Abstract 5088: Evaluating TNF-receptor associated factor 2 (TRAF2) as a targetable driver of immune resistance in LKB1 deficient non-small cell lung cancer
Authors: Nourmohammadi Bahareh , Amann Joseph M. , Shivahare Rahul , Ma Qin , Li Zihai , Carbone David P. , Kaufman Jacob 
Published: March 2024

Abstract
STK11 is a serine-threonine kinase and tumor suppressor lost in about 25% of NSCLC. It potently regulates a network of downstream effector kinases in the AMPK family, thereby exerting major effects on cell signaling, metabolic activity, and epigenetic patterning. Clinically loss of STK11 in NSCLC is associated with poor response to immune checkpoint blockade. Several mechanisms of immune resistance have been identified involving both tumor intrinsic pathways as well as changes in the immune microenvironment. Dysregulation of cellular inhibitor of apoptosis proteins, specifically cIAP1 has been identified as a specific resistance mechanism, which was shown to also influence the STING pathway in the context of STK11 loss. However, there is a gap in understanding how loss of STK11 influences cIAP1 signaling.We evaluated cIAP1, its TRAF family member binding partners, and downstream NF-kB and immune signaling using a multiomic approach. Using CPTAC multiomic data of 110 lung adenocarcinomas, we observe discordance between protein vs mRNA expression for cIAP1, which shows no significant association with STK11 loss in mRNA, but is significantly over-expressed at the protein level (P&lt;1e-4). Conversely, we identify TRAF2 as the only TRAF member whose expression is increased in STK11-deficient NSCLC, with concordant increase in both mRNA (P&lt;1e-8) and protein (P&lt;1e-10). Further, on the protein level TRAF2 and cIAP1 levels were highly correlated (P&lt;1e-12), strongly suggesting that TRAF2 is the proximal factor driving dysregulation of cIAP1 signaling in these tumors. We also observe a correlated pattern of phosphorylation sites within cIAP1, TRAF2, and other NF-kB signaling members that we putatively link to STK11 loss. We confirm that TRAF2 mRNA is consistently over-expressed in STK11 deficient NSCLC across multiple additional transcriptomic datasets together comprising &gt;2000 tumors. Across this large dataset we observe that among STK11-deficient tumors, TRAF2 is anti-correlated with NF-kB signaling and immune infiltration signatures, a relationship that is strikingly absent among the STK11-WT subset. Using GEMM cell lines (KRAS, TP53, STK11 GEMM; Winslow lab, Stanford), we derived STK11 mutant vs WT isogenic pairs and performed T-cell co-culture experiments using ovalbumin antigen and OT-I CD8 T-cells. This showed that inhibition of cIAP1 using birinapant was synergistic to CD8 cytotoxicity, as previously known, but the synergy was much more pronounced in STK11 mutant vs STK11-WT context (Bliss index 38, P&lt;1e-10). Together, these data demonstrate that the link between STK11-loss and cIAP1 dysregulation is likely through over-expression of TRAF2, and support the strategy of targeting TRAF2/cIAP1 to overcome immune resistance STK11-deficient NSCLC.
Citation Format: Bahareh Nourmohammadi, Joseph M. Amann, Rahul Shivahare, Qin Ma, Zihai Li, David P. Carbone, Jacob Kaufman. Evaluating TNF-receptor associated factor 2 (TRAF2) as a targetable driver of immune resistance in LKB1 deficient non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5088.