Thermodynamics of the anthracycline-nuclei interactions in drug-resistant and drug-sensitive K562 cells.

Fluorescence emission spectra from anthracycline-treated cells suspended in buffer have been used to measure the uptake of three anthracycline derivatives: Adriamycin (ADR), 4'-o-tetrahydropyranyl-Adriamycin (THP-ADR) and aclacinomycin (ACM) in drug-sensitive and drug-resistant K562 cells. The concentration of drug bound to the nucleus and free in the cytoplasm, at steady state, as well as the concentration of drug bound to the nucleus at equilibrium state have been determined at temperatures ranging from 6 degrees to 40 degrees. The enthalpies for the binding of ADR, THP-ADR and ACM to nuclei equal -35 +/- 3, -35 +/- 3 and -30 +/- 3 kJ/mol, respectively. These values compare with the enthalpies of binding of these drugs to naked DNA.