Table 3

Cytotoxicity against topoisomerase I (Topo I) inhibitor-resistant cell line

Cell line pairs	Compound	IC₅₀, nm		Rf^aIC_50R:IC_50S
Cell line pairs	Compound	Resistant	Sensitive	Rf^aIC_50R:IC_50S
KB-STP2/KB	BN80927	230	90	2.6
(T1 down-regulated)	SN38	3000	330	9
	VP-16	5600	3100	1.8

a Rf, resistance factor [defined as the ratio of the IC₅₀ value obtained with the resistant cell line (IC₅₀R) to the one obtained with parent cell line (IC₅₀S)]; VP-16, etoposide.