Abstract A26: Identification of a novel therapeutic target in lung adenocarcinoma
Authors: Enfield Katey S.S. , Marshall Erin A. , Anderson Christine , Ng Kevin W. , Rahmati Sara , Xu Zhaolin , MacAulay Calum E. , Lam Stephen , Lockwood William W. , Chari Raj , Karsan Aly , Jurisica Igor , Lam Wan L. 
Published: February 2019

Abstract
The reactivation of biologic signaling events that occur throughout fetal development has been observed during malignant cell transformation and tumor progression. Transcription factors are typically at the hub of these signaling events, such as NKX2-1 and several ETS transcription factors. ELF3 is an uncharacterized ETS family member that is highly expressed during fetal lung development and could play a biologic role in lung cancer based on its location within the recurrently gained chromosome 1q. We hypothesize that ELF3 is a novel oncogenic transcription factor and a therapeutic target.
Multiple independent datasets encompassing 1,685 clinical samples of lung adenocarcinoma (LUAD), lung squamous cell carcinoma (LUSC), small cell lung cancer, and nonmalignant lung tissues were analyzed to establish the frequency of ELF3 overexpression and underlying genetic mechanisms of selection. ELF3 overexpression was validated by immunohistochemistry. Associations with patient survival were tested using the log-rank method. Isogenic cell lines were established to assess oncogenic phenotypes including tumor growth in a xenograft model. Protein-protein interaction (PPI) networks were constructed around ELF3, and integrated pathway analysis was performed to decipher the signaling network disruptions resulting from ELF3 overexpression.
ELF3 overexpression was frequently observed in LUAD (&gt;2-fold: BCCA 73% TCGA 40%), but was not observed in other lung cancer subtypes. Similarly, high ELF3 expression was significantly associated with poor overall survival of LUAD patients (p&lt;0.0001), but not LUSC patients. These clinical associations prompted further examination of ELF3 in the LUAD subtype of lung cancer. ELF3 knockdown in LUAD cell lines resulted in significantly reduced proliferation, viability, and anchorage-independent growth, demonstrating that ELF3 regulates oncogenic phenotypes. Loss of ELF3 abolished the ability of LUAD cells to establish tumors in xenograft mouse models, demonstrating the requirement of ELF3 expression for tumor growth. ELF3 overexpression is associated with remodeling of 23 direct PPI networks, resulting in loss of interaction with proteins such as NFKB1 and MYC, while forming new interactions with NKX2-1, HOXA5 and ERBB3. Pathway analysis suggests a transcriptional reprogramming from inflammatory and MAPK signallng in nonmalignant and ELF3-low tissues, to adhesion and motility pathways in transformed tissues displaying high ELF3 expression. Core pathways included cell cycle, apoptosis, WNT, and NOTCH signaling, agreeing with our cell models. While mutations in ELF3 were rare, up to 80% of LUAD patients harbored focal amplification, DNA gain, and/or promoter hypomethylation at the ELF3 locus, which resulted in transcript overexpression.
We have deciphered the oncogenic role of ELF3 in LUAD. Its requirement for tumor growth in our model indicates that therapeutic targeting of ELF3 could benefit the 73% of patients who display ELF3 overexpression.
Citation Format: Katey S.S. Enfield, Erin A. Marshall, Christine Anderson, Kevin W. Ng, Sara Rahmati, Zhaolin Xu, Calum E. MacAulay, Stephen Lam, William W. Lockwood, Raj Chari, Aly Karsan, Igor Jurisica, Wan L. Lam. Identification of a novel therapeutic target in lung adenocarcinoma [abstract]. In: Proceedings of the Fifth AACR-IASLC International Joint Conference: Lung Cancer Translational Science from the Bench to the Clinic; Jan 8-11, 2018; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(17_Suppl):Abstract nr A26.