IntroductionMercaptopurine (MP) belongs to a general group of drugs known as antimetabolites, and is used to treat several types of cancers, including leukemia. MP interferes with the synthesis of nucleic acids, and thus disrupts the growth of cancer cells, which are then destroyed. However, because this drug can not distinguish cancer and normal cells, it causes side effects, since some normal cells are affected. Therefore, it is important to develop sensitive quantitative methods for controlling its administration.A number of spectrometric and fluorometric methods have already been successfully used for determining MP. For example, Tawa et al. developed a sensitive fluorometric method, based on the enzymatic oxidation of MP with xanthine oxidase to the oxypurine, followed by oxidation with acidic chromate to the corresponding fluorescent sulfonate. 1 Several liquid chromatographic methods have also been described. [2][3][4][5][6] Jonkers et al. determined MP in human plasma using HPLC, including post-column derivatization and fluorometric detection. 4 Van Os et al. measured MP using solid-phase extraction and reversed-phase HPLC. 5 Georget et al. determined MP in capsules prepared for paediatric patients by capillary zone electrophoresis. 6 Chemiluminescence (CL) has been exploited with a wide range of applications in different fields, such as biotechnology, pharmacology, molecular biology, and clinical and environmental chemistries.7-10 However, only one CL method was reported for the determination of MP, which was based on reactions among tris-(2,2′-bipyridine)ruthenium(II), MP, hydrogen peroxide, Tween 20 and hydroxide ion. 11 In this method, the mixing order of the reagents considerably affects the CL signal. Still, a simple and convenient method to measure mercaptopurine would be highly desirable.Here, we report on such a simple and convenient CL method for the determination of MP. We found that weak CL emitted after mixing H2O2 and luminol under alkaline conditions could be greatly enhanced by MP. Most importantly, this new reaction had a longer light signal, which was very convenient for routine applications, especially with a simple setup, since the mixing of CL reagents could generally be performed outside of the measuring device. Based on this fact, a simple and robust technique for the convenient measurement of MP was developed. The linear range was 1.5 mM -5 µM with a detection limit of 1 µM. Overall, the proposed CL method was simple, convenient and sufficiently sensitive for the determination of MP in the drug powder.
Experimental
ChemicalsA stock solution for 10 -2 M MP (Wako, Japan) was prepared by dissolving in 0.1 M NaOH. Other standard solutions were made by gradually diluting relative stock solutions with 0.1 M NaOH containing 2.5 mM EDTA. Hydrogen peroxide, luminol and other organic compounds were also purchased from Wako, Japan. An MP-containing drug, Leukerin, was obtained from Takeda Pharmaceutical Company, Japan.
CL detection proceduresLight-producing reactions were carried out in 12 ×...