Cytotoxic effects of 125I-labeled PBZr ligand PK 11195 in prostatic tumor cells: therapeutic implications.

The effect of [125I]PK 11195 was examined in human prostatic tumor cells (DU 145) in culture and compared with Na[125I] and non-radioactive PK 11195. [125I]PK 11195 was clearly cytocidal. The data for dose-related cell survival with [125I]PK 11195 showed a linear relationship. Na[125I] or non-labeled PK 11195 at similar concentrations did not lead to any cell killing. The uptake of [125I]PK 11195 and [3H]PK 11195 in cells was very similar. Fragmentation of DNA measured by agarose gel electrophoresis showed that exposure of DU 145 cells to [1251]PK 11195 for 1, 4 or 24 h caused no fragmentation. These results indicate that nuclear DNA is not the prime binding site for [125I]PK 11195, which is consistent with the presence of specific peripheral benzodiazepine receptors (PBZr) in the mitochondria. The cell killing effect of [125I]PK 11195 suggests the use of PBZr ligand for radiotherapy.