Toxic and phototoxic effects of tetraphenylporphinesulphonate and haematoporphyrin derivative in vitro.

The toxic and phototoxic effects of tetraphenylporphinesulphonate (TPPS4) and haematoporphyrin derivative (HpD) have been examined in vitro. TPPS4 was found to have less dark toxicity to the cells than HpD as measured by inhibition of cell multiplication and colony formation at comparable extracellular concentrations. TPPS4 was also less effective than was HpD in photoinactivating NHIK 3025 cells by more than a factor 2 which should be expected on the basis of cellular uptake. Spectrofluorometric data suggest that HpD in cells interacts more with lipids than TPPS4. This might explain the large photosensitizing effect of HpD compared to TPPS4 since the lifetime of singlet oxygen is about a factor of 10 longer in a lipid environment than in an aqueous environment. The uptake of TPPS4 and HpD by cancer cells in vitro does not correlate with previous in vivo data, indicating retention of TPPS4 in the tumour stroma. This makes in vitro/in vivo extrapolation difficult with regard to the use of TPPS4 as an agent for photodynamic therapy.