On the reversal by deoxyribonucleic acid of the binding of adriamycin to cardiolipin-containing liposomes.

The binding of the cytotoxin adriamycin (doxorubicin) to phospholipids, DNA, and RNA was investigated using (i) fluorescence quenching by this drug of liposomes containing pyrene-labeled phospholipids and (ii) monomolecular cardiolipin films on an air/water interface. In accordance with previous studies, our fluorescence experiments revealed that the acidic phospholipids, phosphatidylglycerol, phosphatidylmethanol, and phosphatidic acid all have high and comparable affinities to adriamycin mainly due to electrostatic interactions whereas binding to phosphatidylcholine was much weaker. Highest affinity, however, was possessed by cardiolipin. Addition of 4 mM CaCl2 reduced the binding of adriamycin to the above lipids. Moreover, in the presence of calcium the affinity of the drug to the different lipids was similar. Ca2+ concentrations > 100 microM began to reverse the binding of adriamycin to cardiolipin-containing liposomes whereas lower concentrations had only an insignificant effect. The association of adriamycin with DNA, RNA, and cardiolipin was then compared by observing the reversal of the cytotoxin-cardiolipin association by nucleic acids. The affinity of adriamycin was found to decrease in the sequence DNA > cardiolipin > RNA with relative affinities of 7.8, 2.3, and 1, respectively. Penetration of the drug into cardiolipin monolayers spread on an air/water interface resulted in an increase in surface pressure pi whereas only a very weak increase was observed using dimyristoylphosphatidylcholine films. Removal of adriamycin from lipid monolayers was achieved by adding DNA into the aqueous subphase. Similar to the fluorescence quenching studies increase in pi after the inclusion of adriamycin into the aqueous subphase was significantly reduced in the presence of Ca2+ concentrations > 100 microM, whereas lower concentrations had only an insignificant effect. Residual drug-phospholipid interactions in the lipid monolayer observed in the presence of Ca2+ were also reversed by DNA.