In vitro activity: Voreloxin exhibits potent inhibitory effect in topoisomerase II relaxation with IC50 of 3.2 μg /mL without effect on topoisomerase II cleavage. Voreloxin has a cytotoxic activity against human tumor cell lines more potent than that of etoposide. Voreloxin has broad anti-proliferative activity in 15 cell lines, including 4 drug-resistant lines, with IC50 ranging from 0.04 to 1.155 μM.

Cell Assay: Cells are put into wells of a 96-well microtiter plate in the amount of 0.1 mL/well, preincubated for 24 h except for P388 cells, and incubated with various concentrations of a test compound in the 5% CO2 incubator at 37 ° for 72 h. After the culturing, 0.02 mL of a MTT solution (5 mg/mL) is put in each well, and the cells are cultured for a further 4 h. The medium is removed by suction, and 0.2 mL of DMSO is put in each well to dissolve the formed formazan. The absorbance is measured by Multiskan Bichromatic. The IC50 is defined as the drug concentration needed to produce a 50% reduction of absorbance relative to the control.