In vitro characterization of sarizotan metabolism: hepatic clearance, identification and characterization of metabolites, drug-metabolizing enzyme identification, and evaluation of cytochrome p450 inhibition.
In vitro biotransformation studies of sarizotan using human liver microsomes (HLM) showed aromatic and aliphatic monohydroxylation and dealkylation. Recombinant cytochromes P450 (P450) together with P450-selective inhibitors in HLM/hepatocyte cultures were used to evaluate the relative contribution of different P450s and revealed major involvement of CYP3A4, CYP2C9, CYP2C8, and CYP1A2 in sarizotan metabolism. The apparent K(m, u) and V(max) of sarizotan clearance, as investigated in HLM, were 9 microM and 3280 pmol/mg/min, predicting in vivo hepatic clearance of 0.94 l/h, which indicates that sarizotan is a low-clearance compound in humans and suggests nonsaturable metabolism at the targeted plasma concentration (< or =1 microM). This finding is confirmed by the reported human clearance (CL/F of 3.6-4.4 l/h) and by the dose-linear area under the curve increase observed with doses up to 25 mg. The inhibitory effect of sarizotan toward six major P450s was evaluated using P450-specific marker reactions in pooled HLM. K(i, u) values of sarizotan against CYP2C8, CYP2C19, and CYP3A4 were >10 microM, whereas those against CYP2D6 and CYP1A2 were 0.43 and 8.7 microM, respectively. Based on the estimates of sarizotan concentrations at the enzyme active sites, no clinically significant drug-drug interactions (DDIs) due to P450 inhibition are expected. This result has been confirmed in human DDI studies in which no inhibition of five major P450s was observed in terms of marker metabolite formation.
Gallemann
Dieter
D
Merck KGaA, Am Feld 32, D-85567 Grafing, Germany. dieter.gallemann@merck.de
Wimmer
Elmar
E
Höfer
Constance C
CC
Freisleben
Achim
A
Fluck
Markus
M
Ladstetter
Bernhard
B
Dolgos
Hugues
H
D001189:Aryl Hydrocarbon Hydroxylases / Q000302:isolation & purification / Q000378:metabolism*; D001711:Biotransformation; D065702:Cytochrome P-450 CYP2B6; D065731:Cytochrome P-450 CYP2C19; D065729:Cytochrome P-450 CYP2C9; D019389:Cytochrome P-450 CYP2D6 / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A / Q000378:metabolism; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000302:isolation & purification*; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D008099:Liver / Q000201:enzymology; D008657:Metabolic Clearance Rate; D008862:Microsomes, Liver / Q000201:enzymology; D009930:Organic Chemicals / Q000378:metabolism / Q000494:pharmacology; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism; D011355:Prodrugs / Q000378:metabolism*
D065607:Cytochrome P-450 Enzyme Inhibitors; D007004:Hypoglycemic Agents; D009930:Organic Chemicals; D011355:Prodrugs; C400322:cytochrome P-450 CYP2C subfamily; C443959:sarizotan; D003577:Cytochrome P-450 Enzyme System; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; C585599:CYP2B6 protein, human; C045793:CYP2C19 protein, human; D065702:Cytochrome P-450 CYP2B6; D065731:Cytochrome P-450 CYP2C19; D019389:Cytochrome P-450 CYP2D6; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D010089:Oxidoreductases, N-Demethylating