Effect of the amine non‐leaving group on the structure and stability of DNA complexes with cis‐[Pt(R‐NH₂)₂(NO₃)₂]

Abstract

The antitumor compound c i~-[ P t ( N H~)~C l~l (cisplatin), conserves two ammine ligands during the reaction with its cellular target DNA. Modifications of these non-leaving groups change the antineoplastic properties of this compound and its genotoxic effects. It is therefore of interest to determine the influence of non-leaving groups on the structure and stability of DNA in vitro. We have investigated platinum-DNA adducts formed by cis-[Pt(R-NH2)2(N03)2] (where R-NH2 = NH3, methylamine, cyclobutylamine, cyclopentylamine and cyclohexylamine) as a function of DNA binding. All compounds quantitatively reacted with DNA in less than 1 h at 37°C. They formed bifunctional adducts with adjacent nucleotides judging from the displacement of the intercalating molecule ethidium bromide, ultraviolet absorption spectroscopy and circular dichroism. Substitution of a H on the NH3 ligand by alkyl groups dramatically destabilized the platinum-DNA complex. Thermal stability decreased progressively with an increasing number of carbon atoms, At,, = -4.4"C for 3 cyclohexylamine-platinum-DNA adducts/ 1000 nucleotides, conditions where cisplatin had no effect. DNA adducts with cyclobutylamine and cyclohexylamine ligdnds inhibited the hydrolysis of platinum-DNA complexes by S1 nuclease. K, for the digestion of DNA containing these lesions was 2.3 times greater than for cisplatin, indicating steric inhibition of enzymesubstrate complex formation. These results show that the non-leaving groups of substituted cis-Pt(1I) compounds may destabilize DNA and interfere with protein-DNA interactions. These perturbations may have consequences for the genotoxic and antitumor activities of platinum compounds.

Interactions of DNA with a New Platinum(IV) Azide Dipyridine Complex Activated by UVA and Visible Light: Relationship to Toxicity in Tumor Cells

“…Fluorescence measurements of CT DNA modified by platinum complexes in the presence of EtBr were performed at an excitation wavelength of 546 nm, and the emitted fluorescence was analyzed at 590 nm. The fluorescence intensity was measured at 25 °C in NaCl (0.4 M) to avoid secondary binding of EtBr to DNA (28,29). The concentrations were 0.01 mg mL -1 for DNA and 0.04 mg mL -1 for EtBr, which corresponded to the saturation of all sites of EtBr 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 in DNA (29).…”

“…The fluorescence intensity was measured at 25 °C in NaCl (0.4 M) to avoid secondary binding of EtBr to DNA (28,29). The concentrations were 0.01 mg mL -1 for DNA and 0.04 mg mL -1 for EtBr, which corresponded to the saturation of all sites of EtBr 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 in DNA (29). Terbium fluorescence measurements were performed by adding TbCl 3 to modified or control DNA (8 µg mL -1 ) at a final concentration equivalent twice the monomeric nucleotide content.…”

Dichlorobis(cycloalkylamine)platinum(II) complexes structure activity relationship on the human MDA-MB-231 breast cancer cell line

“…the non-leaving group) influences the cytotoxic activity of the homologous cis-dichlorobis(cycloalkylamine)platinum(II) complexes in another, still incompletely characterized way. Important information on this question is provided by physiochemical and biochemical studies of Butour et al [21] on adducts of DNA with cis-[-Pt(RNH2)2(N03)2] (where R represents H, CH 3, or cyclobutyl to cyclohexyl). These compounds, which are immediately transformed into the corresponding active ~Pt(H20)2] 2+ species under physiological conditions, exhibit quantitative reaction with DNA in less than 1 h at 37 °C forming bifunctional adducts with adjacent nucleotides.…”

“…This perturbation should influence the recognition and the repair of platinum-DNA adducts of 9 and 10 (compare Refs. [21] and [25]). …”

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

“…The¯uorescence intensity was measured at 25°C in 0.4 M NaCl to avoid secondary binding of EtBr to DNA [16,17]. The concentrations were 0.01 mg/mL for DNA and 0.04 mg/mL for EtBr, which corresponded to the saturation of all intercalation sites of EtBr in DNA [16,17].…”