TABLE 1

Kinetic parameters for the metabolism of TAM to N-desmethyl-TAM and 4-hydroxy-TAM in HLMs (n = 3) The HLMs used were characterized with respect to the activity of individual P450: CYP2D6 activity (measured by bufuralol 1′-hydroxylation) in HG23 and HG112 was 135 and 24.5 pmol/min/mg of protein, respectively, whereas in HG06 it was undetectable. The activity of CYP3A (measured by testosterone 6β-hydroxylation) in HG112, HG23, and HG06 was 17,205, 3320, and 3000 pmol/min/mg of protein, respectively. Formation rates of metabolites versus TAM concentrations were best fit to a two-site binding equation using a nonlinear regression model (see Data Analyses).


HLMs

TAM to N-Desmethyl-TAM

TAM to 4-Hydroxy-TAM
Vmax1
Km1
Vmax1/Km1
Vmax2
Km2
Vmax2/Km2
Vmax1
Km1
Vmax1/Km1
Vmax2
Km2
Vmax2/Km2
HG06 33.3 1.1 31.1 1740 611 2.9 0.7 1.3 0.6 0.8 16.2 0.05
HG23 13.5 2.1 6.4 150 55.6 2.7 3.8 0.7 5.5 4.3 46.0 0.09
HL112 142 3.3 43.0 1719 910 1.9 1.2 0.8 1.5 4.2 11.5 0.4
Mean 62.9 2.2 26.8 1203 526 2.5 1.92 0.9 2.0 3.1 24.6 0.17
±S.D.
69.2
1.1
18.7
912
434
0.5
1.67
0.3
2.6
2.0
18.4
0.17
  • Vmax, pmol/min/mg of protein; Km, μM; and Vmax/Km, μl/min/mg of protein.