Potentiation of chlorin e6 photodynamic activity in vitro with peptide-based intracellular vehicles

Bioconjug Chem. Nov-Dec 1999;10(6):982-92. doi: 10.1021/bc990020u.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biotinylation
  • CHO Cells
  • Cell Death
  • Cell Line
  • Cell Nucleus / drug effects
  • Cricetinae
  • Drug Synergism
  • Fibroblasts
  • Flow Cytometry
  • Kinetics
  • Microscopy, Confocal
  • Microscopy, Electron
  • Microscopy, Fluorescence
  • Molecular Structure
  • Peptides* / administration & dosage
  • Peptides* / chemistry
  • Peptides* / metabolism
  • Porphyrins / administration & dosage*
  • Porphyrins / chemistry
  • Porphyrins / metabolism
  • Radiation-Sensitizing Agents
  • Reactive Oxygen Species / metabolism


  • Peptides
  • Porphyrins
  • Radiation-Sensitizing Agents
  • Reactive Oxygen Species
  • phytochlorin