Photodynamic Therapy: ALA esters hydrolysis and porphyrin synthesis regulation

DI VENOSA G, FUKUDA H, MACROBERT A, CASAS A & BATLLE A.

Buenos Aires. Argentina

Workshop; 5th International Workshop on Photodynamic Therapy and Photodetection with Porphyrin Precursors; 2006

A Batlle (Argentina), Q Peng (Noruega)

Introduction: 5-aminolevulinic acid (ALA) the natural precursor of porphyrins is used as a pro-photosensitiser in PDT. Exposing cells to excess exogenous ALA, bypasses the firs limiting step causing accumulation of PPIX. With the aim to improve the treatment, we prepared ALA derivatives with the chemical esterification with aliphatic alcohols and  studied the nature of porphyrin synthesis regulation from these esters. Materials and Methods: Cell line LM3 derived form the murine aenocarcinoma M3 was used. He-ALA and R, S-ALA-2-(hydroxymethyl) tetrahydropyranyl ester (THP-ALA) were synthesised according to the method of Takeya (Chem Abs 1992, 116, 189633m(, and dissolved in water immediately before use. ALA, ALA esters and PBG were separated using ion exchange chromatography and determined with the Ehrlich reagent. Results: The rate of incorporation linto the cells increased as follows ALA < THP-ALA< He-ALA. However, at concentrations leading to plateau porphyrin levels,, ALA and its derivatives induced identical rates of porphyrin synthesis. Although at low concentrations, ALA uptake is a regulatory factor, thisis not the case with ALA derivatives. At high concentrations, porphobilinogenase is regulating the ALA conversion into porphyrins, while esterases regulate ALA-ester hydrolisis, step in which porphyrins are not involved. In the presence of succinyl acetone, inhibitor of ALA-dehydratase, no changes in total ALA derivative intracellular accumulation or in the amount of hydrolysed ALA were observed. Conclusions: Our results suggest that the use of ALA esters has to be limited to low concentrations where no regulation on porphyrin synthesis takes place