Analysis of urinary nucleosides as potential tumor markers in human breast cancer by high performance liquid chromatography/electrospray ionization tandem mass spectrometry

Breast cancer is the most common female cancer and the fourth leading cause of cancer death among women in Taiwan. We measured urinary nucleoside levels in female breast cancer patients (n = 36) to evaluate the diagnostic value of nucleosides as potential tumor markers. Purification of urinary nucleosides was performed using a 96-well solid phase extraction (SPE, cation-exchange column) procedure to decrease the variation between the single column preparations and to shorten the pretreatment time. Cation-exchange allows for the comprehensive purification of modified nucleosides, such as 2-deoxynucleosides, that are not purifiable by phenylboronic acid-based SPE. High-performance liquid chromatography (HPLC) coupled with mass spectrometry (MS) in selected reaction monitoring (SRM) mode was used to quantify multiple nucleosides. Tubercidin was used as an internal standard. The qualitative parameters, retention time, and the parent and daughter ions used revealed that the method was more specific and sensitive than traditional UV detection. Urinary levels of 3 nucleosides, cytidine, 3-methylcytidine, and inosine were significantly higher in breast cancer patients than in normal controls (p < 0.01). The discriminative powers of cytidine, 3-methylcytidine, and inosine were 58%, 58%, and 62%, respectively. LC/MS/MS is a highly specific and sensitive method for rapidly screening a large number of urinary nucleosides that may be potential cancer markers. The 3-methylcytidine may be a candidate marker for breast cancer.