In vitro evaluation of the cytotoxic and mutagenic potential of the 5-aminolevulinic acid hexylester-mediated photodynamic therapy

Photodynamic therapy (PDT) of tumors with 5-aminolevulinic acid hexylester (h-ALA) causes photo-oxidative reactions in treated tissues. In order to study cytotoxic and/or mutagenic effects, cells of the tumor cell line RPMI 2650 as well as fibroblasts of the cell line WS 1 were given photodynamic treatment in vitro. The cells were photosensitized with a 1 mM h-ALA-medium solution for 5 h and illuminated with different light doses (0.5, 1.0, 1.5 and 2.0 J/cm(2)) using red light (633 +/- 20 nm). PDT-induced cytotoxic effects were determined by measurement of the mitotic index (MI) and the nuclear division index (NDI). Chromosome aberrations (CA) and micronuclei (MN) were recorded to study mutagenicity. After treatment of the photosensitized RPMI 2650 cells with a light dose of 2.0 J/cm(2), the MI was significantly decreased to 16.9parts per thousand in comparison with that of the h-ALA control (33.8parts per thousand). In photosensitized WS 1 cells, light doses up to 2.0 J/cm(2) showed no significant effect. The NDI of photosensitized RPMI 2650 cells was significantly decreased by light doses from 1.0 to 2.0 J/cm(2), whereas no significant effect was seen in WS 1 cultures. Thus, h-ALA-PDT only induced desirable cytotoxic effects in tumor cells, but not in the fibroblasts. After application of light doses from 0.5 to 2.0 J/cm(2), photosensitized RPMI 2650 cultures showed CA in 7.0-7.5% of the metaphases, which was not a significant increase (h-ALA control: 5.5%). In WS 1 cultures metaphases containing CA varied non-significantly from 5.0 to 7.5%. The MN rates were approximately the same in illuminated RPMI 2650 cultures and in the corresponding h-ALA control (4.4-4.9%). The MN rates of the illuminated WS 1 cultures also varied non-significantly from 4.5 to 5.0parts per thousand in comparison with the h-ALA control (5.5%). In the mutagenicity tests the h-ALA-PDT had no significant effect, neither on the tumor cells nor on the fibroblasts. In addition to the cytogenetic analysis, spectral karyotyping (SKY) was used to characterize the cell lines and gain more detailed information on possibly PDT-induced CA. The SKY evaluation also showed no significant increase of the CA rate, but confirmed the result of the CA test. Thus, within the scope of the experiments performed, a mutagenic potential of the h-ALA-PDT can be excluded. (C) 2004 Elsevier B.V. All rights reserved.