Photodynamic effects of a novel series of silicon(IV) phthalocyanines against human colon adenocarcinoma cells

The photodynamic activities of a novel series of silicon(IV) phthalocyanines with different axial substituents including the 1,3-bis(dimethylamino)-2-propoxy group, isopropylidene-protected galactose, and polyethylene glycol have been investigated against HT29 and T84 human colon adenocarcinoma cells. While these compounds are not cytotoxic in the absence of light, they exhibit high photocytotoxicities with IC50 values as low as 17 nM. The photodynamic activities of these compounds against HT29 are correlated with the cellular uptake as reflected by the relative intracellular fluorescence intensity and the Q-band absorbance of the dyes in the organic extracts. The most potent compound 1, having a 1,3-bis(dimethylamino)-2-propoxy group and a methoxy group as the axial substituents, has a high and selective affinity to the mitochondria of HT29 cells, as revealed by fluorescence microscopy.