5-Aminolevulinic acid ester–induced protoporphyrin IX in a murine melanoma cell line

The use of 5-aminolevulinic acid (5-ALA) ester derivatives as precursors of endogenous protoporphyrin IX (PpIX) has been proposed as a good strategy for improved drug diffusion across biological membranes. In the present work, the 5-ALA ester derivatives hexyl-ALA (h-ALA), octyl-ALA (o-ALA), and decyl-ALA (d-ALA) were synthesized, and their efficacy to induce endogenous PpIX was explored in a murine melanoma cell line (B-16) as compared with that of 5-ALA. The maximum level of PpIX induced in cells treated with 5-ALA, h-ALA, o-ALA, and d-ALA was reached at optimal concentrations of 0.3, 0.075, 0.1, and 0.075 mM, respectively. The derivatives h-ALA and o-ALA appear as the most efficient PpIX precursors in this cell line, since a higher or similar PpIX production could be achieved with a fourfold and threefold lower dose of these precursors compared with 5-ALA. The phototoxicity effect of h-ALA and o-ALA ester derivatives showed the same phototoxicity behavior detected for 5-ALA but at much lower drug doses. Our study suggests that h-ALA and o-ALA esters improve intracellular PpIX formation in B-16 cells at reduced concentrations. This should enable clinical applications at lower precursor doses with reduced effective costs.