Hypermetabolic state is associated with circadian rhythm disruption in mouse and human cancer cells

Crosstalk between cellular metabolism and circadian rhythms is a fundamental building block of multicellular life, and disruption of this reciprocal communication could be relevant to degenerative disease, including cancer. Here, we investigated whether maintenance of circadian rhythms depends upon specific metabolic pathways, particularly in the context of cancer. We found that in adult mouse fibroblasts, ATP levels were a major contributor to overall levels of a clock gene luciferase reporter, although not necessarily to the strength of circadian cycling. In contrast, we identified significant metabolic control of circadian function in an in vitro mouse model of pancreatic adenocarcinoma. Metabolic profiling of a library of congenic tumor cell clones revealed significant differences in levels of lactate, pyruvate, ATP, and other crucial metabolites that we used to identify candidate clones with which to generate circadian reporter lines. Despite the shared genetic background of the clones, we observed diverse circadian profiles among these lines that varied with their metabolic phenotype: the most hypometabolic line had the strongest circadian rhythms while the most hypermetabolic line had the weakest rhythms. Treatment of these tumor cell lines with bezafibrate, a peroxisome proliferator-activated receptor (PPAR) agonist shown to increase OxPhos, decreased the amplitude of circadian oscillation in a subset of tumor cell lines. Strikingly, treatment with the Complex I antagonist rotenone enhanced circadian rhythms only in the tumor cell line in which glycolysis was also low, thereby establishing a hypometabolic state. We further analyzed metabolic and circadian phenotypes across a panel of human patient-derived melanoma cell lines and observed a significant negative association between metabolic activity and circadian cycling strength. Together, these findings suggest that metabolic heterogeneity in cancer directly contributes to circadian function, and that high levels of glycolysis or OxPhos independently disrupt circadian rhythms in these cells.

Intratumoral Administration of High-Concentration Nitric Oxide and Anti-mPD-1 Treatment Improves Tumor Regression Rates and Survival in CT26 Tumor-Bearing Mice

BACKGROUND

Immune checkpoint inhibitors have transformed clinical oncology. However, their use is limited as response is observed in only ~20-50% of patients. Previously, we demonstrated that treating CT26 tumor-bearing mice with ultra-high-concentration gaseous nitric oxide (UNO) followed by tumor resection stimulated antitumor immune responses. Accordingly, UNO may improve tumor response to immune checkpoint inhibitors. Here, we investigated the ability of UNO to improve the efficacy of a programmed cell death protein-1 (PD-1) antibody in vitro and in treating CT26 tumor-bearing mice.

METHODS

CT26 cells were injected into the flank of Balb/c mice (n = 15-16 per group). On day 6, CT26 cells were injected into the contralateral flank, and anti-mPD-1 injections commenced. Primary tumors were treated with intratumoral UNO on day 8. Tumor volume, response rates, toxicity, and survival were monitored.

RESULTS

(1) Short exposure to 25,000-100,000 parts per million (ppm) UNO in vitro resulted in significant upregulation of PD-L1 expression on CT26 cells. (2) UNO treatment in vivo consistently reduced cell viability in CT26 tumors. (3) Treatment reduced regulatory T-cell (Treg) levels in the tumor and increased levels of systemic M1 macrophages. UNO responders had increased CD8+ T-cell tumor infiltration. (4) Nine days after treatment, primary tumor growth was significantly lower in the combination arm vs. anti-mPD-1 alone (p = 0.0005). (5) Complete tumor regression occurred in 8/15 (53%) of mice treated with a combination of 10 min UNO and anti-mPD-1, 100 days post-treatment, compared to 4/16 (25%) of controls treated with anti-mPD-1 alone (p = 0.1489). (6) There was no toxicity associated with UNO treatment. (7) Combination treatment showed a trend toward increased survival 100 days post-treatment compared to anti-mPD-1 alone (p = 0.0653).

CONCLUSION

Combining high-concentration NO and immune checkpoint inhibitors warrants further assessment especially in tumors resistant to checkpoint inhibitor therapy.

SWIP-a stabilized window for intravital imaging of the murine pancreas

Pancreatitis and pancreatic ductal adenocarcinoma (PDAC) are grave illnesses with high levels of morbidity and mortality. Intravital imaging (IVI) is a powerful technique for visualizing physiological processes in both health and disease. However, the application of IVI to the murine pancreas presents significant challenges, as it is a deep, compliant, visceral organ that is difficult to access, easily damaged and susceptible to motion artefacts. Existing imaging windows for stabilizing the pancreas during IVI have unfortunately shown poor stability for time-lapsed imaging on the minutes to hours scale, or are unable to accommodate both the healthy and tumour-bearing pancreata. To address these issues, we developed an improved stabilized window for intravital imaging of the pancreas (SWIP), which can be applied to not only the healthy pancreas but also to solid tumours like PDAC. Here, we validate the SWIP and use it to visualize a variety of processes for the first time, including (1) single-cell dynamics within the healthy pancreas, (2) transformation from healthy pancreas to acute pancreatitis induced by cerulein, and (3) the physiology of PDAC in both autochthonous and orthotopically injected models. SWIP can not only improve the imaging stability but also expand the application of IVI in both benign and malignant pancreas diseases.

Bcl-xL Enforces a Slow-Cycling State Necessary for Survival in the Nutrient-Deprived Microenvironment of Pancreatic Cancer

Solid tumors possess heterogeneous metabolic microenvironments where oxygen and nutrient availability are plentiful (fertile regions) or scarce (arid regions). While cancer cells residing in fertile regions proliferate rapidly, most cancer cells in vivo reside in arid regions and exhibit a slow-cycling state that renders them chemoresistant. Here, we developed an in vitro system enabling systematic comparison between these populations via transcriptome analysis, metabolomic profiling, and whole-genome CRISPR screening. Metabolic deprivation led to pronounced transcriptional and metabolic reprogramming, resulting in decreased anabolic activities and distinct vulnerabilities. Reductions in anabolic, energy-consuming activities, particularly cell proliferation, were not simply byproducts of the metabolic challenge, but rather essential adaptations. Mechanistically, Bcl-xL played a central role in the adaptation to nutrient and oxygen deprivation. In this setting, Bcl-xL protected quiescent cells from the lethal effects of cell-cycle entry in the absence of adequate nutrients. Moreover, inhibition of Bcl-xL combined with traditional chemotherapy had a synergistic antitumor effect that targeted cycling cells. Bcl-xL expression was strongly associated with poor patient survival despite being confined to the slow-cycling fraction of human pancreatic cancer cells. These findings provide a rationale for combining traditional cancer therapies that target rapidly cycling cells with those that target quiescent, chemoresistant cells associated with nutrient and oxygen deprivation.

SIGNIFICANCE

The majority of pancreatic cancer cells inhabit nutrient- and oxygen-poor tumor regions and require Bcl-xL for their survival, providing a compelling antitumor metabolic strategy.

MYC Hyperactivates Wnt Signaling in APC/CTNNB1-Mutated Colorectal Cancer Cells through miR-92a-Dependent Repression of DKK3

Activation of Wnt signaling is among the earliest events in colon cancer development. It is achieved either via activating mutations in the CTNNB1 gene encoding β-catenin, the key transcription factor in the Wnt pathway, or most commonly by inactivating mutations affecting APC, a major β-catenin binding partner and negative regulator. However, our analysis of recent Pan Cancer Atlas data revealed that CTNNB1 mutations significantly co-occur with those affecting Wnt receptor complex components (e.g., Frizzled and LRP6), underscoring the importance of additional regulatory events even in the presence of common APC/CTNNB1 mutations. In our effort to identify non-mutational hyperactivating events, we determined that KRAS-transformed murine colonocytes overexpressing direct β-catenin target MYC show significant upregulation of the Wnt signaling pathway and reduced expression of Dickkopf 3 (DKK3), a reported ligand for Wnt co-receptors. We demonstrate that MYC suppresses DKK3 transcription through one of miR-17-92 cluster miRNAs, miR-92a. We further examined the role of DKK3 by overexpression and knockdown and discovered that DKK3 suppresses Wnt signaling in Apc-null murine colonic organoids and human colon cancer cells despite the presence of downstream activating mutations in the Wnt pathway. Conversely, MYC overexpression in the same cell lines resulted in hyperactive Wnt signaling, acquisition of epithelial-to-mesenchymal transition markers, and enhanced migration/invasion in vitro and metastasis in a syngeneic orthotopic mouse colon cancer model. IMPLICATIONS: Our results suggest that the MYC→miR-92a-|DKK3 axis hyperactivates Wnt signaling, forming a feed-forward oncogenic loop.

Dissecting phenotypic transitions in metastatic disease via photoconversion-based isolation

Cancer patients often harbor occult metastases, a potential source of relapse that is targetable only through systemic therapy. Studies of this occult fraction have been limited by a lack of tools with which to isolate discrete cells on spatial grounds. We developed PIC-IT, a photoconversion-based isolation technique allowing efficient recovery of cell clusters of any size – including single-metastatic cells – which are largely inaccessible otherwise. In a murine pancreatic cancer model, transcriptional profiling of spontaneously arising microcolonies revealed phenotypic heterogeneity, functionally reduced propensity to proliferate and enrichment for an inflammatory-response phenotype associated with NF-κB/AP-1 signaling. Pharmacological inhibition of NF-κB depleted microcolonies but had no effect on macrometastases, suggesting microcolonies are particularly dependent on this pathway. PIC-IT thus enables systematic investigation of metastatic heterogeneity. Moreover, the technique can be applied to other biological systems in which isolation and characterization of spatially distinct cell populations is not currently feasible.

Epigenetic and Transcriptional Control of the Epidermal Growth Factor Receptor Regulates the Tumor Immune Microenvironment in Pancreatic Cancer

Although immunotherapy has revolutionized cancer care, patients with pancreatic ductal adenocarcinoma (PDA) rarely respond to these treatments, a failure that is attributed to poor infiltration and activation of T cells in the tumor microenvironment (TME). We performed an in vivo CRISPR screen and identified lysine demethylase 3A (KDM3A) as a potent epigenetic regulator of immunotherapy response in PDA. Mechanistically, KDM3A acts through Krueppel-like factor 5 (KLF5) and SMAD family member 4 (SMAD4) to regulate the expression of the epidermal growth factor receptor (EGFR). Ablation of KDM3A, KLF5, SMAD4, or EGFR in tumor cells altered the immune TME and sensitized tumors to combination immunotherapy, whereas treatment of established tumors with an EGFR inhibitor, erlotinib, prompted a dose-dependent increase in intratumoral T cells. This study defines an epigenetic-transcriptional mechanism by which tumor cells modulate their immune microenvironment and highlights the potential of EGFR inhibitors as immunotherapy sensitizers in PDA. SIGNIFICANCE: PDA remains refractory to immunotherapies. Here, we performed an in vivo CRISPR screen and identified an epigenetic-transcriptional network that regulates antitumor immunity by converging on EGFR. Pharmacologic inhibition of EGFR is sufficient to rewire the immune microenvironment. These results offer a readily accessible immunotherapy-sensitizing strategy for PDA.This article is highlighted in the In This Issue feature, p. 521.

Global Regulation of the Histone Mark H3K36me2 Underlies Epithelial Plasticity and Metastatic Progression

Epithelial plasticity, reversible modulation of a cell's epithelial and mesenchymal features, is associated with tumor metastasis and chemoresistance, leading causes of cancer mortality. Although different master transcription factors and epigenetic modifiers have been implicated in this process in various contexts, the extent to which a unifying, generalized mechanism of transcriptional regulation underlies epithelial plasticity remains largely unknown. Here, through targeted CRISPR/Cas9 screening, we discovered two histone-modifying enzymes involved in the writing and erasing of H3K36me2 that act reciprocally to regulate epithelial-to-mesenchymal identity, tumor differentiation, and metastasis. Using a lysine-to-methionine histone mutant to directly inhibit H3K36me2, we found that global modulation of the mark is a conserved mechanism underlying the mesenchymal state in various contexts. Mechanistically, regulation of H3K36me2 reprograms enhancers associated with master regulators of epithelial-to-mesenchymal state. Our results thus outline a unifying epigenome-scale mechanism by which a specific histone modification regulates cellular plasticity and metastasis in cancer. SIGNIFICANCE: Although epithelial plasticity contributes to cancer metastasis and chemoresistance, no strategies exist for pharmacologically inhibiting the process. Here, we show that global regulation of a specific histone mark, H3K36me2, is a universal epigenome-wide mechanism that underlies epithelial-to-mesenchymal transition and mesenchymal-to-epithelial transition in carcinoma cells. These results offer a new strategy for targeting epithelial plasticity in cancer.This article is highlighted in the In This Issue feature, p. 747.

Abstract A03: All the roads bring to Rome: How acetyl-CoA metabolism supports multistep pancreatic carcinogenesis

Mutant KRAS is thought to initiate pancreatic tumorigenesis, orchestrating a program that leads to cell de-differentiation, proliferation, and symbiotic cooperation with neighboring cells, enabling the cancer cells to thrive in a particularly harsh microenvironment. Recent studies have highlighted the role of metabolites in regulating the epigenome. Although oncogenic KRAS is known to reprogram cellular metabolism, the role of metabolic control of the epigenome in pancreatic tumorigenesis is poorly understood. We showed that expression of KRASG12D in mouse pancreas promotes elevated histone acetylation levels in pancreatic acinar cells, and that this precedes tumor development. We hypothesized that augmented acetyl-CoA metabolism may play a role in facilitating pancreatic tumorigenesis. To test this, we generated mice deficient for Acly (acetyl-CoA producing enzyme) in pancreas (Pdx1-Cre; Aclyf/f mice). In the context of KRASG12D expression, ACLY deficiency reduces histone acetylation levels in pancreatic acinar cells and impairs formation of neoplastic lesions. ACLY deficiency also impairs pancreatitis-induced tumor development. In testing roles for acetyl-CoA-dependent processes in ADM, we found that targeting either histone acetylation by BET inhibition or cholesterol synthesis with statins suppressed tumor onset. In vivo, response to BET and cholesterol synthesis blockade is associated with recruitment of CD8+ T-cells. The findings indicate that ACLY-dependent metabolic and epigenetic remodeling promote tumor development and point to the potential to target acetyl-CoA metabolism for pancreatic cancer. Potential role of tumor-infiltrating leukocytic cells in modulating acetyl-CoA metabolism in vivo, cancer cell-autonomous mechanisms for acetyl-CoA levels regulation, as well as consequences for therapeutic targeting and dietary interventions, will be discussed.

Citation Format: Alessandro Carrer, Sophie Trefely, Steven Zhao, Sydney Campbell, Yogev Sela, Simone Sidoli, Benjamin A. Garcia, Nathaniel W. Snyder, Ben Z. Stanger, Kathryn E. Wellen. All the roads bring to Rome: How acetyl-CoA metabolism supports multistep pancreatic carcinogenesis [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr A03.

Abstract A28: Investigation of tumor-cell-intrinsic factors regulating immune infiltration and response to immunotherapy in pancreatic cancer

Resistance to immunotherapy is one major problem of current clinical care for cancer patients. While T-cell abundance is essential for tumor responsiveness to immunotherapy, factors that dictate T-cell infiltration in tumor microenvironments are not fully understood. To understand the tumor cell-intrinsic factors underlying the heterogeneity of tumor immunity and sensitivity to immunotherapy, we established a new experimental system by generating a library of congenic pancreatic tumor cell clones from a genetic mouse model driven by mutant Kras and p53. These tumor cell clones robustly formed implanted tumors that recapitulated the T cell-inflamed and non-T cell-inflamed tumor microenvironments in human patients, associated with distinct patterns of infiltration by T cells and myeloid cells. We found that the non-T cell-inflamed phenotype was dominant over the T cell-inflamed phenotype in the local tumor microenvironment. Both quantitative and qualitative features, specifically expression of markers of prior TCR activation, of intratumoral CD8+ T cells predicted the response to immunotherapies. An integrated transcriptomic and epigenetic analysis revealed that tumor cell-intrinsic expression of the chemokine CXCL1 as a major determinant of the non-T cell-inflamed microenvironment, and ablation of tumor cell-intrinsic CXCL1 promoted T-cell infiltration and sensitivity to a combination of chemotherapies, CD40 agonist, and checkpoint blockades. Similarly, we identified tumor cell-intrinsic EPHA2 and PTGS2 as key regulators of immune infiltration and immunotherapy response in our experimental system. Ablation of tumor cell-intrinsic EPHA2 or PTGS2 enhanced T-cell infiltration and suppressed myeloid cell infiltration in implanted pancreatic tumors, and increased sensitivities of tumors to the combined immunotherapy. These results demonstrated that heterogeneity of tumor immune phenotypes is driven by tumor cell-intrinsic factors that can be manipulated to influence the outcome of immunotherapies. The observation that non-T cell-inflamed phenotype is dominant emphasized the importance of targeting mechanisms driving T-cell low phenotype for improving immunotherapy response.

Citation Format: Jinyang Li, Katelyn T Byrne, Nune Markosyan, Taiji Yamazoe, Fangxue Yan, Zeyu Chen, Yu H. Sun, Jeffrey Lin, Yogev Sela, Robert J. Norgard, Salina Yuan, Allyson J. Merrell, John W. Tobias, Robert H. Vonderheide, Ben Z. Stanger. Investigation of tumor-cell-intrinsic factors regulating immune infiltration and response to immunotherapy in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr A28.

Abstract B33: Tumor cell-intrinsic EPHA2 suppresses antitumor immunity by regulating PTGS2 (COX-2) in pancreatic adenocarcinoma

Pancreatic adenocarcinoma (PDA) is highly refractory to immunotherapy, a consequence of T-cell exclusion from the tumor microenvironment (TME). Based on a pathway analysis of human PDAs, we hypothesized that the receptor tyrosine kinase ephrin A2 (EPHA2) drives this immunosuppressive TME, as its expression negatively correlated with CD8A, CD3, PRF1, GZMB, and patient survival (EPHA2low/EPHA2high log rank hazard ratio 0.115, 95% CI of ratio 0.0315-0.416, TCGA dataset). Deletion of Epha2 in tumor cells increased T-cell influx, decreased the number of infiltrating myeloid suppressor cells, and sensitized tumors to therapy. Treatment of Epha2-deficient tumors with combination of chemo and immunotherapy resulted in suppressed tumor growth or tumor regression in up to 85% of cases. Examination of Epha2-dependent gene expression nominated Ptgs2 as a downstream mediator of T-cell exclusion. Like EPHA2, PTGS2 exhibited a negative correlation with intratumoral T cells, cytolytic activity, and patient survival (PTGS2low/PTGS2high log rank hazard ratio 0.152, 95% CI of ratio 0.054-0.430, TCGA dataset). KPCY mice (mutant KrasG12D (K), dominant negative p53R172H (P), Cre recombinase (C), YFP protein (Y)) deficient in pancreatic ductal cell Ptgs2 had significantly increased overall survival compared to Ptgs2 sufficient KPCY mice (Ptgs2def/Ptgs2suff log rank hazard ratio 0.5001, 95% CI of ratio 0.294-0.851). Ptgs2 deletion promoted T-cell influx in both autochthonous and implanted tumors. Inversely, overexpression of Ptgs2 decreased the number of tumor-infiltrating T cells, increased the proportion of suppressor myeloid cells, and conferred resistance to the combination therapy. Remarkably, pharmacologic inhibition of PTGS2 sensitized the tumors to immunotherapy, suppressing the growth of implanted tumors and increasing the survival of treated KPCY mice (median survival of untreated and treated mice 151 and 199 days, respectively; survival curve log rank p-value= 0.017). These studies suggest that a tumor cell-intrinsic EPHA2-PTGS2 signaling axis regulates the immune TME in PDA and suggests that a two-step approach targeting T-cell exclusion and exhaustion holds promise for this treatment-refractory disease.

Citation Format: Nune Markosyan, Jinyang Li, Yu Sun, Lee Richman, Jeffrey Lin, Fangxue Yan, Liz Quinones, Yogev Sela, Taiji Yamazoe, Naomi Gordon, John Tobias, Katelyn Byrne, Andrew Rech, Garret FitzGerald, Ben Stanger, Robert Vonderheide. Tumor cell-intrinsic EPHA2 suppresses antitumor immunity by regulating PTGS2 (COX-2) in pancreatic adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr B33.

Abstract C50: Dissecting vulnerabilities of pancreatic tumors’ silent fraction unravels secrets of an alternative cell state

Tumors contain a heterogeneous mixture of live cells that are either undergoing proliferation or reside in a nonproliferative state. Cells that do not divide are often associated with increased chemoresistance, challenging therapies that target rapidly proliferating cells. In pancreatic cancer, paucity of blood vessels frequently generates hypoperfused, “arid” regions that constrain tumor cell metabolism and proliferation. Nonetheless, experimental conditions for studying tumor cells in vitro typically mimic well-nourished, “fertile” environments optimized for supporting proliferating cells rather than the more prevalent quiescent state. Characterization of the poorly vascularized KPC model confirmed that the quiescent phenotype is common and is strongly correlated to reduced tissue perfusion. To formulate culture conditions that will emulate the arid microenvironment associated with the nonproliferative state in vitro, we systematically deprived various nutrients from tumor cells and established the necessary components for attaining cell quiescence. Deprivation of amino acids on top of glucose, oxygen, and serum levels was essential for obtaining a complete and reversible cell cycle arrest without loss of viability. Cell cycle arrest was accompanied by a number of physiologic adaptations. Metabolomic analysis indicated reduction in the levels of TCA cycle and mevalonate pathway intermediates indicative of increased reliance on nonglycolytic metabolism. In addition, free amino acid pools were diminished and tumor cells exhibited a significant increase in autophagic flux and micropinocytosis, suggesting that amino acid availability is limited under arid conditions. Concomitant with reduced proliferation and metabolic rewiring, tumor cells under arid conditions exhibited remarkable resistance to gemcitabine. To explore alternative strategies to target these nonproliferating pancreatic tumor cells, we performed a comprehensive genome-wide CRISPR/Cas9-based genetic screen and compared vulnerabilities under ”fertile” and “arid” conditions. Functional annotation of sgRNAs depleted under arid conditions indicated a striking dependence on oxidative phosphorylation for survival. Remarkably, our analysis also revealed that a number of targetable genetic and epigenetic programs driving cell cycle progression were not essential and, in some instances, even hazardous for cells under arid conditions. These results suggest that pancreatic tumor cells that cease proliferation in a nutrient-depleted environment are physiologically rewired and may exhibit a distinct drug response profile from rapidly proliferating cells. The experimental model we developed allows investigation of this dominant yet understudied cell population and may serve as a platform for identification of agents targeting the quiescent fraction of tumors.

Citation Format: Yogev Sela, Jinyang Li, Miriam Doepner, Shivahamy Maheswaran, Clementina Mesaros, Ian Blair, Ophir Shalem, Ben Stanger. Dissecting vulnerabilities of pancreatic tumors’ silent fraction unravels secrets of an alternative cell state [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr C50.

Abstract B38: Calcium signaling induces a partial EMT in pancreatic ductal adenocarcinoma

Metastasis and chemoresistance—the two main reasons for the high mortality of cancer—are associated with a form of cellular plasticity known as epithelial-to-mesenchymal transition (EMT). Cancer cells undergoing EMT become invasive, facilitating metastasis, and undergo a shift in their vulnerability to antineoplastic drugs. In recent work, it has been shown that EMT does not involve a single mechanism but rather a diversity of programs, yielding a continuum of cell phenotypes along the epithelial-mesenchymal spectrum. We previously developed a lineage-traced model of pancreatic ductal adenocarcinoma (PDA) to study EMT in the context of stochastically-arising tumors. As expected, epithelial-mesenchymal plasticity in some tumors involves transcriptional repression of the epithelial state, resulting in a “classical EMT” (C-EMT) phenotype. Surprisingly, however, epithelial-mesenchymal plasticity in the majority of tumors involves post-transcriptional repression of the epithelial state, resulting in a “partial EMT” (P-EMT) phenotype. These two plasticity programs are associated with other aspects of tumor biology as well, including distinct modes of cellular invasion. Here, we identify calcium signaling in pancreatic cancer cells as a regulator of the P-EMT phenotype. Prolonged calcium flux induces PDA cells to remove E-cadherin (ECAD) and other epithelial proteins from the surface and relocalize it intracellularly. This loss of the epithelial phenotype occurs without changes in the abundance of mRNAs for these proteins, reminiscent of the P-EMT phenotype observed in tumors in vivo. In addition, inhibition of the calcium-signaling protein calmodulin blunts this EMT-inducing effect. These results implicate calcium signaling as a mediator of partial EMT phenotypes.

Citation Format: Robert J. Norgard, Ravikanth Maddipati, Nicole M. Aiello, David Balli, Jason R. Pitarresi, Derick N. Rosario-Berrios, Jinyang Li, Salina Yuan, Taiji Yamazoe, Yogev Sela, Allyson J. Merrell, Maximilian D. Wengyn, Kathryn Sun, Anil K. Rustgi, Ben Z. Stanger. Calcium signaling induces a partial EMT in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr B38.

Tumor cell-intrinsic EPHA2 suppresses anti-tumor immunity by regulating PTGS2 (COX-2)

Resistance to immunotherapy is one of the biggest problems of current oncotherapeutics. WhileT cell abundance is essential for tumor responsiveness to immunotherapy, factors that define the T cell inflamed tumor microenvironment are not fully understood. We conducted an unbiased approach to identify tumor-intrinsic mechanisms shaping the immune tumor microenvironment(TME), focusing on pancreatic adenocarcinoma because it is refractory to immunotherapy and excludes T cells from the TME. From human tumors, we identified EPHA2 as a candidate tumor intrinsic driver of immunosuppression. Epha2 deletion reversed T cell exclusion and sensitized tumors to immunotherapy. We found that PTGS2, the gene encoding cyclooxygenase-2, lies downstream of EPHA2 signaling through TGFβ and is associated with poor patient survival. Ptgs2 deletion reversed T cell exclusion and sensitized tumors to immunotherapy; pharmacological inhibition of PTGS2 was similarly effective. Thus, EPHA2-PTGS2 signaling in tumor cells regulates tumor immune phenotypes; blockade may represent a novel therapeutic avenue for immunotherapy-refractory cancers. Our findings warrant clinical trials testing the effectiveness of therapies combining EPHA2-TGFβ-PTGS2 pathway inhibitors with anti-tumor immunotherapy, and may change the treatment of notoriously therapy-resistant pancreatic adenocarcinoma.

Oncogenic Notch Promotes Long-Range Regulatory Interactions within Hyperconnected 3D Cliques

Chromatin loops enable transcription-factor-bound distal enhancers to interact with their target promoters to regulate transcriptional programs. Although developmental transcription factors such as active forms of Notch can directly stimulate transcription by activating enhancers, the effect of their oncogenic subversion on the 3D organization of cancer genomes is largely undetermined. By mapping chromatin looping genome-wide in Notch-dependent triple-negative breast cancer and B cell lymphoma, we show that beyond the well-characterized role of Notch as an activator of distal enhancers, Notch regulates its direct target genes by instructing enhancer repositioning. Moreover, a large fraction of Notch-instructed regulatory loops form highly interacting enhancer and promoter spatial clusters termed "3D cliques." Loss- and gain-of-function experiments show that Notch preferentially targets hyperconnected 3D cliques that regulate the expression of crucial proto-oncogenes. Our observations suggest that oncogenic hijacking of developmental transcription factors can dysregulate transcription through widespread effects on the spatial organization of cancer genomes.

Acetyl-CoA Metabolism Supports Multistep Pancreatic Tumorigenesis

Pancreatic ductal adenocarcinoma (PDA) has a poor prognosis, and new strategies for prevention and treatment are urgently needed. We previously reported that histone H4 acetylation is elevated in pancreatic acinar cells harboring Kras mutations prior to the appearance of premalignant lesions. Because acetyl-CoA abundance regulates global histone acetylation, we hypothesized that altered acetyl-CoA metabolism might contribute to metabolic or epigenetic alterations that promote tumorigenesis. We found that acetyl-CoA abundance is elevated in KRAS-mutant acinar cells and that its use in the mevalonate pathway supports acinar-to-ductal metaplasia (ADM). Pancreas-specific loss of the acetyl-CoA-producing enzyme ATP-citrate lyase (ACLY) accordingly suppresses ADM and tumor formation. In PDA cells, growth factors promote AKT-ACLY signaling and histone acetylation, and both cell proliferation and tumor growth can be suppressed by concurrent BET inhibition and statin treatment. Thus, KRAS-driven metabolic alterations promote acinar cell plasticity and tumor development, and targeting acetyl-CoA-dependent processes exerts anticancer effects. SIGNIFICANCE: Pancreatic cancer is among the deadliest of human malignancies. We identify a key role for the metabolic enzyme ACLY, which produces acetyl-CoA, in pancreatic carcinogenesis. The data suggest that acetyl-CoA use for histone acetylation and in the mevalonate pathway facilitates cell plasticity and proliferation, suggesting potential to target these pathways.See related commentary by Halbrook et al., p. 326.This article is highlighted in the In This Issue feature, p. 305.

Tumor Cell-Intrinsic Factors Underlie Heterogeneity of Immune Cell Infiltration and Response to Immunotherapy

The biological and functional heterogeneity between tumors-both across and within cancer types-poses a challenge for immunotherapy. To understand the factors underlying tumor immune heterogeneity and immunotherapy sensitivity, we established a library of congenic tumor cell clones from an autochthonous mouse model of pancreatic adenocarcinoma. These clones generated tumors that recapitulated T cell-inflamed and non-T-cell-inflamed tumor microenvironments upon implantation in immunocompetent mice, with distinct patterns of infiltration by immune cell subsets. Co-injecting tumor cell clones revealed the non-T-cell-inflamed phenotype is dominant and that both quantitative and qualitative features of intratumoral CD8+ T cells determine response to therapy. Transcriptomic and epigenetic analyses revealed tumor-cell-intrinsic production of the chemokine CXCL1 as a determinant of the non-T-cell-inflamed microenvironment, and ablation of CXCL1 promoted T cell infiltration and sensitivity to a combination immunotherapy regimen. Thus, tumor cell-intrinsic factors shape the tumor immune microenvironment and influence the outcome of immunotherapy.

Human embryonic stem cells exhibit increased propensity to differentiate during the G1 phase prior to phosphorylation of retinoblastoma protein

While experimentally induced arrest of human embryonic stem cells (hESCs) in G1 has been shown to stimulate differentiation, it remains unclear whether the unperturbed G1 phase in hESCs is causally related to differentiation. Here, we use centrifugal elutriation to isolate and investigate differentiation propensities of hESCs in different phases of their cell cycle. We found that isolated G1 cells exhibit higher differentiation propensity compared with S and G2 cells, and they differentiate at low cell densities even under self-renewing conditions. This differentiation of G1 cells was partially prevented in dense cultures of these cells and completely abrogated in coculture with S and G2 cells. However, coculturing without cell-to-cell contact did not rescue the differentiation of G1 cells. Finally, we show that the subset of G1 hESCs with reduced phosphorylation of retinoblastoma has the highest propensity to differentiate and that the differentiation is preceded by cell cycle arrest. These results provide direct evidence for increased propensity of hESCs to differentiate in G1 and suggest a role for neighboring cells in preventing differentiation of hESCs as they pass through a differentiation sensitive, G1 phase.

Intra-arterial injection of human embryonic stem cells in athymic rat hind limb ischemia model leads to arteriogenesis

Shear stress can enhance differentiation of human embryonic stem cells (hESC) to vascular cells. We tested the hypothesis that intra-arterial hESC injection will lead to arteriogenesis while intramuscular injection will have no effect on vascularization.

METHODS AND RESULTS

The superficial femoral arteries were excised on both hind limbs in athymic rats. hESC (2×10(6)) were injected intra-arterially (shear stress) or intramuscular (no shear stress) in one limb after arterial excision. Blood flow, muscle perfusion, and number of arteries/mm(2) muscle were studied at 10 and 21 days after injection. Blood flow in the common iliac artery improved significantly at 10 days after intra-arterial injection of hESC (22±9%, P<.02), and tight muscle perfusion improved significantly both at 10 and 21 days (9±2%, 16±5% respectively, both P<.02). In comparison, intramuscular injection of hESC did not affect blood flow at 10 and 21 days (-3±10% and 4±6%, respectively), while perfusion showed no significant effect of hESC injection after 10 days (1±8%) and was increased 21 days after hESC injection (11±5%, P=.03). Arterial density did not improve after intra-arterial hESC injection at 10 days (15±13%, P=.15) and significantly improved at 21 days (13±4%, P<.05). No significant change was demonstrated after intramuscular injection.

SUMMARY

Intra-arterial injection of hESC resulted in moderate improvement of flow and perfusion and increased number of arteries in the ischemic hind limb. No consistent change in perfusion, flow, and number of arteries was observed after intramuscular injection.

A prospective, randomised study comparing the percutaneous compression plate and the compression hip screw for the treatment of intertrochanteric fractures of the hip

Limited access surgery is thought to reduce post-operative morbidity and provide faster recovery of function. The percutaneous compression plate (PCCP) is a recently introduced device for the fixation of intertrochanteric fractures with minimal exposure. It has several potential mechanical advantages over the conventional compression hip screw (CHS). Our aim in this prospective, randomised, controlled study was to compare the outcome of patients operated on using these two devices. We randomised 104 patients with intertrochanteric fractures (AO/OTA 31.A1-A2) to surgical treatment with either the PCCP or CHS and followed them for one year postoperatively. The mean operating blood loss was 161.0 ml (8 to 450) in the PCCP group and 374.0 ml (11 to 980) in the CHS group (Student's t-test, p < 0.0001). The pain score and ability to bear weight were significantly better in the PCCP group at six weeks post-operatively. Analysis of the radiographs in a proportion of the patients revealed a reduced amount of medial displacement in the PCCP group (two patients, 4%) compared with the CHS group (10 patients, 18.9%); Fisher's exact test, p < 0.02. The PCCP device was associated with reduced intra-operative blood loss, less postoperative pain and a reduced incidence of collapse of the fracture.

Anxiogenic behavior in the light-dark paradigm follwoing intraventricular administration of cholecystokinin-8S, restraint stress, or uncontrollable footshock in the CD-1 mouse

The influence of restraint stress (0, 15, 30, or 60 min), uncontrollable footshock (0, 15, 30, or 60 shocks), or intraventricular CCK-8S administration (0, 5, 25, or 50 ng delivered in a 1 microliter volume) were evaluated on transition frequency and cumulative time in light among CD-1 mice in the light-dark paradigm. Mice exposed to restraint stress of either 15 or 60 min were indistinguishable from nonrestrained animals, while the 30-min session of restraint decreased time in light and transition scores. The presentation of 15, 30, or 60 uncontrollable footshocks were equally effective in decreasing cumulative time in light but had no effect on transition scores. Intraventricular infusion of 25 and 50 ng doses of cholecystokinin-8S reduced cumulative time in light and transition frequency in CD-1 mice relative to vehicle or 5 ng CCK-8S-treated animals in the light-dark paradigm. The time in light and transition data secured among mice with repeated light-dark exposure and 30 min of restraint were comparable to the corresponding scores secured when performance was only evaluated on trial 1. Transition scores were reduced on trial 1 of mice exposed to 30 min of footshock, but time in light was reminiscent of the performance detected among mice with prior light-dark experience. Potential neurochemical correlates associated with the anxiogenic effects associated with stressor exposure and CCK-8S administration in the light-dark task are discussed.