Combination efficacy of mTOR and MEK inhibitor in malignant pleural mesothelioma (MPM).

Abstract

e18557 Background: Malignant pleural mesothelioma (MPM) is an aggressive tumor and poor prognosis. Active new agents is an urgent priority for patients with MPM. PI3K/AKT/mTOR pathway inhibitors in MPM have reported, but, the results has limited. Because PI3K/AKT/mTOR pathway inhibitors will make signaling feedback loops and cross-talk between signaling pathways. Combining PI3K/AKT/mTOR pathway inhibitors with other inhibitors might improve efficacy. Activation of RTKs stimulates both the PI3K/AKT/mTOR and RAS/RAF/MEK signaling pathways, and some study shows that inhibition of both pathways may be more effective than targeting either alone. We speculated that simultaneous inhibition both of mTOR and MEK by everolimus and selumetinib might improve the treatment of MPM. Methods: At first, we examined the growth inhibitory effects of everolimus or selumetinib alone on MPM cell lines. Next we examined combination efficacyofeverolimus with selumetinib on MPM cell lines, H226 was examined by computer-assisted analysis using the CalcuSyn software. We next confirmed the in vivo efficacy of everolimus or selumetinib alone, and the combination of both compounds in H226 MPM xenograft model. Results: Everolimus inhibited the growth of MPM cell lines with IC50 values 1.19-21.5 μM. Selumetinib also inhibited the growth of MPM cell lines with IC50 values 4.68-88.2μM. Next we examined combination efficacyofeverolimus with selumetinib on MPM cell lines, H226 was examined by computer-assisted analysis using the CalcuSyn software. With H226, the combination index (CI) at fraction (Fa) 0.5 and 0.8 were (0.56 ± 0.30) and (0.76 ± 0.48), respectively, indicating everolimus and selumetinib act synergistic, respectively. Everolimus or selumetinib alone showed significant antitumor activity, and the combination of everolimus and selumetinib enhanced the individual antitumor activity in H226 MPM xenograft model. (p<0.05). Conclusions: These findings indicate that the combination of everolimus and selumetinib is effective in MPM growth inhibition not only in vitro but in vivo and chemotherapy regimens involving the combination of everolimus and selumetinib may be new molecular target therapy for MPM patients