Targeting mitochondrial permeability in cancer drug development

The past decade has seen the emergence of a new mechanistic paradigm of cancer therapeutics. Not only have mitochondria taken centre stage as key cellular organelles mediating intrinsic pathways of cell death by apoptosis, but nonapoptotic pathways have also been shown to involve mitochondrial mechanisms. Both pathways of cell death involve permeabilization of mitochondrial membranes, but the exact nature of the molecular complexes involved at the inner mitochondrial membrane (IMM) and outer mitochondrial membrane (OMM) remains uncertain in the light of recent gene knockout studies. Consequently, the boundary between mitochondrially-mediated apoptotic and nonapoptotic cell death is controversial. Here, we discuss the nature of the pore complexes involved in permeabilization of the IMM and OMM. Several compounds that interact directly with components of these pore complexes and have been shown to exhibit anticancer activity are discussed while other compounds appear to act indirectly through stress-related pathways.