Preparation of anti-orotate phosphoribosyltransferase antibody and its application to immunochemical detection in human tumor cells.

Orotate phosphoribosyltransferase (OPRT) is a key enzyme in the anabolism of 5-fluorouracil (5-FU), and its expression in tumors is thought to increase the efficacy of 5-FU against the tumor. To detect the OPRT protein by immunoblot and/or immunohistochemical methods, we prepared highly specific antibody to the peptides contained in the human OPRT amino acid sequence. The anti-OPRT polyclonal antibodies, obtained by immunizing rabbits with the OPRT peptides, had a high specificity for the OPRT protein in human tumor xenografts when it was analyzed by immunoblotting, and furthermore, there was a positive correlation between OPRT activity and protein content in 12 human tumors (R2 = 0.632). These results suggest that immunohistochemical detection of tumoral OPRT protein expression with our anti-OPRT antibodies may provide a useful method for predicting the clinical response to 5-FU-based chemotherapy.