Multidimensional screening of pancreatic cancer spheroids reveals vulnerabilities in mitotic and cell-matrix adhesion signaling that associate with metastatic progression and decreased patient survival

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy, with a median survival of less than 12 months and a 5-year survival of less than 10 %. Here, we have established an image-based screening pipeline for quantifying single PDAC spheroid dynamics in genetically and phenotypically diverse PDAC cell models. Wild-type KRas PDAC cells formed tight/compact spheroids - compaction of these structures was completely blocked by cytoplasmic dynein and focal adhesion kinase (FAK) inhibitors. In contrast, PDAC cells containing mutant KRas formed loosely aggregated spheroids that grew significantly slower following inhibition of polo-like kinase 1 (PLK1) or focal adhesion kinase (FAK). Independent of genetic background, multicellular PDAC-mesenchymal stromal cell (MSC) spheroids self-organized into structures with an MSC-dominant core. The inclusion of MSCs into wild-type KRas PDAC spheroids modestly affected their compaction; however, MSCs significantly increased the compaction and growth of mutant KRas PDAC spheroids. Notably, exogenous collagen 1 potentiated PANC1 spheroid compaction while ITGA1 knockdown in PANC1 cells blocked MSC-induced PANC1 spheroid compaction. In agreement with a role for collagen-based integrin adhesion complexes in stromal cell-induced PDAC phenotypes, we also discovered that MSC-induced PANC1 spheroid growth was completely blocked by the ITGB1 immunoneutralizing antibody mAb13. Finally, multiplexed single-cell immunohistochemical analysis of a 25 patient PDAC tissue microarray revealed a relationship between decreased variance in Spearman r correlation for ITGA1 and PLK1 expression within the tumor cell compartment of PDAC in patients with advanced disease stage, and elevated expression of both ITGA1 and PLK1 in PDAC was found to be associated with decreased patient survival. Taken together, this work uncovers new therapeutic vulnerabilities in PDAC that are relevant to the progression of this stromal cell-rich malignancy and which may reveal strategies for improving patient outcomes.

Targeting SMAD-Dependent Signaling: Considerations in Epithelial and Mesenchymal Solid Tumors

SMADs are the canonical intracellular effector proteins of the TGF-β (transforming growth factor-β). SMADs translocate from plasma membrane receptors to the nucleus regulated by many SMAD-interacting proteins through phosphorylation and other post-translational modifications that govern their nucleocytoplasmic shuttling and subsequent transcriptional activity. The signaling pathway of TGF-β/SMAD exhibits both tumor-suppressing and tumor-promoting phenotypes in epithelial-derived solid tumors. Collectively, the pleiotropic nature of TGF-β/SMAD signaling presents significant challenges for the development of effective cancer therapies. Here, we review preclinical studies that evaluate the efficacy of inhibitors targeting major SMAD-regulating and/or -interacting proteins, particularly enzymes that may play important roles in epithelial or mesenchymal compartments within solid tumors.

Patient-Derived Organoids as Therapy Screening Platforms in Cancer Patients

Patient-derived organoids (PDOs) developed ex vivo and in vitro are increasingly used for therapeutic screening. They provide a more physiologically relevant model for drug discovery and development compared to traditional cell lines. However, several challenges remain to be addressed to fully realize the potential of PDOs in therapeutic screening. This paper summarizes recent advancements in PDO development and the enhancement of PDO culture models. This is achieved by leveraging materials engineering and microfabrication technologies, including organs-on-a-chip and droplet microfluidics. Additionally, this work discusses the application of PDOs in therapy screening to meet diverse requirements and overcome bottlenecks in cancer treatment. Furthermore, this work introduces tools for data processing and analysis of organoids, along with their microenvironment. These tools aim to achieve enhanced readouts. Finally, this work explores the challenges and future perspectives of using PDOs in drug development and personalized screening for cancer patients.

Aqueous humor TGFβ and fibrillin-1 in Tsk mice reveal clues to POAG pathogenesis

Aqueous humor (AH) and blood levels of transforming growth factor β (TGFβ) are elevated in idiopathic primary open angle glaucoma (POAG) representing a disease biomarker of unclear status and function. Tsk mice display a POAG phenotype and harbor a mutation of fibrillin-1, an important regulator of TGFβ bioavailability. AH TGFβ2 was higher in Tsk than wild-type (WT) mice (by 34%; p = 0.002; ELISA); similarly, AH TGFβ2 was higher in human POAG than controls (2.7-fold; p = 0.00005). As in POAG, TGFβ1 was elevated in Tsk serum (p = 0.01). Fibrillin-1 was detected in AH from POAG subjects and Tsk mice where both had similar levels relative to controls (p = 0.45). 350 kDa immunoblot bands representing WT full-length fibrillin-1 were present in human and mouse AH. A 418 kDa band representing mutant full-length fibrillin-1 was present only in Tsk mice. Lower molecular weight fibrillin-1 antibody-reactive bands were present in similar patterns in humans and mice. Certain bands (130 and 32 kDa) were elevated only in human POAG and Tsk mice (p ≤ 0.04 relative to controls) indicating discrete isoforms relevant to disease. In addition to sharing a phenotype, Tsk mice and human POAG subjects had common TGFβ and fibrillin-1 features in AH and also blood that are pertinent to understanding glaucoma pathogenesis.

Fibronectin, DHPS and SLC3A2 Signaling Cooperate to Control Tumor Spheroid Growth, Subcellular eIF5A1/2 Distribution and CDK4/6 Inhibitor Resistance

Extracellular matrix (ECM) protein expression/deposition within and stiffening of the breast cancer microenvironment facilitates disease progression and correlates with poor patient survival. However, the mechanisms by which ECM components control tumorigenic behaviors and responses to therapeutic intervention remain poorly understood. Fibronectin (FN) is a major ECM protein controlling multiple processes. In this regard, we previously reported that DHPS-dependent hypusination of eIF5A1/2 is necessary for fibronectin-mediated breast cancer metastasis and epithelial to mesenchymal transition (EMT). Here, we explored the clinical significance of an interactome generated using hypusination pathway components and markers of intratumoral heterogeneity. Solute carrier 3A2 (SLC3A2 or CD98hc) stood out as an indicator of poor overall survival among patients with basal-like breast cancers that express elevated levels of DHPS. We subsequently discovered that blockade of DHPS or SLC3A2 reduced triple negative breast cancer (TNBC) spheroid growth. Interestingly, spheroids stimulated with exogenous fibronectin were less sensitive to inhibition of either DHPS or SLC3A2 - an effect that could be abrogated by dual DHPS/SLC3A2 blockade. We further discovered that a subset of TNBC cells responded to fibronectin by increasing cytoplasmic localization of eIF5A1/2. Notably, these fibronectin-induced subcellular localization phenotypes correlated with a G0/G1 cell cycle arrest. Fibronectin-treated TNBC cells responded to dual DHPS/SLC3A2 blockade by shifting eIF5A1/2 localization back to a nucleus-dominant state, suppressing proliferation and further arresting cells in the G2/M phase of the cell cycle. Finally, we observed that dual DHPS/SLC3A2 inhibition increased the sensitivity of both Rb-negative and -positive TNBC cells to the CDK4/6 inhibitor palbociclib. Taken together, these data identify a previously unrecognized mechanism through which extracellular fibronectin controls cancer cell tumorigenicity by modulating subcellular eIF5A1/2 localization and provides prognostic/therapeutic utility for targeting the cooperative DHPS/SLC3A2 signaling axis to improve breast cancer treatment responses.

Fibrillin-1 mutant mouse captures defining features of human primary open glaucoma including anomalous aqueous humor TGF beta-2

Primary open angle glaucoma (POAG) features an optic neuropathy, elevated aqueous humor (AH) TGFβ2, and major risk factors of central corneal thickness (CCT), increasing age and intraocular pressure (IOP). We examined Tight skin (Tsk) mice to see if mutation of fibrillin-1, a repository for latent TGFβ, is associated with characteristics of human POAG. We measured: CCT by ocular coherence tomography (OCT); IOP; retinal ganglion cell (RGC) and optic nerve axon counts by microscopic techniques; visual electrophysiologic scotopic threshold responses (STR) and pattern electroretinogram (PERG); and AH TGFβ2 levels and activity by ELISA and MINK epithelial cell-based assays respectively. Tsk mice had open anterior chamber angles and compared with age-matched wild type (WT) mice: 23% thinner CCT (p < 0.003); IOP that was higher (p < 0.0001), more asymmetric (p = 0.047), rose with age (p = 0.04) and had a POAG-like frequency distribution. Tsk mice also had RGCs that were fewer (p < 0.04), declined with age (p = 0.0003) and showed increased apoptosis and glial activity; fewer optic nerve axons (p = 0.02); abnormal axons and glia; reduced STR (p < 0.002) and PERG (p < 0.007) visual responses; and higher AH TGFβ2 levels (p = 0.0002) and activity (p = 1E-11) especially with age. Tsk mice showed defining features of POAG, implicating aberrant fibrillin-1 homeostasis as a pathogenic contributor to emergence of a POAG phenotype.

Abstract 2414: Retinoic acid induced 14 drives pancreatic cancer progression and metastasis

Pancreatic ductal adenocarcinoma (PDAC) is associated with very poor outcomes - fewer than 10 percent of patients survive beyond five years after diagnosis. The primary hurdles facing PDAC patients and clinicians are early dissemination, a lack of therapeutic targets and desmoplasia that renders the primary tumor refractory to chemotherapy. In this regard, we have previously reported that pseudopodium-enriched atypical kinase 1 (PEAK1) and integrin α1 (ITGA1) mediate gemcitabine resistance and metastasis in PDAC. To identify new mechanisms of PDAC progression, we mined the Cancer BioPortal and Human Cell Map BioID databases for additional pseudopodium-enriched (PDE) proteins that predict poor patient outcomes, correlate with PEAK1 and ITGA1 expression in PDAC, and interact with PEAK1 and ITGA1. Here, we identify Retinoic Acid Induced 14 (RAI14, Ankycorbin or NORPEG) as a new candidate driver of PDAC that is a constituent of the KRasG12D PDAC cell autonomous phosphoproteome, localizes to cytoskeleton/adhesion domains in PDAC cells and correlates in expression with ITGA1-binding collagens in PDAC. Knockdown or knockout of RAI14 in KRas mutant PDAC cells impaired adhesion-dependent proliferation/survival in vitro and tumor growth and metastasis in vivo. Single cell cyclic immunofluorescence (CycIF) further revealed that RAI14 supports a subpopulation of PDAC cells positive for proliferation, epithelial to mesenchymal transition (EMT) and antiapoptotic programs. By using a RAI14-focused bioinformatics pipeline in combination with proteomic and immunofluorescence data on the composition of ITGA1-dependent adhesion complexes in PDAC cells, we identified Polo-Like Kinase 1 (PLK1) as a candidate that may control RAI14 function and adhesion-regulated mitosis during PDAC progression. Notably, the potency of volasertib, a PLK1-specific inhibitor, was reduced in RAI14 knockout cells, supporting a model in which RAI14 mediates adhesion-dependent PLK1 functions in PDAC. Taken together, these studies uncover a mechanism for RAI14-driven PDAC progression and the development of strategies to increase chemotherapy sensitivity, reduce primary/metastatic tumor burden and improve patient outcomes.

Citation Format: Farhana Runa, Luke Tomaneng, Yvess Adamian, Nathan Cox, Albert-Fred Aquino, Matthew Wallace, Carolina Gonzalez, Kishan Bhakta, Malachia Hoover, Laurelin Wolfenden, Jonathan D. Humphries, Martin J. Humphries, Michael Boyce, Jonathan A. Kelber. Retinoic acid induced 14 drives pancreatic cancer progression and metastasis [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 2414.

Abstract 996: Fibronectin exposes a targetable DHPS/SLC3A2 vulnerability that can be leveraged to decrease cytoplasmic levels of eIF5A1/2 and proliferation/survival in TNBC

Breast cancer ranks first among female cancer-related deaths in 2021, and fewer than 20% of patients survive five years after metastasis. Triple negative breast cancer (TNBC or basal) is highly aggressive and particularly difficult to treat due to the lack therapeutic target receptors. Notably, elevated fibronectin expression within the microenvironment of TNBC is an indicator of advanced disease stage. In this regard, we previously reported that the two-step, hypusination reaction that activates eukaryotic initiation factor 5A 1/2 (eIF5A1/2) is necessary for PEAK1 pseudokinase translation and fibronectin/TGFβ-mediated TNBC metastasis. In our current study, we observed intratumoral heterogeneity of DOHH, DHPS, eIF5A and eIF5A2 expression in TNBC patient tumor samples, suggesting a role for this pathway in disease progression and therapy resistance. Using bioinformatics tools, we identified a correlation between elevated solute carrier 3A2 (SLC3A2 or CD98) and decreased survival in breast cancer patients with amplified SMAD3 loci. Given that SMAD3-dependent transcription is one mechanism by which canonical TGFβ signaling elicits tumor suppressive outcomes, we asked whether SLC3A2 may function to prime TNBC cells for tumor promoting outcomes in response to TGFβ. In this regard, inhibition of SLC3A2 or DHPS decreased TNBC spheroid growth. Notably, spiking fibronectin into 3D culture media partially rescued spheroid growth from SLC3A2 inhibition - an effect blocked by dual DHPS/SLC3A2 inhibition. In agreement with these data, dual DHPS/SLC3A2 inhibition in TNBC cells cultured with exogenous fibronectin significantly reduced the percentage of cells in S phase and subsequently increased the percentage of cells in either G0/G1 or Sub-G0/G1 phases, suggesting that DHPS and SLC3A2 cooperatively promote TNBC cell proliferation/survival in fibronectin-rich contexts. eIF5A1/2 carries out hypusination-dependent functions in both the nucleus (i.e., mRNA export) and cytoplasm (i.e., translation). Interestingly, it undergoes nucleocytoplasmic transport via exportin four (XPO4) - the same nuclear pore complex protein that is used for nuclear export of SMAD3. Using structured illumination microscopy, we discovered that fibronectin promotes an increase in cytoplasmic eIF5A1/2 levels - an effect blocked by dual DHPS/SLC3A2 inhibition. In contrast, DHPS inhibition alone increased nuclear SMAD3 levels independent of extracellular matrix proteins. Taken together, these data provide a possible mechanism for the antiproliferative/cytotoxic effects of dual DHPS/SLC3A2 inhibition and suggest that this treatment strategy may be efficacious in TNBC patients with advanced stage disease.

Citation Format: Cameron Geller, Joanna Maddela, Ranel Tuplano, Joseph Cantor, Jonathan A. Kelber. Fibronectin exposes a targetable DHPS/SLC3A2 vulnerability that can be leveraged to decrease cytoplasmic levels of eIF5A1/2 and proliferation/survival in TNBC [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 996.

DHPS-dependent hypusination of eIF5A1/2 is necessary for TGFβ/fibronectin-induced breast cancer metastasis and associates with prognostically unfavorable genomic alterations in TP53

Metastasis is the leading cause of mortality in patients with solid tumors. In this regard, we previously reported that Pseudopodium-Enriched Atypical Kinase One (PEAK1) is necessary for non-canonical Transforming Growth Factor β (TGFβ) signaling and TGFβ/fibronectin-induced metastasis. Here, we demonstrate that inhibition of DHPS-dependent eIF5A1/2 hypusination blocks PEAK1 and E-Cadherin expression, breast cancer cell viability and TGFβ/fibronectin-induced PEAK1-dependent breast cancer metastasis. Interestingly, TGFβ stimulation of high-grade metastatic breast cancer cells increases and sustains eIF5A1/2 hypusination. We used a suite of bioinformatics platforms to search biochemical/functional interactions and clinical databases for additional control points in eIF5A1/2 and PEAK1-Epithelial to Mesenchymal Transition (EPE) pathways. This effort revealed that interacting EPE genes were enriched for TP53 transcriptional targets and were commonly co-amplified in breast cancer patients harboring inactivating TP53 mutations. Taken together, these results suggest that combinatorial therapies targeting DHPS and protein activities elevated in TP53-mutant breast cancers may reduce systemic tumor burden and improve patient outcomes.

Abstract LB-129: Metastatic breast cancer cells promote anti-inflammatory MSC actions and release Lipocalin 2 to induce a tumor-supportive premetastatic lung microenvironment

Cancer metastasis is responsible for the vast majority of cancer-related deaths. Survival and proliferation of cancer cells within distant tissues requires that these foreign microenvironments acquire tumor-supportive characteristics. While it has been established that primary tumor cells can reprogram the molecular and cellular composition of the premetastatic niche by releasing soluble factors and extracellular vesicles, efforts to date have been limited by the use of in vivo models lacking a fully-functional immune system and/or the need for finely-tuned experiment end points to limit direct reprogramming effects of early-disseminating cells from the primary tumor. To address this need, we developed the immune-competent PyMT syngeneic murine model of breast cancer for elucidating events during premetastatic niche reprogramming in the absence of tumor cell allografting. We demonstrate that metastatic mouse PyMT breast cancer cells differentially influence the premetastatic lung and brain, selectively promoting a tumor-supportive lung microenvironment with increased CD73 expression and decreased TNFalpha expression. Using in vitro models of CD73-positive mesenchymal stem cells (MSCs) and monocytes/macrophages, we next tested whether MSCs can selectively mediate anti-inflammatory effects of metastatic breast cancer cells. Notably, conditioned media from metastatic Py230 cells reprogrammed MSCs to selectively increase anti-inflammatory CCL1 and MRC1 transcripts in monocytes/macrophages. In contrast, conditioned media from non-metastatic Py8119 cells reprogrammed MSCs to selectively increase pro-inflammatory IL23alpha and TNFalpha in monocytes/macrophages. Mining transcriptome data from Py8119 and Py230 cells revealed a lipocalin 2 (LCN2) axis that is selectively expressed in the metastatic Py230 cells and predicts poor breast cancer patient survival. Finally, we demonstrate that immunoneutralization of LCN2 in Py230 conditioned media renders it unable to reprogram the premetastatic lung microenvironment toward a tumor-supportive state. Taken together, these results establish the utility of a tumor cell-free in vivo model for interrogating breast cancer priming of the premetastatic niche, demonstrate that MSCs can mediate the anti-inflammatory state within the tumor microenvironment, and identify LCN2 as an important therapeutic target for blocking breast cancer progression.

Citation Format: Francesca Sanchez, Kayla Meade, Analine Aguayo, Nathalie Nadeles, Sarkis Hamalian, Toni Uhlendorf, Lisa Banner, Jonathan A. Kelber. Metastatic breast cancer cells promote anti-inflammatory MSC actions and release Lipocalin 2 to induce a tumor-supportive premetastatic lung microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-129.

Identification of myosin II as a cripto binding protein and regulator of cripto function in stem cells and tissue regeneration

Cripto regulates stem cell function in normal and disease contexts via TGFbeta/activin/nodal, PI3K/Akt, MAPK and Wnt signaling. Still, the molecular mechanisms that govern these pleiotropic functions of Cripto remain poorly understood. We performed an unbiased screen for novel Cripto binding proteins using proteomics-based methods, and identified novel proteins including members of myosin II complexes, the actin cytoskeleton, the cellular stress response, and extracellular exosomes. We report that myosin II, and upstream ROCK1/2 activities are required for localization of Cripto to cytoplasm/membrane domains and its subsequent release into the conditioned media fraction of cultured cells. Functionally, we demonstrate that soluble Cripto (one-eyed pinhead in zebrafish) promotes proliferation in mesenchymal stem cells (MSCs) and stem cell-mediated wound healing in the zebrafish caudal fin model of regeneration. Notably, we demonstrate that both Cripto and myosin II inhibitors attenuated regeneration to a similar degree and in a non-additive manner. Taken together, our data present a novel role for myosin II function in regulating subcellular Cripto localization and function in stem cells and an important regulatory mechanism of tissue regeneration. Importantly, these insights may further the development of context-dependent Cripto agonists and antagonists for therapeutic benefit.

Abstract 1990: Aberrant cell surface expression of GRP78 in breast cancer cells marks a stem-like population that has increased metastatic potential in vivo

Reliable approaches to identify and target stem-cell mechanisms that mediate aggressive cancer could have great therapeutic value, based on the growing evidence of embryonic signatures in metastatic cancers. However, how to best identify and target stem-like mechanisms aberrantly utilized by cancer cells has been challenging. We harnessed the power of induced pluripotent stem cells (iPSCs) to identify embryonic mechanisms exploited by cancer. A screen comparing the cell surface proteome of iPSCs and breast cancer cells identified GRP78, a heat shock protein that is normally ER-restricted, but has been shown to be aberrantly expressed on the cell surface of several cancers, where it can act as a signaling molecule by poorly understood mechanisms. Although cell surface GRP78 (sGRP78) has emerged as an attractive chemotherapeutic target, understanding how sGRP78 is functioning in cancer has been complicated by the fact that GRP78 can function to regulate a variety of cellular responses, using a diverse array of reported binding partners, which can vary by cell type. Therefore, without insight into the specific GRP78-dependent mechanisms that are responsible for mediating aggressive cancer, it will be difficult to determine how to best target GRP78. We have discovered that (1) sGRP78 is expressed on iPSCs (but not their somatic parental populations) and plays an important role in reprogramming, (2) sGRP78 promotes cellular functions such as proliferation/survival and migration in both stem cells and breast cancer cells (3) overexpression of GRP78 in breast cancer cells leads to an induction of a previously established CD24-/CD44+ 'cancer stem cell' (CSC) population (4) sGRP78+ breast cancer cell populations are enriched for genes involved in stemness and appear to be a subset of previously established CSCs (5) sGRP78+ breast cancer cell populations show a significantly enhanced ability to seed metastatic organ sites in vivo (6) GRP78 interacts with Dermcidin (DCD) at the cell surface of cancer cells and iPSCs, where it is important in regulating stem cell and cancer cell migration and survival/proliferation. These collective findings suggest that sGRP78 marks a stem-like population in breast cancer cells that has increased metastatic potential in vivo, and that sGRP78 and DCD cooperate to regulate key cellular functions important in mediating tumorigenesis. Overall, this work has implications for understanding how cancer cells exploit embryonic-like mechanisms, which could provide novel strategies for chemotherapeutic targeting of aggressive breast cancer cell populations.

Citation Format: Tyson W. Lager, Henry C. Conner, Ian H. Guldner, Michael Z. Wu, Yuriko Hishida, Tomoaki Hishida, Sergio Ruiz, Amanda E. Yamasaki, Juan Carlos Izpisua Belmonte, Peter C. Gray, Jonathan A. Kelber, Siyuan Zhang, Athanasia D. Panopoulos. Aberrant cell surface expression of GRP78 in breast cancer cells marks a stem-like population that has increased metastatic potential in vivo [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 1990.

Abstract 2140: Mesenchymal stromal cells expressing a PEAK1/Cripto axis sustain pro-survival NF-κB signaling in adjacent tumor cells to promote disease progression and therapy resistance

The cellular and molecular heterogeneity of solid tumors, like breast cancer, is a significant hurdle in the effort to develop effective therapies. The complex breast cancer microenvironment (BCME) includes mesenchymal stromal cells (MSCs) that engage in paracrine/juxtacrine signaling with adjacent tumor cells to support disease progression. Since PEAK1 (Pseudopodium-Enriched Atypical Kinase One) is a cytoskeleton-associated kinase that regulates growth factor-integrin signaling crosstalk in mesenchymal cell types and recent evidence demonstrates that stromal expression of PEAK1 correlates with breast cancer recurrence, we hypothesized that PEAK1 expression in the mesenchymal compartment of the BCME promotes tumorigenesis. We report that PEAK1 is expressed in patient-derived cancer-associated fibroblasts (CAFs) from all breast cancer subtypes. Additionally, PEAK1hi CAF conditioned media promoted breast cancer cell (BCC) proliferation, migration and therapy resistance in vitro. We established in vitro co-culture and in vivo co-xenografting models for evaluating the effects of defined MSC populations on BCC proliferation/survival, metastasis and therapy response. Co-xenografting PEAK1hi CAFs or MSCs with BCCs increased the mass of HER2-positive and ER-positive primary tumors. In agreement with these data, co-culturing MSCs with BCCs promoted cancer cell proliferation and resistance to lapatinib or tamoxifen treatment, while MSC conditioned media supported BCC expansion under serum-free conditions in vitro. Notably, PEAK1 knockdown in MSCs abrogated their ability to promote tumor growth in vivo and therapy/stress resistance in vitro. Using the highly multiplexed cyclic immunofluorescence (CycIF) platform, we analyzed tumor cell states in these MSC-BCC co-cultures at different time points following lapatinib treatment. We demonstrate that MSCs sustain NF-κB (p65) signaling and anti-apoptotic gene expression within BCCs in the presence of lapatinib. Finally, we discovered that PEAK1 is required for MSC expression of Cripto, a GPI-anchored glycoprotein previously reported to activate NF-κB signaling in trans. Taken together, this work identifies new PEAK1-dependent stroma-tumor signaling vulnerabilities that may be exploited for improving patient responses to current therapeutic interventions.

Citation Format: Sarkis Hamalian, Robert Güth, Ioannis Zervantonakis, Erika Duell, Jia-Ren Lin, Preston Shisgal, Justin Molnar, Cameron Geller, Megan Agajanian, Julia Tchou, Peter K. Sorger, Joan S. Brugge, Jonathan A. Kelber. Mesenchymal stromal cells expressing a PEAK1/Cripto axis sustain pro-survival NF-κB signaling in adjacent tumor cells to promote disease progression and therapy resistance [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 2140.

Abstract 4998: Targeting DHPS to abrogate TGFβ-induced metastasis in breast cancer

Progression of solid tumors to a metastatic stage accounts for over 90% of cancer mortality. Thus, it is critical to identify therapeutic strategies that target both primary and metastatic tumors. Epithelial-mesenchymal transition (EMT) negatively correlates with therapy response, contributing to intratumoral heterogeneity and systemic dissemination in breast cancer. We previously reported that pseudopodium-enriched atypical kinase one (PEAK1) promotes breast cancer cell EMT and metastasis by potentiating fibronectin-transforming growth factor beta (TGFβ) signaling cross-talk. Since eukaryotic initiation factor five A (eIF5A), a unique translation factor that is activated by deoxyhypusine synthase (DHPS)-dependent post-translational hypusination, is required for PEAK1 expression, we hypothesized that TGFβ may directly regulate eIF5A activity to promote EMT, and that targeted inhibition of this pathway may provide a novel means to inhibit or reverse metastatic progression. In this regard, we provide evidence of an active eIF5A-EMT program in undifferentiated breast cancer tissue. Notably, blockade of DHPS activity and eIF5A hypusination reduces PEAK1 translation, cell viability and TGFβ-induced EMT in vitro and metastasis in vivo. Conversely, we demonstrate that TGFβ induces post-translational hypusination of eIF5A in metastatic breast cancer cells. TGFβ is known to activate histone deacetylase six (HDAC6) and HDAC6 was independently reported to promote eIF5A deacetylation and nuclear export to support its translation functions. When delivered in combination, HDAC6 and DHPS inhibitors synergize to sequester eIF5A to the nucleus, suppress eIF5A-dependent translation and potently kill metastatic breast cancer cells. To identify candidate pathways downstream of the eIF5A/PEAK1 axis during EMT, we generated a Cytoscape interactome using eIF5A signaling and PEAK1-induced EMT genes as search terms. All interactome component genes were then analyzed across two breast cancer patient studies available on the Cancer BioPortal. Interestingly, SOX2, PIK3CA and EIF4A2 were the interactome nodes that exhibited copy number amplifications among patients harboring genomic alterations in the initial interactome search genes, and SOX2 amplification significantly and independently associated with decreased patient survival (p = 0.0476). Taken together, our results establish a novel node/axis by which TGFβ signaling stimulates HDAC6 and/or DHPS function to activate cytoplasmic eIF5A and promote EMT and survival of breast cancer cells within the metastatic niche, identifying new targeted therapy strategies that may improve cancer patient survival.

Citation Format: Robert Guth, Lindsay Kutscher, Yvess Adamian, Cameron Geller, Kishan Bahkta, Kayla Meade, Jonathan A. Kelber. Targeting DHPS to abrogate TGFβ-induced metastasis in breast cancer [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 4998.

Tumor microenvironment heterogeneity: challenges and opportunities

The tumor microenvironment (TME) has been recognized as an integral component of malignancies in breast and prostate tissues, contributing in confounding ways to tumor progression, metastasis, therapy resistance and disease recurrence. Major components of the TME are immune cells, fibroblasts, pericytes, endothelial cells, mesenchymal stroma/stem cells (MSCs), and extracellular matrix (ECM) components. Herein, we discuss the molecular and cellular heterogeneity within the TME and how this presents unique challenges and opportunities for treating breast and prostate cancers.

ITGA1 is a pre-malignant biomarker that promotes therapy resistance and metastatic potential in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) has single-digit 5-year survival rates at <7%. There is a dire need to improve pre-malignant detection methods and identify new therapeutic targets for abrogating PDAC progression. To this end, we mined our previously published pseudopodium-enriched (PDE) protein/phosphoprotein datasets to identify novel PDAC-specific biomarkers and/or therapeutic targets. We discovered that integrin alpha 1 (ITGA1) is frequently upregulated in pancreatic cancers and associated precursor lesions. Expression of ITGA1-specific collagens within the pancreatic cancer microenvironment significantly correlates with indicators of poor patient prognosis, and depleting ITGA1 from PDAC cells revealed that it is required for collagen-induced tumorigenic potential. Notably, collagen/ITGA1 signaling promotes the survival of ALDH1-positive stem-like cells and cooperates with TGFβ to drive gemcitabine resistance. Finally, we report that ITGA1 is required for TGFβ/collagen-induced EMT and metastasis. Our data suggest that ITGA1 is a new diagnostic biomarker and target that can be leveraged to improve patient outcomes.

Abstract LB-149: ITGA1 marks pre-malignant pancreatic lesions and drives stem-like cell survival and TGFβ/collagen-induced therapy resistance and metastasis in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) remains one of few malignancies to have single-digit 5-year survival rates at &lt;7%. This dismal prognosis is due in part to the limited ability of clinicians to make pre-metastatic diagnoses and effectively treat localized pancreatic tumors. Thus, there is a dire need to improve early detection methods and identify new therapeutic targets for abrogating PDAC progression. To this end, we mined our previously published pseudopodium-enriched (PDE) protein/phosphoprotein datasets to identify novel PDAC-specific biomarkers and/or therapeutic targets. We discovered that 37 of the top 100 PDE proteins are frequently upregulated in human pancreatic cancer and other tumor types. Integrin alpha 1 (ITGA1) was of primary interest because its high expression in pancreatic cancer precursor lesions may provide a path toward earlier diagnoses, while targeting its cell surface function may abrogate tumor-stroma interactions known to exacerbate PDAC. In this regard, the expression of ITGA1-specific collagens within the pancreatic cancer microenvironment significantly correlates with indicators of poor patient prognosis such as high tumor grade, p53/SMAD4 mutation status and erlotinib resistance. Depleting ITGA1 from PDAC cells revealed that it is required for collagen-induced migration and survival. We further demonstrate that collagen induces PDAC cell attachment and spreading in an ITGA1-dependent manner. Notably, collagen/ITGA1 signaling promotes the survival of ALDH1-positive stem-like cells and cooperates with TGFβ to drive gemcitabine resistance. Finally, we report that increased ITGA1 expression in PDAC tissue indicates the presence of epithelial-mesenchymal transition (EMT) and that ITGA1 is required for TGFβ/collagen-induced EMT and hepatotropic metastasis. Our data suggest that ITGA1 is a new biomarker for PDAC initiation and, when targeted, can sensitize tumors to available chemotherapies to suppress the growth of pancreatic tumors at primary and metastatic sites.

Citation Format: Sa La Kim, Armen Gharibi, Justin Molnar, Daniel Brambilla, Yvess Adamian, Malachia Hoover, Joy Lin, Julie Hong, Jonathan A. Kelber. ITGA1 marks pre-malignant pancreatic lesions and drives stem-like cell survival and TGFβ/collagen-induced therapy resistance and metastasis 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 LB-149. doi:10.1158/1538-7445.AM2017-LB-149

Abstract LB-263: Analysis of microenvironment effects on pancreatic cancer biomarker expression using a novel method for FFPE RNA extraction

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer-related deaths. There are virtually no biomarkers to aid in early detection or predicting therapy response, newly diagnosed patients have less than a 7% 5-year survival rate and the median survival from the time of diagnosis is less than 12 months. Next-Generation Sequencing (NGS) together with in vitro/in vivo functional studies is likely to identify and validate new biomarkers of PDAC onset, progression and therapy resistance. Importantly, the substantial archives of formalin-fixed, paraffin-embedded (FFPE) samples from PDAC patients are likely to be a rich resource for linking molecular signatures to relevant clinical data. However, NGS methods on FFPE samples are severely hindered because extracting high-quality nucleic acid material from these samples is time-consuming and inefficient. We have sought to develop novel methods for improving the extraction of high-quality RNA from FFPE samples within the context of commercially-available FFPE RNA kits and protocols. Together with researchers and clinicians at Claremont BioSolutions, AntiCancer Inc. and UCSD our laboratory has developed a novel nucleic acid extraction method that significantly increases RNA yield and integrity from PDAC cell line and Patient-Derived Xenograft FFPE samples. By briefly (&lt;5 minutes) integrating the newly designed Claremont BioSolutions’ microhomogenizer (mH) tool within the commercially available Qiagen FFPE RNA extraction protocol, RNA recovery from these samples is increased by approximately 3-fold while maintaining standard 260/280 ratios (2.03 +/- 0.02 w/ mH step) and high RNA Quality Index (RQI) values (7.3 +/- 0.6 w/ mH step). Bioanalyzer testing further demonstrated that the mH-purified FFPE RNA was longer. Previous studies have revealed that PDAC cell gene expression signatures vary significantly when cells are propagated in vitro versus in vivo as subcutaneous or orthotopic xenografts. Notably, we found that the previously published expression patterns for KRas dependency genes within these three microenvironments were most accurately reproduced when extracting PDAC FFPE RNA with our mH-based method. Finally, we used our mH-based method to test the effects of the in vivo tumor microenvironment (TME) on the expression trends of a panel of novel PDAC biomarkers. In this regard, we demonstrate that PEAK1 and MST1R expression levels are decreased and increased, respectively, by over 100 fold in the orthotopic microenvironment relative to the subcutaneous microenvironment. These results reveal the critical nature of the tumor microenvironment when evaluating the clinical relevance of new biomarkers in cell lines or patient-derived samples. Furthermore, this new mH-based FFPE RNA extraction method has the potential to positively impact the FFPE-RNA-NGS workflow for cancer biomarker identification/validation.

Citation Format: Malachia Hoover, Yvess Adamian, Mark Brown, Ali A. Maawy, Robert Hoffman, Michael Bouvet, Robert Doebler, Jonathan A. Kelber. Analysis of microenvironment effects on pancreatic cancer biomarker expression using a novel method for FFPE RNA extraction. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-263.

Abstract 4426: The PEAK1/ZEB1/ITGA1 pathway mediates survival, stemness and TGFbeta-induced EMT in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer-related deaths in the United States with a five-year survival rate of approximately 7%. Its highly invasive characteristics, lack of biomarkers for early detection, limited therapeutic targets and inherent resistance to chemotherapy are the central factors that lead to an overall poor prognosis for this malignancy. Since most cancer-related deaths are a result of metastatic tumors, we reasoned that our previously published proteomic signature of the cell pseudopodium (PD) may be a good pool from which to identify novel protein biomarkers or therapeutic targets in pancreatic cancer. We cross-referenced PD enriched proteins with Oncomine and identified 37 genes that are upregulated in pancreatic cancer. The function of integrin alpha 1 (ITGA1), a cell surface receptor for collagen and regulator of cell adhesion, has not been previously characterized in the context of PDAC. Our results indicate that ITGA1 is required for PDAC cell viability, promoting cell survival and tumor growth. We further analyzed ITGA1 cell-surface levels and discovered that ITGA1hi cells represent a subpopulation of Aldehyde Dehyrogenase high (ALDH1hi) cells, and that ITGA1 knockdown reduces the ALDH1hi cell population. One mechanism by which PDAC cells acquire metastatic potential is via epithelial-mesenchymal transition (EMT). Thus, we searched for prominent EMT genes among the top ITGA1 co-expressors using RNA-Seq data from the Cancer Bio Portal. Interestingly, ZEB1 (a transforming growth factor beta, TGFbeta, response gene and central regulator of EMT) and PEAK1 kinase (a protein we’ve shown to be required for pancreatic cancer progression and TGFbeta/ZEB1-induced EMT) co-expresses with ITGA1. We tested the function of ITGA1 on TGFbeta-induced EMT and found that ITGA1 is upregulated by TGFbeta during EMT, and required for metastasis and a complete EMT response to TGFbeta. We also demonstrate that PEAK1 is required for TGFbeta-induced ITGA1 in PDAC cells. Finally, we demonstrate that ITGA1 is responsible for collagen-induced spreading and an EMT-like shift in PDAC cell morphology. Taken together, these results point to a novel TGFbeta/PEAK1/ZEB1/ITGA1 signaling cascade that when targeted can abrogate PDAC cell survival, stemness, EMT and tumor growth/metastasis.

Citation Format: Armen Gharibi, Sa La Kim, Daniel Brambilla, Yvess Adamian, Malachia Hoover, Joy Lin, Megan Agajanian, Laurelin Wolfenden, Jonathan A. Kelber. The PEAK1/ZEB1/ITGA1 pathway mediates survival, stemness and TGFbeta-induced EMT in pancreatic cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4426.

Cellular and molecular aspects of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a deadly malignancy that affects nearly 50,000 patients each year. The overall 5-year survival rate for this malignancy remains the lowest of any cancer at around 7% due to limited diagnostic methods, disease aggressiveness and a lack of targeted therapeutic interventions. This review highlights the successes achieved over the past several decades as well as the significant cellular and molecular hurdles that remain in combatting this deadly disease at a translational level.

Ascending the PEAK1 toward targeting TGFβ during cancer progression: Recent advances and future perspectives

Cancer is the second leading cause of death in the United States. Mortality in patients with solid, epithelial-derived tumors strongly correlates with disease stage and the systemic metastatic load. In such cancers, notable morphological and molecular changes have been attributed to cells as they pass through a continuum of epithelial-mesenchymal transition (EMT) states and many of these changes are essential for metastasis. While cancer metastasis is a complex cascade that is regulated by cell-autonomous and microenvironmental influences, it is well-accepted that understanding and controlling metastatic disease is a viable method for increasing patient survival. In the past 5 years, the novel non-receptor tyrosine kinase PEAK1 has surfaced as a central regulator of tumor progression and metastasis in the context of solid, epithelial cancers. Here, we review this literature with a special focus on our recent work demonstrating that PEAK1 mediates non-canonical pro-tumorigenic TGFβ signaling and is an intracellular control point between tumor cells and their extracellular microenvironment. We conclude with a brief discussion of potential applications derived from our current understanding of PEAK1 biology.

PEAK1 Acts as a Molecular Switch to Regulate Context-Dependent TGFβ Responses in Breast Cancer

Transforming Growth Factor β (TGFβ) has dual functions as both a tumor suppressor and a promoter of cancer progression within the tumor microenvironment, but the molecular mechanisms by which TGFβ signaling switches between these outcomes and the contexts in which this switch occurs remain to be fully elucidated. We previously identified PEAK1 as a new non-receptor tyrosine kinase that associates with the cytoskeleton, and facilitates signaling of HER2/Src complexes. We also showed PEAK1 functions downstream of KRas to promote tumor growth, metastasis and therapy resistance using preclinical in vivo models of human tumor progression. In the current study, we analyzed PEAK1 expression in human breast cancer samples and found PEAK1 levels correlate with mesenchymal gene expression, poor cellular differentiation and disease relapse. At the cellular level, we also observed that PEAK1 expression was highest in mesenchymal breast cancer cells, correlated with migration potential and increased in response to TGFβ-induced epithelial-mesenchymal transition (EMT). Thus, we sought to evaluate the role of PEAK1 in the switching of TGFβ from a tumor suppressing to tumor promoting factor. Notably, we discovered that high PEAK1 expression causes TGFβ to lose its anti-proliferative effects, and potentiates TGFβ-induced proliferation, EMT, cell migration and tumor metastasis in a fibronectin-dependent fashion. In the presence of fibronectin, PEAK1 caused a switching of TGFβ signaling from its canonical Smad2/3 pathway to non-canonical Src and MAPK signaling. This report is the first to provide evidence that PEAK1 mediates signaling cross talk between TGFβ receptors and integrin/Src/MAPK pathways and that PEAK1 is an important molecular regulator of TGFβ-induced tumor progression and metastasis in breast cancer. Finally, PEAK1 overexpression/upregulation cooperates with TGFβ to reduce breast cancer sensitivity to Src kinase inhibition. These findings provide a rational basis to develop therapeutic agents to target PEAK1 expression/function or upstream/downstream pathways to abrogate breast cancer progression.

A hypusine-eIF5A-PEAK1 switch regulates the pathogenesis of pancreatic cancer

Deregulation of protein synthesis is a hallmark of cancer cell proliferation, survival, and metastatic progression. eIF5A1 and its highly related isoform eIF5A2 are translation initiation factors that have been implicated in a range of human malignancies, but how they control cancer development and disease progression is still poorly understood. Here, we investigated how eIF5A proteins regulate pancreatic ductal adenocarcinoma (PDAC) pathogenesis. eIF5A proteins are the only known proteins regulated by a distinct posttranslational modification termed hypusination, which is catalyzed by two enzymes, deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase (DOHH). The highly selective nature of the hypusine modification and its amenability to pharmacologic inhibition make eIF5A proteins attractive therapeutic targets. We found that the expression and hypusination of eIF5A proteins are upregulated in human PDAC tissues and in premalignant pancreatic intraepithelial neoplasia tissues isolated from Pdx-1-Cre: LSL-KRAS(G12D) mice. Knockdown of eIF5A proteins in PDAC cells inhibited their growth in vitro and orthotopic tumor growth in vivo, whereas amplification of eIF5A proteins increased PDAC cell growth and tumor formation in mice. Small-molecule inhibitors of DHPS and DOHH both suppressed eIF5A hypusination, preventing PDAC cell growth. Interestingly, we found that eIF5A proteins regulate PDAC cell growth by modulating the expression of PEAK1, a nonreceptor tyrosine kinase essential for PDAC cell growth and therapy resistance. Our findings suggest that eIF5A proteins utilize PEAK1 as a downstream effector to drive PDAC pathogenesis and that pharmacologic inhibition of the eIF5A-hypusine-PEAK1 axis may provide a novel therapeutic strategy to combat this deadly disease.

Abstract 1932: Parallel functions of the endoplasmic reticulum chaperone protein GRP78 in tumorigenesis and the induction of pluripotency

Increasing evidence supports the concept that instances of cancer recurrence may be due to a subpopulation of cells within a tumor that behave as stem cells. Previous studies have demonstrated that pathways critical in oncogenesis parallel those necessary for the induction of pluripotency, suggesting that similar mechanisms regulate both processes. By therefore understanding the mechanisms that govern reprogramming, we may gain insight into the methods by which cancer cells acquire and exploit stem cell properties, and enable more strategic targeting of these cell populations to prevent malignant relapse. Members of the TGF-beta superfamily (e.g. activin/Nodal), which regulate many important normal cellular responses including cell growth and differentiation, have also been shown to promote tumorigenesis. Cripto, a regulator of TGF-beta superfamily ligand signaling expressed on human embryonic stem cells, is overexpressed in many types of cancer, and has also been shown to promote tumor growth and metastasis. Previous work has demonstrated that Cripto regulates TGF-beta function in tumor cell lines by forming a complex with GRP78, a protein generally restricted to the endoplasmic reticulum in normal tissues, but expressed at the cell surface in many types of tumors. Targeting GRP78 in mouse models suppresses tumor growth, and cell surface GRP78 has been shown to be a molecular target on human tumor samples. Although these studies have suggested an important role for GRP78 in promoting tumorigenesis, the mechanisms are not yet fully understood. We have discovered that GRP78 expression is induced during reprogramming, and becomes localized to the cell surface in pluripotent cells, where it co-localizes with Cripto. Overexpression of GRP78 in somatic cells induced their reprogramming efficiency. We further found that a GRP78 antibody, that disrupts cell surface GRP78/Cripto binding and Cripto-mediated TGF-beta superfamily signaling, inhibited reprogramming. Treatment of pluripotent stem cell populations with this GRP78 antibody also decreased proliferation, but did not impact pluripotency. These combined findings suggest that GRP78 may be localized to the cell surface during reprogramming where it functions to inhibit TGF-beta signaling and promote stem cell proliferation and/or survival. Interestingly, overexpression of GRP78 in human breast cancer cell lines caused an increased resistance to cisplatin. Furthermore, inhibiting cell surface function of GRP78 in these breast cancer lines resulted in a higher susceptibility to cisplatin treatment, demonstrating a specific function for cell surface GRP78 in cisplatin resistance. These combined stem cell functions of GRP78 therefore parallel many of the functions of GRP78 for cancer cells, and thus provide insight into understanding how cancer cells acquire and exploit stem cell properties.

Citation Format: Athanasia D. Panopoulos, Yuriko Hishida, Min-Zu Wu, Sergio Ruiz, Erika Batchelder, Tomoaki Hishida, Jonathan A. Kelber, Peter C. Gray, Juan Carlos Izpisua Belmonte. Parallel functions of the endoplasmic reticulum chaperone protein GRP78 in tumorigenesis and the induction of pluripotency. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1932. doi:10.1158/1538-7445.AM2014-1932

Abstract 3035: Cripto/GRP78 signaling promotes the stem cell phenotype in normal and neoplastic mammary epithelial cells

Microenvironmental factors are critical regulators of stem cell and tumor cell behavior. However, few stem cell factors have been identified and targeted in breast and other cancers. Using a highly enriched stem cell pool isolated from fetal mammary rudiments and single cell analyses, we have identified the onco-fetal protein Cripto as a potent soluble factor that regulates the mammary stem cell state. Cripto is a GPI-anchored/secreted signaling protein and a known regulator of PI3K/AKT and TGF-beta pathways. Here, we develop a novel Cripto antagonist, ALK4L75A-Fc, which selectively blocks the growth factor-like effects of soluble Cripto. We show that this antagonist promotes the differentiation of mammary stem cells cultured ex vivo while Cripto treatment maintains the stem cell phenotype and yields colonies with enhanced mammary gland reconstitution capacity. We previously discovered that Cripto signaling requires binding to cell surface Glucose Response Protein 78kDa (GRP78). GRP78 is an HSP70 family member that is induced by stresses including hypoxia and glucose deprivation and it is highly expressed in tumors where these conditions prevail. We show here that cell surface GRP78 marks fetal mouse mammary stem cells and a population of bipotent adult mammary epithelial cells that are selectively responsive to soluble Cripto in vitro. GRP78high mammary epithelial cells also harbor substantially higher stem cell activity upon transplantation than GRP78low cells. Consistently, we further show that deletion of GRP78 from adult mammary epithelial cells ex vivo blocks mammary gland reconstitution. Finally, we find that Cripto antagonism with ALK4L75A-Fc inhibits the proliferation of triple negative breast cancer cell lines in vitro and that this antagonist can also inhibit tumor growth in vivo. Since Cripto and GRP78 are both induced by hypoxia and other stressful conditions found in tumors, our data raise the possibility that Cripto/GRP78 signaling may exacerbate breast and other cancers by increasing the number of stem cell-like tumor cells in tumor microenvironments where these conditions predominate.

Citation Format: Benjamin T. Spike, Jonathan A. Kelber, Evan Booker, Madhuri Kalathur, Rose Rodewald, Julia Lipianskaya, Justin La, Marielle He, Tracy Wright, Richard Klemke, Geoffrey Wahl, Peter C. Gray. Cripto/GRP78 signaling promotes the stem cell phenotype in normal and neoplastic mammary epithelial cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3035. doi:10.1158/1538-7445.AM2014-3035

CRIPTO/GRP78 signaling maintains fetal and adult mammary stem cells ex vivo

Little is known about the extracellular signaling factors that govern mammary stem cell behavior. Here, we identify CRIPTO and its cell-surface receptor GRP78 as regulators of stem cell behavior in isolated fetal and adult mammary epithelial cells. We develop a CRIPTO antagonist that promotes differentiation and reduces self-renewal of mammary stem cell-enriched populations cultured ex vivo. By contrast, CRIPTO treatment maintains the stem cell phenotype in these cultures and yields colonies with enhanced mammary gland reconstitution capacity. Surface expression of GRP78 marks CRIPTO-responsive, stem cell-enriched fetal and adult mammary epithelial cells, and deletion of GRP78 from adult mammary epithelial cells blocks their mammary gland reconstitution potential. Together, these findings identify the CRIPTO/GRP78 pathway as a developmentally conserved regulator of fetal and adult mammary stem cell behavior ex vivo, with implications for the stem-like cells found in many cancers.

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CRIPTO/GRP78 signaling activates PI3K/AKT in fetal mammary epithelial cells ex vivo

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Cell-surface GRP78 marks a CRIPTO-responsive adult mammary stem cell population

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An antagonist, ALK4^L75A-Fc, blocks soluble CRIPTO growth-factor-like activity

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CRIPTO promotes and ALK4^L75A-Fc inhibits mammary stem cell maintenance ex vivo

Abstract A136: Deconstructing stemness from the fetal mammary perspective

Somatic stem cells govern the development, maintenance and regeneration of tissues, and their dysregulation is associated with diverse pathologies including cancer. Given the significance of these cells both biologically and therapeutically, it is critical to elucidate the signaling mechanisms that dictate their behavior. Our recent work on the fetal mammary gland has dissected complementary roles for the stem cell compartment and stromal cues in fetal mammary stem cell function. We also identified significant similarities between the gene expression profiles of some of the most aggressive and untreatable forms of human breast cancer and those of the mouse fetal stem cell enriched mammary epithelial and stromal fractions. These similarities suggest that stem cell regulatory mechanisms operative during organogenesis, including those specified by the stromal niche, may serve as novel therapeutic targets in these cancers.

We also discovered significant gene expression heterogeneity within the fetal stem cell compartment when analyzed at single cell resolution. While such heterogeneity likely reflects the natural diversity of stem and non-stem cell states comprising the system, it confounds the interpretation of expression profiles from mixed populations and the delineation of stem cell specific and niche specific molecular components. Our current objective is to utilize genome wide single cell RNA-Sequencing to hasten the identification of functionally relevant, stem cell specific regulators and markers in the context of this multi-cellular/multi-signal system. Among other candidates, we have identified the Cripto/GRP78 signaling axis as a critical regulator of mammary stem cell activity, and have developed novel molecular genetic tools to temporally control the activity of candidate stem cell regulators in vivo in normal and neoplastic contexts. Integration of these tools promises to deliver a new molecular understanding of stem cell biology in the mammary gland and other systems and of stem cell-like cancer cells.

Citation Format: Benjamin T. Spike, Danielle D. Engle, Jennifer C. Lin, Jonathan A. Kelber, Justin La, Samantha K. Cheung, Evan Booker, Rose Rodewald, Christopher Dravis, Peter C. Gray, Geoffrey M. Wahl. Deconstructing stemness from the fetal mammary perspective. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr A136.

Role of connexins in metastatic breast cancer and melanoma brain colonization

Breast cancer and melanoma cells commonly metastasize to the brain using homing mechanisms that are poorly understood. Cancer patients with brain metastases display poor prognosis and survival due to the lack of effective therapeutics and treatment strategies. Recent work using intravital microscopy and preclinical animal models indicates that metastatic cells colonize the brain, specifically in close contact with the existing brain vasculature. However, it is not known how contact with the vascular niche promotes microtumor formation. Here, we investigate the role of connexins in mediating early events in brain colonization using transparent zebrafish and chicken embryo models of brain metastasis. We provide evidence that breast cancer and melanoma cells utilize connexin gap junction proteins (Cx43, Cx26) to initiate brain metastatic lesion formation in association with the vasculature. RNAi depletion of connexins or pharmacological blocking of connexin-mediated cell-cell communication with carbenoxolone inhibited brain colonization by blocking tumor cell extravasation and blood vessel co-option. Activation of the metastatic gene twist in breast cancer cells increased Cx43 protein expression and gap junction communication, leading to increased extravasation, blood vessel co-option and brain colonization. Conversely, inhibiting twist activity reduced Cx43-mediated gap junction coupling and brain colonization. Database analyses of patient histories revealed increased expression of Cx26 and Cx43 in primary melanoma and breast cancer tumors, respectively, which correlated with increased cancer recurrence and metastasis. Together, our data indicate that Cx43 and Cx26 mediate cancer cell metastasis to the brain and suggest that connexins might be exploited therapeutically to benefit cancer patients with metastatic disease.

KRas induces a Src/PEAK1/ErbB2 kinase amplification loop that drives metastatic growth and therapy resistance in pancreatic cancer

Early biomarkers and effective therapeutic strategies are desperately needed to treat pancreatic ductal adenocarcinoma (PDAC), which has a dismal 5-year patient survival rate. Here, we report that the novel tyrosine kinase PEAK1 is upregulated in human malignancies, including human PDACs and pancreatic intraepithelial neoplasia (PanIN). Oncogenic KRas induced a PEAK1-dependent kinase amplification loop between Src, PEAK1, and ErbB2 to drive PDAC tumor growth and metastasis in vivo. Surprisingly, blockade of ErbB2 expression increased Src-dependent PEAK1 expression, PEAK1-dependent Src activation, and tumor growth in vivo, suggesting a mechanism for the observed resistance of patients with PDACs to therapeutic intervention. Importantly, PEAK1 inactivation sensitized PDAC cells to trastuzumab and gemcitabine therapy. Our findings, therefore, suggest that PEAK1 is a novel biomarker, critical signaling hub, and new therapeutic target in PDACs.

Cancer cell migration within 3D layer-by-layer microfabricated photocrosslinked PEG scaffolds with tunable stiffness

Our current understanding of 3-dimensional (3D) cell migration is primarily based on results from fibrous scaffolds with randomly organized internal architecture. Manipulations that change the stiffness of these 3D scaffolds often alter other matrix parameters that can modulate cell motility independently or synergistically, making observations less predictive of how cells behave when migrating in 3D. In order to decouple microstructural influences and stiffness effects, we have designed and fabricated 3D polyethylene glycol (PEG) scaffolds that permit orthogonal tuning of both elastic moduli and microstructure. Scaffolds with log-pile architectures were used to compare the 3D migration properties of normal breast epithelial cells (HMLE) and Twist-transformed cells (HMLET). Our results indicate that the nature of cell migration is significantly impacted by the ability of cells to migrate in the third dimension. 2D ECM-coated PEG substrates revealed no statistically significant difference in cell migration between HMLE and HMLET cells among substrates of different stiffness. However, when cells were allowed to move along the third dimension, substantial differences were observed for cell displacement, velocity and path straightness parameters. Furthermore, these differences were sensitive to both substrate stiffness and the presence of the Twist oncogene. Importantly, these 3D modes of migration provide insight into the potential for oncogene-transformed cells to migrate within and colonize tissues of varying stiffness.

Abstract 4167: KRas induces a Src/PEAK1/ErbB2 kinase amplification loop to drive pancreatic cancer growth, metastasis and therapy resistance

Early biomarkers and effective therapeutic strategies are desperately needed to treat pancreatic ductal adenocarcinoma (PDAC), which has a dismal 5-year patient survival rate. We recently identified PEAK1 (pseudopodium-enriched atypical kinase one, SGK269) as a catalytically active tyrosine kinase that associates with the cytoskeleton and regulates cell migration and proliferation. Tyrosine kinases are highly sought after candidates as biomarkers and therapeutic targets because they induce specific phoshorylation signatures and because their catalytic activity and downstream signals can be inhibited by small molecules. The goal of this current study was to assess the role of PEAK1 expression as a diagnostic/prognostic biomarker and potential therapeutic target in human malignancies. Here, we report that the novel tyrosine kinase PEAK1 is upregulated in human malignancies, including human PDAC and pancreatic intraepithelial neoplasia (PanIN). Oncogenic KRas induced a PEAK1-dependent kinase amplification loop between Src, PEAK1 and ErbB2 to drive PDAC tumor growth and metastasis in vivo. Suprisingly, blockade of ErbB2 increased Src-dependent PEAK1 expression, PEAK1-dependent Src activation and tumor growth in vivo, suggesting a mechanism for the resistance of PDAC to therapeutic intervention. Indeed, PEAK1 mediates multiple therapy resistance phenotypes that present major hurdles in the clinical treatment of this disease. Thus, PEAK1 is a novel biomarker, critical signaling hub, and new therapeutic target in PDAC.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4167. doi:1538-7445.AM2012-4167

Abstract 3493: Soluble ALK4 extracellular domain antagonizes the cancer/stem cell phenotype caused by Nodal and Cripto signaling in mammary epithelia

We recently determined that a fraction of cells in a highly enriched fetal mammary stem cell pool expresses the oncofetal protein Cripto and its receptor/co-factor GRP78 on their surfaces. Cripto is a GPI-anchored protein important for embryonic stem cell self-renewal and developmental plasticity. It is also selectively overexpressed in multiple human tumors including ∼80% of human breast tumors. Cripto overexpression increases cellular proliferation, invasion and migration in vitro and promotes mammary tumor growth in mice. Cripto functions as an obligatory co-receptor for Smad2/3 activation by the TGF-β superfamily member Nodal but attenuates activin-A and TGF-β1 signaling and the cytostatic effects of these ligands on human mammary epithelial cells. Cripto can be secreted from cells and soluble forms activate Src, ras/raf/MAPK and PI3K/Akt pathways. We recently identified the HSP70 family member GRP78 as a cell surface receptor/co-factor that is required for Cripto signaling via TGF-β and Src/MAPK/PI3K pathways. Here, we developed a soluble and highly specific Cripto antagonist based on the extracellular domain of the Activin/Nodal Type I serine/threonine kinase receptor ALK4 (sALK4-ECD). We tested the ability of this antagonist to block Cripto signaling via TGF-β and Src/MAPK/PI3K pathways in oncogenic and stem cell phenotypes in mammary epithelial cells and breast cancer cell lines. The sALK4-ECD protein dose-dependently and specifically inhibited 125I-Cripto binding to 293T cells transfected with full length ALK4. In addition, sALK4-L75A-Fc blocked 125I-Cripto binding to native human mammary epithelial MCF10A cells. sALK4-ECD inhibited Cripto-dependent Nodal signaling in 293T cells and inhibited Nodal-induced Smad2 phosphorylation in native NCCIT cells. sALK4-ECD also blocked Cripto-induced PI3K activation, cell proliferation and migration in MCF10A cells. Cripto and Nodal signaling had profound effects on MCF10A growth in suspension and mammosphere reseeding capacity that were also inhibited by sALK4-ECD. We evaluated Nodal/Cripto signaling in cancer cell lines and primary fetal mammary stem cells and tested the efficacy of sALK-ECD mediated suppression of Nodal and Cripto effects in vitro and in vivo. These studies were designed to test if Cripto represents a functional cell surface marker of normal stem cells and/or the cells that initiate or perpetuate breast cancers. Our results point to distinct roles for Cripto and Nodal/Cripto signaling in promoting the oncogenic phenotype via activation of Smad2/3 and PI3K pathways, and support a role for Cripto antagonism such as that afforded by sALK4-ECD as a potential therapeutic strategy for the treatment of human disease.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3493. doi:1538-7445.AM2012-3493

Designer TGFβ superfamily ligands with diversified functionality

Transforming Growth Factor – beta (TGFβ) superfamily ligands, including Activins, Growth and Differentiation Factors (GDFs), and Bone Morphogenetic Proteins (BMPs), are excellent targets for protein-based therapeutics because of their pervasiveness in numerous developmental and cellular processes. We developed a strategy termed RASCH (Random Assembly of Segmental Chimera and Heteromer), to engineer chemically-refoldable TGFβ superfamily ligands with unique signaling properties. One of these engineered ligands, AB208, created from Activin-βA and BMP-2 sequences, exhibits the refolding characteristics of BMP-2 while possessing Activin-like signaling attributes. Further, we find several additional ligands, AB204, AB211, and AB215, which initiate the intracellular Smad1-mediated signaling pathways more strongly than BMP-2 but show no sensitivity to the natural BMP antagonist Noggin unlike natural BMP-2. In another design, incorporation of a short N-terminal segment from BMP-2 was sufficient to enable chemical refolding of BMP-9, without which was never produced nor refolded. Our studies show that the RASCH strategy enables us to expand the functional repertoire of TGFβ superfamily ligands through development of novel chimeric TGFβ ligands with diverse biological and clinical values.

Blockade of Cripto binding to cell surface GRP78 inhibits oncogenic Cripto signaling via MAPK/PI3K and Smad2/3 pathways

Cripto is a developmental oncoprotein that signals via mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK), phosphatidylinositol 3-kinase (PI3K)/Akt and Smad2/3 pathways. However, the molecular basis for Cripto coupling to these pathways during embryogenesis and tumorigenesis is not fully understood. In this regard, we recently demonstrated that Cripto forms a cell surface complex with the HSP70 family member glucose-regulated protein-78 (GRP78). Here, we provide novel functional evidence demonstrating that cell surface GRP78 is a necessary mediator of Cripto signaling in human tumor, mammary epithelial and embryonic stem cells. We show that targeted disruption of the cell surface Cripto/GRP78 complex using shRNAs or GRP78 immunoneutralization precludes Cripto activation of MAPK/PI3K pathways and modulation of activin-A, activin-B, Nodal and transforming growth factor-beta1 signaling. We further demonstrate that blockade of Cripto binding to cell surface GRP78 prevents Cripto from increasing cellular proliferation, downregulating E-Cadherin, decreasing cell adhesion and promoting pro-proliferative responses to activin-A and Nodal. Thus, disrupting the Cripto/GRP78 binding interface blocks oncogenic Cripto signaling and may have important therapeutic value in the treatment of cancer.

Cripto is a noncompetitive activin antagonist that forms analogous signaling complexes with activin and nodal

Cripto plays critical roles during embryogenesis and has been implicated in promoting the growth and spread of tumors. Cripto is required for signaling by certain transforming growth factor-beta superfamily members, such as Nodal, but also antagonizes others, such as activin. The opposing effects of Cripto on Nodal and activin signaling seem contradictory, however, because these closely related ligands utilize the same type I (ALK4) and type II (ActRII/IIB) receptors. Here, we have addressed this apparent paradox by demonstrating that Cripto forms analogous receptor complexes with Nodal and activin and functions as a noncompetitive activin antagonist. Our results show that activin-A and Nodal elicit similar maximal signaling responses in the presence of Cripto that are substantially lower than that of activin-A in the absence of Cripto. In addition, we provide biochemical evidence for complexes containing activin-A, Cripto, and both receptor types and show that the assembly of such complexes is competitively inhibited by Nodal. We further demonstrate that Nodal and activin-A share the same binding site on ActRII and that ALK4 has distinct and separable binding sites for activin-A and Cripto. Finally, we show that ALK4 mutants with disrupted activin-A binding retain Cripto binding and prevent the effects of Cripto on both activin-A and Nodal signaling. Together, our data indicate that Cripto facilitates Nodal signaling and inhibits activin signaling by forming receptor complexes with these ligands that are structurally and functionally similar.