Crizotinib has potent anti-tumor activity in patients with advanced MET-amplified non-small cell lung cancer (NSCLC). However, the therapeutic effect is still not satisfying. Thus, developing approaches that improve the efficacy of crizotinib remains a significant challenge. MET-amplified NSCLC cell lines were treated with crizotinib and cyclosporine A (CsA). Cell viability was determined by MTS assay. The changes of apoptosis, cell cycle and calcineurin-Erk pathways were assessed by western blot. Xenograft mouse model, primary human NSCLC cells and hollow fiber assays were utilized to confirm the effects of CsA. We demonstrated that CsA significantly increased the anti-tumor effect of crizotinib on multiple MET-amplified NSCLC cells in vitro and in vivo. Mechanistically, crizotinib treatment led to the activation of Ca2+-calcineurin (CaN)-Kinase suppressor of Ras 2 (KSR2) signaling, resulting in Erk1/2 activation and enhanced survival of cancer cells. CsA effectively blocked CaN-KSR2-Erk1/2 signaling, promoting crizotinib-induced apoptosis and G2/M arrest. Similarly, pharmacologic or genetic inhibition of Erk1/2 also enhanced crizotinib-induced growth inhibition in vitro. Xenograft studies further confirmed that CsA or Erk1/2 inhibitor PD98059 enhanced the anti-cancer activity of crizotinib through inhibition of CaN-Erk1/2 axis. The results were also validated by primary human NSCLC cells in vitro and hollow fiber assays in vivo. This study provides preclinical evidences that combination therapy of CsA and crizotinib is a promising approach for targeted treatment of MET-amplified lung cancer patients. FUND: This work was supported by the National Natural Science Foundation of China, the Key Projects of Natural Foundation of Zhejiang Province, the Ten thousand plan youth talent support program of Zhejiang Province, the Zhejiang Natural Sciences Foundation Grant, and the Zhejiang medical innovative discipline construction project-2016.
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