Fractionated ALA-PDT in PAM212 cells

DE BRUIJN H; CASAS A; DI VENOSA G; RODRIGUEZ L; STERENBORGN H; BATLLE A; ROBINSON D

Innsbruck

Congreso; 13er Congreso de la International Photodynamic Association (IPA); 2011

International Photodynamic Association (IPA)

Introduction/Background: The efficacy of photodynamic therapy (PDT) using the protoporpyrin IX (PpIX) precursor 5-aminolevulinic acid (ALA) is significantly improved by applying light fractionation with a long dark interval. The illumination parameters are important and suggest the involvement of a cellular mechanism. In the present study we investigated the response of cells in-vitro to light fractionation in search of the cellular mechanism.   Methods: In PAM212 cells we investigated the response to light fractionation in-vitro. The illumination parameters used were carefully translated from in-vivo experience to the response observed in-vitro.   Results: Light fractionation with illuminations at 3+5 hrs of 0.36+0.84 J/cm2 resulted in 66.3 ± 23.3% cell death compared to 79.0±17.5% after a single illumination at 5 hrs of 1.2 J/cm2. This may be explained by the increased PpIX accumulation observed after 5 hrs compared to 3hrs of 2 mM ALA incubation (38.7±6.5 µg/105 vs 25.0±4.4). PpIX accumulation plateaued when the ALA concentration was reduced to 0.2 mM and ALA was withdrawn after the first 2 hr incubation (2.8 µg/105 cells at 2 hrs vs 2.8 at 4 hrs). Using this ALA concentration, cell death was significantly increased from 83.0±3.3 after a single illumination (1.8 J/cm2 at 4 hrs) to 96.0±0.8% after light fractionation with illuminations at 2+4 hrs of 0.84+1.08 J/cm2.   Conclusion: Light fractionation increases the effectiveness of ALA-PDT in-vitro which suggests that there is a cellular mechanism involved. Besides the illumination parameters also the amount of PpIX present are critically important. These results may explain the increase in efficacy observed in-vivo.