title: Development and validation of a high-performance liquid chromatography-tandem mass spectrometry method for the simultaneous determination of irinotecan and its main metabolites in human plasma and its application in a clinical pharmacokinetic study.
abstract: Irinotecan is currently used in several cancer regimens mainly in colorectal cancer (CRC). This drug has a narrow therapeutic range and treatment can lead to side effects, mainly neutropenia and diarrhea, frequently requiring discontinuing or lowering the drug dose. A wide inter-individual variability in irinotecan pharmacokinetic parameters and pharmacodynamics has been reported and associated to patients' genetic background. In particular, a polymorphism in the UGT1A1 gene (UGT1A1*28) has been linked to an impaired detoxification of SN-38 (irinotecan active metabolite) to SN-38 glucuronide (SN-38G) leading to increased toxicities. Therefore, therapeutic drug monitoring of irinotecan, SN-38 and SN-38G is recommended to personalize therapy. In order to quantify simultaneously irinotecan and its main metabolites in patients' plasma, we developed and validated a new, sensitive and specific HPLC-MS/MS method applicable to all irinotecan dosages used in clinic. This method required a small plasma volume, addition of camptothecin as internal standard and simple protein precipitation. Chromatographic separation was done on a Gemini C18 column (3 μM, 100 mm x 2.0 mm) using 0.1% acetic acid/bidistilled water and 0.1% acetic acid/acetonitrile as mobile phases. The mass spectrometer worked with electrospray ionization in positive ion mode and selected reaction monitoring. The standard curves were linear (R2 ≥0.9962) over the concentration ranges (10-10000 ng/mL for irinotecan, 1-500 ng/mL for SN-38 and SN-38G and 1-5000 ng/mL for APC) and had good back-calculated accuracy and precision. The intra- and inter-day precision and accuracy, determined on three quality control levels for all the analytes, were always <12.3% and between 89.4% and 113.0%, respectively. Moreover, we evaluated this bioanalytical method by re-analysis of incurred samples as an additional measure of assay reproducibility. This method was successfully applied to a pharmacokinetic study in metastatic CRC patients enrolled in a genotype-guided phase Ib study of irinotecan administered in combination with 5-fluorouracil/leucovorin and bevacizumab.
authors.affiliation: CRO, National Cancer Institute, Aviano (PN), Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Marangon
authors.affiliation: CRO, National Cancer Institute, Aviano (PN), Italy.
authors.forename: Bianca
authors.initials: B
authors.lastname: Posocco
authors.affiliation: CRO, National Cancer Institute, Aviano (PN), Italy.
authors.forename: Elisa
authors.initials: E
authors.lastname: Mazzega
authors.affiliation: CRO, National Cancer Institute, Aviano (PN), Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Toffoli
mesh_terms: D001774:Blood Chemical Analysis / Q000379:methods*; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D016903:Drug Monitoring; D006801:Humans; D000077146:Irinotecan; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D000077146:Irinotecan; D002166:Camptothecin