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Absolute bioavailability studies of a new oral topotecan formulation in Chinese patients using UHPLC–MS/MS

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Abstract

Xinze® is a new capsule formulation of topotecan being made in China which is similar to Hycamtin®, the currently available oral formulation approved in 2007 for the treatment of relapsed small cell lung cancer (SCLC). As topotecan bioavailability and pharmacokinetic data for Chinese patients is limited, the aim of the study was to assess the absolute bioavailability and pharmacokinetics of Xinze® in Chinese patients with SCLC treated intravenously (i.v.) with 1.5 mg/m2/d topotecan (Hycamtin®) on day 1 and treated orally with 1.5 mg/m2/d topotecan on day 2. An ultra high-performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) method was developed and validated for the determination of total topotecan (lactone and carboxylate forms) and of topotecan in the lactone form in human plasma samples. The method was validated with respect to selectivity, extraction recovery, matrix effect, linearity, intra- and inter-day precision, accuracy, and stability. The quantification limits were 0.5 ng/mL for total topotecan and 0.1 ng/mL for topotecan in the lactone form. The mean absolute bioavailability of total topotecan and topotecan in the lactone form was 42.24 ± 12.9% and 47.18 ± 16.9%, respectively, values which illustrate good systemic exposure. The presented results demonstrated this method can be a sensitive and efficient tool for bioavailability studies of topotecan.

Highlights

► The absolute bioavailability of a new oral topotecan formulation was estimated. ► The pharmacokinetics of oral topotecan in Chinese patients was first studied. ► A sensitive and time saving UPLC–MS/MS assay has been developed. ► The conversion between the lactone and carboxylate forms of topotecan was studied. ► The present study builds a bridge for further clinical research of oral topotecan.

Introduction

Topotecan [SK&F 104864, (S)-9-dimethylaminomethyl-10-hydroxy camptothecin] is a semi-synthetic water-soluble analog of camptothecin; it exists in a lactone form and a carboxylate form (Fig. 1) at physiological pH. As a specific inhibitor of topoisomerase I [1], topotecan interferes with the resealing of DNA single-strand breaks. It has shown good anticancer activity against a variety of human tumor types, including ovarian cancer [2], [3], cervical cancer [4], lung cancer [5], and malignant brain gliomas [6].

The intravenous (i.v.) formulation of topotecan received marketing approval for the treatment of ovarian cancer and relapsed small-cell lung cancer (SCLC) in 1996 and 1998, respectively, and the original capsule formulation (Hycamtin®) was recently approved (2007) for the treatment of relapsed SCLC. Xinze® is a new capsule formulation of topotecan being made in China which is similar to Hycamtin®. A bioequivalence study in dogs comparing Xinze® to Hycamtin® indicated 90% confidence intervals in the range of 0.80–1.29 for both AUC0−t and Cmax (unpublished observations), indicating that the new oral topotecan appears to be biologically equivalent to the prior formulation. Studies conducted in the Netherlands have reported the absolute bioavailability of topotecan to be 30–40% [7], [8]; it is not known whether the bioavailability in Chinese patients would also fall in this range. The objective of this study was to determine the absolute bioavailability and pharmacokinetics of this new oral topotecan formulation (Xinze®) in Chinese patients with SCLC.

Previously, high-performance liquid chromatography (HPLC) with fluorometric detection has been used to quantify topotecan in human plasma [9], [10], [11], [12]; topotecan levels can also be assessed with HPLC tandem mass spectrometry (HPLC–MS/MS)[13], [14]. To reach an optimized lower limit of quantification (LLOQ) for total topotecan and topotecan in the lactone form, we elected to use ultra high-performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) to establish our quantification in human plasma methodology for our bioavailability studies.

Section snippets

Reagents and materials

Topotecan hydrochloride (99.4% pure) was purchased from The National Institute for the Control of Pharmaceutical and Biological Products (Beijing, China). Acetonitrile and methanol (HPLC grade) were purchased from Fisher Scientific (Fair Lawn, NJ). Formic acid (HPLC grade) was purchased from Sigma–Aldrich (St. Louis, MO, USA). Ultra-pure water was prepared using a Milli-Q water purification system (Millipore Corp, Bedford, MA).

Instruments and analytical conditions

Chromatography was performed on an Acquity-UPLC® system (Waters

LC–MS/MS method development and sample preparation

We found that positive ionization was better than negative ionization for LC–MS/MS detection of topotecan in plasma. The CE in the LC–MS/MS mode was modulated to optimize the sensitivity, and the optimal values were found to be 29 and 34 eV for the lactone form and the carboxylate form, respectively.

As shown in Fig. 2, the properties of topotecan were closely related to the pH conditions. Topotecan samples were analyzed at moderately acidic and physiological pH on the basis of their mass spectra

Conclusion

Plasma concentration–time and pharmacokinetic analysis data were used to estimate the absolute bioavailability of topotecan in Chinese patients with SCLC. Although the sample size studied here was small, our findings indicate that oral topotecan administered at a dose of 1.5 mg/m2/d can produce bioavailability similar to that seen with i.v. administration. Hence, the present results indicate that oral topotecan treatment (Xinze®) can be used clinically at a safe dose in Chinese patients. The

Acknowledgements

The authors thank the patients and the physicians who participated in the study. The work was supported by the Ministry of Science and Technology of the People's Republic of China's and Beijing Municipal Science & Technology Commission, with the grant number 2012ZX09303012 and Z111102071011001, respectively.

References (19)

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