Citations

Disruption of epigenetic mechanisms has been intimately linked to the etiology of human cancer. Understanding how these epigenetic mechanisms (including DNA methylation [5mC], hydroxymethylation [5hmC], and histone post‐translational modifications) work in concert to drive cancer initiation and progression remains unknown. Hepatocellular carcinoma (HCC) is increasing in frequency in Western countries but lacks efficacious treatments. The epigenome of HCC remains understudied. To better understand the epigenetic underpinnings of HCC, we performed a genome‐wide assessment of 5mC, 5hmC, four histone modifications linked to promoter/enhancer function (H3K4me1, H3K27ac, H3K4me3, and H3K27me3), and transcription across normal, cirrhotic, and HCC liver tissue. Implementation of bioinformatic strategies integrated these epigenetic marks with each other and with transcription to provide a comprehensive epigenetic profile of how and when the liver epigenome is perturbed during progression to HCC. Our data demonstrate significant deregulation of epigenetic regulators combined with disruptions in the epigenome hallmarked by profound loss of 5hmC, locus‐specific gains in 5mC and 5hmC, and markedly altered histone modification profiles, particularly remodeling of enhancers. Data integration demonstrates that these marks collaborate to influence transcription (e.g., hyper‐5hmC in HCC‐gained active enhancers is linked to elevated expression) of genes regulating HCC proliferation. Two such putative epigenetic driver loci identified through our integrative approach, COMT and FMO3 , increase apoptosis and decrease cell viability in liver‐derived cancer cell lines when ectopically re‐expressed. Conclusion : Altogether, integration of multiple epigenetic parameters is a powerful tool for identifying epigenetically regulated drivers of HCC and elucidating how epigenome deregulation contributes to liver disease and HCC.

Abstract CCGA [NCT02889978] is the largest study of cfDNA-based early cancer detection; the first CCGA learnings from multiple cfDNA assays are reported here. This prospective, multi-center, observational study has enrolled 10,012 of 15,000 demographically-balanced participants at 141 sites. Blood was collected from participants with newly diagnosed therapy-naive cancer (C, case) and participants without a diagnosis of cancer (noncancer [NC], control) as defined at enrollment. This preplanned substudy included 878 cases, 580 controls, and 169 assay controls (n=1627) across 20 tumor types and all clinical stages. All samples were analyzed by: 1) Paired cfDNA and white blood cell (WBC)-targeted sequencing (60,000X, 507 gene panel); a joint caller removed WBC-derived somatic variants and residual technical noise; 2) Paired cfDNA and WBC whole-genome sequencing (WGS; 35X); a novel machine learning algorithm generated cancer-related signal scores; joint analysis identified shared events; and 3) cfDNA whole-genome bisulfite sequencing (WGBS; 34X); normalized scores were generated using abnormally methylated fragments. In the targeted assay, non-tumor WBC-matched cfDNA somatic variants (SNVs/indels) accounted for 76% of all variants in NC and 65% in C. Consistent with somatic mosaicism (i.e., clonal hematopoiesis), WBC-matched variants increased with age; several were non-canonical loss-of-function mutations not previously reported. After WBC variant removal, canonical driver somatic variants were highly specific to C (e.g., in EGFR and PIK3CA, 0 NC had variants vs 11 and 30, respectively, of C). Similarly, of 8 NC with somatic copy number alterations (SCNAs) detected with WGS, 4 were derived from WBCs. WGBS data revealed informative hyper- and hypo-fragment level CpGs (1:2 ratio); a subset was used to calculate methylation scores. A consistent “cancer-like” signal was observed in <1% of NC participants across all assays (representing potential undiagnosed cancers). An increasing trend was observed in NC vs stages I-III vs stage IV (nonsyn. SNVs/indels per Mb [Mean±SD] NC: 1.01±0.86, stages I-III: 2.43±3.98; stage IV: 6.45±6.79; WGS score NC: 0.00±0.08, I-III: 0.27±0.98; IV: 1.95± 2.33; methylation score NC: 0±0.50; I-III: 1.02±1.77; IV: 3.94±1.70). These data demonstrate the feasibility of achieving >99% specificity for invasive cancer, and support the promise of cfDNA assay for early cancer detection. Additional data will be presented on detected plasma:tissue variant concordance and on multi-assay modeling. Citation Format: Alexander A. Aravanis, Geoffrey R. Oxnard, Tara Maddala, Earl Hubbell, Oliver Venn, Arash Jamshidi, Ling Shen, Hamed Amini, John A. Beausang, Craig Betts, Daniel Civello, Konstantin Davydov, Saniya Fazullina, Darya Filippova, Sante Gnerre, Samuel Gross, Chenlu Hou, Roger Jiang, Byoungsok Jung, Kathryn Kurtzman, Collin Melton, Shivani Nautiyal, Jonathan Newman, Joshua Newman, Cosmos Nicolaou, Richard Rava, Onur Sakarya, Ravi Vijaya Satya, Seyedmehdi Shojaee, Kristan Steffen, Anton Valouev, Hui Xu, Jeanne Yue, Nan Zhang, Jose Baselga, Rosanna Lapham, Daron G. Davis, David Smith, Donald Richards, Michael V. Seiden, Charles Swanton, Timothy J. Yeatman, Robert Tibshirani, Christina Curtis, Sylvia K. Plevritis, Richard Williams, Eric Klein, Anne-Renee Hartman, Minetta C. Liu. Development of plasma cell-free DNA (cfDNA) assays for early cancer detection: first insights from the Circulating Cell-Free Genome Atlas Study (CCGA) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-343.

Abstract INTRODUCTION AND OBJECTIVES: Patient responses to cancer immunotherapy such as checkpoint inhibitor drugs vary greatly between patients and there remains no biomarker to predict sensitivity to these drugs. We describe a patient derived xenograft (PDX) avatar system that predicts cancer immunotherapy responses in the context of tumor heterogeneity within 8-10 days. This avatar model preserves the original tumor microenvironment and tumor infiltrating lymphocytes (TILs) at a high tumor take rate for evaluation of various immunotherapy drugs. This prediction model also involves tumor infiltrating lymphocyte isolation and primary cell generation for confirming the immunotherapy response in vitro. This PDX avatar platform generates rapid actionable information and readily identifies patients that would maximally benefit from checkpoint inhibitor therapies in a phenotype-based manner. METHODS: Tissue from patients that underwent a nephrectomy for RCC or metastasectomy were engrafted into the chorioallantoic membrane of avian embryos with a portion used for TIL isolation and primary cell generation. PD-1 and PD-L1 checkpoint inhibitors were intravenously injected and high frequency ultrasound imaging and immunophenotyping was used to quantitate changes in tumor volume, vascularity, and TIL expansion in all treatment groups. Isolated TILs were expanded and co-cultured with respective primary cells to confirm and examine immunotherapy response at a molecular level. RESULTS: Patient PDXs demonstrated heterogeneous responses to immunotherapy that relates to presence and expansion of TILs after checkpoint inhibitor injection. Patient #1 demonstrated the greatest response with a >50% reduction in tumor volume and 4X expansion of T-cells over 8 days of treatment. Patient #2 demonstrated intratumoral heterogeneities in terms of tumor volume change after checkpoint inhibitors treatment despite TIL expansion in all treatment groups. Patient #3 showed no response that correlated to lack of TILs in the PDX. In vitro expansion of TILs and co-culture with primary cell line demonstrated a specific immune response via INF-gamma release and changes in immunomodulatory molecules. CONCLUSIONS: This PDX system preserves TILs and permits rapid large scale prediction of tumor specimens to various systemic therapy agents such as checkpoint inhibitors without the need for humanized models. This avatar system is a useful tool to rapidly predict and examine response to checkpoint inhibitors on a per-patient basis to improve the assignment of cancer immunotherapies to specific RCC patients. Citation Format: Mario Cepeda, Matthew Lowerison, Cindy Liu, Yarolslav Fedyshyn, Vidhu Joshi, Paras Shah, John Cheville, R. Houston Thompson, Boorjian Stephen, Bradley Leibovich, Haidong Dong, Hon S. Leong. Rapid patient derived xenograft avatars that consider tumor heterogeneity for prediction of cancer immunotherapy responses in metastatic renal cell carcinoma patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-155.

Abstract Ramucirumab (RAM) is a high affinity, humanized, monoclonal antibody that binds to the extra-cellular domain of the vascular endothelial growth factor receptor (VEGFR). RAM prevents the binding of VEGF ligands with VEGFR-2, the most potent receptor of the VEGF tumor angiogenesis pathway. RAM is FDA approved for adults with NSCLC, as well as for gastric and colorectal adenocarcinoma where higher exposure was associated with better outcomes. Based on population pharmacokinetic (PK) analysis of the adult data, a minimum steady state concentration (Cmin ss) of ≥ 50 µg/ml of RAM was considered the target concentration for pediatrics. The Children's Oncology Group (COG) conducted a phase 1 study using a rolling six design to define the maximum tolerated dose (MTD) and /or a recommended phase 2 dose (RP2D), evaluate toxicities and explore circulating angiogenic cells as a biomarker for RAM monotherapy in children with recurrent/refractory solid tumors. The starting dose of 8 mg/kg IV q2 weeks (DL1) was chosen based on the adult safety profile and effective Cmin ss. Since adult data suggested that lower body weight was associated with lower Cmin ss, dose escalation to 12 mg/kg IV q2 weeks (DL2) was planned provided the MTD was not exceeded in DL1 and up to 16 mg/kg IV q2 weeks (DL3) if Cmin ss was < 50 µg/ml in 1 of 6 subjects on DL2 without exceeding the MTD. An expansion cohort was planned at the lowest dose where at least 5 of 6 subjects exceeded the target in order to generate PK data in at least 6 additional subjects < 12 years of age. In the absence of an MTD, the RP2D was defined as the dose achieving Cmin ss ≥ 50 µg/ml on day 42 ± 2, after 3 doses of RAM administered IV every 2 weeks, in at least 10 of 12 subjects. Sixteen subjects (15 eligible; 7 females), median age of 14 years (3-21 yrs.) have been enrolled. Of the 7 subjects on DL1, two had insufficient PK sampling to establish Cmin ss, including 1 who experienced grade 2 proteinuria (DLT). In the remaining 5, the median (range) Cmin ss was 66 (40-136) µg/ml; 2/5 did not achieve the target of ≥ 50 µg/ml. Of the 8 subjects on DL2, two had insufficient PK sampling, including 1 with grade 2 proteinuria (DLT). In the remaining 6, the median (range) Cmin ss was 64 (51-101) µg/ml, all ≥ 50 µg/ml; thus 12mg/kg IV q2 weeks was identified for the expansion cohort. The most common RAM related non-DLT toxicities were grade 1/2 headache in 6 subjects, grade 1/2 elevation in aspartate aminotransferase in 7 subjects and grade 2/3 hypertension in 2 subjects. Due to low participation, circulating angiogenic cells could not be analyzed. This is the first COG study in which dose escalation and RP2D for a targeted agent incorporated a primary PK endpoint (Cmin ss) based upon efficacy data from adult studies and paves the way for similar study design for future phase-1 studies. Citation Format: Kamnesh Pradhan, Stacey L. Berg, Xiaowei Liu, Charles G. Minard, James Croop, Joel M. Reid, Elizabeth Fox, Brenda J. Weigel. A dose escalation and toxicity study using pre-determined target concentration of Ramucirumab, a novel anti-angiogenic agent in children with recurrent / refractory solid tumors: A report from the children's oncology group phase I/ pilot consortium (ADVL1416) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr CT054.

Abstract Lung cancer is the leading cause of cancer-related death worldwide. In this study, we demonstrate that elevated expression of dopamine and cyclic adenosine monophosphate-regulated phosphoprotein, Mr 32000 (DARPP-32) and its truncated splice variant t-DARPP promotes lung tumor growth, while abrogation of DARPP-32 expression in human non-small cell lung cancer (NSCLC) cells reduces tumor growth in orthotopic mouse models. We observe a novel physical interaction between DARPP-32 and inhibitory kappa B kinase-α (IKKα) that promotes NSCLC cell migration through non-canonical nuclear factor kappa-light-chain-enhancer of activated B cells 2 (NF-κB2) signaling. Bioinformatics analysis of 513 lung adenocarcinoma patients reveals elevated t-DARPP isoform expression is associated with poor overall survival. Histopathological investigation of 62 human lung adenocarcinoma tissues also showed that t-DARPP expression is elevated with increasing tumor (T) stage. Our data suggest that DARPP-32 is a negative prognostic marker associated with increasing stages of NSCLC and may represent a novel therapeutic target. Citation Format: Sk. Kayum Alam, Matteo Astone, Ping Liu, Stephanie R. Hall, Abbygail M. Coyle, Erin N. Dankert, Dane K. Hoffman, Wei Zhang, Rui Kuang, Anja C. Roden, Aaron S. Mansfield, Luke H. Hoeppner. DARPP-32 and t-DARPP promote non-small cell lung cancer growth through regulation of IKKα-dependent cell migration and Akt/Erk-mediated cell survival [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5161.

Abstract While it is known that nuclear factor κ-B (NF-κB) signaling within macrophages regulates expression of downstream targets that can mediate either pro- or antitumor functions, the mechanisms that define predominant characteristics are not well understood. As macrophages are present in the tumor microenvironment of diverse tumor types, their characteristics have the potential to either support or hinder tumor growth and metastatic spread. Therefore, a method to shift the balance of tumor associated macrophages from pro- to antitumor functions could potentially target tumor cells directly and also recruit and activate other immune cells, resulting in significant therapeutic benefit. Our studies are designed to gain an understanding of how to use modulation of NF-κB signaling as the “pinch point” to generate antitumor phenotypes and determine how to achieve this modulation in a patient. We are using immortalized bone marrow-derived macrophages or ex vivo tumor-associated macrophages in cell culture approaches and inducible transgenic mice in in vivo approaches to investigate the mechanisms by which NF-κB defines macrophage characteristics. Interactions with tumor cells are also being investigated using co-culture and murine models. Our data suggests that high levels of NFκ-B activity in macrophages induce both direct tumor cell killing and immune stimulating responses. We are testing two different translational approaches. The first is liposomal muramyl tripeptide ethanolamine that acts as an immune stimulant by increasing NF-κB activity in macrophages. The second is preferential delivery of siRNA against the inhibitor of NFκ-B (IκB-alpha) to tumor-associated macrophages using polymeric nanoparticles. We hope to better understand the mechanisms by which NFκ-B regulates macrophage functions to inform development of a novel macrophage-based immunotherapy that could be effective across a wide spectrum of solid tumors and metastatic disease. Citation Format: Esther Liu, Alyssa A. Hoover, Whitney R. Harris, Whitney Barham, Oleg Tikhomirov, Dineo Khabele, Zahra Mirafzahli, Todd D. Giorgio, Andrew J. Wilson, Fiona E. Yull. Modulation of NFκ-B signaling to optimize antitumor characteristics in macrophages [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4711.

Abstract Introduction Circulating tumor cells (CTCs) have been shown to be prognostic in patients (pts) with metastatic breast cancer (MBC) (Pukazhendhi, Gluck, J Carcinog. 2014). The tnAcity trial evaluated the efficacy/safety of 3 chemotherapy combination regimens (nab-P/carboplatin [C], nab-P/gemcitabine [G], or G/C) as first-line treatment for pts with mTNBC. nab-P/C resulted in a significantly longer PFS & numerically higher ORR vs nab-P/G or G/C (Yardley. SABCS 2016; manuscript in process). CTC levels were assessed at baseline (BL) & during treatment to determine correlation with clinical benefit. Methods Pts with pathologically confirmed mTNBC & no prior cytotoxic chemotherapy for MBC received (1:1:1) nab-P 125 mg/m2 with C area under the curve (AUC) 2, nab-P 125 mg/m2 with G 1000 mg/m2, or G 1000 mg/m2 with C AUC 2, all given d1 & 8 q3w. Primary endpoint: investigator-assessed PFS. Secondary endpoints included ORR & OS; CTC enumeration was a prespecified exploratory objective. CTC levels, assessed (CELLSEARCH®) at BL & start of cycles 3 & 5 (post-BL), were grouped as follows: 0 CTCs/7.5 mL blood at BL (−−), ≥ 1 CTCs/7.5 mL blood at BL & post-BL (++), & ≥ 1 CTCs/7.5 mL blood at BL & clearance of CTCs in ≥ 1 post-BL measurement (+−). Results In total, 126 pts were included: 48, 24, & 54 in the −−, ++, & +− groups, respectively. Mean BL CTC levels for the ++ & +− groups were 55 & 66 CTCs/7.5 mL blood. Pts with BL CTCs of ≥ 1 vs 0 had numerically similar median PFS (7.0 vs 5.9 mo; HR 1.45 [95% CI 0.93 - 2.25]) & OS (15.0 vs 16.0 mo; HR 0.90 [95% CI 0.57 - 1.42]) & higher ORR (64% vs 44%). Mean cycle 3 & 5 CTC levels in the ++ group were 17 & 111 CTCs/7.5 mL blood. Pts in the −− & +− groups had longer PFS vs the ++ group (median 5.9, 8.5, & 4.7 months). Similar improvements in OS & ORR were noted (Table). Conclusions Absence of CTCs at BL & during treatment & clearance of CTCs from BL at least once during treatment were generally associated with improved efficacy outcomes in pts with mTNBC treated with combination chemotherapy. Table. Outcomes by Change in CTC Level from BaselineGroupOutcome−− n = 48+− n = 54++ n = 24PFS, median, mo HR (95% CI)5.9 0.60 (0.34-1.06)a8.5 0.30 (0.17-0.54)a4.7OS, median, mo HR (95% CI)16.0 0.40 (0.22-0.73)a17.8 0.35 (0.20-0.62)a9.8ORR, %43.879.629.2CR6.316.74.2PR37.563.025.0SD35.420.454.2PD16.7—16.7NE4.2——CR, complete response; HR, hazard ratio; NE, not evaluable; ORR, overall response rate; OS, overall survival; PD, progressive disease; PFS, progression-free survival; PR, partial response; SD, stable disease. a vs ++ group. Citation Format: Minetta C. Liu, Wolfgang Janni, Vassilis Georgoulias, Denise A. Yardley, Nadia Harbeck, Xin Wei, Desmond McGovern, Robert Beck. First-line doublet chemotherapy for mTNBC: circulating tumor cell analysis of the tnAcity trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4209.

Abstract The amplified MYCN gene serves as an oncogenic driver in approximately 20% of high-risk pediatric neuroblastomas. Here we show that c-MYC itself is a potent transforming gene in a separate subset of high-risk neuroblastoma cases (~10%), based on (i) its upregulation by focal enhancer amplification or genomic rearrangements leading to enhancer hijacking, and (ii) its ability to transform neuroblastoma precursor cells in a transgenic animal model. The aberrant regulatory elements associated with oncogenic c-MYC activation include focally amplified distal enhancers or translocation of highly active enhancers from other genes to within topologically associating domains containing the c-MYC gene locus. The clinical outcome for patients with high levels of c-MYC expression is virtually identical to that of patients with amplification of the MYCN gene, a known high-risk feature of this disease. Together, these findings establish c-MYC as a bona fide oncogene in a clinically significant group of high risk childhood neuroblastomas. Citation Format: Mark W. Zimmerman, Yu Liu, Shuning He, Adam D. Durbin, Brian J. Abraham, John Easton, Ying Shao, Xu Beisi, Shizhen Zhu, Xiaoling Zhang, Zhaodong Li, Nina Weichert-Leahey, Richard A. Young, Jinghui Zhang, A. Thomas Look. c-MYC drives a subset of high-risk pediatric neuroblastoma and is activated through mechanisms including enhancer hijacking and focal enhancer amplification [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4135.

Abstract Background. Mutation of the BRAF(V600E) oncogene occurs in ~8% of human colorectal cancers (CRC) and its inhibition is associated with treatment resistance that is due, in part, to paradoxical re-activation of MEK/ERK signaling. Recently, pathway analysis identified cyclin-dependent kinase 1 (CDK1) upregulation in a subset of human BRAFV600E CRCs. We determined whether CDK1 antagonism can enhance the efficacy of MEK inhibition in BRAFV600E CRC cell lines. Methods. Manipulation of gene expression was achieved by siRNA and/or ectopic expression, or using isogenic cell pairs. Cells were treated with the CDK1 selective inhibitor RO-3306 or dinaciclib (CDK1,2,5,9 inhibitor) alone or combined with the MEK inhibitor cobimetinib. Apoptosis was quantified by Annexin V staining with flow cytometry; apoptotic signaling was analyzed by immunoblotting of caspase-8 phosphorylation and caspase cleavage. Long-term cell survival was evaluated by clonogenic assay. In vivo efficacy of the drug combination was determined in a murine flank xenograft model. Results. BRAFV600E CRC cell lines expressed CDK1 whose siRNA knockdown or pharmacological inhibition by RO-3306 or dinaciclib was shown to sensitize them to apoptosis (annexin V labeling). The combination of RO-3306 or dinaciclib with cobimetinib cooperatively enhanced apoptosis and reduced clonogenic survival compared to drug monotherapy. Cells isogenic or ectopic for BRAFV600E displayed apoptosis resistance to CDK inhibitors, as did cells with ectopic expression of constitutively active MEK. CDK1 inhibition by RO-3306 or dinaciclib induced a caspase-8-dependent apoptosis shown by caspase-8 restoration in deficient NB7 cells that enhanced dinaciclib-induced caspase-3 cleavage. Furthermore, CDK inhibitors suppressed procaspase-8 phosphorylation at S387 shown by drug withdrawal that restored phospho-S387 and increased cell mitosis. In a CRC xenograft model, dinaciclib plus cobimetinib produced significantly greater tumor growth inhibition in association with a caspase-dependent apoptosis than did either drug alone. Analysis of TCGA datasets revealed overexpression of CDK1 in human CRCs compared to normal colonic tissue. An inverse relationship existed between expression of CDK1 and the cell cycle inhibitor p16. In CRC cells, ectopic p16 was shown to downregulate CDK1 expression. In conclusion, our data establish CDK1 as a novel mediator of apoptosis resistance in BRAFV600E CRC cells lines whose combined targeting with CDK and MEK/ERK inhibitors may represent an effective therapeutic strategy. Citation Format: Peng Zhang, Hisato Kawakami, Weizhen Liu, Xiangyu Zeng, Klaus Stebhardt, Kaixiong Tao, Shengbing Huang, Frank A. Sinicrope. Targeting CDK1 and MEK/ERK overcomes apoptosis resistance in BRAFV600E human colorectal cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2336.

Abstract Studies have well-established that activation of TNFR1, a ubiquitously expressed cell surface receptor, by TNF can induce either cell survival or cell death signaling cascades, however, the mechanisms regulating TNFR1 to initiate these disparate outcomes are poorly understood. TNF-induced apoptosis is initiated by clustering of activated TNFR1 at the cell surface, followed by internalization of the receptor complexes and subsequent caspase activation. Conversely, surface retention of activated TNFR1 promotes cell survival signaling mediated by NFκB and MAPKs pathways. Our group has identified a glycosylation-dependent mechanism that controls this TNFR1 signaling switch (i.e. apoptosis vs. survival). Specifically, we have found that TNFR1 activity is modified by the addition of a distinct sugar, an α2-6 linked sialic acid, by the Golgi sialyltransferase, ST6Gal-I. Importantly, ST6Gal-I is highly upregulated in numerous cancer types, and through its sialylation of a select cohort of cell surface receptors, various studies have indicated ST6Gal-I as a potent tumor cell survival factor. The effect of sialylation on TNFR1 was examined in multiple cancer cell models, including leukemia and epithelial cancer cell lines with forced overexpression or knockdown of ST6Gal-I. These models show that TNFR1 sialylation blocks TNF-induced apoptosis (indicated by the inhibition of caspase activation), and data from our group suggests that the underlying mechanism of this inhibition of apoptosis involves the sialylation-driven interference of TNFR1 oligomerization and internalization. Considering sialylated TNFR1 is retained on the cell surface following activation, we hypothesize that cells with abundant ST6Gal-I not only block TNFR1-mediated apoptosis but also divert signaling towards survival, indicated by increased activity and expression of many pro-survival factors (NFkB, AKT, etc.). Based on these collective findings, we conclude that the ST6Gal-I-mediated sialylation of TNFR1 controls the cellular response to TNF by blocking TNFR1 internalization, resulting in apoptosis inhibition and the promotion of survival signaling. Considering the tumor microenvironment is rich in immune cell-derived TNF, we posit that ST6Gal-I protects tumor cells within this inflammatory milieu by providing a mechanism by which tumor cells can evade immune cell killing. Citation Format: Andrew T. Holdbrooks, Matthew J. Schultz, Zhongyu Liu, Daniel C. Bullard, Susan L. Bellis. Sialylation of the TNFR1 death receptor promotes cancer cell survival [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2334.