TRANSPORT OF THE ANTICANCER DRUG DOXORUBICIN ACROSS CYTOPLASMIC MEMBRANES AND MEMBRANES COMPOSED OF PHOSPHOLIPIDS DERIVED FROM ESCHERICHIA-COLI OCCURS VIA A SIMILAR MECHANISM

An assay was developed to measure and directly compare transport of do xorubicin across right-side-out cytoplasmic membrane vesicles (ROV) an d across model membranes (LUVET) composed of pure phospholipids, isola ted from the corresponding cells. Escherichia coli was used as a model organism, since mutants are available which differ in phospholipid co mposition. Both in LUVET and ROV only passive diffusion across the bil ayer is involved, because effects of drug concentration, pH, divalent cations, the phospholipid composition, and the active transport inhibi tor verapamil wan comparable. Permeability coefficients were about 2-3 -times higher in ROV compared to LUVET. Furthermore, in LUVET an avera ge activation energy of 87 kJ/mol and in ROV of 50 kJ/mol was observed . These differences are suggested to result from differences in membra ne order between LUVET and ROV and differences in the temperature depe ndence of membrane order in LUVET and ROV, respectively. Because no ba ckground carrier-facilitated doxorubicin transport seems to be present , ROV are an excellent model system to study the effect of phospholipi d composition on drug transport after expression of a multidrug resist ance-conferring protein. Furthermore, data of passive diffusion of dox orubicin obtained with LUVET are representative for more complex, biol ogically relevant membrane systems.