In vitro metabolism of a triclyclic alkaloid (M445526) in human liver microsomes and hepatocytes

Abstract

The in vitro metabolism of M445526 (ZD6126 phenol) was investigated by incubating [¹⁴C]-M445526 at a concentration of 10 µg ml⁻¹ with human hepatic microsomes (4 mg ml⁻¹) or human hepatocytes (2 × 10⁶ cells ml⁻¹) for up to 180 min. Following incubation with microsomes and hepatocytes, up to 78% and 40% of [¹⁴C]-M445526 was metabolized after 180 and 120 min, respectively. High-performance liquid chromatography (HPLC) with radiochemical detection confirmed extensive metabolism of [¹⁴C]-M445526 by microsomes and hepatocytes. Mass spectrometry and ¹H-NMR spectroscopy enabled structural identification of up to eight metabolites. Human liver microsomes formed one major (O-desmethyl) and three minor (a further O-desmethyl and two different hydroxylated) phase I metabolites. Human hepatocytes produced one major metabolite, a sulphate conjugate of the major O-desmethyl metabolite formed by microsomes. Four minor metabolites were also formed, primarily by O-demethylation with subsequent glucuronidation. Taken collectively, [¹⁴C]-M445526 underwent extensive in vitro metabolism by human liver fractions. These data were confirmed by subsequent human in vivo studies.

Key Words::

• ZD6126
• vascular targeting agent
• human microsomal metabolism
• human hepatocyte metabolism

Acknowledgement

The authors would like to acknowledge Jenny Stewart of InforMed Direct for support in the preparation of this paper.