Effect of ifosfamide treatment on glutathione and glutathione conjugation activity in patients with advanced cancers.
(9/10)Several studies have suggested that the glutathione/glutathione S-transferase (GSH/GST) system is involved in resistance of tumors toward ifosfamide and other cytostatic agents. Besides, ifosfamide metabolites (in vitro) as well as ifosfamide treatment (in vivo) have been shown to decrease cellular GSH availability. In the present study, the in vivo effects of three different ifosfamide treatment schedules on the GSH/GST system were studied in patients with advanced cancers (n = 24): continuous i.v. infusions of 1300 mg/m2 daily for 10 days and 5000 mg/m2/day for 24 h, as well as a 4-h infusion of 3000 mg/m2 daily for 3 days. The GSH/GST system was characterized by administering bromisoval, a probe drug to assess GSH conjugation activity in vivo, as well as by daily monitoring of GSH concentrations in blood cells and plasma. Bromisoval pharmacokinetics was assessed before and at the end of the ifosfamide treatment. Blood cell GSH levels decreased significantly (P < 0.05) during the 3- and 10-day ifosfamide treatment schedules; the 24-h treatment had no effect. The ifosfamide treatment schedules had only minimal effects on bromisoval pharmacokinetics. Assuming that the kinetics of the probe drug provide an accurate reflection of enzyme activity, this suggests that GST activity remains unchanged. Because GSH conjugation of bromisoval enantiomers requires both GST activity and GSH availability, these results also indicate that, despite the 35% decrease in GSH in blood cells of two patient groups, the GSH availability of the cancer patients was not rate-limiting for GSH conjugation of bromisoval enantiomers. If GSH levels in blood cells reflect those in tumors/other tissues, the present results indicate that ifosfamide may be used clinically to decrease GSH levels. However, whether a 35% decrease is sufficient to increase tumor sensitivity toward (other) cytostatics remains uncertain. (+info)
Determination of bromvalerylurea and its metabolites in biological samples by frit-fast atom bombardment liquid chromatography-mass spectrometry.
(10/10)A simple, rapid, and sensitive method which allows us to simultaneously determine bromvalerylurea (BVU) and its three metabolites (3-methylbutyrylurea [MVU], alpha-(cystein-S-yl)isovalerylurea [CVU], and alpha-(N-acetylcystein-S-yl)isovalerylurea [AcCVU]) was investigated by frit-fast atom bombardment liquid chromatography-mass spectrometry (frit-FAB LC-MS). The LC-MS analysis was performed after the solid-phase extraction from tissue and urine samples with a Sep-Pak C18 cartridge. Tissue homogenates and urine were adjusted to pH 4.0 and applied to the cartridges. The retained BVU and its metabolites were eluted from the cartridge with 2 mL of acetonitrile/10 mM ammonium acetate buffer (pH 3.5, 50:50, v/v). The eluate was analyzed by LC-MS, which employs a semimicro type L-column ODS column. The proposed conditions are as follows: mobile phase A, 0.4% glycerol in acetonitrile/10 mM ammonium acetate buffer (pH 3.5) (5:95, v/v); mobile phase B, 0.4% glycerol in acetonitrile; elution mode, linear gradient, 100% A (5 min) to 100% B in 15 min; flow rate, 0.2 mL/min; split ratio, 1:40. Extraction recoveries of BVU and its metabolites were 91.90-97.79% from the spiked liver homogenate and 89.68-96.13% from the spiked urine. The detection limits ranged from 10 to 25 ng/g in selected ion monitoring mode. (+info)