Abstract 1106: BRAF and EGFR fusion as a novel mechanism of resistance mechanism to Lazertinib, 3rd- generation EGFR-TKI, in EGFR-mutant NSCLC

Abstract

Background: EGFR-TKI is an established first-line therapy for NSCLC with activating EGFR mutations. Osimertinib, third-generation EGFR TKI, was investigated as a first-in-class drug, but lazertinib(YH25448) was also reported as an outstanding drug which had similar efficacy as osimertinib. Nevertheless, acquired resistance is inevitably developed by third-generation EGFR-TKIs in clinic. Even though EGFR C797S mutation has been identified as a major resistant mechanism, the remaining resistance mechanisms to these TKIs are largely unknown. Methods: To explore the mechanism of resistance to lazertinib, we firstly established drug-resistant cells to lazertinib in vitro using four NSCLC cells including the patient-derived cell line (PDC), patient-derived tumor xenograft cell line (PDTC), and ATCC cell lines. To analyze the changes in global genetic alterations and gene expression of established lazertinib-resistant cell lines(YH1R), whole exome sequencing (WES) and RNA sequencing (RNA-seq) were performed. The effect of EGFR/BRAF fusion was investigated in vitro using established YH1R cell line and various patient-derived tumor xenograft samples. Western blot study was used to investigate EGFR and MAPK cascade signaling pathway. We evaluated antitumor activity of MEK inhibitor and lazertinib combination treatment in lazertinib-resistant NSCLC cells with EGFR/BRAF fusion in vitro and in vivo. Results: RNA-seq data revealed a novel EGFR/BRAF fusion transcript (EGFR Exon 19-BRAF Exon 9, in-frame fusion) in lazertinib-resistant PC9GR_YH1R. The fusion gene consisted of EGFR (Exon 1-19) portion and BRAF kinase domain (Exon 9-18). The EGFR/BRAF fusion mRNA and protein were specifically upregulated in PC9GR_YH1R compared to parental cells. Intriguingly, we detected the EGFR/BRAF fusion gene expression in patient-derived xenografts (YHIM-1045 and YHIM-1035) obtained from patients who experienced acquired resistance to lazertinib. Compared with treatment with either single agent, combination treatment of lazertinib and MEK inhibitor, trametinib or selumetinib, was significantly effective at inhibiting cell proliferation as well as EGFR signaling pathways in PC9GR_YH1R in vitro and in vivo. Conclusion: We found a novel EGFR/BRAF fusion gene, as a key driver of acquired resistant mechanism of lazertinib, in NSCLC cell lines and patient-derived xenografts with acquired resistance to lazertinib. Combination treatment of lazertinib and MEK inhibitor showed a strong antitumor effect in lazertinib-acquired resistant NSCLCs, indicating that the combination therapy of EGFR and MEK inhibitors might be a promising therapeutic option for overcoming lazertinib-acquired resistant NSCLC patients in clinic. Citation Format: Seo-Yoon Jeong, Jiyeon Yun, San-Duk Yang, Soo-Hwan Lee, Sangbin Lim, Seok-Young Kim, Min Hee Hong, Sun Min Lim, Hye Ryun Kim, Hye Ryun Kim, Byoung Chul Cho. BRAF and EGFR fusion as a novel mechanism of resistance mechanism to Lazertinib, 3rd- generation EGFR-TKI, in EGFR-mutant NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1106.

Targeted therapies in non-small cell lung cancer: present and future

“…Unfortunately, in clinical use, we have learned that many patients develop resistance to osimertinib, which limits further definitive treatment options. Based on the current understanding of tumor heterogeneity and complex cellular signaling within the tumor and microenvironment and advances in molecular sequencing, we have identified both EGFR -dependent activating mutations and EGFR -independent mechanisms of resistance 25 – 27 .…”

“…Although BRAF is known as a primary oncogenic driver in NSCLC, it has also been implicated as a mechanism of resistance to EGFR -TKI therapy 61 – 63 . In preclinical studies, Jeong et al discovered EGFR and BRAF fusion as a mechanism of resistance to the third-generation EGFR -TKI, lazertinib 27 . Combination therapy with lazertinib and a MEK inhibitor showed strong anti-tumor activity, suggesting a promising therapeutic option 27 .…”

“…In preclinical studies, Jeong et al discovered EGFR and BRAF fusion as a mechanism of resistance to the third-generation EGFR -TKI, lazertinib 27 . Combination therapy with lazertinib and a MEK inhibitor showed strong anti-tumor activity, suggesting a promising therapeutic option 27 . Some less common but still identifiable resistance mechanisms include HER2 amplification, TP53 mutation, KRAS mutation, induced epithelial-mesenchymal transformation (EMT), ALK resistance, and histologic transformation, including conversion to small cell carcinoma 26 , 47 , 64 – 67 .…”