Library Subscription: Guest
Home Begell Digital Library eBooks Journals References & Proceedings Research Collections
Journal of Environmental Pathology, Toxicology and Oncology

Impact factor: 0.877

ISSN Print: 0731-8898
ISSN Online: 2162-6537

Journal of Environmental Pathology, Toxicology and Oncology

DOI: 10.1615/JEnvironPatholToxicolOncol.v26.i3.10
pages 165-172

A New Method for Photodynamic Therapy of Melanotic Melanoma—Effects of Depigmentation with Violet Light Photodynamic Therapy

Li-Wei Ma
Department of Radiation Biophysics, Institute for Cancer Research, Rikshospital-Radiumhospital HF and Plasma/Room Physics, University of Oslo, Oslo, Norway
Kristian Pagh Nielsen
Department of Physics and Technology, University of Bergen, Bergen, Norway
Vladimir Iani
Department of Radiation Biophysics, Institute for Cancer Research, Rikshospital-Radiumhospital HF and Plasma/Room Physics, University of Oslo, Oslo, Norway
Johan Moan
Department of Radiation Biophysics, Institute for Cancer Research, Rikshospital-Radiumhospital HF and Plasma/Room Physics, University of Oslo; lnstitute of Physics, University of Oslo, Blindern, Oslo, Norway

ABSTRACT

Melanotic melanomas have a poor response to photodynamic therapy (PDT). The reason for this is that melanin absorbs light over the entire wavelength region used for PDT (400−750 nm). Photobleaching of melanin is an approach to overcome this obstacle. In the present work, reflectance spectroscopy was applied to study depigmentation of human and murine skin with different melanin contents, and effects induced by PDT with topical application of methyl 5-aminolevulinate (MAL) on B16F10 melanotic melanomas transplanted to nude mice. Depigmentation and inhibition of tumor growth after violet light (420 nm) exposure, red light (634 nm) exposure, and combinations of both were studied. Reflectance spectroscopy was suitable for evaluation of the pigmentation of both human and murine skin. Skin depigmentation leads to increase in reflectance. PDT with violet light bleached some of the melanin in the skin above the B16F10 melanomas, and possibly also in the upper part of the melanomas. This resulted in a larger growth inhibition of tumors first given PDT with violet light and then with red light compared to treatments using the reverse order of illumination, namely, red light before violet light. It is concluded that violet light PDT can bleach melanin in melanotic tumors and therefore increase their sensitivity to red light PDT. This finding indicates a new PDT modality that can be further developed for treatment of superficial melanotic melanomas and possibly other diseases where pigmentation is a problem.