Regulation of 5-aminolevulinic acid-mediated protoporphyrin IX accumulation in human urothelial carcinomas

Purpose: The purpose of this study was to clarify the regulatory mechanism of protoporphyrin IX (PpIX) synthesis mediated by 5-aminolevulinic acid (ALA) in human urothelial carcinoma (UC), leading to improved accuracy in photodynamic diagnosis and therapy using ALA. Experimental Design: PpIX accumulation in cultured UC cells after incubation for 1-5 h with 0.5-5 mM ALA was analyzed by fluorescence analysis using fluorescence microscopy and flow cytometry technique. Results: PpIX fluorescence mediated by ALA was increased, and the intensity of PpIX fluorescence was time-dependently increased in UC cells compared to noncancerous cells. The distribution of endogenous PpIX fluorescence primarily coincided with mitochondria, and then increased at a specific perinuclear region in the cells during the time of incubation. The ALA-mediated PpIX synthesis in UC cells was suppressed by β-alanine, an inhibitor of β-transporters of cell membrane, and carbonylcyanide p- trifluoromethoxyphenyl hydrazone, an uncoupler of mitochondrial oxidative phosphorylation. In contrast, the ALA-mediated PpIX accumulation was increased by deferoxamine, an iron chelator, manganese and nitric oxide, which is contributed to PpIX metabolism by inhibiting ferrochelatase activity, generated by a nitric oxide-generating reagent NOC-18. As observed above, ALA-mediated PpIX synthesis in human UC cells was regulated by the process of ALA uptake, ALA conversion to PpIX and metabolism of accumulated PpIX to heme. Conclusions: This shows that the suppression of ferrochelatase increased PpIX accumulation in UC cells using small amount of ALA, thus leading to an improved clinical practicability of photodynamic diagnosis and therapy.