Figure 5. The Doxycycline (1 μM) plus Azithromycin (1 μM) combination is initially non-toxic under anchorage-independent growth conditions. MCF7 cells were first treated with the combination for 48 hours, as monolayers, and then they were trypsinized and re-seeded onto low-attachment plates for 12 hours, before they were subjected to a live/dead assay. Note that the combination has no effect on the number of live cells, indicating that it is non-toxic under anchorage-independent growth conditions. Nevertheless, the combination effectively inhibits the propagation of CSCs. DOX, Doxycycline (1 μM); AZI, Azithromycin (1 μM).