CELLULAR DELIVERY AND RETENTION OF PHOTOFRIN .3. ROLE OF PLASMA-PROTEINS IN PHOTOSENSITIZER CLEARANCE FROM CELLS

Human plasma proteins, albumin, globulins and low density (LDL), high density (HDL) and very low density (VLDL) lipoproteins were tested for their effects on retention of Photofrin and three other photosensitizers in cultured cells. This was assessed by incubating the cells, subsequent to the exposure to Photofrin, in the photosensitizer-free medium containing various concentrations of different plasma proteins. Photofrin clearance levels differed with individual plasma proteins and also were dependent on concentration of these proteins in the incubation medium. All of the proteins except VLDL promoted clearance of Photofrin taken up by the cells in the presence of 5% human serum. Subsequent to some Photofrin exposure conditions (in the presence of 5% fetal bovine serum, or in protein-free medium), albumin, in contrast to LDL, HDL and globulins, exhibited decreased capacity for promoting the photosensitizer clearance from the cells. The VLDL showed very little or no effect in promoting cellular clearance of Photofrin, tetraphenyl porphine tetrasulfonate (TPPS4), and di- and tetrasulfonated chloroaluminum phthalocyanine (AlPcS2 and AlPcS4, respectively). The LDL seem to be particularly effective in promoting clearance of Photofrin and AlPCS2 from the cells, whereas albumin and globulins were shown to be more effective than LDL and HDL in promoting the cellular clearance of TPPS4.