The significance of dihydropyrimidine dehydrogenase (DPD) activity in bladder cancer

Dihydropyrimidine dehydrogenase (DPD) is the rate-limiting enzyme in the pathway of uracil and thymine catabolism. DPD is also the principal enzyme involved in the degradation of 5-fluorouracil (5-FU), which is one of the anticancer chemotherapeutic agents currently used in the treatment of bladder cancer. Little is known about the significance of DPD activity in human cancers. We investigated the activity of DPD in 74 bladder cancers and the relationship between the DPD activity and the sensitivity to 5-FU. The levels of DPD activity in bladder cancer and normal bladder tissues were determined by the 5-FU degradation assay. The sensitivity to 5-FU was assessed by the microculture tetrazolium dye (dimethylthiazolyl-2-5-diphenyltetrazolium bromide; MTT) assay. The activity of DPD was approximately 2-fold higher in bladder cancer tissues compared with normal bladder tissues. DPD activity in invasive bladder cancers was approximately 2-fold higher than that in superficial cancers. In addition, the levels of DPD activity in grade 2 and grade 3 bladder cancers were approximately 3-fold and 4-fold higher than that in grade 1 cancers, respectively. Patients with superficial bladder cancer with a low DPD activity had a slightly longer postoperative tumour-free period than those with a high DPD activity over a 2-year follow-up period, but this was not significant. There was an inverse correlation between DPD activity in bladder cancer cells and their sensitivity to 5-FU. Furthermore, 5-chloro-2,4-dihydroxypyridine (CDHP), a potent DPD inhibitor, enhanced the sensitivity to 5-FU. The present study has demonstrated that the level of DPD activity correlated with the progression of the stage and an increase in the grade of the bladder cancer. These results suggest that an elevated DPD activity might be associated with the malignant potential of the bladder cancer. In addition, it might be possible to overcome 5-FU insensitivity by using DPD inhibitors in the treatment protocols of 5-FU-based chemotherapy for bladder cancers.