Induction of adenocarcinoma from hamster pancreatic islet cells treated with N-nitrosobis(2-oxopropyl)amine in vitro

Molecular signaling in pancreatic ductal metaplasia: emerging biomarkers for detection and intervention of early pancreatic cancer

Pancreatic ductal metaplasia (PDM) is the transformation of potentially various types of cells in the pancreas into ductal or ductal-like cells, which eventually replace the existing differentiated somatic cell type(s). PDM is usually triggered by and manifests its ability to adapt to environmental stimuli and genetic insults. The development of PDM to atypical hyperplasia or dysplasia is an important risk factor for pancreatic intraepithelial neoplasia (PanIN) and pancreatic ductal adenocarcinoma (PDA). Recent studies using genetically engineered mouse models, cell lineage tracing, single-cell sequencing and others have unraveled novel cellular and molecular insights in PDM formation and evolution. Those novel findings help better understand the cellular origins and functional significance of PDM and its regulation at cellular and molecular levels. Given that PDM represents the earliest pathological changes in PDA initiation and development, translational studies are beginning to define PDM-associated cell and molecular biomarkers that can be used to screen and detect early PDA and to enable its effective intervention, thereby truly and significantly reducing the dreadful mortality rate of PDA. This review will describe recent advances in the understanding of PDM biology with a focus on its underlying cellular and molecular mechanisms, and in biomarker discovery with clinical implications for the management of pancreatic regeneration and tumorigenesis.

Long-term in vitro culture of hamster pancreatic β-cells and induction of adenocarcinoma by treatment with N-nitrosobis(2-oxopropyl)amine

OBJECTIVES

Earlier studies indicated that hamster pancreatic ductal adenocarcinoma not only derives from ductal/ductular structures but also from cells within the islet. So far unidentified cells within the islet are responsive to the carcinogenic effect of N-nitrosobis (2-oxopropyl) amine (BOP) forming poorly differentiated ductal adenocarcinoma. However, studies indicated a major role of β-cells during carcinogenesis. To find out, if β-cells are the primary target cells of BOP and if they are capable to form ductal adenocarcinoma after malignant transformation, we established a long-term culture of undifferentiated cells deriving from isolated β-cells and treated them with BOP.

METHODS

Langerhans' islets from pancreata of Syrian golden hamsters were isolated and dispersed into single cells by dispase digestion. Cells were labeled with a highly specific β-cell surface antibody (K14D10) and these K14D10+ cells were extracted from the suspension by paramagnetic Dynabeads. Cells were cultured in vitro and treated with BOP. Untreated cells served as control.

RESULTS

K14D10+ cells formed a monolayer and produced insulin over a period of 28 days in culture. However, with time in culture they became undifferentiated with a higher proliferation rate and after about 60 days in culture BOP treated cells showed anchorage independent growth. These cells autotransplanted s.c. formed a well-differentiated ductal adenocarcinoma.

CONCLUSIONS

Pancreatic β-cells are the primary target of BOP without necessarily being embedded in the compound of the Langerhans' islet. With time in culture, they give rise to undifferentiated cells and after malignant transformation they are able to form ductal adenocarcinoma.

Islet cells contribute to pancreatic carcinogenesis in an animal model

OBJECTIVES

In the hamster model, pancreatic ductal adenocarcinoma develops after treatment with N-nitrosobis-(2-oxopropyl)amino (BOP). In this model, Langerhans islets play a central role in carcinogenesis. In contrast, treatment with BOP in rats and mice did not result in cancer development. We investigated whether pancreatic tumors develop after orthotopic implantation of hamster islets into severe combined immunodeficiency mouse pancreases and subsequent treatment with BOP. This occurrence would suggest that pancreatrophic carcinogens are metabolized by islet cells.

METHODS

Twenty-four severe combined immunodeficiency mice were separated into 2 groups of 12 animals. Five hundred hamster islets were implanted in the splenic lobe of the mouse pancreases in the treatment group, whereas animals of the control group received a sham operation. All animals were treated with BOP for 5 weeks. One year later, the animals were killed and investigated for tumors.

RESULTS

Carcinomas developed in 3 animals in the treatment group and none in the control group. The tumors displayed the histomorphological phenotype pancreatic ductal adenocarcinoma.

CONCLUSIONS

Islet cells seem to play a role in pancreatic carcinogenesis in this animal model and therefore represent useful targets for future investigations on the putative role of islet cells during pancreatic ductal adenocarcinoma tumorigenesis.

Progressive metaplastic and dysplastic changes in mouse pancreas induced by cyclooxygenase-2 overexpression

Cyclooxygenase-2 (COX-2) overexpression is an established factor linking chronic inflammation with metaplastic and neoplastic change in various tissues. We generated transgenic mice (BK5.COX-2) in which elevation of COX-2 and its effectors trigger a metaplasia-dysplasia sequence in exocrine pancreas. Histologic evaluation revealed a chronic pancreatitis-like state characterized by acinar-to-ductal metaplasia and a well-vascularized fibroinflammatory stroma that develops by 3 months. By 6 to 8 months, strongly dysplastic features suggestive of pancreatic ductal adenocarcinoma emerge in the metaplastic ducts. Increased proliferation, cellular atypia, and loss of normal cell/tissue organization are typical features in transgenic pancreata. Alterations in biomarkers associated with human inflammatory and neoplastic pancreatic disease were detected using immunohistochemistry. The abnormal pancreatic phenotype can be completely prevented by maintaining mice on a diet containing celecoxib, a well-characterized COX-2 inhibitor. Despite the high degree of atypia, only limited evidence of invasion to adjacent tissues was observed, with no evidence of distant metastases. However, cell lines derived from spontaneous lesions are aggressively tumorigenic when injected into syngeneic or nude mice. The progressive nature of the metaplastic/dysplastic changes observed in this model make it a valuable tool for examining the transition from chronic inflammation to neoplasia.

Proliferation, hyperplasia, neogenesis, and neoplasia in the islets of Langerhans

Pancreatic disease is responsible for significant morbidity and mortality as a result of pancreatic carcinoma and diabetes mellitus. Regulation of endocrine cell mass is thought to have a central role in the pathogenesis of both these diseases. Islet cell proliferation, hypertrophy, neogenesis, and apoptosis are the main determinants of endocrine cell mass in the pancreas, and their understanding has been improved by new clues of their genetic and molecular basis. Beta cells have attracted most research interest because of potential implications in the treatment of diabetes mellitus and hypoglycemic disorders. The processes that operate during pancreatic adaptation to a changing hormonal milieu are important in pancreatic carcinogenesis. There is evidence that somatostatin and its receptors are fundamental regulators of endocrine cell mass and are involved in islet tumorigenesis.

Pancreatic cancer microenvironment

Pancreatic ductal adenocarcinoma remains an extremely aggressive malignancy that is virtually therapy-resistant and has therefore one of the worst prognoses of all human cancers. The focus of research, which had been placed mostly on genetic and epigenetic alterations of the cancer cells themselves, has shifted gradually towards the microenvironment. The cancer microenvironment consists of various components, including fibroblasts, endothelial cells, immune cells, and endocrine cells, that interact with each other and the cancer cells in a complex fashion. This interplay has implications for pancreatic cancer cell growth, migration and invasion, angiogenesis, and immunological recognition of cancer cells. Evidence is accumulating that the cancer microenvironment plays an active role in disease progression, and efforts are being made to target this interplay between cancer cells and host cells to improve the outcome of this deadly disease.

Beta cell transdifferentiation does not contribute to preneoplastic/metaplastic ductal lesions of the pancreas by genetic lineage tracing in vivo

Inflammatory injury to the pancreas results in regeneration of normal tissue and formation of metaplastic lesions of a ductal phenotype. These metaplastic ductal lesions (MDL) are called tubular complexes (TC), mucinous metaplasia, or pancreatic intraepithelial neoplasia. Because they are regularly found in chronic pancreatitis and pancreatic cancer, their formation is thought to represent a step in inflammation-mediated carcinogenesis. Despite these lesions' ductal character, their origin is controversial. All known pancreatic cell lineages have been suggested as the origin. In vitro studies suggest that differentiated cells in the pancreas remain highly plastic and can transdifferentiate as a mechanism of regeneration and metaplasia. In vivo studies suggest that islets, specifically beta cells, may be the cell of origin. However, in vitro studies are subject to ductal cell contamination, and previous in vivo studies interpret static data rather than direct evidence. Using genetic lineage tracing in vivo, we investigate whether transdifferentiation of beta cells contributes to regeneration or metaplasia in pancreatitis. RIP-CreER;Z/AP mice were used to heritably tag beta cells in the adult pancreas. Injury by cerulein pancreatitis resulted in regeneration of normal tissue and metaplasia with formation of two distinct types of TC and mucinous lesions. Lineage tracing revealed that none of these MDL are of beta cell origin; nor do beta cells contribute to regeneration of normal acinar and ductal tissue, which indicates that the plasticity of differentiated pancreatic islet cells, suggested by earlier static and in vitro studies, plays no role in regeneration, metaplasia, and carcinogenesis in vivo.

Expression of Oct4, a stem cell marker, in the hamster pancreatic cancer model

BACKGROUND

Oct4 has been shown to present a stem cell marker that is expressed in embryonic cells and in germ cell tumors. Recently, its expression in a few human tissues and cancer cells has been reported. Because in the hamster pancreatic cancer model most tumors develop from within islets presumably from stem cells, we investigated the expression of Oct4 in this model.

METHODS

Two normal pancreases and 15 pancreatic cancers induced by N-nitrosobis(2-oxypropyl)amine (BOP) were processed for immunohistochemistry using a monoclonal Oct4 antibody at a concentration of 1:500.

RESULTS

In the normal pancreas, Oct4 was expressed only in islet cells in a diffuse cytoplasmic pattern. No nuclear staining was found in any cells. In 14 of the pancreatic cancers, nuclear staining was detected in many cells or in small foci. Diffuse cytoplasmic but no nuclear staining was found in one tumor and a mixed Golgi type and nuclear staining in two cases. Nuclear staining was also identified in early intrainsular ductular and in Ca in situ lesions.

CONCLUSIONS

BOP reactivates the Oct4 gene and can be considered an early tumor marker in this model.

Are there any stem cells in the pancreas?

A vast number of studies indicate the presence of stem/progenitor cells virtually in all tissues in adult organs, particularly in bone marrow. Recent studies, however, cast doubt about the existence of true stem cells in adult tissue. The complex integrity of several cells with distinct morphologic and functional properties in the mature pancreas confers an appropriate status for stem cell research. Several different types of cells residing in the islets or in the ductal epithelium have been proposed as adult pancreatic stem cells or progenitor cells. However, these reports do not provide conceivable proof for the presence of true pancreatic stem cells. On the other hand, there is considerable evidence indicating transdifferentiation of all adult pancreatic cells into each other, and under proper conditions, to nonpancreatic cells including oncocytes and hepatocytes. Observations pertaining to the putative pancreatic stem cells, transdifferentiation ability of the differentiated mature pancreatic cells in the normal and diseased pancreas will be discussed, and our own findings supporting the transdifferentiation pathway are presented in this article.

Relationship between ?Gal epitope expression and decrease of tumorigenicity in pancreatic adenocarcinoma model

The alphaGal epitope is a carbohydrate structure, Galalpha1,3Galbeta1,4GlcNAc-R, synthesized on glycoconjugates in many mammals by alpha1,3galactosyltransferase. Humans do not express this epitope and present in serum large amounts of naturally occuring antibodies, which recognize the alphaGal epitopes and participate in the hyperacute rejection of xenograft. Studies indicated that the fundamental mechanism of hyperacute rejection involving the alphaGal epitope expression can be used in cancer therapy. We have previously suggested that the alphaGal epitope expression by human pancreatic tumoral cells could decrease the tumorigenic behavior of these cells. To determine whether the expression of the alphaGal epitope can modify the tumorigenicity of pancreatic cancer cells, we used a Syrian golden hamster pancreatic adenocarcinoma experimental model. The expression of alphaGal epitopes in the Syrian golden hamster pancreatic cancer cell line HaP-T1 was obtained by selecting stable cell clones transfected with murine alpha1,3galactosyltransferase gene. The alphaGal epitope expression resulted in a delay in the tumoral development of HaP-T1 cells in vivo after allograft transplantation of Syrian golden hamsters (2.5-fold, P < 0.05) and of nude mice. This result is associated with an 100% increase in survival time of nude mice bearing tumors expressing the alphaGal epitope. Our results confirm that the cell surface expression of alphaGal epitope decreases the tumorigenic behavior of pancreatic cancer cells. This novel property may be useful for the development of cancer gene immunotherapy strategy.

Tissue-culture surfaces with mixtures of aminated and fluorinated functional groups. Part 2. Growth and function of transgenic rat insulinoma cells (betaG I/17)

Interactions of transplantable cells with synthetic polymers can influence the function of biohybrid artificial organs. This study explored growth and secretion of human insulin by betaG I/17 cells cultured on surfaces bearing diamine groups (N2), trifluoropropyl groups (F3) and mixtures of the two. Cells cultured on high-F3 and high-N2 surfaces spread well, grew rapidly and produced >1.8 mol lactate per mol glucose consumed, closely resembling cells grown on the permissive control, glass. On one mixed surface, with a molar ratio of 33 N2 groups:67 F3 groups, cells had a lower lactate/glucose ratio, adopted a rounded form, grew slowly and were quick to form emergent aggregates, similar to cultures on the inhibitory control, untreated polystyrene. Cultures on surfaces with higher F3 content secreted the most insulin and, in the case of the highest-F3 surface, showed improved responsiveness to secretagogues. Hormone secretion was roughly 50% greater when cells were grown on F3 surfaces conditioned by earlier cultures of betaG I/17. Incubation of conditioned surfaces with high concentrations of a polyclonal anti-laminin serum prior to re-plating partially abolished this improvement in secretory function. Polymers bearing trifluoropropyl groups appear to be attractive candidates for use in the artificial endocrine pancreas. Surface coatings that include laminin might promote function of transgenic insulinoma cells in vitro and in vivo.

Diabetes and its relationship to pancreatic carcinoma

INTRODUCTION

The mechanism of impaired glucose metabolism that develops in most patients with pancreatic cancer (PC) is obscure and the association between PC and diabetes is controversial. According to the published data, about 70% of patients with PC have an impaired glucose tolerance (IGT) or frank diabetes, whereas 30% do not. Up to 60% of the patients with IGT or diabetes show improvement in glucose metabolism after surgery, whereas other patients show only mild or no improvement.

AIM

To investigate our theory that there are three types of PC: 1) PC not associated with IGT or diabetes (IGT- subtype, approximately 20-30%); 2) PC associated with IGT or diabetes (IGT+ subtype, approximately 70-80%), in which the abnormality improves postoperatively (IGT+/- subtype, approximately 40-60%); or 3) PC associated with IGT or diabetes that does not improve after the tumor resection (IGT+/+ subtype, approximately 40-60%).

METHODOLOGY AND RESULTS

The review of the literature and our own experience, which is the subject of this article, suggests that the reason for impaired glucose metabolism in most patients is the alteration of islet cells, from which, in our view, cancer cells develop. There is a good possibility that the altered islet cells, and/or tumors derived from them, produce diabetogenic substances. The extent of the islet alteration (i.e., focal or diffuse) may determine whether the removal of the tumor alone can improve the metabolic alteration.

CONCLUSION

The elucidation of the mechanism is of immense importance for providing an early tumor marker and for developing preventative and therapeutic modalities.

Are islet cells the gatekeepers of the pancreas?

The pancreas is one of the body's most complex tissues composed of a mixture of endocrine and exocrine cell components. Although, islets comprise 1-2% of the pancreatic volume, there is some evidence that they control the function and the integrity of the pancreas and play the role of a gatekeeper. This review intends to highlight the importance of islet cells, not only for glucose metabolism, but also for their significant role in drug metabolism and diseases, especially in pancreatic cancer.

What is the origin of pancreatic adenocarcinoma?

The concept of pancreatic cancer origin is controversial. Acinar, ductal or islet cells have been hypothesized as the cell of origin. The pros and cons of each of these hypotheses are discussed. Based on the world literature and recent observations, pancreatic cells seem to have potential for phenotypical transdifferentiation, i.e ductal-islet, ductal-acinar, acinar-ductal, acinar-islet, islet-acinar and islet-ductal cells. Although the possibility is discussed that cancer may arise from either islet, ductal or acinar cells, the circumstances favoring the islet cells as the tumor cell origin include their greater transdifferentiation potency into both pancreatic and extrapancreatic cells, the presence of a variety of carcinogen-metabolizing enzymes, some of which are present exclusively in islet cells and the growth factor-rich environment of islets.

Abnormal differentiation of islet cells in pancreatic cancer

Pancreatic cancer in many patients is associated with altered glucose metabolism and abnormalities in pancreatic islet hormones at serum and tissue levels. Our previous studies have indicated a tendency of islet cells to differentiate toward ductal cell lineage, but the specificity of these findings for pancreatic cancer was not investigated. In the present study, we examined the immunoreactivity of pancreatic islets to antibodies against tumor-associated antigens DU-PAN-2, TAG-72 and CA19-9 in tissues from the normal pancreas, chronic pancreatitis and pancreatic cancer. Although no immunoreactive islet cells were found in the 12 normal pancreases and 20 chronic pancreatitis patients, 25 of 37 pancreatic cancer tissues showed the expression of these antigens, primarily CA19-9 and TAG-72, where the number of immunoreactive cells varied considerably from case to case. In 4 cases over 50% and in 2 of them more than 75% of the islets showed positive staining of 60-70% of islet cells within each islet. The presence of intrainsular ductular structures expressing the same antigen as the surrounding islet cells suggested transformation of antigen expressing islet cells to ductal cells. All but four islets were within or around the cancer favoring the notion that factors produced by cancer cells are responsible for the altered islet cell differentiation.

Pancreatic cell lines: a review

Pancreatic cancer has an extremely poor prognosis and lacks early diagnostic and therapeutic possibilities, mainly because of its silent course and explosive fatal outcome. The histogenesis of the disease and early biochemical and genetic alterations surrounding carcinogenesis are still controversial. In vitro studies offer a useful tool to study physiologic, pathophysiologic, differentiation, and transformation processes of cells and to understand some of these shortcomings. The extreme difficulties in isolating individual pancreatic cells and their purification by maintaining their native characteristics have limited research in this area. This review is intended to present and discuss the current availability of rodent and pancreatic cell lines, their differences as well as the difficulties, limitations, and characteristics of these cultured cells. Discussed are in vitro models; ductal, islet, and acinar cell culture; cell differentiation; cell transformation, including genetic and chromosomal alterations; as well as tumor cell markers. Also addressed are the advantages and problems associated with the cell culture in humans and rodents. Advancements in tissue culture technique and molecular biology offer steady progress in this important line of research. The improved methods not only promise the establishment of beta-cell cultures for the treatment of diabetes, but also for studying sequential genetic alterations during pancreatic carcinogenesis and in understanding the tumor cell origin.

In vitro induction of giant cell tumors from cultured hamster islets treated with N-Nitrosobis(2-Oxopropyl)amine

Giant cell carcinoma of the pancreas is a rare tumor. Its histogenesis is still controversial. In a Syrian hamster pancreatic cancer model, tumors similar to human giant cell carcinomas have been induced at an extremely low rate of incidence and after the use of high doses of pancreatic carcinogens. Thus far no tumors of giant cell type have been induced by the in vitro treatment of hamster pancreatic ductal cells with the potent pancreatic carcinogen N-nitrosobis(2-oxopropyl)amine (BOP). In the present study we report the induction of giant cell carcinoma from hamster islets treated with BOP in vitro. The results suggest that in hamsters some component of islet cells, probably stem cells, are the origin of giant cell carcinoma.