Table 1. Effect of Tariquidar on the Cytotoxicity of Drugs Effluxed by Three ABC Transporters, P-gp, BCRP, and MRP1.

		cytotoxicity value
		drug alone		drug +100 nM tariquidar
cell line	cytotoxic drug	IC50a (nM)	RRb	IC50a (nM)	RRb
B1 resistant (P-gp)	doxorubicin	4498 ± 398	121c	132 ± 11	4c
B1 parental	doxorubicin	37 ± 6		27 ± 8	0.7
G2 resistant (BCRP)	mitoxantrone	1058 ± 135	24c	549 ± 37	13d
G2 parental	mitoxantrone	43 ± 5		25 ± 5	0.6
C1 resistant (MRP1)	doxorubicin	704 ± 290	2	667 ± 39	2
C1 parental	doxorubicin	337 ± 23		373 ± 81	1

^aMean ± SD from three independent experiments.

^bRR = resistance ratio, which is the quotient of the IC₅₀ value of each cell line to that of the parental line not treated with tariquidar.

^cP < 0.001 by one-way analysis of variance followed by Bonferronni post t-test (α = 0.05).

^dP < 0.05 by one-way analysis of variance followed by Bonferronni post t-test (α = 0.05).