Co-targeting Ral-Fum hybrids block proliferation, clonogenic growth and mammosphere formation of breast cancer cells. (A) MCF-7 cells were treated with various drug concentrations in the presence of E2 (10nM) for 72hrs. Each drug’s inhibitory activity was calculated as % of E2 alone, which is set to 100%. (B) MCF-7 cells are seeded as single cells in estrogenized growth media (GM), then treated with the indicated concentration every 3–4 days for 2 weeks. Colonies were stained and quantified with ImageJ. Each drug’s inhibitory activity was calculated as % of GM alone, which is set to 100%. (C) MCF-7 cells were seeded as single cells on low attachment plates in MS media. DMSO (Veh) or drugs were added next day, and 7 days later the number of MS (MS>75μm in diameter) was quantified. ** P<0.01.