Disposition of [g-h]paclitaxel and Cremophor El in a Patient with Severely Impaired Renal Function

In the present work, we studied the pharmacokinetics and metabolic disposition of [G-H]paclitaxel in a female patient with recurrent ovarian cancer and severe renal impairment (creatinine clearance: ;20 ml/min) due to chronic hypertension and prior cisplatin treatment. During six 3-weekly courses of paclitaxel at a dose level of 157.5 mg/m (viz. a 10% dose reduction), the renal function remained stable. Pharmacokinetic evaluation revealed a reproducible and surprisingly high paclitaxel area under the plasma concentration-time curve of 26.0 6 1.11 mM.h (mean 6 S.D.; n 5 6; c.v. 5 4.29%), and a terminal disposition half-life of ;29 h. Both parameters are substantially increased (;1.5-fold) when compared with kinetic data obtained from patients with normal renal function. The cumulative urinary excretion of the parent drug was consistently low and averaged 1.58 6 0.417% (6 S.D.) of the dose. Total fecal excretion (measured in one course) was 52.9% of the delivered radioactivity, and mainly comprised known monoand dihydroxylated metabolites, with unchanged paclitaxel accounting for only 6.18%. The plasma area under the plasma concentration-time curve of the paclitaxel vehicle Cremophor EL, which can profoundly alter the kinetics of paclitaxel, was 114.9 6 5.39 ml.h/ml, and not different from historic data in patients with normal or mild renal dysfunction. Urinary excretion of Cremophor EL was less than 0.1% of the total amount administered. These data indicate that the substantial increase in systemic exposure of the patient to paclitaxel relates to decreased renal metabolism and/or urinary elimination of polar radioactive species, most likely lacking an intact taxane ring fragment. The antineoplastic agent paclitaxel has been known as a highly effective chemotherapeutic agent in platinum-refractory ovarian cancer since 1989 (McGuire et al., 1989; Ozols, 1998; Wiseman and Spencer, 1998). Fifteen to thirty percent of patients with cisplatinresistant disease respond to paclitaxel treatment, and in up to 7% of the cases complete remissions can be achieved. These response rates are even higher in patients with tumors still sensitive to platinumcontaining chemotherapy. Treatment with paclitaxel at a dose of 175 mg/m infused over 3 h once every 3 weeks is a widely accepted and studied regimen in this indication (Ozols, 1998). The clinical pharmacokinetic behavior of paclitaxel is characterized by a distinct nonlinear disposition profile (Sonnichsen and Relling, 1994; Gianni et al., 1995), with renal elimination pathways of the parent drug accounting for less than 15% of the dose (Rowinsky, 1995; Walle et al., 1995). The primary routes of paclitaxel elimination consist of successive hydroxylation reactions and biliary and intestinal secretion of the parent drug and its metabolic products (Monsarrat et al., 1993; Sparreboom et al., 1997). The major metabolic products identified in humans correspond to two monohydroxylated compounds with a hydroxyl function on the a-position at C6 of the taxane ring (6a-hydroxypaclitaxel) or on the para-position of the phenyl group at C39 in the C13 side chain (39-p-hydroxypaclitaxel) and 1 dihydroxylated compound (6a,39-p-dihydroxypaclitaxel) (Harris et al., 1994a; Sparreboom et al., 1995; Royer et al., 1995). The 6ahydroxylation has been shown to be catalyzed by cytochrome P-450 2C8 (Rahman et al., 1994; Cresteil et al., 1994), whereas formation of 39-p-hydroxypaclitaxel appears to be dependent on cytochrome P-450 3A4 (Harris et al., 1994b; Kumar et al., 1994). Consistent with the importance of hepatic elimination by the cytochrome P-450 family, a recent clinical study with paclitaxel administered to a large group of patients with liver dysfunction showed a substantial increase in experienced toxicity (Venook et al., 1998). In contrast, published pharmacologic data on paclitaxel in adults with renal failure are very limited and available only in abstract form (Schilder et al., 1994; Fazeny et al., 1995; Conley et al., 1997). In addition, it is noteworthy that there are no data of patients with severe, predialysis renal impairment treated with paclitaxel. In the present report, we describe the pharmacokinetics of paclitaxel and its formulation vehicle Cremophor EL in a patient with recurrent ovarian cancer and severely impaired renal function who was treated with six 3-weekly courses of paclitaxel. In one of the courses, we used [G-H]paclitaxel to allow detailed assessment of the elimination routes of paclitaxel and to determine its complete metabolic fate. Patient, Materials, and Methods Patient Characteristics and History. The patient studied was a 65-yearold Caucasian female, initially diagnosed at 55 years of age with FIGO (i.e., the International Federation of Gynaecology and Obstetrics) stage 3C poorly Send reprint requests to: Alex Sparreboom, Ph.D., Department of Medical Oncology, Rotterdam Cancer Institute (Daniel den Hoed Kliniek) and University Hospital Rotterdam, P.O. Box 5201, 3008 AE Rotterdam, the Netherlands. E-mail: [email protected] 0090-9556/99/2711-1300–1305$02.00/0 DRUG METABOLISM AND DISPOSITION Vol. 27, No. 11 Copyright © 1999 by The American Society for Pharmacology and Experimental Therapeutics Printed in U.S.A. 1300 at A PE T Jornals on Jne 2, 2017 dm d.aspurnals.org D ow nladed from differentiated serous ovarian cancer. She was also known to have poorly regulated hypertension and chronic, slowly progressive renal insufficiency, presumably due to nephrosclerosis, although a histologic biopsy to prove the diagnosis was never performed. After successful debulking surgery, the patient was treated with six cycles of combination chemotherapy consisting of cisplatin and cyclophosphamide. She remained in complete remission for 7 years, until December 1996, when there was a local relapse. Second line chemotherapy with carboplatin and cyclophosphamide again induced a complete remission; at that time, the creatinine clearance was 30 ml/min. One and a half years later, the patient again relapsed locally, and was simultaneously diagnosed with a metastasis adjacent to the transverse colon in the upper abdomen. The creatinine clearance was decreased to around 20 ml/min, whereas hematopoiesis and the results of liver function tests were all normal. It was decided to treat the patient with a 3-weekly schedule of paclitaxel at the recommended dose of 175 mg/m minus 10% (viz. 157.5 mg/m) to avoid potential risks related to the critical preterminal renal insufficiency. During therapy, the patient did not use any comedication that might have interfered with paclitaxel disposition. Throughout six courses of treatment, the creatinine clearance remained stable. The courses were very well tolerated without any sign of substantial bone marrow suppression or deterioration of other organ functions. A computer tomographic scan performed after three courses showed a partial response, which was sustained after an additional three cycles. Chemicals. Paclitaxel powder (batch 484034; purity 98.3% by reversed phase HPLC) and commercially available paclitaxel formulated in a mixture of Cremophor EL and dehydrated ethanol USP (Taxol; 1:1, v/v) were kindly provided by Bristol-Myers Squibb (Woerden, the Netherlands). The internal standard for quantitative paclitaxel analysis, docetaxel (batch 14RPOC92320; purity 98.0% by reversed phase HPLC), was obtained from Rhone-Poulenc Rorer (Vitry-sur-Seine Cedex, France). Authentic reference standards for 6ahydroxypaclitaxel, 39-p-hydroxypaclitaxel, and 6a,39-p-dihydroxypaclitaxel were obtained after isolation and purification of patient fecal samples, as described (Sparreboom et al., 1995). Chemical structures of the standards were confirmed by on-line photodiode array detection and fast atom bombardment ionization/mass spectrometry, with the compounds dissolved in methanol added to a glycerol matrix, using a JMS-SX/SX102A Tandem Mass Spectrometer (Jeol, Tokyo, Japan) with a 6-keV xenon atom beam and a 10-kV accelerating voltage. Standards of baccatin III (purity: .95.0%) and 10deacetylbaccatin III (purity: .95.0%) from Taxus baccata were purchased from Sigma-Aldrich Chemie (Zwijndrecht, the Netherlands). [G-H]Paclitaxel (batch 227-163-0024; radiochemical purity 99.7%) with a specific activity of 2.4 Ci/mmol was supplied by Moravek Biochemicals, Inc. (Brea, CA). The majority of the tritium is in the mand p-positions of the aromatic rings, with minor amounts in the 10-, 39-, and 2-positions of the taxane ring system (see Fig. 1). The Cremophor EL reference material was obtained from Sigma Chemical Co. (St. Louis, MO), and Coomassie brilliant blue G-250 was purchased from Bio-Rad Laboratories (Munich, Germany) as a concentrated solution in 85% (w/v) phosphoric acid/95% (v/v) ethanol (2:1, v/v). All other chemicals and reagents used were of reagent grade or better, and originated from Rathburn (Walkerburn, UK). HPLC-grade water was obtained from a Millipore (Milford, MA) Milli-Q-UF system. Ultima Gold scintillation cocktail was purchased from Packard (Meriden, CT). Treatment and Sampling Schedule. The patient studied received the courses of paclitaxel at a dose level of 175 mg/m minus 10% (viz. 157.5 mg/m) by a 3-h i.v. infusion. In the third course, the dosing solution for administration was prepared by adding a stock solution of [G-H]paclitaxel in absolute ethanol USP to unlabeled paclitaxel in Cremophor EL/ethanol (1:1, v/v; 6 mg/ml), and diluting this mixture with an aqueous solution composed of 5.25% (w/v) glucose and 0.9% (w/v) sodium chloride. The final dose solution contained 56.9 ng of [G-H]paclitaxel per ml, 512 mg of unlabeled paclitaxel per ml, and 42.7 ml of Cremophor EL per ml (target dose volume, 308 ml/m). Blood samples (;5 ml) for pharmacokinetic studies were obtained during all treatment courses in glass hemogard vacutainer tubes with lyophilized sodium heparin (Becton Dickinson, Meylan, France) as anticoagulant, and were obtained at the following time points: immediately before dosing; at 0.5, 1, 1.5, 2, 2.5, and 3 h after start of infusion; and at 5, 15, 30, and 45 min and 1, 2, 4, 6, 8, 12, and 24 h after the end of infusion. Samples were centrifuged at 4000g for 5 min (4°C) to yield the plasma fraction, which was stored frozen at 280°C in polypropylene vials (Eppendorf, Hamburg, Germany). Complete urine and feces collections were obtained for up to 5 days, and were stored immediately at 280°C in polystyrene containers. Aliquots of urine samples were diluted in 10 volumes of drug-free human plasma to prevent continuing degradation of the analytes (Rangel et al., 1994). Weighted feces samples were homogenized individually in 10 volumes of water using five 1-min bursts of an Ultra-Turrax T25 homogenizer (IKA-Labortechnik, Dottingen, Germany) operating at 20,500 rpm. Aliquots of the feces homogenate were diluted with human plasma before additional sample processing as described above for urine. Drug Measurement. Paclitaxel concentrations in plasma, urine, and feces homogenate were measured by reversed phase HPLC with UV detection after a single solvent extraction, as described (Sparreboom et al., 1998a). Radioactivity in urine and triplicate aliquots of feces homogenate was determined by liquid scintillation counting using Ultima Gold scintillation cocktail, with a Wallac System 1400 counter (Turku, Finland). Each sample was pretreated with a 5-fold volume of acetonitrile by vigorous mixing to remove particulates. Estimates of residual radioactivity in the particulates were determined after digestion with 200 ml of sulfuric acid and neutralization of the solubilization mixture with a 25% (v/v) solution of ammonium hydroxide. All samples were counted until a preset time of 20 min was reached, with quench correction performed by external standardization. The analytical procedure for Cremophor EL in plasma was based on a colorimetric binding assay (Sparreboom et al., 1998b), with modifications as described (Brouwer et al., 1998), using the Coomassie brilliant blue G-250 dye. Cremophor EL concentrations in urine were determined using a modification of the same assay, using 1-ml samples for clean-up and a calibration curve constructed in drug-free urine over a range of 0.01 to 0.2 ml/ml. Separation and Identification of Metabolites. Paclitaxel metabolites in unextracted urine (;1 ml) and fecal extracts (corresponding to approximately 100 mg of feces) were separated and quantified by HPLC with UV detection or by liquid scintillation counting of collected fractions. The isocratic HPLC system consisted of a constaMetric 3200 solvent delivery system (LDC Analytical, Riviera Beach, FL), a Waters 717plus autosampling device (Milford, MA), a model SpH99 column oven (Spark Holland, Meppel, the Netherlands), a SpectraPhysics UV-2000 variable wavelength detector (San Jose, CA), and a FRAC-100 fraction collector equipped with a PSV-50 valve (Pharmacia Biotech, Uppsala, Sweden). Analytes were separated on a stainless steel analytical column (150 3 4.6 mm i.d.) packed with a stationary phase of 5 mm of Inertsil ODS-80A material (GL Science, Tokyo, Japan) supplied with a Lichrospher 100 PR-18 guard column (4.0 3 4.0 mm; 5-mm particles). The FIG. 1. Chemical structures of paclitaxel and its known human metabolites. 1301 PACLITAXEL DISPOSITION IN RENAL FAILURE at A PE T Jornals on Jne 2, 2017 dm d.aspurnals.org D ow nladed from mobile phase consisted of water/methanol/tetrahydrofuran/ammonium hydroxide (54.5:45:2.5:0.1, v/v/v/v), with the pH adjusted to 6.0 (formic acid). The flow rate of the mobile phase was set at 1.0 ml/min with detection performed simultaneously at 230 and 254 nm, at a column temperature of 60°C. Effluent fractions (1 ml) were collected, and H-labeled metabolites were quantified by liquid scintillation counting. In each case, the recovery of radioactivity from the HPLC column was typically .95%. Mass spectra of isolated compounds were obtained from liquid chromatography/dual mass spectrometry analysis using a Finnigan MAT LCQ mass spectrometer (ThermoQuest Co., San Jose, CA) operated with an electrospray ionization probe. Samples were introduced into the interface through a heated nebulizer probe (500°C) using nitrogen as nebulizing gas. A discharge voltage of 3.3 kV was applied to the corona discharge needle to produce a discharge current of 5 mA, with a capillary temperature adjusted to 175°C. The tube lens offset voltage was adjusted to 140 V to maximize sensitivity by balancing desolvation with fragmentation. mass spectrometry data were collected over m/z 200 to 1000. Pharmacokinetic Data Analysis. Plasma concentration versus time data were analyzed using the Siphar software package (version 4.0; SIMED, Créteil, France), by determination of slopes and intercepts of the plotted curves with multiexponential functions. The program determined initial parameter estimates, and these were improved using an iterative numerical algorithm based on Powell’s method. Model discrimination was assessed by a variety of considerations including visual inspection of the predicted curves, dispersion of residuals, minimization of the sum of weighted squares residuals, and the Akaike and Schwartz information criteria. Final values of the iterated parameters of the best-fit equation were used to calculate pharmacokinetic parameters, including drug disposition half-lives (T1/2), area under the plasma concentration-time curve (AUC) from zero to infinity, total plasma clearance, and steady-state volume of distribution, using standard equations. The peak plasma concentration (Cmax) was put on par with the observed drug level at the end of infusion. Statistical evaluation and noncompartmental analysis of Cremophor EL plasma concentration data was performed as described previously (Sparreboom et al., 1998c).