Photochemical activation of the recombinant HER2-targeted fusion toxin MH3-B1/rGel; Impact of HER2 expression on treatment outcome

J Control Release. 2014 May 28;182:58-66. doi: 10.1016/j.jconrel.2014.03.014. Epub 2014 Mar 15.


HER2 is overexpressed in 20-30% of breast tumors and is associated with aggressiveness and increased risk of recurrence and death. The HER2 protein is internalized as a part of its activity, and may therefore be utilized as a target for the specific intracellular delivery of drugs. Photochemical internalization (PCI) is a novel technology now undergoing clinical evaluation for its ability to improve the release into the cytosol of drugs entrapped in the endo/lysosomal compartment. PCI employs an amphiphilic photosensitizer which localizes in the membranes of endo/lysosomes. Subsequent light exposure (visible light) causes destabilization of the endo/lysosomal membranes. PCI has been proven highly effective for improving the cytosolic delivery of targeted toxins based on type I ribosome inactivating protein toxins such as gelonin. We examined the impact of the level of target antigen expression on PCI efficacy. Four human breast cancer cell lines (MDA-MB-231, BT-20, Zr-75-1 and SK-BR-3) covering a wide range of HER2 expression were included in the present study. PCI of the HER2-targeted fusion toxin MH3-B1/rGel was found to be highly effective in all four cell lines. The increase in PCI-mediated efficacy was not directly correlated with the cellular levels of HER2 as assessed by western blots, the overall uptake of MH3-B1/rGel as measured by flow cytometry, the amount of MH3-B1/rGel localized to endo/lysosomes assessed by confocal microscopy or the cell sensitivity to the photochemical treatment itself (photosensitizer and light without MH3-B1/rGel). However, correcting the PCI efficacy for the baseline cellular sensitivity to rGel revealed a linear correlation (R(2)=0.80) with HER2 expression. The present report therefore concludes the cellular sensitivity to the toxin as an important parameter for PCI efficacy and also indicates PCI of a HER2-targeted fusion toxin as an attractive treatment alternative for breast cancer patients with both HER2-low and -high expression.

Keywords: Breast cancer; HER2/neu/ErbB2; Immunotoxin; Photochemical internalization; Photodynamic; Triple negative breast cancer.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies / administration & dosage*
  • Cell Line, Tumor
  • Cell Survival / drug effects
  • Humans
  • Immunotoxins / administration & dosage*
  • Light*
  • Photochemical Processes
  • Photosensitizing Agents / administration & dosage
  • Porphyrins / administration & dosage
  • Receptor, ErbB-2 / immunology
  • Receptor, ErbB-2 / metabolism*
  • Recombinant Fusion Proteins / administration & dosage*
  • Ribosome Inactivating Proteins, Type 1 / administration & dosage*


  • Antibodies
  • Immunotoxins
  • Photosensitizing Agents
  • Porphyrins
  • Recombinant Fusion Proteins
  • Ribosome Inactivating Proteins, Type 1
  • meso-tetraphenyl chlorin disulphonate
  • Receptor, ErbB-2