Vol. 305, Issue 1, 219-224, April 2003

-Aminolevulinic Acid Transport in Cancer Cells of the Human Extrahepatic Biliary Duct

Jana Neumann and Matthias Brandsch

Membrane Transport Group, Biozentrum of the Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany

This study was performed to characterize the transport of the endogenous photosensitizer -aminolevulinic acid in tumor cells of the extrahepatic biliary duct. Uptake of [³H]-aminolevulinic acid into human cholangiocarcinoma SK-ChA-1 cells was linear for up to 10 min, independent of a Na⁺ gradient, but stimulated 3- to 4-fold by an inwardly directed H⁺ gradient. Uptake of -aminolevulinic acid was mediated by a single transport system with an apparent affinity (K_t) of 2.1 mM and a maximal velocity (V_max) of 60.1 nmol · 10 min¹ · mg of protein¹. Glycylsarcosine, alanylalanine, and cefadroxil strongly inhibited the [³H]-aminolevulinic acid uptake with K_i values of 1.3, 0.2, and 3.6 mM, respectively. In contrast, -aminobutyric acid, glycine, L-glutamic acid, and L-aspartic acid (all 10 mM) had no effect on the total [³H]-aminolevulinic acid uptake, neither at pH 6.0 nor at pH 7.5. Applying a Dixon type of experiment and the ABC test revealed that glycylsarcosine and -aminolevulinic acid are transported via the same system, PEPT1. Treatment of the cells with phorbol 12-myristate 13-acetate, a phorbol ester that activates protein kinase C, resulted in a significant inhibition of the transport rate. This inhibition could be blocked by cotreatment with staurosporine. We conclude that -aminolevulinic acid is transported by the H⁺/peptide cotransporter PEPT1 into epithelial cells of the extrahepatic biliary duct. -Aminolevulinic acid can be accumulated specifically in bile duct tumor cells before photodynamic therapy.