Targeting cancer stem cell OXPHOS with tailored ruthenium complexes as a new anti-cancer strategy

BACKGROUND

Previous studies by our group have shown that oxidative phosphorylation (OXPHOS) is the main pathway by which pancreatic cancer stem cells (CSCs) meet their energetic requirements; therefore, OXPHOS represents an Achille's heel of these highly tumorigenic cells. Unfortunately, therapies that target OXPHOS in CSCs are lacking.

METHODS

The safety and anti-CSC activity of a ruthenium complex featuring bipyridine and terpyridine ligands and one coordination labile position (Ru1) were evaluated across primary pancreatic cancer cultures and in vivo, using 8 patient-derived xenografts (PDXs). RNAseq analysis followed by mitochondria-specific molecular assays were used to determine the mechanism of action.

RESULTS

We show that Ru1 is capable of inhibiting CSC OXPHOS function in vitro, and more importantly, it presents excellent anti-cancer activity, with low toxicity, across a large panel of human pancreatic PDXs, as well as in colorectal cancer and osteosarcoma PDXs. Mechanistic studies suggest that this activity stems from Ru1 binding to the D-loop region of the mitochondrial DNA of CSCs, inhibiting OXPHOS complex-associated transcription, leading to reduced mitochondrial oxygen consumption, membrane potential, and ATP production, all of which are necessary for CSCs, which heavily depend on mitochondrial respiration.

CONCLUSIONS

Overall, the coordination complex Ru1 represents not only an exciting new anti-cancer agent, but also a molecular tool to dissect the role of OXPHOS in CSCs. Results indicating that the compound is safe, non-toxic and highly effective in vivo are extremely exciting, and have allowed us to uncover unprecedented mechanistic possibilities to fight different cancer types based on targeting CSC OXPHOS.

Macrophages direct cancer cells through a LOXL2-mediated metastatic cascade in pancreatic ductal adenocarcinoma

OBJECTIVE

The lysyl oxidase-like protein 2 (LOXL2) contributes to tumour progression and metastasis in different tumour entities, but its role in pancreatic ductal adenocarcinoma (PDAC) has not been evaluated in immunocompetent in vivo PDAC models.

DESIGN

Towards this end, we used PDAC patient data sets, patient-derived xenograft in vivo and in vitro models, and four conditional genetically-engineered mouse models (GEMMS) to dissect the role of LOXL2 in PDAC. For GEMM-based studies, K-Ras +/LSL-G12D;Trp53 LSL-R172H;Pdx1-Cre mice (KPC) and the K-Ras +/LSL-G12D;Pdx1-Cre mice (KC) were crossed with Loxl2 allele floxed mice (Loxl2Exon2 fl/fl) or conditional Loxl2 overexpressing mice (R26Loxl2 KI/KI) to generate KPCL2KO or KCL2KO and KPCL2KI or KCL2KI mice, which were used to study overall survival; tumour incidence, burden and differentiation; metastases; epithelial to mesenchymal transition (EMT); stemness and extracellular collagen matrix (ECM) organisation.

RESULTS

Using these PDAC mouse models, we show that while Loxl2 ablation had little effect on primary tumour development and growth, its loss significantly decreased metastasis and increased overall survival. We attribute this effect to non-cell autonomous factors, primarily ECM remodelling. Loxl2 overexpression, on the other hand, promoted primary and metastatic tumour growth and decreased overall survival, which could be linked to increased EMT and stemness. We also identified tumour-associated macrophage-secreted oncostatin M (OSM) as an inducer of LOXL2 expression, and show that targeting macrophages in vivo affects Osm and Loxl2 expression and collagen fibre alignment.

CONCLUSION

Taken together, our findings establish novel pathophysiological roles and functions for LOXL2 in PDAC, which could be potentially exploited to treat metastatic disease.

Deletion of NEMO Inhibits EMT and Reduces Metastasis in KPC Mice

Pancreatic ductal adenocarcinoma (PDAC) remains a largely incurable cancer type. Its high mortality is attributed to the lack of efficient biomarkers for early detection combined with its high metastatic properties. The aim of our study was to investigate the role of NF-κB signaling in the development and metastasis of PDAC. We used the well-established KPC mouse model, and, through genetic manipulation, we deleted NF-κB essential modulator (NEMO) in the pancreata of KPC mice. Interestingly, NEMO deletion altered the differentiation status of the primary tumor but did not significantly affect its development. However, in the absence of NEMO, the median survival of the mice was prolonged by 13.5 days (16%). In addition, examination of the liver demonstrated that, whereas KPC mice occasionally developed liver macro-metastasis, NEMO deletion completely abrogated this outcome. Further analysis of the tumor revealed that the expression of epithelial-mesenchymal transition (EMT) transcription factors was diminished in the absence of NEMO. Conclusively, our study provides evidence that NF-κB is dispensable for the progression of high-grade PanINs towards PDAC. In contrast, NF-κB signaling is essential for the development of metastasis by regulating the gene expression program of EMT.

Functional Genomic Screening During Somatic Cell Reprogramming Identifies DKK3 as a Roadblock of Organ Regeneration

Somatic cell reprogramming and tissue repair share relevant factors and molecular programs. Here, Dickkopf-3 (DKK3) is identified as novel factor for organ regeneration using combined transcription-factor-induced reprogramming and RNA-interference techniques. Loss of Dkk3 enhances the generation of induced pluripotent stem cells but does not affect de novo derivation of embryonic stem cells, three-germ-layer differentiation or colony formation capacity of liver and pancreatic organoids. However, DKK3 expression levels in wildtype animals and serum levels in human patients are elevated upon injury. Accordingly, Dkk3-null mice display less liver damage upon acute and chronic failure mediated by increased proliferation in hepatocytes and LGR5+ liver progenitor cell population, respectively. Similarly, recovery from experimental pancreatitis is accelerated. Regeneration onset occurs in the acinar compartment accompanied by virtually abolished canonical-Wnt-signaling in Dkk3-null animals. This results in reduced expression of the Hedgehog repressor Gli3 and increased Hedgehog-signaling activity upon Dkk3 loss. Collectively, these data reveal Dkk3 as a key regulator of organ regeneration via a direct, previously unacknowledged link between DKK3, canonical-Wnt-, and Hedgehog-signaling.

Telomerase and Pluripotency Factors Jointly Regulate Stemness in Pancreatic Cancer Stem Cells

To assess the role of telomerase activity and telomere length in pancreatic CSCs we used different CSC enrichment methods (CD133, ALDH, sphere formation) in primary patient-derived pancreatic cancer cells. We show that CSCs have higher telomerase activity and longer telomeres than bulk tumor cells. Inhibition of telomerase activity, using genetic knockdown or pharmacological inhibitor (BIBR1532), resulted in CSC marker depletion, abrogation of sphere formation in vitro and reduced tumorigenicity in vivo. Furthermore, we identify a positive feedback loop between stemness factors (NANOG, OCT3/4, SOX2, KLF4) and telomerase, which is essential for the self-renewal of CSCs. Disruption of the balance between telomerase activity and stemness factors eliminates CSCs via induction of DNA damage and apoptosis in primary patient-derived pancreatic cancer samples, opening future perspectives to avoid CSC-driven tumor relapse. In the present study, we demonstrate that telomerase regulation is critical for the "stemness" maintenance in pancreatic CSCs and examine the effects of telomerase inhibition as a potential treatment option of pancreatic cancer. This may significantly promote our understanding of PDAC tumor biology and may result in improved treatment for pancreatic cancer patients.

Modeling plasticity and dysplasia of pancreatic ductal organoids derived from human pluripotent stem cells

Personalized in vitro models for dysplasia and carcinogenesis in the pancreas have been constrained by insufficient differentiation of human pluripotent stem cells (hPSCs) into the exocrine pancreatic lineage. Here, we differentiate hPSCs into pancreatic duct-like organoids (PDLOs) with morphological, transcriptional, proteomic, and functional characteristics of human pancreatic ducts, further maturing upon transplantation into mice. PDLOs are generated from hPSCs inducibly expressing oncogenic GNAS, KRAS, or KRAS with genetic covariance of lost CDKN2A and from induced hPSCs derived from a McCune-Albright patient. Each oncogene causes a specific growth, structural, and molecular phenotype in vitro. While transplanted PDLOs with oncogenic KRAS alone form heterogenous dysplastic lesions or cancer, KRAS with CDKN2A loss develop dedifferentiated pancreatic ductal adenocarcinomas. In contrast, transplanted PDLOs with mutant GNAS lead to intraductal papillary mucinous neoplasia-like structures. Conclusively, PDLOs enable in vitro and in vivo studies of pancreatic plasticity, dysplasia, and cancer formation from a genetically defined background.

Synergistic targeting and resistance to PARP inhibition in DNA damage repair-deficient pancreatic cancer

OBJECTIVE

ATM serine/threonine kinase (ATM) is the most frequently mutated DNA damage response gene, involved in homologous recombination (HR), in pancreatic ductal adenocarcinoma (PDAC).

DESIGN

Combinational synergy screening was performed to endeavour a genotype-tailored targeted therapy.

RESULTS

Synergy was found on inhibition of PARP, ATR and DNA-PKcs (PAD) leading to synthetic lethality in ATM-deficient murine and human PDAC. Mechanistically, PAD-induced PARP trapping, replication fork stalling and mitosis defects leading to P53-mediated apoptosis. Most importantly, chemical inhibition of ATM sensitises human PDAC cells toward PAD with long-term tumour control in vivo. Finally, we anticipated and elucidated PARP inhibitor resistance within the ATM-null background via whole exome sequencing. Arising cells were aneuploid, underwent epithelial-mesenchymal-transition and acquired multidrug resistance (MDR) due to upregulation of drug transporters and a bypass within the DNA repair machinery. These functional observations were mirrored in copy number variations affecting a region on chromosome 5 comprising several of the upregulated MDR genes. Using these findings, we ultimately propose alternative strategies to overcome the resistance.

CONCLUSION

Analysis of the molecular susceptibilities triggered by ATM deficiency in PDAC allow elaboration of an efficient mutation-specific combinational therapeutic approach that can be also implemented in a genotype-independent manner by ATM inhibition.

The CXCL12 Crossroads in Cancer Stem Cells and Their Niche

Simple Summary

CXCL12 and its receptors have been extensively studied in cancer, including their influence on cancer stem cells (CSCs) and their niche. This intensive research has led to a better understanding of the crosstalk between CXCL12 and CSCs, which has aided in designing several drugs that are currently being tested in clinical trials. However, a comprehensive review has not been published to date. The aim of this review is to provide an overview on how CXCL12 axes are involved in the regulation and maintenance of CSCs, their presence and influence at different cellular levels within the CSC niche, and the current state-of-the-art of therapeutic approaches aimed to target the CXCL12 crossroads.

Abstract

Cancer stem cells (CSCs) are defined as a subpopulation of “stem”-like cells within the tumor with unique characteristics that allow them to maintain tumor growth, escape standard anti-tumor therapies and drive subsequent repopulation of the tumor. This is the result of their intrinsic “stem”-like features and the strong driving influence of the CSC niche, a subcompartment within the tumor microenvironment that includes a diverse group of cells focused on maintaining and supporting the CSC. CXCL12 is a chemokine that plays a crucial role in hematopoietic stem cell support and has been extensively reported to be involved in several cancer-related processes. In this review, we will provide the latest evidence about the interactions between CSC niche-derived CXCL12 and its receptors—CXCR4 and CXCR7—present on CSC populations across different tumor entities. The interactions facilitated by CXCL12/CXCR4/CXCR7 axes seem to be strongly linked to CSC “stem”-like features, tumor progression, and metastasis promotion. Altogether, this suggests a role for CXCL12 and its receptors in the maintenance of CSCs and the components of their niche. Moreover, we will also provide an update of the therapeutic options being currently tested to disrupt the CXCL12 axes in order to target, directly or indirectly, the CSC subpopulation.

Exploiting oxidative phosphorylation to promote the stem and immunoevasive properties of pancreatic cancer stem cells

Pancreatic ductal adenocarcinoma (PDAC), the fourth leading cause of cancer death, has a 5-year survival rate of approximately 7-9%. The ineffectiveness of anti-PDAC therapies is believed to be due to the existence of a subpopulation of tumor cells known as cancer stem cells (CSCs), which are functionally plastic, and have exclusive tumorigenic, chemoresistant and metastatic capacities. Herein, we describe a 2D in vitro system for long-term enrichment of pancreatic CSCs that is amenable to biological and CSC-specific studies. By changing the carbon source from glucose to galactose in vitro, we force PDAC cells to utilize OXPHOS, resulting in enrichment of CSCs defined by increased CSC biomarker and pluripotency gene expression, greater tumorigenic potential, induced but reversible quiescence, increased OXPHOS activity, enhanced invasiveness, and upregulated immune evasion properties. This CSC enrichment method can facilitate the discovery of new CSC-specific hallmarks for future development into targets for PDAC-based therapies.

Nintedanib plus mFOLFOX6 as second-line treatment of metastatic, chemorefractory colorectal cancer: The randomised, placebo-controlled, phase II TRICC-C study (AIO-KRK-0111)

Nintedanib is a triple angiokinase inhibitor of vascular endothelial growth factor receptor 1-3, fibroblast growth factor receptor 1-3 and platelet-derived growth factor receptor-a/-b. Thereby, it targets angiogenic escape mechanisms. The trial TyRosine kinase Inhibitor for the treatment of Chemorefractory Colorectal Cancer (TRICC-C) trial evaluates the addition of nintedanib to mFOLFOX6 (fluorouracil, folinic acid and oxaliplatin) in patients with metastatic colorectal cancer (mCRC). TRICC-C is a randomised controlled, double-blinded, phase II trial in mCRC patients that received a first-line non-oxaliplatin containing chemotherapy. Patients received mFOLFOX6 + nintedanib (F + N) (2 × 200 mg p.o./d, d1-d14) or mFOLFOX6 + placebo (F + P), in a 1:1 ratio. Primary endpoint was median progression free survival (mPFS) and secondary overall response rate (ORR), overall survival (OS) and safety. Fifty-three patients (27 F + N; 26 F + P) were randomised between 12/2012 and 5/2016 (scheduled n = 180). The trial was terminated prematurely due to slow accrual. The trial did not reach its primary endpoint but mPFS, median overall survival (mOS) and disease control rate (DCR) were numerically higher in the F + N arm compared to the F + P arm; however, the difference was not significant (mPFS: F + P: 4.6 months vs F + N: 8.1 months; HR 0.65; 95% CI 0.32-1.30; P = .2156; mOS: F + P: 9.9 months vs F + N: 17.1 months; HR 1.03, 95% CI 0.48-2.23; P = .9387; DCR: F + P: 50% vs F + N: 66,7%; P = .2709). Toxicity was moderate and only different for neutropenia (F + P: 11.5%, F + N: 19.2%) and gastrointestinal disorders (F + P: 65.4%, F + N: 84.6%). Final results show safety and a nonsignificant trend towards improved PFS and DCR for the combination of mFOLFOX6 + nintedanib in the second-line therapy of mCRC.

ISG15 and ISGylation is required for pancreatic cancer stem cell mitophagy and metabolic plasticity

Pancreatic cancer stem cells (PaCSCs) drive pancreatic cancer tumorigenesis, chemoresistance and metastasis. While eliminating this subpopulation of cells would theoretically result in tumor eradication, PaCSCs are extremely plastic and can successfully adapt to targeted therapies. In this study, we demonstrate that PaCSCs increase expression of interferon-stimulated gene 15 (ISG15) and protein ISGylation, which are essential for maintaining their metabolic plasticity. CRISPR-mediated ISG15 genomic editing reduces overall ISGylation, impairing PaCSCs self-renewal and their in vivo tumorigenic capacity. At the molecular level, ISG15 loss results in decreased mitochondrial ISGylation concomitant with increased accumulation of dysfunctional mitochondria, reduced oxidative phosphorylation (OXPHOS) and impaired mitophagy. Importantly, disruption in mitochondrial metabolism affects PaCSC metabolic plasticity, making them susceptible to prolonged inhibition with metformin in vivo. Thus, ISGylation is critical for optimal and efficient OXPHOS by ensuring the recycling of dysfunctional mitochondria, and when absent, a dysregulation in mitophagy occurs that negatively impacts PaCSC stemness.

The ubiquitin-like modifier ISG15 exerts post-translational protein regulation through ISGylation. Here, the authors show that ISGylation is necessary for pancreatic cancer stem cell self-renewal and tumourigenesis by supporting the recycling of non-functional mitochondria.

Pancreatic cancer-derived organoids - a disease modeling tool to predict drug response

BACKGROUND

Organotypic cultures derived from pancreatic ductal adenocarcinoma (PDAC) termed pancreatic ductal cancer organoids (PDOs) recapitulate the primary cancer and can be derived from primary or metastatic biopsies. Although isolation and culture of patient-derived pancreatic organoids were established several years ago, pros and cons for individualized medicine have not been comprehensively investigated to date.

METHODS

We conducted a feasibility study, systematically comparing head-to-head patient-derived xenograft tumor (PDX) and PDX-derived organoids by rigorous immunohistochemical and molecular characterization. Subsequently, a drug testing platform was set up and validated in vivo. Patient-derived organoids were investigated as well.

RESULTS

First, PDOs faithfully recapitulated the morphology and marker protein expression patterns of the PDXs. Second, quantitative proteomes from the PDX as well as from corresponding organoid cultures showed high concordance. Third, genomic alterations, as assessed by array-based comparative genomic hybridization, revealed similar results in both groups. Fourth, we established a small-scale pharmacotyping platform adjusted to operate in parallel considering potential obstacles such as culture conditions, timing, drug dosing, and interpretation of the results. In vitro predictions were successfully validated in an in vivo xenograft trial. Translational proof-of-concept is exemplified in a patient with PDAC receiving palliative chemotherapy.

CONCLUSION

Small-scale drug screening in organoids appears to be a feasible, robust and easy-to-handle disease modeling method to allow response predictions in parallel to daily clinical routine. Therefore, our fast and cost-efficient assay is a reasonable approach in a predictive clinical setting.

IgG4-Related Diseases in the Gastrointestinal Tract: Clinical Presentation, Diagnosis and Treatment Challenges

BACKGROUND

IgG4-related diseases are a rare but an important entity. Due to the variable clinical presentation, this multiorgan disease was attributed to single-organ systems for many years. Also, it often remains a challenge to differentiate between IgG4-related diseases and malignancies. The pathogenesis seems to be a mixture of Th1- and Th2- immune responses, whereas the role of the non-pathogenic IgG4 antibodies is still unclear. Histopathological characteristics are a lymphoplasmacellular infiltrate with IgG4+ plasma cells, a storiform fibrosis and an obliterative phlebitis. This can lead to the functional destruction of every organ affected. In most cases, glucocorticoid treatment leads to remission and is used as maintenance therapy as well. Immune modulatory therapies are employed in case of steroid resistance. However, a majority of patients achieve remission without any therapy.

SUMMARY

In this study, we review the current state-of-the-art regarding pathophysiology, diagnostics, organ manifestation and therapeutic approaches. Key Messages: While the diagnosis of IgG4-related diseases is still challenging, there have been significant improvements in diagnostic as well as in therapeutic approaches. This is partially due to a better understanding of the pathophysiology of the disease but also due to improved imaging modalities and novel, more targeted therapies.

Tumor-associated macrophage-secreted 14-3-3ζ signals via AXL to promote pancreatic cancer chemoresistance

Pancreatic ductal adenocarcinoma (PDAC) is an inherently chemoresistant tumor. Chemotherapy leads to apoptosis of cancer cells, and in previous studies we have shown that tumor-associated macrophage (TAM) infiltration increases following chemotherapy in PDAC. Since one of the main functions of macrophages is to eliminate apoptotic cells, we hypothesized that TAMs phagocytose chemotherapy-induced apoptotic cells and secrete factors, which favor PDAC chemoresistance. To test this hypothesis, primary human PDAC cultures were treated with conditioned media (CM) from monocyte-derived macrophage cultures incubated with apoptotic PDAC cells (MØ^ApopCM). MØ^ApopCM pretreatment rendered naïve PDAC cells resistant to Gemcitabine- or Abraxane-induced apoptosis. Proteomic analysis of MØ^ApopCM identified YWHAZ/14-3-3 protein zeta/delta (14-3-3ζ), a major regulator of apoptotic cellular pathways, as a potential mediator of chemoresistance, which was subsequently validated in patient transcriptional datasets, serum samples from PDAC patients and using recombinant 14-3-3ζ and inhibitors thereof. Moreover, in mice bearing orthotopic PDAC tumors, the antitumor potential of Gemcitabine was significantly enhanced by elimination of TAMs using clodronate liposomes or by pharmacological inhibition of the Axl receptor tyrosine kinase, a 14-3-3ζ interacting partner. These data highlight a unique regulatory mechanism by which chemotherapy-induced apoptosis acts as a switch to initiate a protumor/antiapoptotic mechanism in PDAC via 14-3-3ζ/Axl signaling, leading to phosphorylation of Akt and activation of cellular prosurvival mechanisms. The data presented therefore challenge the idea that apoptosis of tumor cells is therapeutically beneficial, at least when immune sensor cells, such as macrophages, are present.

Human pluripotent stem cell-derived acinar/ductal organoids generate human pancreas upon orthotopic transplantation and allow disease modelling

OBJECTIVE

The generation of acinar and ductal cells from human pluripotent stem cells (PSCs) is a poorly studied process, although various diseases arise from this compartment.

DESIGN

We designed a straightforward approach to direct human PSCs towards pancreatic organoids resembling acinar and ductal progeny.

RESULTS

Extensive phenotyping of the organoids not only shows the appropriate marker profile but also ultrastructural, global gene expression and functional hallmarks of the human pancreas in the dish. Upon orthotopic transplantation into immunodeficient mice, these organoids form normal pancreatic ducts and acinar tissue resembling fetal human pancreas without evidence of tumour formation or transformation. Finally, we implemented this unique phenotyping tool as a model to study the pancreatic facets of cystic fibrosis (CF). For the first time, we provide evidence that in vitro, but also in our xenograft transplantation assay, pancreatic commitment occurs generally unhindered in CF. Importantly, cystic fibrosis transmembrane conductance regulator (CFTR) activation in mutated pancreatic organoids not only mirrors the CF phenotype in functional assays but also at a global expression level. We also conducted a scalable proof-of-concept screen in CF pancreatic organoids using a set of CFTR correctors and activators, and established an mRNA-mediated gene therapy approach in CF organoids.

CONCLUSIONS

Taken together, our platform provides novel opportunities to model pancreatic disease and development, screen for disease-rescuing agents and to test therapeutic procedures.

Detection of Hot-Spot Mutations in Circulating Cell-Free DNA From Patients With Intraductal Papillary Mucinous Neoplasms of the Pancreas

Intraductal papillary mucinous neoplasms (IPMNs) are the most frequent cystic pancreatic tumors. Little is known about their molecular alterations, but mutations in GNAS have been reported to promote IPMN formation. A tumor-derived fraction of circulating cell-free DNA (cfDNA), isolated from blood samples, contains many of the same mutations as the primary tumor, and could be a tool for noninvasive disease monitoring. We found that the total amount of cfDNA can discriminate between individuals without pancreatic lesions (controls) and patients with Fukuoka-negative branch-duct IPMN or pancreatic cancer. Furthermore, we detected GNAS mutations in cfDNA from patients with IPMN, but not in patients with serous cystadenoma or controls. Analyses of cfDNA might therefore be used in the diagnosis of patients with IPMN or in monitoring disease progression.

The ever-changing landscape of pancreatic cancer stem cells

Over the past decade, the cancer stem cell (CSC) concept in solid tumors has gained enormous momentum as an attractive model to explain tumor heterogeneity. The model proposes that tumors contain a subpopulation of rare cancer cells with stem-like properties that maintain the hierarchy of the tumor and drive tumor initiation, progression, metastasis, and chemoresistance. The identification and subsequent isolation of CSCs in pancreatic ductal adenocarcinoma (PDAC) in 2007 provided enormous insight into this extremely metastatic and chemoresistant tumor and renewed hope for developing more specific therapies against this disease. Unfortunately, we have made only marginal advances in applying the knowledge learned to the development of new and more effective treatments for pancreatic cancer. The latter has been partly due to the lack of adequate in vitro and in vivo systems compounded by the use of markers that do not reproducibly nor exclusively select for an enriched CSC population. Thus, attempts to define a pancreatic CSC-specific genetic, epigenetic or proteomic signature has been challenging. Fortunately recent advances in the CSC field have overcome many of these challenges and have opened up new opportunities for developing therapies that target the CSC population. In this review, we discuss these current advances, specifically new methods for the identification and isolation of pancreatic CSCs, new insights into the metabolic profile of CSCs at the level of mitochondrial respiration, and the utility of genetically engineered mouse models as surrogate systems to both study CSC biology and evaluate CSC-specific targeted therapies in vivo.

Proteolytic processing of human serum albumin generates EPI-X4, an endogenous antagonist of CXCR4

The chemokine receptor CXCR4 is an important G protein-coupled receptor. Signaling via CXCL12 regulates a number of important biologic processes, including immune responses, organogenesis, or hematopoiesis. Dysregulation of CXCR4 signaling is associated with a variety of diseases, such as cancer development and metastasis, immunodeficiencies, or chronic inflammation. Here, we review our findings on endogenous peptide inhibitor of CXCR4 as a novel antagonist of CXCR4. This peptide is a 16-residue fragment of human serum albumin and was isolated as an inhibitor of CXCR4-tropic human immunodeficiency virus type 1 from a blood-derived peptide library. Endogenous peptide inhibitor of CXCR4 binds the second extracellular loop of CXCR4, thereby preventing engagement of CXCL12 and antagonizing the receptor. Consequently, endogenous peptide inhibitor of CXCR4 inhibits CXCL12-mediated migration of CXCR4-expressing cells in vitro, mobilizes hematopoietic stem cells, and suppresses inflammatory responses in vivo. We discuss the generation of endogenous peptide inhibitor of CXCR4, its relevance as biomarker for disease, and its role in human immunodeficiency virus/acquired immunodeficiency syndrome pathogenesis and cancer. Furthermore, we discuss why optimized endogenous peptide inhibitor of CXCR4 derivatives might have advantages over other CXCR4 antagonists.

The role of pluripotency factors to drive stemness in gastrointestinal cancer

A better molecular understanding of gastrointestinal cancers arising either from the stomach, the pancreas, the intestine, or the liver has led to the identification of a variety of potential new molecular therapeutic targets. However, in most cases surgery remains the only curative option. The intratumoral cellular heterogeneity of cancer stem cells, bulk tumor cells, and stromal cells further limits straightforward targeting approaches. Accumulating evidence reveals an intimate link between embryonic development, stem cells, and cancer formation. In line, a growing number of oncofetal proteins are found to play common roles within these processes. Cancer stem cells share features with true stem cells by having the capacity to self-renew in a de-differentiated state, to generate heterogeneous types of differentiated progeny, and to give rise to the bulk tumor. Further, various studies identified genes in cancer stem cells, which were previously shown to regulate the pluripotency circuitry, particularly the so-called "Yamanaka-Factors" (OCT4, KLF4, SOX2, and c-MYC). However, the true stemness potential of cancer stem cells and the role and expression pattern of such pluripotency genes in various tumor cell types remain to be explored. Here, we summarize recent findings and discuss the potential mechanisms involved, and link them to clinical significance with a particular focus on gastrointestinal cancers.

Microenvironmental hCAP-18/LL-37 promotes pancreatic ductal adenocarcinoma by activating its cancer stem cell compartment

OBJECTIVES

The tumour stroma/microenvironment not only provides structural support for tumour development, but more importantly it provides cues to cancer stem cells (CSCs) that regulate their self-renewal and metastatic potential. This is certainly true for pancreatic ductal adenocarcinomas (PDAC), where tumour-associated fibroblasts, pancreatic stellate cells and immune cells create an abundant paracrine niche for CSCs via microenvironment-secreted factors. Thus understanding the role that tumour stroma cells play in PDAC development and CSC biology is of utmost importance.

DESIGN

Microarray analyses, tumour microarray immunohistochemical assays, in vitro co-culture experiments, recombinant protein treatment approaches and in vivo intervention studies were performed to understand the role that the immunomodulatory cationic antimicrobial peptide 18/LL-37 (hCAP-18/LL-37) plays in PDAC biology.

RESULTS

We found that hCAP-18/LL-37 was strongly expressed in the stroma of advanced primary and secondary PDAC tumours and is secreted by immune cells of the stroma (eg, tumour-associated macrophages) in response to tumour growth factor-β1 and particularly CSC-secreted Nodal/ActivinA. Treatment of pancreatic CSCs with recombinant LL-37 increased pluripotency-associated gene expression, self-renewal, invasion and tumourigenicity via formyl peptide receptor 2 (FPR2)- and P2X purinoceptor 7 receptor (P2X7R)-dependent mechanisms, which could be reversed by inhibiting these receptors. Importantly, in a genetically engineered mouse model of K-Ras-driven pancreatic tumourigenesis, we also showed that tumour formation was inhibited by either reconstituting these mice with bone marrow from cathelicidin-related antimicrobial peptide (ie, murine homologue of hCAP-18/LL-37) knockout mice or by pharmacologically inhibiting FPR2 and P2X7R.

CONCLUSIONS

Thus, hCAP-18/LL-37 represents a previously unrecognised PDAC microenvironment factor that plays a critical role in pancreatic CSC-mediated tumourigenesis.

Nicotine promotes initiation and progression of KRAS-induced pancreatic cancer via Gata6-dependent dedifferentiation of acinar cells in mice

BACKGROUND & AIMS

Although smoking is a leading risk factor for pancreatic ductal adenocarcinoma (PDAC), little is known about the mechanisms by which smoking promotes initiation or progression of PDAC.

METHODS

We studied the effects of nicotine administration on pancreatic cancer development in Kras(+/LSLG12Vgeo);Elas-tTA/tetO-Cre (Ela-KRAS) mice, Kras(+/LSLG12D);Trp53+/LSLR172H;Pdx-1-Cre (KPC) mice (which express constitutively active forms of KRAS), and C57/B6 mice. Mice were given nicotine for up to 86 weeks to produce blood levels comparable with those of intermediate smokers. Pancreatic tissues were collected and analyzed by immunohistochemistry and reverse transcriptase polymerase chain reaction; cells were isolated and assayed for colony and sphere formation and gene expression. The effects of nicotine were also evaluated in primary pancreatic acinar cells isolated from wild-type, nAChR7a(-/-), Trp53(-/-), and Gata6(-/-);Trp53(-/-) mice. We also analyzed primary PDAC cells that overexpressed GATA6 from lentiviral expression vectors.

RESULTS

Administration of nicotine accelerated transformation of pancreatic cells and tumor formation in Ela-KRAS and KPC mice. Nicotine induced dedifferentiation of acinar cells by activating AKT-ERK-MYC signaling; this led to inhibition of Gata6 promoter activity, loss of GATA6 protein, and subsequent loss of acinar differentiation and hyperactivation of oncogenic KRAS. Nicotine also promoted aggressiveness of established tumors as well as the epithelial-mesenchymal transition, increasing numbers of circulating cancer cells and their dissemination to the liver, compared with mice not exposed to nicotine. Nicotine induced pancreatic cells to acquire gene expression patterns and functional characteristics of cancer stem cells. These effects were markedly attenuated in K-Ras(+/LSL-G12D);Trp53(+/LSLR172H);Pdx-1-Cre mice given metformin. Metformin prevented nicotine-induced pancreatic carcinogenesis and tumor growth by up-regulating GATA6 and promoting differentiation toward an acinar cell program.

CONCLUSIONS

In mice, nicotine promotes pancreatic carcinogenesis and tumor development via down-regulation of Gata6 to induce acinar cell dedifferentiation.

Multimodal Treatment Eliminates Cancer Stem Cells and Leads to Long-Term Survival in Primary Human Pancreatic Cancer Tissue Xenografts

Purpose

In spite of intense research efforts, pancreatic ductal adenocarcinoma remains one of the most deadly malignancies in the world. We and others have previously identified a subpopulation of pancreatic cancer stem cells within the tumor as a critical therapeutic target and additionally shown that the tumor stroma represents not only a restrictive barrier for successful drug delivery, but also serves as a paracrine niche for cancer stem cells. Therefore, we embarked on a large-scale investigation on the effects of combining chemotherapy, hedgehog pathway inhibition, and mTOR inhibition in a preclinical mouse model of pancreatic cancer.

Experimental Design

Prospective and randomized testing in a set of almost 200 subcutaneous and orthotopic implanted whole-tissue primary human tumor xenografts.

Results

The combined targeting of highly chemoresistant cancer stem cells as well as their more differentiated progenies, together with abrogation of the tumor microenvironment by targeting the stroma and enhancing tissue penetration of the chemotherapeutic agent translated into significantly prolonged survival in preclinical models of human pancreatic cancer. Most pronounced therapeutic effects were observed in gemcitabine-resistant patient-derived tumors. Intriguingly, the proposed triple therapy approach could be further enhanced by using a PEGylated formulation of gemcitabine, which significantly increased its bioavailability and tissue penetration, resulting in a further improved overall outcome.

Conclusions

This multimodal therapeutic strategy should be further explored in the clinical setting as its success may eventually improve the poor prognosis of patients with pancreatic ductal adenocarcinoma.

Abstract C83: Nicotine triggers initiation and progression of K-Ras-driven pancreatic ductal adenocarcinoma

Smoking has been identified as a leading risk factor for pancreatic ductal adenocarcinoma. Nicotine is an important active ingredient of tobacco smoke and replacement products, but does not bear carcinogenic properties. While nicotine has been shown to induce proliferation, invasion and metastasis of fully transformed pancreatic cancer cells, its role in pancreatic cancer development and/or progression has not been determined yet. First, our in vivo studies showed a marked acceleration of carcinogenesis in two distinct genetically engineered mouse models for pancreatic cancer. Moreover, nicotine promoted tumor progression as evidence by enhancing the cancer stem cell signature and invasiveness via epithelial-to-mesenchymal-transition. This translated into increased numbers of circulating cancer cells and metastatic lesions. Using two independent model systems, i.e. pharmacological nAChR inhibition and knockout of the alpha7-nAChR, we demonstrate that nicotine activates the pancreatic progenitor compartment resulting in their subsequent expansion and enhanced susceptibility for K-Ras induced pancreatic carcinogenesis. Mechanistically, we found that nicotine-medicated Ca2+ influx induced mitochondrial ROS production and activation of the non-canonical Wnt pathway. Intriguingly, co-treatment with metformin prevented the accelerated pancreatic carcinogenesis and progression independent of AMPK. In conclusion, our findings reveal for the first time that nicotine promotes activation of the pancreatic (cancer) stem cell compartment and subsequently drives K-Ras-initiated pancreatic cancer development and progression.

Citation Format: Patrick C. Hermann, Bruno Sainz, Jr., Patricia Sancho, Christopher Heeschen. Nicotine triggers initiation and progression of K-Ras-driven pancreatic ductal adenocarcinoma. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr C83.

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.

Vascular incorporation of endothelial colony-forming cells is essential for functional recovery of murine ischemic tissue following cell therapy

OBJECTIVE

Cord blood-derived human endothelial colony-forming cells (ECFCs) bear a high proliferative capacity and potently enhance tissue neovascularization in vivo. Here, we investigated whether the leading mechanism for the functional improvement relates to their physical vascular incorporation or perivascular paracrine effects and whether the effects can be further enhanced by dual-cell-based therapy, including mesenchymal stem cells (MSCs).

METHODS AND RESULTS

ECFCs or MSCs were lentivirally transduced with thymidine kinase suicide gene driven by the endothelial-specific vascular endothelial growth factor 2 (kinase insert domain receptor) promoter and evaluated in a hindlimb ischemia model. ECFCs and MSCs enhanced neovascularization after ischemic events to a similar extent. Dual therapy using ECFCs and MSCs further enhanced neovascularization. Mechanistically, 3 weeks after induction of ischemia followed by cell therapy, ganciclovir-mediated elimination of kinase insert domain receptor(+) cells completely reversed the therapeutic effect of ECFCs but not that of MSCs. Histological analysis revealed that ganciclovir effectively eliminated ECFCs incorporated into the vasculature.

CONCLUSIONS

Endothelial-specific suicide gene technology demonstrates distinct mechanisms for ECFCs and MSCs, with complete abolishment of ECFC-mediated effects, whereas MSC-mediated effects remained unaffected. These data strengthen the notion that a dual-cell-based therapy represents a promising approach for vascular regeneration of ischemic tissue.

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.

Inhibition of ataxia telangiectasia- and Rad3-related function abrogates the in vitro and in vivo tumorigenicity of human colon cancer cells through depletion of the CD133(+) tumor-initiating cell fraction

The identification of novel approaches to specifically target the DNA-damage checkpoint response in chemotherapy-resistant cancer stem cells (CSC) of solid tumors has recently attracted great interest. We show here in colon cancer cell lines and primary colon cancer cells that inhibition of checkpoint-modulating phosphoinositide 3-kinase-related (PIK) kinases preferentially depletes the chemoresistant and exclusively tumorigenic CD133(+) cell fraction. We observed a time- and dose-dependent disproportionally pronounced loss of CD133(+) cells and the consecutive lack of in vitro and in vivo tumorigenicity of the remaining cells. Depletion of CD133(+) cells was initiated through apoptosis of cycling CD133(+) cells and further substantiated through subsequent recruitment of quiescent CD133(+) cells into the cell cycle followed by their elimination. Models using specific PIK kinase inhibitors, somatic cell gene targeting, and RNA interference demonstrated that the observed detrimental effects of caffeine on CSC were attributable specifically to the inhibition of the PIK kinase ataxia telangiectasia- and Rad3-related (ATR). Mechanistically, phosphorylation of CHK1 checkpoint homolog (S. pombe; CHK1) was significantly enhanced in CD133(+) as compared with CD133(-) cells on treatment with DNA interstrand-crosslinking (ICL) agents, indicating a preferential activation of the ATR/CHK1-dependent DNA-damage response in tumorigenic CD133(+) cells. Consistently, the chemoresistance of CD133(+) cells toward DNA ICL agents was overcome through inhibition of ATR/CHK1-signaling. In conclusion, our study illustrates a novel target to eliminate the tumorigenic CD133(+) cell population in colon cancer and provides another rationale for the development of specific ATR-inhibitors.

Adiponectin pretreatment counteracts the detrimental effect of a diabetic environment on endothelial progenitors

OBJECTIVE

It has been shown that vascular progenitors from patients with diabetes are dysfunctional. However, therapeutic strategies to counteract their reduced functional capacity are still lacking. Because adiponectin has reported salutary effects on endothelial function, we investigated the functional effects of globular adiponectin (gAcrp), the active domain of adiponectin, on isolated endothelial colony-forming cells (ECFC).

RESEARCH DESIGN AND METHODS

ECFC were isolated from peripheral blood of type 2 diabetic patients (dmECFC) and compared with ECFC of healthy young volunteers (yECFC) and nondiabetic age-matched control subjects (hECFC). Cells were treated with gAcrp for 48 h followed by assessment of cell counts, cell cycle analysis, and migration capacity. For in vivo evaluation, human ECFC were injected into normoglycemic or streptozotocin-induced hyperglycemic nu/nu mice after hind limb ischemia.

RESULTS

Whereas dmECFC were functionally impaired compared with yECFC and hECFC, gAcrp significantly enhanced their in vitro proliferation and migratory activity. In vitro effects were significantly stronger in hECFC compared with dmECFC and were mediated through the cyclooxygenase-2 pathway. Most important, however, we observed a profound and sustained increase of the in vivo neovascularization in mice receiving gAcrp-pretreated dmECFC compared with untreated dmECFC under both normoglycemic and hyperglycemic conditions.

CONCLUSIONS

Pretreatment of ECFC with gAcrp enhanced the functional capacity of ECFC in vitro and in vivo in normoglycemic and hyperglycemic environments. Therefore, preconditioning of dmECFC with gAcrp may be a novel approach to counteract their functional impairment in diabetes.

Combination of injectable multiple growth factor-releasing scaffolds and cell therapy as an advanced modality to enhance tissue neovascularization

OBJECTIVE

Vasculogenic progenitor cell therapy for ischemic diseases bears great potential but still requires further optimization for justifying its clinical application. Here, we investigated the effects of in vivo tissue engineering by combining vasculogenic progenitors with injectable scaffolds releasing controlled amounts of proangiogenic growth factors.

METHODS AND RESULTS

We produced biodegradable, injectable polylactic coglycolic acid-based scaffolds releasing single factors or combinations of vascular endothelial growth factor, hepatocyte growth factor, and angiopoietin-1. Dual and triple combinations of scaffold-released growth factors were superior to single release. In murine hindlimb ischemia models, scaffolds releasing dual (vascular endothelial growth factor and hepatocyte growth factor) or triple combinations improved effects of cord blood-derived vasculogenic progenitors. Increased migration, homing, and incorporation of vasculogenic progenitors into the vasculature augmented capillary density, translating into improved blood perfusion. Most importantly, scaffold-released triple combinations including the vessel stabilizer angiopoietin-1 enhanced the number of perivascular smooth muscle actin(+) vascular smooth muscle cells, indicating more efficient vessel stabilization.

CONCLUSIONS

Vasculogenic progenitor cell therapy is significantly enhanced by in vivo tissue engineering providing a proangiogenic and provasculogenic growth factor-enriched microenvironment. Therefore, combined use of scaffold-released growth factors and cell therapy improves neovascularization in ischemic diseases and may translate into more pronounced clinical effects.

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.

Cancer stem cells as new therapeutic target to prevent tumour progression and metastasis

Over the past decade, increasing evidence suggested that stem cells play a crucial role not only in the generation of complex multicellular organisms, but also in the development and progression of malignant diseases. For the most abundant tumours, it has been shown that they contain a subset of distinct cancer cells that is exclusively responsible for tumour initiation and propagation These cells are termed cancer stem cells or tumour-initiating cells and they are also highly resistant to chemotherapeutic agents. Because CSC are preferentially endowed with the self-renewal capacity, it has further been hypothesized that they are also exclusively responsible for metastasis. Indeed, we were able to show that pancreatic cancer stem cells contain a subpopulation of migrating cancer stem cells characterized by CXCR4 co-expression. Only these cells are capable of evading the primary tumour and metastasizing. Laboratories around the world are now aiming to further characterize these cells to eventually identify novel treatment modalities to fight cancer. Thus, cancer stem cells are promising new targets to counteract the growth-promoting and metastatic potential of solid tumours.

Pancreatic cancer stem cells--insights and perspectives

BACKGROUND

Solid tumours are the most common cancers and represent a major therapeutic challenge. The cancer stem cell (CSC) 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.

OBJECTIVE

Here we review the most recent advances in the CSC 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.

METHODS

This review focuses on the role of CSC in the promotion and metastasis of solid tumours and summarizes recent findings regarding the targeting of signalling pathways that are of particular importance for the maintenance and the elimination of CSC as the proposed root of the tumour.

RESULTS/CONCLUSIONS

There is increasing evidence that solid tumours, including pancreatic cancer, are hierarchically organized and sustained by a distinct subpopulation of CSC. Direct evidence for the CSC hypothesis has emerged from mouse models only recently. While the clinical relevance of CSC remains a fundamental issue, current findings suggest that specific targeting of these cells is possible and therapeutically relevant.

Combined targeted treatment to eliminate tumorigenic cancer stem cells in human pancreatic cancer

BACKGROUND & AIMS

Pancreatic cancers contain exclusively tumorigenic cancer stem cells (CSCs), which are highly resistant to chemotherapy, resulting in a relative increase in CSC numbers during gemcitabine treatment. Signaling through sonic hedgehog and mammalian target of rapamycin (mTOR), respectively, may be essential for CSC self-renewal and could represent putative targets for novel treatment modalities.

METHODS

We used in vitro and in vivo models of pancreatic cancer to examine the effects of sonic hedgehog inhibition (cyclopamine/CUR199691) and mTOR blockade (rapamycin) on the tumorigenic CSC population.

RESULTS

Surprisingly, neither cyclopamine nor rapamycin alone or as supplements to chemotherapy were capable of effectively diminishing the CSC pool. Only the combined inhibition of both pathways together with chemotherapy reduced the number of CSCs to virtually undetectable levels in vitro and in vivo. Most importantly, in vivo administration of this triple combination in mice with established patient-derived pancreatic tumors was reasonably tolerated and translated into significantly prolonged long-term survival.

CONCLUSIONS

The combined blockade of sonic hedgehog and mTOR signaling together with standard chemotherapy is capable of eliminating pancreatic CSCs. Further preclinical investigation of this promising approach may lead to the development of a novel therapeutic strategy to improve the devastating prognosis of patients with pancreatic cancer.

Prostaglandin E positively modulates endothelial progenitor cell homeostasis: an advanced treatment modality for autologous cell therapy

AIMS

The mobilization of endothelial progenitor cells (EPC) and their functioning in postnatal neovascularization are tightly regulated. To identify new modulators of EPC homeostasis, we screened biologically active prostaglandin E compounds for their effects on EPC production, trafficking and function.

METHODS AND RESULTS

We found that EPC are a rich source for prostaglandin E(2) (PGE(2)), stimulating their number and function in an auto- and paracrine manner. In vivo blockade of PGE(2) production by selective cyclooxygenase-2 inhibition virtually abrogated ischemia-induced EPC mobilization demonstrating its crucial role in EPC homeostasis following tissue ischemia. Conversely, ex vivo treatment of isolated EPC with the clinically approved PGE(1) analogue alprostadil enhanced EPC number and function. These effects were mediated by increased expression of the chemokine receptor CXCR4 and were dependent on nitric oxide synthase activity. Most importantly, ex vivo PGE(1) pretreatment of isolated EPC significantly enhanced their neovascularization capacity in a murine model of hind limb ischemia as assessed by laser Doppler analysis, exercise stress test and immunohistochemistry.

CONCLUSIONS

The conserved role for PGE in the regulation of EPC homeostasis suggests that ex vivo modulation of the prostaglandin pathway in isolated progenitor cells may represent a novel and safe strategy to facilitate cell-based therapies.

Concentration of bone marrow total nucleated cells by a point-of-care device provides a high yield and preserves their functional activity

Stem and progenitor cell therapy is a novel strategy to enhance cardiovascular regeneration. Cell isolation procedures are crucial for the functional activity of the administered cellular product. Therefore, new isolation techniques have to be evaluated in comparison to the Ficoll isolation procedure as the current gold standard. Here we prospectively evaluated a novel point-of-care device (Harvest BMAC System) for the concentration of bone marrow total nucleated cells (TNC) in comparison to the Ficoll isolation procedure for bone marrow mononucleated cells (MNC). The yield in total numbers of TNC was 2.4-fold higher for Harvest compared to Ficoll. Despite significant differences in their cellular compositions, the colony-forming capacity was similar for both products. Intriguingly, the migratory capacity was significantly higher for the Harvest TNC (164 +/- 66%; p = 0.007). In a mouse model of hind limb ischemia, the increase in blood flow recovery was similar between Harvest BM-TNC and Ficoll BM-MNC (0.53 +/- 0.20 vs. 0.46 +/- 0.15; p = 0.88). However, adjustment of the injected cell number based on the higher yield of Harvest TNC resulted in a significant better recovery (0.64 +/- 0.16 vs. 0.46 +/- 0.15; p = 0.003). Cells concentrated by the Harvest point-of-care device show similar or greater functional activity compared to Ficoll isolation. However, the greater yield of cells and the wider range of cell types for the Harvest device may translate into an even greater therapeutic effect.

Distinct populations of cancer stem cells determine tumor growth and metastatic activity in human pancreatic cancer

Pancreatic adenocarcinoma is currently the fourth leading cause for cancer-related mortality. Stem cells have been implicated in pancreatic tumor growth, but the specific role of these cancer stem cells in tumor biology, including metastasis, is still uncertain. We found that human pancreatic cancer tissue contains cancer stem cells defined by CD133 expression that are exclusively tumorigenic and highly resistant to standard chemotherapy. In the invasive front of pancreatic tumors, a distinct subpopulation of CD133(+) CXCR4(+) cancer stem cells was identified that determines the metastatic phenotype of the individual tumor. Depletion of the cancer stem cell pool for these migrating cancer stem cells virtually abrogated the metastatic phenotype of pancreatic tumors without affecting their tumorigenic potential. In conclusion, we demonstrate that a subpopulation of migrating CD133(+) CXCR4(+) cancer stem cells is essential for tumor metastasis. Strategies aimed at modulating the SDF-1/CXCR4 axis may have important clinical applications to inhibit metastasis of cancer stem cells.

Inhibition of the mammalian target of rapamycin impedes lymphangiogenesis

Lymphatic complications are common side effects of mammalian target of rapamycin (mTOR) inhibitor-based immunosuppression in kidney transplantation. Therefore, we investigated whether the mTOR inhibitor rapamycin, besides its known antihemangiogenic effect, also impedes regenerative lymphangiogenesis. In a murine skin flap model, rapamycin impaired recovery of lymphatic flow across surgical incisions resulting in prolonged wound edema in these animals. Importantly, the antilymphangiogenic effect of rapamycin was not related to a general inhibition of wound healing as demonstrated an in vivo Matrigeltrade mark lymphangiogenesis assay and a model of lymphangioma. Rapamycin concentrations as low as 1 ng/ml potently inhibited vascular endothelial growth factor (VEGF)-C driven proliferation and migration, respectively, of isolated human lymphatic endothelial cells (LECs) in vitro. Mechanistically, mTOR inhibition impairs downstream signaling of VEGF-A as well as VEGF-C via mTOR to the p70S6 kinase in LECs. In conclusion, we provide extensive experimental evidence for an antilymphangiogenic activity of mTOR inhibition suggesting that the early use of mTOR inhibitor following tissue injury should be avoided. Conversely, the antilymphangiogenic properties of rapamycin and its derivates may provide therapeutic value for the prevention and treatment of malignancies, respectively.