Table 2

Potency of XR9576 and GG918 in enhancing cytotoxicity of various drugs in MDR cell lines^a

Cytotoxic drug	Modulator EC₅₀^b (nm) for potentiating cytotoxicity
	EMT6/AR1.0		H69/LX4		2780AD
	XR9576	GG918	XR9576	GG918	XR9576	GG918
Doxorubicin	15 ± 2	20 ± 6	16 ± 5	26 ± 21	20 ± 3	32 ± 18
Vincristine	22^c	36^c	38 ± 3	34^d	30 ± 10	49^d
Paclitaxel	12^d	35^d	22 ± 16	63^d	34 ± 10	51^d
Colchicine	17 ± 11	14 ± 10	18 ± 1	34 ± 5	ND^e	ND
Actinomycin D	12 ± 9	28 ± 13	34 ± 16	34 ± 6	ND	ND
Etoposide	14^d	19^d	18 ± 10	44 ± 22	ND	ND

a Values are mean ± SD, where n ≥ 3 separate experiments except where indicated.
b Concentration of modulator required to reverse resistance to cytotoxic drug by 50%. For method see “Drug Potentiation Assay” section in “Material and Methods.”
c Value from a single experiment.
d Mean values from two experiments.
e ND, not determined.