title: Potentiation of chlorin e6 photodynamic activity in vitro with peptide-based intracellular vehicles.
abstract: Photodynamic therapy (PDT) is a targeted treatment modality where photosensitizers accumulate into cells and are selectively activated by light leading to the production of toxic species and cell death. Focusing the action of photosensitizers to a unique intracellular target may enhance their cytotoxicity. In this study, we demonstrate that the routing of the porphyrin-based photosensitizer chlorin e(6), to the nucleus of cells can significantly alter its toxicity profile. The cellular localization of chlorin e(6) was achieved by coupling the chromophore during solid-phase synthesis to a nucleus-directed linear peptide (Ce6-peptide) or a branched peptide (Ce6-loligomer) composed of eight identical arms displaying the sequence of the Ce6-peptide. These constructs incorporated signals guiding their cytoplasmic uptake and nuclear localization. Ce6-peptide and Ce6-loligomer displayed an enhanced photodynamic activity compared to unconjugated chlorin e(6), lowering the observed CD(50) values for CHO and RIF-1 cells by 1 or more orders of magnitude. The intracellular accumulation of Ce6-peptide and Ce6-loligomer was assessed by electron and confocal microscopy as well as by flow cytometry. Constructs were internalized by cells within an hour and by 6 h, the release of active oxygen species could be observed within the nucleus of cells pretreated with Ce6-loligomer. These results highlight the utility of designing peptides as vehicles for regulating the intracellular distribution of photosensitizers such as chlorin e(6) in order to maximize their efficacy in PDT.
authors.affiliation: Department of Medical Biophysics, University of Toronto, Princess Margaret Hospital, Ontario, Canada.
authors.forename: S K
authors.initials: SK
authors.lastname: Bisland
authors.forename: D
authors.initials: D
authors.lastname: Singh
authors.forename: J
authors.initials: J
authors.lastname: Gariépy
mesh_terms: D000818:Animals; D019921:Biotinylation; D016466:CHO Cells; D016923:Cell Death; D002460:Cell Line; D002467:Cell Nucleus / Q000187:drug effects; D002735:Chlorophyllides; D006224:Cricetinae; D004357:Drug Synergism; D005347:Fibroblasts; D005434:Flow Cytometry; D007700:Kinetics; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D015394:Molecular Structure; D010455:Peptides / Q000008:administration & dosage / Q000737:chemistry / Q000378:metabolism; D011166:Porphyrins / Q000008:administration & dosage* / Q000737:chemistry / Q000378:metabolism; D011838:Radiation-Sensitizing Agents; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D002735:Chlorophyllides; D010455:Peptides; D011166:Porphyrins; D011838:Radiation-Sensitizing Agents; D017382:Reactive Oxygen Species; C062985:phytochlorin