The photocytotoxicity characteristics of aluminium phthalocyanine chloride 
(AIPc), aluminium phthalocyanine disulphonate (AlS2Pc), aluminium phthalocyanine 
tetrasulphonate (AlS4PC) and haematoporphyrin derivative (HpD) were compared 
using primary cultures of human meningioma cells. Cells were preincubated with 
the photosensitising agent for 16 h, then illuminated for 15 min with broad band 
red light (5 OW/cm2). The resultant cytotoxicity was assessed by tetrazolium 
(MTT) reduction 24 h later. AlPc was found to be 400, 10,000 and 250 times more 
potent that AlS2Pc, AlS4Pc and HpD, respectively, as an in vitro 
photosensitizing agent for meningioma cells. The subcellular localisation of 
AlPc, AlS2Pc, AlS4Pc and HpD in meningioma cells was determined by confocal 
laser scanning microscopy. None of the agents localized to the nucleus. The 
distribution of ALPc was quite diffuse through the cytoplasm. In contrast, 
AlS2Pc and AlS4Pc were localized vesicles suggestive of lysosomes, and HpD in 
membranous organelles distinct from mitochondria. AlPc and HpD were tested with 
five different meningioma samples and provided a range of IC50 values from 0.009 
to 0.022 OM and from 3.5 to 6.5 OM, respectively. When the MTT assay with AlPc 
was performed 0, 24, 48 and 72 h after illumination, the mean IC50 values were 
0.25, 0.037, 0.019 and 0.012 OM, respectively, indicating that the cytotoxic 
effect continued to increase up to 72 h. Cells were incubated with AlPc and HpD 
for different times up to 24 h before exposure to light. AlPc cytotoxicity was 
half-maximal with an incubation time of 8 h, whereas HpD cytotoxicity was 
half-maximal with an incubation time of 2 h, implying slower uptake kinetics for 
AlPc than for HpD. These data indicate unique features of AlPc which suggests 
its application as a potent, non-toxic photosensitizer in the photodynamic 
therapy of human meningiomas.