Benzylacyclouridine (BAU) is a specific and orally available uridine phosphorylase (UrdPase) inhibitor that plays a major role in the regulation of uridine metabolism and is able to potentiate the toxicity of 5-Fluorouracil against human prostate cancer cells with antitumor potential.

Benzylacyclouridine (BAU) is a potent and selective inhibitor of uridine phosphorylase (UrdPase). In multiple human cancer cell lines, BAU increased 5-fluorouracil (5-FU) cytotoxicity when administered prior to 5-FU, demonstrating its potential to sensitize tumor cells to chemotherapy by inhibiting UrdPase activity[1].

In dogs and pigs, oral or intravenous Benzylacyclouridine (30 or 120 mg/kg) markedly inhibited uridine degradation and produced sustained increases in plasma uridine (t₁/₂ = 1.8–3.6 h in dogs, 1.6–2.3 h in pigs; tissue:plasma ratio ≈ 0.7). In a Phase I trial in advanced cancer patients, oral Benzylacyclouridine at 200–1600 mg/m² produced dose-linear pharmacokinetics (Cmax = 19–99 μM; t₁/₂ = 3.0–3.9 h) and raised plasma uridine by 120–250%. No dose-limiting toxicity was observed, and 800 mg/m² is recommended as the Phase II starting dose when combined with 5-FU[1].