[Determination of new anticancer drug, paclitaxel, in biological fluids by high performance liquid chromatography]

Pharmacokinetics of Weekly Paclitaxel and Feasibility of Dexamethasone Taper in Japanese Patients with Advanced Non-small Cell Lung Cancer

PURPOSE

Weekly paclitaxel combined with a platinum-based agent has been advocated as an alternative regimen for patients with advanced non-small cell lung cancer (NSCLC). Limited studies exist on the tolerability of weekly paclitaxel in Japanese patients with advanced NSCLC. Furthermore, the feasibility of dexamethasone taper in the premedication regimen for weekly paclitaxel has not been examined in these patients. To address this issue, we assessed the maximum tolerated dose, dose-limiting toxicity, and pharmacokinetics of weekly paclitaxel in Japanese patients with advanced NSCLC in a dose-escalation Phase I trial and examined the feasibility of dexamethasone taper in these patients.

METHODS

Weekly 1-hour infusions of paclitaxel were administered at doses of 80 to 120 mg/m(2) (dose escalation of 20 mg/m(2)). The 7-week treatment cycle consisted of 6 infusions followed by a 2-week treatment interval. Pharmacokinetics were assessed during the first cycle. Dexamethasone was commenced at 16 mg and doses were successively halved if hypersensitivity reactions were absent.

FINDINGS

A total of 15 patients with either Stage IIIB or IV NSCLC were enrolled. Although no dose-limiting toxicity was observed at 120 mg/m(2), 4 of 6 patients with peripheral neuropathy required discontinuation of treatment. The maximum accepted dose and the recommended dose were 120 and 100 mg/m(2), respectively. No grade ≥3 adverse events were observed at 100 mg/m(2). The maximum drug concentration and AUC correlated with dose escalation. The pharmacokinetic parameters after the first and sixth infusions were similar, indicating that repeated administration of paclitaxel did not result in drug accumulation or affect its pharmacokinetic profile. Partial response was observed in 3 of 15 patients. Plasma adrenocorticotropic hormone and cortisol levels decreased during treatment but approached baseline levels after a dexamethasone-free interval.

IMPLICATIONS

Weekly paclitaxel at 100 mg/m(2) given as a 1-hour infusion for 6 weeks followed by a 2-week treatment interval was well tolerated by Japanese patients with advanced NSCLC. Dexamethasone taper was feasible in these patients, and no clear trend in plasma adrenocorticotropic hormone or cortisol levels was observed.

Complete regression of xenografted human carcinomas by a paclitaxel-carboxymethyl dextran conjugate (AZ10992)

Clinically available taxanes, such as paclitaxel and docetaxel, represent one of the most promising classes of anticancer agents, despite their toxicity. To improve their pharmacological profiles, AZ10992 was synthesized based on the concept that a rational design of a polymer-drug conjugate would increase the efficacy of the parent drug. This prodrug is a paclitaxel-carboxymethyl dextran conjugate (molecular weight 150,000 g/mol) via a gly-gly-phe-gly linker. The in vivo antitumor study using AZ10992 against colon26 carcinoma cells, resistant to paclitaxel, supported this concept. Additionally, the comparative efficacy studies of AZ10992 and paclitaxel using a panel of human tumor xenografts in nude mice showed the advantages of drug-polymer conjugation. The maximum tolerated dose of AZ10992 was more than twice as high as the MTD of paclitaxel. A repeated intravenous administration of AZ10992 at 30 mg/kg/day (five injections for 4-days) showed complete regression of MX-1 mammary carcinoma xenografts. Also, HT-29 colorectal tumor xenografts, which are highly refractory to paclitaxel, showed complete regression after AZ10992 administered at 30 mg/kg/day (seven injections for 4-days). Pharmacokinetic studies showed that there were significant increases in the amount and the exposure time of total paclitaxel in the tumors after intravenous administration of AZ10992, which explains the enhanced efficacy of AZ10992.

Effects of naringin on the pharmacokinetics of intravenous paclitaxel in rats

It was reported that paclitaxel is an inhibitor of hepatic P-glycoprotein (P-gp) and hepatic microsomal cytochrome P450 (CYP) 3A1/2, and that naringin is an inhibitor of biliary P-gp and CYP3A1/2 in rats. The purpose of this study was to report the effects of oral naringin on the pharmacokinetics of intravenous paclitaxel in rats. Oral naringin (3.3 and 10 mg/kg) was pretreated 30 min before intravenous (3 mg/kg) administration of paclitaxel. After intravenous administration of paclitaxel, the AUC was significantly greater (40.8% and 49.1% for naringin doses of 3.3 and 10 mg/kg, respectively), and Cl was significantly slower (29.0% and 33.0% decrease, respectively) than controls. The significantly greater AUC could be due mainly to an inhibition of metabolism of paclitaxel via CYP3A1/2 by oral naringin. The inhibition of hepatic P-gp by oral naringin could also contribute to the significantly greater AUC of intravenous paclitaxel by oral naringin.

Enhanced bioavailability of paclitaxel by bamboo concentrate administration

The purpose of this study was to investigate the effect of a cotreatment of bamboo concentrates (Jukcho solution; 0.75, 1.5, and 3.0 mL/kg) with the chemotherapeutic agent paclitaxel on the bioavailability of orally administered paclitaxel (50 mg/kg) in rats. The effect of a pretreatment of bamboo concentrates (1.5 and 3.0 mL/kg for 1.0 h or a consecutive 3 day) was also examined. The paclitaxel plasma concentrations of rats orally administered paclitaxel plus bamboo concentrates (coadministration, 3.0 mL/kg and pretreatment, 1.5 and 3.0 mL/kg) were significantly higher than those of rats treated with paclitaxel alone. Plasma concentrations of paclitaxel in groups pretreated with bamboo concentrates for 3 day were markedly higher than those of a paclitaxel control group at the measured time points. The areas under plasma concentration-time curves (AUCs) of paclitaxel in groups pretreated with bamboo concentrates were elevated and the absolute bioavailability (AB%) and relative bioavailability (RB%) of paclitaxel were also significantly higher than those in the control group. The peak concentration (Cmax), half-life (t1/2), and the elimination rate constant (Kel) of paclitaxel after 3 day of pretreatment with bamboo concentrates were also significantly higher than those in the control, but the time required to reach the maximum plasma concentration (Tmax) of paclitaxel was unaffected by the bamboo concentrates. Western blot analyses demonstrated that the level of CYP3A4 was increased in the livers of rats treated orally with paclitaxel, but this was reversed by pretreating with bamboo concentrates. These results show that bamboo concentrates enhance the bioavailability of orally administered paclitaxel and this effect may be associated with a diminished expression of CYP3A4 in the liver.

Enhanced paclitaxel bioavailability after oral coadministration of paclitaxel prodrug with naringin to rats

The aim of this study was to investigate the effect of naringin on the bioavailability and pharmacokinetics of paclitaxel after oral administration of paclitaxel or its prodrug coadministered with naringin to rats. Paclitaxel (40 mg/kg) and prodrug (280, 40 mg/kg paclitaxel equivalent) were coadministered orally to rats with naringin (1, 3, 10 and 20 mg/kg). The plasma concentrations of paclitaxel coadministered with naringin increased significantly (p<0.01 at paclitaxel, p<0.05 at prodrug) compared to the control. The areas under the plasma concentration-time curve (AUC) and the peak concentrations (C(max)) of paclitaxel with naringin significantly higher (p<0.01) than the control. The half-life (t(1/2)) was significantly (p<0.05) longer than the control. The absolute bioavailability (AB, %) of paclitaxel with naringin was significantly higher (3.5-6.8%, p<0.01) than the control (2.2%). Absorption rate constant (K(a)) of paclitaxel with naringin increased, but not significantly. The AUC of paclitaxel after coadministration of prodrug with naringin to rats was significantly (p<0.05) higher than the prodrug control. The relative bioavailability (RB, %) of paclitaxel after coadministration of prodrug with naringin was 1.35-1.69-fold higher than prodrug control. The absolute bioavailability (AB, %) of paclitaxel after coadministration of prodrug with naringin increased significantly (p<0.05) from 6.6 to 9.0% and 11.2%. The bioavailability of paclitaxel coadministered as a prodrug with or without naringin was remarkably higher than the control. Paclitaxel prodrug, a water-soluble compound concerning with its physicochemical properties, passes through the gastrointestinal mucosa more easily than paclitaxel without obstruction of P-gp and cytochrome P-450 in the gastrointestinal mucosa. Oral paclitaxel preparations which is more convenient than the IV dosage forms could be developed with a prodrug form with naringin.

The effect of verapamil on the pharmacokinetics of paclitaxel in rats

The purpose of this study was to investigate the effect of verapamil on the pharmacokinetic parameters of paclitaxel (50 mg/kg) when paclitaxel is co-administered with verapamil (1, 5, and 15 mg/kg) or pretreated with verapamil (5 mg/kg) for 0.5 h, 3 days, and 6 days orally in rats. When paclitaxel was either co-administered or pretreated with verapamil, the peak plasma concentrations (C(max)) of paclitaxel with verapamil were significantly higher (p<0.05 at 5 mg/kg and 0.5 h; p<0.01 at 15 mg/kg, 3 days and 6 days) than that of the control. The areas under the plasma concentration-time curve (AUC) of paclitaxel with verapamil were significantly (p<0.05 at 5 mg/kg and 0.5 h; p<0.01 at 15 mg/kg, 3 days and 6 days) higher than that of the control. The AUCs of paclitaxel were increased with verapamil in the dose dependent manner. The half-life (t(1/2)) of paclitaxel with verapamil was significantly prolonged compared with that of the control, except for 1 mg/kg co-administration. The absolute bioavailability of paclitaxel with verapamil (3.9-5.4%) was significantly (p<0.05 at 5 mg/kg and 0.5 h; p<0.01 at 15 mg/kg, 3 days and 6 days) higher than that of the control (2.2%). The relative bioavailability of paclitaxel pretreated with verapamil was higher than that of co-administration in rats. Based on these results, it might be considered that the pharmacokinetic parameters of paclitaxel was significantly affected by verapamil which is an inhibitor of the metabolizing enzyme (CYP3A4) in the intestinal mucosa and liver, and the p-glycoprotein efflux pump in the intestinal mucosa. If these results are confirmed in humans in a clinical setting, the paclitaxel dose should be adjusted when it is given concomitantly with verapamil.

Enhanced bioavailability of paclitaxel after oral coadministration with flavone in rats

The purpose of this study was to investigate the effect of flavone on the bioavailability of paclitaxel orally coadministered in rats. Paclitaxel (40 mg/kg) and flavone (2, 10, 20 mg/kg) were orally administered to rats orally. The plasma concentration of paclitaxel with flavone increased significantly (P < 0.01) compared to that of paclitaxel control. Area under the plasma concentration-time curve (AUC) of paclitaxel with the dose of 2-20 mg/kg flavone was significantly (P < 0.05 at 10 mg/kg, P < 0.01 at 20 mg/kg) higher than that of control. AUCs of paclitaxel were increased dose-dependently in the dose range of flavone. The absorption rate constant (Ka) of paclitaxel with the dose of 10-20 mg/kg flavone was significantly increased (P < 0.05 at 10 mg/kg, P < 0.01 at 20 mg/kg) compared to that of control. Peak concentration (Cmax) of paclitaxel with the dose of 10-20 mg/kg flavone were significantly increased (P < 0.05 at 10 mg/kg, P < 0.01 at 20 mg/kg) compared to that of control. Half-life (t(1/2)) of paclitaxel with the dose of 10-20 mg/kg flavone was significantly prolonged (P < 0.05 at 10 mg/kg, P < 0.01 at 20 mg/kg) compared to that of control. The relative bioavailability increased significantly by about 2.38- or 3.10-fold (P < 0.05 at 10 mg/kg, P < 0.01 at 20 mg/kg) compared to that of paclitaxel control. Based on these results, It might be considered that the bioavailability of paclitaxel coadministered with flavone was significantly enhanced by the both inhibition of cytochrome P-450 and the P-gp efflux pump in the intestinal mucosa. It could be possible to administer paclitaxel orally besides the established i.v. route.

Pharmacokinetics of paclitaxel in rabbits with carbon tetrachloride-induced hepatic failure

The pharmacokinetic of paclitaxel (1 mg/kg, i.v.) was investigated in rabbits with carbon tetrachloride-induced hepatic failure. The area under the plasma concentration-time curve (AUC) of paclitaxel was significantly (p<0.01) increased in severe carbon tetrachloride-induced hepatic failure rabbits (1,364.54 +/- 382.07 ng/ml x hr) compared to that of normal rabbits (567.52 +/- 141.88 ng/ml x hr), but not significantly in moderate carbon tetrachloride-induced hepatic failure rabbits (803.1 +/- 208.81 ng/ml x hr). The volume of distribution (Vd) (6.25 +/- 1.56 L) and the elimination rate constant(beta) (0.09 +/- 0.025 hr(-1)) of paclitaxel in severe carbon tetrachloride-induced hepatic failure rabbits were significantly (p<0.05) decreased compared to those of normal rabbits (11.65 +/- 2.91 L, 0.12 +/- 0.030 hr(-1)), but not significantly in moderate carbon tetrachloride-induced hepatic failure rabbits (9.46 +/- 2.37 L, 0.10 +/- 0.026 hr'). Total body clearance (CLt) of paclitaxel in severe carbon tetrachloride-induced hepatic failure rabbits (0.733 +/- 0.183 L/hr/kg) was significantly (p<0.01) decreased compared to that of normal rabbits (1.762 +/- 0.440 L/hr/kg), but not significantly in moderate carbon tetrachloride-induced hepatic failure rabbits (1.245 +/- 0.311 L/hr/kg). The half-life(t 1/2) of paclitaxel in severe carbon tetrachloride-induced hepatic failure rabbits (7.71 +/- 2.16 hr) was significantly (p<0.05) increased compared to that of normal rabbits (5.75 +/- 1.44 hr), but not significantly in moderate carbon tetrachloride-induced hepatic failure rabbits (6.77 +/- 1.76 hr). This results could be due to inhibition of paclitaxel metabolism in liver disorder rabbits since paclitaxel is essentially metabolized in liver. The findings suggest that the dosage regimen of paclitaxel should be adjusted when the drug would be administered in patients with liver disorder in a clinical situation.

Paclitaxel delivery systems: the use of amino acid linkers in the conjugation of paclitaxel with carboxymethyldextran to create prodrugs

Paclitaxel was bound via its hydroxyl group to carboxymethyldextran (CMDex, 150 kDa) by means of an amino acid linker; the linker was introduced into the 2'- or 7-hydroxyl group of the paclitaxel through an ester bond. These conjugates--CMDex-2'-paclitaxel and CMDex-7-paclitaxel--were designed to be water-soluble with a paclitaxel content between 6-8% (w/w) with a degree of subsititution (DS) of the CM groups at 0.6 per sugar residue. The release of the paclitaxel from the conjugates was influenced by the hydroxyl group (2'- or 7-) of paclitaxel to which the amino acid linker was introduced, and by what amino acid was used as the linker. In mouse plasma incubated at 37 degrees C for 72 h, the most paclitaxel was released using CMDex-paclitaxel conjugate with 2'gly followed by, in descending order, 2'-ala, 2'-leu, 2'-ile, and 7-gly as the amino linkers. Colon 26, a Taxol resistant cancer, was introduced into mice and the conjugates were intravenously administered by bolus injection for a tumor distribution study, and intermittently intravenously administered for a tumor growth regression study. In both studies the highest amount of paclitaxel release was found in the CMDex-2'-gly-paclitaxel followed by CMDex-2'-ala-paclitaxel, CMDex-2'-leu-paclitaxel and paclitaxel. There was a direct correlation between the amount of paclitaxel released and the observed efficacy. CMDex-2'-ile-paclitaxel and CMDex-7-gly-paclitaxel did not show any anti-tumor activity. These results clearly demonstrate that a CMDex-paclitaxel with an appropriate amino acid linker has significant anti-tumor activity against colon 26, and that these anti-tumor effects appear to correlate with the amounts of paclitaxel released in the tumor.

Rapid and sensitive determination of paclitaxel in mouse plasma by high-performance liquid chromatography

This report describes a rapid, simple and sensitive isocratic high-performance liquid chromatography with diode array UV detection for micro-sample analysis of paclitaxel in mouse plasma. The analysis utilized a Capcell-pak octadecyl analytical column and a mobile phase consisting of acetonitrile--0.1% phosphoric acid in deionized water (55:45, v/v). Paclitaxel and n-hexyl p-hydroxybenzoic acid (internal standard) were extracted from plasma by one-step extraction with tert.-butyl methyl ether. Peak purity was determined over a UV wavelength range of 200 to 400 nm. Paclitaxel and the internal standard were eluted at 3.4 min and 5.4 min, respectively, at a mobile phase flow-rate of 1.3 ml/min. No interfering peaks were observed and the total run time was 10 min. The standard curve was linear (r = 0.9999) over the concentration range of 0.010-500 micrograms/ml. The extraction recovery was > 90% for both paclitaxel and n-hexyl p-hydroxybenzoic acid. The intra- and inter-day assay variabilities of paclitaxel ranged from 0.4 to 2.2% and 0.6 to 7.8%, respectively. The LOD and LOQ were 5 and 10 ng/ml, respectively, for paclitaxel using a plasma sample volume of 100 microliters. This highly sensitive and simple assay method was successfully applied to a pharmacokinetic study after i.v. administration of paclitaxel 20 mg/kg to mice.

Determination of paclitaxel in human plasma using single solvent extraction prior to isocratic reversed-phase high-performance liquid chromatography with ultraviolet detection

An isocratic reversed-phase high-performance liquid chromatographic method with ultraviolet detection at 230 nm has been developed for the determination of paclitaxel in human plasma. Plasma samples were prepared by a selective one-step liquid-liquid extraction involving a mixture of acetonitrile-n-butyl chloride (1:4, v/v). Paclitaxel and the internal standard docetaxel were separated using a column packed with ODS-80A material, and a mobile phase consisting of water-methanol-tetrahydrofuran-ammonium hydroxide (37.5:60:2.5:0.1, v/v). The calibration graph for paclitaxel was linear in the range 10-500 ng/ml, with a lower limit of quantitation of 10 ng/ml, using 1 ml plasma samples. The extraction recoveries of spiked paclitaxel and docetaxel to drug-free human plasma were 89.6+/-8.52 and 93.7+/-5.0%, respectively. Validation data showed that the assay for paclitaxel is sensitive, selective, accurate and reproducible. The assay has been used in a single pharmacokinetic experiment in a patient to investigate the applicability of the method in vivo.