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Summary.-The photosensitizing effect of haematoporphyrin (HP) on human cells of the established line NHIK 3025 has been studied. Fluorescence measurements show that HP is bound to these cells. Serum proteins also bind HP, and the presence of 10% human serum during incubation with HP (3 x 10-4M) reduces the cellular uptake of HP by 75%o or more. The photosensitized inactivation is enhanced when the cells are suspended in D20-buffer during irradiation. This indicates that singlet oxygen is involved in the inactivation.Two findings indicate that the photoinduced damage is repairable: firstly, the fraction of cells surviving a given light dose decreases with decreasing irradiation temperature, and secondly, the survival curves have a shoulder at low exposures of light.

Two octa-substituted phthalocyanines, namely 1,4,8,11,15,18,22,25-octakis(decyl)phthalocyaninato zinc(II) (ZnODPc) and 1,4,8,11,15,18,22,25-octakis(pentyl)phthalocyaninato zinc(II) (ZnOPPc), were investigated for their use in photodynamic therapy (PDT) after topical application. Both substances exhibited favourable properties as photosensitisers in vitro: absorption maxima around 700 nm with absorption coefficients of about 190000 (M(-1) cm(-1)), a singlet oxygen quantum yield of 0.47 +/- 0.02 (ZnODPc), and good accumulation in keratinocytes and fibroblasts. Cell death after phthalocyanine-photosensitisation appeared to occur mainly via apoptosis. The in vivo experiments demonstrated a good accumulation of the phthalocyanines after topical application in a tetrahydrofuran-azone formulation onto the dorsal skin of Balb/c mice: [(4.6-4.7) +/- 1.0]% of deposited dye could be recovered after 3 h from deposition. ZnODPc showed significantly better skin-photosensitising properties than ZnOPPc and is therefore a potential candidate for the treatment of psoriasis.

Further investigation of the pellicle formed in 2 h on cleaned human teeth in vivo is reported. Electron micrographs demonstrating the presence of a thin organic layer 2 h after the teeth were brushed with pumice are shown. The pellicle material contained several sugars, with glucose as the most abundant. Material from secretors and non-secretors of blood group substances was analysed, but no difference in carbohydrate composition was found. Tests for biological activities indicated the presence of blood group substance and virus haemagglutination inhibition activities in the 2-hour pellicle.