Abstract LB-C22: Acquired resistance to the cMET inhibitor savolitinib in lung cancer models through EGFR/mTOR/MYC deregulation and adoption of PIM signaling

Lung cancer is the most common cause of cancer death globally with a significant, unmet need for more efficacious treatments. Aberrant receptor tyrosine kinase (RTK) signaling is a well-documented driver of disease onset and progression in multiple cancer types, including non-small cell lung cancer (NSCLC), where the cMET RTK contributes to tumor progression, maintenance and resistance to targeted therapies. Here, we explore the therapeutic potential of the potent and selective cMET inhibitor savolitinib (volitinib, AZD6094, HMPL-504) in NSCLC and begin to elucidate mechanisms of acquired savolitinib resistance in preclinical models. Using in vitro proliferation assays and immunoblot analysis, we determine that savolitinib rapidly inhibits cMET auto-phosphorylation/activation and reduces the viability of NSCLC cell lines NCI-H1993 and EBC-1 with a GI 50 of 4.20 nM and 2.14 nM, respectively. In vivo, once daily treatment of NCI-H1993 xenografts with 3.0 mg/kg savolitinib significantly slows tumor growth, whereas treatment of EBC-1 xenografts with 30.0 mg/kg results in tumor stasis. Importantly, we observe tumor regressions in a patient-derived xenograft model of a NSCLC lymph node metastasis, HLXF-036LN, dosed with savolitinib 50.0 mg/kg once daily. Pharmacodynamic analysis of in vitro and in vivo models shows that savolitinib sensitivity correlates with blockade of PI3K/AKT and MAPK signaling, and interestingly, with cMYC (MYC) protein down-regulation. To elucidate mechanisms of acquired resistance in NSCLC, we generated savolitinib resistance in vitro using the NCI-H1993 and EBC-1 cell lines and further sub-cloned resistant NCI-H1993 cells to study the heterogeneity of resistance mechanisms. Using small-molecule screening, phospho-protein arrays and interrogation of signaling pathway activity by immunoblot, we identify 1) deregulated mTORC1/2 signaling and 2) the uncoupling of MYC expression from cMET activation as commonly contributing to resistance in all clones tested. RNA interference (siRNA) and MYC over-expression experiments confirm the novel finding that sustained MYC expression can partially drive resistance to a tyrosine kinase inhibitor such as savolitinib. Additionally, we identify clone-specific resistance mechanisms arising via a previously-described switch to EGFR dependence or by our novel finding of a de novo requirement for PIM signaling. Taken together, this work demonstrates the preclinical efficacy of savolitinib in NSCLC and provides an initial characterization of potential resistance mechanisms, identifying core resistance targets and clone-specific vulnerabilities that could be exploited to counter acquired savolitinib resistance that may emerge in the clinic. Citation Format: Ryan E. Henry, Evan R. Barry, Brendon Ladd, Aleksandra Markovets, Garry J. Beran, Yongxin Ren, Feng Zhou, Lillian Castriotta, Ammar Adam, Weiguo Qing, Weiguo Su, Edwin Clark, Celina M. D9Cruz, Alwin Schuller. Acquired resistance to the cMET inhibitor savolitinib in lung cancer models through EGFR/mTOR/MYC deregulation and adoption of PIM signaling. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr LB-C22.