TABLE 4

Effect of preincubation with CsA on the inhibition of OATP1B1-mediated uptake of [³H]E₂G, [³H]E₁S, [³H]BSP, pitavastatin, and atorvastatin

The inhibitory effect of CsA on OATP1B1-mediated uptake of [³H]E₂G (0.1 µM), [³H]E₁S (0.01 µM), [³H]BSP (0.01 µM), pitavastatin (0.1 µM), and atorvastatin (0.1 µM) was examined in the absence and presence of 1-hour preincubation with or without CsA as shown in Fig. 4. The IC₅₀ values were estimated by a nonlinear least-squares regression analysis (mean ± S.D., n = 3). The R values of CsA were calculated by eqs. 5 and 6 with the exception that IC₅₀ values instead of K_i values were used for the calculations because the applicability of eq. 4 to preincubation-dependent inhibition by CsA remains to be established.

Substrates	No Preincubation^{^a}			After 1-Hour Preincubation without CsA^{^b}			After 1-Hour Preincubation with CsA^{^c}
	IC₅₀ of CsA	R Value (= 1+[I]/IC₅₀)^{^d}		IC₅₀ of CsA	R Value (= 1+[I]/IC₅₀)^{^d}		IC₅₀ of CsA	R Value (= 1+[I]/IC₅₀)^{^d}
	IC₅₀ of CsA	[I] = C_max	[I] = [I]_u,inlet,max	IC₅₀ of CsA	[I] = C_max	[I] = [I]_u,inlet,max	IC₅₀ of CsA	[I] = C_max	[I] = [I]_u,inlet,max
	μM			μM			μM
E₂G	0.0620 ± 0.0142	16.3	20.4	0.0458 ± 0.0041	21.7	27.2	0.0139 ± 0.0066	69.3	87.3
E₁S	0.253 ± 0.088	4.75	5.74	0.134 ± 0.017	8.09	9.96	0.0264 ± 0.0085	37.0	46.5
BSP	0.283 ± 0.070	4.36	5.24	0.252 ± 0.057	4.77	5.76	0.0799 ± 0.0273	12.9	16.0
Pitavastatin	0.144 ± 0.015	7.60	9.33	0.102 ± 0.037	10.3	12.8	0.0263 ± 0.0040	37.1	46.6
Atorvastatin	0.176 ± 0.018	6.40	7.82	0.112 ± 0.028	9.48	11.7	0.0259 ± 0.0037	37.7	47.3

↵^a Cells were coincubated with a substrate and CsA (0.01–10 µM) for 1 ([³H]E₁S and atorvastatin), 2 (pitavastatin), or 5 minutes ([³H]E₂G and [³H]BSP).
↵^b Cells were coincubated with a substrate and CsA (0.01–10 µM) for 1 ([³H]E₁S and atorvastatin), 2 (pitavastatin), or 5 minutes ([³H]E₂G and [³H]BSP) after 1-hour preincubation with KH buffer without CsA.
↵^c Cells were coincubated with a substrate and CsA (0.001–1 µM) for 1 ([³H]E₁S and atorvastatin), 2 (pitavastatin), or 5 minutes ([³H]E₂G and [³H]BSP) after 1-hour preincubation with KH buffer containing CsA (0.001–1 µM).
↵^d R values that were calculated based on 200-mg dose of CsA are presented.