Earliest Metabolic Changes Associated with the Initiation of Pancreatic Cancer.

Pancreatic cancer is usually detected at a late stage, when tumors have already metastasized; therefore, it has a poor prognosis with a 5-year survival rate of 11% to 12%. A key to targeting this high mortality is to develop methods for detecting the disease at a stage in which it is still local to the pancreas. However, this needs a better understanding of the events that govern pancreatic cancer oncogenesis. In this issue of Cancer Research, Neuß and colleagues report metabolic changes associated with acinar-to-ductal metaplasia (ADM), an initiating event that leads to the formation of precursor lesions for pancreatic ductal adenocarcinoma (PDAC). Their findings reveal a switch to aerobic glycolysis, increased c-MYC signaling, and increased serine metabolism as driving factors for the ADM process. These findings are important as they demonstrate that metabolic changes that drive the proliferation and metastasis of full-blown PDAC begin in the earliest lesions. The data not only provide insights into how PDAC develops but also a potential explanation for previously described findings, such as circulating lesion cells can be detected even when no carcinoma in situ is present. In summary, this article is highly relevant for furthering our understanding of how metabolic reprogramming drives the earliest events leading to PDAC development and could lay the groundwork for developing methods for early detection or intervention. See related article by Neuß et al., p. 2297.

Cytokine CCL9 Mediates Oncogenic KRAS-Induced Pancreatic Acinar-to-Ductal Metaplasia by Promoting Reactive Oxygen Species and Metalloproteinases.

Pancreatic ductal adenocarcinoma (PDAC) can originate from acinar-to-ductal metaplasia (ADM). Pancreatic acini harboring oncogenic Kras mutations are transdifferentiated to a duct-like phenotype that further progresses to become pancreatic intraepithelial neoplasia (PanIN) lesions, giving rise to PDAC. Although ADM formation is frequently observed in KrasG12D transgenic mouse models of PDAC, the exact mechanisms of how oncogenic KrasG12D regulates this process remain an enigma. Herein, we revealed a new downstream target of oncogenic Kras, cytokine CCL9, during ADM formation. Higher levels of CCL9 and its receptors, CCR1 and CCR3, were detected in ADM regions of the pancreas in p48cre:KrasG12D mice and human PDAC patients. Knockdown of CCL9 in KrasG12D-expressed pancreatic acini reduced KrasG12D-induced ADM in a 3D organoid culture system. Moreover, exogenously added recombinant CCL9 and overexpression of CCL9 in primary pancreatic acini induced pancreatic ADM. We also showed that, functioning as a downstream target of KrasG12D, CCL9 promoted pancreatic ADM through upregulation of the intracellular levels of reactive oxygen species (ROS) and metalloproteinases (MMPs), including MMP14, MMP3 and MMP2. Blockade of MMPs via its generic inhibitor GM6001 or knockdown of specific MMP such as MMP14 and MMP3 decreased CCL9-induced pancreatic ADM. In p48cre:KrasG12D transgenic mice, blockade of CCL9 through its specific neutralizing antibody attenuated pancreatic ADM structures and PanIN lesion formation. Furthermore, it also diminished infiltrating macrophages and expression of MMP14, MMP3 and MMP2 in the ADM areas. Altogether, our results provide novel mechanistic insight into how oncogenic Kras enhances pancreatic ADM through its new downstream target molecule, CCL9, to initiate PDAC.

Macrophage-induced reactive oxygen species in the initiation of pancreatic cancer: a mini-review.

Pancreatic inflammation is a risk factor for the development of pancreatic cancer. Increased presence of inflammatory macrophages can be found in response to a KRAS mutation in acinar cells or in response to experimentally-induced pancreatitis. Inflammatory macrophages induce pancreatic acinar cells to undergo dedifferentiation to a duct-like progenitor stage, a process called acinar-to-ductal metaplasia (ADM). Occurrence of ADM lesions are believed to be the initiating event in tumorigenesis. Here we will discuss how macrophage-induced oxidative stress contributes to ADM and how ADM cells shape the fibrotic stroma needed for further progression.

Protein kinase D1 - A targetable mediator of pancreatic cancer development.

Members of the Protein kinase D (PKD) kinase family each play important cell-specific roles in the regulation of normal pancreas functions. In pancreatic diseases PKD1 is the most widely characterized isoform with roles in pancreatitis and in induction of pancreatic cancer and its progression. PKD1 expression and activation increases in pancreatic acinar cells through macrophage secreted factors, Kirsten rat sarcoma viral oncogene homolog (KRAS) signaling, and reactive oxygen species (ROS), driving the formation of precancerous lesions. In precancerous lesions PKD1 regulates cell survival, growth, senescence, and generation of doublecortin like kinase 1 (DCLK1)-positive cancer stem cells (CSCs). Within tumors, regulation by PKD1 includes chemoresistance, apoptosis, proliferation, CSC features, and the Warburg effect. Thus, PKD1 plays a critical role throughout pancreatic disease initiation and progression.

Roles of differently polarized macrophages in the initiation and progressionof pancreatic cancer.

During development of pancreatic cancer macrophage-mediated inflammatory processes and the formation of cancerous lesions are tightly connected. Based on insight from mouse models we provide an overview on the functions of classically-activated pro-inflammatory and alternatively-activated anti-inflammatory macrophages in the initiation and progression of pancreatic cancer. We highlight their roles in earliest events of tumor initiation such as acinar-to-ductal metaplasia (ADM), organization of the fibrotic lesion microenvironment, and growth of low-grade (LG) lesions. We then discuss their roles as tumor-associated macrophages (TAM) in progression to high-grade (HG) lesions with a cancerous invasive phenotype and an immunosuppressive microenvironment. Another focus is on how targeting these macrophage populations can affect immunosuppression, fibrosis and responses to chemotherapy, and eventually how this knowledge could be used for novel therapy approaches for patients with pancreatic ductal adenocarcinoma (PDA).

Inflammatory and alternatively activated macrophages independently induce metaplasia but cooperatively drive pancreatic precancerous lesion growth.

The innate immune system has a key role in pancreatic cancer initiation, but the specific contribution of different macrophage populations is still ill-defined. While inflammatory (M1) macrophages have been shown to drive acinar-to-ductal metaplasia (ADM), a cancer initiating event, alternatively activated (M2) macrophages have been attributed to lesion growth and fibrosis. Here, we determined cytokines and chemokines secreted by both macrophage subtypes. Then, we analyzed their role in ADM initiation and lesion growth, finding that while M1 secrete TNF, CCL5, and IL-6 to drive ADM, M2 induce this dedifferentiation process via CCL2, but the effects are not additive. This is because CCL2 induces ADM by generating ROS and upregulating EGFR signaling, thus using the same mechanism as cytokines from inflammatory macrophages. Therefore, while effects on ADM are not additive between macrophage polarization types, both act synergistically on the growth of low-grade lesions by activating different MAPK pathways.

AT-101 Enhances the Antitumor Activity of Lenalidomide in Patients with Multiple Myeloma.

Bcl-2 and Mcl-1 proteins play a role in multiple myeloma (MM) cell survival, for which targeted inhibitors are being developed. AT-101 is an oral drug, which disrupts Bcl-2 and Mcl-1 function, impedes mitochondrial bioenergetic processes and induces apoptosis in MM cells. When combined with lenalidomide and dexamethasone (Rd), AT-101 significantly reduced tumor burden in an in vivo xenograft model of MM. These data provided rationale for a phase I/II study to establish the effective dose of AT-101 in combination with Rd (ARd regimen) in relapsed/refractory MM. A total of 10 patients were enrolled, most with high-risk cytogenetics (80%) and prior stem cell transplant (70%). Three patients were lenalidomide-refractory, 2 were bortezomib-refractory and 3 were daratumumab-refractory. The ARd combination was well tolerated with most common grade 3/4 adverse events being cytopenia's. The overall response rate was 40% and clinical benefit rate was 90%. The median progression free survival was 14.9 months (95% CI 7.1-NE). Patients responsive to ARd showed a decrease in Bcl-2:Bim or Mcl-1:Noxa protein complexes, increased CD8+ T and NK cells and depletion of T and B-regulatory cells. The ARd regimen demonstrated an acceptable safety profile and promising efficacy in patients with relapsed/refractory MM prompting further investigation in additional patients.

Elevating microglia TREM2 reduces amyloid seeding and suppresses disease-associated microglia.

TREM2 is exclusively expressed by microglia in the brain and is strongly linked to the risk for Alzheimer's disease (AD). As microglial responses modulated by TREM2 are central to AD pathogenesis, enhancing TREM2 signaling has been explored as an AD therapeutic strategy. However, the effective therapeutic window targeting TREM2 is unclear. Here, by using microglia-specific inducible mouse models overexpressing human wild-type TREM2 (TREM2-WT) or R47H risk variant (TREM2-R47H), we show that TREM2-WT expression reduces amyloid deposition and neuritic dystrophy only during the early amyloid seeding stage, whereas TREM2-R47H exacerbates amyloid burden during the middle amyloid rapid growth stage. Single-cell RNA sequencing reveals suppressed disease-associated microglia (DAM) signature and reduced DAM population upon TREM2-WT expression in the early stage, whereas upregulated antigen presentation pathway is detected with TREM2-R47H expression in the middle stage. Together, our findings highlight the dynamic effects of TREM2 in modulating AD pathogenesis and emphasize the beneficial effect of enhancing TREM2 function in the early stage of AD development.

Ym1+ macrophages orchestrate fibrosis, lesion growth, and progression during development of murine pancreatic cancer.

Desmoplasia around pancreatic lesions is a barrier for immune cells and a hallmark of developing and established pancreatic cancer. However, the contribution of the innate immune system to this process is ill-defined. Using the KC mouse model and primary cells in vitro, we show that alternatively activated macrophages (AAM) crosstalk with pancreatic lesion cells and pancreatic stellate cells (PSCs) to mediate fibrosis and progression of lesions. TGFß1 secreted by AAM not only drives activation of quiescent PSCs but also in activated PSCs upregulates expression of TIMP1, a factor previously shown as crucial in fibrosis. Once activated, PSCs auto-stimulate proliferation via CXCL12. Furthermore, we found that TIMP1/CD63 signaling mediates PanIN lesion growth and TGFß1 contributes to a cadherin switch and drives structural collapse of lesions, indicating a potential progression step. Taken together, our data indicate TGFß1 produced by Ym1+ AAM as a major driver of processes that initiate the development of pancreatic cancer.

Generation of Hydrogen Peroxide and Downstream Protein Kinase D1 Signaling Is a Common Feature of Inducers of Pancreatic Acinar-to-Ductal Metaplasia.

Pancreatic acinar-to-ductal metaplasia (ADM) is a reversible process that occurs after pancreatic injury, but becomes permanent and leads to pancreatic lesions in the presence of an oncogenic mutation in KRAS,. While inflammatory macrophage-secreted chemokines, growth factors that activate epidermal growth factor receptor (EGFR) and oncogenic KRAS have been implicated in the induction of ADM, it is currently unclear whether a common underlying signaling mechanism exists that drives this process. In this study, we show that different inducers of ADM increase levels of hydrogen peroxide, most likely generated at the mitochondria, and upregulate the expression of Protein Kinase D1 (PKD1), a kinase that can be activated by hydrogen peroxide. PKD1 expression in acinar cells affects their survival and mediates ADM, which is in part due to the PKD1 target NF-κB. Overall, our data implicate ROS-PKD1 signaling as a common feature of different inducers of pancreatic ADM.

CXCL10/CXCR3 signaling contributes to an inflammatory microenvironment and its blockade enhances progression of murine pancreatic precancerous lesions.

The development of pancreatic cancer requires recruitment and activation of different macrophage populations. However, little is known about how macrophages are attracted to the pancreas after injury or an oncogenic event, and how they crosstalk with lesion cells or other cells of the lesion microenvironment. Here, we delineate the importance of CXCL10/CXCR3 signaling during the early phase of murine pancreatic cancer. We show that CXCL10 is produced by pancreatic precancerous lesion cells in response to IFNγ signaling and that inflammatory macrophages are recipients for this chemokine. CXCL10/CXCR3 signaling in macrophages mediates their chemoattraction to the pancreas, enhances their proliferation, and maintains their inflammatory identity. Blocking of CXCL10/CXCR3 signaling in vivo shifts macrophage populations to a tumor-promoting (Ym1+, Fizz+, Arg1+) phenotype, increases fibrosis, and mediates progression of lesions, highlighting the importance of this pathway in PDA development. This is reversed when CXCL10 is overexpressed in PanIN cells.

Dysfunctional EGFR and oxidative stress-induced PKD1 signaling drive formation of DCLK1+ pancreatic stem cells.

Doublecortin-like kinase 1 (DCLK1)-positive pancreatic cancer stem cells develop at a precancerous stage and may contribute to the lack of efficacy of pancreatic cancer therapy. Although PanIN cells express oncogenic KRas and have an increased activity of epidermal growth factor receptor (EGFR), we demonstrate that, in DCLK1+ PanIN cells, EGFR signaling is not propagated to the nucleus. Mimicking blockage of EGFR with erlotinib in PanIN organoid culture or in p48cre;KrasG12D mice led to a significant increase in DCLK1+ PanIN cells. As a mechanism of how EGFR inhibition leads to formation of DCLK1+ cells, we identify an increase in hydrogen peroxide contributing to activation of Protein Kinase D1 (PKD1). Active PKD1 then drives stemness and abundance of DCLK1+ cells in lesions. Our data suggest a signaling mechanism that leads to the development of DCLK1+ pancreatic cancer stem cells, which can be exploited to target this population in potential therapeutic approaches.

Carcinogenesis of Pancreatic Ductal Adenocarcinoma.

Although the estimated time for development of pancreatic ductal adenocarcinoma (PDA) is more than 20 years, PDAs are usually detected at late, metastatic stages. PDAs develop from duct-like cells through a multistep carcinogenesis process, from low-grade dysplastic lesions to carcinoma in situ and eventually to metastatic disease. This process involves gradual acquisition of mutations in oncogenes and tumor suppressor genes, as well as changes in the pancreatic environment from a pro-inflammatory microenvironment that favors the development of early lesions, to a desmoplastic tumor microenvironment that is highly fibrotic and immune suppressive. This review discusses our current understanding of how PDA originates.

The GEF-H1/PKD3 signaling pathway promotes the maintenance of triple-negative breast cancer stem cells.

Protein kinase D3 (PKD3) is upregulated in triple-negative breast cancer (TNBC) and associated with cell proliferation and metastasis development but its precise pro-oncogenic function is unknown. Here we show that PKD3 is required for the maintenance of the TNBC stem cell population. The depletion of PKD3 in MDA-MB-231 cells reduced the cancer stem cell frequency in vitro and tumor initiation potential in vivo. We further provide evidence that the RhoGEF GEF-H1 is upstream of PKD3 activation in TNBC stem cells. Most importantly, pharmacological PKD inhibition in combination with paclitaxel synergistically decreased oncosphere and colony formation efficiency in vitro and tumor recurrence in vivo. Based on our results we propose that targeting the GEF-H1/PKD3 signaling pathway in combination with chemotherapy might provide an effective therapeutic option for TNBC.

Sangivamycin and its derivatives inhibit Haspin-Histone H3-survivin signaling and induce pancreatic cancer cell death.

Current treatment options for patients with pancreatic cancer are suboptimal, resulting in a five year survival rate of about 9%. Difficulties with treatment are due to an immunosuppressive, fibrotic tumor microenvironment that prevents drugs from reaching tumor cells, but also to the limited efficacy of existing FDA-approved chemotherapeutic compounds. We here show that the nucleoside analog Sangivamycin and its closely-related compound Toyocamycin target PDA cell lines, and are significantly more efficient than Gemcitabine. Using KINOMEscan screening, we identified the kinase Haspin, which is overexpressed in PDA cell lines and human PDA samples, as a main target for both compounds. Inhibition of Haspin leads to a decrease in Histone H3 phosphorylation and prevents Histone H3 binding to survivin, thus providing mechanistic insight of how Sangivamycin targets cell proliferation, mitosis and induces apoptotic cell death. In orthotopically implanted tumors in mice, Sangivamycin was efficient in decreasing the growth of established tumors. In summary, we show that Sangivamycin and derivatives can be an efficient new option for treatment of PDA.

Protein kinase D up-regulates transcription of VEGF receptor-2 in endothelial cells by suppressing nuclear localization of the transcription factor AP2ß.

Vascular endothelial growth factor A (VEGF) signals primarily through its cognate receptor VEGF receptor-2 (VEGFR-2) to control vasculogenesis and angiogenesis, key physiological processes in cardiovascular disease and cancer. In human umbilical vein endothelial cells (HUVECs), knockdown of protein kinase D-1 (PKD1) or PKD2 down-regulates VEGFR-2 expression and inhibits VEGF-induced cell proliferation and migration. However, how PKD regulates VEGF signaling is unclear. Previous bioinformatics analyses have identified binding sites for the transcription factor activating enhancer-binding protein 2 (AP2) in the VEGFR-2 promoter. Using ChIP analyses, here we found that PKD knockdown in HUVECs increases binding of AP2ß to the VEGFR-2 promoter. Luciferase reporter assays with serial deletions of AP2-binding sites within the VEGFR-2 promoter revealed that its transcriptional activity negatively correlates with the number of these sites. Next we demonstrated that AP2ß up-regulation decreases VEGFR-2 expression and that loss of AP2ß enhances VEGFR-2 expression in HUVECs. In vivo experiments confirmed increased VEGFR-2 immunostaining in the spinal cord of AP2ß knockout mouse embryos. Mechanistically, we observed that PKD phosphorylates AP2ß at Ser258 and Ser277 and suppresses its nuclear accumulation. Inhibition of PKD activity with a pan-PKD inhibitor increased AP2ß nuclear localization, and overexpression of both WT and constitutively active PKD1 or PKD2 reduced AP2ß nuclear localization through a Ser258- and Ser277-dependent mechanism. Furthermore, substitution of Ser277 in AP2ß increased its binding to the VEGFR-2 promoter. Our findings uncover evidence of a molecular pathway that regulates VEGFR-2 expression, insights that may shed light on the etiology of diseases associated with aberrant VEGF/VEGFR signaling.

Mucin-1 is required for Coxsackie Virus B3-induced inflammation in pancreatitis.

The Muc-1 oncoprotein is a tumor-associated mucin often overexpressed in pancreatic cancer. We report that knockout of Muc-1 reduced the degree of pancreatic inflammation that resulted from infection with Coxsackievirus B3 (CVB3) in a mouse model. CVB3-infected Muc-1-deficient (Muc-1KO) mice had significantly reduced infiltration of macrophages into the murine pancreas. We found that Muc-1 signaling through NF-κB increased expression of ICAM-1, a pro-inflammatory mediator that recruits macrophages. Further investigation revealed that bone marrow derived macrophages (BMDM) from the Muc-1KO mice exhibited defective migration properties, in part due to low expression of the C-C motif chemokine receptor (CCR2) and the integrin Very Late Antigen 4 (VLA-4). The results presented here provide novel insight into the role of Muc-1 in regulating the inflammatory response and the cellular microenvironment in pancreatitis.

Targeting the tumor microenvironment in pancreatic ductal adenocarcinoma.

Introduction: The dismally slow improvement in patient survival over the years for pancreatic cancer patients is mainly due to two factors: the late diagnosis, at which point the disease is spread to distant organs; and the fact that tumor cells are surrounded by a dense, highly immunosuppressive microenvironment. The tumor microenvironment not only shields pancreatic cancer cells from chemotherapy but also leaves it unsusceptible to various immunotherapeutic strategies that have been proven successful in other types of cancer. Areas covered: This review highlights the main components of the pancreatic tumor microenvironment, how they cross-talk with each other to generate stroma and promote tumor growth. Additionally, we discuss the most promising treatment targets in the microenvironment whose modulation can be robustly tested in combination with standard of care chemotherapy. Currently, active clinical trials for pancreatic cancer involving components of the microenvironment are also listed. Expert opinion: Although immunotherapeutic approaches involving checkpoint inhibition are being pursued enthusiastically, there is still more work to be done with several other emerging immune targets that could provide therapeutic benefit.