Figure 4.

Met increases the cytotoxicity of Dox to TS by inhibiting the STAT3 and AKT signaling pathways. Synergistic cytotoxic effects of Met on (A) Lapa-treated TS cultured cells and (B) Dox-treated TS cultured cells. 4T1 cells were treated with various concentrations of Lapa or Dox in the presence of 1 mM Met for 3 days and viabilities were assessed using WST-8 reagent. Results represent three independent experiments performed in triplicate. Error bars represent the standard deviations of the means. (C) Inhibitory effect of Met on the expressions of p-STAT3 and p-AKT in Dox-treated TS. TS were treated with 0.5 µM Dox and/or 1 mM Met for 3 days and then western blotted. **P<0.01 vs. Con; ^##P<0.01 vs. Dox group. STAT3, signal transducer and activator of transcription 3; AKT, protein kinase; TS, tumorspheres; Lapa, lapatinib; Dox, doxorubicin; Met, metformin; DM, doxorubicin+metformin; p, phosphorylated; Con, control.