Photodynamic therapy with mTHPC and polyethylene glycol-derived mTHPC: a comparative study on human tumour xenografts

Br J Cancer. 1999 Mar;79(7-8):1061-6. doi: 10.1038/sj.bjc.6690170.


The photosensitizing properties of m-tetrahydroxyphenylchlorin (mTHPC) and polyethylene glycol-derivatized mTHPC (pegylated mTHPC) were compared in nude mice bearing human malignant mesothelioma, squamous cell carcinoma and adenocarcinoma xenografts. Laser light (20 J/cm2) at 652 nm was delivered to the tumour (surface irradiance) and to an equal-sized area of the hind leg of the animals after i.p. administration of 0.1 mg/kg body weight mTHPC and an equimolar dose of pegylated mTHPC, respectively. The extent of tumour necrosis and normal tissue injury was assessed by histology. Both mTHPC and pegylated mTHPC catalyse photosensitized necrosis in mesothelioma xenografts at drug-light intervals of 1-4 days. The onset of action of pegylated mTHPC seemed slower but significantly exceeds that of mTHPC by days 3 and 4 with the greatest difference being noted at day 4. Pegylated mTHPC also induced significantly larger photonecrosis than mTHPC in squamous cell xenografts but not in adenocarcinoma at day 4, where mTHPC showed greatest activity. The degree of necrosis induced by pegylated mTHPC was the same for all three xenografts. mTHPC led to necrosis of skin and underlying muscle at a drug-light interval of 1 day but minor histological changes only at drug-light intervals from 2-4 days. In contrast, pegylated mTHPC did not result in histologically detectable changes in normal tissues under the same treatment conditions at any drug-light interval assessed. In this study, pegylated mTHPC had advantages as a photosensitizer compared to mTHPC. Tissue concentrations of mTHPC and pegylated mTHPC were measured by high-performance liquid chromatography in non-irradiated animals 4 days after administration. There was no significant difference in tumour uptake between the two sensitizers in mesothelioma, adenocarcinoma and squamous cell carcinoma xenografts. Tissue concentration measurements were of limited use for predicting photosensitization in this model.

Publication types

  • Comparative Study

MeSH terms

  • Adenocarcinoma / drug therapy
  • Adenocarcinoma / metabolism
  • Animals
  • Antineoplastic Agents / chemistry
  • Antineoplastic Agents / pharmacokinetics
  • Antineoplastic Agents / therapeutic use*
  • Carcinoma, Squamous Cell / drug therapy
  • Carcinoma, Squamous Cell / metabolism
  • Dermatitis, Phototoxic / etiology
  • Dermatitis, Phototoxic / pathology
  • Humans
  • Mesoporphyrins / chemistry
  • Mesoporphyrins / pharmacokinetics
  • Mesoporphyrins / therapeutic use*
  • Mesothelioma / drug therapy
  • Mesothelioma / metabolism
  • Mice
  • Mice, Inbred BALB C
  • Mice, Nude
  • Neoplasms / drug therapy*
  • Neoplasms / metabolism
  • Photochemotherapy / methods*
  • Polyethylene Glycols / chemistry
  • Polyethylene Glycols / pharmacokinetics
  • Polyethylene Glycols / therapeutic use*
  • Radiation-Sensitizing Agents / chemistry
  • Radiation-Sensitizing Agents / pharmacokinetics
  • Radiation-Sensitizing Agents / therapeutic use*
  • Transplantation, Heterologous


  • Antineoplastic Agents
  • Mesoporphyrins
  • Radiation-Sensitizing Agents
  • Polyethylene Glycols
  • temoporfin