Response of a Rodent Fibrosarcoma to Photodynamic Therapy Using 5-aminolaevulinic Acid or Polyhaematoporphyrin

The effects of 5-aminolaevulinic acid (ALA)-based photodynamic therapy (PDT) on the growth of an intradermal rat fibrosarcoma have been determined following topical, intravenous, or intratumour application of ALA. The pattern of tumour growth was identical following each type of therapy and we conclude that the efficacy of ALA-PDT is independent of the route of drug administration, at least in this tumour system. We have also compared the efficacy of interstitial ALA-based PDT with similar therapy using a conventional photosensitizer, polyhaematoporphyrin (PHP). ALA-PDT was less effective than PHP-based therapy at inhibiting the growth of a subcutaneous rat fibrosarcoma at light doses over 300 J. It is suggested that protoporphyrin IX photobleaching may limit the effectiveness of treatment, whilst the more bleach-resistant PHP may continue to be effective at higher light doses.