Figure 7.

Etoposide quinone inactivates human topoisomerase IIβ when incubated with the enzyme prior to the addition of DNA. The enzyme was incubated in the presence of 15 μM etoposide quinone (closed circles, blue) prior to a DNA cleavage assay. The inset shows cleavage levels established following incubation for 6 min in the absence of drug (ND, black bar) or in the presence of 30 μM etoposide (Etop, red bar), 15 μM etoposide quinone and DTT (EQ+DTT, open blue bar), or 15 μM etoposide quinone in the absence of DTT (EQ, blue bar). Error bars represent the standard deviation of three independent experiments.