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      New photosensitizers for photodynamic therapy

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          Abstract

          Photodynamic therapy (PDT) was discovered more than 100 years ago, and has since become a well-studied therapy for cancer and various non-malignant diseases including infections. PDT uses photosensitizers (PSs, non-toxic dyes) that are activated by absorption of visible light to initially form the excited singlet state, followed by transition to the long-lived excited triplet state. This triplet state can undergo photochemical reactions in the presence of oxygen to form reactive oxygen species (including singlet oxygen) that can destroy cancer cells, pathogenic microbes and unwanted tissue. The dual-specificity of PDT relies on accumulation of the PS in diseased tissue and also on localized light delivery. Tetrapyrrole structures such as porphyrins, chlorins, bacteriochlorins and phthalocyanines with appropriate functionalization have been widely investigated in PDT, and several compounds have received clinical approval. Other molecular structures including the synthetic dyes classes as phenothiazinium, squaraine and BODIPY (boron-dipyrromethene), transition metal complexes, and natural products such as hypericin, riboflavin and curcumin have been investigated. Targeted PDT uses PSs conjugated to antibodies, peptides, proteins and other ligands with specific cellular receptors. Nanotechnology has made a significant contribution to PDT, giving rise to approaches such as nanoparticle delivery, fullerene-based PSs, titania photocatalysis, and the use of upconverting nanoparticles to increase light penetration into tissue. Future directions include photochemical internalization, genetically encoded protein PSs, theranostics, two-photon absorption PDT, and sonodynamic therapy using ultrasound.

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          Author and article information

          Journal
          2984726R
          1011
          Biochem J
          Biochem. J.
          The Biochemical journal
          0264-6021
          1470-8728
          10 March 2016
          15 February 2016
          15 February 2017
          : 473
          : 4
          : 347-364
          Affiliations
          [* ]Laser Research Centre, Faculty of Health Science, University of Johannesburg, Doornfontein 2028, South Africa
          []Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA 02114, U.S.A
          []Department of Dermatology, Harvard Medical School, Boston, MA 02115, U.S.A
          [§ ]Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA 02139, U.S.A
          Author notes
          [1 ]To whom correspondence should be addressed: Hamblin@ 123456helix.mgh.harvard.edu
          Article
          PMC4811612 PMC4811612 4811612 nihpa766571
          10.1042/BJ20150942
          4811612
          26862179
          a987e11f-b528-428e-9a98-145bab8f24db
          History
          Categories
          Article

          synthetic dyes,tetrapyrroles,photosensitizers,photodynamic therapy,photochemical mechanisms,naturally occurring photosensitizers

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