Mechanistic studies on δ-aminolevulinic acid uptake and efflux in a mammary adenocarcinoma cell line

Abstract

d-aminolevulinic acid (ALA) is the precursor in the biosynthesis of porphyrins. The knowledge of both the regulation of ALA entrance and efflux from the cells and the control of porphyrin biosynthesis is essential to improve ALA-mediated photodynamic therapy. In this work, we studied the regulation of ALA uptake and efflux by endogenously accumulated ALA and/or porphyrins in murine mammary adenocarcinoma cells. Under our set of conditions, the haem synthesis inhibitor succinyl acetone completely prevented porphobilinogen and porphyrin synthesis from ALA, and led to an increase in the intracellular ALA pool. However, neither intracellular ALA nor porphyrin pools regulate ALA uptake or efflux during the first 15 min of the process. Based on temperature dependence data, ALA but not g-aminobutyric acid (GABA) efflux is mediated by a diffusion mechanism. Moreover, the addition of extracellular GABA not only did not influence the rate of ALA efflux but on the contrary it affected ALA uptake, showing the contribution of a saturable mechanism for the uptake, but not for the efflux of ALA from the cells.

Inativação fotodinâmica de microrganismos

“…ALA, quando fornecido para a célula, subverte esse controle e resulta na acumulação da PpIX, que é convertida em heme pela ferroquelatase pela adição de ferro ao núcleo da PpIX. Uma vez que essa conversão é um processo lento 54 , altos níveis de PpIX são encontrados no tecido, embora para produzir um efeito fotodinâmico necessite da exposição à luz 55,56 . Há várias vantagens na fotosensibilização por PpIX induzida pelo ALA, uma delas é que o organismo elimina PpIX rapidamente, o que limita o risco da fotossensibilidade a 1-2 dias.…”

Effect of Oil-in-Water Emulsions on 5-Aminolevulinic Acid Uptake and Metabolism to PpIX in Cultured MCF-7 Cells

“…Both the PEPT2 and BETA transporters have been suggested to transport ALA There is strong evidence for the presence of the PEPT2 transporter in mammary gland epithelium (15). Contrastingly, the BETA transporter, but not the PEPT2 transporter (16) has been identified in a mammary epithelial cell line (19,20).…”

“…In intestinal Caco-2 cells, mainly the PEPT1 and the basolateral peptide transporter with the k m values of 1.6 and 2.4 mM, respectively, translocated ALA (18), and the uptake of ALA was only slightly inhibited by GABA. On the contrary, in a murine mammary adenocarcinoma cell line, the uptake of ALA was mediated by a BETA transporter, as inhibition was seen with GABA and not with substrates for the PEPT1 and PEPT2 transporters (19); here, the ALA efflux was diffusion controlled (20). Also in a human colonic adenocarcinoma cell line, ALA was found to be a substrate for the BETA transporter (21).…”

Mechanisms of Resistance to Photodynamic Therapy

“…However intracellular accumulation of the three PS per protein was equal in both parental and resistant clones, showing that PS content is not crucial for photodynamic resistance in all the cases [7]. ALA ester derivatives hexyl-ALA and undecanoyl-ALA did show cross resistance with ALA-PDT (Fig 10), although both lypophyllic ALA derivatives do not enter the cell through the same transporter [254] and are probably not effluxed by the same mechanism [255]. This reinforces the hypothesis that cross resistance depends on PpIX formed from ALA or ALA derivatives and not ALA itself.…”