Design of Novel Inhibitors of Human Thymidine Phosphorylase: Synthesis, Enzyme Inhibition, in Vitro Toxicity, and Impact on Human Glioblastoma Cancer

Overexpressed human thymidine phosphorylase (hTP) has been associated with cancer aggressiveness and poor prognosis by triggering pro-angiogenic and anti-apoptotic signaling. Designed as transition state analogs by mimicking the oxacarbenium ion, novel pyrimidine-2,4-diones were synthesized and evaluated as inhibitors of hTP activity. The most potent compound (8g) inhibited hTP in the submicromolar range with a non-competitive inhibition mode regarding both thymidine and inorganic phosphate substrates. Furthermore, compound 8g was devoid of apparent toxicity to a panel of mammalian cells, showed no genotoxicity signals, low probability of drug-drug interactions, and moderate in vitro metabolic rates. Finally, treatment with 8g (50 mg/kg/day) for two weeks (5 days/week) significantly reduced tumor growth using an in vivo glioblastoma model. To the best of our knowledge, this active compound is the most potent in vitro hTP inhibitor with a kinetic profile that cannot be reversed by the accumulation of any enzyme substrates.