Mitochondrial targeting liposomes incorporating daunorubicin and quinacrine for treatment of relapsed breast cancer arising from cancer stem cells

Breast cancer stem cells play a crucial role in the relapse of breast cancers because they are resistant to a standard chemotherapy and the residual cancer stem cells are able to proliferate indefinitely. The objectives of present study were to construct a kind of mitochondrial targeting daunorubicin plus quinacrine liposomes for treating and for preventing the recurrence of breast cancer arising from the cancer stem cells. MCF-7 cancer stem cells were identified as CD44+/CD24− cells and cultured in free-serum medium. Evaluations were performed on MCF-7 cancer stem cells, MCF-7 cancer stem cell mammospheres, and the relapsed tumor by xenografting MCF-7 cancer stem cells into female NOD/SCID mice. The particle size of mitochondrial targeting daunorubicin plus quinacrine liposomes was approximately 98 nm. The mitochondrial targeting liposomes evidently increased the mitochondrial uptake of drugs, were selectively accumulated into mitochondria, activated the pro-apoptotic Bax protein, dissipated the mitochondrial membrane potential, opened the mitochondrial permeability transition pores, released cytochrome C by translocation, and initiated a cascade of caspase 9 and 3 reactions, thereby inducing apoptosis of MCF-7 cancer stem cells. The mitochondrial targeting liposomes showed the strongest efficacy in treating MCF-7 cancer cells in vitro, in treating MCF-7 cancer stem cells in vitro, and in treating the relapsed tumor in mice. Mitochondrial targeting daunorubicin plus quinacrine liposomes would provide a new strategy for treating and preventing the relapse of breast cancers arising from cancer stem cells.