Abstract B087: CTNNB1 mutations can mediate resistance to EGFR targeted therapies in Non-Small Cell Lung Cancer
Authors: Majumder Anurima , Bridenstine Liznair , Meyer Benjamin , Kinose Fumi , Hicks J. Kevin , Boyle Theresa A , Haura Eric B 
Published: December 2023

Abstract
Resistance to targeted therapy remains an ongoing challenge in lung cancer. β-Catenin (CTNNB1) mutations are observed in lung cancer, often co-occurring with known oncogenic alterations such as EGFR/KRAS/ALK. Oncogenic CTNNB1 mutations disrupt the β-catenin destruction complex upregulating Wnt signaling that may cause resistance to therapies targeting oncogenic drivers. An example of this was identified in post-mortem donated NSCLC tissue of a patient treated with a combination of carboplatin, pemetrexed, and bevacizumab that harbored both an acquired CTNNB1-T41A mutation and an EGFR exon 20 insertion. In addition, the CTNNB1 mutation spectrum was analyzed in lung cancer patients at Moffitt Cancer Center to identify prevalent CTNNB1 mutations for functional analyses. T41A, along with the most frequent Exon 3 CTNNB1 mutations were selected and transduced into HCC827 mutant cell lines to determine their ability to drive resistance to targeted therapies. Subsequently, western blotting and RNA sequencing were performed to assess differences between cells expressing wild-type and the most-resistant CTNNB1 mutant. A viability screen was also performed in which these cells were treated with a panel of drugs with known targets (COCKTAIL), in combination with EGFR TKI erlotinib, to identify new vulnerabilities of this CTNNB1 mutant erlotinib-resistant cells. Our data indicate that some CTNNB1 mutations, T41A, S37F, S45C and D32H, can cause resistance to EGFR inhibitor therapy, while others, D32Y, S33C, S33Y, S45P, and S37C, do not. Western blot analysis shows corresponding stabilization and higher accumulation of active β-catenin in cells expressing CTNNB1 mutants that are resistant to erlotinib. Of the mutations tested, cells expressing CTNNB1 T41A demonstrated the strongest resistance to erlotinib. Further analysis reveals higher levels of β-catenin regulated proteins, like axin2 and survivin, as well as EMT markers, such as vimentin and N-cadherin, in HCC827 CTNNB1 T41A cells when compared to the HCC827 CTNNB1 WT. Pathway analysis of genes differentially expressed between the WT and T41A mutant cells reveal WNT pathway to be the top upregulated pathway in the mutant cells. HCC827 T41A also showed sustained ERK, AKT and GSK3β signaling, and lower PARP cleavage compared to wild type, which may explain the resistance to EGFR TKI seen in these cells. COCKTAIL screening, comparing drug sensitivities of the WT and T41A mutant HCC827 cells to erlotinib in combination with various other targeted agents, identified PI3K, mTOR and MEK inhibitors that can reverse erlotinib resistance in the HCC827 CTNNB1 T41A cells. Our data suggests that CTNNB1 may be an important co-occurring alteration in developing resistance to targeted EGFR therapy. However, we show that different CTNNB1 mutations have differing abilities to drive resistance to EGFR TKI which correlates with the level of stabilization and activation of CTNNB1 and its downstream targets by these mutations.
Citation Format: Anurima Majumder, Liznair Bridenstine, Benjamin Meyer, Fumi Kinose, J. Kevin Hicks, Theresa A Boyle, Eric B Haura. CTNNB1 mutations can mediate resistance to EGFR targeted therapies in Non-Small Cell Lung Cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B087.