Cubic phase gel as a drug delivery system for topical application of 5-ALA, its ester derivatives and m-THPC in photodynamic therapy (PDT)

The ability of the cubic liquid–crystalline phase to incorporate and control the release of drugs of varying size and polar characteristics makes it an interesting candidate as a drug delivery system. In the present study we investigated a new potential application of the cubic phase (monoolein/water; 70:30, w/w) to deliver pro-drugs and a photosensitizer for topical application in photodynamic therapy (PDT). Therefore the pro-drug 5-aminolevulinic acid (5-ALA, a PpIX precursor), its ester derivatives (hexylester, octylester and decylester), and the chlorine compound meso-tetra(hydroxyphenyl)chlorine (m-THPC) were incorporated into the cubic phase gel of monoolein/water and their physicochemical and spectroscopic properties were investigated at 37 °C. Drug stability was monitored for short and long periods of time. 5-ALA and its ester derivatives as non-fluorescent probes had their properties studied after chemical reaction leading to a fluorescent derivative. For all the compounds analyzed in this study the spectroscopic properties were clearly defined with potential photodynamic activity in the gel formulation. We are currently evaluating the potential of monoolein/water as a drug delivery system in the treatment of different cutaneous diseases and other PDT applications.