Table 1

Formation of M2 and M4 in incubations of 1 with human liver microsomes in the presence of chemical inhibitors or inhibitory antibodies^1-a

Inhibitor or anti-P450 IgG	Target P450	M2	M4
		% control
Sulfaphenazole 20 μM	2C9	100	100
Troleandomycin 40 μM	3A4	60	21
Quinidine 40 μM	2D6	100	100
Anti-3A4 IgG 5 mg/IgG/nmol of P450^1-b	3A4	70	16
Anti-2D6 IgG 5 mg/IgG/nmol of P450^1-b	2D6	100	100

↵1-a 1 in phosphate buffer was added to human liver microsomes suspended in phosphate buffer (0.1 M, pH 7.4) containing EDTA. The final concentration of the compound was 25 μM. Sulfaphenazole and quinidine were preincubated with microsomes for 10 min, and troleandomycin was preincubated with microsomes in the presence of NADPH for 15 min at 37°C. Reactions were initiated by adding the substrate and another portion of NADPH and proceeded for an additional 10 min. The products were analyzed by LC/MS/MS.
↵1-b Anti-CYP 2D6 IgG or anti-CYP3A4 IgG was preincubated with microsomes for 30 min at room temperature. Control incubations contained preimmune IgG. Reactions were initiated by adding the substrate and another portion of NADPH and proceeded for additional 10 min. The products were analyzed by LC/MS/MS.