S-1 as a core anticancer fluoropyrimidine agent

5-FU is a core anticancer agent for GI and other malignancies, and infusional 5-FU regimens have been widely utilized. Orally administrable fluoropyrimidine prodrugs have been developed to enhance the anticancer efficacy of 5-FU and to reduce its adverse reactions.

S-1 is an FT-based oral 5-FU prodrug in combination with a DPD inhibitor (CDHP) and an OPRT inhibitor (Oxo), which exerts the following effects: i) maintaining normal gut immunity, Oxo can decrease GI toxicities of 5-FU; ii) sustaining high plasma 5-FU concentrations, Cmax of FBAL after S-1 administration is extremely low, which dramatically decreases adverse reactions such as HFS, neurotoxicities and cardiotoxicities; iii) plasma 5-FU concentrations vary less extensively after S-1 administration and iv) S-1 can be safely administered to patients with DPD deficiency. Furthermore, the alternate-day S-1 administration can reduce the GI toxicities and myelotoxicities of 5-FU without reducing its anticancer efficacy, enabling patients to continue the oral administration for 6 - 12 months.

Replacement of regimens with infusional 5-FU and other fluoropyrimidines by the alternate-day S-1 administration may be recommended because the latter procedure is efficient for patients while sustaining the enhanced anticancer efficacy of 5-FU and without reducing its dose intensity.