title: Major determinants of photoinduced cell death: Subcellular localization versus photosensitization efficiency.
abstract: We present a study on whether and to what extent subcellular localization may compete favorably with photosensitization efficiency with respect to the overall efficiency of photoinduced cell death. We have compared the efficiency with which two cationic photosensitizers, namely methylene blue (MB) and crystal violet (CV), induce the photoinduced death of human cervical adenocarcinoma (HeLa) cells. Whereas MB is well known to generate singlet oxygen and related triplet excited species with high quantum yields in a variety of biological and chemical environments (i.e., acting as a typical type II photosensitizer), the highly mitochondria-specific CV produces triplet species and singlet oxygen with low yields, acting mostly via the classical type I mechanism (e.g., via free radicals). The findings described here indicate that the presumably more phototoxic type II photosensitizer (MB) does not lead to higher degrees of cell death compared to the type I (CV) photosensitizer. In fact, CV kills cells with the same efficiency as MB, generating at least 10 times fewer photoinduced reactive species. Therefore, subcellular localization is indeed more important than photochemical reactivity in terms of overall cell killing, with mitochondrial localization representing a highly desirable property for the development of more specific/efficient photosensitizers for photodynamic therapy applications.
authors.affiliation: Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, 05508-000 São Paulo, SP, Brazil.
authors.forename: Carla S
authors.initials: CS
authors.lastname: Oliveira
authors.forename: Rozane
authors.initials: R
authors.lastname: Turchiello
authors.forename: Alicia J
authors.initials: AJ
authors.lastname: Kowaltowski
authors.forename: Guilherme L
authors.initials: GL
authors.lastname: Indig
authors.forename: Mauricio S
authors.initials: MS
authors.lastname: Baptista
mesh_terms: D000230:Adenocarcinoma / Q000378:metabolism / Q000628:therapy* / Q000648:ultrastructure; D016923:Cell Death / Q000187:drug effects / Q000528:radiation effects; D005609:Free Radicals / Q000378:metabolism; D005840:Gentian Violet / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use*; D006367:HeLa Cells; D006801:Humans; D008751:Methylene Blue / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use*; D008854:Microscopy, Electron; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects / Q000648:ultrastructure; D010787:Photosensitivity Disorders; D017319:Photosensitizing Agents / Q000627:therapeutic use*; D010789:Phototherapy; D021381:Protein Transport; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D005609:Free Radicals; D017319:Photosensitizing Agents; D017382:Reactive Oxygen Species; D005840:Gentian Violet; D008751:Methylene Blue