New analogues of benzylacyclouridines, specific and potent inhibitors of uridine phosphorylase from human and mouse livers.

Kinetic parameters for the phosphorolytic activity of uridine phosphorylase (UrdPase) from human and mouse livers have been determined. The values of these parameters are: KPi = 279.0 +/- 66.0 microM, KUrd = 242.0 +/- 63.0 microM and Vmax = 3940 +/- 175 pmol/min/mg, and KPi = 76.0 +/- 7.0 microM, KUrd = 143.0 +/- 9.0 microM and Vmax = 293.0 +/- 5.0 pmol/min/mg, for human and mouse livers respectively. Benzylacyclouridines, the specific inhibitors of UrdPase, and seventeen newly synthesized derivatives, modified at the pyrimidine ring, the benzyl moiety or the acyclo tail, have been tested for their potency to inhibit UrdPase and thymidine phosphorylase (dThdPase) from both human and mouse livers. None inhibited dThdPase. In contrast, all of the compounds tested inhibited UrdPase. Competitive inhibition was observed in all cases. Several of the new compounds were superior in their inhibition of UrdPase to the parent compounds. The inhibitory potencies of these compounds with UrdPase from human liver roughly paralleled those obtained with UrdPase from mouse liver. The most potent of these compounds was AM-BBAU (aminomethyl-BBAU or 5-(3'-benzyloxybenzyl)-1-[(1'-aminomethyl-2'-hydroxyethoxy)methyl] uracil) with a Ki value of 18 nM with UrdPase from mouse liver. Structure-activity relationships of the binding of these inhibitors of UrdPase are discussed.