Table 1.

Pharmacological targeting of mitochondrial dynamics reduces cancer stemness.

CSCs can typically grow as spherical clusters of self-replicating cells and, based on this characteristic, tumorsphere-forming platforms are used as a sorting method to study self-renewal and tumorigenicity. Accordingly, the number of mammospheres reflects the quantity of CSC-like cells capable of self-renewal in vitro, while the size of mammosphere measures the self-renewal capacity of each mammosphere-generating CSC-like cell. We used the newly developed Cell2Sphere Kit™ to evaluate the impact of the small molecule M1, a cell-permeable phenylhydrazone identified as a mitochondrial fusion promoter [64] and mdivi-1, a cell-permeable small-molecule mitochondrial fission inhibitor that can block Drp1-related yeast Dnm1 GTPase activity [55], on the ability of CSCs to survive and proliferate as floating microtumors. Under non-adherent/non-differentiating conditions, the size and number of the mammospheres formed by MDA-MB-436 breast cancer cells growing in the presence of M1 and mdivi-1 was significantly lower than in untreated control cells (Figure. 3(a)). Indeed, there was an almost complete absence of mammospheres >100 μm in size. When synchronized monolayers of CSC-enriched SUM-159 and HMLERshEcad breast cancer cells were cultured in the presence of mdivi-1, trypsinized, and then evaluated as above, we observed a striking dose-dependent reduction in mammosphere-forming efficiency. Overall, these findings strongly support the notion that pharmacological targeting of mitochondrial dynamics decreases the magnitude of the tumor-initiating population as well as the self-renewal capacity of CSC-like cells within heterogeneous cancer cell populations.