Other fluorinated pyrimidines in the treatment of solid tumors

Researchers, primarily in Japan, Europe, and the United States, have evaluated several new fluorinated pyrimidines in recent years. Most of these drugs are orally active prodrugs of fluorouracil (5-FU), and some also contain modulators of its pharmacological properties. S-1 is a rationally developed combination of tegafur, a prodrug of 5-FU; CDHP, an inhibitor of 5-FU catabolism; and potassium oxonate, an inhibitor of 5-FU-induced diarrhea. S-1 underwent phase I and II trials in Japan, where it is now approved for use in the treatment of advanced gastric cancer. Two phase I studies conducted recently in Europe and the United States identified diarrhea as the dose-limiting toxicity of S-1. BOF-A2, which contains a 5-FU prodrug and CNDP, an inhibitor of 5-FU catabolism, demonstrated clinical activity in preliminary studies in Japan. This article summarizes the preclinical and clinical development of S-1 and BOF-A2.