Elsevier

Biophysical Chemistry

Volume 60, Issue 3, 11 June 1996, Pages 135-142
Biophysical Chemistry

The effect of ionic strength on melting of DNA modified by platinum(II) complexes

https://doi.org/10.1016/0301-4622(96)00010-5Get rights and content

Abstract

Thermal denaturation of calf thymus DNA modified by antitumor cis-diamminedichloroplatinum(II) (cis-DDP) and by two related Pt(II) compounds which had been shown to be clinically inefective, viz. trans-diamminedichloroplatinum(II) (trans-DDP) or monodentate diethylenetriaminechloroplatinum(II) chloride {[Pt(dien)Cl)]Cl}, was studied by monitoring changes of absorbance at 260 nm. The melting of DNA platinated to different levels was investigated in neutral media containing varying concentrations of Na+. It has been shown that the ionic strength has a strong influence on the character and magnitude of changes in the melting temperature of DNA (Tm) induced by the platination. The modification of DNA by either platinum complex used in this work results in an increase of Tm if DNA melting is measured in media containing low Na+ concentrations (ca. 1 mM). This effect is reversed at higher Na+ concentrations. The concentration of Na+ at which this reversal occurs is, however, markedly lower for DNA modified by cis-DDP than for DNA modified by the other two platinum complexes. These results have been iterpreted to mean that at least three factors affect the thermal stability of DNA modified by the platinum(II) complexes: stabilization effects of the positive charge on the platinum moiety and of interstrand cross-links, and a destabilization effect of conformational distortions in DNA. Thus, in order to compare and interpret the melting behavior of DNA modified by different compounds, a great attention has to be paid to the composition of the medium in which the melting experiments are carried out.

References (24)

  • A. Eastman

    Pharmacol. Ther.

    (1987)
  • V. Brabec et al.

    Biophys. Chem.

    (1990)
  • V. Brabec et al.

    Biophys. Chem.

    (1976)
  • J. Chambron et al.

    Biochim. Biophys. Acta

    (1966)
  • V. Kleinwächter et al.

    Biochim. Biophys. Acta

    (1969)
  • J. Drobník

    Cancer Chemother. Pharmacol.

    (1983)
  • P.J. Loehrer et al.

    Ann. Intern. Med.

    (1984)
  • J. Reedijk

    Pure Appl. Chem.

    (1987)
  • N.P. Johnson et al.

    Prog. Clin. Biochem. Med.

    (1989)
  • C.A. Lepre et al.

    Nucleic Acids Molec. Biol.

    (1990)
  • M. Leng et al.
  • P.D. Bancroft et al.

    J. Am. Chem. Soc.

    (1990)
  • Cited by (0)

    View full text