Biophysical analysis of natural, double-helical DNA modified by a dinuclear platinum(II) organometallic compound in a cell-free medium

Abstract

Modifications of natural DNA by the dinuclear platinum(II) organometallic complex [[Pt(Me)Cl(Me(2)SO)](2)(mu-N-N)] [where N-N=H(2)N(CH(2))(6)NH(2)] (ORGANObisPt) were studied by methods of molecular biophysics. These methods include DNA binding studies using atomic absorption spectrophotometry, HPLC analysis of enzymatically digested DNA, interstrand cross-linking employing gel electrophoresis under denaturing conditions, DNA unwinding studied by gel electrophoresis, mapping of DNA adducts by transcription assay, DNA melting curves measured by absorption spectrophotometry and conformational analysis of platinated DNA by differential pulse polarography. The results indicate that the complex ORGANObisPt binds irreversibly to DNA. Its DNA binding mode is, however, different from that of the formally equivalent [[cis-PtCl(NH(3))(2)](2)(mu-N-N)] (1,1/c,c), which exhibits antitumor activity including that in the tumor cells resistant to cisplatin. Interestingly, ORGANObisPt binds to DNA considerably faster than 1,1/c,c and cisplatin. In addition, when ORGANObisPt binds to DNA it exhibits a strong base sequence specificity to guanine residues. ORGANObisPt forms mainly monofunctional adducts on double-helical DNA. It forms also a small amount of DNA interstrand cross-links (approximately 2%), i.e. a radically smaller amount in comparison with the complex 1,1/c,c. Importantly, these interstrand cross-links of ORGANObisPt are capable of terminating RNA synthesis in vitro, while its major monofunctional adducts are not. In addition, the adducts of ORGANObisPt affect the conformation of DNA, but in a different way than its dinuclear analogue 1,1/c,c or cisplatin. Some structural features of ORGANObisPt, such as the charge or nature of the trans and cis activating groups relative to the labile chloride, might be responsible for the altered DNA binding mode and biological activity in comparison with the 1,1/c,c compound.

DNA Interactions of Monofunctional Organometallic Ruthenium(II) Antitumor Complexes in Cell-free Media

“…EtBr as a fluorescent probe can be used to distinguish intercalating and nonintercalating ligands (34) Figure 6). In contrast, the decrease of the fluorescence intensity by the adducts of Ru-CYM was only very small and similar to that induced by the adducts of [PtCl(dien)]Cl (35).…”

Osmium Tetroxide Complexes as Versatile Tools for Structure Probing and Electrochemical Analysis of Biopolymers

“…These early studies revealed, in contrast to previous suppositions that the native dsDNA is not reactive towards the osmium tetroxide reagents, certain extent of modification of duplex DNA that depended on the content of structural "defects" [53]. These studies also provided evidence of structural alterations of dsDNA induced by covalent modification with osmium complexes detectable by DPP or other experimental techniques [66] (analogous phenomena have also been observed upon DNA modification with various platinum complexes [70,71]). Application of adsorptive stripping [5] or adsorptive transfer stripping [48,54] techniques in connection with measurements of the catalytic osmium signal offered determination of nanogram quantities of the modified ss DNA [5,54] and allowed sensitive monitoring of duplex opening transitions in plasmid DNA molecules differing in the levels of negative superhelicity [48].…”

Synthesis, DNA interaction and cytotoxicity studies of cis-{[1, 2-bis(aminomethyl)cyclohexane]dihalo}platinum(II) complexes

“…2). In these four platinum complexes two main tendencies were observed: (a) Complexes that produced an stabilizing interaction with DNA (increase of the ellipticity values at the DNA maximum), behaving in a similar way than cisplatin, and (b) Compounds that produced a decrease in the ellipticity due to an destabilization of the DNA B form, in a similar way that transplatin (and other similar compounds that have promising biological activity in vitro) [18,19].…”

“…The cytotoxicity results obtained for compounds [16][17][18][19][20][21][22] showed that compounds with methoxyl or hydroxyl groups only produced moderate activities on cell line. However, the compounds with a methoxyl group and without a C@C double bond (18 and 19) produced appreciable activity in the cytotoxicity assay.…”