Mitochondrially targeted ceramides preferentially promote autophagy, retard cell growth, and induce apoptosis

C₆-pyridinium (D-erythro-2-N-[6′-(1″-pyridinium)- hexanoyl]sphingosine bromide [LCL29]) is a cationic mitochondrion-targeting ceramide analog that promotes mitochondrial permeabilization and cancer cell death. In this study, we compared the biological effects of that compound with those of D-erythro-C₆-ceramide, its non-mitochondrion-targeting analog. In MCF7 cells it was found that C₆-pyridinium ceramide preferentially promoted autophagosome formation and retarded cell growth more extensively than its uncharged analog. This preferential inhibition of cell growth was also observed in breast epithelial cells and other breast cancer cells. In addition, this compound could promote Bax translocation to mitochondria. This redistribution of Bax in MCF7 cells could be blocked by the pan-caspase inhibitor zVAD-fmk but via a Bid-independent signaling pathway. Moreover, C₆-pyridinium ceramide-induced translocation of Bax to mitochondria led to mitochondrial permeabilization and cell death. Overall, we show that mitochondrial targeting of C₆-pyridinium ceramide significantly enhances cellular response to this compound.