Topoisomerase inhibition by lucanthone, an adjuvant in radiation therapy

To determine whether lucanthone can inhibit human topoisomerases in vitro.

Lucanthone was incubated with human topoisomerases II and I together with their plasmid substrates, to determine if lucanthone interfered with the catalytic activities of topoisomerases and if it enhanced the formation of DNA strand breaks, as determined by agarose gel electrophoresis of the resultant plasmid forms.

Incubation of the enzymes with lucanthone inhibited the catalytic activity of topoisomerases II and I. With topoisomerase II, it increased the abundance of DNA double strand breaks (cleavable complexes).

Lucanthone, like actinomycin D, inhibited topoisomerases II and I. It may act to enhance the yield of DNA double strand breaks in cells through a mechanism of topoisomerase II inhibition.