Comparison of photodynamic targets in a carcinoma cell line and its mitochondrial DNA-deficient derivative

The relative contribution, to cell death, of photodynamic damage to respira tory proteins (known targets of photodynamic therapy with many photosensiti zers) and other cellular sites was examined. The models were a human ovaria n carcinoma cell line 2008, and its mitochondrial DNA-deficient derivative ET3, which lacks several key respiratory protein subunits, Phototoxicity wa s compared in the two cell lines with photosensitizers that localized to di fferent cellular compartments. Photosensitizers included Victoria Blue BO ( VBBO; mitochondria); Photofrin with a short incubation, (plasma membrane) o r a long incubation (intracellular membranes including mitochondria); and N ile Blue A (NBA; lysosomes), Photosensitizer content and localization did n ot differ between the 2008 and ET3 cells. For sensitizers without a primary mitochondrial localization (NBA and Photofrin with a short incubation), th ere was no significant difference between 2008 and ET3 toxicity. Consistent with a mitochondrial localization of VBBO and independence from respirator y-chain damage, ET3 cells were less susceptible than 2008 to both dark- and light-activated VBBO-mediated damage. Statistical analysis of the data dem onstrated minimal photobleaching of VBBO and a significant difference betwe en the phototoxicity curves of ET3 and 2008, For Photofrin with a long incu bation, dark- and phototoxicity effects were similar for both cell lines. I nhibition of respiratory enzymes is thus only a minor component of Photofri n-mediated (long incubation) phototoxicity in these cell lines and is overw helmed by more significant damage elsewhere, whereas it is a major but not the exclusive element of death mediated by VBBO.