Formation of 5-aminolevulinic-acid (ALA) induced protoporphyrin IX (PPIX) and photodynamic effectiveness in human urothelial cell lines

Background: To optimize differential effectiveness of aminulevulinic acid (ALA)-induced protoporphyrin IX (PPIX)- mediated photodynamic therapy (PDT) on normal and tumor urothelial cells, aspects of PPIX formation and parameters responsible for treatment efficiency were examined in vitro. Material and Methods: Plateau phase cells of a bladder cancer and a normal urothelial cell line were incubated using various incubation conditions and analyzed with respect to their PPIX content and cellular sensitizer distribution. PDT was performed using incoherent light from a Xenon coldlight projector. Photo toxicity was investigated using flow cytometric analysis of propidium iodide exclusion and analysis of cell size and number. Results: Following 3h incubation intervals, both cell lines showed similar PPIX localization with an amount of sensitizer three times higher in RT4 tumor cells. 1h incubation times resulted in the same ratio of PPIX amount but lead to different cellular PPIX distribution. After 3h incubation, PDT resulted in complete tumor cell kill accomplished by a marked fraction of damaged normal urothelial cells. TR4 cell kill with significantly reduced damage of UROtsa cells could be achieved using 1h incubation times. Discussion: Besides sensitizer amount, cellular localization is crucial for PDT effectiveness. Differential effectiveness of tumor and normal cells can be enhanced utilizing the finding of different PPIX distribution after short incubation times.