Properties of the nucleic acid photoaffinity labeling agent 3-azidoamsacrine

This paper reports the study of the photochemical, physical, and biological properties of 3-azidoamsacrine. The binding of 3-azidoamsacrine to DNA was studied with UV spectroscopy. The UV spectral behavior is quite similar to that of the parent amsacrine and argues that 3-azidoamsacrine is a good photoaffinity labeling agent for amsacrine. The biological properties (cytotoxicity and mutagenicity) of 3-azidoamsacrine in the mammalian mutagenesis V79 and L5178Y assay systems were measured. Light-activated 3-azidoamsacrine is toxic, but not mutagenic, to V79 cells. 3-Azidoamsacrine with and without light activation, as well as amsacrine, are toxic and mutagenic to L5178Y cells. To probe the interactions of 3-azidoamsacrine with DNA, studies of the photoreactivity of this compound were conducted. 3-Azidoamsacrine was photolyzed in the presence of the plasmid pBR322, and the effect of the photoadducts on restriction endonuclease cleavage was investigated. Amsacrine and 3-azidoamsacrine, without light activation, did not block any of the restriction endonucleases. Light-activated 3-azidoamsacrine blocked cleavage by the restriction endonucleases AluI, HinfI, NciI, NaeI, DraI, Sau96I, HpaII, and HaeIII. Photolysis experiments with mononucleosides, blocked mononucleosides, dinucleotides, and DNA all indicated that 3-azidoamsacrine formed adducts with G and A. The structures of these adducts are discussed based upon mass spectral data. Thus, it appears that 3-azidoamsacrine covalently attaches to DNA and that this covalent binding results in the production of toxic and, in some cases, mutagenic lesions in mammalian cells and the inhibition of restriction endonuclease cleavage of DNA.