Membranes affinity of promising anticancer agent DB-67 determined by fluorescence spectra analysis

Camptothecins are fluorescent compounds which exhibit anticancer properties. A disadvantage which seriously limits application of camptothecins in antitumor chemotherapy is the hydrolysis of these compounds. They convert into inactive carboxylate forms. The process of hydrolysis is inhibited when the molecules of camptothecin are bound to cell membranes. So it is desirable that camptothecins molecules bind easily to membranes. A quantitative measure of drugs affinity to membranes is the association constant. To determine the association constant to membranes the lipid bilayers i.e. liposomes are used as model membranes. In this work affinity of hydroxycamptothecin DB-67 to model membranes is determined. Fluorescence spectra of this analogue change in presence of liposomes: the fluorescence intensity is bigger and besides green band the blue band appears. The spectra of hydroxycamptothecins change over lipids concentration. On the basis of this changes the association constant to membranes is calculated.