Article révisé par les pairs
Résumé : The uptake of adriamycin (ADM) and several derivatives into large unilamellar vesicles (LUV) displaying a transmembrane potential and having a lipid composition close to that of the inner mitochondrial membrane has been measured. Drug association to neutral liposomes, made of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) (70:30, w/w) was shown to be potential-dependent: in the absence of potential, accumulation of drug was almost undetectable, whereas between 11 and 50 nmol of drug/mumol phospholipid, depending on the anthracycline used, was associated to LUV exhibiting a membrane potential after 1 h incubation. Association of drugs to LUV with a lipid composition closer to that of the inner mitochondrial (cardiolipin, CL, 20%; PC 50%; PE, 30%, w/w) and displaying a membrane potential is higher than with neutral vesicles (between 40 and 76 nmol of anthracycline/mumol phospholipid after 1 h incubation). Since it is known that ADM and derivatives have a high affinity for CL, a fraction of the associated drug may bind to CL on the outer side of the vesicles. This was confirmed by the fact that, in the absence of potential, between 40 and 56 nmol of anthracycline/mumol phospholipid was still associated to LUV containing CL. In order to discriminate between drug adsorbed at the surface of the LUV and drug accumulated inside the LUV, an anthracycline fluorescence quencher (I-) was used. It was shown on neutral LUV displaying a membrane potential, that between 55 and 81% of the associated drug is actually entrapped inside the vesicles, inaccessible to the quencher. These percentages decreased to between 41 and 68%, respectively, in the presence of LUV containing CL and exhibiting a membrane potential, whereas for LUV of the same composition but displaying no membrane potential almost all the associated drug is adsorbed on the outer face of the LUV, accessible to the quencher, and likely bound to CL. This study brings evidence that antitumour anthracyclines despite important structural homologies do not accumulate to the same extent into vesicles mimicking the lipid composition and the membrane potential of mitoplasts. This ability to reach the matrix compartment of mitochondria could partly explain the differences of cardiotoxicities associated to anthracyclines with closely related molecular structure.