Chromatographic retention of drug molecules on immobilised liposomes prepared from egg phospholipids and from chemically pure phospholipids

The partitioning of a chemically diverse set of drugs into liposomes was studied by immobilised liposome chromatography (ILC). For this purpose liposomes composed of (i) purified egg phospholipids (EPL), (ii) synthetic phosphatidylcholine (PC), (iii) PC-synthetic phosphatidylethanolamine (PE) 80:20 (mol/mol) and (iv) PC-synthetic phosphatidylserine (PS) 80:20 (mol/mol) were immobilised in gel beads by freeze-thawing. The drug partitioning was assessed from the retention volume, which was expressed as a capacity factor, K-s, normalised with respect to the amount of immobilised phospholipid. The drug retention on EPL, PC and PC-PE Liposomes was very similar, whereas the negatively charged PC-PS liposomes increased the retention of positively charged and decreased retention of negatively charged drugs. The partitioning of drugs on liposome columns (log K-s) versus their octanol-water partitioning (log P-oct) showed three separate rectilinear relationships, depending on the charge of the compound (neutral, positive, or negative). Statistical analysis (ANCOVA) proved that the lines had similar slopes. Repeated analysis of four reference compounds showed a low variation (<0.12 log units) over time (about 250 days). A close relationship was observed between the drug retention in short EPL columns with a low content of phospholipids and the retention in longer standard EPL columns. The short 'quick screen bilayer columns' permit analysis of highly lipophilic compounds within 30 min and are thus applicable for medium-throughput screening in drug discovery settings. A very strong rectilinear relationship (r(2) = 0.95, n = 13) between log K-s (EPL) and published liposome partitioning data (log D-mem) confirmed that the ILC drug retention reflects the drug partitioning into the lipid bilayers. A moderate to fair rectilinear relationship was observed between the normalised retention on PC, PC-PE and EPL liposomes (r(2) = 0.79, 0.86 and 0.85, respectively, n = 24) and corresponding published log k(IAM)' data obtained on immobilised artificial membrane (IAM) columns. Transport across Caco-2 cell monolayers (log P-c) showed curvilinear relationships with log K-s, log k(IAM)' log P-oct and log D-oct. The drug fraction absorbed in humans showed a similar relationship to log K-s values as to surface plasmon resonance signals representing drug-liposome interaction (Danelian et al., 2000 J Med Chem, 43, 2083-2086). (C) 2001 Elsevier Science B.V. All rights reserved.