Differential scanning calorimetric study of antibiotic distamycin A binding with chromatin within isolated rat liver nuclei.

CONTEXT: Natural oligopeptide antibiotic distamycin A (Dst) biosynthesized by Streptomyces distallicus is traditionally used in medical practice as an anti-inflammatory and antitumour drug.

OBJECTIVE: Dst was investigated for its effect on the structural components of native chromatin directly within isolated rat liver nuclei in the presence of physiologically significant cations (magnesium or spermine and spermidine).

MATERIALS AND METHODS: Differential scanning calorimetry (DSC) was used to study the Dst action at molar ratio Dst/DNA = 0.1 and 0.15 mM Dst on the melting profile of nuclei suspension in different conditions.

RESULTS: Results showed that the thermodynamic parameters of control nuclei in the presence of polyamines or Mg2+  were different. The incubation of nuclei with Dst raised transition temperatures of relaxed (peak II) and topologically constrained DNA (peak III) by 6-8 °C and decreased by 2-4 °C that of core-histones (peak I). The total excess transition enthalpy (ΔHexc ) in buffer with polyamines (24.7 kJ/mol DNA nucleotides) increased by1.5 times versus control but in buffer with Mg2+ , the value of ΔHexc (35.8 kJ/mol DNA nucleotides) remained unchanged.

CONCLUSIONS: The association of Dst with chromatin in the nucleus weakens histone-DNA contacts and causes additional strengthening of interaction between two complementary DNA chains. Our results contribute towards validation of DSC to test drug ability to modulate chromatin structure in the physiological environment and to clarify the mechanism of these modulations.