SUICIDAL INACTIVATION OF HUMAN DIHYDROPYRIMIDINE DEHYDROGENASE BY (E)-5-(2-BROMOVINYL)URACIL DERIVED FROM THE ANTIVIRAL, SORIVUDINE

An enzymatic study was performed to clarify the mechanism of 18 acute deaths in patients who had received the new oral antiviral drug, soriv udine (SRV), during anticancer chemotherapy with 5-fluorouracil (5-FU) prodrugs. Human dihydropyrimidine dehydrogenase (hDPD), playing a key role in the liver as the rate-limiting enzyme in catabolism of 5-FU, was expressed in E. coli, purified and incubated in the presence of NA DPH with SRV or (E)-5-(2-bromovinyl)uracil (BVU), a metabolite of SRV produced by human gut flora. hDPD was rapidly and irreversibly inactiv ated by BVU, but not by SRV. Radioactivity of [C-14]BVU was incorporat ed into hDPD in the presence of NADPH in a manner reciprocal to the en zyme inactivation. In the absence of NADPH, hDPD was not inactivated b y BVU, nor radiolabeled with [C-14]BVU, Thus, as we demonstrated previ ously with studies using the rat, the acute deaths were strongly sugge sted to be attributable to markedly elevated tissue 5-FU levels which were responsible for irreversible inhibition of hDPD by covalent bindi ng of a reduced form of BVU as a suicide inactivator. (C) 1998 Elsevie r Science Ireland Ltd.