title: On the synergistic effect of doxorubicin and mitomycin C against breast cancer cells.
abstract: The combination of doxorubicin and mitomycin C has been shown previously to result in supra-additive tumor cell killing in vitro in both murine and human breast cancer cells and in vivo against murine breast cancer cells. Median effect analysis was used to determine the significance and degree of interaction. The origin of this synergy was sought by evaluating the contribution of membrane efflux pump modulation, formaldehyde production, reactive oxygen species, DNA cross-linking, and DNA double-strand breaks to this effect. The interaction of mitomycin C and doxorubicin in vitro was found to be a true synergy whose mechanism was efflux pump-independent. DNA cross-links were only found to increase additively with co-administration of the drugs; however, a supra-additive increase in DNA double-strand breaks was observed. The results suggest that poisoning of topoisomerase IIalpha by doxorubicin may interact with drug-induced DNA cross-links to enhance the formation of DNA double-strand breaks. This interaction, together with glutathione depletion and mitomycin C-derived formaldehyde, may be the underlying mechanism(s) of the synergy observed between mitomycin C and doxorubicin.
authors.affiliation: Leslie Dan Faculty of Pharmacy, University of Toronto, Ontario, Canada.
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Shuhendler
authors.forename: Peter J
authors.initials: PJ
authors.lastname: O'Brien
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Rauth
authors.forename: Xiao Yu
authors.initials: XY
authors.lastname: Wu
mesh_terms: D000704:Analysis of Variance; D000951:Antigens, Neoplasm / Q000378:metabolism; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000188:drug therapy*; D045744:Cell Line, Tumor; D004249:DNA Damage; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004317:Doxorubicin / Q000627:therapeutic use*; D004357:Drug Synergism; D005260:Female; D005557:Formaldehyde / Q000032:analysis / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D016685:Mitomycin / Q000627:therapeutic use*; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D000951:Antigens, Neoplasm; D004268:DNA-Binding Proteins; D017382:Reactive Oxygen Species; D005557:Formaldehyde; D016685:Mitomycin; D004317:Doxorubicin; D004250:DNA Topoisomerases, Type II; D005978:Glutathione