5-Aminolevulinic Acid in Aqueous Gel : Effective Delivery System for ALA Based PDT

The new aqueous gel compositions based on 5-aminolevulinic acid (ALA) for fluorescent diagnostics and photodynamic therapy of superficial diseases have been elaborated. Biodegradable polymer was used as gel-forming component and some additives - solubilizer, emulgator etc - were used to improve distribution uniformity and penetration ability. These new compositions represent colorless and transparent gels which are long-term stable at the storage temperature of ≤5°C. The effectiveness of aqueous gels as ALA delivery systems is demonstrated. After topical administration of the gel at the skin with Ehrlich tumor inoculated subcutaneously, ALA effectively induces the synthesis of protoporphyrine IX (PPIX) in the skin and in the tumor. Intensity of ALA-induced PPIX fluorescence grows with increasing ALA concentration in the gel and time of gel application. The deepness of ALA penetration in the tumor reaches 5-6 mm after 4 h gel application. A distribution of ALA-induced PPIX in mouse tumor tissue after 4 h gel application depends on ALA concentration in gel. Intensity of PPIX fluorescence in deep-located part of tumor was substantially higher with gel containing 20% ALA than with ones containing 10% or 5% ALA.