AKT1 and breast cancer: To determine whether this feedback mechanism explains the synergy between mTORis and BETis in SCLC, we compared the effects of mTOR inhibition on AKT T308 phosphorylation (an indicator of RTK feedback activation; ref. 14–17) between breast cancer (MDA-MB-468) and SCLC (COR-L279 and LX95) cell lines.