Table 2

Resistance to etoposide and vincristine conferred by rat and human MRP2

Cell Line	Control		LY335979		BSO
	Control		0.25 μM		20 μM
	IC₅₀^2-a	RR^2-b	IC₅₀^2-a	RR^2-b	IC₅₀^2-a	RR^2-b
Etoposide
MDCK-Co	163 ± 35	1.0	56 ± 20	1.0	113 ± 9	1.0
MDCK-Mrp2	612 ± 164	3.8^2-c	189 ± 6	3.4^2-c	235 ± 22	2.1^2-c
MDCK-MRP2	809 ± 63	5.0^2-c	366 ± 66	6.5^2-c	197 ± 6	1.7^2-c

Vincristine
MDCK-Co	8.2 ± 0.1	1.0	4.7 ± 0.1	1.0	9.2 ± 0.2	1.0
MDCK-Mrp2	49.3 ± 1.9	6.0^2-c	36.7 ± 0.6	7.8^2-c	25.9 ± 0.7	2.8^2-c
MDCK-MRP2	18.7 ± 0.1	2.3^2-c	16.9 ± 0.1	3.6^2-c	19.0 ± 0.7	2.1^2-c

Sensitivity to etoposide and vincristine was determined using MTT cell viability assays as described in Experimental Procedures. Trichostatin A (125 nM) was added to enhance the expression of recombinant MRP2 in the transfected cells. Data represent the mean ± S.D. (n ≥ 6). The significance of relative resistance factors (RR) was calculated by Student’s t test.

↵2-a IC₅₀ values are given in μM
↵2-b The relative resistance factor (RR) was calculated by dividing the IC₅₀ value of cells transfected with MRP2 expression vectors by the IC₅₀ value of cells transfected with the control vector (MDCK-Co).
↵2-c P ≤ .01 compared to MDCK-Co.