The cytotoxicity of (−)-lomaiviticin A arises from induction of double-strand breaks in DNA

The metabolite (−)-lomaiviticin A, which contains two diazotetrahydrobenzo[b]fluorene (diazofluorene) functional groups, inhibits the growth of cultured human cancer cells at nanomolar–picomolar concentrations; however, the mechanism responsible for the potent cytotoxicity of this natural product is not known. Here we report that (−)-lomaiviticin A nicks and cleaves plasmid DNA by a pathway that is independent of reactive oxygen species and iron, and that the potent cytotoxicity of (−)-lomaiviticin A arises from the induction of DNA double-strand breaks (dsbs). In a plasmid cleavage assay, the ratio of single-strand breaks (ssbs) to dsbs is 5.3 ± 0.6:1. Labelling studies suggest that this cleavage occurs via a radical pathway. The structurally related isolates (−)-lomaiviticin C and (−)-kinamycin C, which contain one diazofluorene, are demonstrated to be much less effective DNA cleavage agents, thereby providing an explanation for the enhanced cytotoxicity of (−)-lomaiviticin A compared to that of other members of this family. (−)-Lomaiviticin A inhibits the growth of cancer cells at nanomolar to picomolar concentrations; however, the basis for this potent cytotoxicity is not known. This natural product has now been shown to induce production of DNA double-strand breaks at nanomolar concentrations. Evidence demonstrates that strand cleavage proceeds via reactive carbon-centred free radical intermediates.