Kinetics and mechanistic study of competitive inhibition of thymidine phosphorylase by 5-fluoruracil derivatives

tIn a previous investigation, cationic liposomes formulated with new 5-FU derivatives, differing for thelength of the polyoxyethylenic spacer that links the N3position of 5-FU to an alkyl chain of 12 carbonatoms, showed a higher cytotoxicity compared to free 5-FU, the cytotoxic effect being directly relatedto the length of the spacer. To better understand the correlation of the spacer length with toxicity, wecarried out initial rate studies to determine inhibition, equilibrium and kinetic constants (KI, KM, kcat), andget inside inhibition activity of the 5-FU derivatives and their mechanism of action, a crucial informationto design structural variations for improving the anticancer activity. The experimental investigation wassupported by docking simulations based on the X-ray structure of thymidine phosphorylase (TP) fromEscherichia coli complexed with 3-azido-2-fluoro-dideoxyuridin. Theoretical and experimental resultsshowed that all the derivatives exert the same inhibition activity of 5-FU either as monomer and whenembedded in lipid bilayer.