Abstract 4100: Mechanisms of resistance to type I and type II MET inhibitors in non-small cell lung cancer
Authors: Bahcall Magda , Kuang Yanan , Paweletz Cloud P. , Jänne Pasi A. 
Published: July 2017

Abstract
Background: MET targeted therapies are clinically effective in MET amplified and MET exon 14 deletion mutant non-small cell lung cancers (NSCLC). At least 8 MET tyrosine kinase inhibitors (TKIs), including both type I and II, have been developed and are under clinical evaluation. We recently described a resistance mechanism in a patient with a unique MET secondary mutation, D1228V, refractory to all type I but sensitive to type II MET TKIs (Bahcall et al. Cancer Discovery 2016). We examined whether the sensitivity and resistance of other MET secondary mutations were similarly dependent on the mode of inhibitor binding, and sought to determine the optimal sequence of MET inhibitor use, so as to achieve the longest combined latency before the emergence of resistance.
Methods: TPR-MET Ba/F3 cells were mutagenized with ENU and treated with each of the type I TKIs - crizotinib; savolitinib; capmatinib, or type II TKIs - cabozantinib; glesatinib; merestinib, until resistant clones emerged. Resistant mutations were identified by sequencing, constructed in the TPR-MET background, and expressed in Ba/F3 and NIH-3T3 cells. Cross-resistance to the 6 MET TKIs was evaluated. Next, low frequency (0.1%) of mutant Ba/F3 cells was spiked into parental TPR-MET Ba/F3 cells and sequentially exposed to different MET TKIs to identify the sequence associated with the longest combined time to resistance. Clonal evolution was assessed by droplet digital PCR (ddPCR).
Results: Of 300 plated wells per drug used at either 0.1μM or 0.5μM, crizotinib yielded 210 and 2 clones; savolitinib 51 and 1 clone; capmatinib 9 and 3 clones; cabozantinib 38 and 3 clones; glesatinib 300 and 300 clones; merestinib 18 and 3 clones, respectively. Of the mutations, those at Y1230 were common to all 3 type I TKIs and the most frequently seen with savolitinib and capmatinib; D1228 was shared by savolitinib and capmatinib; V1155L, the most common mutation with crizotinib, was shared with savolitinib; M1211L emerged with capmatinib. Mutated F1200 residue was shared by and exclusive to all type II TKIs and was the single identified mutation for both glesatinib and merestinib. Cabozantinib gave rise to a broader array of unique mutants - with F1200 mutations being the most common - and shared G1163R with crizotinib. We show D1228 and Y1230 mutations being moderately resistant to crizotinib and strongly resistant to both savolitinib and capmatinib, while retaining sensitivity to all type II TKIs. G1163R and L1195V were slightly to moderately resistant to crizotinib, cabozantinib and glesatinib, but strongly sensitive to savolitinib and capmatinib. In this assay, merestinib had the broadest, while crizotinib most narrow activity against the tested mutants.
Conclusions: Here we highlight key differences between and within the 2 types of MET inhibitors that define their activity against MET secondary mutants likely to emerge in patients, providing rationale for the specific use of these inhibitors in the clinic.
Citation Format: Magda Bahcall, Yanan Kuang, Cloud P. Paweletz, Pasi A. Jänne. Mechanisms of resistance to type I and type II MET inhibitors in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4100. doi:10.1158/1538-7445.AM2017-4100