Porphyrin synthesis from ALA derivatives for photodynamic therapy. In vitro and in vivo studies

Abstract

The aim of this work was to test in vitro and in vivo the efficacy of the derivatives of 5-aminolevulinic acid (ALA): hexyl-ALA (He-ALA), undecanoyl-ALA and R,S-2-(hydroximethyl)tetrahydropyranyl-ALA (THP-ALA) as pro-photosensitising agents. The compounds were assayed in a cell line derived from a murine mammary tumour, in tumour explants and after injection of the cells into mice. In vitro, undecanoyl-ALA and THP-ALA did not improve ALA efficacy in terms of porphyrin synthesis. On the other hand, half of the amount of ALA is required to obtain the same plateau amount of photosensitiser from He-ALA. However, this plateau value cannot be surpassed in spite of the four-times higher accumulation of ALA/He-ALA from the ALA derivative. This shows that He-ALA conversion to porphyrins but not He-ALA entry to the cells is limiting. Employing ionic exchange chromatography, we found that 80% of total uptake was He-ALA whereas only 20% was ALA. This suggests that the esterases, probably themselves regulated by the heme pathway, are limiting the conversion of ALA derivatives into porphyrins. A similar situation occurs with THP-ALA. Tumour explant porphyrin results correlate well with cell line data. However, i.p. injection of ALA derivatives to mice resulted in a lower porphyrin concentration in the tumour when compared to the administration of equimolar amounts of ALA, indicating that there should be retention of ALA derivatives either within the blood vessels in the initial phase of distribution and/or within the capillaries of the tumour.

Tumor cell lines resistant to ALA-mediated photodynamic therapy and possible tools to target surviving cells

“…LM3 cell line cultured in 25-cm 2 flasks was exposed for 3 h to 0.6 mM ALA in medium without serum and increasing light doses (0.36-5.4 J/cm 2 ) aimed at achieving survival levels in the 5-10% range. The initial ALA and light doses were established in previous work (13). The surviving cells were harvested 24 h after the treatment and replated.…”

Photodynamic therapy with hexenyl ester of 5-aminolevulinic acid induces necrotic cell death in salivary gland adenocarcinoma cells

“…Several ALA esters has been synthesized and investigated as promising precursors to PpIX in vitro and in vivo as well (15). The esterified ALA derivatives significantly increase PpIX levels over ALA in a variety of cell types (12)(13)(14)(15)(16)(17).…”

“…To overcome the limit of uptake and distribution of ALA, the existing drug has been converted into its esters to increase its lipophilic nature (15)(16)(17). Several ALA esters has been synthesized and investigated as promising precursors to PpIX in vitro and in vivo as well (15).…”

5-aminolevulinic acid-incorporated nanoparticles of methoxy poly(ethylene glycol)-chitosan copolymer for photodynamic therapy

“…1,[10][11][12] In addition to these successful experiences, some drawbacks of 5-ALA, such as hydrophilicity and low specificity for tumor cells, have been noted to induce lower cellular uptake and low bioavailability of ALA. 13 To overcome these drawbacks, various kinds of modified 5-ALA have been developed. [14][15][16] For example, esterification of ALA, such as methyl-or hexyl-ester conjugated 5-ALA was reported to show enhanced cellular uptake and a better interconversion rate to PpIX than the parent compound. [14][15][16] Drug delivery strategies using colloidal drug carriers such as polymeric nanoparticles and liposomes have also been studied for their enhancement of 5-ALA cellular uptake.…”

“…[14][15][16] For example, esterification of ALA, such as methyl-or hexyl-ester conjugated 5-ALA was reported to show enhanced cellular uptake and a better interconversion rate to PpIX than the parent compound. [14][15][16] Drug delivery strategies using colloidal drug carriers such as polymeric nanoparticles and liposomes have also been studied for their enhancement of 5-ALA cellular uptake. [17][18][19][20] Among them, nanoscopic vehicles such as polymeric micelles and nanoparticles have been investigated as ideal carriers for drugs, including photosensitizers.…”