Changes In Gene Expression Research Articles

Abstract 2593: Spatial multi-omics profiling of tumor cell phenotypes in primary cutaneous melanoma at single-cell resolution

Abstract Primary cutaneous melanomas develop in stages from melanoma precursor cells that may progress to melanoma in situ (MIS) and eventually to invasive disease. Molecular changes, such as tumor cell state switches from melanocytic to undifferentiated and neural-crest-like phenotypes, have been associated with the development of melanoma metastases and therapeutic resistance. However, it is unknown whether cell states or gene expression changes enriched in advanced tumors exist at the premalignant stage and if they can elicit tumor-infiltrating lymphocytes (TILs). To address this gap, we analyzed a cohort of clinical samples from 43 patients with primary cutaneous melanoma using whole-slide cyclic multiplex immunofluorescence imaging (CyCIF), morphology-guided micro-regional RNA sequencing, and high-resolution 3D imaging. Each specimen contained multiple histologically-distinct regions representing a progression axis from normal to precursor to melanoma in situ to invasion. Subsequently, we examined the molecular profiles of both atypical melanocytes and tumor cells, and the gene expression and tumor microenvironmental (TME) changes that occurred during these progression stages. We identified major intra- and inter-specimen heterogeneity in the tumor intrinsic and extrinsic features across progression stages. Multiple tumor samples contained regions where publicly available gene signatures linked to both melanocytic and undifferentiated cell phenotypes were enriched. CyCIF analysis confirmed that various tumor cell phenotypes can coexist in close proximity to each other in early-stage untreated melanomas, and that the majority of undifferentiated tumor cells were located within regions of dermal invasion. Moreover, the cellular neighborhoods around undifferentiated tumor cells had a higher proportion of CD8+ T cells and cells of myeloid lineage compared to the neighborhoods around melanocytic tumor cell phenotypes. When assessing the localization and abundance of various tumor cell phenotypes, the levels of spatial and regional heterogeneity increased proportionally along normal to premalignant to malignant progression. Furthermore, the regional entropy of tumor cell phenotypes decreased along tumor depth in the majority (63%) of the samples, and even the melanoma in situ regions showed varying levels of spatial heterogeneity. Our in-depth multimodal molecular analyses highlight the presence of spatial heterogeneity among tumor cell phenotypes as well as the organization of early-stage primary melanomas, and are suggestive of tumor cell adaptation to the local environment. Citation Format: Tuulia Vallius, Edward Novikov, Ajit Nirmal Johnson, Shi Yingxiao, Roxanne Pelletier, Shishir Pant, Zoltan Maliga, Alyce Chen, Clarence Yapp, Sabrina Chan, Christine Lian, George F. Murphy, Sandro Santagata, Peter Sorger. Spatial multi-omics profiling of tumor cell phenotypes in primary cutaneous melanoma at single-cell resolution [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 2593.

Histone lactylation in macrophages is predictive for gene expression changes during ischemia induced-muscle regeneration

ObjectivesWe have previously shown that lactate is an essential metabolite for macrophage polarisation during ischemia-induced muscle regeneration. Recent in vitro work has implicated histone lactylation, a direct derivative of lactate, in macrophage polarisation. Here, we explore the in vivo relevance of histone lactylation for macrophage polarisation after muscle injury. MethodsTo evaluate macrophage dynamics during muscle regeneration, we subjected mice to ischemia-induced muscle damage by ligating the femoral artery. Muscle samples were harvested at 1, 2, 4, and 7 days post injury (dpi). CD45+CD11b+F4/80+CD64+ macrophages were isolated and processed for RNA sequencing, Western Blotting, and CUT&Tag-sequencing to investigate gene expression, histone lactylation levels, and histone lactylation genomic localisation and enrichment, respectively. ResultsWe show that, over time, macrophages in the injured muscle undergo extensive gene expression changes, which are similar in nature and in timing to those seen after other types of muscle-injuries. We find that the macrophage histone lactylome is modified between 2 and 4 dpi, which is a crucial window for macrophage polarisation. Absolute histone lactylation levels increase, and, although subtly, the genomic enrichment of H3K18la changes. Overall, we find that histone lactylation is important at both promoter and enhancer elements. Lastly, H3K18la genomic profile changes from 2 to 4 dpi were predictive for gene expression changes later in time, rather than being a reflection of prior gene expression changes. ConclusionsOur results suggest that histone lactylation dynamics are functionally important for the function of macrophages during muscle regeneration.

Abstract 307: Generation and characterization of a glioblastoma stem cell model with acquired resistance to LSD1 inhibition

Abstract Epigenetic modifications play an important role in the initiation of various cancer types, including glioblastoma (GBM), and in the development of therapeutic resistance. Patients with GBM, a common malignant brain tumor, have an average survival of 12-15 months after first-line therapy. Lysine-specific demethylase 1 (LSD1) is a histone demethylase that is overexpressed in glioblastoma stem cells (GSCs) and functions to promote proliferation, inhibit differentiation, and enhance motility. Previous work from our group has investigated LSD1 as a therapeutic target in glioblastoma and identified genes that may predict resistance to pharmacological LSD1 inhibitors using RNA-seq. Five upregulated genes, HKDC1, RAB3IL1, RAB39B, FTH1, and FAM213A, were associated with LSD1 inhibitor (LSD1i) resistance and were validated in brain tissue of a GBM model treated with GSK-LSD1 after succumbing to tumor burden. In order to determine whether selection pressure from LSD1 inhibitor treatment caused upregulation of these genes, we created a model of acquired resistance in GSC lines in vitro. Isogenic resistant lines were generated by treating MDA-GSC17 cells with increasing concentrations of LSD1i or diluent (DMSO), as tolerated starting at 50 uM (which was five fold below the IC50 for these lines). In parallel, MDA-GSC17 controls were exposed to DMSO. The resistant line was created over 4 weeks and monitored by cell number and viability to reach 90%. To assess the change in gene expression, we conducted quantitative PCR for the five genes in the parental and resistant MDA-GSC17 line and saw upregulation in 3 of the 5 genes. Two genes, HKDC1 and RAB3IL1, were unable to be assessed due to low basal expression. However, 3 genes were upregulated which are RAB39B, FTH1, and FAM213A. RAB39B is a Ras-analog in brain (RAB) small GTPase and a member of the RAS oncogene family, involved in vesicular trafficking. High expression of ferritin heavy chain 1 (FTH1) is correlated with high-grade gliomas and poor prognosis in glioblastoma. Lastly, the redox regulatory protein, FAM213A, can activate antioxidant proteins and elevated expression is associated with worse outcomes for AML patients. This suggests that modulating the RAS signaling pathways and specific redox pathways may overcome LSD1 resistance. Understanding the changes in gene expression as the cells acquire resistance to LSD1 inhibitors will help us understand the mechanism of resistance to LSD1 inhibitors in glioblastoma and to design new treatment strategies. Citation Format: Kareena H. Patel, Lea Stitzlein, Deokhwa Nam, Frederick Lang, Joy Gumin, Joya Chandra. Generation and characterization of a glioblastoma stem cell model with acquired resistance to LSD1 inhibition [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 307.

“R” U ready?: a case study using R to analyze changes in gene expression during evolution

As high-throughput methods become more common, training undergraduates to analyze data must include having them generate informative summaries of large datasets. This flexible case study provides an opportunity for undergraduate students to become familiar with the capabilities of R programming in the context of high-throughput evolutionary data collected using macroarrays. The story line introduces a recent graduate hired at a biotech firm and tasked with analysis and visualization of changes in gene expression from 20,000 generations of the Lenski Lab’s Long-Term Evolution Experiment (LTEE). Our main character is not familiar with R and is guided by a coworker to learn about this platform. Initially this involves a step-by-step analysis of the small Iris dataset built into R which includes sepal and petal length of three species of irises. Practice calculating summary statistics and correlations, and making histograms and scatter plots, prepares the protagonist to perform similar analyses with the LTEE dataset. In the LTEE module, students analyze gene expression data from the long-term evolutionary experiments, developing their skills in manipulating and interpreting large scientific datasets through visualizations and statistical analysis. Prerequisite knowledge is basic statistics, the Central Dogma, and basic evolutionary principles. The Iris module provides hands-on experience using R programming to explore and visualize a simple dataset; it can be used independently as an introduction to R for biological data or skipped if students already have some experience with R. Both modules emphasize understanding the utility of R, rather than creation of original code. Pilot testing showed the case study was well-received by students and faculty, who described it as a clear introduction to R and appreciated the value of R for visualizing and analyzing large datasets.

Abstract 3159: VHL1 activation with a CRISPR-based gene activation platform causes increased MLKL expression and triggers necroptosis in renal cell carcinoma

Abstract Background: Kidney cancer is a common and deadly disease. Over 90% of all kidney cancers are classified as renal cell carcinoma (RCC), of which clear-cell RCC (ccRCC) is the most predominant subtype. VHL is a tumor suppressor and plays a pivotal role in ccRCC development. While >50% of ccRCC patients present with pathogenic VHL mutations, deep deletions and low VHL expression are also common. Over the past two decades, therapeutic advances have been made for metastatic ccRCC; however, none directly target VHL, and the five-year overall survival for metastatic ccRCC remains ~12%. Here, we used a fusion protein, consisting of a deactivated Cas9 (dCas9) linked to the histone acetyltransferase protein p300, to determine if VHL activation initiates programmed cell death in a preclinical model of ccRCC. Methods: Caki-1 cells are a human ccRCC line, are wild-type VHL with low-moderate expression. Caki-1 cells were stably transduced with our dCas9-p300 system via lentivirus, and then transfected with either sgRNAs targeting VHL or a non-targeting (NT) sgRNA. Ten targeting sgRNAs were designed, with eight starting within -120 bp from the VHL1 transcriptional start site (chr3:10141778), and two starting within +50 bp after the TSS. VHL gene expression changes from baseline were evaluated by RT-qPCR at 8h, 24h and 48h after sgRNA transfection. At 24-72h, Caki-1 cells were harvested and stained with Annexin V and propidium iodide; apoptosis and necrosis were then assessed by flow cytometry. Last, to determine whether VHL reactivation triggered necroptosis, MLKL gene expression changes were evaluated by RT-qPCR at 8h, 24h and 48h. Results: Four targeting sgRNAs met internal thresholds for evaluation within our dCas9-300 system: sgRNA3 bp), sgRNA4, sgRNA9, and sgRNA10. Significant increases in VHL expression were observed at 8h for sgRNA3 and sgRNA10 (62.4% and 56.5%, respectively; both P<0.0001, n=3), at 24h for all four sgRNAs (range 91.1-236.1%; all P<0.0001, n=3), and again at 48h for all four sgRNAs (range 84.4-194.4%; P<0.0001, n=3). At 48h and 72h, sgRNA4 (6.78% and 7.35%) and sgRNA9 (6.71% and 6.76%) showed evidence of necroptosis activation. sgRNA4 demonstrated significantly increased MLKL expression at 24h and 48h (199.6% and 144.6%; both P<0.0001, n=3) as did sgRNA9 (192.7% and 235.6%; both P<0.0001, n=3) suggesting necrosome activation. Conclusions: To our knowledge, this is the first study to associate VHL reactivation with increased MLKL expression and necroptosis initiation. These data support continued development of an experimental system we have pioneered (PMID: 31712774), which will leverage chemical-induced proximity to reactivate VHL. Citation Format: Manfred S. Meng, Ryan M. Kemper, Travis J. Nelson, Nathaniel A. Hathaway, Daniel James Crona. VHL1 activation with a CRISPR-based gene activation platform causes increased MLKL expression and triggers necroptosis in renal cell carcinoma [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 3159.

Gastrulation-stage gene expression in Nipbl+/- mouse embryos foreshadows the development of syndromic birth defects.

In animal models, Nipbl deficiency phenocopies gene expression changes and birth defects seen in Cornelia de Lange syndrome, the most common cause of which is Nipbl haploinsufficiency. Previous studies in Nipbl+/- mice suggested that heart development is abnormal as soon as cardiogenic tissue is formed. To investigate this, we performed single-cell RNA sequencing on wild-type and Nipbl+/- mouse embryos at gastrulation and early cardiac crescent stages. Nipbl+/- embryos had fewer mesoderm cells than wild-type and altered proportions of mesodermal cell subpopulations. These findings were associated with underexpression of genes implicated in driving specific mesodermal lineages. In addition, Nanog was found to be overexpressed in all germ layers, and many gene expression changes observed in Nipbl+/- embryos could be attributed to Nanog overexpression. These findings establish a link between Nipbl deficiency, Nanog overexpression, and gene expression dysregulation/lineage misallocation, which ultimately manifest as birth defects in Nipbl+/- animals and Cornelia de Lange syndrome.

Abstract 3052: Investigating the role of FOXA1/2 & HNF4⍺ in pancreatic ductal adenocarcinoma

Abstract PDAC represents a formidable challenge with an alarmingly low 5-year survival rate of less than 12%. Integrated genomic, transcriptomic, and proteomic analyses have identified two distinct PDAC subtypes: classical and basal. The critical difference between these subtypes lies in the expression of endodermal lineage specifiers, with the classical subtype expressing FOXA1, FOXA2 (FOXA1/2), and HNF4⍺, critical for pancreatic cell-fate determination, while the basal subtype downregulates these genes, leading to the loss of endodermal identity. We reason that the transcription factors (TF), FOXA1/2 and HNF4α, that play critical roles in pancreatic development, are not only biomarkers of the classical subtype but are essential regulators of PDAC subtype differentiation state. Despite their relevance in other cancers, their specific functions in PDAC remain largely unexplored. We aim to define the functional roles of FOXA1/2 and HNF4⍺ in the classical PDAC subtype, exploring their regulation of growth and cellular identity. Previous published work in our lab has shown that exogenous HNF4⍺ restrains growth in a panel of human and murine PDAC cell lines. Furthermore, we have shown that HNF4⍺ regulates the classical subtype program of PDAC. While FOXA1/2 and HNF4⍺ cooperatively enact gene expression changes in normal tissue, the extent to which cooperative interactions between these TFs are required to activate the classical gene expression program of PDAC remains unknown. Overall, we will test the central hypothesis that FOXA1/2 and HNF4⍺ are critical regulators of the transcriptional network governing the cellular identity of classical PDAC. To test this hypothesis, we will be reconstituting and modulating the expression of these factors in human and murine PDAC cell and organoid lines. We will assess gene expression changes through RNA-seq and genomic localization of these TFs through ChIP-seq. We have conducted bulk RNA sequencing on Foxa1/2-positive and negative organoids to transcriptionally identify differences brought on by Foxa1/2 deletion and found over 2,200 differentially expressed genes. Foxa1/2 deletion led to a significant decline in the classical PDAC signature based on gene ontology. Furthermore, we show that HNF4α can inhibit organoid growth in the absence of FOXA1/2. We discovered that HNF4⍺ targets, such as Lgals4, expression levels are unaltered at the RNA level independent of FOXA1/2. By assessing the roles of FOXA1/2 and HNF4α in PDAC, we aim to determine the transcriptional network governed by these factors in the classical subtype of PDAC Citation Format: Walter A. Orellana, Katherine Gillis, Pengshu Fang, Gabriela Fort, Eric L. Snyder. Investigating the role of FOXA1/2 & HNF4⍺ in pancreatic ductal adenocarcinoma [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 3052.

Abstract 524: Using acquired resistance to explore the mechanism of action of the integrated stress response/GCN2 activator NXP800 - A new developmental agent for platinum-resistant ARID1A mutant ovarian cancer

Abstract Background: NXP800 is a potent, oral activator of the Integrated Stress response (ISR), inhibitor of heat shock factor 1 (HSF1) activation and tumor cell proliferation, which is in early clinical studies in ARID1A-mutated, platinum resistant, clear cell ovarian cancer (NCT05226507). We discovered NXP800 using multiparameter medicinal chemistry optimization of a hit identified from a cell-based phenotypic screen. Owing to the unbiased nature of phenotypic screening, target identification is crucial to understand the biological and therapeutic activity of hit compounds. Methods and Results:: By RNAseq profiling human cancer cells treated with NXP800 we identified changes in expression of genes regulated by HSF1 or ATF4 - effects accompanied by eIF2alpha (eIF2a) phosphorylation and resulting activation of the ISR. To further understand this response, we explored whether NXP800 resistance models could inform on its mechanism of action (MoA). We used ARID1A mutant SK-OV-3 human ovarian carcinoma cells that are 1) highly sensitive to NXP800, 2) model the target patient population and 3) MSI-high so likely to have an elevated mutation rate contributing to acquisition of resistance. We generated two independent NXP800-resistant SK-OV-3 cell lines in which NXP800-mediated ATF4 induction and concomitant inhibition of global translation were abolished. By whole exome sequencing, we identified a heterozygous L99P mutation in the alpha subunit of eIF2B (eIF2Ba), the nucleotide exchange factor for eIF2a. Expression of eIF2BaL99P, but not wild-type, in parental SK-OV-3 cells reduced sensitivity to NXP800 to the same level as cells with NXP800-induced resistance. Using fluorescence recovery after photobleaching to monitor the dynamic association of the eIF2B:eIF2a complex, we elucidated that the eIF2BaL99P mutation reduces NXP800-mediated inhibition of eIF2a-GFP recycling through eIF2B bodies. Phosphorylation of eIF2a is regulated by four stress-controlled kinases GCN2, HRI, PKR and PERK. Using systematic siRNA knockdown or small-molecule inhibitors, we showed that GCN2 alone is required for ISR activation by NXP800 and that ISR induction inhibited HSF1 activation. Furthermore, inactivation of GCN2 reduced the antiproliferative activity of NXP800 to the same extent observed in NXP800-resistant SK-OV-3 cells. In contrast, exposure of resistant or parental SK-OV-3 cells expressing eIF2BaL99P to GCN2 inhibitors did not cause further reduction in NXP800 sensitivity - confirming the importance of the eIF2BaL99P mutation in the resistance mechanism. Conclusions: We have used acquired resistance to understand the MoA of NXP800 as a potent activator of GCN2 and the ISR pathway. Further studies are underway to determine the exact proximal molecular target of NXP800 and the mechanism of GCN2/ISR activation. Citation Format: Marissa V. Powers, Rachel Hodgson, Swee Y. Sharp, Toby Roe, K. Elizabeth Allen, Susan Campbell, Robert te Poele, Matthew Cheeseman, Keith Jones, Paul A. Clarke, Paul Workman. Using acquired resistance to explore the mechanism of action of the integrated stress response/GCN2 activator NXP800 - A new developmental agent for platinum-resistant ARID1A mutant ovarian 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 524.

Single Cell RNAseq analysis of cytokine-treated human islets: Association of cellular stress with impaired cytokine responsiveness

Abstract Pancreatic β-cells are essential for survival, being the only cell type capable of insulin secretion. While they are believed to be vulnerable to damage by inflammatory cytokines such as interleukin-1 beta (IL-1β) and interferon-gamma (IFN-γ), we have recently identified physiological roles for cytokine signaling in rodent β-cells that include the stimulation of antiviral and antimicrobial gene expression and the inhibition of viral replication. In this study, we examine cytokine-stimulated changes in gene expression in human islets using single-cell RNA sequencing. Surprisingly, the global responses of human islets to cytokine exposure were remarkably blunted compared to our previous observations in the mouse. The small population of human islet cells that were cytokine responsive exhibited increased expression of IL-1β-stimulated antiviral guanylate binding proteins, just like in the mouse. Most human islet cells were not responsive to cytokines, and this lack of responsiveness was associated with high expression of genes encoding ribosomal proteins. We further correlated the expression levels of RPL5 with stress response genes, and when expressed at high levels, RPL5 is predictive of failure to respond to cytokines in all endocrine cells. We postulate that donor cause of death and isolation methodologies may contribute to stress of the islet preparation. Our findings indicate that activation of stress responses in human islets limits cytokine-stimulated gene expression, and we urge caution in the evaluation of studies that have examined cytokine-stimulated gene expression in human islets without evaluation of stress-related gene expression.

Abstract 6842: The effect of intra-tumoral Candida albicans on host gene expression

Abstract The gut and tumor microbiome have been shown to affect tumorigenesis, tumor immune infiltration, and response to traditional cancer therapeutics such as radiation therapy. Further, specific microbe-cancer relationships have been established. One such microbe is Candida albicans, which has been identified within several gastrointestinal cancers and is associated with an increased risk of metastases and decreased overall survival. By completing RNA-sequencing on murine rectal tumors colonized with C. albicans, we can better understand whether intratumoral changes in gene expression exist based on colonization of specific microbes. This study utilizes gut-to-tumor translocation and whole transcriptome analysis for a discovery-based approach to identify the effects of C. albicans on the host tumor. We established a rectal tumor model with C57BL/6 mice using MC38 rectal cancer cells subcutaneously injected on the right flank, local radiation to the tumor (standard-of-care for rectal cancer), and gavage with either C. albicans (Ca) or PBS. Fungal presence within tumors was validated by staining with calcofluor white and subsequently, tumors were sent for bulk RNA-sequencing to determine differences in gene expression using DeSeq2 and a gene set enrichment analysis (GSEA). In unsupervised analysis of gene expression differences between PBS-gavaged and Ca-gavaged with bulk RNA sequencing, tumors gavaged with C. albicans possessed unique gene expression and pathway analysis when compared to PBS-gavaged mice. Global differential gene expression showed 1,947 genes upregulated in Ca gavage and 593 genes upregulated in the PBS gavage (p < 0.05). C. albicans colonized tumors showed decreased expression in gene pathways relating to immune activation (interferon alpha response, IL-6 and STAT3 signaling), p53 expression, DNA repair, oxidative phosphorylation, NOTCH signaling, and apoptosis. We subsequently used a network-based approach to identify the most important genes driving the differences in the tumors, calculating the degree, closeness, and betweenness centralities. Several microbes have been regarded as potential contributors to decreased treatment response and survival in rectal cancer. In the case of tumors colonized with C. albicans, bulk RNA-sequencing indicates down regulation of gene pathways related to cell proliferation, immune activation, and DNA maintenance. Down regulation of gene pathways related to cell cycle control and arrest suggests that intratumoral colonization of C. albicans may causally affect tumorigenesis. Decreases in immune signaling in tumors suggest a potentially causal role of C. albicans immune suppression. These results highlight initial steps to understand how intratumoral C. albicans may be affecting rectal cancer progression and treatment response and serve as a technique to allow better insight to individual microbial impact on tumors. Citation Format: Alexander Loncar, Dennis Grencewicz, Rebecca Hoyd, Aaditya Pallerla, Nyelia Williams, Martin Benej, Yogita Mehra, Shiva Jahanbakhshi, Matthew Anderson, Nicholas Denko, Daniel Spakowicz. The effect of intra-tumoral Candida albicans on host gene expression [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 6842.

Abstract 995: Preservation of patient whole blood preserves cancer immune cell biology at single cell resolution

Abstract Blood is an easily accessible clinical sample type that helps inform treatments, investigate disease mechanisms, and monitor outcomes. Logistical challenges in the transportation and processing of blood samples impact data output from single cell RNA sequencing (scRNA-seq). Recent scRNA-seq studies have shown that significant changes in gene expression and immune cell populations occur in as little as a few hours post collection. Thus, there is a need for rapid preservation of blood upon collection before biological changes can occur. Existing preservation approaches compromise the cell membrane, making samples incompatible with single cell transcriptomic analyses. Here, we describe a novel workflow for fixation and long-term storage of whole blood, and isolation of peripheral blood mononuclear cells (PBMCs) from the fixed blood using a readily available, low-cost, high-throughput procedure. We then profile the gene expression of these cells using the fixation-compatible Single Cell Gene Expression Flex workflow. Importantly, this novel blood collection and preparation workflow eases blood transportation logistical constraints, allowing distributed sample collection and batched shipping of blood samples for scRNA-seq and potentially enabling large-scale translational research studies. We compared whole blood fixed immediately after collection using our workflow with clinical blood samples stored at ambient temperature. This revealed that immune cell populations and biological pathways shift significantly as early as five hours following sample collection, if not immediately stabilized. Across a time course of ambient temperature storage of whole blood without immediate stabilization, we observe significant upregulation of stress-related genes (FOS, JUN, CIRBP) in samples using Single Cell Gene Expression Flex profiling. Additionally, expression of a proto-oncogene TNFAIP3 was upregulated in whole blood stored at 20°C compared to samples stored at 4°C for the same lengths of time, unless samples were stabilized using the novel workflow shown here. This novel whole blood fixation method, coupled with automatable cell isolation methods and Single Cell Gene Expression Flex-enabled multiplexed single cell sequencing, will usher in a new age of economical, large-scale translational research studies that result in valuable clinical insights. Citation Format: Kelly Martin, Connor Kunihiro, Jawad Abousoud, Tingsheng Drennon, Yina Li, Sean Marrache, Nandhini Raman, Veronica Rodriguez, Paul Lund, Jens Durruthy Durruthy, Sarah Taylor, Andrew Kohlway, Peter Smibert, Dagmar Walter, Jill Herschleb. Preservation of patient whole blood preserves cancer immune cell biology at single cell resolution [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 995.

Abstract 4403: The crosstalk between the tumor microbiome and epigenomic changes in penile squamous cell carcinoma

Abstract Penile squamous cell carcinoma (PSCC) is approximately three times more prevalent in Puerto Rico when compared to other ethnic groups in the United States. Moreover, the mortality rate for PSCC among Puerto Rican men is significantly higher when compared to the US population. Infection with human papillomavirus (HPV) has been identified as a risk factor for an average of 48% of PSCC cases in Puerto Rico. The molecular etiology of HPV+ and HPV- PSCC remains poorly understood. To date, the role of the microbiota in the pathogenesis of PSCC is unknown, as there are no studies that characterize the microbiome in association with penile cancer. Furthermore, the role of DNA methylation, which is an epigenetic alteration that can be found in cancer cells that can lead to changes in gene expression and cellular function, is also unknown. Therefore, there is an urgent need to address this knowledge gap. This study aims to analyze the DNA methylation patterns and bacterial communities in HPV-positive and HPV-negative PSCC tissues from Puerto Rican men. DNA was extracted from twenty-one fresh PSCC tissue samples from Puerto Rican patients. HPV status and genotyping were determined using the DNA ELISA kit HPV SPF10 protocol. DNA methylation assay was performed using the Infinium Methylation EPIC v2.0 BeadChip Kit to identify and compare average DNA methylation levels (%) in 7 HPV-positive and 14 HPV-negative penile cancer samples. Microbiota analyses were performed using 16S rRNA genes with the Illumina MiSeq platform. Demultiplexed data was deposited in QIITA for quality control and bioinformatic analyses and downstream analyses were done in R and Qiime2. Our results demonstrated that 45 loci methylation patterns were significantly different between HPV-positive and HPV-negative samples, with an adjusted p-value <0.1 (Benjamini-Hochberg method). Three loci methylation patterns were significantly affected by species diversity and richness. The abundance of Firmicutes, Proteobacteria, Bacteroidetes, Fusobacteria, and Actinobacteria was individually associated with number of affected loci (27, 19, 12, 6, and 3, respectively). We found that HPV status is associated with methylation patterns and microbiome in PSCC in Puerto Rican men. Both changes may be involved in triggering inflammatory responses and oncogenesis. Although many challenges must be overcome to dissect the specific interactions of coinfecting bacteria and methylation patterns during the penile cancer infectious process, our findings demonstrate that microbes may be involved in these cellular processes. Citation Format: Jorge Viera-Vera, Yarelis M. Roque-Reyes, Daniel Santiago-Negron, María Sánchez-Vázquez, Yakshi Ortiz Maldonado, Gabriel Borges-Vélez, Jasmine Figueroa-Díaz, Carlos A. Rivera-López, Niki M. Zacharias Millward, María J. Marcos-Martínez, Filipa Godoy-Vitorino, Antonio Puras-Baez, Julie Dutil, Josué Pérez-Santiago, Magaly Martínez-Ferrer. The crosstalk between the tumor microbiome and epigenomic changes in penile squamous cell carcinoma [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 4403.

Abstract 1681: Characterizing signaling and localization of Daple-FLT3 gene fusion in leukemia cells

Abstract Receptor tyrosine kinases (RTKs) are cell surface receptors that regulate cell survival, cell proliferation, and cell migration upon ligand binding. Genetic mutations leading to hyperactivation of RTKs are often seen in cancer and allow signaling pathways to be constitutively active. In some hematological malignanices, the coiled-coil domain (CCD) of Daple, a cell signaling scaffold protein, has been found in gene fusions with the RTKs FLT3 and PDGFRB, and to the intracellular kinase JAK2. It is hypothesized that this gene fusion product causes the tyrosine kinase domain of FLT3 to become activated and mislocalizes in the cell, leading to rampant cell signaling of either the MAPK, AKT, and STAT5 signal transduction cascades. Using fluorescently tagged Daple-FLT3, it was shown that the gene fusion product is subcellularly localizes to the peri-centrosome space across all leukemia cell lines tested. Ectopic expression demonstrated activation of the kinase domain and subsequent increases in phosphorylation of STAT5α and AKT, but no significant increase in the phosphorylation of MAPK was observed. Further investigation is needed to identify direct substrates of the Daple-FLT3 gene fusion and transcriptional changes. Identifying the direct kinase substrates and insights gained through understanding the gene fusion localization, affects on cell signaling, and changes in gene expression, may unveil novel therapeutic strategies into targeting this protein in cancer. Citation Format: Michael Acquazzino, Jason Ear. Characterizing signaling and localization of Daple-FLT3 gene fusion in leukemia cells [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 1681.

Abstract 1112: Modulated dNTP pools and their influence on DNA repair mechanisms and apoptosis in therapy resistant cancers

Abstract Glioblastoma (GBM) is a deadly primary tumor of the brain, accounting for almost half of all diagnosed malignant gliomas. Ionizing radiation (IR) and some chemotherapeutics strategically target cancer cells by causing DNA double-strand breaks (DSBs). However, cancers like GBM often develop resistance to DSB-inducing therapeutics due to dysregulated DNA repair. Homologous Recombination (HR) is an error-free DSB-repair process consisting of proteins that are often dysregulated in GBM, causing overactive DNA-repair, therapy resistance, and poor patient outcomes. Proteins involved in the HR-repair process have been extensively investigated; however, therapeutic resistance remains common. Here, we provide an alternative approach to target DSB-resistant GBM by modulating the dNTP pool instead of solely targeting DNA-repair proteins. Our goal is to understand the interplay between dNTP pools and DSB- repair. dNTPs are a necessary constituent to repair DSBs; however, the role of the dNTP pool in DNA damage repair is not fully understood. Previous research shows that the dNTP pool remains unchanged after inducing DSBs, highlighting the importance of a tightly regulated dNTP pool. Using a neutral comet assay, we quantified accumulated double-stranded breaks in different treatment groups. We then analyzed these groups using immunofluorescent microscopy to examine distinct proteins involved in HR-mediated repair. We carried out RNA sequencing analysis to determine differential gene expression. We quantified cell viability and apoptotic cell populations via flow cytometry and Alamar blue assays. We determined protein interactions using immunoblotting and immunoprecipitation assays. We found that increasing the dNTP pool prior to IR treatment led to impaired DNA DSB repair in GBM cells as determined by a neutral comet assay. When analyzing key proteins involved in HR via immunofluorescence, we observed a significant decrease in RPA70 localization to the DNA damage site, indicating a disruption in end resection, a necessary phase of HR. Our RNA sequencing results show that increasing the dNTP pool in LN229 GBM cells prior to IR treatment caused significant changes in gene expression when compared to IR treatment alone. The most impacted pathways most were apoptosis, p53 cell cycle arrest, and DNA repair. The pathway analysis has identified genes of interest in the synergistic dNTP + IR treatment model. Significant increases in apoptosis and decreases in viability were observed 48 hours after inducing DSBs in LN229 cells with elevated dNTP pools. Not only do these data suggest that HR efficiency is reduced due to end resection impairment, but they also show that as a result, cell viability is destabilized due to prolonged DNA damage, resulting in apoptosis. The identification of this impairment may be essential in finding novel therapeutic approaches to sensitize therapy resistant GBM. Citation Format: Dominique Monroe, Mercy Kehinde-Ige, Edidiong Usoro, Arilyn Williams, Emily Steinbeck, Shelby Aycox, Huidong Shi, Waaqo Daddacha. Modulated dNTP pools and their influence on DNA repair mechanisms and apoptosis in therapy resistant cancers [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 1112.

Abstract 6459: Molecular profiling of advanced non-small cell lung cancer in response to first-line immune checkpoint inhibitors and/or chemotherapy using multimodal real-world data

Abstract Background: Up to 85% of lung cancer patients have non-small cell lung cancer (NSCLC). Standard of care for NSCLC includes immune checkpoint inhibitors (ICI) and/or platinum-based chemotherapy (CT). However, therapy success is limited with up to 70% of patients not responding to ICI. Mechanisms of resistance across treatments are not fully understood. In this study, we explore real-world data to characterize molecular and genomic changes in advanced NSCLC treated with ICI, ICI+CT, or CT. Methods: Stage III/IV NSCLC patients receiving first-line (1L) ICI, ICI+CT, or CT were identified from Tempus Labs, Inc.’s de-identified, multimodal real-world database. Patients’ solid tissue biopsies taken pre- or post-1L underwent next generation sequencing with the Tempus xT assays (DNAseq of 648 genes at 500x coverage and whole transcriptome RNAseq). Patients’ clinical and outcome data were abstracted from electronic health records. We analyzed changes in gene expression, pathway enrichment, estimated immune cell components, and somatic mutations in responders (complete/partial response) and non-responders (progression/stable disease) upon 1L treatment. Results: 1L non-responders (70%, 51%, and 47%) were identified across cohorts (143 ICI, 764 ICI+CT, and 228 CT, respectively). 58% of pre-1L biopsies were taken from distal metastatic tissues. Distinct pathways altered post-1L include the downregulated E2F target pathway in CT cohort, and upregulated TNFα/NFκB signaling and the hypoxia and protein secretion pathways in ICI cohort. Significant (FDR < 0.05) augmented expression was observed for 90, 23, and 65 genes in non-responders vs. responders post ICI, ICI+CT, and CT, respectively. RNAseq deconvolution reveals decreased plasma and CD4+ activated T cell fraction in metastatic biopsies, whereas increased CD4+ activated T cell and monocyte fraction was seen after treatment only in ICI cohort. Genes with oncogenic driver mutations reported in NSCLC were detected including TP53 (68%), KRAS (30%), STK11 (13%), EGFR (11%), CDKN2A (10%), KEAP1 (9%), and NF1 (7%). Of the 250 mutated genes, 72 (29%) were commonly not detected post-1L, whereas 38, 3, and 8 unique genes with loss of detectable mutations were identified post-1L of ICI, ICI+CT, and CT, respectively. Since loss of detectable mutations is a sign of loss of subpopulations of cancer cells hosting such mutations that succumb to therapy, these genetic mutations could be used to select patients who can benefit from such therapy. Conclusions: Distinct molecular characteristics including tumor immune components and genomic alterations are associated with 1L response in advanced NSCLC. Real-world data analyses provide opportunity to explore distinct mechanisms of therapy resistance and identify potential biomarkers of therapy response for further validation in clinical studies. Citation Format: Xiaoyong Fu, Jordan Kardos, Paola Correa, Min Wang, Li, Jackson Egen, Shahed Iqbal. Molecular profiling of advanced non-small cell lung cancer in response to first-line immune checkpoint inhibitors and/or chemotherapy using multimodal real-world data [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 6459.

Identification of potential biomarkers for idiopathic pulmonary arterial hypertension using single-cell and bulk RNA sequencing analysis.

Idiopathic pulmonary arterial hypertension (IPAH) is a rare and severe cardiopulmonary disease with a challenging prognosis, and its underlying pathogenesis remains elusive. A comprehensive understanding of IPAH is crucial to unveil potential diagnostic markers and therapeutic targets. In this study, we investigated cellular heterogeneity and molecular pathology in IPAH using single-cell RNA sequencing (scRNA-seq) analysis. Our scRNA-seq results revealed significant alterations in three crucial signaling pathways in IPAH: the hypoxia pathway, TGF β pathway, and ROS pathway, primarily attributed to changes in gene expression within arterial endothelial cells. Moreover, through bulk RNA sequencing analysis, we identified differentially expressed genes (DEGs) enriched in GO and KEGG pathways, implicated in regulating cell adhesion and oxidative phosphorylation in IPAH lungs. Similarly, DEGs-enriched pathways in IPAH arterial endothelial cells were also identified. By integrating DEGs from three IPAH datasets and applying protein-protein interaction (PPI) analysis, we identified 12 candidate biomarkers. Subsequent validation in two additional PAH datasets led us to highlight five potential biomarkers (CTNNB1, MAPK3, ITGB1, HSP90AA1, and DDX5) with promising diagnostic significance for IPAH. Furthermore, real-time quantitative polymerase chain reaction (RT-qPCR) confirmed significant differences in the expression of these five genes in pulmonary arterial endothelial cells from PAH mice. In conclusion, our findings shed light on the pivotal role of arterial endothelial cells in the development of IPAH. Furthermore, the integration of single-cell and bulk RNA sequencing datasets allowed us to pinpoint novel candidate biomarkers for the diagnosis of IPAH. This work opens up new avenues for research and potential therapeutic interventions in IPAH management.

Abstract 1282: Gavage with Candida albicans leads to fungal colonization of colorectal tumors and decreased response to radiotherapy

Abstract The host microbiome in the gut and tumors have been shown to affect tumor growth and therapeutic response in cancer. Furthermore, the presence of specific fungal taxa are associated with tumor hypoxia, tumor progression, therapeutic response, and clinical outcomes in colorectal cancer (CRC). Preliminary data from our group found that the presence of Candida species increased tumor hypoxia and decreased overall survival in CRC. However, whether intratumoral Candida drive, support, or simply inhabit tumors with poor prognoses remains unclear. Here, we investigate a casual role for Candida albicans in tumor progression and therapy response using a syngeneic mouse model of microsatellite-instability high (MSI-H) colorectal cancer. We subcutaneously implanted MC38 colorectal cancer cells into C57BL/6 mice and then orally gavaged these mice with C. albicans, Saccharomyces cerevisiae, or PBS. The site of tumor formation was locally irradiated once (7.5 Gy), and growth of the tumor was measured over time. Differences in tumor volume were assessed by longitudinal mixed-effect models. Tumor sections were stained for fungi using calcofluor white (CFW) and underwent bulk RNA sequencing to detect differential gene expression, which were interpreted using gene set enrichment analysis (GSEA). Mice gavaged with C. albicans showed decreased response to radiation compared to mice gavaged with either S. cerevisiae (p<0.05) or PBS (p<0.001). Additionally, hyphae were observed in murine tumors gavaged with C. albicans, suggesting translocation of gavaged C. albicans from the gut to tumors. Further, tumors from mice gavaged with C. albicans displayed unique gene expression profiles, including decreased interferon alpha and IL-6 and STAT3 signaling, decreased oxidative phosphorylation, and decreased apoptosis-related gene expression. Here, we show that C. albicans may confer resistance to radiation therapy and affects immune and cancer cell activity in the MC38 (MSI-H) syngeneic in vivo model of colorectal cancer. Further, we show that hyphal fungi can be visualized in heterotopic murine tumors from our C. albicans gavage condition. These data establish that fungi can translocate from the gut to distal tumor sites, and that upon translocation, changes in gene expression and therapy response are observed. Future directions will explore the mechanism by which these effects occur and whether these findings can be leveraged to improve radiotherapy outcomes. Citation Format: Dennis J. Grencewicz, Alexander Loncar, Rebecca Hoyd, Aaditya Pallerla, Nyelia Williams, Martin Benej, McKenzie Kreamer, Yogita Mehra, Shiva Jahanbakhshi, Matthew Anderson, Nicholas Denko, Daniel Spakowicz. Gavage with Candida albicans leads to fungal colonization of colorectal tumors and decreased response to radiotherapy [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 1282.

Abstract 4130: Targeting epigenetically-driven inflammation for PDAC metastasis prevention in high-risk individuals

Abstract Background: Pancreatic ductal adenocarcinoma (PDAC) is a lethal cancer with a dire prognosis, in large part due to the late stage at which it is diagnosed in most patients. High-risk individuals (HRIs) identified through family history or germline genetic testing are candidates for imaging-based screening, yet even with intensive surveillance, metastasis often occurs between scans. Our study aims to address this critical clinical challenge by investigating the epigenetic determinants of PDAC metastasis and developing novel strategies for metastasis prevention in HRIs. Methods: Innovative transplantation models of PDAC liver and peritoneal metastasis incorporating DNA barcodes for subclonal tracking were developed to facilitate the identification of subclones with high or low metastatic potential. An in-depth epigenomic characterization and comparison of these subclones was performed utilizing assay for transposase-accessible chromatin with sequencing (ATAC-seq) and RNA-seq. Results: Metastasis-high subclones demonstrate widespread chromatin accessibility differences relative to their metastasis-low peers. These differences are linked to expression changes for genes involved in motility, differentiation, survival, and particularly inflammation. Top epigenetically activated genes in metastasis-high subclones include the pro-inflammatory cytokines IL-1α and IL-23α and the pro-inflammatory cytokine receptor IL-18R1. Discussion: These findings highlight the role of epigenetic changes in PDAC metastasis, especially activation of inflammatory pathways resulting from altered chromatin accessibility. These insights provide a foundation for exploring anti-inflammatory agents for PDAC metastasis prevention. Targeting inflammation, alongside imaging-based screening, could significantly improve outcomes for HRIs. Citation Format: Jesse Handler, Reza Kalhor. Targeting epigenetically-driven inflammation for PDAC metastasis prevention in high-risk individuals [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 4130.

Abstract 444: Lipid exposure re-wires cellular metabolism away from glycolysis toward the serine pathway conferring oncogenic properties to non-transformed breast cells

Abstract Introduction. A lipid metabolism gene signature is associated with the risk of estrogen negative breast cancer (ER-BC). In vitro, lipid exposure alters histone methylation affecting gene expression and increases flux through various metabolic reactions including those involved in serine, one-carbon, glycine (SOG) and methionine. We hypothesized that the metabolism of lipids in preference to glucose and glutamine results in a metabolic shift toward the serine pathway increasing S-adenosylmethionine (SAM) leading to histone methylation increases and changes in gene expression. Methods. MCF-10A cells exposed to octanoic acid (OA) were utilized for U13C-glucose tracing. SAM, glutathione (GSH) and 2-hydroxyglutarate (2-HG) concentrations were measured following treatment with OA ± the PHGDH inhibitor CBR-5884. ROS-induced redox changes were monitored live in cells transduced with ORP1-roGFP2 vectors. CUT&RUN was performed for H3K4me3. Expression of OA-induced genes was measured by rt-qPCR upon exposure to OA ± CBR-5884 or OA ± the histone methyltransferase (HMT) inhibitor Piribedil. Alkaline comet assay was done to detect DNA breaks. Single-cell RNA-seq (scRNAseq) was performed on tissue-derived breast microstructures exposed to ± OA. Results. Upon OA treatment, the Cancer index increased and 1C-THF was redirected to the methionine cycle increasing flux to methylation. OA significantly increased the production of SAM, GSH and 2-HG after 15 min. Blocking the first enzyme in the serine pathway, PHGDH, prevented these increases. After 5 min OA exposure, mitochondrial and nuclear ROS increased significantly (p < 0.0001), peaking at 15 min. H3K4me3 CUT&RUN revealed 661 differential peaks (FDR < 0.05) comparing OA to control. 73% of H3K4me3 OA-associated peaks were in regulatory regions of OA-induced genes (FDR < 0.01) including neural, EMT and ER- BC related genes. Motif analysis revealed an overrepresentation of binding sites for serine pathway transcriptional activators ATF3/4 (p < 0.05). Blocking PHGDH or HMT prevented OA-induced gene expression changes. Alkaline comet assay showed that OA significantly increased comet tails. scRNAseq revealed OA increased the numbers of cells within all cell clusters expressing ATF3 and PHGDH. Also observed was an increase in the percentage of basal BSL1, luminal progenitor LP3 and hormone sensing HS1 cells. Conclusions. Metabolism of OA results in a metabolic shift toward the SOG and methionine increasing the production of SAM, GSH and 2-HG which have implications for oncogenesis. The increased SAM fosters epigenetic phenotypic plasticity via altered histone methylation. The increased proportion of specific cell types likely reflects the survival of cells able to mitigate oxidative stress. Increased 2-HG may produce metabolic BRCAness by inhibiting 2-oxoglutarate-dependent dioxygenases. Citation Format: Mariana Bustamante Eduardo, Gannon Cottone, Shiyu Liu, Flavio R. Palma, Maria Paula Zappia, Abul B.M.M.K. Islam, Elizaveta V. Benevolenskaya, Maxim V. Frolov, Jason Locasale, Marcelo G. Bonini, Navdeep S. Chandel, Seema Khan, Susan Clare. Lipid exposure re-wires cellular metabolism away from glycolysis toward the serine pathway conferring oncogenic properties to non-transformed breast cells [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 444.

Abstract 5831: The TLE1 transcriptional and epigenetic machinery contributes to EGFR targeted therapy resistance in human lung adenocarcinoma

Abstract In human lung adenocarcinoma that carry Epidermal Growth Factor Receptor (EGFR) sensitizing mutations, targeting the EGFR pathway with the use of EGFR tyrosine kinase inhibitors (EGFR-TKIs) has emerged as a promising therapeutic strategy providing initial clinical benefit to many patients. Unfortunately, resistance to EGFR-TKIs eventually develops leading to disease progression. In addition to genetic mutations, transcriptional and epigenetic mediated changes in gene expression remain an important mechanism contributing to EGFR-TKI resistance. Here, we report a novel function of the transcriptional corepressor Transducin-Like Enhancer of Split-1 (TLE1) in mediating EGFR-TKI resistance in EGFR mutant LUAD cells through its survival promoting gene transcriptional program. In EGFR mutant, EGFR TKI sensitive LUAD cells, sole activation of the TLE1 nuclear function attenuates EGFR TKI sensitivity with concomittant reduction of EGFR-TKI-mediated apoptosis. Conversely, downregulation of endogenous TLE1 expression via siRNAs/shRNAs and deletion of TLE1 gene via CRISPR-Cas9 in EGFR-mutant, EGFR-TKI resistant cells partially restore EGFR-TKI sensitivity via induction of EGFR-TKI apoptosis. Mechanistically, the anti-apoptosis promoting gene transcriptional program of TLE1 is dependent on its functional interaction with the transcriptional repressor HES-1, a downstream Notch target which has been associated with relapse in LUAD patients following EGFR-TKI treatment. Collectively, these studies indicate the TLE1 corepressor as a determinant of resistance to EGFR targeted therapy and raise the possibility that inhibiting TLE1 nuclear function may serve as an adjuct therapy to circumvent EGFR-TKI resistance. Citation Format: Hector Ramos Biliran, Xin Yao, Nasir Roberts, Prince Iheukwumere, Renwei Chen, Ma. Carmela Dela Cruz. The TLE1 transcriptional and epigenetic machinery contributes to EGFR targeted therapy resistance in human lung adenocarcinoma [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 5831.