Comparison of reversible IC50 values generated from the reversible P450 inhibition screen ( Weaver et al., 2003 ) for sulfaphenazole (SPZ), quinidine (QUI), and ketoconazole (KCZ) and those projected from a single inhibitor concentration in the human liver microsomal, single-time point time-dependent inhibition assay
R + INADPH is the rate of P450 probe reaction when the initial (pre-) incubation is performed in the presence of inhibitor and NADPH. R – INADPH is the rate of P450 probe reaction when the initial (pre-) incubation is performed in the absence of inhibitor (i.e., solvent control) but the presence of NADPH. R + INO NADPH is the rate of P450 probe reaction when the initial (pre-) incubation is performed in the presence of inhibitor but the absence of NADPH.
R + INADPH/R - INADPH | R + INO NADPH/R - INO NADPH | Percentage TDIa | Projected Reversible IC50b | IC50c | |
|---|---|---|---|---|---|
| μM | μM | ||||
| 1 μM SPZ | 0.61 | 0.59 | -4.5 | 0.14 | 0.2 |
| 10 μM SPZ | 0.19 | 0.18 | -5.1 | 0.13 | 0.2 |
| 25 nM QUI | 0.81 | 0.83 | 1.9 | 0.013 | 0.015 |
| 250 nM QUI | 0.49 | 0.54 | 8.2 | 0.022 | 0.015 |
| 5 nM KCZ | 0.97 | 0.92 | -5 | 0.005 | 0.005 |
| 50 nM KCZ | 0.87 | 0.8 | -8 | 0.028 | 0.005 |
↵ a Percentage TDI was calculated according to eq. 2 (Results). Values are the average of duplicate incubations performed within a single experiment.
↵ b Projected reversible IC50 was calculated according to eqs. 3 to 5 (Results). Values are the average of duplicate incubations performed within a single experiment.
↵ c Reversible IC50 values were generated from the reversible P450 inhibition screen (set up as described in Weaver et al., 2003). Values are the mean of 150 replicates.