Journal of Pharmaceutical and Biomedical Analysis 59 (2012) 117–122 Contents lists available at SciVerse ScienceDirect Journal of Pharmaceutical and Biomedical Analysis jou rn al h om epage: www.elsevier.com/locate/jpba Quantification of cabazitaxel in human plasma by liquid chromatography/triple-quadrupole mass spectrometry: A practical solution for non-specific binding Peter de Bruijn ∗ , Anne-Joy M. de Graan, Annemieke Nieuweboer, Ron H.J. Mathijssen, Mei-Ho Lam, Ronald de Wit, Erik A.C. Wiemer, Walter J. Loos Department of Medical Oncology, Erasmus MC – Daniel den Hoed Cancer Center, University Medical Center, Rotterdam, The Netherlands a r t i c l e i n f o Article history: Received 12 August 2011 Received in revised form 11 October 2011 Accepted 12 October 2011 Available online 24 October 2011 Keywords: Cabazitaxel LC–MS/MS Human plasma Non specific binding Validated a b s t r a c t A rapid and sensitive liquid chromatography/tandem mass spectrometry (LC–MS/MS) method has been developed and validated for the quantitative determination of cabazitaxel, a novel tubulin-binding tax- ane, in 100 l aliquots of human lithium heparinized plasma with deuterated cabazitaxel as internal standard. The sample extraction and cleaning-up involved a simple liquid–liquid extraction with 20 l aliquots of 4% ammonium hydroxide, 100 l aliquots of acetonitrile and 1 ml aliquots of n-butylchloride. Chromatographic separations were achieved on a reversed phase C 18 column eluted at a flow-rate of 0.20 ml/min on a gradient of acetonitrile. The overall cycle time of the method was 5 min, with cabaz- itaxel eluting at 3.0 min. The multiple reaction monitoring transitions were set at 836 > 555 (m/z), and 842 > 561 (m/z) for cabazitaxel and the internal standard, respectively. The calibration curves were linear over the range of 1.00–100 ng/ml with the lower limit of quantitation validated at 1.00 ng/ml. The within- run and between-run precisions, also at the level of the LLQ, were within 8.75%, while the accuracy ranged from 88.5 to 94.1%. As dilution of samples prior to extraction resulted in a loss of cabazitaxel of approxi- mately 6.5% per dilution step, a second calibration curve ranging from 40.0 to 4000 ng/ml was validated and was also linear. The within-run and between-run precisions in this range were within 4.99%, while the accuracy ranged from 95.8 to 100.3%. The method was successfully applied to samples derived from a clinical study. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Acquired and intrinsic resistance to docetaxel and paclitaxel (i.e., the two approved first generation taxanes) is still an impor- tant concern in daily clinical practice. Therefore, the intravenously available semi-synthetic taxanes, cabazitaxel (Jevtana ® ; XRP6258; TXD258; RPR116258A) and larotaxel (RPR109881A) were selected for clinical development as a result of their efficacy in a broad range of cell-lines and tumor models of mouse and human origin. Also, both compounds showed greater potency than docetaxel in cell lines expressing the drug transporter p-glycoprotein (reviewed in [1–3]). While larotaxel is currently still under clinical evaluation, cabazitaxel has been approved in the US by the Food and Drug ∗ Corresponding author at: Erasmus University Medical Center – Daniel den Hoed Cancer Center, Department of Medical Oncology, Josephine Nefkens Building, Room Be-462, ‘s Gravendijkwal 230, 3015 CE Rotterdam, The Netherlands. Tel.: +31 10 7041252; fax: +31 10 7041053. E-mail address: p.debruijn@erasmusmc.nl (P. de Bruijn). Administration (FDA) in June 2010 [3] and in Europe by the Euro- pean Medicines Agency (EMA) in January 2011 [4] in combination with prednisone for the treatment of patients with castration- resistant metastatic prostate cancer whose disease progresses after docetaxel treatment, based on the results of the TROPIC trail inves- tigating cabazitaxel plus prednisone versus mitoxantrone plus prednisone following docetaxel failure [5]. Cabazitaxel is currently being investigated in the setting of metastatic breast cancer pro- gressing after taxane or anthracycline based chemotherapeutic regimens [6,7]. A population pharmacokinetic model was developed using pharmacokinetic data from five different studies [4], from which two currently have been published as peer reviewed manuscripts [7,8]. The pharmacokinetics of cabazitaxel are linear in the studied dose-range of 10–30 mg/m 2 given as 1 h infusions and are consis- tent with a three-compartment pharmacokinetic model with half lives in the initial, intermediate and terminal phase of approxi- mately 4.4 min, 1.6 h, and 95 h, respectively. The drug has a fast plasma clearance estimated to be 48.5 l/h in the studied population and has a large volume of distribution of 4870 l. The ex vivo protein binding was 91.6%, mainly to albumin and lipoproteins, while the 0731-7085/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jpba.2011.10.010