BIOCHEMICAL AND GENETIC STUDIES OF HUMAN URIDINE PHOSPHORYLASE 1 (EC 2.4.2.3) AS A TARGET FOR THE DEVELOPMENT OF NEW INHIBITORS FOR CANCER CHEMOTHERAPY

Daiana Renck (INCT-TB); Rodrigo Gay Ducati (INCT-TB); Diógenes Santiago Santos (INCT-TB); Luiz Augusto Basso (INCT-TB)

Pyrimidines can be synthesized either through the de novo or salvage pathways. Uridine phosphorylase (UP; EC 2.4.2.3) is a pyrimidine nucleoside phosphorylase that belongs to the nucleoside phosphorylase (NP) super-family of proteins in the NP-1 subset. UP is an enzyme that is present in the pyrimidine salvage pathway and catalyzes the phosphorolysis of uridine to uracil. Although UP is present in most normal tissues and in tumors, its activity as well as its expression is elevated at the second. This enzyme regulates strictly the concentration of uridine in plasma and tissues and affects activation and catabolism of several nucleoside analogues used in chemotherapy of cancer, such as 5-fluorouracil (5-FU). Clinical studies have demonstrated that uridine can be used to reduce 5-FU toxicity, leading to an increased therapeutic index, and to selectively protect normal tissues from this host toxicity; high doses of exogenous uridine are not well tolerated in humans. In humans there are two UP isoforms, hUP1 and hUP2. Therefore, there is a significant interest in the development of compounds that inhibit the hUP1, since it is more widely distributed and the elevated levels of activity in tumor cells may contribute to selectivity. In this study, we describe the amplification and cloning of the gene, and expression and purification of recombinant and kinetic studies of hUP1.