Comparison of δ-aminolaevulinic acid and its methyl ester as an inducer of porphyrin synthesis in cultured cells

Abstract

Summary This study was carried out to test the hypothesis that induction of intracellular porphyrin synthesis by 6-aminolaevulinic acid (ALA) used to sensitize cells in photodynamic therapy would be more efficient if the ALA was used in an esterified form. Contrary to expectation, the generation of tetrapyrroles (TP) by cultured epithelial cells (CNCM-1-221) exposed to equimolar concentrations (0.6 mM) of ALA or its methyl ester (ALA-ME) showed that the mean total TP production rate during 6 h incubation in serum-free medium was 0.13 fmol cell-' h-1 for ALA-exposed cells compared with 0.04 fmol cell-1 h-1 for cells exposed to ALA-ME. Fluorescein diacetate uptake and conversion to fluorescein indicated intracellular non-specific esterase activity, implying that ALA-ME conversion to ALA can occur. Cells exposed to ALA-ME exhibited loss of a greater proportion of total tetrapyrroles in the form of extracellular protoporphyrin IX (PPIX; 22.8%) compared with 11.6% in ALA-treated cells with a corresponding reduction in cell-associated PPIX (P < 0.05). A variable initial elevation in haem levels in ALA-MEtreated cells was observed, but did not reach statistically significant levels.

Addition of novel degenerate electrical waveform stimulation with photodynamic therapy significantly enhances its cytotoxic effect in keloid fibroblasts: First report of a potential combination therapy

“…One of the advantages of lipophilic ALA ester (MAL) is its ability to display enhanced penetration into the cell which is contributed by different uptake mechanisms including active transporters of non-polar amino acids or by diffusion while ALA is taken up by bamino acids and g-aminobutyric acid (GABA) [19][20][21]. MAL was eliminated faster than ALA in cultured epithelial cells [22] which coincided with our results. However, our results were contradictory to Casas et al where less ALA was needed than MAL for the formation of PPIX in murine mammary adenoma carcinoma cell line, LM2s [23].…”

Aminolevulinic Acid Derivatives and Liposome Delivery as Strategies for Improving 5-Aminolevulinic Acid- Mediated Photodynamic Therapy

“…demonstrated in cell lines and animal models, that several ALA pro-drugs were capable of being taken up, desterified and converted into PpIX with higher efficiency than ALA itself. Gaullier and collaborators [20] found that longchained ALA esters (C 6 -C 8 ) reduced 30-150-fold the amount of ALA needed to reach the same level of PpIX accumulation as compared with that obtained with nonesterified ALA in a human cell line, whereas short-chained pro-ALAs (C 1 -C 3 ) were less efficient than ALA. Washbrook and Riley [21] also found the methyl short-chained ester of ALA (1) to be less efficient than ALA itself at inducing porphyrin synthesis in epithelial cells.…”

Porphyrin accumulation induced by 5-aminolaevulinic acid esters in tumour cells growing in vitro and in vivo

“…Non-specific esterase activities in tissue homogenates, lysates of cultured cells and in cell-conditioned or fresh culture medium were determined using an adaptation of the fluorescein diacetate method described by Washbrook and Riley (1997).…”