Hepatocyte spheroids as a viable model for recapitulation of complex metabolism pathways of loratadine in humans.

Accurate prediction of metabolic pathways in humans can be challenging because liver matrices may fail to produce certain metabolites.Rat and human spheroids, generated from cryopreserved hepatocytes in media that contained minimal amount of serum, maintained morphology, viability and cytochrome P450 (CYP) activities for at least a week without media exchange.With spheroid cultures, multiple Phase I and Phase II metabolites were observed in rat and human spheroid cultures that were incubated with loratadine (LOR) for multiple days.

Effects of CYP inhibitors on precocene I metabolism and toxicity in rat liver slices.

We present a comprehensive in vitro approach to assessing metabolism-mediated hepatotoxicity using male Sprague-Dawley rat liver slices incubated with the well characterized hepatotoxicant, precocene I, and inhibitors of cytochrome P450 (CYP) enzymes. This approach combines liquid chromatography mass spectrometry (LC MS) detection methods with multiple toxicity endpoints to enable identification of critical metabolic pathways for hepatotoxicity. The incubations were performed in the absence and presence of the non-specific CYP inhibitor, 1-aminobenzotriazole (ABT) and isoform-specific inhibitors.

Development and evaluation of a multiple-plate fraction collector for sample processing: application to radioprofiling in drug metabolism studies.

Microplate scintillation counters are utilized routinely in drug metabolism laboratories for the off-line radioanalysis of fractions collected during HPLC radioprofiling. In this process, the current fraction collection technology is limited by the number of plates that can be used per injection as well as the potential for sample loss due to dripping or spraying as the fraction collector head moves from well to well or between plates. More importantly, sample throughput is limited in the conventional process, since the collection plates must be manually exchanged after each injection.

Biotransformation profiling of [(14)C]ixabepilone in human plasma, urine and feces samples using accelerator mass spectrometry (AMS).

Ixabepilone (BMS-247550, Ixempra is a semi-synthetic analog of the natural product epothilone B and marketed for its use in the treatment of cancer. A conventional human ADME study using decay counting methods for (14)C detection could not be conducted due to the radiolytic instability of [(14)C]ixabepilone at a typical specific activity (generally 1-10 microCi/mg). However, [(14)C]ixabepilone was sufficiently stable at low specific activity (1-2 nCi/mg).

Metabolism and excretion of an oral taxane analog, [14C]3'-tert-butyl-3'-N-tert-butyloxycarbonyl-4-deacetyl-3'-dephenyl-3'-N-debenzoyl-4-O-methoxy-paclitaxel (BMS-275183), in rats and dogs.

3'-tert-Butyl-3'-N-tert-butyloxycarbonyl-4-deacetyl-3'-dephenyl-3'-N-debenzoyl-4-O-methoxy-paclitaxel (BMS-275183) is a taxane analog that has the potential for oral use in the treatment of various types of cancer. In this study, the metabolism and excretion of [(14)C]BMS-275183 were evaluated after a single oral administration of [(14)C]BMS-275183 to rats and dogs (15 and 1 mg/kg, respectively). To aid metabolite identification by mass spectrometry (MS), a stable labeled (phenyl-(13)C(6)) BMS-275183 was included in 1:1 ratio of (13)C(6)/(12)C in the dose administration.

CYP3A4-mediated ester cleavage as the major metabolic pathway of the oral taxane 3'-tert-butyl-3'-N-tert-butyloxycarbonyl-4-deacetyl-3'-dephenyl-3'-N-debenzoyl-4-O-methoxycarbonyl-paclitaxel (BMS-275183).

3'-tert-Butyl-3'-N-tert-butyloxycarbonyl-4-deacetyl-3'-dephenyl-3'-N-debenzoyl-4-O-methoxycarbonyl-paclitaxel (BMS-275183) is an orally available taxane analog that has the potential to be used as an oral agent to treat cancers. The compound is similar to the two clinically intravenously administered taxanes, paclitaxel and docetaxel, in that it contains a baccatin ring linked to a side chain through an ester bond. Unlike the other taxanes, the hydrolysis of this ester bond leads to formation of a free baccatin core (M13) that was the major metabolism pathway in incubations of [(14)C]BMS-275183 in human liver microsomes (HLMs) in the presence of NADPH, but it was not formed in incubations with human liver cytosol or HLM in the absence of NADPH.

The effect of ketoconazole on the pharmacokinetics and pharmacodynamics of ixabepilone: a first in class epothilone B analogue in late-phase clinical development.

Purpose: To determine if ixabepilone is a substrate for cytochrome P450 3A4 (CYP3A4) and if its metabolism by this cytochrome is clinically important, we did a clinical drug interaction study in humans using ketoconazole as an inhibitor of CYP3A4.

Experimental Design: Human microsomes were used to determine the cytochrome P450 enzyme(s) involved in the metabolism of ixabepilone. Computational docking (CYP3A4) studies were done for epothilone B and ixabepilone.