Stromal gene expression defines poor-prognosis subtypes in colorectal cancer

Recent molecular classifications of colorectal cancer (CRC) based on global gene expression profiles have defined subtypes displaying resistance to therapy and poor prognosis. Upon evaluation of these classification systems, we discovered that their predictive power arises from genes expressed by stromal cells rather than epithelial tumor cells. Bioinformatic and immunohistochemical analyses identify stromal markers that associate robustly with disease relapse across the various classifications. Functional studies indicate that cancer-associated fibroblasts (CAFs) increase the frequency of tumor-initiating cells, an effect that is dramatically enhanced by transforming growth factor (TGF)-β signaling. Likewise, we find that all poor-prognosis CRC subtypes share a gene program induced by TGF-β in tumor stromal cells. Using patient-derived tumor organoids and xenografts, we show that the use of TGF-β signaling inhibitors to block the cross-talk between cancer cells and the microenvironment halts disease progression.

Determinants of metastatic competency in colorectal cancer

Colorectal cancer (CRC) is one of the most common cancer types and represents a major therapeutic challenge. Although initial events in colorectal carcinogenesis are relatively well characterized and treatment for early‐stage disease has significantly improved over the last decades, the mechanisms underlying metastasis – the main cause of death – remain poorly understood. Correspondingly, no effective therapy is currently available for advanced or metastatic disease. There is increasing evidence that colorectal cancer is hierarchically organized and sustained by cancer stem cells, in concert with various stromal cell types. Here, we review the interplay between cancer stem cells and their microenvironment in promoting metastasis and discuss recent insights relating to both patient prognosis and novel targeted treatment strategies. A better understanding of these topics may aid the prevention or reduction of metastatic burden.

Intracellular autofluorescence: a biomarker for epithelial cancer stem cells

Cancer stem cells (CSCs) are thought to drive tumor growth, metastasis and chemoresistance. Although surface markers such as CD133 and CD44 have been successfully used to isolate CSCs, their expression is not exclusively linked to the CSC phenotype and is prone to environmental alteration. We identified cells with an autofluorescent subcellular compartment that exclusively showed CSC features across different human tumor types. Primary tumor-derived autofluorescent cells did not overlap with side-population (SP) cells, were enriched in sphere culture and during chemotherapy, strongly expressed pluripotency-associated genes, were highly metastatic and showed long-term in vivo tumorigenicity, even at the single-cell level. Autofluorescence was due to riboflavin accumulation in membrane-bounded cytoplasmic structures bearing ATP-dependent ABCG2 transporters. In summary, we identified and characterized an intrinsic autofluorescent phenotype in CSCs of diverse epithelial cancers and used this marker to isolate and characterize these cells.

Pancreatic stellate cells form a niche for cancer stem cells and promote their self-renewal and invasiveness

Chronic pancreatitis and pancreatic ductal adenocarcinoma (PDAC) are characterized by extensive fibrosis. Importantly, in PDAC, this results in poor vascularization and impaired drug delivery to the cancer cells. Therefore, the combined targeting of pancreatic tumor stroma and chemotherapy should enhance response rates, but the negative outcome of a recent phase III clinical trial for the combination of chemotherapy and hedgehog pathway inhibition suggests that other means also need to be considered. Emerging data indicate that elimination of cancer stem cells as the root of the cancer is of pivotal importance for efficient treatment of pancreatic cancer. Recently, we demonstrated in a highly relevant preclinical mouse model for primary pancreatic cancers that the combination of cancer stem cell-targeting strategies in combination with a stroma-targeting agent, such as a hedgehog pathway inhibitor and chemotherapy, results in significantly enhanced long-term and progression-free survival. In the present study, we demonstrate mechanistically that Nodal-expressing pancreatic stellate cells are an important component of the tumor stroma for creating a paracrine niche for pancreatic cancer stem cells. Secretion of the embryonic morphogens Nodal/Activin by pancreatic stellate cells promoted in vitro sphere formation and invasiveness of pancreatic cancer stem cells in an Alk4-dependent manner. These data imply that the pancreatic cancer stem cell phenotype is promoted by paracrine Nodal/Activin signaling at the tumor-stroma interface. Therefore, targeting the tumor microenvironment is not only able to improve drug delivery but, even more importantly, destroys the cancer stem cell niche and, therefore, should be an integral part of cancer stem cell-based treatment strategies.

Metformin targets the metabolic achilles heel of human pancreatic cancer stem cells

Pancreatic ductal adenocarcinomas contain a subset of exclusively tumorigenic cancer stem cells (CSCs), which are capable of repopulating the entire heterogeneous cancer cell populations and are highly resistant to standard chemotherapy. Here we demonstrate that metformin selectively ablated pancreatic CSCs as evidenced by diminished expression of pluripotency-associated genes and CSC-associated surface markers. Subsequently, the ability of metformin-treated CSCs to clonally expand in vitro was irreversibly abrogated by inducing apoptosis. In contrast, non-CSCs preferentially responded by cell cycle arrest, but were not eliminated by metformin treatment. Mechanistically, metformin increased reactive oxygen species production in CSC and reduced their mitochondrial transmembrane potential. The subsequent induction of lethal energy crisis in CSCs was independent of AMPK/mTOR. Finally, in primary cancer tissue xenograft models metformin effectively reduced tumor burden and prevented disease progression; if combined with a stroma-targeting smoothened inhibitor for enhanced tissue penetration, while gemcitabine actually appeared dispensable.

The miR-17-92 cluster counteracts quiescence and chemoresistance in a distinct subpopulation of pancreatic cancer stem cells

OBJECTIVE

Cancer stem cells (CSCs) represent the root of many solid cancers including pancreatic ductal adenocarcinoma, are highly chemoresistant and represent the cellular source for disease relapse. However the mechanisms involved in these processes still need to be fully elucidated. Understanding the mechanisms implicated in chemoresistance and metastasis of pancreatic cancer is critical to improving patient outcomes.

DESIGN

Micro-RNA (miRNA) expression analyses were performed to identify functionally defining epigenetic signatures in pancreatic CSC-enriched sphere-derived cells and gemcitabine-resistant pancreatic CSCs.

RESULTS

We found the miR-17-92 cluster to be downregulated in chemoresistant CSCs versus non-CSCs and demonstrate its crucial relevance for CSC biology. In particular, overexpression of miR-17-92 reduced CSC self-renewal capacity, in vivo tumourigenicity and chemoresistance by targeting multiple NODAL/ACTIVIN/TGF-β1 signalling cascade members as well as directly inhibiting the downstream targets p21, p57 and TBX3. Overexpression of miR-17-92 translated into increased CSC proliferation and their eventual exhaustion via downregulation of p21 and p57. Finally, the translational impact of our findings could be confirmed in preclinical models for pancreatic cancer.

CONCLUSIONS

Our findings therefore identify the miR-17-92 cluster as a functionally determining family of miRNAs in CSCs, and highlight the putative potential of developing modulators of this cluster to overcome drug resistance in pancreatic CSCs.

G protein-coupled receptor APJ and its ligand apelin act downstream of Cripto to specify embryonic stem cells toward the cardiac lineage through extracellular signal-regulated kinase/p70S6 kinase signaling pathway

RATIONALE

Pluripotent stem cells represent a powerful model system to study the early steps of cardiac specification for which the molecular control is largely unknown. The EGF-CFC (epidermal growth factor-Cripto/FRL-1/Cryptic) Cripto protein is essential for cardiac myogenesis in embryonic stem cells (ESCs).

OBJECTIVE

Here, we study the role of apelin and its G protein-coupled receptor, APJ, as downstream targets of Cripto both in vivo and in ESC differentiation.

METHODS AND RESULTS

Gain-of-function experiments show that APJ suppresses neuronal differentiation and restores the cardiac program in Cripto(-/-) ESCs. Loss-of-function experiments point for a central role for APJ/apelin in the gene regulatory cascade promoting cardiac specification and differentiation in ESCs. Remarkably, we show for the first time that apelin promotes mammalian cardiomyogenesis via activation of mitogen-activated protein kinase/p70S6 through coupling to a Go/Gi protein.

CONCLUSIONS

Together our data provide evidence for a previously unrecognized function of APJ/apelin in the Cripto signaling pathway governing mesoderm patterning and cardiac specification in mammals.

Pancreatic cancer stem cells - update and future perspectives

Solid tumours are the most common cancers and represent a major therapeutic challenge. The cancer stem cell hypothesis is an attractive model to explain the functional heterogeneity commonly observed in solid tumours. It proposes a hierarchical organization of tumours, in which a subpopulation of stem cell-like cells sustains tumour growth, metastasis, and resistance to therapy. We will present the most recent advances in the cancer stem cell field, with particular emphasis on pancreatic cancer as one of the deadliest human tumours, and highlight open questions and caveats to be addressed in future studies. There is increasing evidence that solid tumours including pancreatic cancer are hierarchically organized and sustained by a distinct subpopulation of cancer stem cells. However, direct evidence for the validity of the cancer stem cell hypothesis in human pancreatic cancer remains controversial due to the limitations of xenograft models but supportive data are now emerging from mouse models using related or different sets of markers for the identification of murine cancer stem cells. Therefore, while the clinical relevance of cancer stem cells remains a fundamental issue for this rapidly emerging field, current findings clearly suggest that specific elimination of these cells is possible and therapeutically relevant. Targeting of signalling pathways that are of particular importance for the maintenance and the elimination of cancer stem cell as the proposed root of the tumour may lead to the development of novel treatment regimens for pancreatic cancer. Here we will review the current literature on pancreatic cancer stem cells and the future perspective of this rapidly emerging field.

TGF-β1 secreted by pancreatic stellate cells promotes stemness and tumourigenicity in pancreatic cancer cells through L1CAM downregulation

Pancreatic stellate cells (PSCs) secrete high levels of transforming growth factor-β1 (TGF-β1) that contributes to the development of pancreatic ductal adenocarcinoma (PDAC). TGF-β1 modulates the expression of L1 cell adhesion molecule (L1CAM), but its role in tumour progression still remains controversial. To clarify L1 function in PDAC and cellular phenotypes, we performed L1CAM cell sorting, silencing and overexpression in several primary pancreatic cancer cells. PSCs silenced for TGF-β1 were used for crosstalk experiments. We found that TGF-β1 secreted by PSCs negatively regulates L1CAM expression, through canonical TGF-β-Smad2/3 signalling, leading to a more aggressive PDAC phenotype. Cells with reduced expression of L1CAM harboured enhanced stemness potential and tumourigenicity. Inactivation of TGF-β1 signalling in PSCs strongly reduced the aggressiveness of PDAC cells. Our data provide functional proof and mechanistic insights for the tumour-suppressive function of L1CAM via reducing stemness. Rescuing L1CAM expression in cancer cells through targeting of TGF-β1 reverses stemness and bears the potential to improve the still miserable prognosis of PDAC patients.

ZFP57 maintains the parent-of-origin-specific expression of the imprinted genes and differentially affects non-imprinted targets in mouse embryonic stem cells

ZFP57 is necessary for maintaining repressive epigenetic modifications at Imprinting control regions (ICRs). In mouse embryonic stem cells (ESCs), ZFP57 binds ICRs (ICRBS) and many other loci (non-ICRBS). To address the role of ZFP57 on all its target sites, we performed high-throughput and multi-locus analyses of inbred and hybrid mouse ESC lines carrying different gene knockouts. By using an allele-specific RNA-seq approach, we demonstrate that ZFP57 loss results in derepression of the imprinted allele of multiple genes in the imprinted clusters. We also find marked epigenetic differences between ICRBS and non-ICRBS suggesting that different cis-acting regulatory functions are repressed by ZFP57 at these two classes of target loci. Overall, these data demonstrate that ZFP57 is pivotal to maintain the allele-specific epigenetic modifications of ICRs that in turn are necessary for maintaining the imprinted expression over long distances. At non-ICRBS, ZFP57 inactivation results in acquisition of epigenetic features that are characteristic of poised enhancers, suggesting that another function of ZFP57 in early embryogenesis is to repress cis-acting regulatory elements whose activity is not yet required.

Cripto-1 is required for hypoxia to induce cardiac differentiation of mouse embryonic stem cells

Cripto-1 is a membrane-bound protein that is highly expressed in embryonic stem cells and in human tumors. In the present study, we investigated the effect of low levels of oxygen, which occurs naturally in rapidly growing tissues, on Cripto-1 expression in mouse embryonic stem (mES) cells and in human embryonal carcinoma cells. During hypoxia, Cripto-1 expression levels were significantly elevated in mES cells and in Ntera-2 or NCCIT human embryonal carcinoma cells, as compared with cells growing with normal oxygen levels. The transcription factor hypoxia-inducible factor-1alpha directly regulated Cripto-1 expression by binding to hypoxia-responsive elements within the promoter of mouse and human Cripto-1 genes in mES and NCCIT cells, respectively. Furthermore, hypoxia modulated differentiation of mES cells by enhancing formation of beating cardiomyocytes as compared with mES cells that were differentiated under normoxia. However, hypoxia failed to induce differentiation of mES cells into cardiomyocytes in the absence of Cripto-1 expression, demonstrating that Cripto-1 is required for hypoxia to fully differentiate mES cells into cardiomyocytes. Finally, cardiac tissue samples derived from patients who had suffered ischemic heart disease showed a dramatic increase in Cripto-1 expression as compared with nonischemic heart tissue samples, suggesting that hypoxia may also regulate Cripto-1 in vivo.

A small synthetic cripto blocking Peptide improves neural induction, dopaminergic differentiation, and functional integration of mouse embryonic stem cells in a rat model of Parkinson's disease

Cripto is a glycosylphosphatidylinositol-anchored coreceptor that binds Nodal and the activin type I (ALK)-4 receptor, and is involved in cardiac differentiation of mouse embryonic stem cells (mESCs). Interestingly, genetic ablation of cripto results in increased neuralization and midbrain dopaminergic (DA) differentiation of mESCs, as well as improved DA cell replacement therapy (CRT) in a model of Parkinson's disease (PD). In this study, we developed a Cripto specific blocking tool that would mimic the deletion of cripto, but could be easily applied to embryonic stem cell (ESC) lines without the need of genetic manipulation. We thus screened a combinatorial peptide library and identified a tetrameric tripeptide, Cripto blocking peptide (BP), which prevents Cripto/ALK-4 receptor interaction and interferes with Cripto signaling. Cripto BP treatment favored neuroectoderm formation and promoted midbrain DA neuron differentiation of mESCs in vitro and in vivo. Remarkably, Cripto BP-treated ESCs, when transplanted into the striatum of PD rats, enhanced functional recovery and reduced tumor formation, mimicking the effect of genetic ablation of cripto. We therefore suggest that specific blockers such as Cripto BP may be used to improve the differentiation of ESC-derived DA neurons in vitro and their engraftment in vivo, bringing us closer towards an application of ESCs in CRT.

A synergic approach to enhance long-term culture and manipulation of MiaPaCa-2 pancreatic cancer spheroids

Tumour spheroids have the potential to be used as preclinical chemo-sensitivity assays. However, the production of three-dimensional (3D) tumour spheroids remains challenging as not all tumour cell lines form spheroids with regular morphologies and spheroid transfer often induces disaggregation. In the field of pancreatic cancer, the MiaPaCa-2 cell line is an interesting model for research but it is known for its difficulty to form stable spheroids; also, when formed, spheroids from this cell line are weak and arduous to manage and to harvest for further analyses such as multiple staining and imaging. In this work, we compared different methods (i.e. hanging drop, round-bottom wells and Matrigel embedding, each of them with or without methylcellulose in the media) to evaluate which one allowed to better overpass these limitations. Morphometric analysis indicated that hanging drop in presence of methylcellulose leaded to well-organized spheroids; interestingly, quantitative PCR (qPCR) analysis reflected the morphometric characterization, indicating that same spheroids expressed the highest values of CD44, VIMENTIN, TGF-β1 and Ki-67. In addition, we investigated the generation of MiaPaCa-2 spheroids when cultured on substrates of different hydrophobicity, in order to minimize the area in contact with the culture media and to further improve spheroid formation.

Effects of indole-3-acetic acid on Sinorhizobium meliloti survival and on symbiotic nitrogen fixation and stem dry weight production

We evaluated the effects of the main auxin phytohormone, indole-3-acetic acid (IAA), on the central metabolism of Sinorhizobium meliloti 1021. We either treated S. meliloti 1021 wild-type cells with 0.5 mM IAA, 1021+, or use a derivative, RD64, of the same strain harboring an additional pathway for IAA biosynthesis (converting tryptophan into IAA via indoleacetamide). We assayed the activity of tricarboxylic acid cycle (TCA) key enzymes and found that activity of citrate synthase and alpha-ketoglutarate dehydrogenase were increased in both 1021+ and RD64 as compared to the wild-type strain. We also showed that the intracellular acetyl-CoA content was enhanced in both RD64 and 1021+ strains when compared to the control strain. The activity of key enzymes, utilizing acetyl-CoA for poly-beta-hydroxybutyrate (PHB) biosynthesis, was also induced. The PHB level measured in these cells were significantly higher than that found in control cells. Moreover, 4-week-long survival experiments showed that 80% of 1021 cells died, whereas 50% of RD64 cells were viable. Medicago truncatula plants nodulated by RD64 (Mt-RD64) showed an induction of both acetylene reduction activity and stem dry weight production.

Cripto promotes A-P axis specification independently of its stimulatory effect on Nodal autoinduction

The EGF-CFC gene cripto governs anterior-posterior (A-P) axis specification in the vertebrate embryo. Existing models suggest that Cripto facilitates binding of Nodal to an ActRII-activin-like kinase (ALK) 4 receptor complex. Cripto also has a crucial function in cellular transformation that is independent of Nodal and ALK4. However, how ALK4-independent Cripto pathways function in vivo has remained unclear. We have generated cripto mutants carrying the amino acid substitution F78A, which blocks the Nodal-ALK4-Smad2 signaling both in embryonic stem cells and cell-based assays. In cripto(F78A/F78A) mouse embryos, Nodal fails to expand its own expression domain and that of cripto, indicating that F78 is essential in vivo to stimulate Smad-dependent Nodal autoinduction. In sharp contrast to cripto-null mutants, cripto(F78A/F78A) embryos establish an A-P axis and initiate gastrulation movements. Our findings provide in vivo evidence that Cripto is required in the Nodal-Smad2 pathway to activate an autoinductive feedback loop, whereas it can promote A-P axis formation and initiate gastrulation movements independently of its stimulatory effect on the canonical Nodal-ALK4-Smad2 signaling pathway.

The Revolutionary Roads to Study Cell-Cell Interactions in 3D In Vitro Pancreatic Cancer Models

Pancreatic cancer, the fourth most common cancer worldwide, shows a highly unsuccessful therapeutic response. In the last 10 years, neither important advancements nor new therapeutic strategies have significantly impacted patient survival, highlighting the need to pursue new avenues for drug development discovery and design. Advanced cellular models, resembling as much as possible the original in vivo tumor environment, may be more successful in predicting the efficacy of future anti-cancer candidates in clinical trials. In this review, we discuss novel bioengineered platforms for anticancer drug discovery in pancreatic cancer, from traditional two-dimensional models to innovative three-dimensional ones.

SERS Quantification of Galunisertib Delivery in Colorectal Cancer Cells by Plasmonic-Assisted Diatomite Nanoparticles

The small molecule Galunisertib (LY2157299, LY) shows multiple anticancer activities blocking the transforming growth factor-β1 receptor, responsible for the epithelial-to-mesenchymal transition (EMT) by which colorectal cancer (CRC) cells acquire migratory and metastatic capacities. However, frequent dosing of LY can produce highly toxic metabolites. Alternative strategies to reduce drug side effects can rely on nanoscale drug delivery systems that have led to a medical revolution in the treatment of cancer, improving drug efficacy and lowering drug toxicity. Here, a hybrid nanosystem (DNP-AuNPs-LY@Gel) made of a porous diatomite nanoparticle decorated with plasmonic gold nanoparticles, in which LY is retained by a gelatin shell, is proposed. The multifunctional capability of the nanosystem is demonstrated by investigating the efficient LY delivery, the enhanced EMT reversion in CRCs and the intracellular quantification of drug release with a sub-femtogram resolution by surface-enhanced Raman spectroscopy (SERS). The LY release trigger is the pH sensitivity of the gelatin shell to the CRC acidic microenvironment. The drug release is real-time monitored at single-cell level by analyzing the SERS signals of LY in CRC cells. The higher efficiency of LY delivered by the DNP-AuNPs-LY@Gel complex paves the way to an alternative strategy for lowering drug dosing and consequent side effects.

Nodal-induced L1CAM/CXCR4 subpopulation sustains tumor growth and metastasis in colorectal cancer derived organoids

Background: Colorectal cancer (CRC) is currently the third leading cause for cancer-related mortality. Cancer stem cells have been implicated in colorectal tumor growth, but their specific role in tumor biology, including metastasis, is still uncertain. Methods: Increased expression of L1CAM, CXCR4 and NODAL was identified in tumor section of patients with CRC and in patients-derived-organoids (PDOs). The expression of L1CAM, CXCR4 and NODAL was evaluated using quantitative real-time PCR, western blotting, immunofluorescence, immunohistochemistry and flow cytometry. The effects of the L1CAM, CXCR4 and NODAL on tumor growth, proliferation, migration, invasion, colony-formation ability, metastasis and chemoresistance were investigated both in vitro and in vivo. Results: We found that human colorectal cancer tissue contains cancer stem cells defined by L1CAM^high/CXCR4^high expression that is activated by Nodal in hypoxic microenvironment. This L1CAM^high/CXCR4^high population is tumorigenic, highly resistant to standard chemotherapy, and determines the metastatic phenotype of the individual tumor. Depletion of the L1CAM^high/CXCR4^high population drastically reduces the tumorigenic potential and the metastatic phenotype of colorectal tumors. Conclusion: In conclusion, we demonstrated that a subpopulation of migrating L1CAM^high/CXCR4^high is essential for tumor progression. Together, these findings suggest that strategies aimed at modulating the Nodal signaling could have important clinical applications to inhibit colorectal cancer-derived metastasis.

LAMC2 marks a tumor-initiating cell population with an aggressive signature in pancreatic cancer

BACKGROUND

Tumor-initiating cells (TIC), also known as cancer stem cells, are considered a specific subpopulation of cells necessary for cancer initiation and metastasis; however, the mechanisms by which they acquire metastatic traits are not well understood.

METHODS

LAMC2 transcriptional levels were evaluated using publicly available transcriptome data sets, and LAMC2 immunohistochemistry was performed using a tissue microarray composed of PDAC and normal pancreas tissues. Silencing and tracing of LAMC2 was performed using lentiviral shRNA constructs and CRISPR/Cas9-mediated homologous recombination, respectively. The contribution of LAMC2 to PDAC tumorigenicity was explored in vitro by tumor cell invasion, migration, sphere-forming and organoids assays, and in vivo by tumor growth and metastatic assays. mRNA sequencing was performed to identify key cellular pathways upregulated in LAMC2 expressing cells. Metastatic spreading induced by LAMC2- expressing cells was blocked by pharmacological inhibition of transforming growth factor beta (TGF-β) signaling.

RESULTS

We report a LAMC2-expressing cell population, which is endowed with enhanced self-renewal capacity, and is sufficient for tumor initiation and differentiation, and drives metastasis. mRNA profiling of these cells indicates a prominent squamous signature, and differentially activated pathways critical for tumor growth and metastasis, including deregulation of the TGF-β signaling pathway. Treatment with Vactosertib, a new small molecule inhibitor of the TGF-β type I receptor (activin receptor-like kinase-5, ALK5), completely abrogated lung metastasis, primarily originating from LAMC2-expressing cells.

CONCLUSIONS

We have identified a highly metastatic subpopulation of TICs marked by LAMC2. Strategies aimed at targeting the LAMC2 population may be effective in reducing tumor aggressiveness in PDAC patients. Our results prompt further study of this TIC population in pancreatic cancer and exploration as a potential therapeutic target and/or biomarker.

Studying Pancreatic Cancer Stem Cell Characteristics for Developing New Treatment Strategies

Pancreatic ductal adenocarcinoma (PDAC) contains a subset of exclusively tumorigenic cancer stem cells (CSCs) which have been shown to drive tumor initiation, metastasis and resistance to radio- and chemotherapy. Here we describe a specific methodology for culturing primary human pancreatic CSCs as tumor spheres in anchorage-independent conditions. Cells are grown in serum-free, non-adherent conditions in order to enrich for CSCs while their more differentiated progenies do not survive and proliferate during the initial phase following seeding of single cells. This assay can be used to estimate the percentage of CSCs present in a population of tumor cells. Both size (which can range from 35 to 250 micrometers) and number of tumor spheres formed represents CSC activity harbored in either bulk populations of cultured cancer cells or freshly harvested and digested tumors. Using this assay, we recently found that metformin selectively ablates pancreatic CSCs; a finding that was subsequently further corroborated by demonstrating diminished expression of pluripotency-associated genes/surface markers and reduced in vivo tumorigenicity of metformin-treated cells. As the final step for preclinical development we treated mice bearing established tumors with metformin and found significantly prolonged survival. Clinical studies testing the use of metformin in patients with PDAC are currently underway (e.g., NCT01210911, NCT01167738, and NCT01488552). Mechanistically, we found that metformin induces a fatal energy crisis in CSCs by enhancing reactive oxygen species (ROS) production and reducing mitochondrial transmembrane potential. In contrast, non-CSCs were not eliminated by metformin treatment, but rather underwent reversible cell cycle arrest. Therefore, our study serves as a successful example for the potential of in vitro sphere formation as a screening tool to identify compounds that potentially target CSCs, but this technique will require further in vitro and in vivo validation to eliminate false discoveries.

SERS-based pH-Dependent detection of sulfites in wine by hydrogel nanocomposites

Sulfur dioxide (SO2) and sulfites are well-known additives in winemaking due to their preservative properties. Although they can prevent oxidation and inhibit microbial growth, they pose health risks and require limitations on their use. Consequently, the total level of SO2 is regulated and several quantification strategies have been proposed. The approved detection methods require the extraction of SO2 by heating and/or acid treatment. Then, iodine or acid/base titrations are conducted for the detection of liberated SO2. Although these methods can provide sensitive detection of SO2, they are complex, time-consuming, and require sample preparation steps and skilled operators. Thus, to overcome these disadvantages, an easy-to-use method, involving simple sample preparation steps, and offering high sensitivity and selectivity, is desirable. Herein, we introduce a SERS-based strategy for SO2 detection in liquids using hydrogel nanocomposites. The hydrogels are prepared by poly(ethylene glycol) diacrylate (PEGDA) in the presence of gold nanoparticles (AuNPs), acting as the SERS substrate. The use of hydrogels ensures a homogenous signal distribution and an efficient collection of SO2, and drying the hydrogels enhances and stabilizes the obtained SO2 signal. The detection strategy is based on the pH-dependent dissociation of SO2. By adjusting the pH value of wine to 10 through simple dilutions, SO2 can be directly detected in wine, down to 0.4 ppm, well below the regulatory limits. The proposed method allows for sensitive, direct, cost-effective detection of SO2 by eliminating the loss of the gaseous form of the sample and avoids titration-based detection methods.

Abstract B45: Embryogenesis meets tumorigenesis: Nodal/activin signaling drives self-renewal and invasiveness of pancreatic cancer stem cells

Nodal and activin belong to the TGF-β superfamily and are important regulators of embryonic stem cell fate. Here we investigated whether Nodal and/or Activin regulate self-renewal and invasiveness of pancreatic cancer stem cells. While their expression was hardly detectable in differentiated pancreatic cancer cells, cancer stem cells demonstrate a drastic upregulation for Nodal and, to a lesser extent, Activin while TGF-β remained unchanged. Pancreatic stellate cells as the putative microenvironment for cancer stem cells produce very high amounts of Activin, and, to a lesser extent, Nodal. Knockdown and pharmacological inhibition of their common receptor Alk4/7 both significantly, but reversibly reduced cancer stem cell self-renewal / invasiveness and cancer stem cells subsequently became sensitive to gemcitabine. Importantly, while orthotopically engrafted primary human cancer cell suspensions were highly responsive to Nodal/Activin inhibition plus gemcitabine, engrafted primary human pancreatic cancer tissue xenografts containing massive stroma did not slow down tumor progression. Intriguingly, the addition of a stroma-targeting sonic hedgehog pathway inhibitor resulted in enhanced delivery of the Nodal/Activin inhibitor and gemcitabine, respectively, and translated into long-term disease stabilization. Therefore, modulation of the Alk4/7 pathway, if combined with hedgehog pathway inhibition and gemcitabine, provides a novel therapeutic strategy for targeted elimination of cancer stem cells in order to overcome their resistance towards gemcitabine.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr B45.

Abstract PO-038: LAMC2: New player in stemness and tumor progression in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a devastating and essentially incurable disease, typically characterized by high chemoresistance and metastatic spread attributable to cancer stem cells (CSCs). This subpopulation is critical for tumor initiation and recurrence, but the mechanism through which they acquire metastatic traits is not well understood. Hence, targeting the CSC niche and their plasticity could be a complementary therapeutic strategy against cancer. Laminin subunit-γ-2 (LAMC2) is an epithelial basement membrane protein, which controls cell motility and adhesion and is widely expressed in the majority of human tumors. However, its role in PDAC remains largely unknown. In several patient cohorts we observed that high levels of LAMC2 significantly correlated with shorter overall survival. In addition, the tissue microarray analysis on PDAC sections revealed prognostic significance of LAMC2 expression in tumor with high grade of aggressiveness (i.e., G2 and G3). To determine the role of LAMC2 in sustaining tumorigenicity, we knocked down it in patient-derived xenografts (PDX) cells using lentiviral shRNA constructs. The silencing of LAMC2 resulted in decreased self-renewal, invasiveness, tumorigenicity and gemcitabine resistance both in vitro and in vivo. To identify or track the LAMC2 tumor cell population in an intact environment we engineered primary PDAC cells that carry EGFP cassette knocked in the LAMC2 locus through the CRISPR-Cas9 technique. Analysis of LAMC2-EGFP+ cells isolated from tumor demonstrated that these cells express a gene program similar to that of highly metastatic stem cells and that they initiate and propagate both the primary tumor and the metastasis to recipient mice very efficiently compared to their counterpart. In conclusion, we identified a highly metastatic subpopulation of cancer stem cells, characterized by high levels of LAMC2. Strategies aimed at targeting the LAMC2 population may be effective in reducing tumor aggressiveness in combination with conventional therapy.

Citation Format: Donatella Delle Cave, Tea Teresa Iavazzo, Maria Mangini, Gennaro Andolfi, Teresa Pirozzi, Annalisa Di Domenico, Annachiara De Luca, Enza Lonardo. LAMC2: New player in stemness and tumor progression in pancreatic cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PO-038.

Abstract A48: Quantifying stroma-tumor cell interactions in three-dimensional cell culture systems

Background: In cancer research, studying cell motility is fundamental to investigate cancer invasion and drug resistance. In solid tumors constituted by a huge stroma component, such as pancreatic ductal adenocarcinoma (PDAC), the ability to quantify cell movement and interactions is mandatory to better understand the complex crosstalk between cancer and stroma cells. In PDAC, the pancreatic stellate cells (PSCs) are the principal source of dense fibrotic stroma: these closely interact with the PDAC cells to create a facilitating tumor microenvironment that supports local and distant tumor progression through the secretion and/or the response to a number of cytokines that globally increase cancer invasiveness; moreover, the dense tumor microenvironment contributes to resistance to chemotherapy and radiation therapy. Recent studies have established that targeting the stromal compartment in PDAC may lead to promising outcomes. Unfortunately, significant improvements in the overall survival of patients have not been realized in more than four decades, in part because of the lack of relevant preclinical models.

Methods: To infer interactions existing between stromal and cancer cells in complex 3D environments, we developed a novel platform that combines time-lapse fluorescence microscopy, automated image detection, and extensive statistical analysis. To better mimic in situ PDAC, we created a hydrogel-based (Matrigel, collagen) model that allows cell tracking in 4 dimensions (x, y, z, t), not possible in 2D, using a mixed population of L3.6PL pancreatic cancer cells and PSCs at a ratio of 25% and 75%, respectively. To precisely identify the two populations and facilitate automatic cell detection, cells were transfected with GFP and mCherry vectors. Once in the 3D conformation, the cocultures were monitored through time-lapse confocal microscopy (CLSM) in controlled conditions, and the dataset containing the temporal evolution of the cells was processed by statistical tools.

Results: Key to our approach was the generation of new machine learning-driven automated inferential protocols that resulted in the high-resolution imaging of the strength of the interactions between cells, as well as the potential presence of local chemokine gradients. In our ongoing studies, both commercial PDAC cell lines and pancreatic stellate cells were used to establish the model system. We are currently adopting the model to take full advantage of patient-derived PDAC cells established using the conditionally reprogrammed cells technique, mixed with patient-matched stellate cells. Since cell migration is a hallmark of cancer, we believe that this platform could be used as a reliable and reproducible approach for studying single-cell migration and invasion also in patient-derived models. The research leading to these results received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement No. 759959, ERC-StG “INTERCELLMED”).

Citation Format: Marta Maria Cavo, Francesco Alemanno, Donatella Delle Cave, Eliana D'Amone, Adriano Barra, Enza Lonardo, Erika Parasido, Chris Albanese, Loretta Laureana del Mercato. Quantifying stroma-tumor cell interactions in three-dimensional cell culture systems [abstract]. In: Proceedings of the AACR Special Conference on the Evolving Landscape of Cancer Modeling; 2020 Mar 2-5; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2020;80(11 Suppl):Abstract nr A48.