Synergic antiproliferative and antiangiogenic effects of EGFR and mTor inhibitors on pancreatic cancer cells

The in vitro efficacy of both EGFR inhibitor gefitinib and mTor inhibitor rapamycin, either administrated alone or in different combination schedules, was analysed in four pancreas cancer cell lines. Both drugs were found to induce cell growth inhibition, apoptosis as well as a slight but stable accumulation of cells in the G0/G1 phase. In all cell lines, neither gefitinib nor rapamycin affected EGFR and the expression of its downstream effectors. By contrast, gefitinib inhibited in a fast and completely way p-EGFR and partially p-Akt while a 3 days-rapamycin exposure resulted in the inhibition of the expression of both mTor and p70S6K. Moreover, after early stimulation, the mTor inhibitor produced a progressive, and almost complete inhibition of p-Akt. The analysis of combined gefitinib and rapamycin administration showed a clear schedule-dependent activity which turned out to be synergic only when gefitinib was given before rapamycin. This synergism seemed to depend on increase of both p-Akt and p70S6K inhibition, the greater the induction of apoptosis, the higher the decrease in cell cycle rate. Moreover, the antiangiogenic activity of the two drugs given in combination was demonstrated by a strong reduction of VEGF release which turned out to be more pronounced in the synergic schedule, and HIF-1 alpha inhibition-independent. Our results suggest that the schedule of gefitinib followed by rapamycin, acting at different levels of the EGFR cellular pathway, could induce antitumor and antiangiogenic effects of clinical interest in the pancreas cancer model. (c) 2007 Elsevier Inc. All rights reserved.