Alteration of the endocytotic pathway by photosensitization with fluoroquinolones

The endocytotic pathway is profoundly altered by the UVA-induced photosensi tization of HS 68 fibroblasts by the fluoroquinolone (FQ) antibiotics lomef loxacin, BAYy 3118, norfloxacin and ciprofloxacin, which preferentially loc alize in lysosomes. The endocytosis of low-density lipoproteins (LDL) loade d with two carbocyanine dyes compatible for effective Forster-type resonanc e energy transfer (FRET), namely 3,3'-dioctadecyloxacarbocyanine perchlorat e (DiO) as the donor and 1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyani ne perchlorate (DiI) as the acceptor, has been used as a model system. Bind ing of LDL to their cell surface receptors is impaired by irradiation with 10 J cm(-2) of UVA and/or treatment with 250 muM BAYy 3118 during 2 h, Pert urbation of the plasma membrane by the FQ is revealed by the change in the rate of exchange of DiO from the LDL to the cell membrane as compared to un treated cells. The lysosomal degradation of LDL, demonstrated by the disapp earance of FRET between DiO and DiI, is partly inhibited by the FQ, The act in filament network, involved in the fusion of mature endosomes with lysoso mes, is readily destroyed upon photosensitization with the four FQ, However , actin depolymerization can be avoided by incubation of the cells with tra ns-epoxysuccinyl-1-leucylamido-(4-guanidino) butane, an inhibitor of lysoso mal cathepsins prior to FQ photosensitization, All these data suggest that several components of the endocytotic pathway are impaired by photosensitiz ation with these FQ.