Determination of the activation spectrum of aluminium phthalocyanine chloride against cultured meningioma cells using a tunable laser

Abstract

The activation spectrum of the photosensitising agent aluminium phthalocyanine chloride (ClAlPc) was determined using cultured meningioma cells as the biological target. Cells were irradiated with tunable lasers over the wavelength range 605–1000 nm and photocytotoxicity was measured 24 h later by a tetrazolium assay. The photoactivation spectrum was found to be relatively narrow with a sharply defined maximum at 675–680 nm, a readily accessible wavelength for commercially available diode lasers. The absorption spectrum of ClAlPc in aqueous solution was broad and featureless, contrasting markedly with the activation spectrum. However, as the content of an organic solvent (dimethylsulphoxide) was increased, the absorption spectrum progressively resembled the activation spectrum. It is concluded that the absorption spectrum of ClAlPc in aqueous solution is determined by drug aggregation, which can be prevented by an organic environment. This implies that the active form of ClAlPc in cells is the monomeric species probably located in cellular membranes.