Exclusion of SMAD4 mutation as an early genetic change in human pancreatic ductal tumorigenesis

Pancreatic Ductal Adenocarcinoma: Molecular Pathology and Predictive Biomarkers

Pancreatic ductal adenocarcinoma (PDAC) has an extremely poor prognosis due to the lack of methods or biomarkers for early diagnosis and its resistance to conventional treatment modalities, targeted therapies, and immunotherapies. PDACs are a heterogenous group of malignant epithelial neoplasms with various histomorphological patterns and complex, heterogenous genetic/molecular landscapes. The newly proposed molecular classifications of PDAC based on extensive genomic, transcriptomic, proteomic and epigenetic data have provided significant insights into the molecular heterogeneity and aggressive biology of this deadly disease. Recent studies characterizing the tumor microenvironment (TME) have shed light on the dynamic interplays between the tumor cells and the immunosuppressive TME of PDAC, which is essential to disease progression, as well as its resistance to chemotherapy, newly developed targeted therapy and immunotherapy. There is a critical need for the development of predictive markers that can be clinically utilized to select effective personalized therapies for PDAC patients. In this review, we provide an overview of the histological and molecular heterogeneity and subtypes of PDAC, as well as its precursor lesions, immunosuppressive TME, and currently available predictive molecular markers for patients.

Genetic Mutations of Pancreatic Cancer and Genetically Engineered Mouse Models

Simple Summary

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy. Recent multi-gene analysis approaches such as next-generation sequencing have provided useful information on the molecular characterization of pancreatic tumors. Different types of pancreatic cancer and precursor lesions are characterized by specific molecular alterations. Genetically engineered mouse models (GEMMs) of PDAC are useful tools to understand the roles of altered genes. Most GEMMs are driven by oncogenic Kras, and can recapitulate the histological and molecular hallmarks of human PDAC and comparable precursor lesions. In this review, we summarize the main molecular alterations found in pancreatic neoplasms and GEMMs developed based on these alterations.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy, and the seventh leading cause of cancer-related deaths worldwide. An improved understanding of tumor biology and novel therapeutic discoveries are needed to improve overall survival. Recent multi-gene analysis approaches such as next-generation sequencing have provided useful information on the molecular characterization of pancreatic tumors. Different types of pancreatic cancer and precursor lesions are characterized by specific molecular alterations. Genetically engineered mouse models (GEMMs) of PDAC are useful to understand the roles of altered genes. Most GEMMs are driven by oncogenic Kras, and can recapitulate the histological and molecular hallmarks of human PDAC and comparable precursor lesions. Advanced GEMMs permit the temporally and spatially controlled manipulation of multiple target genes using a dual-recombinase system or CRISPR/Cas9 gene editing. GEMMs that express fluorescent proteins allow cell lineage tracing to follow tumor growth and metastasis to understand the contribution of different cell types in cancer progression. GEMMs are widely used for therapeutic optimization. In this review, we summarize the main molecular alterations found in pancreatic neoplasms, developed GEMMs, and the contribution of GEMMs to the current understanding of PDAC pathobiology. Furthermore, we attempted to modify the categorization of altered driver genes according to the most updated findings.

Effect of Reprimo Down-regulation on Malignant Transformation of Intraductal Papillary Mucinous Neoplasm

OBJECTIVES

Reprimo gene is a cytoplasmic protein belonging to a family of molecules controlled by p53 that inhibits cell cycle progression. Ectopic expression of Reprimo results in cell cycle arrest at the G2 phase. The aim of this study was to investigate the impact of Reprimo expression on tumorigenesis of intraductal papillary mucinous neoplasm (IPMN).

METHODS

Thirty-seven surgical cases of IPMN were collected retrospectively. Twenty-eight patients had benign IPMNs (low-grade dysplasia, n = 18; intermediate-grade dysplasia, n = 10), and the remaining 9 had malignant IPMNs (high-grade dysplasia, n = 4; invasive carcinoma, n = 5). DNA from tumor samples was extracted. DNA methylation patterns of Reprimo were determined by the methods of methylation-specific polymerase chain reaction and immunohistochemistry. The methylation status of Reprimo was compared between benign IPMNs and malignant IPMNs.

RESULTS

The incidence of aberrant DNA methylation of Reprimo was significantly higher in malignant IPMNs than in benign IPMNs (78% vs 32%, P = 0.016). Furthermore, the incidence of immunohistochemical Reprimo expression was significantly lower in malignant IPMNs than in benign IPMNs (22% vs 82%, P = 0.002).

CONCLUSIONS

Reprimo methylation was found more frequently in malignant IPMNs. Reprimo methylation is involved in malignant transformation of IPMNs.

Distinct pathways of pathogenesis of intraductal oncocytic papillary neoplasms and intraductal papillary mucinous neoplasms of the pancreas

Intraductal oncocytic papillary neoplasm (IOPN) of the pancreas is classified as a variant of intraductal papillary mucinous neoplasm (IPMN) in the WHO guidelines. However, the neoplastic cells of IOPNs are unique, with distinctive architecture/oncocytic cytoplasm. Although molecular/immunohistochemical features of other IPMN variants have been extensively studied, those of IOPNs have not been well characterized. Expression profile of antibodies associated with genetic alterations previously described for ductal adenocarcinomas (DAs) and IPMNs (SMAD4/β-catenin/p53/mesothelin/claudin-4) as well as antibodies to mucins and differentiation markers [MUC1/MUC2/MUC5AC/MUC6/CDX2/hepatocyte paraffin-1 (HepPar-1)] was investigated in 24 IOPNs and 22 IPMNs to assess the similarities/differences between these tumors. Expression of mesothelin and claudin-4 was dissimilar between these tumor types: A higher proportion of IOPNs labeled with mesothelin [21/24 (87.5 %) of IOPNs, 6/22 (27 %) of IPMNs, p < 0.001], while the reverse was true for claudin-4 [2/23 (9 %) of IOPNs, 9/22 (41 %) of IPMNs, p = 0.01]. The results of immunolabeling for SMAD4/β-catenin/p53 were similar in both: None of the cases showed SMAD4 loss in the intraductal components, and only 1/21 (5 %) of IOPNs and 2/22 (9 %) of IPMNs revealed abnormal β-catenin expression (p = 0.49). Nuclear p53 accumulation was seen mostly in architecturally complex/high-grade dysplasia areas in both. Immunolabeling for MUC proteins showed that almost all lesions expressed MUC5AC. Twelve of the 24 (50 %) IOPNs and 6/22 (27 %) of IPMNs (p = 0.11) labeled for MUC1, whereas 7/24 (29 %) of IOPNs and 10/22 (45 %) of IPMNs labeled for MUC2 (p = 0.25). MUC6 was expressed in 8/9 (89 %) of IOPNs (strong) and 6/21 (29 %) of IPMNs (weak) (p = 0.002). Fourteen of the 23 (61 %) IOPNs and 4/22 (18 %) of IPMNs labeled for HepPar-1 (p = 0.003). These results show that IOPNs have distinct immunoprofile and provide support for the proposition that IOPN is a distinct entity developing through a mechanism different from other pancreatic ductal neoplasms.

Intraductal papillary mucinous neoplasm of the pancreas: an update

Intraductal papillary mucinous neoplasm (IPMN) is a cystic tumor of the pancreas. The etiology is unknown, but increasing evidence suggests the involvement of several tumorigenesis pathways, including an association with hereditary syndromes. IPMN occurs more commonly in men, with the mean age at diagnosis between 64 and 67 years old. At the time of diagnosis, it may be benign, with or without dysplasia, or frankly malignant with an invasive carcinoma. Tumors arising from the main pancreatic duct are termed main-duct IPMNs, those involving the branch ducts, branch-duct IPMNs. In general, small branch-duct IPMNs are benign, particularly in asymptomatic patients, and can be safely followed. In contrast, main-duct tumors should be surgically resected and examined carefully for an invasive component. In the absence of invasion, patient's survival is excellent, from 94 to 100%. For patients with an IPMN-associated invasive carcinoma, the prognosis overall is better than those with a de novo pancreatic ductal adenocarcinoma, with a 5-year survival of 40% to 60% in some series. However, no survival advantage can be demonstrated if the invasive component in an IPMN patient is that of the conventional tubular type (versus mucinous carcinoma). Several histomorphologic variants are recognized, although the clinical significance of this "subtyping" is not well defined.

Precursor lesions in pancreatic cancer: morphological and molecular pathology

Pancreatic cancer has a dismal prognosis and is the fourth most common cause of cancer related death in Western societies. In large part this is due to its typically late presentation, usually as locally advanced or metastatic disease. Identification of the non-invasive precursor lesions to pancreatic cancer raises the possibility of surgical treatment or chemoprevention at an early stage in the evolution of this disease, when more amenable to therapeutic interventions. Precursor lesions to pancreatic ductal adenocarcinoma, in particular pancreatic intraepithelial neoplasia (PanIN), have been recognised under a variety of synonyms for over 50 years. Over the past decade our understanding of the morphology, biological significance and molecular aberrations of these lesions has grown rapidly and there is now a widely accepted progression model integrating the accumulated morphological and molecular observations. Further progress is likely to be accelerated by improved mouse models of pancreatic cancer and by insight into the cancer genome gained by the International Cancer Genome Consortium (ICGC), in which an Australian consortium is leading the pancreatic cancer initiative. This review also outlines the morphological and molecular features of the other two precursors of pancreatic ductal adenocarcinoma, i.e., intraductal papillary mucinous neoplasms and mucinous cystic neoplasms.

Molecular pathogenesis of intraductal papillary mucinous neoplasms of the pancreas

Over the last 3 decades, there have been substantial improvements in diagnostic imaging and sampling techniques to evaluate pancreatic diseases. The modern technology has helped us to recognize premalignant conditions of pancreas including mucinous cystic neoplasms and intraductal papillary mucinous neoplasms (IPMNs). Differentiation between benign and malignant lesions and early detection of any malignant transformation in premalignant lesion are extremely important for further management decisions. Diagnostic cytology has limited sensitivity to further differentiate between benign, premalignant, and malignant lesions of the pancreas. There is limited information about the epidemiological risk factors and molecular mechanisms leading to development and further progression to malignancy of IPMNs. Several studies have shown that pancreatic juice and pancreatic tissue from the lesion can be tested for molecular markers including K-ras, p53, and p16 to differentiate between cancer and chronic inflammatory process. We review cellular signaling pathways that contribute to pathogenesis of IPMNs of the pancreas to further identify potential biomarkers and molecular targets.

Update on the molecular pathogenesis of pancreatic tumors other than common ductal adenocarcinoma

PURPOSE

Although ductal adenocarcinoma is the most common and well known pancreatic tumor type, other distinct epithelial neoplasms affecting the pancreas that show different symptoms, biological behaviors and outcomes are becoming more frequently recognized and documented. Pancreatic epithelial tumors may be separated into ductal and nonductal neoplasms. The former group includes pancreatic ductal adenocarcinoma, intraductal papillary-mucinous tumor, mucinous cystic tumor and serous cystic tumor. The latter group includes pancreatic endocrine tumor, pancreatic acinar cell carcinoma, pancreatoblastoma and solid-pseudopapillary tumor. The aim of this review is to summarize recently acquired knowledge regarding the molecular characterization of these uncommon pancreatic epithelial neoplasms.

RECENT FINDINGS

Molecular studies of uncommon pancreatic epithelial tumors suggest that the different morphological entities are associated with distinct molecular profiles, highlighting the involvement of different molecular pathways leading to the development of each subtype of pancreatic neoplasm.

CONCLUSION

The correct classification of rare pancreatic epithelial tumors and the identification of their characteristic molecular aspects is the fundamental starting point in identifying novel diagnostic molecular tools and new targets for innovative therapeutic strategies.

The PMAIP1 gene on chromosome 18 is a candidate tumor suppressor gene in human pancreatic cancer

Frequent loss of heterozygosity on the long arm of chromosome 18 is observed in pancreatic cancer. Previous studies suggested the existence of one or more tumor-suppressor genes other than SMAD4 on chromosome 18. To identify the candidate tumor-suppressor gene(s), we compared gene expression by cDNA microarray analyses using a pancreatic cancer cell line Panc-1 and its hybrid cell lines showing suppressed cell growth after introduction of one normal copy of chromosome 18. The microarray analyses identified 38 genes on chromosome 18 that showed differential expressional levels. Among these genes, phorbol-12-myristate-13-acetate-induced protein 1 (PMAIP1/APR/NOXA) was identified as one of the candidates for tumor suppressor. Expression vector-mediated introduction of PMAIP1 suppressed cell proliferation, and RNAi-mediated knockdown of PMAIP1 induced recovery of cell growth. These results suggest that PMAIP1 may play an important role in the progression of pancreatic cancer.

Molecular genetics of intraductal papillary-mucinous neoplasms of the pancreas

Intraductal papillary-mucinous neoplasms of the pancreas show characteristic clinicopathological and molecular pathobiological features which are distinct from those of conventional ductal adenocarcinomas. Alterations of KRAS, AKT/PKB, CDKN2A, TP53, SMAD4, STK11/LKB1, and DUSP6, and other molecular alterations, including global expression studies as well as their clinical implications, are discussed.

Epigenetic alterations in intraductal papillary mucinous neoplasms of the pancreas

Intraductal papillary mucinous neoplasm (IPMN), an increasingly recognized cystic neoplasm of the pancreas with a broad spectrum of malignant potential, has been considered a precursor to infiltrating ductal adenocarcinoma. Because of its unique clinical, radiological, pathological, and molecular features, IPMN has attracted considerable interest among clinicians and researchers. Although some genetic alterations have been described in IPMNs, the molecular features that characterize the evolution and progression of these neoplasms are largely unknown. Recent studies have shown that aberrant methylation of the promoter cytosine-phospho-guanine (CpG) island is a common mechanism associated with the silencing of tumor-suppressor and cancer-related genes in IPMNs. Importantly, the prevalence of such methylation increases along with the grade of neoplasia, suggesting that these epigenetic events may contribute to the progression of IPMNs. Further studies of epigenetic alterations in IPMN will shed light on the molecular pathogenesis of this unique neoplasm and lead to the identification of epigenetic markers that can be applied in the clinical setting.

The early state of invasive pancreatic ductal adenocarcinomas: characteristics of the low papillary type and flat type intraductal carcinoma

OBJECTIVE

To analyze the early state and the mode of advancement of IPDACs.

METHODS

Eighty-two cases of IPDAC were resected, and the noninvasive cancer parts were identified pathohistologically. According to the pancreatic intraepithelial neoplasia (PanIN) classification, noninvasive cancer parts were equivalent to PanIN-3; the noninvasive cancer parts in the invasive area and noninvasive intraductal spread (NIIDS) area were histologically examined. Noninvasive intraductal spread means a diffuse PanIN-3 change that extended continuously outward from the invasive area. In cases with NIIDS, the length of NIIDS was measured.

RESULTS

Histologically, the noninvasive cancer parts were categorized into 3 types: flat (F), low papillary (LP), and mixed (flat and low papillary [FLP]) types; each type comprised 18.3%, 34.1%, and 47.6%, respectively. Cases with NIIDS of 2 mm or more were found in 56.1% of all the patients, and the F, FLP, and LP types comprised 13.3%, 59.0%, and 75.0%, respectively. The maximal NIIDS lengths were 10, 40, and 80 mm with averages of 1.5, 5.7, and 12.5 mm in the F, FLP, and LP types, respectively. The cases with the LP component revealed positive NIIDS and longer NIIDS lengths more frequently than those without the component (F type) (P < 0.001). The survival rates of the F, FLP, and LP types showed no statistical difference. The prognosis was better in cases of less advanced stages.

CONCLUSIONS

The noninvasive cancer parts (PanIN-3 lesions) of IPDACs were divided into 3 types: F, LP, and mixed types; the LP type had a greater tendency than the F type to spread intraductally. The LP type seemed to change to invasive cancer after or while spreading intraductally to some extent, whereas the F type seemed to invade with little intraductal spread.

Molecular mechanisms of pancreatic carcinogenesis

Pancreatic ductal adenocarcinoma is one of the most fatal malignancies. Intensive investigation of molecular pathogenesis might lead to identifying useful molecules for diagnosis and treatment of the disease. Pancreatic ductal adenocarcinoma harbors complicated aberrations of alleles including losses of 1p, 6q, 9p, 12q, 17p, 18q, and 21q, and gains of 8q and 20q. Pancreatic cancer is usually initiated by mutation of KRAS and aberrant expression of SHH. Overexpression of AURKA mapping on 20q13.2 may significantly enhance overt tumorigenesity. Aberrations of tumor suppressor genes synergistically accelerate progression of the carcinogenic pathway through pancreatic intraepithelial neoplasia (PanIN) to invasive ductal adenocarcinoma. Abrogation of CDKN2A occurs in low-grade/early PanIN, whereas aberrations of TP53 and SMAD4 occur in high-grade/late PanIN. SMAD4 may play suppressive roles in tumorigenesis by inhibition of angiogenesis. Loss of 18q precedes SMAD4 inactivation, and restoration of chromosome 18 in pancreatic cancer cells results in tumor suppressive phenotypes regardless of SMAD4 status, indicating the possible existence of a tumor suppressor gene(s) other than SMAD4 on 18q. DUSP6 at 12q21-q22 is frequently abrogated by loss of expression in invasive ductal adenocarcinomas despite fairly preserved expression in PanIN, which suggests that DUSP6 works as a tumor suppressor in pancreatic carcinogenesis. Restoration of chromosome 12 also suppresses growths of pancreatic cancer cells despite the recovery of expression of DUSP6; the existence of yet another tumor suppressor gene on 12q is strongly suggested. Understanding the molecular mechanisms of pancreatic carcinogenesis will likely provide novel clues for preventing, detecting, and ultimately curing this life-threatening disease.

Biological similarities and differences between pancreatic intraepithelial neoplasias and intraductal papillary mucinous neoplasms

BACKGROUND

Ever since the classification of pancreatic intraepithelial neoplasia (PanIN) was published, studies on the precursor lesions of pancreatic cancer have been advancing along a new directions, using standardized terminology. There are few studies that have examined the biological differences between PanIN and intraductal papillary mucinous neoplasm (IPMN) in detail.

AIMS

PanIN and IPMN, which are similar in morphology, were compared using various indicators, with the aim of identifying the similarities and differences between the two.

METHODOLOGY

A total of 46 PanINs and 37 ducts with IPMN were identified in 19 patients with invasive ductal carcinoma and 18 patients with IPMN. These PanINs and IPMNs were examined immunohistologically with respect to the expression patterns of HER2/neu, DPC4/Smad4, Akt/PKB, p53, cyclin A, Ki67, MUC1, and MUC2.

RESULTS

Significant differences in the expression of MUC1 and MUC2 were observed between IPMNadenoma and PanIN-2 and between CIS and PanIN-3 (MUC1: p = 0.001 and p = 0.005, respectively; MUC2: p = 0.002 and p < 0.001, respectively). A significant difference in the p53 expression level was also observed between CIS and PanIN-3 (p = 0.015).

CONCLUSIONS

In both IPMN and PanIN, the grade of atypism increased with increasing expression of HER2/neu, DPC4/Smad4, and Akt/PKB, along with progression in the process of multistage carcinogenesis. Although the expression levels of these factors reflected the grade of atypism, they did not reflect any differences in the grade of biological malignancy between IPMN and PanIN. On the other hand, MUC1 and MUC2 may serve as indicators of the direction of differentiation, i.e., either progression to IDAC or IPMN. Positivity for MUC1 was believed to suggest differentiation into IDAC, and positivity for MUC2 appeared to be indicative of differentiation into IPMN. Such indication of the direction of differentiation seemed to appear in PanIN1-2, even before abnormalities of HER2/neu, Akt/PKB, DPC4/Smad4, p53, and cyclin A expression began to be detected.

Status of the DPC4 tumor suppressor gene in sporadic colon adenocarcinoma of Croatian patients: identification of a novel somatic mutation

Loss of heterozygosity (LOH) of loci on chromosome 18q occurs in a majority of colorectal cancers. The DPC4 (Smad4) tumor suppressor gene, located at 18q21.1, may be a predisposing gene for Juvenile Polyposis Syndrome. To investigate alterations of the DPC4 gene in sporadic colon adenocarcinoma, a panel of 60 tumor specimens from Croatian patients was surveyed for evidence of LOH and also for mutations within the entire DPC4 coding region (exons 1-11). Using three pairs of specific primers for the three DPC4 microsatellite repetitive sequences, we investigated the frequency of LOH. The presence of single nucleotide change at restriction sites of specific codons in exons 2, 8, 10, and 11 (which belong to the conserved region of the gene) was examined by RFLP analysis. The investigation was extended to search for any other mutation within the entire coding region of the DPC4 gene by single strand conformation polymorphism (SSCP) analysis. Our results show a high frequency of heterozygosity in 58 of 60 (97%) colon adenocarcinoma samples. LOH at any one of the three flanking markers was observed in 26 (45%) of the 58 informative cases. The loss of one allele of the DPC4 gene was negatively correlated with tumor size; more frequent in smaller tumors (<5 cm) than in larger ones. A mutation was found in exon 11 in only one tumor sample (T18), and the mutation was verified by sequencing. Sequencing demonstrated a novel mutation-a deletion in exon 11 (134-153 del TAGACGAAGTACTTCATACC) of the DPC4 gene in the MH2 domain. These data suggest that inactivation of the DPC4 gene contributes to the genesis of colorectal carcinoma through allelic loss whereas mutation in the coding region of the DPC4 gene is infrequently detected in Croatian patients with A, B or C stages of colorectal cancers.

Functional Analysis of Chromosome 18 in Pancreatic Cancer: Strong Evidence for New Tumour Suppressor Genes

BACKGROUND

In a previous work, we demonstrated that loss of heterozygosity of 18q is a frequent event significantly associated with poor prognosis in pancreatic cancer. We hypothesized that restoration of heterozygosity of chromosome 18 in pancreatic cancer cells would reduce their tumorigenicity. This study was intended to provide functional evidence for the existence of new tumour suppressor gene(s) located on chromosome 18.

METHOD

Restoration of heterozygosity was achieved by introducing a normal copy of chromosome 18 into pancreatic ductal carcinoma using a microcell-mediated chromosome transfer technique. The tumorigenicity and metastatic ability of both the parental cells and resulting hybrids were assessed in vitro and in vivo.

RESULTS

In vitro growth of hybrid clones was significantly delayed compared to parental cells. This was paralleled by a significantly lower rate of promoting invasive carcinoma in nude mice and a longer latency with hybrid cells compared with parental tumour cells. Hybrid clones showed significant suppression in the number of surface lung metastases when compared with parental cells.

CONCLUSION

These data represent strong functional evidence that chromosome 18q encodes strong tumour and metastasis suppressor activity that is able to switch human pancreatic cancer cells to a dormant phenotype.

Molecular pathology of pancreatic cancer: in quest of tumor suppressor genes

To find molecular clues useful for early detection and effective therapy for pancreatic cancer, we first carried out genomic analysis by means of comparative genomic hybridization and micro-satellite analysis. We found very complicated molecular alterations in multiple chromosomal regions, including 1p, 6q, 9p, 12q, 17p, 18q, and 21q for losses and 8q and 20q for gains. These diverse changes are very characteristic of pancreatic cancer, and from this information, we developed a method for detecting the aberrant copy numbers of specific chromosomal regions by fluorescence in situ hybridization in cells collected from pancreatic juice for early diagnosis of pancreatic neoplasms. The regions of losses suggest the existence of tumor suppressor genes (TSGs). We identified DUSP6/MKP-3 at 12q21-q22 as a strong candidate TSG; it showed epigenetic inactivation in some fractions of invasive pancreatic cancer and growth suppression and apoptosis by overexpression in vitro. To determine the pathologic roles of 18q, we introduced a normal copy of chromosome 18 into cultured pancreatic cancer cells. The introduction induced marked suppressions of tumor formation and metastasis formation in vivo. We continue work to more completely understand the complex molecular mechanisms of pancreatic carcinogenesis and to apply the information gained to the clinical treatment of pancreatic cancer.

The role of chromosome 18 abnormalities in the progression of pancreatic adenocarcinoma

To date, the events that mediate tumor progression in pancreatic cancer are still poorly understood. Cytogenetic, allelotype, and somatic cell hybrid studies in human pancreatic adenocarcinoma have suggested that chromosome 18 may carry tumor suppressor genes (TSGs), including SMAD4. We previously identified that LOH of 18q at the SMAD4 locus, along with LOHs on 17p and 12q, positively associated with poor prognoses of pancreatic cancer patients. However, restoration of the SMAD4 gene did not suppress in vitro proliferation of pancreatic cancer cells that harbored homozygous deletion of this gene. An intraductal papillary mucinous neoplasm (IPMN ) is thought to be one of the premalignant lesions of the pancreas that progresses to carcinoma. Although there were frequent LOH (7/14, 50%) at the SMAD4 locus in IPMN samples, SMAD4 protein was observed immunohistochemically in tumor cells, and no mutations of the SMAD4 gene were observed, suggesting that it is the existence of a TSG in 18q, other than SMAD4, that suppresses cell growth. To functionally assess the activity of chromosome 18 in pancreatic cancer, we transferred a normal copy of the chromosome into pancreatic ductal carcinoma cells with and without completely inactivated SMAD4. In this study, in vitro growth of the hybrid cells was significantly suppressed compared with the parental cells, regardless of the initial SMAD4 status. To estimate the metastatic ability of the hybrids, we used a lung colonization model. At the end of the experiment, there was significant suppression of the number of surface metastases developing in mice injected with hybrids in comparison with those injected with parental cells. To identify and characterize genes that are involved in the progression of pancreatic cancer, we used micro-array expression analysis employing a 20k oligo-array system. It was revealed that there was increased expression of 4 genes relating to apoptosis in the 18 chromosome hybrids cells compared with the parental cells. We are now analyzing the function of these genes.

Restoration of SMAD4 by gene therapy reverses the invasive phenotype in pancreatic adenocarcinoma cells

SMAD4 is a critical cofactor in signal transduction pathways activated in response to transforming growth factor-beta (TGF-beta)-related ligands, regulating cell growth and differentiation. The roles played by SMAD4 inactivation in tumours highlighted it as a tumour-suppressor gene. However, restoration of the TGF-beta antiproliferative pathway following SMAD4 gene transfer in null-tumour cell lines is controversial. Herein, we report the inhibitory effects of SMAD4 on pancreatic tumour invasion and angiogenesis. Adenoviral transfer of this gene in a panel of SMAD4 homozygous-deleted human pancreatic tumour cell lines restored SMAD4 protein expression and function. Although it did not affect proliferation significantly in vitro, SMAD4 inhibited in vivo tumour growth in immunodeficient mice. In this xenograft setting, differential suppression of tumour growth in vivo was mediated, at least in part, through downregulation of vascular endothelial growth factor and expression of gelatinases. We documented the reduced invasion and angiogenesis histologically and by intravital microscopy, and gained mechanistic insight at the messenger and protein level. Finally, we found a negative reciprocal regulation between SMAD4 and ETS-1. ETS-1 is considered a marker for tumour invasion. Upon SMAD4 deletion, we detected high expression levels of ETS-1 in pancreatic tumour cells, suggesting the shift of the pancreatic tumour toward an invasive phenotype.

Phosphorylated Akt/PKB controls cell growth and apoptosis in intraductal papillary-mucinous tumor and invasive ductal adenocarcinoma of the pancreas

INTRODUCTION

Akt/PKB promotes cell proliferation and rescues cells from apoptosis.

AIM

To evaluate the role of Akt/PKB, a key molecule in phosphatidylinositol 3-OH kinase (PI3K) signaling, during the development of pancreatic duct neoplasias such as intraductal papillary-mucinous tumor (IPMT) and invasive ductal adenocarcinoma (IDAC) of the pancreas.

METHODOLOGY AND RESULTS

In PK-45H pancreatic cancer cells, the growth-inhibitory and apoptosis-inducing effects of LY294002, a PI3K inhibitor, were detected in a concentration-dependent manner, followed by the reduction of phosphorylated Akt levels. Immunohistochemical analyses revealed that frequent overexpression of phosphorylated Akt (Ser473) was detected in 10 (63%) of 16 IPMTs and 14 (70%) of 20 IDACs. It is interesting that the incidence of Akt phosphorylation closely correlated with Ki-67 immunoreactivity and had an inverse association with the number of cases of apoptotic bodies in both IPMT and IDAC. Although there was no good correlation with other clinicopathologic parameters, the two patients with recurrent IPMT had high levels of phosphorylated Akt.

CONCLUSION

Our findings suggest that activation of Akt plays an important role during the progression of these pancreatic duct neoplasias at the early stage. Furthermore, inhibition of the PI3K-Akt/PKB pathway may have therapeutic potential in the treatment of pancreatic duct tumors.

Progressive genomic alterations in intraductal papillary mucinous tumours of the pancreas and morphologically similar lesions of the pancreatic ducts

Intraductal papillary mucinous tumours (IPMTs) of the pancreas are rare neoplasms characterized by a prominent intraductal component, and by malignant potential. Little data exists concerning numerical chromosome aberrations in IPMTs. The biological significance of mucinous epithelial changes (mucinous hyperplasia) in small branching ducts adjacent to IPMTs also remains unclear. From a series of 12 IPMTs, we investigated by interphase cytogenetics 22 foci with mucinous hyperplasia, 27 foci with borderline lesions, and 11 samples with either intraductal (CIS) or invasive carcinoma. Chromosome 6 loss was detected in areas with mucinous hyperplasia (36.3%), borderline lesions (96.3%), and CIS/invasive carcinoma (100%). Similar losses, indicating clonal progression, were found for chromosome 17 (18.2%, 81.5%, and 100%), and for chromosome 18 (0%, 18.5%, and 100%). Quantitative analysis showed a significant intraductal expansion of cell clones harbouring these numerical aberrations within the spectrum of IPMTs. Mucinous epithelial changes in 11 resection samples with chronic pancreatitis showed monosomy 6 (36%) and monosomy 17 (27%). Conversely, areas with low-grade pancreatic intraepithelial neoplasia (PanIN-1), obtained from eight surgical specimens with ductal adenocarcinoma, showed monosomies for chromosome 6, 17, and 18 (100%, 87%, and 50%, respectively). We conclude that monosomies, as defined by FISH analysis, are frequent in both IPMTs and mucinous hyperplasia of pancreatic ducts adjacent to IPMTs. Monosomy 6 may represent an early event in the stepwise accumulation of genomic mutations necessary for the neoplastic transformation of pancreatic duct epithelia, whereas loss of chromosome 18 may be implicated in the progression of borderline to malignant IPMT. The detection of complex chromosomal aberrations in mucinous epithelial changes, and the quantitative expansion of monosomic cell clones in pancreatic ducts, provide evidence for a continuum between hyperplastic and dysplastic epithelial changes.

Suppression of the tumorigenic phenotype by chromosome 18 transfer into pancreatic cancer cell lines

A number of lines of evidence have suggested that the long arm of chromosome 18 apart from SMAD4 may carry a tumor-suppressor gene(s) that plays a role in the early stage of pancreatic ductal carcinogenesis. Thus, adenovirus-mediated introduction of SMAD4 does not suppress in vitro growth in cells with completely inactivated SMAD4, and frequent loss of 18q at the SMAD4 locus is observed in pancreatic cancers but no abnormalities of the normal SMAD4 homolog have been detected. In this study, we introduced a normal copy of chromosome 18 into some pancreatic ductal carcinoma cells with and without a complete inactivation of SMAD4. Both anchorage-dependent and -independent proliferation as well as invasiveness were significantly suppressed in the hybrid clones compared with that of their parental cells. Moreover, significant suppression of tumorigenesis was observed after inoculation in nude mice, irrespective of the SMAD4 status. Our present study provides the first functional evidence of the existence of an additional tumor-suppressor gene(s), other than SMAD4 and DCC, that is responsible for the pathogenesis in the early stage of pancreatic ductal carcinogenesis.

Loss of heterozygosity as a predictor to map tumor suppressor genes in cancer: molecular basis of its occurrence

High frequency of chromosomal deletions elicited as losses of heterozygosity is a hallmark of genomic instability in cancer. Functional losses of tumor suppressor genes caused by loss of heterozygosity at defined regions during clonal selection for growth advantage define the minimally lost regions as their likely locations on chromosomes. Loss of heterozygosity is elicited at the molecular or cytogenetic level as a deletion, a gene conversion, single or double homologous and nonhomologous mitotic recombinations, a translocation, chromosome breakage and loss, chromosomal fusion or telomeric end-to-end fusions, or whole chromosome loss with or without accompanying duplication of the retained chromosome. Because of the high level of specificity, loss of heterozygosity has recently become invaluable as a marker for diagnosis and prognosis of cancer. The molecular defects for the occurrence of loss of heterozygosity are derived from disabled caretaker genes, which protect the integrity of DNA, or chromosome segregator genes, which mediate faithful chromosome disjunction.

STK11/LKB1 Peutz-Jeghers gene inactivation in intraductal papillary-mucinous neoplasms of the pancreas

Despite the growing awareness of intraductal papillary-mucinous neoplasms (IPMNs) of the pancreas among clinicians, the molecular features of IPMNs have not been well characterized. Previous reports suggest that inactivation of the STK11/LKB1, a tumor-suppressor gene responsible for Peutz-Jeghers syndrome (PJS), plays a role in the pathogenesis of gastrointestinal hamartomas as well as several cancers, including pancreatic adenocarcinoma. Using polymerase chain reaction amplification of five microsatellite markers from the 19p13.3 region harboring the STK11/LKB1 gene, we analyzed DNA from 22 IPMNs for loss of heterozygosity (LOH). LOH at 19p13.3 was identified in 2 of 2 (100%) IPMNs from patients with PJS and 5 of 20 (25%) from patients lacking features of PJS (7 of 22, 32% overall). Sequencing analysis of the STK11/LKB1 gene in these IPMNs with LOH revealed a germline mutation in one IPMN that arose in a patient with PJS and a somatic mutation in 1 of the 20 sporadic IPMNs. None of the 22 IPMNs showed hypermethylation of the STK11/LKB1 gene. These results suggest that the STK11/LKB1 gene is involved in the pathogenesis of some IPMNs.