Quantitative detection of 6-thioguanine in body fluids based on a free-standing liquid membrane SERS substrate.

The adverse reactions caused by 6-thioguanine (6-TG) in anti-cancer treatment are closely related to the dose, leading to the urgent need for clinical monitoring of its concentration. In this work, a highly reproducible free-standing liquid membrane (FLM) surface-enhanced Raman spectroscopy (SERS) substrate was developed to detect 6-TG in human urine and serum quantitatively. Briefly, a prepared sample was adjusted to pH 2 and mixed with concentrated core-shell bimetallic nanoparticle (AgcoreAushell NP) suspension. The Au/Ag ratio of the AgcoreAushell NPs was optimized. Then the mixture was formed into an FLM using a custom mold. The relative standard deviation (RSD) of the experimental results can be stabilized below 10% (n ≥ 10). The R2 of the calibration curve in the range of 10 ~ 100 µg kg-1 was 0.988. In addition, the limit of detection (LOD) (3σ/k) of 6-TG was 5 µg kg-1. The FLM SERS platform has been successfully applied to the rapid and reliable analysis of 6-TG spiked in body fluids.

Simple and selective determination of 6-thioguanine by using polyethylenimine (PEI) functionalized carbon dots.

In this work, a new selective and simple fluorescence probe based on polyethylenimine(PEI) functionalized carbon dots (PEI-CDs) for fast determination of 6-thioguanine (6-TG) was developed. We successfully prepared the highly fluorescent PEI-CDs by hydrothermal method, and completed the synthesis and modification processes in one step. The fluorescence quantum yield (QY) of the as-synthesized CDs was 38% and higher than that of most previous reports (5-30%). The fluorescence intensity of PEI-CDs decreased obviously with gradually increased concentration of 6-TG. The interference substances caused a negligible effect on the fluorescence intensity of the (PEI-CDs)-6-TG reaction system with the interference ratios all below 2.8%. Under optimum conditions, a great linear relationship between fluorescence intensity function log(F0/F) and concentration of 6-TG in a wide range from 4µM to 800µM with a detection limit (S/N = 3) of 1.33µM was obtained. And this proposed approach was successfully applied for the determination of 6-TG in human serum and urine samples. Furthermore, the PEI-CDs fluorescence probe has superior potential in practical application of detecting 6-TG due to its inexpensive precursors, simple operation, low toxicity and excellent biocompatibility.

Voltammetric determination of 6-thioguanine and folic acid using a carbon paste electrode modified with ZnO-CuO nanoplates and modifier.

ZnO-CuO nanoplates and 2-chlorobenzoyl ferrocene, were synthesized and used to construct a modified carbon paste electrode. The electrooxidation of 6-thioguanine at the surface of the modified electrode was studied. Under the optimized conditions, the square wave voltammetric (SWV) peak current of 6-thioguanine increased linearly in the concentration range 0.05 to 200.0µM and detection limit of 25±2nM was obtained for 6-thioguanine. The prepared modified electrode exhibits a very good resolution between the voltammetric peaks of 6-thioguanine and folic acid which makes it suitable for the detection of 6-thioguanine in the presence of folic acid in real samples.

Simultaneous determination of 6-mercaptopruine, 6-thioguanine and dasatinib as three important anticancer drugs using nanostructure voltammetric sensor employing Pt/MWCNTs and 1-butyl-3-methylimidazolium hexafluoro phosphate.

6-Mercaptopurine, 6-thioguanine and dasatinib are three important anticancer drugs with high adverse effects in human body. In this study, a Pt/MWCNTs-1-butyl-3-methylimidazolium hexafluoro phosphate-modified carbon paste electrode was developed for the simultaneously determination of 6-mercaptopurine, 6-thioguanine and dasatinib for the first time. The Pt/MWCNTs synthesized by polyol method and have been characterized by transmission electron microscopy and X-ray diffraction methods. The obtained data revealed that the electro-oxidation of 6-mercaptopurine, 6-thioguanine and dasatinib is facilitated as a novel voltammetric sensor. After optimization of electrochemical parameters employing this sensor at pH 8.0, the oxidation peak currents for 6-mercaptopurine, 6-thioguanine and dasatinib were found to vary linearly with their concentrations in the range of 0.05-550µM; 0.1-500µM and 5.0-500µM with detection limits of 0.009µM, 0.05µM and 1.0µM respectively using square wave voltammetric method. The modified electrode has been applied for the selective and precise analysis of 6-mercaptopurine, 6-thioguanine and dasatinib in pharmaceutical formulations and urine samples.

Application of the iodine-azide postcolumn reaction in RP-HPLC for the determination of thioguanine in urine.

The study focuses on the analysis of a sensitive, selective, and simple postcolumn detection method for thioguanine determination, based on the sensitizing induction of thioguanine on iodine-azide reaction and the combination technique of HPLC. The analysis was accomplished in the optimum conditions for iodine-azide detection system and HPLC separation. The values for the linear range, the LOD, and DOQ amounted to 0.8-1.7, 0.4, and 0.5 nmol/mL urine, respectively.

Plasma pharmacokinetics and cerebrospinal fluid penetration of thioguanine in children with acute lymphoblastic leukemia: a collaborative Pediatric Oncology Branch, NCI, and Children's Cancer Group study.

PURPOSE: In preclinical studies, thioguanine (TG) has been shown to be more potent than the standard acute lymphoblastic leukemia (ALL) maintenance agent, mercaptopurine (MP), suggesting that TG may be more efficacious than MP in the treatment of childhood ALL. As part of a pilot trial in which TG was used in place of MP, we studied the plasma pharmacokinetics of oral TG and measured steady-state plasma and CSF TG concentrations during a continuous intravenous infusion (CIVI) in children with newly diagnosed standard-risk ALL. METHODS: Nine plasma samples were collected after each patient's first 60 mg/m2 oral TG dose during maintenance. CIVI TG (20 mg/m2/h over 24 h) was administered during the consolidation phase of therapy, and simultaneous plasma and CSF samples were collected near the end of the infusion. TG was measured by reverse-phase HPLC with ultraviolet detection. Erythrocyte TG nucleotide (TGN) concentrations were measured 7 days after a course of CIVI TG and prior to the start of each maintenance cycle. RESULTS: After oral TG (n = 35), the mean (+/- SD) peak plasma concentration was 0.46 +/- 0.68 microM and the AUC ranged from 0.18 to 9.5 microM.h (mean 1.5 microM.h). Mean steady-state plasma and CSF TG concentrations during CIVI (n = 33) were 2.7 and 0.5 microM, respectively. The mean (+/- SD) TG clearance was 935 +/- 463 ml/min per m2. Plasma TG concentrations did not correlate with erythrocyte TGN concentrations after oral or CIVI TG. The 8-OH-TG metabolite was detected in plasma and CSF. CONCLUSIONS: TG concentrations that are cytotoxic to human leukemia cell lines can be achieved in plasma after a 60 mg/m2 oral dose of TG and in plasma and CSF during CIVI of TG.

Kinetics of mercaptopurine and thioguanine nucleotides in renal transplant recipients during azathioprine treatment.

The purpose of this study was to examine the pharmacokinetics of mercaptopurine (6-MP) and thioguanine nucleotides (6-TGN) during azathioprine treatment. Plasma profiles and urinary excretion of 6-MP and 6-TGN concentrations in red blood cells (RBCs) were measured repeatedly during the first 3 weeks following transplantation in 10 adults, who had received kidney grafts from living related donors. Mean maximal 6-MP plasma concentration (Cmax) was 340 nmol/L (SD = 290), mean time to Cmax (Tmax) was 2 h (SD = 1.8), and mean area under the plasma concentration-time curve (AUC) was 930 nmol/L/h (SD = 770). The mean fraction of azathioprine dose excreted as 6-MP in urine was 1.32% (SD = 1.11). Up to eightfold variability of Cmax and AUC was observed from day to day within each patient. The correlation between 6-MP AUC and amount excreted in the urine was weak (r = 0.37, 95% CI from 0.02 to 0.64). In this group of patients the observed 6-TGN levels in RBCs were low; maxima during the observation period ranged from undetectable to 250 pmol/8 x 10(8) RBCs. In individual patients, 6-TGN levels were relatively stable throughout the dosing interval ("within-dose-interval-CV" < 19%), even when sharp and high 6-MP peaks in plasma were observed.

Formation of 6-thioguanine and 6-mercaptopurine from their 9-alkyl derivatives in mice.

Several 9-alkyl, 6-thiopurines have been reported to have more favorable therapeutic indexes than do the parent drugs, 6-mercaptopurine (MP) and 6-thioguanine (TG). Some of these compounds were reported to be active against cells in culture resistant to 6-thiopurines, and it has been assumed that their mechanisms of action may differ from those of TG and MP. 9-(n-Butyl)-6-thioguanine was essentially inactive toward Chinese hamster ovary cells in vitro when compared with TG (50% effective dose, 250 and 1 microM, respectively). However, lethal doses of 9-(n-butyl)-6-thioguanine and TG in mice were similar when these agents were given i.p. daily for 9 consecutive days (50% lethal dose, 13 and 9 mg/kg/day). Similar organ toxicities were observed upon histopathological examination of dying animals. The cumulative, daily urinary excretion of TG was virtually identical in mice given 20- and 10-mg/kg/day of doses of 9-(n-butyl)-6-thioguanine or TG, respectively, for 9 days. The TG formed was identified by ultraviolet light (340 nm) detection following separation on a reverse phase high performance liquid chromatography system and by fluorescent detection of the permanganate oxidation product separated on a strong anion-exchange system. Dealkylation of 9-(n-butyl)-6-mercaptopurine and 9-ethyl-6-mercaptopurine also occurred in AKR mice. At near equitoxic doses, the daily cumulative urinary excretion of MP from 9-(n-butyl)-6-mercaptopurine and 9-ethyl-6-mercaptopurine was about 20-30% of that observed in mice receiving MP. The MP was confirmed in each case by enzymatic peak-shift of MP to 6-thiouric acid and ultraviolet light detection using the high performance liquid chromatography systems referred to above. The results suggest that these 9-alkyl derivatives serve as prodrugs for TG and MP, a finding that explains a number of their pharmacological and toxicological properties.

High-performance liquid chromatographic assay of 6-methylthioguanine, a major metabolite of 6-thioguanine, in urine.

A flow-fluorimetric high-performance liquid chromatographic assay for 6-methylthioguanine in urine has been developed. This compound is a major catabolite of 6-thioguanine, an important drug in cancer chemotherapy. The metabolite was extracted from alkaline urine with ethyl acetate which was injected onto a reversed-phase high-performance liquid chromatographic system for separation and detection. The method is simple, rapid and sensitive to below 500 ng ml-1 which is below the levels encountered following a therapeutic dose of 6-thioguanine. Another metabolite was chromatographically separated from 6-methylthioguanine and partially characterised.

Reversed-phase high-performance liquid chromatography analysis of 6-thioguanine applicable to pharmacologic studies in humans.

6-thioguanine (6TG) and its metabolites were analyzed in human plasma with a reversed-phase high-performance liquid chromatographic methods. 6TG and related compounds were extracted from plasma with an equal volume of 2 N perchloric acid at a 50-100% recovery efficiency. The neutralized extracts were chromatographed on a muBondapak C18 column by two separate isocratic conditions. 6TG, 6-thiouric acid, 6-thioxanthine, 6-thioguanosine, and 6-methylthiouric acid were analyzed with 0.01 M sodium acetate, pH 3.5-10% methanol as the mobile phase and 340 nm for detection. 6-Methylthioguanine and three unknown metabolites were separated with acetate-25% methanol and 310 nm detection. One of the unknowns was identified as 6-methylthioguanosine. External standard calibration was used for quantitation. The 6TG detection limit was 0.8 nmol/ml in plasma.

Quantitative high pressure liquid chromatography of 6-thioguanine in biological fluids.

The determination of 6-thioguanine in human plasma and urine is described. By using isocratic reversed-phase high pressure liquid chromatography (HPLC) the purine analogues, 6-thioguanine, guanine, 8-azaguanine, allopurinol, oxipurinol, and uric acid, are completely separated within 8 min. the sensitivity of the assay for 6-thioguanine is 0.2 microgram/ml (1.2 x 10(-6) M) with a precision of 3.7%. The applicability for clinical monitoring in a patient's plasma and urine is demonstrated.