PIK3CA and breast cancer: However, a recent report by Rodrik-Outmezguine et al. showed that phosphorylation of AKT at the Thr308 site and of the AKT substrates including PRAS40, GSK-3β and FOXO1/3 are only transiently repressed by mTORKIs in PIK3CA mutant (MCF7, BT474) and PTEN-deficient (MDA-MB-468) breast cancer cell lines [48].