Chromatographic, capillary electrophoretic and matrix-assisted laser desorption ionization time-of-flight mass spectrometry analysis of urinary modified nucleosides as tumor markers

Modified nucleosides are formed posttranscriptionally in RNA. During RNA turnover free modified nucleosides are formed which circulate in the blood stream and are excreted in the urine. Their levels are increased in a number of malignant diseases, and they can be used in clinical chemistry as tumor markers. The analysis includes the isolation of the nucleosides from urine with phenylboronate gel and their separation and quantitation by HPLC on C18 columns or by capillary electrophoresis on uncoated columns applying a sodium dodecyl sulfate–borate–phosphate buffer. Identification of the nucleosides is performed with matrix-assisted laser desorption ionization time-of-flight mass spectrometry including post source decay spectra. In two clinical studies the diagnostic value of urinary modified nucleosides is investigated, in a study on children with leukemia and other malignant diseases and a study on women with breast cancer. Candidate markers are pseudouridine, 1-methylguanosine, N2-methylguanosine, 3-methyluridine and 1-methyl-inosine.