Prognostic significance of orotate phosphoribosyltransferase activity in bladder carcinoma

5-Fluorouracil (5-FU), an antitumor agent, is used clinically against a variety of malignancies, including bladder carcinoma. 5-FU is a prodrug, and orotate phosphoribosyltransferase (OPRT) is the principal enzyme that converts 5-FU directly into an active antitumor metabolite, 5-fluoro-2'-deoxyuridine 5'-monophosphate. In addition, OPRT is the key enzyme in the de novo DNA and RNA synthetic process. To the authors' knowledge, little is known regarding the significance of OPRT in various malignancies, including bladder carcinoma. The authors analyzed the activity levels of OPRT in 60 bladder carcinomas and evaluated the association between the level of OPRT activity and the stage and grade status of bladder carcinoma. They also examined the prognostic significance of OPRT activity in patients with bladder carcinoma and the correlation between OPRT activity levels in bladder carcinoma cells and the sensitivity of those cells to 5-FU.

OPRT activity levels in nonfixed, fresh-frozen specimens of bladder carcinoma and normal bladder were determined enzymatically using a 5-FU phosphorylation assay. The sensitivity of bladder cells to 5-FU was assessed using a microculture tetrazolium dye assay.

The activity levels of OPRT were approximately 7.5-fold higher in bladder carcinoma specimens compared with the activity levels in normal bladder specimens. OPRT activity in muscle-invasive bladder carcinoma was 2-fold higher compared with the activity in superficial bladder carcinoma (classified as Ta and T1). In addition, the activity of OPRT in T1 bladder carcinoma was 2-fold higher compared with the activity in Ta bladder carcinoma. The level of OPRT activity in Grade 3 bladder carcinoma was 6-fold and 2-fold higher compared with the activity in Grade 1 and Grade 2 bladder carcinoma, respectively. Patients who had Ta and T1 bladder carcinoma with low OPRT activity had a longer postoperative tumor free period compared with patients who had bladder carcinoma with high OPRT activity in the 3-year follow-up. There was a positive association between the activity levels of OPRT and thymidylate synthase/thymidine kinase, which are the key enzymes in the de novo/salvage DNA synthetic process. OPRT activity in bladder carcinoma cells was correlated positively with their sensitivity to 5-FU.

to the authors' knowledge, the current study is the first to demonstrate that OPRT activity levels in bladder carcinoma were higher compared with its activity in the normal bladder tissues and that OPRT activity levels were correlated positively with the stage and grade of bladder carcinoma. In addition, high OPRT activity levels in patients with superficial bladder carcinoma predicted early recurrence and high sensitivity to 5-FU. These results suggest that the level of OPRT activity may be used both as a prognostic parameter and as a predictive indicator for 5-FU efficacy in patients with bladder carcinoma and that OPRT may be a molecular therapeutic target in bladder carcinoma.