Determination of extracellular and intracellular thiopurines and methylthiopurines by high-performance liquid chromatography.

The thiopurine antimetabolites 6-thioguanine and 6-mercaptopurine are important chemotherapeutic drugs in the treatment of childhood acute lymphoblastic leukaemia. Measurement of metabolites of these thiopurines is important because correlations exist between levels of these metabolites and the prognosis in childhood acute lymphoblastic leukaemia. The reversed-phase method for the determination of extracellular thiopurine nucleosides and bases was previously developed and has been modified such that methylthiopurine nucleosides, bases, thioxanthine and thiouric acid can be measured also. The anion-exchange method enables the determination of intracellular mono-, di- and triphosphate (methyl)thiopurine nucleotides in one run. Extraction on ice with perchloric acid and dipotassium hydrogenphosphate results in good recoveries for (methyl)thiopurine nucleotides in lymphoblasts and peripheral mononuclear cells and for methylthioinosine nucleotides in red blood cells. Measurement of the low concentrations of mono-, di- and triphosphate thioguanine nucleotides in red blood cells (detection limit 20 pmol/10(9) cells) is possible after extraction with methanol and methylene chloride, followed by oxidation of thioguanine nucleotides with permanganate and fluorimetric detection.