Schedule-dependent effects of the epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor gefitinib in combination with the mammalian target of rapamycin (mTOR) inhibitor everolimus (RAD001)

3074 Background: mTOR plays a critical role in transducing proliferative signals mediated through the PI3-K/AKT pathway. We have previously demonstrated that everolimus (E) decreased p-4E-BP1 and p-p70S6K levels, the two known downstream targets of mTOR, and inhibited tumor cell proliferation. Interestingly, E-treatment increased the p-AKT levels. We investigated whether the blockade of EGFR by gefitinib (G) could prevent E-induced p-AKT and to determine the optimal schedule of combining E and G. Methods: Cell growth inhibition and western blot assays were performed on BT-474, MDA-MB-468 and DU-145 cancer cell lines. For the simultaneous exposure, cells were incubated for 72 hours with G and/or E, at doses including the IC50 for each drug and cell type. For the sequential exposure, cells were treated with G for 48 hours, washed twice and incubated for a further 48 hours with E, and viceversa. Results were analysed using the combination index (CI) method. Results: The simultaneous treatment of BT-474 and D...