Mecanism of ALA and ALA derivatives transport in transgenic yeast

RODRIGUEZ L, DI VENOSA G, BATTAH S, DANIEL H, MACROBERT A, CASAS A & BATLLE A.

Buenos Aires. Argentina

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

Accumulation of endogenous porphyrins produced after administration of 5-aminolevulinic acid (ALA) is applied in Photodynamic Therapy  (PDT). Due to its low membrane permeability, esterified ALA- derivatives which are less hydrophilic than ALA are under current investigation as possible alternatives to ALA. In this work it was assessed the interaction of ALA derivatives with the mammalian peptide transport system through inhibition studies employing radiolabelled ALA in Pichia pastoris cells expressing the intestinal PEPT1 and renal transporter PEPT2.  It was found that all the ALA derivatives, namely Undecanoyl-ALA (Und-ALA), Hexyl-ALA (He-ALA), R, S-ALA-2-(hydroxymethyl)tetrahydropyranyl ester (THP-ALA), Methyl-ALA (Me-ALA) and the dendron 3m-ALA inhibited 14C-ALA uptake by PEPT2.  However, only the more lipophlilic derivative Und-ALA inhibited ALA uptake by PEPT1. Direct colorimetric quantification of intracellular ALA and ALA derivatives showed that the increasing rates of affinity for PEPT2 were: THP-ALA>He-ALA>ALA=3m-ALA>Me-ALA>Und-ALA; and for PEPT1: ALA>3m-ALA>He-ALA>THP-ALA>Me-ALA=Und-ALA. Und-ALA binds with high affinity to the membranes of PEPT2 and PEPT1-expressing yeasts.  Our results suggest that the derivatives THP-ALA and He-ALA could improve ALA-PDT outcome when applied in tissues expressing PEPT2 such as kidney, mammary gland, brain, lung but not in tissues like intestine, expressing PEPT1.