5-aminolevulinic acid - mediated photodynamic therapy of human glioma cells in vitro

Abstract

OBJECTIVE To investigate the effect of 5-aminolevulinic acid (ALA)-mediated photodynamic therapy (PDT) on U251 human glioma cells in vitro . METHODS U251 human glioma cells were routinely cultured and then treated with ALA, a type of photosensitizer, at various concentrations followed by light irradiation. The PDT-induced phototoxicity of the cells was determined by a MTT assay. In addition, cells were treated with ALA at a fixed concentration and subjected to various doses of light irradiation. RESULTS With the same light dosage (25.0 J/cm2), the cell survival rates were 70.16%+_5.02%, 50.19%+_4.79%, 34.97%+5.34%, 27.04%+-4.34%, and 24.26% _+2.76% at ALA concentrations of 0.25, 0.5, 1.0, 2.0, and 4.0 mM, respectively (F =279.88, P =0.0000). But the survival rates of the cells incubated with 2.0 mM ALA compared to those with 4.0 mM ALA (27.04%+-4.34% vs 24.26%+2.76%) showed no significant difference (P=0.611). At a single ALA concentration, the cell survival rates were 83.48% +- 6.79%, 68.09%+6.02%, 33.75%+- 6.70%, 23.34%+ 5.08% and 15.14%+ 3.60% for light doses of 6.25, 12.5, 25.0, 50.0, and 100 J/cm 2, respectively (F=422.03, P =0.0000). Without exposure to light, however, the cell survival rates were 96.64% +-6.56%, 97.71% +5.48%, 98.10% +-6.25%,99.44% +-7.02%, and 95.86% +7.80% for ALA concentrations at 0.25, 0.5, 1.0, 2.0, and 4.0 mM, respectively (F =0.68, P =0.6085). Without ALA in the medium, the cell survival rates were 98.74% +6.20%, 96.49% +-7.13%, 97.60% +5.94%, 95.70%+4.86%, 98.08%+-6.26% for light doses of 6.25, 12.5, 25.0, 50.0, and 100 J/cm 2, respectively (F=0.6400, P =0.6368). CONCLUSION The PDT damage to the U251 cells increased with ALA concentration within a relative lower range, but then plateaued at higher concentrations. PDT damage was proportional to the doses of irradiated light. Without ALA, the light alone caused no photodynamic damage and ALA itself was nontoxic. The ALA-induced PDT appears to be a promising therapy for glioma.