Table 1. Effect of AG1478, verapamil and valspodar on ABCB1-mediated resistance to colchicine, vinblastine, paclitaxel and cisplatin.^a.

To examine the effects of AG1478, verapamil and valspodar on ABCB1-mediated resistance to colchicine, vinblastine, paclitaxel and cisplatin, cells were pre-incubated with or without AG1478, verapamil and valspodar for 1 h and then incubated with various concentrations of colchicine, vinblastine, paclitaxel and cisplatin. Cell survival was determined by the MTT assay as described in “Materials and Methods”. Data are means ± SD of at least three independent experiments performed in triplicate.

Compounds	IC50 ± SD (μM)
	KB-3-1	KB-C2
Colchicine	0.0069±0.0010(1.0)a	6.9543±0.2437(947.8)
+ AG1478 10 μM	0.0069±0.0004(1.0)	3.6490±0.2268(505.8)
+ Verapamil 10 μM	0.0060±0.0003(0.9)	0.1077±0.0134(15.6)
	0.0059±0.0007(0.9)	0.0097±0.0056(1.41)
+ Valspodar 5 μM
Vinblastine	0.0476±0.0043(1.0)a	0.3057±0.0152(6.4)
+ AG1478 10 μM	0.0428±0.0008(0.9)	0.1644±0.0245(3.5)
+ Verapamil 10 μM	0.0408±0.0062(0.9)	0.0419±0.0078(0.9)
	0.0389±0.0045(0.8)	0.0399±0.0098(0.8)
+ Valspodar 5 μM
Paclitaxel	0.0084±0.0023(1.0)a	5.5643±1.1098(662.3)
+ AG1478 10 μM	0.0079±0.0004(1.0)	1.4461±0.2839(172.1)
+ Verapamil 10 μM	0.0072±0.0018(0.9)	0.0173±0.0077(2.0)
	0.0068±0.0021(0.8)	0.0093±0.0064(1.1)
+ Valspodar 5 μM
Cisplatin	1.8867±0.0446(1.0)a	1.8235±0.0782(1.0)
+ AG1478 10 μM	1.8365±0.0578(1.0)	1.8293±0.0811(1.0)
+ Verapamil 10 μM	1.8116±0.0824(1.0)	1.7244±0.0387(0.9)
	1.8233±0.0718(1.0)	1.8401±0.0702(1.0)
+ Valspodar 5 μM

^aFold-resistance was determined by dividing the IC₅₀ values of KB-C2 cells by the IC₅₀ values for KB-3-1 cells in the absence or presence of AG1478, verapamil or valspodar.