Netrin-1 feedforward mechanism promotes pancreatic cancer liver metastasis via hepatic stellate cell activation, retinoid, and ELF3 signaling

The biology of metastatic pancreatic ductal adenocarcinoma (PDAC) is distinct from that of the primary tumor due to changes in cell plasticity governed by a distinct transcriptome. Therapeutic strategies that target this distinct biology are needed. We detect an upregulation of the neuronal axon guidance molecule Netrin-1 in PDAC liver metastases that signals through its dependence receptor (DR), uncoordinated-5b (Unc5b), to facilitate metastasis in vitro and in vivo. The mechanism of Netrin-1 induction involves a feedforward loop whereby Netrin-1 on the surface of PDAC-secreted extracellular vesicles prepares the metastatic niche by inducing hepatic stellate cell activation and retinoic acid secretion that in turn upregulates Netrin-1 in disseminated tumor cells via RAR/RXR and Elf3 signaling. While this mechanism promotes PDAC liver metastasis, it also identifies a therapeutic vulnerability, as it can be targeted using anti-Netrin-1 therapy to inhibit metastasis using the Unc5b DR cell death mechanism.

Conditional Dependency of LP-184 on Prostaglandin Reductase 1 is Synthetic Lethal in Pancreatic Cancers with DNA Damage Repair Deficiencies

The greater efficacy of DNA-damaging drugs for pancreatic adenocarcinoma (PDAC) relies on targeting cancer-specific vulnerabilities while sparing normal organs and tissues due to their inherent toxicities. We tested LP-184, a novel acylfulvene analog, for its activity in preclinical models of PDAC carrying mutations in the DNA damage repair (DDR) pathways. Cytotoxicity of LP-184 is solely dependent on prostaglandin reductase 1 (PTGR1), so that PTGR1 expression robustly correlates with LP-184 cytotoxicity in vitro and in vivo. Low-passage patient-derived PDAC xenografts with DDR deficiencies treated ex vivo are more sensitive to LP-184 compared with DDR-proficient tumors. Additional in vivo testing of PDAC xenografts for their sensitivity to LP-184 demonstrates marked tumor growth inhibition in models harboring pathogenic mutations in ATR, BRCA1, and BRCA2. Depletion of PTGR1, however, completely abrogates the antitumor effect of LP-184. Testing combinatorial strategies for LP-184 aimed at deregulation of nucleotide excision repair proteins ERCC3 and ERCC4 established synergy. Our results provide valuable biomarkers for clinical testing of LP-184 in a large subset of genetically defined characterized refractory carcinomas. High PTGR1 expression and deleterious DDR mutations are present in approximately one third of PDAC making these patients ideal candidates for clinical trials of LP-184.

Trogocytosis of cancer-associated fibroblasts promotes pancreatic cancer growth and immune suppression via phospholipid scramblase anoctamin 6 (ANO6)

In pancreatic ductal adenocarcinoma (PDAC), the fibroblastic stroma constitutes most of the tumor mass and is remarkably devoid of functional blood vessels. This raises an unresolved question of how PDAC cells obtain essential metabolites and water-insoluble lipids. We have found a critical role for cancer-associated fibroblasts (CAFs) in obtaining and transferring lipids from blood-borne particles to PDAC cells via trogocytosis of CAF plasma membranes. We have also determined that CAF-expressed phospholipid scramblase anoctamin 6 (ANO6) is an essential CAF trogocytosis regulator required to promote PDAC cell survival. During trogocytosis, cancer cells and CAFs form synapse-like plasma membranes contacts that induce cytosolic calcium influx in CAFs via Orai channels. This influx activates ANO6 and results in phosphatidylserine exposure on CAF plasma membrane initiating trogocytosis and transfer of membrane lipids, including cholesterol, to PDAC cells. Importantly, ANO6-dependent trogocytosis also supports the immunosuppressive function of pancreatic CAFs towards cytotoxic T cells by promoting transfer of excessive amounts of cholesterol. Further, blockade of ANO6 antagonizes tumor growth via disruption of delivery of exogenous cholesterol to cancer cells and reverses immune suppression suggesting a potential new strategy for PDAC therapy.

Intrapancreatic fat, pancreatitis, and pancreatic cancer

Pancreatic cancer is typically detected at an advanced stage, and is refractory to most forms of treatment, contributing to poor survival outcomes. The incidence of pancreatic cancer is gradually increasing, linked to an aging population and increasing rates of obesity and pancreatitis, which are risk factors for this cancer. Sources of risk include adipokine signaling from fat cells throughout the body, elevated levels of intrapancreatic intrapancreatic adipocytes (IPAs), inflammatory signals arising from pancreas-infiltrating immune cells and a fibrotic environment induced by recurring cycles of pancreatic obstruction and acinar cell lysis. Once cancers become established, reorganization of pancreatic tissue typically excludes IPAs from the tumor microenvironment, which instead consists of cancer cells embedded in a specialized microenvironment derived from cancer-associated fibroblasts (CAFs). While cancer cell interactions with CAFs and immune cells have been the topic of much investigation, mechanistic studies of the source and function of IPAs in the pre-cancerous niche are much less developed. Intriguingly, an extensive review of studies addressing the accumulation and activity of IPAs in the pancreas reveals that unexpectedly diverse group of factors cause replacement of acinar tissue with IPAs, particularly in the mouse models that are essential tools for research into pancreatic cancer. Genes implicated in regulation of IPA accumulation include KRAS, MYC, TGF-β, periostin, HNF1, and regulators of ductal ciliation and ER stress, among others. These findings emphasize the importance of studying pancreas-damaging factors in the pre-cancerous environment, and have significant implications for the interpretation of data from mouse models for pancreatic cancer.

Tumor-Suppressive and Immune-Stimulating Roles of Cholesterol 25-hydroxylase in Pancreatic Cancer Cells

Cholesterol dependence is an essential characteristic of pancreatic ductal adenocarcinoma (PDAC). Cholesterol 25-hydroxylase (CH25H) catalyzes monooxygenation of cholesterol into 25-hydroxycholesterol, which is implicated in inhibiting cholesterol biosynthesis and in cholesterol depletion. Here, we show that, within PDAC cells, accumulation of cholesterol was facilitated by the loss of CH25H. Methylation of the CH25H gene and decreased levels of CH25H expression occurred in human pancreatic cancers and was associated with poor prognosis. Knockout of Ch25h in mice accelerated progression of Kras-driven pancreatic intraepithelial neoplasia. Conversely, restoration of CH25H expression in human and mouse PDAC cells decreased their viability under conditions of cholesterol deficit, and decelerated tumor growth in immune competent hosts. Mechanistically, the loss of CH25H promoted autophagy resulting in downregulation of MHC-I and decreased CD8+ T-cell tumor infiltration. Re-expression of CH25H in PDAC cells combined with immune checkpoint inhibitors notably inhibited tumor growth. We discuss additional benefits that PDAC cells might gain from inactivation of CH25H and the potential translational importance of these findings for therapeutic approaches to PDAC.

IMPLICATIONS

Loss of CH25H by pancreatic cancer cells may stimulate tumor progression and interfere with immunotherapies.

Abstract B033: LP-184, a tumor site activated small molecule therapeutic, is synthetically lethal in pancreatic cancers with DNA damage repair defects

Biomarker-based therapeutic strategies associated with increased efficacy, manageable toxicity and extended disease-free survival are urgently needed in pancreatic cancer (PaCa). 15-20% of PaCa carry mutations in DNA repair pathways (BRCA1/BRCA2/PALB2/RAD51/ATR/ATM/FANCD2). Additionally, mutations in nucleotide excision repair (NER) genes (ERCC2/3/4/5/6) have been reported in ~5% of PaCa. LP-184 is an acylfulvene analog that is converted to an active alkylating agent in the strict dependency on the oxidoreductase, prostaglandin reductase 1 (PTGR1). LP-184 induced tumor cell kill is enhanced in the presence of DNA damage repair (DDR) defects. Mutation or expression driven TC-NER and/or HR deficiency is expected to predispose PaCa cells to increased sensitivity to LP-184. To test the idea of LP-184 activity in DNA repair-deficient tumors, we evaluated the anti-tumor effects of LP-184 in mouse subcutaneous PDX models harboring pathogenic frameshift mutations in ATR (CTG-1522 model) or BRCA1 (CTG-1643 model) representing HR deficiency in PaCa. Two cycles of LP-184 treatment in CTG-1522 resulted in 140% tumor growth inhibition (TGI), relative to 80% TGI with gemcitabine in this FOLFIRONOX non-responder. Similarly, complete and durable tumor regression with 112% TGI was observed in CTG-1643 with single agent LP-184. There was <5% body weight loss and no significant hematological toxicity in both these models during or after LP-184 treatment. In selected PaCa models, we determined LP-184 efficacy to be synergistic in combination with multiple treatment modalities including standard of care agent gemcitabine, and ERCC3 degrader spironolactone in vitro, and with radiation therapy (RT) in vivo. Overall Bliss synergy scores (score > 10 indicates synergy) of 12.37 for LP-184 + gemcitabine in Capan-1, and 14.08, 16.47 and 15.52 for LP-184 + spironolactone in Capan-1 (BRCA2 loss), Hs766t (ATR mutant) and Panc03.27 cell lines respectively were achieved. Taking advantage of the transcriptional regulation underlying the NRF2 mediated anti-oxidant response pathway, we reasoned that induction of PTGR1 expression, a downstream NRF2 target gene, in irradiated PaCa tumors would thereafter poise them for LP-184 treatment. Indeed, we found that Panc03.27 xenograft tumors treated with 3 mg/kg i.p. LP-184 + 4 Gy RT once weekly for 3 weeks were significantly smaller than those receiving LP-184 alone or RT alone, thus capitalizing on the opportunity to increase PTGR1 expression (and linked LP-184 anti-tumor cytotoxicity) selectively in irradiated tumors. Increased PTGR1 expression has emerged as a promising biomarker for LP-184 cytotoxicity. Moreover, LP-184 can become synthetically lethal in multiple contexts when combined with genetic or pharmacologic DDR pathway aberrations, or with RT. Based on these properties, we anticipate that LP-184 will extend therapeutic opportunities to a large subset of PaCa patients.

Citation Format: Aditya Kulkarni, Diana Restifo, Troy Dos Santos, Dusica Cvetkovic, Joseph McDermott, Kishor Bhatia, Panna Sharma, Charlie Ma, Igor Astsaturov. LP-184, a tumor site activated small molecule therapeutic, is synthetically lethal in pancreatic cancers with DNA damage repair defects [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B033.

Abstract C047: Phospholipid scramblase TMEM16F in cancer associated fibroblasts regulates trogocytosis to sustain critical dependency of pancreatic cancer cells on exogenous lipids

Pancreatic ductal adenocarcinoma (PDAC) cells derive their resistance to therapy and aggressive clinical course from the symbiotic signaling and metabolic interactions with cancer-associated fibroblasts (CAFs). Trogocytosis is a process of “nibbling” of plasma membranes between two living cells. Here, we demonstrate CAFs are the primary recipients of exogenous lipids which they transfer to metabolically “parasitic” PDAC cells via a contact-mediated trogocytosis. Whereas trogocytosis has been described in immune system and in normal development, the biochemical and signaling regulators of trogocytosis between CAFs and PDAC cells have not been defined. Results: We determine that trogocytosis occurs through heterotypic CAF-PDAC cell contacts: membrane blebbing (readily observed in activated CAFs and exaggerated by release of Ca2+ from the ER stores) results in the blebs uptake by the PDAC cells. The CAF blebs express externalized phosphatidylserine (PtdSer), and blockade of PtdSer in vitro transiently deters trogocytic uptake of CAF membranes. Probing a short list of candidate targets involved in regulation of cholesterol trafficking, membrane fusion and membrane protrusions using CRISPRi, has shown that CAFs deficient in CD81, ARF6 or TMEM16F exhibit markedly reduced ability to support the viability of cholesterol-auxotrophic PDAC cells in lipid-poor media. As a promising therapy target, TMEM16F is a Ca2+-regulated scramblase increasing PtdSer on the outer leaflet of the plasma membrane. TMEM16F protein is highly expressed in human PDAC CAFs compared to fibroblasts isolated from the adjacent non-malignant pancreatic tissues. The TMEM16F-null CAFs are unable to sustain of cholesterol-auxotrophic PDAC cells in lipid-poor co-cultures, and do not support the growth of PDAC cells in orthotopic co-implantation model. Furthermore, several clinically available antibiotics used to treat tapeworms are selective TMEM16F inhibitors. One of the widely available TMEM16F inhibitors, niclozamide, is effective in blocking cholesterol transfer from CAFs to PDAC cells in vivo. Conclusion: Our overall model is that activated CAFs initiate trogocytosis by expressing PtdSer as “eat me” signals on the surfaces of their membrane blebs. This process is regulated by Ca2+-dependent phospholipid scramblase TMEM16F which is an attractive drug-amenable target to dismantle the critical metabolic dependency in PDAC on the exogenous lipids. Re-purposing of clinically available TMEM16 inhibitors will make a tangible impact on treatment of PDAC patients in the near term.

Citation Format: Charline Ogier, Alena Klochkova, Linara Gabitova-Cornell, Battuya Bayarmagnai, Diana Restifo, Aizhan Surumbayeva, Debora Barbosa Vendramini-Costa, Ralph Francescone, Janusz Franco-Barraza, Jaye Gardiner, Emmanuelle Nicolas, Andrei Efimov, Elizabeth A. Handorf, Kathy Q. Cai, Bojana Gligorijevic, Edna Cukierman, Igor Astsaturov. Phospholipid scramblase TMEM16F in cancer associated fibroblasts regulates trogocytosis to sustain critical dependency of pancreatic cancer cells on exogenous lipids [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C047.

Abstract PR017: Stromal Netrin G1 ligand (NGL-1): A new modulator of tumorigenesis and immunosuppression in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is soon to be the second deadliest types of cancer, with a 5-year survival of only 10%. The unique features of PDAC are the expansion of cancer-associated fibroblasts (CAFs), presence of a dense fibrous stroma with high bundled collagen I and immunosuppression, representing a challenge for therapies. Ways to overcome these unique pro-tumor features will be key for the development of better therapeutic strategies for PDAC. Herein we report that, in addition to the identified ectopic expression of NGL-1 in PDAC cells, it is also expressed in the stroma (CAFs and immune cells) of PDAC patients, inversely correlating with overall survival. Stromal NGL-1 was important for tumorigenesis in vivo, as NGL-1 knockout mice (KO) orthotopically allografted with pancreatic cancer cells presented less tumor burden. Further analysis showed that the tumors from KO mice presented more CD8+ T cells and less immunosuppressive cytokines, such as TGFβ. Single cell RNAseq analysis of these tumors showed decreased expression of pro-tumor factors, such as immune checkpoint molecules in T cells and TGFβ related genes across different cellular compartments (epithelial, immune and fibroblasts). In accordance with these results, these tumors presented a limited amount of desmoplastic bundled collagen, suggestive of a TGFβ-deficient environment. In order to further dissect between the NGL-1-dependent contributions of immune vs. local stroma (e.g., CAFs) cells, we generated bone marrow chimeras and performed orthotopic injections to generate tumors. The loss of NGL-1 in each cellular compartment alone failed to phenocopy the full body loss of NGL-1, suggesting that NGL-1 in both immune cells and local stromal are important for tumorigenesis. Functionally, NGL-1 deficient CAFs failed to support the survival of starved PDAC cells in vitro, downregulated important myofibroblastic molecules such as p-smad, and produced less immunosuppressive cytokines, suggesting a role for NGL-1 in key pro-tumor features of CAFs. In fact, the fibroblastic NGL-1 dependent immunomodulatory effects were confirmed with human CD8+ T cells from healthy donors, which lost their cytotoxic profile in the presence of conditioned media (CM) from NGL-1+ CAFs, but were able to keep this profile when exposed to CM from NGL-1 deficient CAFs. Bone marrow derived macrophages from KO mice produced less pro-tumor cytokines and CD8+ T cells lacking NGL-1 proliferated more than those from wild type animals, when stimulated in vitro. Mechanistically, while immune cells and CAFs deficient in NGL-1 are both tumor suppressive, the latter can regain pro-tumor functions in response to TGFβ, explaining the need for a global modulation of NGL-1 expression for an anti-tumor effect. Finally, NGL-1 KO mice orthotopically allografted with PDAC cells responded better (smaller tumors) to chemotherapeutical regimen (FOLFIRINOX) compared to WT animals. All these results point to NGL-1 as a potential new target to modulate immunosuppression and tumorigenesis in pancreatic cancer.

Citation Format: Debora Barbosa Vendramini Costa, Ralph Francescone, Janusz Franco-Barraza, Tiffany Luong, Esteban Martinez, Stephen Sykes, Nina Steele, Marina Pasca di Magliano, Dmitry Zhigarev, Charline Ogier, Huamin Wang, Igor Astsaturov, Kerry Campbell, Edna Cukierman. Stromal Netrin G1 ligand (NGL-1): A new modulator of tumorigenesis and immunosuppression in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr PR017.

Abstract B019: Inflammatory response to dietary carbohydrates contributes to the formation of hepatic metastatic niche

Mortality from colon and pancreatic cancers arises from cancer metastatic dissemination to the liver. The glycemic load from carbohydrates (carbs) has been specifically linked to the risk of metastatic recurrence of stage 3 colorectal cancer, but the mechanism of how dietary carbs contribute to the formation of liver metastases remains poorly understood. Our analyses now demonstrate that feeding mice a high carb diet (HCD) promotes liver colonization by tumor cells, and supports the survival of these cells, once in the liver. HCD also induces expression of a Type I interferon (IFN) inflammatory gene signatures which may contribute to its ability to promote metastatic seeding of the liver. Notably, this inflammatory phenotype in hepatocytes was completely abolished if animals are fed a diet enriched in fats (75% of calories), indicating a direct link between liver inflammation and consumption of carbohydrates. Specifically, we have discovered that: 1) dietary carbohydrates, but not a high-fat ketogenic diet, activate multiple independent inflammatory cascades in hepatocytes, including Type-I IFN/STAT1, NFkB, and IL6-STAT3 pathways; 2) the inflammatory signaling in hepatocytes is retained in Scid and NSG mice, indicating that it occurs in the absence of adaptive immunity; 3) HCD, but not fasting or ketogenic diet, markedly increases abundance of retained intronic sequences and formation of double-stranded RNA (dsRNAs). We nominate these yet uncharacterized dsRNAs as potential viral mimics which may trigger the Type I IFN signature observed in HCD-fed livers; and (4) a ketogenic diet showed a trend to reduce liver metastatic colonization, but was associated with mild hepatic steatosis. Overall, this study establishes a new paradigm in nutrient sensing by normal hepatocytes and nominates alternative RNA splicing as the potential trigger of inflammatory responses to HCDs via accumulation of dsRNAs. We suggest that a reduction of dietary carbohydrates, by suppressing the diet-induced hepatic inflammation, will improve the survival of cancer patients, and reduce the risk of liver metastases.

Citation Format: Aizhan Surumbayeva, Riley Williams, Michael Kotliar, Maryclare Taylor, Débora B. Vendramini Costa, Charline Ogier, Diana Restifo, Kathy Q. Cai, Xueyang He, Paul Boutz, Siddharth Balachandran, Igor Astsaturov. Inflammatory response to dietary carbohydrates contributes to the formation of hepatic metastatic niche [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B019.

Abstract B020: Retinoic acid produced by hepatic stellate cells facilitates Netrin-1 mediated pancreatic cancer metastasis

A hallmark of pancreatic ductal adenocarcinoma (PDAC) is its proclivity for metastasis as evidenced by the fact that 85% are stage IV at diagnosis. This highlights the need to better understand the biology of metastatic PDAC and identify novel therapies for this patient population. Axon guidance genes have been shown to be involved in PDAC progression, but their role is unclear. We have investigated the role of the axon guidance molecule Netrin-1 and its receptors Unc5b and DCC in PDAC. We found that in both murine and human samples that NTN1 expression is increased in metastatic PDAC and the quasi-mesenchymal subtype. Murine and TCGA data indicate that Unc5b is the dominant NTN1 receptor and genetic knock-down (KD) or knock-out (KO) of either Netrin-1 or Unc5b decreases migration, invasion, and cell survival in vitro and hepatic metastatic growth in vivo. The mechanism of Netrin-1 upregulation in metastatic PDAC is unknown. We found that hepatic stellate cell (HSC) secreted retinoic acid upregulates NTN1 through both an RXR/RAR and Elf mediated mechanism. To determine if NTN1 is involved in the process of HSC activation we found that recombinant NTN1 added to HSCs in vitro induced activation. We examined the livers of mice harboring orthotopic PDAC tumors using murine pancreatic cancer lines that were either NTN1 wild type (WT) or KO, and found that the NTN-expressing lines increased HSC activation providing evidence that NTN1 is important for long distance intercellular communication between primary pancreatic tumors and the pre-metastatic liver. We detected NTN1 within extracellular vesicles, and mice pre-conditioned with EVs from NTN1 KO cells demonstrated a decreased metastatic burden as compared mice preconditioned with NTN1 WT cells. Treatment of several murine PDAC models (autochthonous and metastatic) with a monoclonal antibody to NTN1 led to decreased metastases and increased survival. These studies reveal that NTN1 is upregulated in metastatic PDAC mediated by a novel mechanism that involves EVs, HSC activation and RXR/RAR signaling. These studies provide pre-clinical evidence to support a human clinical trial of anti-NTN1 therapy in PDAC.

Citation Format: Crissy Dudgeon, Anthony Casabianca, Chris Harris, Igor Astsaturov, Charline Ogier, Xiaoyang Su, Jason Pitarresi, Wade Narrow, Fady Soliman, Tracy Withers, Patrick Mehlen, Darren Carpizo. Retinoic acid produced by hepatic stellate cells facilitates Netrin-1 mediated pancreatic cancer metastasis [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B020.

Suppression of Ca2+ signaling enhances melanoma progression

The role of store-operated Ca2+ entry (SOCE) in melanoma metastasis is highly controversial. To address this, we here examined UV-dependent metastasis, revealing a critical role for SOCE suppression in melanoma progression. UV-induced cholesterol biosynthesis was critical for UV-induced SOCE suppression and subsequent metastasis, although SOCE suppression alone was both necessary and sufficient for metastasis to occur. Further, SOCE suppression was responsible for UV-dependent differences in gene expression associated with both increased invasion and reduced glucose metabolism. Functional analyses further established that increased glucose uptake leads to a metabolic shift towards biosynthetic pathways critical for melanoma metastasis. Finally, examination of fresh surgically isolated human melanoma explants revealed cholesterol biosynthesis-dependent reduced SOCE. Invasiveness could be reversed with either cholesterol biosynthesis inhibitors or pharmacological SOCE potentiation. Collectively, we provide evidence that, contrary to current thinking, Ca2+ signals can block invasive behavior, and suppression of these signals promotes invasion and metastasis.

Abstract 3649: Stromal netrinG1-ligand (NGL1) constitutes a new modulator of pancreatic cancer immunosuppression

Pancreatic cancer (PC), is currently the third and predicted to soon become the second deadliest cancer in the US. A unique feature of PC is its fibrous tumor microenvironment (TME), marked by the expansion of cancer-associated fibroblasts (CAFs), highly bundled collagen I, and absence or inactivation of antitumor immune cells. As this TME is a physical and biochemical therapeutic barrier, a better understanding of how pro-tumor immunosuppression is modulated constitutes a highly sought-after goal. Herein we report that in addition to the identified ectopic expression of NetrinG1-Ligand (NGL1) in PC cells, NGL1 is detected in both immune cells and CAFs, with increased levels in CAFs associated with short PC patient overall survival. Further, in tumor-bearing mice, fibroblastic NGL1 expression correlates with PC progression while assorted immune cells express high levels of NGL1. To question the pro-PC role of stromal NGL1, we evaluated tumor progression in NGL1 knockout (KO) mice, using orthotopic PC allografts, and observed that tumors were significantly smaller. Single-cell RNA sequencing pointed to downregulation of pro-tumor transcripts in key assorted KO TME cells (e.g., T Cells). We also noted that tumor-bearing KO tissues included a TME with limited immunosuppressive cytokines, increased CD8+ and CD4+ T cells expressing low levels of tumor-promoting factors, and a limited amount of desmoplastic bundled collagen, all suggestive of a TGFβ-deficient milieu. In order to further dissect between the NGL1-dependent contributions of hematopoietic/immune vs. local stroma (e.g., CAFs) cells, we generated bone marrow KO/WT chimeras. Results suggested that loss of NGL1 in one of the two compartments fails to phenocopy the full-body loss of NGL1, and was thus insufficient to hinder PC tumorigenesis. Further, depletion of selected immune cell subsets informed on NGL1-dependent T- and myeloid-cell contributions. Functional assays showed that KO macrophages released limited pro-tumor factors while KO T cells displayed increased proliferation compared to the WTs of both cell types. Fibroblastic NGL1-dependent immuno-regulatory effects were confirmed with human immune cells collected from healthy donors. Mechanistically, while immune cells and CAFs deficient in NGL1 are both tumor-suppressive, the latter can regain pro-tumor functions in response to TGFβ, explaining the chimera and full-body KO results. Finally, KO effects were mirrored in WT CAFs treated with an NGL1-neutralizing molecule. Overall, our data suggest that stromal NGL1 is a novel and targetable modulator of PC immunosuppression

Citation Format: Débora B. Vendramini-Costa, Ralph Francescone, Janusz Franco-Barraza, Tiffany Luong, Esteban Martinez, Stephen Sykes, Nina G. Steele, Benjamin L. Allen, Marina Pasca di Magliano, Dmitry I. Zhigarev, Charline Ogier, Igor Astsaturov, Kathy Q. Cai, Andres J. Klein-Szanto, Huamin Wang, Kerry Campbell, Edna Cukierman. Stromal netrinG1-ligand (NGL1) constitutes a new modulator of pancreatic cancer immunosuppression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3649.

Abstract 1571: Cancer associated fibroblasts sustain critical dependency of pancreatic cancer cells on exogenous lipids

Pancreatic ductal adenocarcinoma (PDAC) cells derive their resistance to therapy and aggressive clinical course from the symbiotic signaling and metabolic interactions with cancer-associated fibroblasts (CAFs). CAFs have been shown to provide nutrients to "parasitic" PDAC cells including water soluble glucose and amino acids. In hypoxic tumor microenvironments, aggressive PDAC are functional auxotroph for lipids, and scavenge exogenous lipids to build cellular membranes. However, the mechanism by which PDAC cells obtain these water-insoluble essential membrane building materials remains poorly understood. To gain insights into the mechanism of lipid scavenging, we generated cholesterol-auxotrophic human and mouse PDAC PDAC cells since cholesterol is the major constituent of lipid cellular membranes. Here, we discovered that PDAC cells utilize CAFs as a main source of lipids in vivo through direct heterotypic cellular contacts. In this process, PDAC cells directly acquire the CAF plasma membrane (PM) via trogocytosis. In response to yet unidentified paracrine “feed me” signals activating CAF-dependent trogocytosis, CAFs upregulate phosphatidylserine (PtdSer) on the outer leaflet of the PM. Consequently, blockade of PtdSer on CAFs partially deterred trogocytic transfer of CAF membranes to PDAC cells in vitro. Furthermore, Ca2+-dependent phospholipid scramblase TMEM16F is a critical regulator of PtdSer externalization. TMEM16F is highly expressed in human PDAC CAFs compared to fibroblasts isolated from the matching adjacent non-malignant pancreatic tissues CAFs deficient in TMEM16F scramblase exhibited markedly reduced ability to support the growth of cholesterol-auxotrophic PDAC cells cultured in lipid depleted media. We propose trogocytosis as a new mode of lipid scavenging by PDAC cells from CAFs involving activation of Ca2+-dependent phospholipid scramblase TMEM16F in CAFs and increased expression of PtdSer as “eat me” signals on CAF PM. To inactivate trogocytosis, we nominate TMEM16F as a plausible PDAC therapy target using clinically available TMEM16 inhibitors with a potential for impact on treatment of PDAC patients in the near term.

Citation Format: Charline Ogier, Alena Klochkova, Battuya Bayarmagnai, Linara Gabitova, Diana Restifo, Aizhan Surumbayeva, Janusz Franco-Barraza, Debora Vendramini Costa, Ralph Francescone, Jaye Gardiner, Emmanuelle Nicolas, Elizabeth A. Handorf, Kathy Q. Cai, Edna Cukierman, Igor Astsaturov. Cancer associated fibroblasts sustain critical dependency of pancreatic cancer cells on exogenous lipids [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1571.

Abstract 2178: Diet-modulated SCAP-SREBP signaling is essential for acinar cell differentiation, pancreatic morphogenesis, and pancreatic adiposity

High levels of dietary fats are associated with pancreatitis, diabetes, and pancreatic cancer. Sterol regulatory element binding protein Cleavage-Activating Protein (SCAP) is an essential intermediate in lipid-regulated activation of Sterol Regulatory Element Binding Protein (SREBP) transcription factors, which induce expression of genes regulating lipid homeostasis. We previously demonstrated that the elevated SREBP1 arising from inhibition of the cholesterol biosynthetic pathway in mice genetically predisposed to pancreatic cancer additionally transcribed genes that induced epithelial-mesenchymal transition, promoting basal rather than glandular cancer. To further evaluate SCAP and SREBP function in the pancreas, we developed a new mouse model with selective pancreatic knockout of the Scapf/f gene under the control of the Pdx1-Cre promoter (ScapΔpanc mice).

Although size of the pancreas in ScapΔpanc neonates was unaffected, and number of islets was normal, there was a reduced number of acinar cells, and some evidence of disorganized tissue structure. Preliminary histopatholgical assessment of pancreatic tissue of ScapΔpanc neonates indicated no acinar cell apoptosis, and unimpaired acinar proliferation, suggesting loss of Scap may cause a differentiation defect. Further supporting this idea, siRNA depletion of Scap in the rat AR42J acinar cell line resulted in loss of markers of mature acinar cell identity. ScapΔpanc pancreata underwent progressive and selective loss of acinar cells as mice aged, with three-month old mice having large areas of acinar cell loss, and mislocalization of ductal cells. Coupled with this loss was a large increase in pancreatic adipocytes and mesenchymal cells, resulting in a highly disorganized tissue morphology accompanied by signs of inflammation. These phenotypes were exacerbated in mice maintained on high fat or high carbohydrate diet. Together, these results imply that SCAP and SREBP signaling in the pancreas plays an important role in mediating dietary modulation of pancreatic development, acinar cell homeostasis, and restraint of pancreatic adiposity. Intrapancreatic fat, associated with obesity and chronic pancreatitis, is a known risk factor for pancreatic cancer, and SCAP polymorphisms have been to interact with diet in regulating obesity and blood pressure in humans; we propose SCAP-SREBP signaling in the pancreas may mediate dietary promotion of pancreatic cancer risk.

Citation Format: Anna C. Lilly, Aizhan Surumbayeva, Theodore Nguyen, Igor Astsaturov, Erica A. Golemis. Diet-modulated SCAP-SREBP signaling is essential for acinar cell differentiation, pancreatic morphogenesis, and pancreatic adiposity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2178.

Platelet microRNAs inhibit primary tumor growth via broad modulation of tumor cell mRNA expression in ectopic pancreatic cancer in mice

We investigated the contributions of platelet microRNAs (miRNAs) to the rate of growth and regulation of gene expression in primary ectopic tumors using mouse models. We previously identified an inhibitory role for platelets in solid tumor growth, mediated by tumor infiltration of platelet microvesicles (microparticles) which are enriched in platelet-derived miRNAs. To investigate the specific roles of platelet miRNAs in tumor growth models, we implanted pancreatic ductal adenocarcinoma cells as a bolus into mice with megakaryocyte-/platelet-specific depletion of mature miRNAs. We observed an ~50% increase in the rate of growth of ectopic primary tumors in these mice compared to controls including at early stages, associated with reduced apoptosis in the tumors, in particular in tumor cells associated with platelet microvesicles-which were depleted of platelet-enriched miRNAs-demonstrating a specific role for platelet miRNAs in modulation of primary tumor growth. Differential expression RNA sequencing of tumor cells isolated from advanced primary tumors revealed a broad cohort of mRNAs modulated in the tumor cells as a function of host platelet miRNAs. Altered genes comprised 548 up-regulated transcripts and 43 down-regulated transcripts, mostly mRNAs altogether spanning a variety of growth signaling pathways-notably pathways related to epithelial-mesenchymal transition-in tumor cells from platelet miRNA-deleted mice compared with those from control mice. Tumors in platelet miRNA-depleted mice showed more sarcomatoid growth and more advanced tumor grade, indicating roles for host platelet miRNAs in tumor plasticity. We further validated increased protein expression of selected genes associated with increased cognate mRNAs in the tumors due to platelet miRNA depletion in the host animals, providing proof of principle of widespread effects of platelet miRNAs on tumor cell functional gene expression in primary tumors in vivo. Together, these data demonstrate that platelet-derived miRNAs modulate solid tumor growth in vivo by broad-spectrum restructuring of the tumor cell transcriptome.

Abstract PR-015: Cancer-associated fibroblasts sustain critical dependency of pancreatic cancer cells on exogenous lipids

Pancreatic ductal adenocarcinoma (PDAC) cells derive their resistance to therapy and aggressive clinical course from the symbiotic signaling and metabolic interactions with cancer-associated fibroblasts (CAFs). CAFs have been shown to provide to metabolically “parasitic” PDAC cells with water-soluble metabolites such as glucose and amino acids, or bulk protein via micropinocytosis. To meet the elevated demands for cellular membrane lipids, cancer cells rely on uptake of the exogenous lipids. However, the mechanism by which PDAC cells obtain water-insoluble essential lipids, such as cholesterol, remains poorly understood. Here, we define CAFs as a main source of lipids for PDAC cells by direct “feeding” of the CAF plasma membrane (PM) to cancer cells via heterotypic cellular contacts, a phenomenon known as trogocytosis. To gain insights into the mechanisms of regulation of CAF trogocytosis, we engineered cholesterol-auxotrophic human and mouse PDAC cells. In the absence of exogenously provided cholesterol, these cancer cells undergo apoptosis, which is completely rescued in CAF co-cultures. Using CRISPRi-mediated depletion in CAFs of select genes involved in cholesterol trafficking, membrane fusion and membrane protrusions, we found that CAFs deficient in CD81, TMEM16F, or ARF6 exhibited markedly reduced ability to support the viability of cholesterol-auxotrophic PDAC cells in lipid-poor media. As a promising therapy target, TMEM16F is a Ca2+-regulated scramblase increasing phosphatidylserine (PtdSer) on the outer leaflet of the PM. TMEM16F protein is highly expressed in human PDAC CAFs compared to fibroblasts isolated from the adjacent non-malignant pancreatic tissues. The TMEM16F-null CAFs are unable to sustain of cholesterol-auxotrophic PDAC cells in lipid-poor co-cultures. Our overall model is that, to initiate trogocytosis, PDAC cells release paracrine “feed me” signals activating Ca2+-dependent phospholipid scramblase TMEM16F. As the result, increased outward expression of PtdSer on CAF PM is a hallmark “eat me” signal that is recognized by the trogocytic PDAC cells. We conclude that trogocytosis is the critical metabolic dependency in PDAC, and nominated TMEM16F as a plausible PDAC therapy target. Re-purposing of clinically available TMEM16 inhibitors will make a tangible impact on treatment of PDAC patients in the near term.

Citation Format: Charline Ogier, Alena Klochkova, Linara Gabitova, Battuya Bayarmagnai, Diana Restifo, Aizhan Surumbayeva, Janusz Franco-Barraza, Ralph Francescone, Debora B. Barbosa Vendramini-Costa, Jaye Gardiner, Emmanuelle Nicolas, Elizabeth A. Handorf, Kathy Q. Cai, Edna Cukierman, Igor Astsaturov. Cancer-associated fibroblasts sustain critical dependency of pancreatic cancer cells on exogenous lipids [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PR-015.

Abstract PO-096: The synaptic protein Netrin G1 ligand (NGL-1) modulates tumorigenesis and immunosuppression in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest types of cancer, with a 5-year survival of 10%. A major feature of PDAC is the presence of a dense fibrous stroma, due to the expansion of cancer associated fibroblasts (CAFs) and their extracellular matrix. This unique environment represents a challenge for therapies as it promotes immunosuppression, limits access to nutrients, and excludes or inactivates antitumor immune cells. Recently, we identified the ectopic expression of the neuronal protein Netrin G1 Ligand (NGL-1) in PDAC tissue, including its novel expression in immune cells and CAFs. However, the roles of NGL-1 in the tumor microenvironment (TME) of PDAC and in immune cell function are unknown and warranted further investigation. The contribution of NGL-1 to PDAC tumorigenesis was assessed by measuring the expression of NGL-1 in different models of PDAC and by orthotopically injecting PDAC cells in wild type (WT) or NGL-1 full body knockout mice (KO). Using our in vitro 3D system we evaluated if NGL-1+ CAFs, compared to NGL-1 knockdown (KD) CAFs, produced less immunosuppressive factors and were able to rescue PDAC cell survival under nutrient deprivation. For NGL-1 dependent immune cell functions we isolated naïve immune cells from WT and KO mice and performed ex-vivo functional assays. NGL-1 expression in fibroblasts correlated with disease development in different models of PDAC, and myeloid, T and NK cells from tumor bearing mice tended to overexpress NGL-1 when compared with cells from naïve mice. Accordingly, NGL-1 KO mice orthotopically injected with PDAC cells developed smaller tumors with decreased secretion of immunosuppressive factors, increased presence of CD8+ T cells and CD4+ T cells expressing less pro-tumor markers. Single cell RNA sequencing data from tumors from KO mice showed downregulation of pro-tumor genes in different cell populations, with the fibroblastic populations differing between WT and KO mice. In order to evaluate the contribution of the immune system for tumorigenesis in WT and KO mice, we performed bone marrow chimeras and depletion of specific immune cells. Functionally, CD8+ and CD4+ T cells from KO mice proliferated more when stimulated in vitro, suggesting that NGL-1 could represent a functional brake for T cells, inhibiting their anti-tumor capacity. The lack of NGL-1 in stimulated bone marrow-derived macrophages decreased pro-inflammatory cytokine secretion, further suggesting a functional role for NGL-1 in myeloid cells. Of note, NGL-1 KD CAFs did not support PDAC cell survival in vitro and produced less immunosuppressive cytokines, which was phenocopied by the treatment with a peptide targeting NGL-1. Translationally, we assessed the overall survival of 140 PDAC patients according to NGL-1 expression in the TME, where low expression of NGL-1 in CAFs and immune cells correlated with better survival of PDAC patients. Overall, this suggests NGL-1 as potential new target in PDAC, that could be manipulated in different compartments in pancreatic cancer.

Citation Format: Debora Barbosa Vendramini Costa, Ralph Francescone, Janusz Franco-Barraza, Tiffany Luong, Nina Steele, Benjamin Allen, Marina Pasca di Magliano, Charline Ogier, Igor Astsaturov, Kathy Q. Cai, Andres J. Klein-Szanto, Huamin Wang, Kerry Campbell, Edna Cukierman. The synaptic protein Netrin G1 ligand (NGL-1) modulates tumorigenesis and immunosuppression in pancreatic cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PO-096.

Abstract PO-036: LP184, a novel alkylating agent, is highly effective in pancreatic cancers with DNA damage repair defects

Biomarker-based chemotherapy with increased efficacy and prolonged disease-free survival are urgently needed in pancreatic cancer (PDAC). A 15-20% subset of PDAC tumors carry mutations in DNA repair pathway (BRCA1/BRCA2/PALB2/RAD51/ATM/FANCD2). Additionally, mutations in nucleotide excision repair (NER) genes (ERCC2/3/4/5/6) have been reported in ~5% of PDAC. LP184 is a novel synthetic small molecule acylfulvene analog. Using precise synthetic chemistry, we determined that only a negative enantiomer of LP184 is converted to an active alkylating agent in the strict dependency on oxidoreductase, prostaglandin reductase 1 (PTGR1). By computational analyses, we demonstrate a strong positive correlation of LP184 sensitivity with PTGR1 transcript levels (r=0.89, p<10−15) in a broad panel of cancer cell lines. Once activated by PTGR1, highly reactive LP-184 nucleophile creates covalent DNA adducts that are selectively repaired via Nucleotide Excision Repair (NER) mechanism coupled to transcription (TC-NER) and/or homologous recombination (HR). We reasoned that mutation or expression driven TC-NER and HR deficiency would predispose PDAC cells to increased sensitivity to LP184. To test the idea of LP184 activity in DNA repair-deficient tumors, we evaluated LP184 chemosensitivity in genetically defined PDAC models in vitro, ex vivo, and in xenografts. Testing in six different pancreatic cancer cell lines (Capan-1, CFPAC-1, Panc1, MiaPaCa2, Panc03.27 and BxPC-3) resulted in very potent inhibition with LP184 IC50 values ranging from 114 to 182 nM. In this cell line panel, LP184 sensitivity correlated negatively with transcript levels of an NER pathway gene ERCC8 (r = -0.94). In comparison to these PDAC cell lines, a normal pancreatic epithelial cell line HPNE was 3-6 times less sensitive to LP184 (IC50 670 nM). Ex vivo cultures of 4 out of 5 low-passage patient-derived xenografts with HR deficiency showed nanomolar sensitivity to LP184 with IC50s ranging from 45 to 270 nM. These tumor graft models which were at least 6 times less sensitive to olaparib in the same assay. Depletion of ERCC4 enhanced sensitivity to LP184 about 2-fold relative to the parental cell line. To define PTGR1 as a biomarker for LP184 activity, we used CRISPR/Cas9-mediated gene editing to deplete PTGR1 expression. We found PTGR1-null Capan-1 cell line-derived xenografts were poorly sensitive to LP184, whereas PTGR1-expressing xenografts showed near complete tumor regression in all LP184 treated animals with 109% tumor growth inhibition relative to the control group in this study. Furthermore, PTGR1 depleted cells were completely resistant to LP184 in vitro. Our preclinical data demonstrate that PDAC models carrying a range of DNA repair pathway mutations are highly sensitive to LP-184 in vitro and in vivo. Increased PTGR1 expression is a validated biomarker for LP184 cytotoxicity, and is the exclusive convertase of LP184 to an active alkylator drug. We anticipate LP184 will extend the therapeutic opportunities to a large subset of PDAC patients carrying these genetic alterations.

Citation Format: Diana Restifo, Aditya Kulkarni, Caleb Schimke, Joseph McDermott, Umesh Kathad, Kishor Bhatia, Panna Sharma, Igor Astsaturov. LP184, a novel alkylating agent, is highly effective in pancreatic cancers with DNA damage repair defects [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PO-036.

Abstract PO-068: Cholesterol auxotrophy promotes the expansion of centroacinar cells giving rise to the basal subtype of pancreatic adenocarcinoma

Gene expression analyses established at least two molecular subtypes of pancreatic adenocarcinoma (PDAC), the classical (or glandular), and the basal (or mesenchymal), each of which is associated with distinct prognoses and sensitivity to chemotherapy. It remains unclear, however, whether the basal carcinoma cells arise from a separate cell-of-origin, or are emerging from the pre-existing well-differentiated “classical” PDAC cells. To distinguish these alternatives, we conducted single-cell transcriptome analyses and virtual lineage tracing comparing cellular populations at pre-malignant stages in basal versus classical PDAC mouse models. We previously reported that chemical or genetic inhibition of the cholesterol biosynthetic pathway in KrasG12D; Trp53 (KPPC) mice predisposes to basal rather than glandular PDAC development because of the pancreas-specific increased sterol response element-binding protein 1 (SREBP1) activity and TGFβ signaling that induces cancer cell stemness and the EMT (PMID: 32976774). Pancreas-selective knockout of a conditional allele of cholesterol pathway gene, Nsdhl (NAD(P)-dependent steroid dehydrogenase-like), renders pancreatic epithelial cells cholesterol auxotrophs and drives basal PDAC in the majority of animals (KPPCN mice). At 5-6 weeks of age, grossly and microscopically tumor-free pancreatic tissues were selected for single-cell isolation and single-cell RNA sequencing (scRNA seq) using the 10X platform. After standard filtering and sample normalization procedures, downstream analyses included identification of relevant cell clusters using Seurat, lineage tracing algorithms, and in silico modeling of autocrine and paracrine signaling interactions between subsets of PDAC and non-malignant cells. Our key findings are as follows: 1) premalignant KPPCN pancreata exhibit a massive expansion of cancer-associated fibroblasts (CAFs) of predominantly inflammatory differentiation (iCAFs); 2) despite relatively fewer ADM and PanIN pre-malignant lesions in KPPCN compared to KPPC, scRNA seq identifies the significant expansion of epithelial cells with features of centroacinar and stem-like cells (increased expression of Aldh1a2, Nes, Sox9, Ly6a, Cxcl12, and Met); these centroacinar-like cells, while retaining epithelial identity (Epcam, Cdh1), also exhibit features of pluripotency by co-expression of Ins2 and other stem cell markers; 3) alignment with basal PDAC (KPPCN) and classical (KPPC) carcinoma cell populations strongly suggests the continuity of clonal evolution of the centroacinar-like cells towards the basal PDAC. While our genetic model does not recapitulate the multiple alternative pathways leading to basal PDAC development, cholesterol auxotrophy via SREBP1 may be a factor governing the expansion of undifferentiated precursors, which via interactions with cancer-promoting iCAFs, drive basal PDAC development.

Citation Format: Michael Kotliar, Aizhan Surumbayeva, Linara Gabitova, Suraj Peri, Diana Restifo, Kathy Q. Cai, Artem Barski, Igor Astsaturov. Cholesterol auxotrophy promotes the expansion of centroacinar cells giving rise to the basal subtype of pancreatic adenocarcinoma [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PO-068.

Evaluating the impact of age on immune checkpoint therapy biomarkers

Both tumors and aging alter the immune landscape of tissues. These interactions may play an important role in tumor progression among elderly patients and may suggest considerations for patient care. We leverage large-scale genomic and clinical databases to perform comprehensive comparative analysis of molecular and cellular markers of immune checkpoint blockade (ICB) response with patient age. These analyses demonstrate that aging is associated with increased tumor mutational burden, increased expression and decreased promoter methylation of immune checkpoint genes, and increased interferon gamma signaling in older patients in many cancer types studied, all of which are expected to promote ICB efficacy. Concurrently, we observe age-related alterations that might be expected to reduce ICB efficacy, such as decreases in T cell receptor diversity. Altogether, these changes suggest the capacity for robust ICB response in many older patients, which may warrant large-scale prospective study on ICB therapies among patients of advanced age.

Feasibility of Fitness Tracker Usage to Assess Activity Level and Toxicities in Patients With Colorectal Cancer

PURPOSE

Performance status (PS) is a subjective assessment of patients' overall health. Quantification of physical activity using a wearable tracker (Fitbit Charge [FC]) may provide an objective measure of patient's overall PS and treatment tolerance.

MATERIALS AND METHODS

Patients with colorectal cancer were prospectively enrolled into two cohorts (medical and surgical) and asked to wear FC for 4 days at baseline (start of new chemotherapy [± 4 weeks] or prior to curative resection) and follow-up (4 weeks [± 2 weeks] after initial assessment in medical and postoperative discharge in surgical cohort). Primary end point was feasibility, defined as 75% of patients wearing FC for at least 12 hours/d, 3 of 4 assigned days. Mean steps per day (SPD) were correlated with toxicities of interest (postoperative complication or ≥ grade 3 toxicity). A cutoff of 5,000 SPD was selected to compare outcomes.

RESULTS

Eighty patients were accrued over 3 years with 55% males and a median age of 59.5 years. Feasibility end point was met with 68 patients (85%) wearing FC more than predefined duration and majority (91%) finding its use acceptable. The mean SPD count for patients with PS 0 was 6,313, and for those with PS 1, it was 2,925 (122 and 54 active minutes, respectively) (P = .0003). Occurrence of toxicity of interest was lower among patients with SPD > 5,000 (7 of 33, 21%) compared with those with SPD < 5,000 (14 of 43, 32%), although not significant (P = .31).

CONCLUSION

Assessment of physical activity with FC is feasible in patients with colorectal cancer and well-accepted. SPD may serve as an adjunct to PS assessment and a possible tool to help predict toxicities, regardless of type of therapy. Future studies incorporating FC can standardize patient assessment and help identify vulnerable population.

Large-scale analysis of KMT2 mutations defines a distinctive molecular subset with treatment implication in gastric cancer

Frequent mutations of genes in the histone-lysine N-methyltransferase 2 (KMT2) family members were identified in gastric cancers (GCs). Understanding how gene mutations of KMT2 family affect cancer progression and tumor immune microenvironment may provide new treatment strategies. A total of 1245 GCs were analyzed using next-generation sequencing, whole transcriptome sequencing, immunohistochemistry (Caris Life Sciences, Phoenix, AZ). The overall mutation rate of genes in the KMT2 family was 10.6%. Compared to KMT2-wild-type GCs, genes involved in epigenetic modification, receptor tyrosine kinases/MAPK/PI3K, and DNA damage repair (DDR) pathways had higher mutation rates in KMT2-mutant GCs (p < 0.05). Significantly higher rates of high tumor mutational burden, microsatellite instability-high/mismatch-repair deficiency (dMMR), and PD-L1 positivity were observed in KMT2-mutant GCs (p < 0.01), compared to KMT2-wild-type GCs. The association between PD-L1 positivity and KMT2 mutations remained significant in the proficient-MMR and microsatellite stable subgroup. Based on transcriptome data from the TCGA, cell cycle, metabolism, and interferon-α/β response pathways were significantly upregulated in KMT2-mutant GCs than in KMT2-wild-type GCs. Patients with KMT2 mutation treated with immune checkpoint inhibitors had longer median overall survival compared to KMT2-wild-type patients with metastatic solid tumors (35 vs. 16 months, HR = 0.73, 95% CI: 0.62-0.87, p = 0.0003). In conclusion, this is the largest study to investigate the distinct molecular features between KMT2-mutant and KMT2-wild-type GCs to date. Our data indicate that GC patients with KMT2 mutations may benefit from ICIs and drugs targeting DDR, MAPK/PI3K, metabolism, and cell cycle pathways.

Abstract LT019: The synaptic protein netrin G1 ligand (NGL-1) modulates the immunosuppressive environment in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC), one of the deadliest cancers, features a highly immunosuppressive environment, with expansion of cancer-associated fibroblasts (CAFs), and absence/inactivation of antitumor immune cells. Therefore, ways to manipulate this environment, favoring the antitumor cells, will be critical for effective therapies for PDAC. Recently, we identified the neuronal protein Netrin G1 Ligand (NGL-1) to be overexpressed in PDAC tissue, including its novel expression in immune cells and CAFs. However, the role that NGL-1 plays in the tumor microenivronment (TME) is unknown and warrented further investigation. Using wild-type and NGL-1 full body knockout mice orthotopically injected or not with pancreatic tumor cells, we assessed tumorigenesis and secretion of immunosuppresive factors. Moreover, using our in vitro 3D system we explored the ability of NGL-1+ CAFs to rescue PDAC cell survival under nutrient deprivation, their immunosuppressive profile and the ability of a peptide targeting NGL-1 to reverse these features. Finally, we assessed the overall survival of 140 PDAC patients according to NGL-1 expression in the TME. Comparing immune cells from naïve and tumor-bearing mice we observed that myeloid, T and NK cells from tumor-bearing mice tend to overexpress NGL-1. Moreover, CD8+ and CD4+ T cells from NGL-1 KO mice proliferated more when stimulated in vitro, suggesting that NGL-1 could represent a functional brake for T cell activation and proliferation. Interestingly, the absence of NGL-1 in bone marrow-derived macrophages stimulated in vitro led to decreased production of pro-inflammatory cytokines, further suggesting a functional role for NGL-1 in myeloid cells. Importantly, NGL-1 KO mice orthotopically injected with PDAC cells developed smaller tumors and these produced less immunosuppressive factors. In accordance, CAFs lacking NGL-1 were not supportive of PDAC cell survival in vitro and produced less immunosuppressive cytokines, which was phenocopied by the treatment with the peptide targeting NGL-1. Finally, data from PDAC patients showed that low expression of NGL-1 in CAFs and immune cells correlated with better survival of these patients, therefore highlighting NGL-1 as a potential new target that could be manipulated in different compartments in pancreatic cancer (cancer cells, CAFs, immune cells). This represents an innovative perspective for such a complex disease.

Citation Format: Debora Barbosa Vendramini-Costa, Ralph Francescone, Tiffany Luong, Janusz Franco-Barraza, Igor Astsaturov, Kathy Q. Cai, Andres J. Klein-Szanto, Huamin Wang, Kerry Campbell, Edna Cukierman. The synaptic protein netrin G1 ligand (NGL-1) modulates the immunosuppressive environment in pancreatic cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr LT019.

Netrin G1 Promotes Pancreatic Tumorigenesis through Cancer-Associated Fibroblast-Driven Nutritional Support and Immunosuppression

Pancreatic ductal adenocarcinoma (PDAC) has a poor 5-year survival rate and lacks effective therapeutics. Therefore, it is of paramount importance to identify new targets. Using multiplex data from patient tissue, three-dimensional coculturing in vitro assays, and orthotopic murine models, we identified Netrin G1 (NetG1) as a promoter of PDAC tumorigenesis. We found that NetG1+ cancer-associated fibroblasts (CAF) support PDAC survival, through a NetG1-mediated effect on glutamate/glutamine metabolism. Also, NetG1+ CAFs are intrinsically immunosuppressive and inhibit natural killer cell-mediated killing of tumor cells. These protumor functions are controlled by a signaling circuit downstream of NetG1, which is comprised of AKT/4E-BP1, p38/FRA1, vesicular glutamate transporter 1, and glutamine synthetase. Finally, blocking NetG1 with a neutralizing antibody stunts in vivo tumorigenesis, suggesting NetG1 as potential target in PDAC. SIGNIFICANCE: This study demonstrates the feasibility of targeting a fibroblastic protein, NetG1, which can limit PDAC tumorigenesis in vivo by reverting the protumorigenic properties of CAFs. Moreover, inhibition of metabolic proteins in CAFs altered their immunosuppressive capacity, linking metabolism with immunomodulatory function.See related commentary by Sherman, p. 230.This article is highlighted in the In This Issue feature, p. 211.

Cholesterol Pathway Inhibition Induces TGF-β Signaling to Promote Basal Differentiation in Pancreatic Cancer

Oncogenic transformation alters lipid metabolism to sustain tumor growth. We define a mechanism by which cholesterol metabolism controls the development and differentiation of pancreatic ductal adenocarcinoma (PDAC). Disruption of distal cholesterol biosynthesis by conditional inactivation of the rate-limiting enzyme Nsdhl or treatment with cholesterol-lowering statins switches glandular pancreatic carcinomas to a basal (mesenchymal) phenotype in mouse models driven by Kras^G12D expression and homozygous Trp53 loss. Consistently, PDACs in patients receiving statins show enhanced mesenchymal features. Mechanistically, statins and NSDHL loss induce SREBP1 activation, which promotes the expression of Tgfb1, enabling epithelial-mesenchymal transition. Evidence from patient samples in this study suggests that activation of transforming growth factor β signaling and epithelial-mesenchymal transition by cholesterol-lowering statins may promote the basal type of PDAC, conferring poor outcomes in patients.

Phase Ib Study of Wnt Inhibitor Ipafricept with Gemcitabine and nab-paclitaxel in Patients with Previously Untreated Stage IV Pancreatic Cancer

PURPOSE

The recombinant fusion protein ipafricept blocks Wnt signaling, and in combination with gemcitabine and nab-paclitaxel caused tumor regression in xenografts. This phase Ib study evaluated the combination of ipafricept with nab-paclitaxel + gemcitabine in patients with untreated metastatic pancreatic adenocarcinoma (mPDAC).

PATIENTS AND METHODS

Dose escalation started with standard dose nab-paclitaxel + gemcitabine and ipafricept (3.5 mg/kg days 1, 15). Because of fragility fractures seen with different anti-Wnt agents, following cohorts had ≥6 patients treated with ipafricept 3 to 5 mg/kg on day 1, and included bone marker monitoring and prophylactic bisphosphonates as indicated. On the basis of preclinical data, sequential dosing was evaluated in cohort 4 (ipafricept day 1 followed nab-paclitaxel + gemcitabine day 3). Objectives included safety, MTD, recommended phase II dose, pharmacokinetics, immunogenicity, pharmacodynamics, and efficacy.

RESULTS

A total of 26 patients were enrolled, five in cohort 1 and seven each in cohorts 2-4. ipafricept-related adverse events (AEs) of any grade included fatigue, nausea, vomiting, anorexia, and pyrexia. ipafricept-related AEs grade ≥3 included two events of aspartate aminotransferase elevation, and one each of nausea, rash, vomiting, and leucopenia. No dose-limiting toxicities or fragility fractures were observed. Nine patients (34.6%) had partial response, 12 (46.2%) stable disease as best response, with clinical benefit rate of 81%. Median progression-free survival was 5.9 m [95% confidence interval (CI), 3.4-18.4], median overall survival was 9.7 m (95% CI, 7.0-14). The study was terminated by the sponsor due to bone-related toxicity within this therapeutic program and concerns for commercial viability. One patient remains on therapy under compassionate use.

CONCLUSIONS

Ipafricept can be administered with nab-paclitaxel + gemcitabine with reasonable tolerance. Wnt pathway remains a therapeutic target of interest in mPDAC.

A framework for advancing our understanding of cancer-associated fibroblasts

Cancer-associated fibroblasts (CAFs) are a key component of the tumour microenvironment with diverse functions, including matrix deposition and remodelling, extensive reciprocal signalling interactions with cancer cells and crosstalk with infiltrating leukocytes. As such, they are a potential target for optimizing therapeutic strategies against cancer. However, many challenges are present in ongoing attempts to modulate CAFs for therapeutic benefit. These include limitations in our understanding of the origin of CAFs and heterogeneity in CAF function, with it being desirable to retain some antitumorigenic functions. On the basis of a meeting of experts in the field of CAF biology, we summarize in this Consensus Statement our current knowledge and present a framework for advancing our understanding of this critical cell type within the tumour microenvironment.

Abstract C09: Inhibition of tumor growth and post-treatment regrowth by SM08502, a novel, small-molecule CDC-like kinase (CLK) inhibitor, in combination with standard of care in pancreatic cancer models

Relapse and treatment resistance rates remain high in pancreatic cancer (PC) with standard-of-care (SOC) chemotherapy regimens, although combining them with targeted drug therapies holds promise for improving treatment outcomes and clinical benefits. The Wnt signaling pathway is implicated in multiple cancer hallmarks, including immune evasion, and regulation and survival of cancer stem cells. Aberrant activation of Wnt signaling is common in PC and many other cancers, making it a therapeutic target of interest. SM08502 is a novel, oral, small-molecule pan-CLK inhibitor that potently inhibits the Wnt signaling pathway. These studies were performed to assess the tolerability and efficacy of SM08502 in combination with chemotherapy regimens including gemcitabine (G), paclitaxel (P), and nab-paclitaxel (Nab-P) in xenograft models of PC. First, the effect of oral SM08502 in combination with G or G/P on tumor growth inhibition (TGI) relative to vehicle was assessed over 20-21 days in nude mice (n=6 per group) bearing Capan-1 or HPAFII cell-line-derived xenografts. In Capan-1 xenografts, SM08502 (12.5 mg/kg QD) + G (25 mg/kg Q7D i.p.) induced significant TGI (73%, p=0.009) and was more effective than either treatment alone. In HPAFII xenografts, SM08502 (6.25, 12.5 or 25 mg/kg QD) + G/P (75/30 mg/kg Q7D i.p.) induced ≥ 92% TGI (p&lt;0.001) and tumor regressions in ≥ 4 of 6 mice per group at all tested doses. Next, the effect of initial treatment of SOC (G/Nab-P) alone or combined with SM08502 (6.25, 12.5, or 25 mg/kg QD) on tumor regrowth during an observation phase was assessed in Capan-1 xenografts and a patient-derived xenograft (PDX) model. TGI was calculated both during (treatment phase) and up to 40 days after (observation phase) treatment relative to vehicle and SOC alone, respectively. In Capan-1, SM08502 + G/Nab-P (75/30 mg/kg Q7D) induced strong TGI (88-94%, p&lt;0.001) and increased tumor regressions vs. G/Nab-P at the end of treatment (day 27). In the PDX model, SM08502 + G/Nab-P (50/30 mg/kg Q7D) inhibited tumor growth earlier than G/Nab-P in the treatment phase, but TGI was similar after 21 days of treatment (94-96% p&lt;0.0001). At the end of observation in both the Capan-1 and PDX models, SM08502 + G/Nab-P significantly inhibited tumor regrowth (Capan-1, 25 mg/kg, 73.5%, p=0.003; PDX, 12.5 mg/kg, 71.4%; p=0.01). Additionally, survival was improved with all doses of SM08502 + G/Nab-P in Capan-1 xenografts (p&lt;0.05 vs. G/Nab-P). Based on body weight measurements, all treatments were well tolerated except for SM08502 (25 mg/kg) + G/Nab-P in the PDX model (not carried through observation phase). Oral SM08502 potently inhibited tumor growth in combination with chemotherapy and extended antitumor effects in genetically distinct PC models. These data show that the combined application of SM08502 with SOC therapy has potential to provide clinical benefit in PC. A phase 1 study assessing safety, tolerability, and pharmacokinetics of SM08502 in subjects with advanced solid tumors is ongoing (NCT03355066).

Citation Format: Carine Bossard, Igor Astsaturov, Nathalia Cruz, Brian Eastman, Chi-Ching Mak, K.C. Sunil, Betty Tam, Gail Bucci, Josh Stewart, Timothy Phalen, Steven Cha. Inhibition of tumor growth and post-treatment regrowth by SM08502, a novel, small-molecule CDC-like kinase (CLK) inhibitor, in combination with standard of care in pancreatic cancer models [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 C09.

Abstract C06: Cholesterol deprivation induces TGFβ signaling to promote basal differentiation in pancreatic cancer

Oncogenic transformation alters the metabolism of cellular nutrients to sustain tumor growth. We here define a mechanism by which modifications in cholesterol metabolism control the formation of pancreatic ductal adenocarcinoma (PDAC). Disruption of distal cholesterol biosynthesis by means of conditional inactivation of Nsdhl in mice bearing a tumor-inducing Kras mutation (KrasG12D) prevented PDAC formation in the context of a heterozygous Trp53f/+ genotype without impairing normal pancreatic development. In mice with pancreatic Nsdhl ablation and homozygous loss of Trp53, the emerging tumors presented with the aggressive basal (mesenchymal) phenotype as opposed to the classic (glandular) PDAC. This paralleled significantly reduced expression of cholesterol metabolic pathway genes in human basal PDAC subtype. Mechanistically, we demonstrate that genetic or metabolic reduction in cellular cholesterol induces the expression of transforming growth factor beta (TGF) and activates pro-mesenchymal effectors in human and murine PDAC, providing a direct transcriptional mechanism by which cholesterol metabolism can condition tumor differentiation. Activity of TGF beta pathway estimated via pSMAD2 expression in surgical PDAC samples inversely correlated with patients’ blood cholesterol levels, especially in patients taking cholesterol-lowering statins. Conclusions: Low levels of cellular cholesterol induce autocrine TGF beta signaling in PDAC. Malnutrition or cholesterol-lowering statins may be mechanistically linked to basal PDAC differentiation.

Citation Format: Linara Gabitova, Suraj Peri, Ralph Francescone, Janusz Franco-Barraza, Neelima Shah, Emmanuelle Nicolas, Elizabeth A. Handorf, Kathy Q. Cai, Ido Sloma, Rachel Chiaverelli, Richard Moffitt, Erica A. Golemis, Carolyn Fang, Shannon Lynch, Edna Cukierman, Igor Astsaturov. Cholesterol deprivation induces TGFβ signaling to promote basal differentiation 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 C06.

Abstract 3469: Dual inhibition of the EGFR and Aurora A pathways in Kras mutated non-small cell lung cancers

Lung cancer is the leading cause of cancer related death in the US. Patients with advanced disease generally have a poor prognosis with a median survival of around 10 to 12 months with standard chemotherapy. In patients with non-squamous non-small cell lung cancers (NSCLC) incidence of KRAS mutations reach ~22%. Specific treatments for Kras mutated NSCLC have not been developed although recent reports suggest an advantage for treatment with immunotherapy over chemotherapy in the second line setting. Published reports using a synthetic lethal screening method show that the combined inhibition of the EGFR and Aurora A kinase pathways could have synergistic effect on viability in head and neck and colon cancer cell lines suggesting a potential benefit of such combination therapy in these patients (Astsaturov and colleagues, 2010). Our study aims to examine the effects of combination of erlotinib (E), an EGFR small-molecule inhibitor, and Alisertib (MLN8237, A), an inhibitor of Aurora A kinase, in lung cancer models with different KRAS status. Human NSCLC cell lines with both wild type and mutated KRAS showed weak or moderate sensitivity to both drugs in vitro. Treatment with both E and A had synergistic activity in all examined cell lines, wild type KRAS (H2228, H1299) or mutated KRAS (A549, H1299, H358, H460, and H62). Western blot analysis confirmed that combination treatment enhanced apoptosis compared to single drug use as evidenced by cleaved PARP. In xenograft models, CB17 SCID mice were treated with single drug or E+A for three weeks. H322M xenograft tumors bearing wild type KRAS were moderately sensitive to growth inhibition by E (10 mg/kg/day) and A (20 mg/kg/twice daily) alone and the combination had an additive effect. A549 and H358 xenografts were insensitive to E because of the mutated KRAS and moderately sensitive to A. However, the combination of E+A had a synergistic effect and significantly inhibited tumor growth. Western blot analysis of signaling pathways downstream of the EGFR and Aurora A in tumor xenografts shows synergistic inhibition after two-drug treatment. Our results suggest that combined inhibition of both pathways might be an effective treatment strategy for lung cancers harboring KRAS mutations.

Citation Format: Tetyana Bagnyukova, Brian Egleston, Mackenzie Kramer, Igor Astsaturov, Erica Golemis, Hossein Borghaei. Dual inhibition of the EGFR and Aurora A pathways in Kras mutated non-small cell lung cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3469.

Statins Synergize with Hedgehog Pathway Inhibitors for Treatment of Medulloblastoma

Purpose: The role of cholesterol biosynthesis in hedgehog pathway activity and progression of hedgehog pathway medulloblastoma (Hh-MB) were examined in vivo Statins, commonly used cholesterol-lowering agents, were utilized to validate cholesterol biosynthesis as a therapeutic target for Hh-MB.Experimental Design: Bioinformatic analysis was performed to evaluate the association between cholesterol biosynthesis with hedgehog group medulloblastoma in human biospecimens. Alterations in hedgehog signaling were evaluated in medulloblastoma cells after inhibition of cholesterol biosynthesis. The progression of endogenous medulloblastoma in mice was examined after genetic blockage of cholesterol biosynthesis in tumor cells. Statins alone, or in combination with vismodegib (an FDA-approved Smoothened antagonist), were utilized to inhibit medulloblastoma growth in vivoResults: Cholesterol biosynthesis was markedly enhanced in Hh-MB from both humans and mice. Inhibition of cholesterol biosynthesis dramatically decreased Hh pathway activity and reduced proliferation of medulloblastoma cells. Statins effectively inhibited medulloblastoma growth in vivo and functioned synergistically in combination with vismodegib.Conclusions: Cholesterol biosynthesis is required for Smoothened activity in the hedgehog pathway, and it is indispensable for the growth of Hh-MB. Targeting cholesterol biosynthesis represents a promising strategy for treatment of Hh-MB. Clin Cancer Res; 24(6); 1375-88. ©2018 AACR.

Molecular characteristics of hepatocellular carcinomas from different age groups

While most patients in Western countries who are diagnosed with HCC are in their 50s and 60s, HCCs diagnosed at extremes of the age spectrum (i.e., < 40 years and ≥ 75 years) are less common and have been linked with distinct geographic locations and etiologies. Using multiplatform profiling, we identified differences in genetic alterations and protein expression in different age groups within a large cohort of HCC patients (N = 421). Young adult HCC patients (18-39 years' old) were more likely to be female, living in the West and Midwestern United States, and showed decreased androgen receptor, drug resistance and pro-angiogenic protein expression compared to older patients. TP53 mutations were the most frequent alteration in young adults (19%), whereas CTNNB1 mutations occurred in 30-33% of patients ≥ 40 years' old. The overall frequency of pathogenic and presumed pathogenic mutations was observed to increase significantly with advancing age. To our knowledge, these data represent one of the only studies to analyze age-specific molecular profiles in HCC, and provide a basis for further exploration and validation of these findings with respect to their clinical and therapeutic implications.

Future Clinical Trials: Genetically Driven Trials

The design of modern oncology clinical trials seeks to match patients' cancer molecular biomarkers with medications that specifically target those biomarkers, a general paradigm shift in cancer care coined clinical cancer biology. This approach exploits the synthetic lethality between a specific genetic alteration in the cancer cell and a drug: rapid termination of exaggerated kinase activity exemplifies this phenomenon. Synthetic lethality-based investigations are driven by rapidly evolving technologies for cancer molecular profiling. As these technologies evolve, future clinical trials will test drugs' activity based on the molecular mechanisms rather than by the tumor's appearance under a microscope.

Anti-pancreatic cancer activity of ONC212 involves the unfolded protein response (UPR) and is reduced by IGF1-R and GRP78/BIP

Pancreatic cancer is chemo-resistant and metastasizes early with an overall five-year survival of ∼8.2%. First-in-class imipridone ONC201 is a small molecule in clinical trials with anti-cancer activity. ONC212, a fluorinated-ONC201 analogue, shows preclinical efficacy in melanoma and hepatocellular-cancer models. We investigated efficacy of ONC201 and ONC212 against pancreatic cancer cell lines (N=16 including 9 PDX-cell lines). We demonstrate ONC212 efficacy in 4 in-vivo models including ONC201-resistant tumors. ONC212 is active in pancreatic cancer as single agent or in combination with 5-fluorouracil, irinotecan, oxaliplatin or RTK inhibitor crizotinib. Based on upregulation of pro-survival IGF1-R in some tumors, we found an active combination of ONC212 with inhibitor AG1024, including in vivo. We show a rationale for targeting pancreatic cancer using ONC212 combined with targeting the unfolded-protein response and ER chaperones such as GRP78/BIP. Our results lay the foundation to test imipridones, anti-cancer agents, in pancreatic cancer, that is refractory to most drugs.

Abstract 1124: Assessment of HRD score as predictor of chemosensitivity of PDAC PDX xenograft models to DNA-damaging chemotherapy

Pancreatic ductal adenocarcinoma (PDAC) is a devastating malignancy that affects 44,000 individuals annually in the US, with almost 90% lethality even when diagnosed prior to metastasis. There is an urgent unmet medical need both for new therapies as well as better matching of existing therapies to patients. To address this emergency, we are assessing the feasibility of implementing a strategy of using HRD (Homologous Recombination Deficiency) scores for better therapy matching in PDAC patients. Using a panel of 77 patient-derived xenograft (PDX) models that were developed from fresh surgical PDAC tumor samples, HRD scores were generated based on analysis of three biomarkers (LOH, TAI and LST) and mutational data for 45 genes. All 77 samples met inclusion criteria, 75 FFPE specimens generated mutation data. HRD analysis was successful for 71 specimens (range= 1 - 63 (median=22)), with the primary cause of failure identified as high non-tumor content. 53 PDX models had mutations in KRAS gene and 45 in TP53. We have also identified 4 PDX models with mutations in BRCA2, 3 models with mutations in ATM, 4 models with mutations in RAD51. We have also found frequent mutations in several other DNA repair genes (ATR, PALB2, MLH1, MSH2, MSH3, MSH6, FANCM), but most of these models retained one functional allele and were not associated with a high HRD score. Using this genomic analysis, all 71 PDX models were stratified into three clusters with high, medium and low HRD scores. Three PDX models with the highest and lowest HRD scores each were selected for an in vivo study with DNA-damaging platinum-based chemotherapeutic agents Cisplatin and Carboplatin, as well as with a clinically relevant PARP inhibitor Niraparib. The results of the PDX study will be reported and compared with responses to chemotherapy using RECIST V1.1 in patients.

Note: This abstract was not presented at the meeting.

Citation Format: Vladimir Khazak, Natalia Skobeleva, Anastasiia Vetkina, Ilya Serebriiskii, Kirsten M. Timms, Angela Davies, Igor Astsaturov. Assessment of HRD score as predictor of chemosensitivity of PDAC PDX xenograft models to DNA-damaging chemotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1124. doi:10.1158/1538-7445.AM2017-1124

Abstract 438: Cholesterol biosynthesis is a critical metabolic dependency in pancreatic cancer

Pancreatic cancer is rapidly rising to become the 2nd leading cause of cancer deaths by 2020 in the USA. The rise in pancreatic cancer incidence is paralleled by the epidemic of obesity, type 2 diabetes, and associated increase in blood cholesterol, although mechanistic explanations for this are currently unknown. We and others have demonstrated that cancers with activated EGFR and KRAS signaling have increased demands for cholesterol and are vulnerable to interference with cholesterol uptake or endogenous cholesterol biosynthesis. We recently identified a metabolic step in the distal cholesterol pathway, mediated by SC4MOL and NSDHL enzymes, as a critical regulator of cell growth in the keratinocyte model of KRAS-induced carcinogenesis via the LXR agonistic effect of accumulating C4-methylsterols. Based on these preliminary data, we set out to test if pancreatic cancer initiation and progression depend on accelerated cholesterol biosynthesis in a genetic mouse model containing a conditional cholesterol pathway enzyme deficiency (conditional knockout of Nsdhlf/f) in the context of pancreatic cancer development in KPC mice (LSL-KrasG12D;Tp53f/f;Pdx1-Cre).

Results: Conditional inactivation of NSDHL alone in pancreatic tissue during normal development produced no apparent phenotype. As expected, the NSDHL-sufficient KPC mice as well as heterozygous Nsdhlf/+ littermates did not survive beyond 8 weeks of age due to rapid development of progressive pancreatic tumors showing complete displacement of pancreatic tissue with adenocarcinoma and high-grade PanIN lesions. Contrastingly, the survival of pancreatic conditional NSDHL-null mice was significantly extended beyond the median survival of 50 days in NSDHL-sufficient age-matched controls. Furthermore, the progression of pancreatic lesions from ADM to PanIN3 was remarkably delayed on NSDHL-null background, with only a proportion of animals developing adenocarcinoma. Evaluation of pancreatic tissues revealed a dramatic reduction of tumor-induced desmoplasia at all stages of pancreatic cancer development. Our ongoing studies will address the role of cholesterol metabolism in pancreatic cancer progression via regulation of tumor-specific production of stroma-recruiting growth factors.

Conclusions: Our studies demonstrated for the first time essential genetic evidence for metabolic dependency of pancreatic cancer on cholesterol metabolism. We identified NSDHL as a critical target in the endogenous pathway of cholesterol biosynthesis, and determined that blockade of NSDHL has dramatic consequences on the reciprocal signaling between the KRAS-transformed pancreatic cancer cells and the stroma.

Citation Format: Linara Gabitova, Alena Klochkova, Diana Restifo, Aleksandra Mazitova, Edna Cukierman, Tiffiney Hartman, Igor Astsaturov. Cholesterol biosynthesis is a critical metabolic dependency in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 438. doi:10.1158/1538-7445.AM2017-438

Perspectives of HER2-targeting in gastric and esophageal cancer

INTRODUCTION

The blockade of HER2 signaling has significantly improved the outlook for esophagogastric cancer patients. However, targeting HER2 still remains challenging due to complex biology of this receptor in gastric and esophageal cancers. Areas covered: Here, we review complex HER2 biology, current methods of HER2 testing and tumor heterogeneity of gastroesophageal cancer. Ongoing and completed clinical research data are discussed. Expert opinion: HER2 overexpression is a validated target in gastroesophageal cancer, with therapeutic implications resulting in prolonged survival when inhibited in the front-line setting. With standardized HER2 testing in gastro-esophageal cancer, the ongoing trials are testing newer agents and combinations including combination of anti-HER2 antibodies with immunotherapy. Clonal heterogeneity and emergence of resistance will challenge our approach to treating these patients beyond the frontline settings.

LDL cholesterol counteracts the antitumour effect of tyrosine kinase inhibitors against renal cell carcinoma

Background:

Treatment with tyrosine kinase inhibitors (TKIs) significantly improves survival of patients with renal cell carcinoma (RCC). However, about one-quarter of the RCC patients are primarily refractory to treatment with TKIs.

Methods:

We examined viability of RCC and endothelial cells treated with low-density lipoprotein (LDL) and/or TKIs. Next, we validated the potential role of PI3K/AKT signalling in LDL-mediated TKI resistance. Finally, we examined the effect of a high-fat/high-cholesterol diet on the response of RCC xenograft tumours to sunitinib.

Results:

The addition of LDL cholesterol increases activation of PI3K/AKT signalling and compromises the antitumour efficacy of TKIs against RCC and endothelial cells. Furthermore, RCC xenograft tumours resist TKIs in mice fed a high-fat/high-cholesterol diet.

Conclusions:

The ability of renal tumours to maintain their cholesterol homoeostasis may be a critical component of TKI resistance in RCC patients.

Abstract A77: Screening of conditionally reprogrammed patient-derived carcinoma cells identifies ERCC3-MYC interactions as a target in pancreatic cancer

Methods: Pancreatic ductal adenocarcinoma (PDAC) is a devastating malignancy that affects 44,000 individuals yearly in the US. The list of agents active against PDAC is limited. We explored in an unbiased fashion the clinically available drugs to identify novel cytotoxics using new physiological models for PDAC including cells rapidly expanded in vitro from surgical or xenografted tumors (PDX).

Results: Not unexpectedly, only a small minority of agents showed activity against pancreatic carcinoma cells in vitro. Among these, transcriptional repressors and drugs interfering with protein folding and biosynthesis ranked as most cytotoxic. Triptolide, a covalent inhibitor of the ERCC3, a bifunctional regulator of transcription and DNA repair, was most consistently effective in vitro and highly effective in vivo, causing prolonged complete regression in multiple PDX models. Importantly, triptolide showed superior activity in MYC-amplified PDX models, suggesting a critical role for ERCC3 in this subset. Triptolide elicited rapid and profound depletion of MYC oncoprotein, a transcriptional co-factor for ERCC3. Expression of ERCC3 was MYC-dependent, while resistance to triptolide was associated with elevated ERCC3 and MYC expression. Furthermore, high ERCC3 mRNA level was associated with decreased survival of PDAC patients.

Conclusions: These findings provide preclinical evidences for transcriptional vulnerability in PDAC via ERCC3 targeting and a new mechanistic approach for disruption of MYC-dependent pancreatic cancers.

Citation Format: Igor Astsaturov, Sandra A. Jablonski, Yan Zhou, Ilya Serebriiskii, Paz Keren, Louis M. Weiner, Erica Golemis, Vladimir Khazak.{Authors}. Screening of conditionally reprogrammed patient-derived carcinoma cells identifies ERCC3-MYC interactions as a target in pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr A77.

Screening of Conditionally Reprogrammed Patient-Derived Carcinoma Cells Identifies ERCC3-MYC Interactions as a Target in Pancreatic Cancer

PURPOSE

Even when diagnosed prior to metastasis, pancreatic ductal adenocarcinoma (PDAC) is a devastating malignancy with almost 90% lethality, emphasizing the need for new therapies optimally targeting the tumors of individual patients.

EXPERIMENTAL DESIGN

We first developed a panel of new physiologic models for study of PDAC, expanding surgical PDAC tumor samples in culture using short-term culture and conditional reprogramming with the Rho kinase inhibitor Y-27632, and creating matched patient-derived xenografts (PDX). These were evaluated for sensitivity to a large panel of clinical agents, and promising leads further evaluated mechanistically.

RESULTS

Only a small minority of tested agents was cytotoxic in minimally passaged PDAC cultures in vitro Drugs interfering with protein turnover and transcription were among most cytotoxic. Among transcriptional repressors, triptolide, a covalent inhibitor of ERCC3, was most consistently effective in vitro and in vivo causing prolonged complete regression in multiple PDX models resistant to standard PDAC therapies. Importantly, triptolide showed superior activity in MYC-amplified PDX models and elicited rapid and profound depletion of the oncoprotein MYC, a transcriptional regulator. Expression of ERCC3 and MYC was interdependent in PDACs, and acquired resistance to triptolide depended on elevated ERCC3 and MYC expression. The Cancer Genome Atlas analysis indicates ERCC3 expression predicts poor prognosis, particularly in CDKN2A-null, highly proliferative tumors.

CONCLUSIONS

This provides initial preclinical evidence for an essential role of MYC-ERCC3 interactions in PDAC, and suggests a new mechanistic approach for disruption of critical survival signaling in MYC-dependent cancers. Clin Cancer Res; 22(24); 6153-63. ©2016 AACR.

EGFR and RB1 as Dual Biomarkers in HPV-Negative Head and Neck Cancer

Clinical decision making for human papillomavirus (HPV)-negative head and neck squamous cell carcinoma (HNSCC) is predominantly guided by disease stage and anatomic location, with few validated biomarkers. The epidermal growth factor receptor (EGFR) is an important therapeutic target, but its value in guiding therapeutic decision making remains ambiguous. We integrated analysis of clinically annotated tissue microarrays with analysis of data available through the TCGA, to investigate the idea that expression signatures involving EGFR, proteins regulating EGFR function, and core cell-cycle modulators might serve as prognostic or drug response-predictive biomarkers. This work suggests that consideration of the expression of NSDHL and proteins that regulate EGFR recycling in combination with EGFR provides a useful prognostic biomarker set. In addition, inactivation of the tumor suppressor retinoblastoma 1 (RB1), reflected by CCND1/CDK6-inactivating phosphorylation of RB1 at T356, inversely correlated with expression of EGFR in patient HNSCC samples. Moreover, stratification of cases with high EGFR by expression levels of CCND1, CDK6, or the CCND1/CDK6-regulatory protein p16 (CDKN2A) identified groups with significant survival differences. To further explore the relationship between EGFR and RB1-associated cell-cycle activity, we evaluated simultaneous inhibition of RB1 phosphorylation with the CDK4/6 inhibitor palbociclib and of EGFR activity with lapatinib or afatinib. These drug combinations had synergistic inhibitory effects on the proliferation of HNSCC cells and strikingly limited ERK1/2 phosphorylation in contrast to either agent used alone. In summary, combinations of CDK and EGFR inhibitors may be particularly useful in EGFR and p^T356RB1-expressing or CCND1/CDK6-overexpressing HPV-negative HNSCC. Mol Cancer Ther; 15(10); 2486-97. ©2016 AACR.

Molecular profiling of neuroendocrine malignancies to identify prognostic and therapeutic markers: a Fox Chase Cancer Center Pilot Study

BACKGROUND

The rarity of neuroendocrine malignancies limits the ability to develop new therapies and thus a better understanding of the underlying biology is critical.

METHODS

Through a prospective, IRB-approved protocol, patients with neuroendocrine malignancies underwent next-generation sequencing of their tumours to detect somatic mutations (SMs) in 50 cancer-related genes. Clinicopathologic correlation was made among poorly differentiated neuroendocrine carcinomas (NECs/poorly differentiated histology and Ki-67 >20%) and pancreatic neuroendocrine tumours (PanNETs/Ki67 ⩽20%) and non-pancreatic neuroendocrine tumours (NP-NETs/Ki67 ⩽20%).

RESULTS

A total of 77 patients were enrolled, with next-generation sequencing results available on 63 patients. Incidence of SMs was 83% (19 out of 23) in poorly differentiated NECs, 45% (5 out of 11) in PanNETs and 14% (4 out of 29) in NP-NETs. TP53 was the most prevalent mutation in poorly differentiated NECs (57%), and KRAS (30%), PIK3CA/PTEN (22%) and BRAF (13%) mutations were also found. Small intestinal neuroendocrine tumours (Ki67 <2%/n=9) did not harbour any mutations. Prevalence of mutations correlated with higher risk of progression within the previous year (32% (low risk) vs 11% (high risk), P=0.01) and TP53 mutation correlated with worse survival (2-year survival 66% vs 97%, P=0.003).

CONCLUSIONS

Poorly differentiated NECs have a high mutation burden with potentially targetable mutations. The TP53 mutations are associated with poor survival in neuroendocrine malignancies. These findings have clinical trial implications for choice of therapy and prognostic stratification and warrant confirmation.

Endogenous Sterol Metabolites Regulate Growth of EGFR/KRAS-Dependent Tumors via LXR

Meiosis-activating sterols (MAS) are substrates of SC4MOL and NSDHL in the cholesterol pathway and are important for normal organismal development. Oncogenic transformation by epidermal growth factor receptor (EGFR) or RAS increases the demand for cholesterol, suggesting a possibility for metabolic interference. To test this idea in vivo, we ablated Nsdhl in adult keratinocytes expressing KRAS(G12D). Strikingly, Nsdhl inactivation antagonized the growth of skin tumors while having little effect on normal skin. Loss of Nsdhl induced the expression of ATP-binding cassette (ABC) transporters ABCA1 and ABCG1, reduced the expression of low-density lipoprotein receptor (LDLR), decreased intracellular cholesterol, and was dependent on the liver X receptor (LXR) α. Importantly, EGFR signaling opposed LXRα effects on cholesterol homeostasis, whereas an EGFR inhibitor synergized with LXRα agonists in killing cancer cells. Inhibition of SC4MOL or NSDHL, or activation of LXRα by sterol metabolites, can be an effective strategy against carcinomas with activated EGFR-KRAS signaling.