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 proangiogenic and
antiapoptotic signaling. Designed as transition-state analogues 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
noncompetitive inhibition mode with both thymidine and inorganic phosphate
substrates. Furthermore, compound 8g was devoid of apparent
toxicity to a panel of mammalian cells, showed no genotoxicity signals,
and had low probability of drug–drug interactions and moderate
in vitro metabolic rates. Finally, treatment with 8g (50
mg/(kg day)) for 2 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.