we observed the induction of high quantities of apoptosis by both BKM120 and BGT226 was restricted to PIK3CA mutant lines and the PTEN negative MDA MB 415 and ZR75 1 cell lines. Included in these are inhibitors of PI3K catalytic subunits, inhibitors of the Akt serine threonine kinase, inhibitors of mTOR, and multi targeted agents, which routinely have mTOR kinase inhibitors and dual specificity PI3K. This paper focuses on three of these four classes of RAD001, agent, BKM120 and BGT226. To show the inhibitory activities of BGT226, BKM120 and RAD001 on PI3K path MAPK inhibitors signaling, the phosphorylation levels of Akt and S6 were assessed by western blotting in MDA MB 231, MCF7, T47D, or HCC712 cell lines in the presence of increasing dose of drug. BGT226 and BKM120 inhibited the phosphorylation of both Akt and S6 in every tested lines, as expected. BGT226 therapy made very nearly complete inhibition of PI3K signaling at low nanomolar concentrations, indicating a similar, or greater, strength weighed against that of the combined PI3K/mTOR inhibitor BEZ235. In contrast, significant inhibition of PI3K signaling following BKM120 therapy occurred in the mid nanomolar to high nanomolar concentration range in most Cellular differentiation cell lines. . In most cell lines, RAD001 treatment totally inhibited S6 phosphorylation at low nanomolar concentrations, with the increase in Akt phosphorylation MCF7 cells already known by other investigators. These data show that PI3K pathway inhibitors efficiently suppressed their respective goals regardless of individual variations in PI3K pathway mutation status. PIK3CA mutation sensitizes short term estrogen deprived ER positive breast cancer cells to PI3K pathway inhibitors To prolong our previous observations regarding the sensitizing effect of estrogen deprivation on the apoptotic effect of PI3K pathway inhibitors in ER positive breast cancer, a larger screen of ER positive HCV protease inhibitor breast cancer cell lines was examined that varied with regard to PIK3CA and PTEN mutation status. Cells in the screen were extremely deprived of estrogen for 1 to 3 months prior to therapy with BGT226, BKM120 or RAD001 at concentrations that were found to be sufficient to abrogate pathway signaling. The MDA MB 231 line served as a control for off target inhibitor results since this line doesn’t endure apoptosis when treated with the dual PI3K/mTOR inhibitor BEZ235 or combined siRNA knock-down of PIK3CB and PIK3CA. Induction of apoptosis was measured by TUNEL assay after treatment with BGT226, BKM120 or RAD001. In the absence of estrogen, BGT226 treatment induced the best levels of apoptosis, followed by BKM120, while RAD001 treatment created only a modest increase in apoptosis in a few cell lines, suggesting this type of agent may be a somewhat ineffective companion for endocrine therapy combinations.