We investigated the utility of three-dimensional (3D) spheroid cultures of human hepatocytes in discovering drug metabolites. Metabolites of acetaminophen, diclofenac, lamotrigine, midazolam, propranolol and salbutamol were analyzed by liquid chromatography-tandem mass spectrometry (LC/MS/MS) to measure enzyme activities in this system cultured for 2 and 7 days. Sequential metabolic reactions by Phase I and then Phase II enzymes were found in diclofenac [CYP2C9 and UDP-glucuronyltransferases (UGTs)], midazolam (CYP3A4 and UGTs) and propranolol (CYP1A2/2D6 and UGTs). Moreover, lamotrigine and salbutamol were metabolized to lamotrigine-N-glucuronide and salbutamol 4-O-sulfate, respectively. These metabolites, which are human specific, could be observed in clinical studies, but not in conventional hepatic culture systems as in previous reports. Acetaminophen was metabolized to glucuronide and sulfate conjugates, and N-acetyl-p-benzo-quinoneimine (NAPQI) and its metabolites were not observed. In addition, mRNA of drug-metabolism enzymes [CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4, UGT1A1, UGT2B7, sulfotransferase 1A1 (SULT1A1) and glutathione S-transferase pi 1 (GSTP1)], which were measured by qRT-PCR, were expressed in the human hepatocyte spheroids. In conclusion, these results suggest that human hepatocyte spheroids are useful in discovering drug metabolites.

-Drug-induced hepatotoxicity is a common reason for discontinuing the development of candidate clinical drugs. In the present study, we investigated the utility of three-dimensionally cultured human hepatocytes (spheroids) for prediction of hepatotoxicity, using a panel of model drugs: acetaminophen, benzbromarone, chlorpromazine, cyclosporin A, diclofenac, fialuridine, flutamide, imipramine, isoniazid, ticlopidine and troglitazone. Cultured spheroids showed a significant increase of albumin secretion from 2 to 7 days; the secretion started to decrease at 14 days, but continued from 14 days to 21 days. The morphology of the spheroids was well maintained for 21 days. Long-term exposure of spheroids to hepatotoxic drugs resulted in concentration-dependent depression of albumin secretion and elevation of aspartate aminotransferase (AST) leakage. The estimated 50% effective concentration (IC 50 ) values for decrease of albumin secretion changed from 7 days to 14 days, but similar values were obtained at 14 and 21 days, except for diclofenac. Since the IC 50 values and the values of drug concentration inducing 1.2-fold elevation of AST leakage (F1.2) were similar at 14 and 21 days, an incubation period of 14 days was

We developed 3 liquid chromatography (LC) methods coupled to tandem mass spectrometry for comprehensive high-throughput profiling of drug metabolism, employing different columns with gradient systems of aqueous 10 mmol/L ammonium acetate and acetonitrile. The methods were established using testosterone (TST), imipramine (IMP), acetaminophen (APAP) and salbutamol (SBM), which have markedly different values of partition coefficient, P. Method I, using an octadecylized silica (ODS) column (ACQUITY UPLC BEH C18) with a steep gradient, was suitable for analyzing TST and its metabolites, and IMP and its metabolites. These substrates could not be analyzed by Method II, using another ODS column (Atlantis dC18), or Method III, using an Atlantis HILIC silica column. APAP and its metabolites could be analyzed simultaneously by Method II, but not Method I or III. SBM and its metabolites could be detected simultaneously only by Method III. The developed analytical methods were further evaluated with a panel of 18 additional drugs. Based on the retention times and peak shapes, we propose general criteria, in terms of calculated LogP (cLogP) value, for method selection. Broadly speaking, drugs with high cLogP, those with intermediate cLogP and those with low cLogP were best analyzed by Methods I, II and III, respectively, although drugs with borderline values of cLogP could be evaluated by both the relevant methods. The injection cycle for each method was within 10 min, including up to 3 min conditioning time. These methods are expected be useful in high-throughput screening assays to examine biotransformations of candidate drugs.