Received for publication February 14, 2008.
Revised May 1, 2008.
Accepted for publication May 15, 2008.

Extensive metabolism and hepatic accumulation of gemcitabine following multiple oral and intravenous administration in mice

Abstract

In a clinical study with oral gemcitabine (2',2'-difluorodeoxycytidine, dFdC), we found that gemcitabine was hepatotoxic and extensively metabolized to 2',2'-difluorodeoxyuridine (dFdU) after continuous oral dosing. The main metabolite dFdU had a long terminal half-life after oral administration. Our hypothesis was that dFdU and/or phosphorylated metabolites of gemcitabine accumulated in the liver after multiple oral dosing. In this study, mice were treated with oral or intravenous (i.v.) dFdC at a single dose (1qdx1d) or at multiple doses once daily for 7 days (1qdx7d) or seven times daily (7qdx1d). Blood, liver, kidneys, and lungs were collected at several time-points. Urine samples were collected after i.v. dFdC and peripheral blood mononuclear cells after 7qdx1d dosing of dFdC. The nucleosides dFdC and dFdU as well as the nucleotides gemcitabine monophosphate (dFdC-MP), diphosphate (dFdC-DP), triphosphate (dFdC-TP), and dFdU monophosphate (dFdU-MP), diphosphate (dFdU-DP), and triphosphate (dFdU-TP) were simultaneously quantified by high performance liquid chromatography with ultraviolet and radioisotope detection. We demonstrate that phosphorylated metabolites of both dFdC and dFdU are formed in mice, primarily consisting of dFdC-MP, dFdC-TP and dFdU-TP. Multiple dosing of dFdC leads to substantial hepatic and renal accumulation of dFdC-TP and dFdU-TP, which has a more pronounced liver accumulation after oral than after i.v. dosing. The presence of dFdC-MP, dFdC-TP, and dFdU-TP in plasma and urine suggests efflux of these potentially toxic metabolites. Our results show that dFdU, dFdC-TP and dFdU-TP accumulate in the liver after multiple dosing of dFdC in mice and might be associated with hepatotoxicity of oral dFdC in patients.

Key words: absorption, anticancer agents, clinical pharmacokinetics, clinical pharmacology, drug absorption, drug disposition, oral absorption, pharmacokinetics