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Photobleaching during and re‐appearance after photodynamic therapy of topical ALA‐induced fluorescence in UVB‐treated mouse skin
Author(s) -
Van Der Veen Nynke,
De Bruijn Henriëtte S.,
Star Willem M.
Publication year - 1997
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/(sici)1097-0215(19970703)72:1<110::aid-ijc16>3.0.co;2-n
Subject(s) - photodynamic therapy , protoporphyrin ix , fluorescence , photobleaching , hairless , skin cancer , actinic keratosis , chemistry , medicine , dermatology , cancer , pathology , biochemistry , optics , physics , organic chemistry , basal cell
Photodynamic therapy (PDT) using protoporphyrin IX (PpIX) induced by topically applied 5‐aminolevulinic acid (ALA) seems a promising alternative for the treatment of superficial non‐melanoma skin cancer and actinic keratosis. In this study, the kinetics of new PpIX fluorescence arising after a PDT treatment that had photobleached the original fluorescence were determined. Our purpose was to examine the feasibility of multiple irradiations, following a single topical ALA application, to increase PDT efficacy. In addition, photobleaching during PDT and the fluorescence spectra during and after PDT were studied. As a model we used hairless mice with and without UVB‐induced skin lesions. ALA was applied to the skin for 4 hr. An illumination was delivered either immediately after application or 6 hr after the end of the application (at interval of maximum fluorescence). During PDT, the fluorescence of normal skin decreased at a faster rate than the fluorescence of the skin lesions. In the fluorescence study after PDT, the areas treated immediately post‐application showed a fluorescence increase over time similar to that in non‐treated areas on the same mice. A remarkable result was that the fluorescence of areas treated at maximum fluorescence increased, whereas the fluorescence of non‐treated areas did not increase over time. With both treatment intervals the new fluorescence showed a characteristic PpIX spectrum. Our results demonstrate that a second illumination, when new PpIX fluorescence has been formed, may increase PDT efficacy after topical ALA application. This finding has been demonstrated previously for systemic ALA administration. Int. J. Cancer 72:110–118, 1997. © 1997 Wiley‐Liss Inc.