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 st udied by immobilised liposome chromatography (ILC). For this purpose liposo mes composed of (i) purified egg phospholipids (EPL), (ii) synthetic phosph atidylcholine (PC), (iii) PC-synthetic phosphatidylethanolamine (PE) 80:20 (mol/mol) and (iv) PC-synthetic phosphatidylserine (PS) 80:20 (mol/mol) wer e immobilised in gel beads by freeze-thawing. The drug partitioning was ass essed 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 th e negatively charged PC-PS liposomes increased the retention of positively charged and decreased retention of negatively charged drugs. The partitioni ng of drugs on liposome columns (log K-s) versus their octanol-water partit ioning (log P-oct) showed three separate rectilinear relationships, dependi ng on the charge of the compound (neutral, positive, or negative). Statisti cal analysis (ANCOVA) proved that the lines had similar slopes. Repeated an alysis 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 bila yer columns' permit analysis of highly lipophilic compounds within 30 min a nd are thus applicable for medium-throughput screening in drug discovery se ttings. A very strong rectilinear relationship (r(2) = 0.95, n = 13) betwee n log K-s (EPL) and published liposome partitioning data (log D-mem) confir med that the ILC drug retention reflects the drug partitioning into the lip id bilayers. A moderate to fair rectilinear relationship was observed betwe en 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 a cross Caco-2 cell monolayers (log P-c) showed curvilinear relationships wit h 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 pla smon resonance signals representing drug-liposome interaction (Danelian et al., 2000 J Med Chem, 43, 2083-2086). (C) 2001 Elsevier Science B.V. All ri ghts reserved.