title: DNA damage following combination of radiation with the bioreductive drug AQ4N: possible selective toxicity to oxic and hypoxic tumour cells.
abstract: AQ4N (1,4-bis-([2-(dimethylamino-N- oxide)ethyl]amino)5,8-dihydroxyanthracene-9,10-dione) is a novel bioreductive agent that can be reduced to a stable, DNA-affinic compound, AQ4. The alkaline comet assay was used to evaluate DNA damage induced by AQ4N and radiation. Cells prepared from freshly excised T50/80 murine tumours were shown to have the ability to reduce AQ4N to a DNA-damaging agent; this had disappeared within 24 h of excision. When T50/80 tumours implanted in BDF mice were exposed to radiation in vivo a considerable amount of DNA damage was present in tumours excised immediately. Minimal levels of DNA damage were detectable in tumours excised after 2-5 h. AQ4N given 30 min before radiation had no appreciable influence on this effect and AQ4N alone caused only a small amount of damage. When AQ4N and radiation were combined an increasing number of damaged cells were seen in tumours excised 24-96 h after irradiation. This was interpreted as evidence of the continued presence of AQ4, or AQ4-induced damage, which was formed in cells hypoxic at the time of administration of AQ4N. AQ4, a potent topoisomerase II inhibitor, would be capable of damaging cells recruited into the cell cycle following radiation damage to the well-oxygenated cells of the tumour. The kinetics of the expression of the DNA damage is consistent with this hypothesis and shows that AQ4 has persistent activity in vivo.
authors.affiliation: School of Biomedical Science, University of Ulster at Jordanstown, N. Ireland, UK.
authors.forename: M V
authors.initials: MV
authors.lastname: Hejmadi
authors.forename: S R
authors.initials: SR
authors.lastname: McKeown
authors.forename: O P
authors.initials: OP
authors.lastname: Friery
authors.forename: I A
authors.initials: IA
authors.lastname: McIntyre
authors.forename: L H
authors.initials: LH
authors.lastname: Patterson
authors.forename: D G
authors.initials: DG
authors.lastname: Hirst
mesh_terms: D000332:Aerobiosis; D000818:Animals; D000880:Anthraquinones / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D015687:Cell Hypoxia; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D004249:DNA Damage; D004273:DNA, Neoplasm / Q000187:drug effects* / Q000528:radiation effects*; D005260:Female; D006801:Humans; D008325:Mammary Neoplasms, Experimental / Q000188:drug therapy* / Q000473:pathology; D051379:Mice; D014407:Tumor Cells, Cultured
chemical_list: D000880:Anthraquinones; D000970:Antineoplastic Agents; D004273:DNA, Neoplasm; C094428:AQ4N