Interactions of ellipticine with model or natural membranes. A spectrophotometric study.

Ellipticine is the type of a group of substances used against human cancer. It was shown that ellipticine and 9-methoxyellipticine strongly interact with monolayers of negatively charged phospholipids. In the present paper it is shown by spectrophotometric methods that ellipticine interacts with suspensions of a model membrane with a 1/1 charge neutralization, and with a natural membrane, both negatively charged. At a physiological pH, ellipticine undergoes protonation in the presence of these membranes. Its apparent pK is increased by 1, and its spectral behaviour, when the pH is changed, indicates that the drug is in a less polar environment, suggesting that hydrophobic bonds link the drug and the lipids. The existence of such bonds is suggested by the fact that the drug is not significantly released from anionic membranes when the pH is increased to 10, at which value ellipticine is not ionized. The consequences of these ionic and hydrophobic interactions are briefly discussed.