Modification of natural, double-helical DNA by antitumor cis- and trans-[Cl-2(Me2SO4)(4)Ru] in cell-free media

Modifications of natural DNA in cell-free media by the antitumor ruthenium compounds cis- and trans-[Cl-2(Me2SO4)(4)Ru] were studied by various bioche mical and biophysical methods. These methods included: binding studies by m eans of flameless atomic absorption spectrophotometry, mapping of DNA adduc ts by means of transcription assay, use of ethidium bromide as a fluorescen t probe of DNA adducts of metal complexes, an interstrand cross-linking ass ay employing gel electrophoresis under denaturing conditions, measurements of DNA unwinding by ger electrophoresis, differential pulse polarographic a nalysis of DNA conformation, and analysis of liquid crystalline dispersions of DNA by circular dichroism. The results indicated that both ruthenium co mpounds irreversibly coordinated to DNA; the rate of binding of the cis iso mer was considerably lower than that of the trans isomer. The DNA-binding m ode of trans-[Cl-2(Me2SO4)(4)Ru] included formation of bifunctional adducts such as intrastrand cross links between neighboring purine residues and a small amount (similar to1%) of interstrand cross-links. cis-[Cl-2(Me2SO4)(4 )Ru] formed mainly monofunctional lesions on natural DNA. Both ruthenium is omers induced conformational alterations of non-denaturational character in DNA, the trans compound being more effective. In addition, DNA adducts of trans-[Cl-2(Me2SO4)(4)Ru] were capable of inhibiting RNA synthesis by DNA-d ependent RNA polymerases, while the adducts of the cis isomer were not. Thu s, several features of the DNA-binding mode of trans-[Cl-2(Me2SO4)(4)Ru] we re similar to those of antitumor cis-diamminedichloroplatinum (II), which m ay be relevant to the biological effects of this antitumor ruthenium drug. On the other hand, the different DNA-binding mode of cis-[Cl-2(Me2SO4)(4)Ru ] was consistent with its less pronounced biological effects. BIOCHEM PHARM ACOL 60;12:1761-1771, 2000. (C) 2000 Elsevier Science Inc.