Table 1

5-FU formation from tegafur catalyzed by human liver microsomes, cytosol, and in combination

Tegafur (100 μm or 1 mm) was incubated with human liver microsomes (0.5 mg/ml) in the presence of an NADPH-generating system, human liver cytosol (2.5 mg/ml) in the absence of the NADPH-generating system, and with the combination of human liver microsomes and cytosol in the presence of the NADPH-generating system and 5-chloro-2,4-dihydroxypyridine (100 μm), a DPD inhibitor. Results are presented as mean ± SD for 14 samples; values in parentheses indicate the ranges.
5-FU formation (pmol/min)
100 μm tegafur1 mm tegafur
Microsomes4.5 ± 2.4 (1.4–8.6)36 ± 18 (15–72)
Cytosol0.9 ± 0.3 (0.4–1.6)18 ± 4 (11–24)
Microsomes and cytosol5.5 ± 3.1 (2.2–11.1)53 ± 20 (31–95)
Cytosol:microsomesa0.25 ± 0.17 (0.10–0.64)0.60 ± 0.32 (0.29–1.40)
  • a Cytosol:microsomes indicates the ratio of 5-FU formation activities by liver cytosol to those by liver microsomes in individual human samples.