Table 1

Topoisomerase II inhibition and growth inhibition of CHO and DZR cells by mitindomide, dexrazoxane (ICRF-187), and ICRF-193

Drug	IC₅₀		Resistance factor
	Topoisomerase II inhibition			Cell growth inhibition
	Human p170 topoisomerase II	CHO nuclear extract topoisomerase II		CHO	DZR
	μm
Mitindomide	200 ± 50 (5)	150 ± 50 (3)	69 ± 12 (5)	2,100 ± 1,000 (3)	30
Dexrazoxane	9.3 ± 2.7 (4)	6.2 ± 1.8^1-a	5.8 ± 2.1 (4)	2,900 ± 190 (4)	500
ICRF-193^1-b	0.6	N.D.	0.017	0.3	18

Topoisomerase II inhibition was measured with a gel assay using catenated kDNA as a substrate as described in Materials and Methods. Cell growth inhibition was measured in 96-well plates using an MTT assay after the cells had been incubated with the drug for 72 hr. Values reported are the means ± standard error; the numbers in parentheses are the number of separate determinations carried out on different days.

↵1-a The mean ± standard error here is from the nonlinear least-squares fit of the data from a single experiment to a logistic equation.
↵1-b Data from Refs. 12 and 21.
N.D., not determined.