Mitochondria are the functional intracellular target for a photosensitizing boronated porphyrin

A photosensitizing boron-containing porphyrin derivative denoted BOPP, which is selectively localised into mitochondria, has been tested on Namalwa cells, in each of two genetic configurations: rho+ cells containing normal mtDNA and mitochondrial respiratory functions, or rho0 cells lacking mtDNA and devoid of mitochondrial oxidative phosphorylation. After short-term cellular uptake for 18 h, BOPP (30 micrograms/ml) was not cytotoxic, but did show marked phototoxicity in Namalwa rho+ cells, concomitant with substantial reduction of mitochondrial respiratory activity. After long-term (3 days or more) exposure to BOPP without light, growth of Namalwa rho+ cells was inhibited at concentrations significantly above 30 micrograms/ml. At such concentrations BOPP was shown to have direct inhibitory effects on mitochondrial azide-sensitive respiration of p+ cells. By contrast, BOPP showed neither cytotoxic nor phototoxic effects in rho0 cells. These results indicate functional mitochondria to be a major cellular target in vivo after BOPP uptake and photoactivation.