Light fractionation does not enhance the efficacy of methyl 5-aminolevulinate mediated photodynamic therapy in normal mouse skin.
Previous work demonstrated that fractionated illumination using two fractions separated by a dark interval of 2 h, significantly enhanced the clinical efficacy of photodynamic therapy (PDT) with 5-aminolevulinic acid (ALA). Considering the increasing clinical use of methyl 5-aminolevulinate (MAL) and the expected gain in efficacy by light fractionation we have investigated the response to MAL-PDT using a single and a two-fold illumination scheme and compared that with ALA-PDT. Our results show that fractionated illumination does not enhance the efficacy of PDT using MAL as it does using ALA despite the comparable fluorescence intensities at the end of the first light fraction and at the start of the second light fraction. Only the initial rate of photobleaching was slightly greater during ALA-PDT although the difference was small. Previously we hypothesized that cells surviving the first fraction are more susceptible to the second fraction. Since this is not true for MAL-PDT our data suggest that the distribution of MAL and ALA in tissues, and therefore the site of PDT induced damage, is an important parameter in the mechanism underlying the 2-fold illumination scheme.
Center for Optical Diagnostics and Therapy, Department of Radiation Oncology, Erasmus MC, Room Wk-319, PO box 2040, 3000, CA, Rotterdam, The Netherlands.
Henriëtte S
HS
de Bruijn
Ellen R M
ER
de Haas
Konnie M
KM
Hebeda
Angélique
A
van der Ploeg-van den Heuvel
Henricus J C M
HJ
Sterenborg
H A Martino
HA
Neumann
Dominic J
DJ
Robinson
D000622:Aminolevulinic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005453:Fluorescence; D007700:Kinetics; D008027:Light; D051379:Mice; D008812:Mice, Hairless; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000494:pharmacology; D012867:Skin / Q000187:drug effects* / Q000528:radiation effects*; D013997:Time Factors
D017319:Photosensitizing Agents; C475457:methyl 5-aminolevulinate; D000622:Aminolevulinic Acid