Antimycin A mimics a cell-death-inducing Bcl-2 homology domain 3

The Bcl-2-related survival proteins confer cellular resistance to a wide range of agents. Bcl-x(L)-expressing hepatocyte cell lines are resistant to tumour necrosis factor and anti-cancer drugs, but are more sensitive than isogenic control cells to antimycin A, an inhibitor of mitochondrial electron transfer. Computational molecular docking analysis predicted that antimycin A interacts with the Bcl-2 homology domain 3 (BH3)-binding hydrophobic groove of Bclx(L). We demonstrate that antimycin A and a Bak BH3 peptide bind competitively to recombinant Bcl-2. Antimycin A and BH3 peptide both induce mitochondrial swelling and loss of Delta Psi (m), on addition to mitochondria expressing Bcl-x(L). The 2-methoxy derivative of antimycin A(3) is inactive as an inhibitor of cellular respiration but still retains toxicity for Bcl-(+)(L) cells and mitochondria. Finally, antimycin A inhibits the pore-forming activity of Bcl-x(L) in synthetic liposomes, demonstrating that a small non-peptide ligand can directly inhibit the function of Bcl-2-related proteins.