Study on nucleic acid (CT-DNA and yeast tRNA) binding behaviors and cytotoxic properties of a heterodinuclear Ru(II)-Co(III) polypyridyl complex

Abstract

A heterodinuclear (Ru(II), Co(III)) metal polypyridyl complex [(phen)(2)Ru(bpibH(2))Co(phen)(2)](5+) {phen = 1,10-phenanthroline, bpibH(2) = 1,4-bis([1,10]phebanthroline-[5,6-d]imidazol-2-yl)-benzene} has been designed and synthesized. The comparative study on the interactions of the Ru(II)-Co(III) complex with calf thymus DNA (CT-DNA) and yeast tRNA has been investigated by UV-visible spectroscopy, fluorescence spectroscopy, viscosity, as well as equilibrium dialysis and circular dichroism (CD). The antitumor activities of the complex have been evaluated by MTT {3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide} method and Giemsa staining experiment. These results indicate that the structures of nucleic acids have significant effects on the binding behaviors of metal complexes. Furthermore, the complex demonstrates different antitumor activity against selected tumor cell lines in vitro, and can make the cell apoptosis.

Graphical abstract

Scheme 1

Synthesis of the Ru(II)–Co(III) complex.

Fig. 1

¹H NMR spectra of the Ru(II)–Co(III) complex in d₆-DMSO.

Fig. 2

Absorption spectra of the Ru(II)–Co(III) complex in CH₃CN.

Fig. 3

UV-vis spectra of the Ru(II)–Co(III) complex upon the addition of CT-DNA (a) and yeast tRNA (b) in buffer. [Ru–Co] = 1.0 × 10^− 5 M, [DNA] = (0–2.9) × 10^− 5 M, [RNA] = (0–1.9) × 10^− 5 M. Arrow shows the absorbance changing upon increasing DNA or RNA concentrations. Inset: plots of (ε_a − ε_f)/(ε_b − ε_f) (in (mol L⁻¹)² cm) versus [Nucleic acid] (in mol L⁻¹) for the titration of DNA or RNA with the Ru(II)–Co(III) complex for the determination of the binding constant K_b at 263 nm.

Fig. 4

Emission spectra of the Ru(II)–Co(III) complex in Tris–HCl buffer at 298 K in the presence of CT-DNA (a) and yeast tRNA (b). [Ru–Co] = 1.0 × 10⁻⁶ M, [DNA] = (0–2.4) × 10⁻⁶ M, [RNA] = (0–3.6) × 10⁻⁵ M. Arrow shows the intensity changing upon increasing DNA or RNA concentrations. Inset: plots of relative integrated emission intensity versus [DNA]/[Ru⁻Co].

Fig. 5

Emission quenching with [Fe(CN)₆]^4- for the Ru(II)–Co(III) complex in the absence (dotted lines) and the presence of CT-DNA (top, solid lines) or RNA (bottom, solid lines). [Ru–Co] = 1.0 × 10⁻⁶ M, [DNA or RNA]/[Ru–Co] = 40, [Fe(CN)₆]⁴⁻ = (0–1.0) mM, where I₀ and I are the fluorescence intensities in the absence and the presence of the quencher, respectively. Inset: plots of I₀/I versus [Fe(CN)₆]⁴⁻.

Fig. 6

Effect of increasing amounts of ethidium bromide (■), [Ru(bpy)₃]²⁺ (●), and the Ru(II)–Co(III) complex (▼) on the relative viscosity of calf thymus DNA at 28 (± 0.1) °C. The total concentration of DNA is 0.5 mM.

Fig. 7

CD spectra of the Ru(II)–Co(III) complex after 32 h of dialysis against yeast tRNA (solid line) or CT-DNA (dotted line) in stirred aqueous solution. [Ru–Co] = 20.0 μM, [DNA] = 1.0 mM.

Fig. 8

Cell viability of the Ru(II)–Co(III) complex on tumor (Hep-G2) cell proliferation in vitro. Light microscopy of HepG2 cell line after treated for 48 h in the absence (control) and presence of same concentrations complexes: [Ru–Co] = 20.0 mM; Cell was observed using an inverted microscope and photographed by a digital camera. cis-Platin (a); absence of complexes (b); the Ru(II)–Co(III) complex (c).