5-fluorouracil and 5-fluoro-2'-deoxyuridine follow different metabolic pathways in the induction of cell lethality in L1210 leukaemia.

The mode of action of 5-fluorouracil (FUra) and 5-fluoro-2'-deoxyuridine (FdUrd) on L1210 leukaemia has been studied. It is shown that FUra and FdUrd follow different routes of metabolism and have different targets with respect to their cytotoxic activity. FUra is converted to 5-fluorouridine-5'triphosphate ( FUTP ), which is incorporated into nascent RNA. FdUrd is converted to 5-fluoro-2'-deoxyuridine-5'-monophosphate (FdUMP), which inhibits the de novo synthesis of 2'-deoxythymidine-5'-monophosphate (dTMP). Conversion of FUra to FdUMP does occur, but this phenomenon does not contribute to the final cytotoxic effect. No conversion of FdUrd to FUra has been detected.