Tailoring protease-sensitive photodynamic agents to specific disease-associated enzymes

Bioconjug Chem. Jul-Aug 2007;18(4):1070-7. doi: 10.1021/bc060321l. Epub 2007 May 4.


We have developed novel polymeric photosensitizer prodrugs (PPPs) for improved photodynamic therapy. In PPPs, multiple photosensitizer units are covalently coupled to a polymeric backbone via protease-cleavable peptide linkers. These initially non-photoactive compounds become fluorescent and phototoxic after specific enzymatic cleavage of the peptide linkers and subsequent release of the photosensitizer moieties. Tethering the photosensitizer via a short and easily modified amino acid sequence to the polymeric backbone allows for the targeting of a wide variety of proteases. Model compounds, sensitive to trypsin-mediated cleavage, with different pheophorbide a-peptide loading ratios and backbone net charges were evaluated with respect to their solubility, "self-quenching" capacity of fluorescence emission, and reactive oxygen species (ROS) generation. In addition, linker sequence impaired selectivity toward enzymatic cleavage was demonstrated either by incubating PPPs with different enzymes having trypsin-like activity or by introducing a single d-arginine mutant in the peptide sequence. In vitro cell culture tests confirmed dose-dependent higher phototoxicity of enzymatically activated PPPs compared to the nonactivated conjugate after irradiation with white light. These data suggest that similar compounds adapted to disease-associated proteases can be used for selective photodynamic therapy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Line, Tumor
  • Cell Survival / drug effects
  • Chlorophyll / analogs & derivatives*
  • Chlorophyll / chemistry
  • Chlorophyll / pharmacology
  • Humans
  • Peptides / chemistry
  • Photochemotherapy*
  • Photosensitizing Agents / chemistry*
  • Photosensitizing Agents / pharmacology
  • Polylysine / chemistry
  • Prodrugs / chemical synthesis*
  • Prodrugs / pharmacology
  • Reactive Oxygen Species / metabolism
  • Trypsin / chemistry


  • Peptides
  • Photosensitizing Agents
  • Prodrugs
  • Reactive Oxygen Species
  • Chlorophyll
  • Polylysine
  • Trypsin
  • pheophorbide a