KRT17High/CXCL8+ tumor cells display both classical and basal features and regulate myeloid infiltration in the pancreatic cancer microenvironment

PURPOSE

Pancreatic ductal adenocarcinoma (PDAC) is generally divided in two subtypes, classical and basal. Recently, single cell RNA sequencing has uncovered the co-existence of basal and classical cancer cells, as well as intermediary cancer cells, in individual tumors. The latter remains poorly understood; here, we sought to characterize them using a multimodal approach.

EXPERIMENTAL DESIGN

We performed subtyping on a single cell RNA sequencing dataset containing 18 human PDAC samples to identify multiple intermediary subtypes. We generated patient-derived PDAC organoids for functional studies. We compared single cell profiling of matched blood and tumor samples to measure changes in the local and systemic immune microenvironment. We then leveraged longitudinally patient-matched blood to follow individual patients over the course of chemotherapy.

RESULTS

We identified a cluster of KRT17-high intermediary cancer cells that uniquely express high levels of CXCL8 and other cytokines. The proportion of KRT17High/CXCL8+ cells in patient tumors correlated with intra-tumoral myeloid abundance, and, interestingly, high pro-tumor peripheral blood granulocytes, implicating local and systemic roles. Patient-derived organoids maintained KRT17High/CXCL8+cells and induced myeloid cell migration in an CXCL8-dependent manner. In our longitudinal studies, plasma CXCL8 decreased following chemotherapy in responsive patients, while CXCL8 persistence portended worse prognosis.

CONCLUSIONS

Through single cell analysis of PDAC samples we identified KRT17High/CXCL8+ cancer cells as an intermediary subtype, marked by a unique cytokine profile and capable of influencing myeloid cells in the tumor microenvironment and systemically. The abundance of this cell population should be considered for patient stratification in precision immunotherapy.

Analysis of donor pancreata defines the transcriptomic signature and microenvironment of early pre-neoplastic pancreatic lesions

The adult healthy human pancreas has been poorly studied given lack of indication to obtain tissue from the pancreas in the absence of disease and rapid postmortem degradation. We obtained pancreata from brain dead donors thus avoiding any warm ischemia time. The 30 donors were diverse in age and race and had no known pancreas disease. Histopathological analysis of the samples revealed PanIN lesions in most individuals irrespective of age. Using a combination of multiplex immunohistochemistry, single cell RNA sequencing, and spatial transcriptomics, we provide the first ever characterization of the unique microenvironment of the adult human pancreas and of sporadic PanIN lesions. We compared healthy pancreata to pancreatic cancer and peritumoral tissue and observed distinct transcriptomic signatures in fibroblasts, and, to a lesser extent, macrophages. PanIN epithelial cells from healthy pancreata were remarkably transcriptionally similar to cancer cells, suggesting that neoplastic pathways are initiated early in tumorigenesis.

Statement of significance

The causes underlying the onset of pancreatic cancer remain largely unknown, hampering early detection and prevention strategies. Here, we show that PanIN are abundant in healthy individuals and present at a much higher rate than the incidence of pancreatic cancer, setting the stage for efforts to elucidate the microenvironmental and cell intrinsic factors that restrain, or, conversely, promote, malignant progression.

Abstract A006: Integrating single cell and spatial transcriptomics define gene signature for pancreatic ductal adenocarcinoma pre-neoplastic lesion

Pancreatic Cancer Ductal Adenocarcinoma (PDAC) is one of the deadliest cancers with 5-year survival of 11%. Understanding the intratumor heterogeneity is a pivotal piece to unravel the complexity of PDAC. While single cell RNASeq identifies the heterogeneous cell populations within the tumor tissue, spatially characterizing the transcriptomic profile of neoplastic and pre-neoplastic populations within the tissue remains a challenge, as the spatial dimension is usually lost upon tissue dissociation. We identified an approach to integrate spatial transcriptomics data with single cell RNASeq data. To characterize the cell populations within the tissue we performed single cell RNASeq on disease pathology-free pancreas tissue and primary PDAC samples. We profiled the transcriptomic profile of Acinar, Ductal, Acinar-to-Ductal (ADM), and Pancreatic Intraepithelial Neoplasia (PanINs) regions of interest (ROIs) across the tissue using the Nanostring GeoMx platform. Differential gene expression analysis using linear mixed-effect models of the cell-type specific ROIs defined pan-marker gene sets for each cell type, which were mapped to UMAP projections of single cell RNA sequencing data using AUCell scoring. As expected, the acinar pan-markers gene set derived from the spatial transcriptomics mapped to the manually annotated acinar population in the single cell data. On the other hand, Ductal, ADM, and PanIN pan-marker gene sets were mapped to distinct clusters that previously were not well-defined by single cell sequencing. The analysis coupled with orthogonal validation using RNAScope revealed gene signatures uniquely specific to ADM lesions and PanINs, respectively. Interestingly, our list included known markers as well as novel findings, supporting the validity of the findings. Furthermore, RNA velocity analysis using scVelo revealed a trajectory of cell evolution originating from acinar cells passing through the newly-defined ADM population and ending towards the ductal population derived from tumor samples. Overall, this integration approach of spatial and single cell transcriptomics can further define the characteristics that differentiate neoplastic and pre-neoplastic populations, as well as the potential drivers for tumorigenesis that could be therapeutically targeted.

Citation Format: Ahmed M. Elhossiny, Eileen Carpenter, Padma Kadiyala, Yaqing Zhang, Filip Bednar, Arvind Rao, Timothy Frankel, Marina Pasca Di Magliano. Integrating single cell and spatial transcriptomics define gene signature for pancreatic ductal adenocarcinoma pre-neoplastic lesion [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 A006.

MHC Class II Expression Influences the Composition and Distribution of Immune Cells in the Metastatic Colorectal Cancer Microenvironment

Despite advances in therapy over the past decades, metastatic colorectal cancer (mCRC) remains a highly morbid disease. While the impact of MHC-I on immune infiltration in mCRC has been well studied, data on the consequences of MHC-II loss are lacking. Multiplex fluorescent immunohistochemistry (mfIHC) was performed on 149 patients undergoing curative intent resection for mCRC and stratified into high and low human leukocyte antigen isotype DR (HLA-DR) expressing tumors. Intratumoral HLA-DR expression was found in stromal bands, and its expression level was associated with different infiltrating immune cell makeup and distribution. Low HLA-DR expression was associated with increased intercellular distances and decreased population mixing of T helper cells and antigen-presenting cells (APC), suggestive of decreased interactions. This was associated with less co-localization of tumor cells and cytotoxic T lymphocytes (CTLs), which tended to be in a less activated state as determined by Ki67 and granzyme B expression. These findings suggest that low HLA-DR in the tumor microenvironment of mCRC may reflect a state of poor helper T-cell interactions with APCs and CTL-mediated anti-tumor activity. Efforts to restore/enhance MHC-II presentation may be a useful strategy to enhance checkpoint inhibition therapy in the future.

ATDC binds to KEAP1 to drive NRF2-mediated tumorigenesis and chemoresistance in pancreatic cancer

Pancreatic ductal adenocarcinoma is a lethal disease characterized by late diagnosis, propensity for early metastasis and resistance to chemotherapy. Little is known about the mechanisms that drive innate therapeutic resistance in pancreatic cancer. The ataxia-telangiectasia group D-associated gene (ATDC) is overexpressed in pancreatic cancer and promotes tumor growth and metastasis. Our study reveals that increased ATDC levels protect cancer cells from reactive oxygen species (ROS) via stabilization of nuclear factor erythroid 2-related factor 2 (NRF2). Mechanistically, ATDC binds to Kelch-like ECH-associated protein 1 (KEAP1), the principal regulator of NRF2 degradation, and thereby prevents degradation of NRF2 resulting in activation of a NRF2-dependent transcriptional program, reduced intracellular ROS and enhanced chemoresistance. Our findings define a novel role of ATDC in regulating redox balance and chemotherapeutic resistance by modulating NRF2 activity.

Teamwork at the Bench: Strategies for Collaborative Surgical Science in a Pandemic

The Center for Basic and Translational Science was formed to address the unique challenges faced by surgeon-scientists. Shortly after its inception, COVID-19 upended research workflows at our institution. We discuss how the collaborative Center for Basic and Translational Science framework was adapted to support laboratories during the pandemic by assisting with ramp-down, promoting mentorship and community building, and maintaining research productivity.

Abstract A51: Using single-cell gene expression profiles to determine the cellular landscape of pancreatic ductal adenocarcinoma

A key feature of pancreatic cancer is the extensive fibroinflammatory stroma that constitutes the bulk of the tumor volume. The stroma includes fibroblasts, extracellular matrix, and abundant infiltrating immune cells. The latter are largely suppressive immune cells, including regulatory T cells, myeloid-derived suppressor cells, and tumor-associated macrophages. Data from our laboratory and many others show that immune cells are a key determinant of pancreatic cancer progression and metastasis. Previous data from the lab showed that the immune infiltration in the pancreas is regulated by signals deriving from oncogenic Kras-expressing epithelial cells. We tested the hypothesis that oncogenic Kras, through activation of its effector pathway MAPK/ERK, directly regulates the accumulation of suppressive myeloid and lymphoid cells at the premetastatic niche. We used a doxycycline-inducible, reversible iKras* cell line derived from genetically engineered mouse model to modulate expression of Kras in orthotopically implanted tumors. We used the 10X Genomics platform for single-cell RNAseq to distinguish populations of cells collected from the tumors in both the Kras-On and Kras-Off groups at single-cell resolution. Using the Seurat R package, we analyzed the data from the two groups using unsupervised clustering methods to define clusters of cells based on their gene expression data. We then broadly defined these populations using cell type-specific gene expression patterns. Our next step is to define subpopulations of cells on which we can perform differential expression analyses to determine the changes in gene expression between the Kras-On and Kras-Off groups.

Citation Format: Veerin R. Sirihorachai, Samantha B. Kemp, Marina Pasca Di Magliano. Using single-cell gene expression profiles to determine the cellular landscape of pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr A51.

Mathematical Modeling of the Metastatic Colorectal Cancer Microenvironment Defines the Importance of Cytotoxic Lymphocyte Infiltration and Presence of PD-L1 on Antigen Presenting Cells

BACKGROUND

Although immune-based therapy has proven efficacious for some patients with microsatellite instability (MSI) colon cancers, a majority of patients receive limited benefit. Conversely, select patients with microsatellite stable (MSS) tumors respond to checkpoint blockade, necessitating novel ways to study the immune tumor microenvironment (TME). We used phenotypic and spatial data from infiltrating immune and tumor cells to model cellular mixing to predict disease specific outcomes in patients with colorectal liver metastases.

METHODS

Formalin fixed paraffin embedded metastatic colon cancer tissue from 195 patients were subjected to multiplex immunohistochemistry (mfIHC). After phenotyping, the G-function was calculated for each patient and cell type. Data was correlated with clinical outcomes and survival.

RESULTS

High tumor cell to cytotoxic T lymphocyte (TC-CTL) mixing was associated with both a pro-inflammatory and immunosuppressive TME characterized by increased CTL infiltration and PD-L1+ expression, respectively. Presence and engagement of antigen presenting cells (APC) and helper T cells (Th) were associated with greater TC-CTL mixing and improved 5-year disease specific survival compared to patients with a low degree of mixing (42% vs. 16%, p = 0.0275). Comparison of measured mixing to a calculated theoretical random mixing revealed that PD-L1 expression on APCs resulted in an environment where CTLs were non-randomly less associated with TCs, highlighting their biologic significance.

CONCLUSION

Evaluation of immune interactions within the TME of metastatic colon cancer using mfIHC in combination with mathematical modeling characterized cellular mixing of TCs and CTLs, providing a novel strategy to better predict clinical outcomes while identifying potential candidates for immune based therapies.

Myeloid Cell-Derived HB-EGF Drives Tissue Recovery After Pancreatitis

BACKGROUND & AIMS

Pancreatitis is a major cause of morbidity and mortality and is a risk factor for pancreatic tumorigenesis. Upon tissue damage, an inflammatory response, made up largely of macrophages, provides multiple growth factors that promote repair. Here, we examine the molecular pathways initiated by macrophages to promote pancreas recovery from pancreatitis.

METHODS

To induce organ damage, mice were subjected to cerulein-induced experimental pancreatitis and analyzed at various times of recovery. CD11b-DTR mice were used to deplete myeloid cells. Hbegf^f/f;LysM-Cre mice were used to ablate myeloid cell-derived heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF). To ablate EGFR specifically during recovery, pancreatitis was induced in Egfr^f/f;Ptf1a^FlpO/+;FSF-Rosa26^CAG-CreERT2 mice followed by tamoxifen treatment.

RESULTS

Macrophages infiltrating the pancreas in experimental pancreatitis make high levels of HB-EGF. Both depletion of myeloid cells and ablation of myeloid cell HB-EGF delayed recovery from experimental pancreatitis, resulting from a decrease in cell proliferation and an increase in apoptosis. Mechanistically, ablation of myeloid cell HB-EGF impaired epithelial cell DNA repair, ultimately leading to cell death. Soluble HB-EGF induced EGFR nuclear translocation and methylation of histone H4, facilitating resolution of DNA damage in pancreatic acinar cells in vitro. Consistent with its role as the primary receptor of HB-EGF, in vivo ablation of EGFR from pancreatic epithelium during recovery from pancreatitis resulted in accumulation of DNA damage.

CONCLUSIONS

By using novel conditional knockout mouse models, we determined that HB-EGF derived exclusively from myeloid cells induces epithelial cell proliferation and EGFR-dependent DNA repair, facilitating pancreas healing after injury.

Spatial and phenotypic immune profiling of metastatic colon cancer

Paramount to the efficacy of immune checkpoint inhibitors is proper selection of patients with adequate tumor immunogenicity and a robust but suppressed immune infiltrate. In colon cancer, immune-based therapies are approved for patients with DNA mismatch repair (MMR) deficiencies, in whom accumulation of genetic mutations results in increased neoantigen expression, triggering an immune response that is suppressed by the PD-L1/PD-1 pathway. Here, we report that characterization of the microenvironment of MMR-deficient metastatic colorectal cancer using multiplex fluorescent immunohistochemistry (mfIHC) identified increased infiltration of cytotoxic T lymphocytes (CTLs), which were more often engaged with epithelial cells (ECs) and improved overall survival. A subset of patients with intact MMR but a similar immune microenvironment to MMR-deficient patients was identified and found to universally express high levels of PD-L1, suggesting that they may represent a currently untreated, checkpoint inhibitor-responsive population. Further, PD-L1 expression on antigen-presenting cells (APCs) in the tumor microenvironment (TME) resulted in impaired CTL/EC engagement and enhanced infiltration and engagement of Tregs. Characterization of the TME by mfIHC highlights the interconnection between immunity and immunosuppression in metastatic colon cancer and may better stratify patients for receipt of immunotherapies.

Tracking Macrophage Infiltration in a Mouse Model of Pancreatic Cancer with the Positron Emission Tomography Tracer [11C]PBR28

BACKGROUND

The tumor microenvironment of pancreatic ductal adenocarcinoma (PDAC) contains abundant immunosuppressive tumor-associated macrophages. High level of infiltration is associated with poor outcome and is thought to represent a major roadblock to lymphocyte-based immunotherapy. Efforts to block macrophage infiltration have been met with some success, but noninvasive means to track tumor-associated macrophagess in PDAC are lacking. Translocator protein (TSPO) is a mitochondrial membrane receptor which is upregulated in activated macrophages. We sought to identify if a radiotracer-labeled cognate ligand could track macrophages in PDAC.

MATERIALS AND METHODS

A murine PDAC cell line was established from a transgenic mouse with pancreas-specific mutations in KRAS and p53. After confirming lack of endogenous TSPO expression, tumors were established in syngeneic mice. A radiolabeled TSPO-specific ligand ([11C] peripheral benzodiazepine receptor [PBR]28) was delivered intravenously, and tumor uptake was assessed by autoradiography, ex vivo, or micro-positron emission tomography imaging.

RESULTS

Resected tumors contained abundant macrophages as determined by immunohistochemistry and flow cytometry. Immunoblotting revealed murine macrophages expressed TSPO with increasing concentration on activation and polarization. Autoradiography of resected tumors confirmed [11C]PBR28 uptake, and whole mount sections demonstrated the ability to localize tumors. To confirm the findings were macrophage specific, experiments were repeated in CD11b-deficient mice, and the radiotracer uptake was diminished. Micro-positron emission tomography imaging validated radiotracer uptake and tumor localization in a clinically applicable manner.

CONCLUSIONS

As new immunotherapeutics reshape the PDAC microenvironment, tools are needed to better measure and track immune cell subsets. We have demonstrated the potential to measure changes in macrophage infiltration in PDAC using [11C]PBR28.

Usp9x Promotes Survival in Human Pancreatic Cancer and Its Inhibition Suppresses Pancreatic Ductal Adenocarcinoma In Vivo Tumor Growth

Usp9x has emerged as a potential therapeutic target in some hematologic malignancies and a broad range of solid tumors including brain, breast, and prostate. To examine Usp9x tumorigenicity and consequence of Usp9x inhibition in human pancreatic tumor models, we carried out gain- and loss-of-function studies using established human pancreatic tumor cell lines (PANC1 and MIAPACA2) and four spontaneously immortalized human pancreatic patient-derived tumor (PDX) cell lines. The effect of Usp9x activity inhibition by small molecule deubiquitinase inhibitor G9 was assessed in 2D and 3D culture, and its efficacy was tested in human tumor xenografts. Overexpression of Usp9x increased 3D growth and invasion in PANC1 cells and up-regulated the expression of known Usp9x substrates Mcl-1 and ITCH. Usp9x inhibition by shRNA-knockdown or by G9 treatment reduced 3D colony formation in PANC1 and PDX cell lines, induced rapid apoptosis in MIAPACA2 cells, and associated with reduced Mcl-1 and ITCH protein levels. Although G9 treatment reduced human MIAPACA2 tumor burden in vivo, in mouse pancreatic cancer cell lines established from constitutive (8041) and doxycycline-inducible (4668) KrasG12D/Tp53R172H mouse pancreatic tumors, Usp9x inhibition increased and sustained the 3D colony growth and showed no significant effect on tumor growth in 8041-xenografts. Thus, Usp9x inhibition may be therapeutically active in human PDAC, but this activity was not predicted from studies of genetically engineered mouse pancreatic tumor models.

IL-22 Promotes Pancreatic Cancer Tumorigenesis through Induction of Stemness and Epithelial to Mesenchymal Transition

Elevated levels of Interleukin 22 (IL-22) and its receptor (IL-22R) are associated with poor prognosis in pancreatic ductal adenocarcinoma (PDAC) and the underlying mechanism is currently unknown. Our aim is to investigate the role of the IL-22 axis in PDAC initiation and progression.

Impact of IL-22 on tumor initiation was assayed by subcutaneous and intravenous inoculation of PDAC cells into wild-type and IL-22−/− mice. The PKCY (Pdx1-Cre; KrasG12D; p53fl/+; RosaYFP) model of pancreas cancer was used to study the in-vivo presence and significance of IL-22 in spontaneous tumors. Results were confirmed in human specimens of surgically resected pancreas cancer.

IL-22R was present in all tested PDAC lines and IL-22 treatment led to STAT3 phosphorylation and subsequent increased expression of EMT (Epithelial to Mesenchymal Transition) transcription factors. Cells transitioned to a mesenchymal phenotype and robust tumor sphere formation was observed. While tumors readily formed in wild-type mice, initiation, establishment and growth were impaired in IL-22−/− mice and PKCY-IL-22−/− mice. Increased levels of IL-22 were found in both spontaneous murine tumors and surgical specimens compared to control tissue. IHC of tumors showed diffuse IL-22R staining with increasing intensity of pSTAT3 and EMT markers as tumors progressed to invasive cancer. FACS analysis identified type 3 innate lymphoid cells and TH22 cells as the source of IL-22 in both human and murine PDAC.

Our data suggests that IL-22 is integral in the initiation, progression and establishment of pancreatic cancer, positioning it as an attractive target for cancer therapy.

Early pancreatic islet fate and maturation is controlled through RBP-Jκ

Notch signaling is known to control early pancreatic differentiation through Ngn3 repression. In later stages, downstream of Notch, the Presenilins are still required to maintain the endocrine fate allocation. Amongst their multiple targets, it remains unclear which one actually controls the maintenance of the fate of the early islets. Conditional deletions of the Notch effector RBP-Jκ with lineage tracing in Presenilin-deficient endocrine progenitors, demonstrated that this factor is central to the control of the fate through a non-canonical Notch mechanism. RBP-Jκ mice exhibit normal islet morphogenesis and function, however, a fraction of the progenitors fails to differentiate and develop into disorganized masses resembling acinar to ductal metaplasia and chronic pancreatitis. A subsequent deletion of RBP-Jκ in forming β-cells led to the transdifferentiation into the other endocrine cells types, indicating that this factor still mediates the maintenance of the fate within the endocrine lineage itself. These results highlight the dual importance of Notch signaling for the endocrine lineage. Even after Ngn3 expression, Notch activity is required to maintain both fate and maturation of the Ngn3 progenitors. In a subset of the cells, these alterations of Notch signaling halt their differentiation and leads to acinar to ductal metaplasia.

GM-CSF Mediates Mesenchymal-Epithelial Cross-talk in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDA) is characterized by a dense stroma consisting of a prevalence of activated fibroblasts whose functional contributions to pancreatic tumorigenesis remain incompletely understood. In this study, we provide the first identification and characterization of mesenchymal stem cells (MSC) within the human PDA microenvironment, highlighting the heterogeneity of the fibroblast population. Primary patient PDA samples and low-passage human pancreatic cancer-associated fibroblast cultures were found to contain a unique population of cancer-associated MSCs (CA-MSC). CA-MSCs markedly enhanced the growth, invasion, and metastatic potential of PDA cancer cells. CA-MSCs secreted the cytokine GM-CSF that was required for tumor cell proliferation, invasion, and transendothelial migration. Depletion of GM-CSF in CA-MSCs inhibited the ability of these cells to promote tumor cell growth and metastasis. Together, these data identify a population of MSCs within the tumor microenvironment that possesses a unique ability, through GM-CSF signaling, to promote PDA survival and metastasis.

SIGNIFICANCE

The role of stroma in pancreatic cancer is controversial. Here, we provide the first characterization of MSCs within the human PDA microenvironment and demonstrate that CA-MSCs promote tumorigenesis through the production of GM-CSF. These data identify a novel cytokine pathway that mediates mesenchymal-epithelial cross-talk and is amenable to therapeutic intervention. Cancer Discov; 6(8); 886-99. ©2016 AACR.This article is highlighted in the In This Issue feature, p. 803.

Autophagy Inhibition Dysregulates TBK1 Signaling and Promotes Pancreatic Inflammation

Autophagy promotes tumor progression downstream of oncogenic KRAS, yet also restrains inflammation and dysplasia through mechanisms that remain incompletely characterized. Understanding the basis of this paradox has important implications for the optimal targeting of autophagy in cancer. Using a mouse model of cerulein-induced pancreatitis, we found that loss of autophagy by deletion of Atg5 enhanced activation of the IκB kinase (IKK)-related kinase TBK1 in vivo, associated with increased neutrophil and T-cell infiltration and PD-L1 upregulation. Consistent with this observation, pharmacologic or genetic inhibition of autophagy in pancreatic ductal adenocarcinoma cells, including suppression of the autophagy receptors NDP52 or p62, prolonged TBK1 activation and increased expression of CCL5, IL6, and several other T-cell and neutrophil chemotactic cytokines in vitro Defective autophagy also promoted PD-L1 upregulation, which is particularly pronounced downstream of IFNγ signaling and involves JAK pathway activation. Treatment with the TBK1/IKKε/JAK inhibitor CYT387 (also known as momelotinib) not only inhibits autophagy, but also suppresses this feedback inflammation and reduces PD-L1 expression, limiting KRAS-driven pancreatic dysplasia. These findings could contribute to the dual role of autophagy in oncogenesis and have important consequences for its therapeutic targeting. Cancer Immunol Res; 4(6); 520-30. ©2016 AACR.

Abstract 1748: Usp9x as a novel therapeutic target in human pancreatic cancer

Usp9x regulates tumor cell survival and responsiveness to targeted-, chemo- and radio-therapy in a broad number of tumors through effects on multiple proteins.

The role of Usp9x in human pancreatic cancer is largely unknown, although a recent study demonstrated that Usp9x co-operated in promoting KrasG12D tumorigenesis in mice. To examine Usp9x tumorigenicity and therapeutic potential of Usp9x inhibition in human pancreatic cancer vs. mouse pancreatic tumor models we developed 3D cultures of cell lines established from constitutive (8041) and doxycycline-inducible (4668) KrasG12D/Tp53R172H mouse pancreatic tumors, established human cell lines (BxPC3, PANC1 and MIAPACA2) and spontaneously immortalized human pancreatic patient tumor derived cell lines (UM2, UM6, UM16 and UM76). The effect of Usp9x knockdown (KD), overexpression (OE) or Usp9x activity inhibition by our small molecule deubiquitinase inhibitor EOAI3402143 (G9) were assessed by growth in 2D and 3D culture and anti-tumor efficacy studies in mouse (8041) and human (MIAPACA2) xenograft models. Usp9x KD in constitutive KrasG12D/Tp53R172H 8041 cells led to a 3-fold increase in the number of colonies formed in 3D and Usp9x KD sustained 3D colony growth even after withdrawal of mutant Kras support in KrasG12D/Tp53R172H inducible 4668 cells. Usp9x-OE in 8041 cells decreased 3D colony growth by 2.5-fold. These results contrast with outcomes in human pancreatic tumors where Usp9x KD induced either rapid apoptosis (in MIAPACA2) or reduced 3D colony formation by >50% (in PANC1). Usp9x-OE in PANC1 cells enhanced 3D colony growth (2-fold) and increased invasion activity in Boyden chambers (3.5-fold). Mechanistically, we found differential effects of Usp9x on mutant Kras protein expression levels in mouse vs human cells. In vivo G9 treatment (15 mg/kg, every other day) of mouse 8041 xenografts showed a statistically insignificant trend towards tumor growth inhibition but effectively inhibited MIAPACA2 tumor growth in mice. Usp9x KD in human pancreatic patient tumor cell lines inhibited 3D colony growth by >75% and this activity was phenocopied by G9 with nM efficacy. We conclude that Usp9x acts as a tumor promoter in established human pancreatic cancer and a tumor suppressor in murine cells from genetically engineered pancreatic tumors, possibly through differential regulation of mutant Kras. Overall, these results suggest that Usp9x may be a novel therapeutic target in pancreatic cancer.

Note: This abstract was not presented at the meeting.

Citation Format: Anupama Pal, Marina Pasca Di Magliano, Diane Simeone, Luke Peterson, Harish Potu, Moshe Talpaz, Nicholas Donato. Usp9x as a novel therapeutic target in human pancreatic cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1748. doi:10.1158/1538-7445.AM2015-1748

Use of [11C]PBR28 to localize and quantify tumor associated macrophages in pancreas cancer (TUM6P.1008)

Tumor associated macrophages (TAM) are an important part of the immune microenvironment in pancreas cancer (PC) and are associated with poor prognosis. We investigated the use of a novel radiolabeled small molecule ([11C]PBR28), which binds to the macrophage translocator protein (TSPO), to track TAMs in-vivo. A murine PC line was generated from a KRAS/P53 mutant transgenic mouse. Immunoblotting confirmed lack of endogenous TSPO expression. After subcutaneous implantation, mice were administered [11C]PBR28. After micro-PET imaging, organs and tumors were harvested for autoradiography. Immunoflourescent co-staining of tumors confirmed TAM infiltration with co-expression of F4/80 and TSPO. Following [11C]PBR28 injection, micro-PET successfully localized tumors and autoradiography demonstrated a 3-fold increase in tumor radioactivity compared to background (muscle). To confirm the observed activity was TAM specific, the experiment was repeated in CD11b+ diphtheria toxin receptor (DTR) transgenic mice. After tumor inoculation, diphtheria toxin (DT) was administered and macrophage depletion confirmed by immunofluorescence and flow cytometry. Autoradiography demonstrated equal tumor uptake relative to background and decreased levels compared to tumors from wild-type mice. We demonstrated a non-invasive method to quantify pancreatic cancer TAM infiltration in-vivo using a novel radiotracer. This could be used prognostically and to determine response to TAM based immunotherapy.