Chemical approaches for the enhancement of 5-aminolevulinic acid-based photodynamic therapy and photodiagnosis.

The administration of 5-aminolevulinic acid (ALA) to generate enhanced intracellular levels of endogenous porphyrins is currently one of the most important approaches for photodynamic therapy (PDT) and photodiagnosis (PDD). Despite the great promise of ALA-based PDT, the physicochemical behaviour and chemical reactivity of ALA are problematic, and a variety of chemical approaches have been brought to bear to improve cellular delivery, enhance porphyrin production, and generate ALA prodrugs that have appropriate stability for convenient clinical use, as well as selectivity for cancerous tissues. While there has been considerable success, there are still a number of challenges to be addressed and opportunities to be exploited through application of chemical insight in this area.