Inhibition of Hedgehog signaling enhances delivery of chemotherapy in a mouse model of pancreatic cancer

Establishment of six new human biliary tract carcinoma cell lines and identification of MAGEH1 as a candidate biomarker for predicting the efficacy of gemcitabine treatment

The aim of this study was to establish new biliary tract carcinoma (BTC) cell lines and identify predictive biomarkers for the potential effectiveness of gemcitabine therapy. Surgical specimens of BTC were transplanted directly into immunodeficient mice to establish xenografts, then subjected to in vitro cell culture. The gemcitabine sensitivity of each cell line was determined and compared with the genome-wide gene expression profile. A new predictive biomarker candidate was validated using an additional cohort of gemcitabine-treated BTC cases. From 55 BTC cases, we established 19 xenografts and six new cell lines. Based on their gemcitabine sensitivity, 10 BTC cell lines (including six new and four publicly available ones) were clearly categorized into two groups, and MAGEH1 mRNA expression in the tumor cells showed a significant negative correlation with their sensitivity to gemcitabine. Immunohistochemically, MAGEH1 protein was detected in three (50%) out of six sensitive cell lines, and four (100%) out of four resistant cell lines. In the validation cohort of gemcitabine-treated recurrence cases, patients were categorized into "effective" and "non-effective" groups according to the RECIST guidelines for assessment of chemotherapeutic effects. MAGEH1 protein expression was detected in two (40%) out of five "effective" cases and all four (100%) "non-effective" cases. We have established a new BTC bioresource that covers a wide range of biological features, including drug sensitivity, and is linked with clinical information. Negative expression of MAGEH1 protein serves as a potential predictive marker for the effectiveness of gemcitabine therapy in BTC.

Molecular mechanism of pancreatic cancer--understanding proliferation, invasion, and metastasis

INTRODUCTION

The purpose of this review is to highlight the molecular mechanisms leading to the development and progression of pancreatic ductal adenocarcinoma (PDAC) with particular emphasis on tumor cell proliferation, local invasion, and metastasis. Recent advances in the field of PDAC biology have shed light on the molecular events that trigger PDAC initiation and maintenance.

RESULTS

It is now clear that apart from the genetic alterations within the tumor cells, interactions of the tumor with its environment are necessary for proliferation and invasion. Interestingly, a number of developmental signaling pathways are reactivated in PDAC. Progress has also been made in the understanding of the molecular events that govern the process of metastasis.

CONCLUSION

Although our understanding of the mechanisms underlying PDAC pathobiology are more advanced than ever, little progress has been made in the clinical treatment of PDAC, and successful bench-to-bedside transfer of knowledge to boost new treatment options is still unsatisfying.

Cell line-based platforms to evaluate the therapeutic efficacy of candidate anticancer agents

Efforts to discover new cancer drugs and predict their clinical activity are limited by the fact that laboratory models to test drug efficacy do not faithfully recapitulate this complex disease. One important model system for evaluating candidate anticancer agents is human tumour-derived cell lines. Although cultured cancer cells can exhibit distinct properties compared with their naturally growing counterparts, recent technologies that facilitate the parallel analysis of large panels of such lines, together with genomic technologies that define their genetic constitution, have revitalized efforts to use cancer cell lines to assess the clinical utility of new investigational cancer drugs and to discover predictive biomarkers.

New promising drug targets in cancer- and metastasis-initiating cells

The unique properties of cancer- and metastasis-initiating cells endowed with a high self-renewal and aberrant differentiation potential (including their elevated expression levels of anti-apoptotic factors, multidrug transporters, and DNA repair and detoxifying enzymes) might be associated with their resistance to current clinical cancer therapies and disease recurrence. The eradication of cancer- and metastasis-initiating cells by molecular targeting of distinct deregulated signaling elements that might contribute to their sustained growth, survival, and treatment resistance, therefore, is of immense therapeutic interest. These novel targeted approaches should improve the efficacy of current therapeutic treatments against highly aggressive, metastatic, recurrent, and lethal cancers.

Smac mimetic increases chemotherapy response and improves survival in mice with pancreatic cancer

Failure of chemotherapy in the treatment of pancreatic cancer is often due to resistance to therapy-induced apoptosis. A major mechanism for such resistance is the expression and activity of inhibitors of apoptosis proteins (IAP). Smac (second mitochondria-derived activator of caspase) is a mitochondrial protein that inhibits IAPs. We show that JP1201, a Smac mimetic, is a potent enhancer of chemotherapy in robust mouse models of pancreatic cancer. Combination of JP1201 with gemcitabine reduced primary and metastatic tumor burden in orthotopic xenograft and syngenic tumor models, induced regression of established tumors, and prolonged survival in xenograft and transgenic models of pancreatic cancer. The effect of JP1201 was phenocopied by XIAP small interfering RNA in vitro and correlated with elevated levels of tumor necrosis factor alpha protein in vivo. The continued development of JP1201 and other strategies designed to enhance therapy-induced apoptosis in pancreatic cancer is warranted.

Forkhead box F1 regulates tumor-promoting properties of cancer-associated fibroblasts in lung cancer

Cancer-associated fibroblasts (CAF) attract increasing attention as potential cancer drug targets due to their ability to stimulate, for example, tumor growth, invasion, angiogenesis, and metastasis. However, the molecular mechanisms causing the tumor-promoting properties of CAFs remain poorly understood. Forkhead box F1 (FoxF1) is a mesenchymal target of hedgehog signaling, known to regulate mesenchymal-epithelial interactions during lung development. Studies with FoxF1 gain- and loss-of-function fibroblasts revealed that FoxF1 regulates the contractility of fibroblasts, their production of hepatocyte growth factor and fibroblast growth factor-2, and their stimulation of lung cancer cell migration. FoxF1 status of fibroblasts was also shown to control the ability of fibroblasts to stimulate xenografted tumor growth. FoxF1 was expressed in CAFs of human lung cancer and associated with activation of hedgehog signaling. These observations suggest that hedgehog-dependent FoxF1 is a clinically relevant lung CAF-inducing factor, and support experimentally the general concept that CAF properties can be induced by activation of developmentally important transcription factors.

Targeting of drugs and nanoparticles to tumors

The various types of cells that comprise the tumor mass all carry molecular markers that are not expressed or are expressed at much lower levels in normal cells. These differentially expressed molecules can be used as docking sites to concentrate drug conjugates and nanoparticles at tumors. Specific markers in tumor vessels are particularly well suited for targeting because molecules at the surface of blood vessels are readily accessible to circulating compounds. The increased concentration of a drug in the site of disease made possible by targeted delivery can be used to increase efficacy, reduce side effects, or achieve some of both. We review the recent advances in this delivery approach with a focus on the use of molecular markers of tumor vasculature as the primary target and nanoparticles as the delivery vehicle.

Overexpression of smoothened activates the sonic hedgehog signaling pathway in pancreatic cancer-associated fibroblasts

PURPOSE

Accumulating evidence suggests that cancer-associated stromal fibroblasts (CAF) contribute to tumor growth by actively communicating with cancer cells. Our aim is to identify signaling pathways involved in tumor-stromal cell interactions in human pancreatic cancer.

EXPERIMENTAL DESIGN

We established primary fibroblast cultures from human pancreatic adenocarcinomas and nonneoplastic pancreas tissues. To identify differentially expressed genes in CAFs, we did gene expression profiling of human pancreatic CAFs and nonneoplastic pancreatic fibroblasts.

RESULTS

The Hedgehog receptor Smoothened (SMO) was upregulated in CAFs relative to control fibroblasts. CAFs expressing SMO could transduce the Sonic hedgehog signal to activate Gli1 expression, and small interfering RNA knockdown of SMO blocked the induction of Gli1 in these cells. Stromal fibroblasts of human primary pancreatic adenocarcinomas overexpressed Smo compared with normal pancreatic fibroblasts.

CONCLUSIONS

These findings implicate overexpression of Smo as a mechanism for the activation of Hedgehog signaling in human pancreatic CAFs and suggest that stromal cells may be a therapeutic target for Smo antagonists in pancreatic cancer.

Activation of EGFR by proteasome inhibition requires HB-EGF in pancreatic cancer cells

Resistance to drug treatments underlies the high lethality of pancreatic ductal adenocarcinoma. Along with others, we have recently identified that proteasome inhibition is a promising therapeutic option in this highly refractory disease. The pleiotropic effects of proteasome inhibition include the activation of apoptotic signaling pathways and also antiapoptotic signaling pathways such as EGFR, AKT and the MAP kinases that reduce the apoptotic potential of this class of drug. In this study, we sought to determine the mechanism behind the activation of EGFR in response to proteasome inhibition in pancreatic cancer cells. We found that the second-generation proteasome inhibitor NPI-0052 induced the mRNA transcription of several EGFR family ligands (EGF, HB-EGF and epiregulin), however only increases in HB-EGF were detected at the protein level. Using both pharmacological inhibitors and lentiviral-mediated shRNA knockdown of EGFR ligand expression, we discovered that ligand cleavage by MMP/ADAMs and HB-EGF expression is required for activation of EGFR in response to proteasome inhibition. Furthermore, we discover that induction of HB-EGF is dependent on reactive oxygen species and p38-MAPK signaling but not ERK and that the transcription factor SP-1 is involved in NPI-0052-induced HB-EGF transcription. Together, these results indicate that stress signaling leading to induction of HB-EGF expression and increases in MMP/ADAM-dependent HB-EGF cleavage are responsible for proteasome inhibitor-induced activation of EGFR in pancreatic cancer cells.

A digest on the role of the tumor microenvironment in gastrointestinal cancers

Experimental studies and analyses of clinical material have convincingly demonstrated that tumor formation and progression occurs through a concerted action of malignant cells and the surrounding microenvironment of the tumor stroma. The tumor microenvironment is comprised of various cell types like fibroblasts, immune cells, vascular cells and bone-marrow-derived cells embedded in the extracellular matrix. This review, focusing on recent findings in the context of gastrointestinal tumors, introduces the different stromal cell types and delineates their contributions to cancer initiation, growth and metastasis. By selected examples we also present how the tumor microenvironment is emerging as a promising target for therapeutic intervention.

Hallmarks of cancer: interactions with the tumor stroma

Ten years ago, Hanahan and Weinberg delineated six "Hallmarks of cancer" which summarize several decades of intense cancer research. However, tumor cells do not act in isolation, but rather subsist in a rich microenvironment provided by resident fibroblasts, endothelial cells, pericytes, leukocytes, and extra-cellular matrix. It is increasingly appreciated that the tumor stroma is an integral part of cancer initiation, growth and progression. The stromal elements of tumors hold prognostic, as well as response-predictive, information, and abundant targeting opportunities within the tumor microenvironment are continually identified. Herein we review the current understanding of tumor cell interactions with the tumor stroma with a particular focus on cancer-associated fibroblasts and pericytes. Moreover, we discuss emerging fields of research which need to be further explored in order to fulfil the promise of stroma-targeted therapies for cancer.

Adeno-associated virus-mediated delivery of kringle 5 of human plasminogen inhibits orthotopic growth of ovarian cancer

Kringle 5 (K5) of human plasminogen is a potent angiogenesis inhibitor. In this study, we investigated the effects of recombinant adeno-associated virus (AAV)-mediated delivery of K5 in mouse models of human ovarian cancer. A single intramuscular injection of AAV-K5 resulted in sustained expression of K5 reaching a maximum serum level of 800 ng ml(-1). Gene therapy inhibited both vascular endothelial growth factor (VEGF)-induced and tumor cell-induced angiogenesis in matrigel plug assays. Furthermore, a single injection of AAV-K5 significantly inhibited both subcutaneous and intraperitoneal growth of human ovarian cancer cells. Immunofluorescence studies of residual tumors surgically resected from the treated animals showed reduced tumor burden, which correlated with the inhibition of tumor neovascularization. In addition, AAV-K5 gene therapy differentially affected the nascent vessels more than mature vasculature and induced apoptotic death of tumor cells. These data show that AAV-K5 can be effectively used to inhibit ovarian cancer.

Masitinib combined with standard gemcitabine chemotherapy: in vitro and in vivo studies in human pancreatic tumour cell lines and ectopic mouse model

BACKGROUND

Tyrosine kinases are attractive targets for pancreatic cancer therapy because several are over-expressed, including PDGFRalpha/beta, FAK, Src and Lyn. A critical role of mast cells in the development of pancreatic cancer has also been reported. Masitinib is a tyrosine kinase inhibitor that selectively targets c-Kit, PDGFRalpha/beta, Lyn, and to a lesser extent the FAK pathway, without inhibiting kinases of known toxicities. Masitinib is particularly efficient in controlling the proliferation, differentiation and degranulation of mast cells. This study evaluates the therapeutic potential of masitinib in pancreatic cancer, as a single agent and in combination with gemcitabine.

METHODOLOGY/FINDINGS

Proof-of-concept studies were performed in vitro on human pancreatic tumour cell lines and then in vivo using a mouse model of human pancreatic cancer. Molecular mechanisms were investigated via gene expression profiling. Masitinib as a single agent had no significant antiproliferative activity while the masitinib/gemcitabine combination showed synergy in vitro on proliferation of gemcitabine-refractory cell lines Mia Paca2 and Panc1, and to a lesser extent in vivo on Mia Paca2 cell tumour growth. Specifically, masitinib at 10 microM strongly sensitised Mia Paca2 cells to gemcitabine (>400-fold reduction in IC(50)); and moderately sensitised Panc1 cells (10-fold reduction). Transcriptional analysis identified the Wnt/beta-catenin signalling pathway as down-regulated in the cell lines resensitised by the masitinib/gemcitabine combination.

CONCLUSIONS

These data establish proof-of-concept that masitinib can sensitise gemcitabine-refractory pancreatic cancer cell lines and warrant further in vivo investigation. Indeed, such an effect has been recently observed in a phase 2 clinical study of patients with pancreatic cancer who received a masitinib/gemcitabine combination.

Pancreatic cancer: pathobiology, treatment options, and drug delivery

Pancreatic cancer is the fourth leading cause of cancer-related deaths in the USA. The high mortality rate is partly due to lack of effective treatments. This review summarizes the pathobiology and current treatment options for pancreatic cancer. Moreover, the review discusses the opportunities of developing novel therapies for pancreatic cancer provided by the progress in understanding the genetic mutations, tumor microenvironment, cancer stem cells, and drug delivery.

Tumor metabolism to blood flow ratio in pancreatic cancer: helpful in patient stratification?

Evaluation of: Komar G, Kauhanen S, Liukko K et al.: Decreased blood flow with increased metabolic activity: a novel sign of pancreatic tumor aggressiveness. Clin. Cancer Res. 15(17), 5511-5517 (2009). Novel methods in assessing pancreas cancer vascularization and metabolism are urgently needed for pretherapeutic patient stratification. Recently, noninvasive quantification of blood flow and metabolic activity of pancreatic tumors using [(15)O]H(2)O and [(18)F] fluorodeoxyglucose positron emission tomography/computed tomography imaging has been demonstrated to be a promising approach to assess these parameters. This also implied that high tumor metabolism and low blood flow (and thus probably also low tissue oxygenation) are linked with an aggressive cancer phenotype, and potentially reflect treatment resistance. Furthermore, such functional imaging might prove clinically that pancreatic cancer differs from other gastrointestinal cancer in its desmoplastic reaction and hypovascularity, which might well explain the enormous heterogeneity in treatment sensitivity. Therefore, determination of the metabolism to blood flow ratio could help in the decision on which (additional) chemotherapies or targeted agents to administer to a particular patient. Chemoresistance in pancreatic cancer might thus be regarded, at least in part, as a result of low drug delivery to the tumor cells, which is a consequence of a hypoxic environment contributing to the stromal reaction, rather than epithelial tumor cell resistance itself.

Systemic therapy for metastatic pancreatic adenocarcinoma

Systemic treatment of metastatic pancreatic adenocarcinoma achieves only modest benefits, with evidence indicating a survival advantage with 5-fluorouracil (5-FU) over best supportive care alone, and further advantage of single-agent gemcitabine over 5-FU. There are very few regimens better than single-agent gemcitabine despite multiple trials of cytotoxic and targeted agents. The addition of a platinum agent has improved response rate but not survival. The addition of erlotinib has improved survival but only by a small margin. The use of gemcitabine in multidrug regimens containing one or more of: a platinum agent; fluoropyrimidine; anthracycline; and taxane has demonstrated advantages in response rate, progression-free survival and, in one randomized study, overall survival. After gemcitabine failure, second-line therapy with oxaliplatin and 5-FU provides a further survival advantage. Further advances depend upon the current and future clinical trials investigating enhanced delivery of current agents, new agents and novel modalities, improved supportive care, and treatment more tailored to the individual patient and tumour.

Modulating tumor vasculature through signaling inhibition to improve cytotoxic therapy

The tumor microenvironment is a key factor in cancer treatment response. Recent work has shown that changes in the tumor vasculature can be achieved by inhibiting tumor cell signaling, resulting in enhanced tumor oxygenation. These changes could promote responses to both chemo- and radiation therapy.

Stromal fibroblasts in digestive cancer

The normal gastrointestinal stroma consists of extra-cellular matrix and a community of stromal cells including fibroblasts, myofibroblasts, smooth muscle cells, pericytes, endothelium and inflammatory cells. α-smooth muscle actin (α-SMA) positive stromal fibroblasts, often referred to as myofibroblasts or activated fibroblasts, are critical in the development of digestive cancer and help to create an environment that is permissive of tumor growth, angiogenesis and invasion. This review focusses on the contribution of activated fibroblasts in carcinogenesis and where possible directly applies this to, and draws on examples from, gastrointestinal cancer. In particular, the review expands on the definition, types and origins of activated fibroblasts. It examines the molecular biology of stromal fibroblasts and their contribution to the peritumoral microenvironment and concludes by exploring some of the potential clinical applications of this exciting branch of cancer research. Understanding the origin and biology of activated fibroblasts will help in the development of an integrated epithelial-stromal sequence to cancer that will ultimately inform cancer pathogenesis, natural history and future therapeutics.

Transcriptome profiles of carcinoma-in-situ and invasive non-small cell lung cancer as revealed by SAGE

Background

Non-small cell lung cancer (NSCLC) presents as a progressive disease spanning precancerous, preinvasive, locally invasive, and metastatic lesions. Identification of biological pathways reflective of these progressive stages, and aberrantly expressed genes associated with these pathways, would conceivably enhance therapeutic approaches to this devastating disease.

Methodology/Principal Findings

Through the construction and analysis of SAGE libraries, we have determined transcriptome profiles for preinvasive carcinoma-in-situ (CIS) and invasive squamous cell carcinoma (SCC) of the lung, and compared these with expression profiles generated from both bronchial epithelium, and precancerous metaplastic and dysplastic lesions using Ingenuity Pathway Analysis. Expression of genes associated with epidermal development, and loss of expression of genes associated with mucociliary biology, are predominant features of CIS, largely shared with precancerous lesions. Additionally, expression of genes associated with xenobiotic metabolism/detoxification is a notable feature of CIS, and is largely maintained in invasive cancer. Genes related to tissue fibrosis and acute phase immune response are characteristic of the invasive SCC phenotype. Moreover, the data presented here suggests that tissue remodeling/fibrosis is initiated at the early stages of CIS. Additionally, this study indicates that alteration in copy-number status represents a plausible mechanism for differential gene expression in CIS and invasive SCC.

Conclusions/Significance

This study is the first report of large-scale expression profiling of CIS of the lung. Unbiased expression profiling of these preinvasive and invasive lesions provides a platform for further investigations into the molecular genetic events relevant to early stages of squamous NSCLC development. Additionally, up-regulated genes detected at extreme differences between CIS and invasive cancer may have potential to serve as biomarkers for early detection.

A fine-needle aspirate-based vulnerability assay identifies polo-like kinase 1 as a mediator of gemcitabine resistance in pancreatic cancer

This work aimed to discover targets for combination treatment with gemcitabine in pancreatic cancer. We selected 11 tumors from our live collection of freshly generated pancreatic cancer xenografts with known degrees of varying gemcitabine sensitivity. We briefly (6 h) exposed fine-needle aspiration material to control vehicle or gemcitabine (1 mumol/L) and compared the gene expression of the treated and untreated samples using a reverse transcription-PCR-based, customized low-density array with 45 target genes of therapeutic interest. The gene expression of the untreated sample (which can be considered a baseline/static readout) was not predictive of gemcitabine efficacy in these tumors. Altogether, the only gene that differentiated sensitive versus resistant cases was polo-like kinase 1 (Plk1), showing >50% downregulation in sensitive cases and no change in the resistant cases. Inhibition of Plk1 by either small interfering RNA gene knockdown or with the Plk1 pathway modulator (ON 01910.Na) synergized with gemcitabine in gemcitabine-refractory in vitro models providing mechanistic proof of concept. In vivo experiments in gemcitabine-resistant xenografts showed synergistic activity decreasing cell proliferation and tumor regressions. A quantitative gene expression-based vulnerability assay identified Plk1 as a relevant target dictating the susceptibility of pancreatic cancer to gemcitabine. Dynamic interrogation of cancer has the potential to provide key information about mechanisms of resistance and to enhance individualization of treatment.

Hedgehog promotes neovascularization in pancreatic cancers by regulating Ang-1 and IGF-1 expression in bone-marrow derived pro-angiogenic cells

Background

The hedgehog (Hh) pathway has been implicated in the pathogenesis of cancer including pancreatic ductal adenocarcinoma (PDAC). Recent studies have suggested that the oncogenic function of Hh in PDAC involves signaling in the stromal cells rather than cell autonomous effects on the tumor cells. However, the origin and nature of the stromal cell type(s) that are responsive to Hh signaling remained unknown. Since Hh signaling plays a crucial role during embryonic and postnatal vasculogenesis, we speculated that Hh ligand may act on tumor vasculature specifically focusing on bone marrow (BM)-derived cells.

Methodology/Principal Findings

Cyclopamine was utilized to inhibit the Hh pathway in human PDAC cell lines and their xenografts. BM transplants, co-culture systems of tumor cells and BM-derived pro-angiogenic cells (BMPCs) were employed to assess the role of tumor-derived Hh in regulating the BM compartment and the contribution of BM-derived cells to angiogenesis in PDAC. Cyclopamine administration attenuated Hh signaling in the stroma rather than in the cancer cells as reflected by decreased expression of full length Gli2 protein and Gli1 mRNA specifically in the compartment. Cyclopamine inhibited the growth of PDAC xenografts in association with regression of the tumor vasculature and reduced homing of BM-derived cells to the tumor. Host-derived Ang-1 and IGF-1 mRNA levels were downregulated by cyclopamine in the tumor xenografts. In vitro co-culture and matrigel plug assays demonstrated that PDAC cell-derived Shh induced Ang-1 and IGF-1 production in BMPCs, resulting in their enhanced migration and capillary morphogenesis activity.

Conclusions/Significance

We identified the BMPCs as alternative stromal targets of Hh-ligand in PDAC suggesting that the tumor vasculature is an attractive therapeutic target of Hh blockade. Our data is consistent with the emerging concept that BM-derived cells make important contributions to epithelial tumorigenesis.

Context-dependent regulation of the GLI code in cancer by HEDGEHOG and non-HEDGEHOG signals

A surprisingly large and unrelated number of human tumors depend on sustained HEDGEHOG-GLI (HH-GLI) signaling for growth. This includes cancers of the skin, brain, colon, lungs, prostate, blood and pancreas among others. The basis of such commonality is not obvious. HH-GLI signaling has also been shown to be active in and required for cancer stem cell survival and expansion in different cancer types, and its activity is essential not only for tumor growth but also for recurrence and metastatic growth, two key medical problems. Here we review recent data on the role of HH-GLI signaling in cancer focusing on the role of the GLI code, the regulated combinatorial and cooperative function of repressive and activating forms of all Gli transcription factors, as a signaling nexus that integrates not only HH signals but also those of multiple tumor suppressors and oncogenes. Recent data support the view that the context-dependent regulation of the GLI code by oncogenes and tumor suppressors constitutes a basis for the widespread involvement of GLI1 in human cancers, representing a perversion of its normal role in the control of stem cell lineages during normal development and homeostasis.

Drug efficacy testing in mice

The traditional path of drug development passes from in vitro screening and response assessment to validation of drug efficacy in cell line xenografts. While xenografts have their merits, historically, more often than not, they have not served as an accurate predictor of drug efficacy in humans. The refinement and increased availability of genetically engineered mouse models (GEMMs) of cancer has made GEMMs an attractive avenue for the preclinical testing of therapeutic agents. The histopathologic and genetic resemblance of GEMMs to human cancer are an important measure to evaluate their suitability for pre-clinical studies and a number of studies using kinase inhibitors have now been performed in GEMMs. We have highlighted several of the salient advantages and challenges associated with GEMM studies. Well-characterized GEM models of human cancer should aide in the prioritization of both established and novel therapeutics.

Genetically engineered mouse models in cancer research

Mouse models of human cancer have played a vital role in understanding tumorigenesis and answering experimental questions that other systems cannot address. Advances continue to be made that allow better understanding of the mechanisms of tumor development, and therefore the identification of better therapeutic and diagnostic strategies. We review major advances that have been made in modeling cancer in the mouse and specific areas of research that have been explored with mouse models. For example, although there are differences between mice and humans, new models are able to more accurately model sporadic human cancers by specifically controlling timing and location of mutations, even within single cells. As hypotheses are developed in human and cell culture systems, engineered mice provide the most tractable and accurate test of their validity in vivo. For example, largely through the use of these models, the microenvironment has been established to play a critical role in tumorigenesis, since tumor development and the interaction with surrounding stroma can be studied as both evolve. These mouse models have specifically fueled our understanding of cancer initiation, immune system roles, tumor angiogenesis, invasion, and metastasis, and the relevance of molecular diversity observed among human cancers. Currently, these models are being designed to facilitate in vivo imaging to track both primary and metastatic tumor development from much earlier stages than previously possible. Finally, the approaches developed in this field to achieve basic understanding are emerging as effective tools to guide much needed development of treatment strategies, diagnostic strategies, and patient stratification strategies in clinical research.

Tumor initiating cells in pancreatic cancer: A critical view

Emerging evidence points to the existence of pancreatic cancer stem cells (CSC) as the culprit in the initiation, maintenance, metastasis, and treatment resistance of pancreatic cancer. The existence of such a cell population would have an important impact on the design of novel therapies against this devastating disease. However, no in vivo validation or rebuttal of the pancreatic CSC hypothesis exists. Major backlashes in the discussion on CSC are firstly, the confusion between the terms CSC and cell of origin of pancreatic ductal adenocarcinoma (PDAC), secondly the ambiguity of the cell of origin itself and thirdly, the fact that the CSC hypothesis is based on cell sorting and xenografting experiments; the latter of which often precludes solid conclusions because of the lack of a natural microenvironment and differences in drug delivery. Nonetheless, recent studies in other cancers partially support the CSC hypothesis by demonstrating a link between epithelial-to-mesenchymal transdifferentiation/transition (EMT) and CSC properties. Such a link is again open to dispute as EMT is a reversible process which is highly dependent on major oncogenic pathways in PDAC [e.g. K-Ras, transforming growth factor-β (TGF-β)] rather than on presumed cancer stem cell pathways. Hence, the available evidence does not robustly support the CSC concept in PDAC and a thorough validation of this hypothesis in well-defined genetically engineered mouse models of pancreatic cancer is required.

Activation of the hedgehog-signaling pathway in human cancer and the clinical implications

The hedgehog pathway, initially discovered by two Nobel laureates Drs E Wieschaus and C Nusslein-Volhard in Drosophila, is a major regulator for cell differentiation, tissue polarity and cell proliferation. Studies from many laboratories reveal activation of this pathway in a variety of human cancer, including basal cell carcinomas (BCCs), medulloblastomas, leukemia, gastrointestinal, lung, ovarian, breast and prostate cancers. It is thus believed that targeted inhibition of hedgehog signaling may be effective in treatment and prevention of human cancer. Even more exciting is the discovery and synthesis of specific signaling antagonists for the hedgehog pathway, which have significant clinical implications in novel cancer therapeutics. In this review, we will summarize major advances in the last 2 years in our understanding of hedgehog signaling activation in human cancer, interactions between hedgehog signaling and other pathways in carcinogenesis, potential antagonists for hedgehog signaling inhibition and their clinical implications for human cancer treatment.

Targeting histone deacetylases in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a dismal disease with a median survival below 6 months and a 5-year survival rate below 1%. Effective therapies for locally advanced or metastatic tumours are missing and curatively resected patients relapse in over 80% of the cases. Although histone deacetylases (HDACs) are involved in the control of proliferation, apoptosis, differentiation, migration and angiogenesis of cancer cells, knowledge about the expression patterns and functions of individual HDAC isoenzymes in pancreatic cancer is sparse. This review summarizes the roles of HDACs as novel therapeutic targets and the molecular mode of action of HDAC-inhibitors (HDACI) in PDACs. Success of HDACI in clinical settings will depend on an increased knowledge of HDAC functions as well as on a better understanding of the mode of action of HDACI. Pre-clinical experimental data that constitute the basis for rational therapeutic strategies to treat PDAC are described here. Translating these rational-based therapies into the clinic will finally increase our chance to establish an effective HDACI-containing combination therapy effective against PDAC.

Translational advances and novel therapies for pancreatic ductal adenocarcinoma: hope or hype?

Biological complexity, inaccessible anatomical location, nonspecific symptoms, lack of a screening biomarker, advanced disease at presentation and drug resistance epitomise pancreatic ductal adenocarcinoma (PDA) as a poor-prognosis, lethal disease. Twenty-five years of research (basic, translational and clinical) have barely made strides to improve survival, mainly because of a fundamental lack of knowledge of the biological processes initiating and propagating PDA. However, isolation of pancreas cancer stem cells or progenitors, whole-genome sequencing for driver mutations, advances in functional imaging, mechanistic dissection of the desmoplastic reaction and novel targeted therapies are likely to shed light on how best to treat PDA. Here we summarise current knowledge and areas where the field is advancing, and give our opinion on the research direction the field should be focusing on to better deliver promising therapies for our patients.

Intrahepatic cholangiocarcinoma progression: prognostic factors and basic mechanisms

In this review, we will examine various molecular biomarkers for their potential to serve as independent prognostic factors for predicting survival outcome in postoperative patients with progressive intrahepatic cholangiocarcinoma. Specific rodent models of intrahepatic cholangiocarcinoma that mimic relevant cellular, molecular, and clinical features of the human disease are also described, not only in terms of their usefulness in identifying molecular pathways and mechanisms linked to cholangiocarcinoma development and progression, but also for their potential value as preclinical platforms for suggesting and testing novel molecular strategies for cholangiocarcinoma therapy. Last, recent studies aimed at addressing the role of desmoplastic stroma in promoting intrahepatic cholangiocarcinoma progression are highlighted in an effort to underline the potential value of targeting tumor stromal components together with that of cholangiocarcinoma cells as a novel therapeutic option for this devastating cancer.

Stroma in breast development and disease

It is increasingly apparent that normal and malignant breast tissues require complex local and systemic stromal interactions for development and progression. During development, mammary cell fate specification and differentiation require highly regulated contextual signals derived from the stroma. Likewise, during breast carcinoma development, the tissue stroma can provide tumor suppressing and tumor-promoting environments that serve to regulate neoplastic growth of the epithelium. This review focuses on the role of the stroma as a mediator of normal mammary development, as well as a critical regulator of malignant conversion and progression in breast cancer. Recognition of the important role of the stroma during the progression of breast cancers leads to the possibility of new targets for treatment of the initial breast cancer lesion as well as prevention of recurrence.

Molecular biology of cancer-associated fibroblasts: can these cells be targeted in anti-cancer therapy?

It is increasingly recognized that the non-neoplastic stromal compartment in most solid cancers plays an active role in tumor proliferation, invasion and metastasis. Cancer-associated fibroblasts (CAFs) are one of the most abundant cell types in the tumor stroma, and these cells are pro-tumorigenic. Evidence that CAFs are epigenetically and possibly also genetically distinct from normal fibroblasts is beginning to define these cells as potential targets of anti-cancer therapy. Here, we review the cell-of-origin and molecular biology of CAFs, arguing that such knowledge provides a rational basis for designing therapeutic strategies to coordinately and synergistically target both the stromal and malignant epithelial component of human cancers.

The reg4 gene, amplified in the early stages of pancreatic cancer development, is a promising therapeutic target

BACKGROUND

The aim of our work was to identify the genes specifically altered in pancreatic adenocarcinoma and especially those that are altered early in cancer development.

METHODOLOGY/PRINCIPAL FINDINGS

Gene copy number was systematically assessed with an ultra-high resolution CGH oligonucleotide microarray in DNA from samples of pancreatic cancer. Several new cancer-associated variations were observed. In this work we focused on one of them, involving the reg4 gene. Gene copy number gain of the reg4 gene was confirmed by qPCR in 14 cancer samples. It was also found with increased copy number in most PanIN3 samples. The relationship betweena gain in reg4 gene copy number and cancer development was investigated on the human pancreatic cancer cell line Mia-PaCa2 xenografted under the skin of nude mice. When cells were transfected with a vector allowing reg4 expression, they generated tumors almost twice larger in size. In addition, these tumors were more resistant to gemcitabine treatment than control tumors. Interestingly, weekly intraperitoneal administration of a monoclonal antibody to reg4 halved the size of tumors generated by Mia-PaCa2 cells, suggesting that the antibody interfered with a paracrine/autocrine mechanism involving reg4 and stimulating cancer progression. The addition of gemcitabine resulted in further reduction, tumors becoming 5 times smaller than control. Exposure to reg4 antibody resulted in a significant decrease in intra-tumor levels of pAkt, Bcl-xL, Bcl-2, survivin and cyclin D1.

CONCLUSIONS/SIGNIFICANCE

It was concluded that adjuvant therapies targeting reg4 could improve the standard treatment of pancreatic cancer with gemcitabine.

Tumour-initiating cells: challenges and opportunities for anticancer drug discovery

The hypothesis that cancer is driven by tumour-initiating cells (popularly known as cancer stem cells) has recently attracted a great deal of attention, owing to the promise of a novel cellular target for the treatment of haematopoietic and solid malignancies. Furthermore, it seems that tumour-initiating cells might be resistant to many conventional cancer therapies, which might explain the limitations of these agents in curing human malignancies. Although much work is still needed to identify and characterize tumour-initiating cells, efforts are now being directed towards identifying therapeutic strategies that could target these cells. This Review considers recent advances in the cancer stem cell field, focusing on the challenges and opportunities for anticancer drug discovery.

Inflammation: a driving force speeds cancer metastasis

It has been increasingly recognized that tumor microenvironment plays an important role in carcinogenesis. Inflammatory component is present and contributes to tumor proliferation, angiogenesis, metastasis and resistance to hormonal and chemotherapy. This review highlights the role of inflammation in the tumor metastasis. We focus on the function of proinflammatory factors, particularly cytokines during tumor metastasis. Understanding of the mechanisms by which inflammation contributes to metastasis will lead to innovative approach for treating cancer. How tumor spread remains an enigma and has received great attention in recent years, as metastasis is the major cause of cancer mortality. The complex and highly selective metastatic cascade not only depends on the intrinsic properties of tumor cells but also the microenvironment that they derive from. An inflammatory milieu consisting of infiltrated immune cells and their secretory cytokines, chemokines and growth factors contribute significantly to the invasive and metastatic traits of cancer cells. Here, we review new insights into the molecular pathways that link inflammation in the tumor microenvironment to metastasis.

Nanomedicine: Silence the target

A new formulation of magnetic nanoparticles steered to cells by external magnets can deliver nucleic acids to turn off the growth of tumour blood vessels in mice.

Understanding the causes of multidrug resistance in cancer: a comparison of doxorubicin and sunitinib

Multiple molecular, cellular, micro-environmental and systemic causes of anticancer drug resistance have been identified during the last 25 years. At the same time, genome-wide analysis of human tumor tissues has made it possible in principle to assess the expression of critical genes or mutations that determine the response of an individual patient's tumor to drug treatment. Why then do we, with a few exceptions, such as mutation analysis of the EGFR to guide the use of EGFR inhibitors, have no predictive tests to assess a patient's drug sensitivity profile. The problem urges the more with the expanding choice of drugs, which may be beneficial for a fraction of patients only. In this review we discuss recent studies and insights on mechanisms of anticancer drug resistance and try to answer the question: do we understand why a patient responds or fails to respond to therapy? We focus on doxorubicin as example of a classical cytotoxic, DNA damaging agent and on sunitinib, as example of the new generation of (receptor) tyrosine kinase-targeted agents. For both drugs, classical tumor cell autonomous resistance mechanisms, such as drug efflux transporters and mutations in the tumor cell's survival signaling pathways, as well as micro-environment-related resistance mechanisms, such as changes in tumor stromal cell composition, matrix proteins, vascularity, oxygenation and energy metabolism may play a role. Novel agents that target specific mutations in the tumor cell's damage repair (e.g. PARP inhibitors) or that target tumor survival pathways, such as Akt inhibitors, glycolysis inhibitors or mTOR inhibitors, are of high interest. In order to increase the therapeutic index of treatments, fine-tuned synergistic combinations of new and/or classical cytotoxic agents will be designed. More quantitative assessment of potential resistance mechanisms in real tumors and in real time, such as by kinase profiling methodology, will be developed to allow more precise prediction of the optimal drug combination to treat each patient.

Pancreatic cancer--could it be that simple? A different context of vulnerability

In a recent issue of Science, Olive and colleagues document that inhibition of Hedgehog (Hh) signaling in a genetically engineered mouse model of pancreatic cancer can enhance the intratumor concentration of certain anticancer drugs. Could this finding provide us with a new method to attack pancreatic cancer?