Metabolism of Irinotecan (CPT-11) by CYP3A4 and CYP3A5 in Humans

Metabolism of Irinotecan (CPT-11) by CYP3A4 and CYP3A5 in Humans1

Centre National de Recherche Scientifique, Unite Mixte de Recherche 8532 [A. S., T. C., A. D., A. G., G. V.] and Departments of Medical Oncology [E. R., V. B.] and Pediatric Oncology [F. P., G. V.], Institut Gustave-Roussy, 94805 Villejuif; Department of Medical Oncology, Centre Léon Bérard, Lyon 69008 [S. Z.]; Rhône- Poulenc-Rorer S.A., Antony 92160 [L. V., M-L. R.]; and Bellon, Montrouge 92120 [L. V., M-L. R.], France

Abstract

7-Ethyl-10[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecin (CPT-11), a DNA topoisomerase I inhibitor, undergoes several metabolic pathways to generate conjugated and unconjugated derivatives that could be excreted from the body. The objective of this study was to determine the oxidative metabolites of CPT-11 recovered in human urine samples and to identify cytochrome P450 (CYP) involved in their formation. In addition to the already known metabolites of CPT-11 [SN-38, SN-38-G, 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]carbonyloxycamptothecin (APC), and 7-ethyl-10-(4-amino-1-piperidino) carbonyloxycamptothecin (NPC)], we isolated three oxidized metabolites from the urine of two children and two adults given CPT-11. M1 and M2 (molecular weight, 602) were hydroxylated, respectively, on the CPT moiety and on the terminal piperidine ring of CPT-11. M3 had a molecular mass of 602, but its urine concentration in patients was too low to establish its chemical structure by liquid chromatography/mass spectrometry.

In vitro incubations with cells expressing CYP2C8, CYP2C9, CYP1A1, CYP1A2, or CYP3A7 did not produce any detectable metabolites. Only CYP3A4 produced both APC and NPC, resulting from the oxidation of the piperidinylpiperidine side chain of CPT-11 along with metabolite M2. The metabolism of CPT-11 by CYP3A5 was markedly different because neither APC or NPC nor M2 was produced, whereas only one new metabolite, M4 (molecular weight, 558), was generated by de-ethylation of the CPT moiety. No previous study has reported the presence of the M4 metabolite. Production of APC, NPC, M2, and M4 was prevented by ketoconazole, a specific CYP3A inhibitor. The parameters of CPT-11 biotransformation into M2 and M4 were examined using cell lines expressing, respectively, with CYP3A4 and CYP3A5, indicating that CPT-11 is preferentially metabolized by CYP3A4. In conclusion, CYP3A plays a major role in the metabolism of CPT-11, with some differences of the metabolic profile exhibited by 3A4 and 3A5.

Footnotes

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↵1 Supported by the Ligue Nationale Contre le Cancer and Rhône-Poulenc Rorer S.A. This study was presented in part at the 90th Annual Meeting of the American Association for Cancer Research, Philadelphia, Pennsylvania, 1999.
↵2 Recipient of a fellowship from the Ligue Nationale Contre le Cancer.
↵3 To whom requests for reprints should be addressed, at Department of Pharmacotoxicology and Pharmacogenetics, UMR 8532, Institut Gustave-Roussy, 39 rue Camille Desmoulins, 94805 Villejuif Cedex, France.
↵4 The abbreviations used are: CPT-11, 7-ethyl-10[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecin; CPT, camptothecin; SN-38, 7-ethyl-10-hydroxycamptothecin; SN-38-G, SN-38-glucuronide; APC, 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]carbonyloxycamptothecin; NPC, 7-ethyl-10-(4-amino-1-piperidino)carbonyloxycamptothecin; CYP, cytochrome P450; HPLC, high-performance liquid chromatography; LC, liquid chromatography; MS, mass spectrometry; MW, molecular weight.
↵5 Unpublished data.
- Accepted January 27, 1900.
- Received September 22, 1999.
- Revision received January 18, 1900.