolite
CYP3A
Cite
Citations (5)
This paper presents the pharmacokinetic properties of newer second generation antidepressants, with an emphasis on the main metabolic pathways of drugs and metabolites as well as their effects on the cytochrome P450 enzymes. Except for Milnacipran all newer antidepressants are biotransformed in the presence of at least one cytochrome P450 izoenzyme. Drugs and their metabolites may be the substrates or inhibitors of cytochromes P450. The knowledge of drugs' metabolic pathways as well as the knowledge of substrates and inhibitors of izoenzymes assists in choice of a proper drug and its dose. It is particularly important in case of polypharmacotherapy when there is a high risk of adverse events. It is also important to remember about genetic polymorphism of some cytochrome P450 izoenzymes (CYP2D6, CYP2C19) that underlies the marked inpatient variability in drug metabolism.
Metabolic pathway
Cite
Citations (8)
SN-38
Glucuronide
Active metabolite
Glucuronosyltransferase
Phenobarbital
Valproic Acid
Cite
Citations (94)
SN-38
Active metabolite
Pazopanib
Glucuronosyltransferase
Glucuronide
Cite
Citations (14)
Active metabolite
Cite
Citations (23)
Article AbstractBecause this piece does not have an abstract, we have provided for your benefit the first 3 sentences of the full text.The cytochrome P450 (CYP) superfamily represents the most important phase I drug metabolizing enzyme system. Genetic mutations play an important role in the activity especially of CYP2D6. Genetic polymorphisms within CYPs affect the metabolism of drugs as substrates for the particular enzymes, resulting in variations in plasma levels of the drugs, differences in drug response, or altered risk for adverse effects.
Affect
Cite
Citations (7)