Abstract LB-122: Combinations of SHP2 inhibitor to overcome RAS activation by receptor tyrosine kinases in response to ERK inhibition

Introduction: The RTK-RAS-MAPK pathway is frequently activated in cancers due to a variety of mechanisms including mutations or amplifications in RTK, KRAS or BRAF. The effectiveness of inhibitors targeting those oncogenic drivers is often limited by the pathway feedback activation originated at the RTK level in response to ERK inhibition. The non-receptor protein tyrosine phosphatase SHP2 mediates RAS activation downstream of various receptor tyrosine kinases. Potent and selective allosteric SHP2 inhibitors such as TNO155 are in clinical development and offer an appealing one-size-fits-all approach to overcome RTK-mediated feedback activation of RAS and enhance the efficacy of inhibitors targeting RTK, BRAF or KRASG12C. We sought to study the combination efficacy and mechanism in pre-clinical models for prioritization in clinical trials. Experimental procedures: The combination efficacy and synergy of TNO155 with EGF816 (a 3rd generation EGFR inhibitor), dabrafenib+trametinib or a tool KRAS G12C inhibitor (G12Ci) were respectively assessed in a number of EGFR mutant lung cancer models, BRAFV600E colorectal cancer models and KRASG12C lung and colorectal cancer models. The effect of the combinations on ERK inhibition was also studied. Results: TNO155 has varying single agent activity in vitro in EGFR mutant lung cancer cell lines and is not affected by clinically relevant resistance mechanisms to EGFR inhibitors such as secondary mutations in EGFR (T790M and C797S) or MET amplification. In addition, the combination of TNO155 and EGF816 is synergistic across cell lines, coincident with sustained ERK inhibition. In BRAFV600E colorectal cancer cell lines with feedback activation of EGFR, MET or FGFR respectively in response to treatment with dabrafenib+trametinib, TNO155 synergistically enhanced the efficacy of dabrafenib+trametinib in all three cell lines, phenocopying respective RTK inhibitors. In KRASG12C lung cancer cell lines, quick rebound of p-ERK was observed as early as 24 hour post treatment with G12Ci and cannot be blocked by increasing concentrations of G12Ci, suggesting feedback activation of wild-type KRAS or other RAS isoforms. In contrast, TNO155 effectively blocked the p-ERK rebound and enhanced the efficacy of G12Ci. Similar observations were made in KRASG12C colorectal cancer cell lines. Conclusions: Our findings suggest that SHP2 inhibition is an effective strategy to block the feedback activation of wild type and G12C KRAS, as well as NRAS and HRAS, by a variety of RTKs, in response to ERK inhibition. Given the mutant selective properties of those inhibitors we studied, the tolerability of their combinations with TNO155 is highly expected. Our data provide pre-clinical rationale to explore those TNO155 combinations in the corresponding cancer indications in clinic. Citation Format: Huaixiang Hao, Chen Liu, Hongyun Wang, Hengyu Lu, Scott Delach, Matthew LaMarche, Jeffrey Engelman, Peter Hammerman, Giordano Caponigro, Susan Moody, Morvarid Mohseni. Combinations of SHP2 inhibitor to overcome RAS activation by receptor tyrosine kinases in response to ERK inhibition [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-122.