title: Scavenger-receptor targeted photodynamic therapy.
abstract: Covalent conjugation of a photosensitizer to a ligand that specifically recognized and internalized by a cell-surface receptor may be a way of improving the selectivity of photodynamic therapy (PDT). The class A Type-I scavenger receptor of macrophages, which among other ligands recognizes maleylated serum albumin and has a high capacity is a good candidate for testing this approach. Chlorin(e6) was covalently attached to bovine serum albumin to give conjugates with molar substitution ratios of 1:1 and 3:1 (dye to protein), and these conjugates could then be further modified by maleylation. A novel way of purifying the conjugates by acetone precipitation was developed in order to remove traces of unbound dye that could not be accomplished by size-exclusion chromatography. Conjugates were characterized by polyacrylamide gel electrophoresis and thin-layer chromatography. Photosensitizer uptake was measured by target J774 murine macrophage-like cells and nontarget OVCAR-5 human ovarian cancer cells, and phototoxicity was examined after illumination by a 660 nm diode laser by a tetrazolium assay. All of the purified conjugates were taken up by and after illumination killed J774 cells while there was only small uptake and no phototoxicity toward OVCAR-5 cells. The higher dye:protein ratio and maleylation of the conjugates both produced higher uptakes and lower survival ratios in J774 cells. The uptake and phototoxicity by J774 cells were decreased after incubation at 4 degrees C demonstrating internalization, and confocal microscopy with organelle-specific green fluorescent probes showed largely lysosomal localization. Uptake and phototoxicity by J774 cells could both be competed by addition of the scavenger receptor ligand maleylated albumin. These data show that scavenger receptor-targeted PDT gives a high degree of specificity toward macrophages and may have applications in the treatment of tumors and atherosclerosis.
authors.affiliation: Wellman Laboratories of Photomedicine, Massachusetts General Hospital and Department of Dermatology, Harvard Medical School, Boston 02114, USA. hamblin@helix.mgh.harvard.edu
authors.forename: M R
authors.initials: MR
authors.lastname: Hamblin
authors.forename: J L
authors.initials: JL
authors.lastname: Miller
authors.forename: B
authors.initials: B
authors.lastname: Ortel
mesh_terms: D000818:Animals; D002460:Cell Line; D002735:Chlorophyllides; D004337:Drug Carriers; D005260:Female; D006801:Humans; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D010051:Ovarian Neoplasms / Q000378:metabolism; D010778:Photochemotherapy / Q000379:methods*; D011166:Porphyrins / Q000008:administration & dosage / Q000737:chemistry; D011838:Radiation-Sensitizing Agents / Q000008:administration & dosage* / Q000737:chemistry / Q000493:pharmacokinetics; D011971:Receptors, Immunologic / Q000378:metabolism*; D051116:Receptors, Scavenger; D051117:Scavenger Receptors, Class A; D012710:Serum Albumin, Bovine / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics; D014407:Tumor Cells, Cultured
chemical_list: D002735:Chlorophyllides; D004337:Drug Carriers; C495139:MSR1 protein, human; C495140:Msr1 protein, mouse; D011166:Porphyrins; D011838:Radiation-Sensitizing Agents; D011971:Receptors, Immunologic; D051116:Receptors, Scavenger; D051117:Scavenger Receptors, Class A; D012710:Serum Albumin, Bovine; C062985:phytochlorin