calcimycin and 1-2-distearoyllecithin

A liposomal irinotecan formulation referred to as Irinophore C relies on the ability of copper to complex irinotecan within the liposome. It is currently being evaluated for critical drug-loading parameters. Studies presented here were designed to determine the optimum copper concentration required for the effective encapsulation and retention of irinotecan into liposomes.. Distearoylphosphatidylcholine/cholesterol liposomes were formulated using buffers containing various copper or manganese concentrations, and irinotecan loading was determined in the presence and absence of divalent metal ionophore A23187. The rate and extent of irinotecan encapsulation and the rate of irinotecan release from the liposomes were assessed. The amount of copper retained inside liposomes following irinotecan loading and the effect of copper on membrane permeability were determined.. Efficient (>98%) irinotecan loading was achieved using encapsulated copper concentrations of 50 mM. However, irinotecan release was copper concentration dependent, with a minimum 300 mM concentration required for optimal drug retention. The presence of copper increased liposomal membrane permeability.. Results explain why irinotecan loading rates are enhanced in the presence of formulations prepared with copper, and we speculate that the Irinophore C formulation exhibits improved drug retention, due to generation of a complex between copper and irinotecan.

Topics: Animals; Antineoplastic Agents; Calcimycin; Camptothecin; Cell Membrane Permeability; Chemistry, Pharmaceutical; Cholesterol; Chromatography, High Pressure Liquid; Copper; Female; Ionophores; Irinotecan; Liposomes; Mice; Mice, Inbred BALB C; Phosphatidylcholines

These studies describe the role of transition metal ions in the liposomal encapsulation of topotecan. Liposomes (1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and cholesterol (CH) (55:45, mole ratio)) were prepared with manganese (Mn), copper (Cu), zinc (Zn) or cobalt (Co) ion gradients (metal inside). Subsequently, topotecan was added to the liposome exterior (final drug-to-lipid ratio (mol/mol) of 0.2) and drug encapsulation was measured as a function of time and temperature. No drug loading was achieved with liposomes containing Co or Zn. Topotecan could be encapsulated into Mn-containing liposomes only in the presence of the ionophore, A23187 suggesting that a transmembrane pH gradient was necessary. However, Cu-containing liposomes, in the presence or absence of an imposed pH gradient, efficiently encapsulated topotecan. It has been reported that Cu(II) can form transition metal complexes with camptothecin; therefore, the Cu-topotecan interaction was characterized in solution as a function of pH. These investigations demonstrated that topotecan inhibited formation of an insoluble Cu hydroxide precipitate. Cryo-TEM analysis of the topotecan-loaded Cu liposomes showed electron-dense intravesicular precipitates. Further studies demonstrated that only the active lactone form of the drug was encapsulated and this form predominated in Cu-containing liposomes. Copper complexation reactions define a viable methodology to prepare liposomal camptothecin formulations.

Topics: Buffers; Calcimycin; Cations, Divalent; Chemical Precipitation; Cholesterol; Copper; Cryoelectron Microscopy; Doxorubicin; Drug Compounding; Hydrogen-Ion Concentration; Lactones; Liposomes; Manganese Compounds; Molecular Structure; Nigericin; Phosphatidylcholines; Proton-Motive Force; Sulfates; Topotecan

Topics: Calcimycin; Cholesterol; Hydrogen-Ion Concentration; Iron; Kinetics; Liposomes; Models, Theoretical; Phosphatidylcholines