TABLE 2

Enzyme kinetic parameters N-DMI metabolism determined on the basis of recombinant P450 enzyme studies and prediction of the hepatic clearance of N-DMI by use of the static ISEF model

P450 Isoform	Pathway	CL_int	f_u,mic	ISEF^{^a}	ISEF and P450 Abundance Adjusted CL_int^{^b}	Scaled CL_int	CL_H	% Total CL_H^{^c}
		µl/min/pmol			µl/min/mg protein	l/h	l/h
CYP1A2	Metabolism	0.03	0.80	BD Sup	0.84	3.6	0.072	4.3
CYP2C8	Metabolism	0.06	0.80	User	2.1	9.2	0.18	11
CYP2D6	Metabolism	0.05	0.80	BD Sup	0.41	1.8	0.035	2.1
CYP3A4	Metabolism	0.50	0.80	User	7.9	34	0.68	40
CYP3A5	Metabolism	0.09	0.80	User	0.76	3.3	0.065	3.9

f_u,mic, unbound fraction of N-DMI in microsomal incubations.
↵^a Intersystem extrapolation factors used in the Simcyp compound file and in the static model calculations; ‘BD Sup’ indicates default values within Simcyp for incubations conducted with microsomes from BD Biosciences, whereas ‘User’ denotes in-house values; 1.16 for CYP2C8, 0.09 for CYP3A4, and 0.06 for CYP3A5. Because the P450 activity between different recombinant enzyme lots may vary, in-house ISEF factors for the key enzymes in imatinib metabolism were preferred. Furthermore, the best accuracy in CYP3A4 interaction predictions was obtained using these values. The in-house ISEF factors are based on V_max for amodiaquine N-deethylation and midazolam 1’-hydroxylation in recombinant CYP2C8, CYP3A4, CYP3A5, and in pooled HLM.
↵^b The average P450 hepatic abundance values used were 52 pmol/mg protein for CYP1A2, 24 pmol/mg protein for CYP2C8, 8 pmol/mg protein for CYP2D6, 137 pmol/mg protein for CYP3A4, and 103 pmol/mg protein for CYP3A5 (these are average values of the North European Caucasian population within Simcyp). Because the sum of the ISEF- and P450 abundance adjusted CL_int values from recombinant P450 enzymes was equivalent to about 60% of the HLM CL_int value (20 µl/min/mg), the model for N-DMI in Simcyp also included an additional HLM CL_int value of 7.9 µl/min/mg.
↵^c Calculated contributions of each P450 enzyme to the total hepatic clearance of N-DMI, assuming that the total CL_H equals 1.7 l/h (calculated based on the HLM CL_int value).