Figure 6

Phosphatidylinositol 3-kinase (PI3K) and mTOR inhibitors inhibit basal-like cell line proliferation whereas apoptosis is induced only by PI3K inhibition. (a) Akt activation is associated with low/lack of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) expression in human basal-like cell lines. The expression of Akt, phospho-Akt (S473) and PTEN were analysed by Western blotting in four basal-like (BT20, HCC38, HCC1937 and MDA-MB-468), one human epidermal growth factor receptor overexpressing (HER2+) (SKBr3) and one luminal (MDA-MB-453) human breast cell lines as well as in epidermal growth factor stimulated (EGF) or not (-) A431 cells. (b) PI3K and mTOR inhibition induce cell growth arrest of basal-like cell lines. BT20 (blue triangle), HCC1937 (red square) and MDA-MB-468 (green diamond) cells were exposed continuously for seven days to increasing concentrations of LY294002 (upper panel) or rapamycin (lower panel). Growth was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) dye conversion and presented as the percentage of control cell growth inhibition obtained from DMSO-treated cells. The x axes represent logarithmic transformed concentration of drugs. (c,d) The inhibition of PI3K, but not mTOR, induces apoptosis in basal-like cell lines. BT20, HCC1937 and MDA-MB-468 were exposed to varying concentrations of LY294002 (0 to 100 μM) or rapamycin (0 to 100 nM) for 24 hours and apoptosis was detected by measuring (c) caspase3/7 activity and the (d) cleavage of PARP (cPARP). (c) Caspase 3/7 activity was normalised by caspase 3/7 activity from vehicle-treated cells. (d) Actin was used as a loading control. The data represented the (b,c) average of three separate experiments performed in triplicates or are representative of (a,d) three separate experiments. Error bars represent standard deviation and p values (** p < 0.01, *** p < 0.001) were calculated by using Student's t test.