Delta-aminolevulinic acid transport in cancer cells of the human extrahepatic biliary duct.
This study was performed to characterize the transport of the endogenous photosensitizer delta-aminolevulinic acid in tumor cells of the extrahepatic biliary duct. Uptake of [(3)H]delta-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 delta-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 min(-1). mg of protein(-1). Glycylsarcosine, alanylalanine, and cefadroxil strongly inhibited the [(3)H]delta-aminolevulinic acid uptake with K(i) values of 1.3, 0.2, and 3.6 mM, respectively. In contrast, gamma-aminobutyric acid, glycine, L-glutamic acid, and L-aspartic acid (all 10 mM) had no effect on the total [(3)H]delta-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 delta-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 delta-aminolevulinic acid is transported by the H(+)/peptide cotransporter PEPT1 into epithelial cells of the extrahepatic biliary duct. delta-Aminolevulinic acid can be accumulated specifically in bile duct tumor cells before photodynamic therapy.
Neumann
Jana
J
Membrane Transport Group, Biozentrum of the Martin-Luther-University Halle-Wittenberg, Halle (Saale), Germany.
Brandsch
Matthias
M
D000622:Aminolevulinic Acid / Q000378:metabolism*; D017734:Bile Ducts, Extrahepatic / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D000074011:Peptide Transporter 1; D010703:Phorbol Esters / Q000494:pharmacology; D027981:Symporters; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D000074011:Peptide Transporter 1; D010703:Phorbol Esters; C082186:SLC15A1 protein, human; D027981:Symporters; D000622:Aminolevulinic Acid