Current limitations of
chemotherapy include toxicity on healthy tissues and multidrug resistance of malignant cells. A number of recent anti-
cancer strategies aim at targeting the mitochondrial apoptotic machinery to induce
tumor cell death. In this study, we set up protocols to purify functional mitochondria from various human cell lines to analyze the effect of peptidic and
xenobiotic compounds described to harbour either Bcl-2 inhibition properties or toxic effects related to mitochondria. Mitochondrial inner and outer membrane permeabilization were systematically investigated in
cancer cell mitochondria versus non-cancerous mitochondria. The truncated (t-)
Bid protein, synthetic BH3
peptides from Bim and Bak, and the small molecule
ABT-737 induced a
tumor-specific and OMP-restricted mitochondrio-toxicity, while compounds like HA-14.1, YC-137,
Chelerythrine,
Gossypol, TW-37 or
EM20-25 did not. We found that
ABT-737 can induce the Bax-dependent release of apoptotic
proteins (
cytochrome c, Smac/Diablo and Omi/HtrA2 but not AIF) from various but not all
cancer cell mitochondria. Furthermore,
ABT-737 addition to isolated
cancer cell mitochondria induced oligomerization of Bax and/or Bak monomers already inserted in the mitochondrial membrane. Finally immunoprecipatations indicated that
ABT-737 induces Bax, Bak and Bim desequestration from Bcl-2 and Bcl-xL but not from Mcl-1L. This study investigates for the first time the mechanism of action of
ABT-737 as a single agent on isolated
cancer cell mitochondria. Hence, this method based on MOMP (mitochondrial outer membrane permeabilization) is an interesting screening tool, tailored for identifying Bcl-2 antagonists with selective toxicity profile against
cancer cell mitochondria but devoid of toxicity against healthy mitochondria.