Transport of the photodynamic therapy agent 5-aminolevulinic acid by distinct H+-coupled nutrient carriers coexpressed in the small intestine

Catriona M.H. Anderson, Mark Jevons, Muthusamy Thangaraju, Noel Edwards, Nichola J. Conlon, Steven Woods, Vadivel Ganapathy, David T. Thwaites

Research output: Contribution to journalArticle

34 Citations (Scopus)

Abstract

5-Aminolevulinic acid (ALA) is a prodrug used in photodynamic therapy, fluorescent diagnosis, and fluorescent-guided resection because it leads to accumulation of the photosensitizer protoporphyrin IX (PpIX) in tumor tissues. ALA has good oral bioavailability, but high oral doses are required to obtain selective PpIX accumulation in colonic tumors because accumulation is also observed in normal gut mucosa. Structural similarities between ALA and GABA led us to test the hypothesis that the H+-coupled amino acid transporter PAT1 (SLC36A1) will contribute to luminal ALA uptake. Radiolabel uptake and electrophysiological measurements identified PAT1-mediated H+-coupled ALA symport after heterologous expression in Xenopus oocytes. The selectivity of the nontransported inhibitors 5-hydroxytryptophan and 4-aminomethylbenzoic acid for, respectively, PAT1 and the H+-coupled di/tripeptide transporter PepT1 (SLC15A1) were examined. 5-Hydroxytryptophan selectively inhibited PAT1-mediated amino acid uptake across the brush-border membrane of the human intestinal (Caco-2) epithelium whereas 4-aminomethylbenzoic acid selectively inhibited PepT1-mediated dipeptide uptake. The inhibitory effects of 5-hydroxytryptophan and 4-aminomethylbenzoic acid were additive, demonstrating that both PAT1 and PepT1 contribute to intestinal transport of ALA. This is the first demonstration of overlap in substrate specificity between these distinct transporters for amino acids and dipeptides. PAT1 and PepT1 expression was monitored by reverse transcriptase-polymerase chain reaction using paired samples of normal and cancer tissue from human colon. mRNA for both transporters was detected. PepT1 mRNA was increased 2.3-fold in cancer tissues. Thus, increased PepT1 expression in colonic cancer could contribute to the increased PpIX accumulation observed. Selective inhibition of PAT1 could enhance PpIX loading in tumor tissue relative to that in normal tissue.

Original languageEnglish (US)
Pages (from-to)220-228
Number of pages9
JournalJournal of Pharmacology and Experimental Therapeutics
Volume332
Issue number1
DOIs
StatePublished - Jan 1 2010

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Aminolevulinic Acid
Photochemotherapy
Small Intestine
Photosensitizing Agents
Food
5-Hydroxytryptophan
Amino Acid Transport Systems
Dipeptides
Neoplasms
Messenger RNA
Ion Transport
Prodrugs
Microvilli
Substrate Specificity
Xenopus
Reverse Transcriptase Polymerase Chain Reaction
Colonic Neoplasms
gamma-Aminobutyric Acid
Biological Availability
Oocytes

ASJC Scopus subject areas

  • Molecular Medicine
  • Pharmacology

Cite this

Transport of the photodynamic therapy agent 5-aminolevulinic acid by distinct H+-coupled nutrient carriers coexpressed in the small intestine. / Anderson, Catriona M.H.; Jevons, Mark; Thangaraju, Muthusamy; Edwards, Noel; Conlon, Nichola J.; Woods, Steven; Ganapathy, Vadivel; Thwaites, David T.

In: Journal of Pharmacology and Experimental Therapeutics, Vol. 332, No. 1, 01.01.2010, p. 220-228.

Research output: Contribution to journalArticle

Anderson, Catriona M.H. ; Jevons, Mark ; Thangaraju, Muthusamy ; Edwards, Noel ; Conlon, Nichola J. ; Woods, Steven ; Ganapathy, Vadivel ; Thwaites, David T. / Transport of the photodynamic therapy agent 5-aminolevulinic acid by distinct H+-coupled nutrient carriers coexpressed in the small intestine. In: Journal of Pharmacology and Experimental Therapeutics. 2010 ; Vol. 332, No. 1. pp. 220-228.
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