Design, synthesis and biological evaluation of 5-aminolaevulinic acid/3-hydroxypyridinone conjugates as potential photodynamic therapeutical agents

5-Aminolaevulinic acid (ALA) prodrugs have been widely used in photodynamic therapy (PDT) as precursors to the natural photosensitizer, protoporphyrin IX (PpIX). The main disadvantage of this therapy is that ALA is poorly absorbed by cells due to its high hydrophilicity. In order to improve the therapeutical effect and induce higher yields of PpIX, a range of prodrugs of ALA conjugated to 3-hydroxypyridin-4-ones (HPO) were synthesized. Pharmacokinetic studies indicated that some of the ALA-HPO conjugates are more efficient than ALA for PpIX production in the human breast adenocarcinoma cell line (MDA-MB-468). The intracellular porphyrin fluorescence levels showed good correlation with cellular phototoxicity following light exposure, suggesting the potential application of the ALA-HPO conjugates in photodynamic therapy.