Early diagnosis of pancreatic cancer: neutrophil gelatinase-associated lipocalin as a marker of pancreatic intraepithelial neoplasia

Pancreatic cancer is a highly lethal malignancy with a dismal 5-year survival of less than 5%. The scarcity of early biomarkers has considerably hindered our ability to launch preventive measures for this malignancy in a timely manner. Neutrophil gelatinase-associated lipocalin (NGAL), a 24-kDa glycoprotein, was reported to be upregulated nearly 27-fold in pancreatic cancer cells compared to normal ductal cells in a microarray analysis. Given the need for biomarkers in the early diagnosis of pancreatic cancer, we investigated the expression of NGAL in tissues with the objective of examining if NGAL immunostaining could be used to identify foci of pancreatic intraepithelial neoplasia, premalignant lesions preceding invasive cancer. To examine a possible correlation between NGAL expression and the degree of differentiation, we also analysed NGAL levels in pancreatic cancer cell lines with varying grades of differentiation. Although NGAL expression was strongly upregulated in pancreatic cancer, and moderately in pancreatitis, only a weak expression could be detected in the healthy pancreas. The average composite score for adenocarcinoma (4.26+/-2.44) was significantly higher than that for the normal pancreas (1.0) or pancreatitis (1.0) (P<0.0001). Further, although both well- and moderately differentiated pancreatic cancer were positive for NGAL, poorly differentiated adenocarcinoma was uniformly negative. Importantly, NGAL expression was detected as early as the PanIN-1 stage, suggesting that it could be a marker of the earliest premalignant changes in the pancreas. Further, we examined NGAL levels in serum samples. Serum NGAL levels were above the cutoff for healthy individuals in 94% of pancreatic cancer and 62.5% each of acute and chronic pancreatitis samples. However, the difference between NGAL levels in pancreatitis and pancreatic cancer was not significant. A ROC curve analysis revealed that ELISA for NGAL is fairly accurate in distinguishing pancreatic cancer from non-cancer cases (area under curve=0.75). In conclusion, NGAL is highly expressed in early dysplastic lesions in the pancreas, suggesting a possible role as an early diagnostic marker for pancreatic cancer. Further, serum NGAL measurement could be investigated as a possible biomarker in pancreatitis and pancreatic adenocarcinoma.

Class III beta-tubulin, a marker of resistance to paclitaxel, is overexpressed in pancreatic ductal adenocarcinoma and intraepithelial neoplasia

AIMS

Class III beta-tubulin (TUBB3) reduces microtubule stability and confers resistance to microtubule-stabilizing taxanes, including paclitaxel and docetaxel. Pancreatic ductal adenocarcinomas show limited responsiveness to taxanes, but little is known of the underlying mechanisms. The aim of this study was to examine TUBB3 expression in pancreatic cancer cell lines, invasive pancreatic adenocarcinoma and pancreatic intraepithelial neoplasia (PanIN).

METHODS AND RESULTS

Reverse transcriptase-polymerase chain reaction and Western blot were used to study TUBB3 expression in pancreatic cancer cell lines. Immunohistochemistry was employed to assess TUBB3 in pancreatic cancer specimens, including 75 invasive adenocarcinomas and 41 PanIN precursor lesions. TUBB3 was undetectable in non-neoplastic ducts of the pancreas. In contrast, the vast majority (78-93%) of pancreatic ductal adenocarcinomas demonstrated either diffuse or focal TUBB3 expression. TUBB3 was found to increase progressively in PanIN lesions from 3/16 of PanIN-1 (19%), 5/17 of PanIN-2 (29%) to 5/8 of PanIN-3 lesions (63%).

CONCLUSIONS

TUBB3 is expressed in most pancreatic ductal adenocarcinomas, possibly accounting for the suboptimal response of these tumours to microtubule-stabilizing agents. Up-regulation of TUBB3 in PanIN lesions suggests that microtubule dysfunction is an early feature of this disease. TUBB3 immunohistochemistry could potentially help identify pancreatic cancer patients lacking TUBB3 expression who might benefit from taxane therapy.

Retinoic acid can induce markers of endocrine transdifferentiation in pancreatic ductal adenocarcinoma: preliminary observations from an in vitro cell line model

BACKGROUND AND HYPOTHESIS

The pancreatic ductal adenocarcinoma (HPAF) cells have a multipotent stem cell potential. It was hypothesised that all-trans-retinoic acid (atRA) can induce transdifferentiation of these cells into cells with an endocrine phenotype.

MATERIAL AND METHODS

To explore this hypothesis, an in vitro system of cells was established. Some cells were treated with atRA at concentrations of 100 nmol/l (non-apoptosis-inducing) and 5 micromol/l (apoptosis-inducing) and harvested. Cells were examined for cell cycle kinetics, apoptosis (terminal deoxynucleotidyl transferase assay and p53 protein expression) and immunomorphological features of redifferentiation (MUC1 and DUPAN-2) and endocrine transdifferentiation (insulin, somatostatin, glucagon, neurone-specific enolase) by using immunoperoxidase staining methods. Levels of insulin, transforming growth factor (TGF) beta2, TGFalpha and epidermal growth factor receptor (EGFR) were measured by enzyme-linked immunosorbent assay (ELISA). The vehicle-treated cells served as a control group.

RESULTS

When compared with untreated cells, cells treated with 100 nmol/l and 5 micromol/l atRA were observed to show (1) decreased proliferative activity (cpm) as indicated by decreased incorporation of thymidine labelled with hydrogen-3; (2) cell cycle arrest; (3) increased apoptotic activity associated with p53 protein overexpression; (4) upregulated expression of the transdifferentiation and redifferentiation markers; (5) morphological changes indicative of transdifferentiation (increased cell size and appearance of dendrites); (6) decreased production of EGFR; (7) upregulation of TGFalpha and TGFbeta2; and (8) increase in basal and glucose-induced insulin secretion.

CONCLUSIONS

Functional endocrine transdifferentiation can be induced in HPAF lines by atRA. Further investigations are mandated to explore the underlying mechanisms of this transdifferentiation and to explore its in vivo extrapolation.

Diabetes mellitus: a risk factor for pancreatic cancer?

The relationship between pancreatic cancer (PC) and diabetes is controversial. While some investigators assume that type II diabetes is a predisposition to PC, recent data argue that diabetes and altered glucose metabolism are a consequence of PC, and yet, the clinical presentation of the altered glucose metabolism in these patients varies considerably. Around 70% of patients with PC have impaired glucose tolerance (IGT) or frank diabetes. Of these, nearly 60% show an improvement of IGT or diabetes after surgery, whereas the rest show only mild or no improvement. It appears that biologically there are three types of PC: (1) PC not associated with IGT or diabetes; (2) PC associated with IGT or diabetes in which the abnormality improves postoperatively; (3) PC associated with IGT or diabetes in which the abnormality does not improve postoperatively. Based on our own studies, we suggest that the reason for impaired glucose metabolism in most patients is the alteration of islet cells either by the carcinogen directly, or by diabetogenic substances released by cancer cells. The extent of the islet alteration (i.e. focal or diffuse) may determine whether the removal of tumor alone can improve the metabolic alteration. The elucidation of the mechanism is of immense importance for providing an early tumor marker and for developing preventative or therapeutic modalities.

MUC4 mucin expression in human pancreatic tumours is affected by organ environment: the possible role of TGFbeta2

MUC4 is highly expressed in human pancreatic tumours and pancreatic tumour cell lines, but is minimally or not expressed in normal pancreas or chronic pancreatitis. Here, we investigated the aberrant regulation of MUC4 expression in vivo using clonal human pancreatic tumour cells (CD18/HPAF) grown either orthotopically in the pancreas (OT) or ectopically in subcutaneous tissue (SC) in the nude mice. Histological examination of the OT and SC tumours showed moderately differentiated and anaplastic morphology, respectively. The OT tumour cells showed metastases to distant lymph nodes and faster tumour growth (P<0.01) compared to the SC tumours. The MUC4 transcripts in OT tumours were very high compared to the undetectable levels in SC tumours. The SC tumour cells regained their ability to express MUC4 transcripts after in vitro culture. Immunohistochemical analysis using MUC4-specific polyclonal antiserum confirmed the results obtained by Northern blot analysis. Interestingly, the OT tumours showed expression of TGFβ2 compared to no expression in SC, suggesting a possible link between MUC4 and TGFβ2. The MUC4 expression, morphology, and metastasis of human pancreatic tumour cells are regulated by a local host microenvironment. TGFβ2 may serve as an interim regulator of this function.

Immortalization with telomerase of the Nestin-positive cells of the human pancreas

Cells expressing the neuronal stem cell marker Nestin are present in the human pancreas but the biological role of these cells has yet to be resolved. We report here the establishment with the catalytic subunit of human telomerase (hTERT) of a line of normal human cells representing this cell type. Primary human cells derived from the ducts of the pancreas were transduced with an hTERT cDNA. The infected cells became positive for telomerase, failed to senesce, and were still proliferating after more than 150 doublings. The immortalized cells were positive for the expression of Nestin (at both the mRNA and protein levels) and were found to be free of cancer-associated changes: diploid and expressing wild type p16(INK4a), p53, and K-Ras. An established line of normal human cells representing this cell type should be of great value to help define the biological properties of this novel cell type.

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.

Identification and sequencing of the Syrian Golden hamster (Mesocricetus auratus) p16(INK4a) and p15(INK4b) cDNAs and their homozygous gene deletion in cheek pouch and pancreatic tumor cells

Previous studies have shown that the p16(INK4a) tumor suppressor gene is inactivated in up to 98% of human pancreatic cancer specimens and 83% of oral squamous cell carcinomas. Inactivation of the related p15(INK4b) gene has also been identified in a number of tumors and cell lines, however, its role as an independent tumor suppressor remains to be elucidated. Chemically-induced tumors in the Syrian Golden hamster (Mesocricetus auratus) have been shown to be excellent representative models for the comparative development and progression of a number of human malignancies. The purpose of this study was to determine the importance of the p16(INK4a) and p15(INK4b) genes in two experimental hamster models for human pancreatic and oral carcinogenesis. First, hamster p16(INK4a) and p15(INK4b) cDNAs were cloned and sequenced. The hamster p16(INK4a) cDNA open reading frame (ORF) shares 78%, 80%, and 81% identity with the human, mouse, and rat p16(INK4a) sequences, respectively. Similarly, the hamster p15(INK4b) cDNA ORF shares 82% and 89% sequence identity with human and mouse p15(INK4b), respectively. Second, a deletion analysis of hamster p16(INK4a) and p15(INK4b) genes was performed for several tumorigenic and non-tumorigenic hamster cell lines and revealed that both p16(INK4a) and p15(INK4b) were homozygously deleted in a cheek pouch carcinoma cell line (HCPC) and two pancreatic adenocarcinoma cell lines (KL5B, H2T), but not in tissue matched, non-tumorigenic cheek pouch (POT2) or pancreatic (KL5N) cell lines. These data strongly suggest that homozygous deletion of the p16(INK4a) and p15(INK4b) genes plays a prominent role in hamster pancreatic and oral tumorigenesis, as has been well established in correlative studies in comparable human tumors. Furthermore, this study supports the comparative importance of the hamster pancreatic and cheek pouch models of carcinogenesis in subsequent mechanistic-, therapeutic-, and preventive-based studies aimed at providing important translational data applicable to pancreatic adenocarcinoma and oral squamous cell carcinoma in humans.

Expression of nerve growth factors in pancreatic neural tissue and pancreatic cancer

One of the characteristics of pancreatic cancer is its tendency to invade neural tissue. We hypothesized that the affinity of cancer cells for nerve tissue is related to the presence of growth factors in neural tissue and their receptors in cancer cells. Sections of pancreatic cancer and normal pancreatic tissue were examined by immunohistochemistry for the expression of the neurotrophins NGF, BDNF, NT-3, NT-4, and their receptors TrkA, TrkB, and TrkC, as well as the low-affinity receptor, p75NTR. TrkA expression was found in duct, islet, and cancer cells; TrkB was found in the alpha-cells of the islet only. The anti-pan-Trk antibody (TrkB3), which is presumed to recognize all three receptors, immunoreacted with duct and acinar cells in normal tissue and with cancer cells. The staining with TrkC was similar to that of TrkA. The low-affinity receptor p75NTR was expressed in the neural tissue and in scattered duct cells of the normal tissue only. Duct and acinar cells, as well as neural tissue and cancer cells, showed weak to strong immunoreactivity with NGF. NT-3 expression was noted in capillary endothelia and erythrocytes. NT-4 showed specific staining for ductule cells. The expression and distribution of neurotrophins and their receptors suggest their role in the potential of pancreatic cancer cells for neural invasion.

Experimental animal models in pancreatic carcinogenesis: lessons for human pancreatic cancer

The silent course of pancreatic cancer and its explosive fatal outcome have hindered studies of tumor histogenesis and the identification of early biochemical and genetic alterations that could help to diagnose the disease at a curable stage and develop therapeutic strategies. Experimental animal models provide important tools to assess risk factors, as well as preventive and therapeutic possibilities. Although several pancreatic cancer models presently exist, only models that closely resemble human tumors in morphological, clinical, and biological aspects present useful media for preclinical studies. Because an estimated 70% of human tumors are induced by carcinogens and because a significant association has been found between cigarette smoking and pancreatic cancer, chemically induced models are of particular value. Moreover, in such models the etiology, modifying factors, effects of diets, and naturally occurring products can be studied and early diagnostic, preventive, and therapeutic possibilities sought out. Many of the existing models are described in this review, and the advantages and shortcomings of each model and their clinical implications are discussed.

Transdifferentiation of human islet cells in a long-term culture

It has been established that ductal cells or precursor cells within the ductal tree of the pancreas can differentiate into islet cells. Although islet cells can also form exocrine cells, it is unclear whether they arise from precursor (stem) cells or from mature endocrine cells by transdifferentiation. Using a defined culture medium and technique for islet purification, for the first time we were able to maintain human islets in culture for more than a year. Multilabeling immunohistochemical and immunoelectron microscopic examination of the islets at different days of culture using islet cell markers (antibodies to hormones, neuron-specific enolase, chromogranin A) and ductal cell markers (cytokeratins 7 and 19, carbonic anhydrase II, DU-PAN2, CA 19-9, and MUC1) revealed that endocrine cells gradually transdifferentiate to ductal, acinar, and intermediary cells. Although islet hormone secretion ceased after day 28 in culture, endocrine cells were still detectable at day 60. However, later, all endocrine and exocrine cells were replaced by undifferentiated cells that expressed neuron-specific enolase, chromogranin A, laminin, vimentin, cytokeratin 7 and 19, alpha-1-antitrypsin, transforming growth factor-alpha, and epidermal growth factor receptor. Our data thus show that, under proper conditions, human islets can be maintained in vitro over a long period and that, in the culture condition, islet cells seem to transdifferentiate to exocrine cells and undifferentiated cells, which may be considered pancreatic precursor (stem) cells.

Pacinian corpuscle in the human pancreas

During our systematic examination of the distribution of cytochrome P450 enzymes in the normal and diseased human pancreas, we observed a Pacinian corpuscle in a serial section of a tissue from a pancreatic cancer patient. We report the histologic and immunohistochemical patterns in this corpuscle and review the literature. The Pacinian corpuscle was situated within the pancreas of a 76-year-old woman with cancer in the head of the pancreas. We could demonstrate immunoreactivity within the corpuscle for the neurofilament protein. neuron-specific enolase, S-100 Protein, and for four cytochrome P450-isozymes. The possible function of Pacinian corpuscles in the mammalian and human pancreas is discussed.

Increased expression of glutathione S-transferase-pi in the islets of patients with primary chronic pancreatitis but not secondary chronic pancreatitis

The mechanism of tissue alteration in chronic pancreatitis (CP) is still unclear. Different hypotheses have been discussed, including increasing oxidant stress in the acinar cells, often as a result of exposure to xenobiotics. To evaluate the role of oxidative stress in CP, the authors investigated the expression of the drug-metabolizing phase II enzyme, glutathione S-transferase-pi (GST-pi), in the pancreatic tissue of patients with CP and compared it with the healthy pancreatic tissue from age-matched donors. Pancreatic tissue from patients with secondary CP resulting from ductal obstruction by pancreatic cancer (PC) was also examined. The percentage of cells immunoreacting with anti-GST-pi was counted within 15 randomly selected islets in each slide of the three groups. In all specimens, ductal and ductular cells, and in PC, cancer cells, expressed GST-pi in a moderate intensity. Acinar cells did not stain. Various numbers of islet cells in each of the three groups were stained strongly. More islet cells expressed GST-pi in CP (42%) than in healthy pancreatic tissue (16%, p < 0.001) or PC (17%, p < 0.001). Our results imply an important role of islet cells in the metabolism of substances, which are the substrate for GST-pi, and lend support to the hypothesis of oxidative stress as the cause of CP.

Prevention of pancreatic cancer induction in hamsters by metformin

BACKGROUND AND AIMS

Our previous study suggested that the known promotional effect of a high fat diet, which in hamsters induces peripheral insulin resistance, is related to a compensatory proliferation of islet cells. The present study was to examine whether the prevention of islet cell proliferation can inhibit the promotional effect of a high-fat diet in pancreatic carcinogenesis.

METHODS

Two groups of high fat-fed hamsters were used. One group received Metformin in drinking water for life (HF+Met group), and the other group served as a control (HF group). At the time when the normalization of the plasma insulin level was expected, all hamsters were treated with the pancreatic carcinogen, N-nitrosobis-(2-oxopropyl)amine, and the experiment was terminated 42 weeks later.

RESULTS

Although 50% of the hamsters in the high-fat group developed malignant lesions, none was found in the HF+Met group (P < 0.05). Also, significantly more hyperplastic and premalignant lesions, most of which were found within the islets, were detected in the high-fat group (8.6 lesions/hamster) than in the HF+Met group (1.8 lesions/hamster).

CONCLUSIONS

The results lend further support on the significant role of islet cells in pancreatic carcinogenesis and may explain the association between pancreatic cancer and obesity, which is usually associated with peripheral insulin resistance.

Inhibition of skin carcinomas but not papillomas by sphingosine, N-methylsphingosine, and N-acetylsphingosine

The sphingoid base backbones of sphingolipids are highly bioactive compounds that affect cell growth, differentiation, diverse cell behaviors, and programmed cell death. Therefore, the efficacy of sphingosine (SPH) and the analogs N-acetylsphingosine (NAS), N-methylsphingosine (NMS), octylamine (OCT), and sterylamine (STR) in the prevention of skin cancer was assessed in female Sencar mice by measuring effects on the induction of epidermal ornithine decarboxylase (ODC) activity and hyperplasia by 12-O-tetradecanoylphorbol-13-acetate (TPA) and effects on the induction of skin tumors by 7, 12-dimethylbenz[a]anthracene (DMBA) and TPA. ODC was measured in the shaved dorsal skin of mice treated topically with 0.05-20 mumol of these compounds 30 minutes before application of 8.5 nmol of TPA in 0.2 ml of acetone. ODC activity was inhibited by > or = 5 mumol of SPH and STR, > or = 10 mumol of NAS and NMS, and 20 mumol of OCT. In contrast, the induction of hyperplasia was not inhibited by application of these compounds 30 minutes before TPA. Two carcinogenesis studies were conducted with 10 nmol of DMBA as the initiator and 3.2 nmol of TPA (2x/wk for 15 wk) as the promoter. In the first study, NAS, NMS, OCT, and STR (0.05 and 0.5 mumol) were applied before each TPA application. Papilloma incidence and multiplicity were not inhibited, but NAS (0.05 mumol) and NMS (0.05 and 0.50 mumol) increased cancer-free survival. In the second experiment, SPH, NAS, and NMS (0.05 and 0.5 mumol) were applied 30 minutes before each TPA treatment and twice weekly for 10 weeks after the final TPA treatment. Papilloma incidence and multiplicity were not inhibited; however, the proportion of mice without carcinoma was increased by both doses of SPH and by 0.5 mumol of NAS. Thus low doses of sphingolipids that were not effective in inhibiting ODC activity, reducing hyperplasia, or preventing epidermal papilloma development were, nonetheless, effective in inhibiting carcinoma development.

The patterns of extrainsular endocrine cells in pancreatic cancer

Abnormal glucose tolerance and frank diabetes mellitus develop in up to 80% of pancreatic cancer patients. Islets within these tumors show a decreased number of beta cells and increased number of alpha cells. The reduced number of beta cells could induce beta cell neogenesis in extrainsular tissue to compensate for the loss of insulin in islets. On the other hand, because the beta cell depletion in pancreatic cancer seems to be the effect of substances released by cancer cells, suppression of extrainsular endocrine cells is expected. We compared the pattern of extrainsular endocrine cells in pancreatic cancer patients with normal pancreas as well as chronic pancreatitis, which is known to be associated with impaired glucose tolerance or frank diabetes. As in the normal tissue, extrainsular endocrine cells were found in chronic pancreatitis and pancreatic cancer. However, in the chronic pancreatitis specimens insulin cells were the predominant cell type, whereas in pancreatic cancer specimens more glucagon than insulin cells were found, although the differences were statistically insignificant. Thus, our results indicate that the alteration of beta cells in pancreatic cancer patients is mainly restricted to the endocrine cells within the islets and that there is no compensatory proliferation of beta cells.

Early changes in islet hormone secretion in the hamster pancreatic cancer model

The diabetic state that is seen at a high frequency in association with pancreatic cancer is characterized by elevated plasma levels of several islet hormones and by marked insulin resistance. Both the diabetic state and insulin sensitivity improve after tumor removal by sub-total pancreatectomy. Impaired glucose tolerance has also been found in the hamster pancreatic cancer model, but conflicting data regarding islet function have been reported. In order to further investigate islet function and secretion during early development of pancreatic cancer, we measured the concentrations of insulin, glucagon, somatostatin, and islet amyloid polypeptide (IAPP) in plasma, pancreatic tissue, and secretin-stimulated pancreatic juice at 12 and 27 weeks after the ductal-cell-specific carcinogen, BOP had been used to induce tumors in Syrian golden hamsters. At 12 weeks after BOP, plasma glucagon levels were significantly increased. An exaggerated plasma-glucose response and concomitant hyperinsulinemia were observed at 27 but not 12 weeks after BOP. Plasma IAPP concentrations, but not glucagon or somatostatin, were elevated at 27 weeks. Tissue concentrations of IAPP were substantially reduced in BOP-treated hamsters at 27 weeks. No differences in hormone concentrations were seen in pancreatic juice from the two groups at either of the two time points investigated. The study showed that islet hormone changes accompany the early development of pancreatic tumors in the hamster pancreatic model. The hormone changes and apparent insulin resistance resemble the metabolic changes found in humans with pancreatic cancer.

Combination of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and actinomycin D induces apoptosis even in TRAIL-resistant human pancreatic cancer cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a novel member of the tumor necrosis factor superfamily of cytokines that induces cell death by apoptosis. TRAIL has been shown to be effective in almost two-thirds of solid tumors tested thus far, but its effect on pancreatic cancer cells is unknown. We tested the effect of TRAIL on seven human pancreatic cancer cell lines (HPAF, Panc1, Miapaca2, Bxpc3, Panc89, SW979, and Aspc1) in vitro. Of these cell lines, all but Aspc1 showed a significant dose-dependent increase in apoptosis. The apoptotic rate, as detected by a terminal deoxynucleotidyl transferase-mediated nick end labeling assay, was highest in Bxpc3 (71.5%), followed by HPAF (38.0%), Miapaca2 (24.9%), Panc1 (16.1%), Panc89 (15.8%), SW979 (13.9%), and Aspc1 (5.2%). Multiple treatments were more effective than a single treatment and caused a sustained and profound cell death in all but Aspc1 cells. There was no correlation between the effect of TRAIL and the differentiation grade of the cell lines, p53 mutation, or bcl-2 or bax expression. The resistance of Aspc1 cells to TRAIL was not related to the lack of TRAIL receptors. The combination of actinomycin D and TRAIL induced an almost complete lysis of Aspc1 cells, whereas actinomycin D alone had no effect on cell survival but inhibited the expression of the Flice inhibitory protein, which is assumed to play a role in the apoptotic pathway of TRAIL. Thus, the combination of actinomycin D and TRAIL appears to be a promising approach for the therapy of pancreatic cancers resistant to TRAIL.

Maintenance of human islets in long-term culture

The long-term maintenance of human islets in culture has remained a challenge. Despite advancements in culture techniques, human islets proved to have a short life span in vitro. For the first time, we have succeeded in maintaining human islets in a defined culture medium for more than 12 months. Freshly isolated islets from a 38-year-old donor were cultured in M3:5 medium and placed on a rocker for 14 days to remove contaminated exocrine and mesenchymal cells which attached to the bottom. The floating islets were purified by daily hand-picking and transfer into fresh medium. After 14 days, purified islets were allowed to attach to the bottom of the flasks and to expand. At various time points, islets were examined immunohistochemically and electron microscopically, and the secretion of islet hormones and their mRNA were determined by radioimmunoassay and reverse transcriptase polymerase chain reaction, respectively. Within seven days of culture, ductular and acinar cells developed within the initially normal islets. With time, exocrine cell types expanded while the number of the endocrine cells and their secretion decreased. At day 60, only a few endocrine cells were identifiable, whereas most of the cells appeared undifferentiated and expressed cytokeratin 7 and 19, neuron specific enolase, tomato lectin, phaseolus leucoagglutinin, laminin, and vimentin. After 60 days, the culture consisted entirely of undifferentiated cells which could be maintained in culture for 270 days before they became senescent. This is the first report on the long-term maintenance of human islet cells in culture and allows an insight into the complex process of endocrine cell differentiation.

Establishment of human pancreatic ductal cells in a long-term culture

Cultivation and preservation of human pancreatic ductal cells have remained a challenge. With a defined culture medium and refinement of culturing techniques, we have been able to maintain human pancreatic ductal cells without any genetic manipulation in culture for more than 16 months. Freshly isolated ductal fragments were placed on a rocker in M3:5 medium free of collagen for 14 days to remove fibroblasts and endocrine cells before allowing them to attach. The cells produced an excessive amount of mucin and expressed the duct specific cytokeratins (CK) 7 and 19, DU-PAN2, CA19-9, carbonic anhydrase II (CA II), and secretin receptors. During the course of the culture, however, the cells gradually lost the expression of CA II, secretin receptors, DU-PAN2, and CA 19-9 and assumed an undifferentiated phenotype, which showed an upregulation of transforming growth factor alpha (TGFalpha) and epidermal growth factor receptor (EGFR), an increase in the expression of Ki-67, and an increased binding to Phaseolus vulgaris leucoagglutinin (PHA-L) and tomato lectin. These ductal cells present a useful source with which to study physiologic aspects of ductal cells including differentiation.

Inhibition of growth and metastatic progression of pancreatic carcinoma in hamster after somatostatin receptor subtype 2 (sst2) gene expression and administration of cytotoxic somatostatin analog AN-238

The sst2 somatostatin receptor mediates the antiproliferative effects of somatostatin analogs. The present study demonstrates that stable expression of sst2 in the hamster pancreatic cancer cells PC-1 and PC-1.0 activates an autocrine negative loop leading to an in vitro inhibition of cell proliferation. In vivo studies conducted in Syrian golden hamsters after orthotopic implantation of PC-1.0 cells showed that both tumor growth and metastatic progression of allografts containing 100% of sst2-expressing cells were significantly inhibited for up to 20 days after implantation, as compared with control allografts that did not express sst2. A local antitumor bystander effect was observed after induction of mixed tumors containing a 1:3 ratio of sst2-expressing cells to control cells. Tumor volume and incidence of metastases of mixed tumors were significantly reduced at day 13 post implantation. This effect decreased with time as at day 20, growth of mixed tumors was similar to that of control tumors. After administration of the cytotoxic somatostatin conjugate AN-238 on day 13, antitumor bystander effect observed in mixed tumors was significantly extended to day 20. We also observed that in vitro invasiveness of sst2-expressing PC-1.0 cells was significantly reduced. Tyrosine dephosphorylation of E-cadherin may participate in restoring the E-cadherin function, reducing in turn pancreatic cancer cell motility and invasiveness. This dephosphorylation depends on the tyrosine phosphatase src homology 2-containing tyrosine phosphatase 1 (SHP-1) positively coupled to sst2 receptor. The inhibitory effect of sst2 gene expression on pancreatic cancer growth and invasion combined with chemotherapy with targeted cytotoxic somatostatin analog administration provides a rationale for a therapeutic approach to gene therapy based on in vivo sst2 gene transfer.

Biologic instability of pancreatic cancer xenografts in the nude mouse

Tumor transplants into nude mice (NM) may reveal abnormal biological behavior compared with the original tumor. Despite this, human tumor xenografts in NM have been widely used to study the biology of tumors and to establish diagnostic and therapeutic modalities. Clearly, precise differences in the biology of a given tumor in human and in NM cannot be assessed. We compared the growth kinetics, differentiation pattern and karyotype of an anaplastic Syrian hamster pancreatic cancer cell line in NM and in allogenic hamsters. As with the original tumor, transplants in hamsters grew fast, were anaplastic and expressed markers related to tumor malignancy like galectin 3, TGF-alpha and its receptor EGFR at high levels. However, tumors in the NM were well-differentiated adenocarcinomas, grew slower, had increased apoptotic rate and had a high expression of differentiation markers such as blood group A antigen, DU-PAN-2, carbonic anhydrase II, TGF-beta(2) and mucin. Karyotypically, the tumors in the NM acquired additional chromosomal damage. Our results demonstrate significant differences in the morphology and biology of tumors grown in NM and the allogenic host, and call for caution in extrapolating data obtained from xenografts to primary cancer.

Differentiation of islet cells in long-term culture

Our previous studies in the hamster pancreatic cancer model have shown that exocrine pancreatic cancer arises from ductal/ductular cells, as well as from within the islets, most probably from islet precursor (stem) cells. To identify and characterize these cells, we established a long-term culture from isolated hamster islets and investigated their growth, differentiation, and expression of biomarkers. Islets maintained their original form and structure within the first 14 days in culture. However, beginning at day 7, ductular structures began to form within the islets. At day 21 in culture, acinar cells, intermediary cells, oncocytes, and cells comparable to pancreatic hepatocytes also appeared between ductular and endocrine cells. The number of duct-like cells gradually increased, whereas the number of hormone-producing cells decreased. After 35 days in culture, the exocrine cells disappeared, and undifferentiated cells formed a monolayer. These cells expressed cytokeratins, alpha1-antitrypsin, transforming growth factor-alpha, epidermal growth factor receptor, carbonic anhydrase II, vimentin, laminin, and showed binding to tomato lectin and Phaseolus vulgaris leukoagglutinin. They did not express the regulatory transcriptional factors, insulin-promoting factor 1, NKx6.1, Pax6, and NeuroD. The results thus indicate that islet cells have potential to form exocrine cells. At present, it is not clear whether these cells originate from preexisting stem cells or from transdifferentiated islet cells.

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.

Alteration of the Langerhans Islets in Pancreatic Cancer Patients

An abnormal glucose metabolism occurs in up to 80% of pancreatic cancer patients shortly or a few months before the first clinical admission. Reasons for this abnormality are obscure. We investigated immunohistochemically the pattern of islets in 14 pancreatic cancer specimens and used 14 chronic pancreatitis samples and 10 normal pancreata as controls. To study the topographical relationship of these islets to the cancer, islets in four different arbitrary zones within and around the cancer were evaluated. Ten out of 14 cancer specimens showed a significant loss of beta cells (p < 0.005) and eight of them also showed a significant increase of alpha cells (p < 0.005), all of them from hyperglycemic patients. Most affected islets were found within zone 1 (intratumoral) and zone 2 (peritumoral), to a lesser extent in zone 3 (acini close to tumor) and none in zone 4 (acini remote from tumor). No comparable changes were found in chronic pancreatitis patients. The incidence of 72% with alteration of islets in our material correlates with the frequency of abnormal glucose levels in human pancreatic cancer patients. Our findings support the notion that islet cell abnormalities is likely caused by substances released from cancer cells.

In vitro pancreatic carcinogenesis

Studies in our laboratories have indicated that pancreatic cancer originates not only from pancreatic ductal/ductular cells but also from within the Langerhans' islets, probably from reserve (precursor, stem) cells. To identify, enrich and characterize these cells, we established a long-term hamster islet culture and studied their growth, differentiation and response to the pancreatic carcinogen, N-nitrosobis(2-oxopropyl)amine (BOP). One group of cultured islets was treated in vitro with BOP (KL5B group) and the other group of islets served as an untreated control (KL5N group). During the early culture days, in both groups all cultured islets showed a progressive loss of endocrine cells and replacement by ductular, acinar and intermediary cells. However, all these cells disappeared after 35 days in culture and gave room to undifferentiated cells, which we believe represent stem cells. No differences were found between KL5N and KL5B cells with regard to cell growth and differentiation until day 35, when the growth of the KL5B cells accelerated and the cells underwent increasing pleomorphism and atypia. At day 133, KL5B cells but not KL5N cells showed colony formation in soft agar and formed invasive, poorly differentiated adenocarcinomas of the ductal type when transplanted into hamsters. All of these tumors showed mutation of the K-ras gene and extensive chromosomal damage. We concluded that like ductal/ductular cells, certain cell populations within islets are responsive to the carcinogenic effect of BOP. We could not ascertain whether these cells present a preexisting (stem, reserve) cell population within the islets or transdifferentiated islet cells.

One thousand faces of Langerhans islets

Studies with different strains of Syrian hamsters and Syrian golden hamsters have revealed the remarkable potential of islet cells to undergo orthotopic and heterotopic metaplasia. The most common spontaneous change included the development of hepatocytes in aged and malnourished hamsters. Of the many other alterations that occurred during carcinogenesis, most of the metaplastic changes originated within the islet periphery and progressed inside and outside the islets. The development of ductular structures within islets and their progression either to structures identical to human serous cystadenoma or to highly invasive adenocarcinomas were the most common alterations. The remarkably greater invasive potential of cancer cells arising within the islets contrasted sharply with the slow growth of the tumors developing within ducts (intraductal tumors). Studies in human tissue also showed development of malignant cells within islets, and, in some cases, transition of islet cells to malignant cells was suggested. The overall results, along with recent findings in other studies in cultured human and hamster islets, indicate the enormous potential of islet cells to differentiate and undergo malignant transformation. Whether the metaplastic and malignant cells derive from stem cells embedded within islets or from transdifferentiated islet cells remains to be seen.

The link between exocrine pancreatic cancer and the endocrine pancreas

CONCLUSION

Experimental and human studies during 20 years of research in our laboratories point to the importance of pancreatic islets in the development of ductal-type adenocarcinomas. We believe that pancreatic cancer that develops within ducts, but more frequently within islets, derives from pancreatic stem cells that are distributed within the ductal trees and within the islets.

BACKGROUND

The histogenesis of pancreatic cancer is still debatable. Ductal, ductular, and acinar cells all have been declared the tumor progenitor cells. Our long-term human and experimental studies indicate that pancreatic ductal adenocarcinomas arise within ductal cells and islets. Supporting studies are presented in this article.

METHODS

Several human studies and experimental studies on Syrian hamsters conducted within the last 20 years were used in this article. Hamster and human islets were established, and their growth and morphologic changes were examined electron microscopically, immunohistochemically, cytogenetically, and molecular biologically.

RESULTS

Studies using the hamster pancreatic cancer model showed that most pancreatic adenocarcinomas develop within islets, most probably from stem cells, which are also believed to be the progenitor cells for tumors that develop within ducts. Studies in newly established human and hamster islets culture validated the immense potential of islet cells to differentiate and become malignant. The higher susceptibility of islet cells to become malignant could be related to their high drug-metabolizing enzymes and their high proliferation rate. Dietary studies indicate that the promoting effect of a high-fat diet on pancreatic carcinogenesis is unrelated to the energy intake, but rather is related to its effect on islet cell replication.

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

Our previous studies in the hamster pancreatic cancer model have indicated that pancreatic ductal adenocarcinomas derive not only from ductal/ductular cells but also from islets. To verify the presence of carcinogen-responsive cells within islets, we tested the effect of the pancreatic carcinogen N-nitrosobis(2-oxopropyl)amine (BOP) on recently established continuous hamster pancreatic islet culture. Isolated pure pancreatic islets of hamsters were treated in vitro with BOP at a concentration of 0.25 mM three times a week for 19 weeks. Each treatment week was designed as a stage. The growth of these cells, designated KL5B, was compared with untreated cultured islets, designated KL5N. As in our previous study, between 14 and 21 days of culture, exocrine and intermediary cells developed within both KL5N and KL5B islets, which were then replaced by undifferentiated cells. No differences were found in the growth patterns of KL5N and KL5B until stage 4, when KL5B cells showed accelerated cell growth and cell pleomorphism, which increased gradually at later stages of treatment. Anchorage-independent and in vivo growth did not appear until stage 19. Mutation of c-Ki-ras at codon 12 (GGT-->GAT) was detected in KL5B cells but not in KL5N cells. In vivo KL5B cells formed anaplastic invasive cancer with areas of glandular formation, overexpressed TGF-alpha and EGFR, expressed cytokeratin, vimentin, laminin and alpha-1 antitrypsin and reacted strongly with L-phytohemagglutinin and tomato lectin. Some cells within islets are responsive to the carcinogenic effects of BOP. Whether these cells represent islet cell precursors (stem cells) or malignant transdifferentiated islet cells remains to be seen.

Establishment of tumor cell culture (ILA) derived from hamster pancreatic islets treated with BOP

ILA cells were established from tumors induced by the pancreatic carcinogen N-nitrosobis(2-oxopropyl)amine (BOP) in hamster islets. The proliferation, morphology, karyotype, immunoreactivity with certain antibodies and growth factor secretion of these tumor cells were compared with the same parameters in tumor cells induced by BOP in hamster ductal cells (TAKA-1-BOP) established in a previous study. Minor differences were found in the morphology and ultrastructure of the 2 cell lines. Contrary to TAKA-1-BOP cells, ILA cells did not express cytokeratins 8.13, 13 or 18 but did express DU-PAN-2 and TAG-72, 2 known human pancreatic cancer-associated antigens. No endocrine cell markers were expressed. A significant difference also was found in the chromosomal pattern in that there were more abnormalities and marker chromosomes in ILA cells than in TAKA-1-BOP cells and the Y or X chromosomes were missing in ILA cells. ILA cells produced TGF-alpha, IGF-I, bombesin and gastrin and expressed specific binding sites for hEGF. TGF-alpha secretion from ILA cells was much greater than that from TAKA-1-BOP cells. Our results indicate that pancreatic cancer cells grown in vitro are not a single clone. We conclude that there are some genetic and biological differences between tumors arising from pancreatic duct and islets and that pancreatic ductal adenocarcinomas originating from islets have a profound malignant potential.

The intracellular mechanism of insulin resistance in the hamster pancreatic ductal adenocarcinoma model

Diabetes associated with pancreatic cancer is characterized by profound peripheral insulin resistance. The intracellular mechanism of insulin resistance was investigated in skeletal muscles from N-nitrosobis(2-oxopropyl)amine (BOP)-treated hamsters. Effects of high-fat diet and exercise also were studied. BOP (20 mg/kg body weight) was administrated weekly for 2 weeks. Hyperinsulinemia was found in BOP-treated hamsters at 20 weeks after BOP treatment, suggesting the peripheral insulin resistance is an early feature in pancreatic cancer. Hamsters were killed at 42 weeks, and soleus muscles were taken for the analysis. Skeletal muscle insulin-receptor binding and insulin receptor tyrosine kinase activities were similar between the control and BOP-treated hamsters. However, maximal muscle glycogen synthase activity was significantly reduced in BOP-treated hamsters compared with the control group. Muscle glycogen phosphorylase activity was increased in the BOP-treated group fed with high-fat diet as well as in BOP-treated groups with exercise. These findings indicate that insulin resistance in the hamster pancreatic cancer model is caused by a postreceptor defect, which led to significant decrease of muscle glycogen synthase activity. Whereas a high-fat diet causes more severe insulin resistance in BOP-treated hamsters, high-fat diet and exercising had no significant effects on skeletal muscle insulin-receptor function and glycogen synthase activity. Furthermore, both high-fat diet and exercise enhanced glycogen phosphorylase activity in BOP-treated hamsters.

Histologic and biologic patterns of microscopic pancreatic ductal adenocarcinomas detected incidentally at autopsy

BACKGROUND

The major clinical problems with pancreatic carcinoma are its silent course and late, fatal clinical manifestation. The results of treatments of small pancreatic carcinomas (<2 cm in greatest dimension) have led to the assumption that the detection of these cancers at earlier stages would lead to better survival and possible cure. Currently, there is no information about the histologic and biologic patterns of early stage pancreatic carcinoma, and the available data on incidentally detected tumors are fragmentary. The authors observed two incidental microscopic pancreatic ductal adenocarcinomas in female patients who died of advanced gastric carcinoma (Case 1) and renal carcinoma (Case 2).

METHODS

The pancreatic lesions were examined histologically in serial sections and immunocytochemically for islet cells. Microdissection was performed so that the lesions could be examined for c-Ki-ras mutation.

RESULTS

In Case 1, the pancreatic lesion was composed of cystic and solid components. The cystic component consisted of four small cysts compatible with a mucinous cystic tumor and showed no invasion. The solid component was a well-differentiated adenocarcinoma that occupied a 4 x 2 mm area. In Case 2, the pancreatic lesion contained two small, separate cysts, one of which was surrounded by two apparently separate, invasive adenocarcinomas 2.6 x 0.7 mm and 1.2 x 0.5 mm in greatest dimension. There was invasion of pancreatic islets and perineural spaces in both cases; and in Case 2, there was invasion of peripancreatic fatty tissue. In both cases, the epithelia of the cystic components and tumors showed mutation of the c-Ki-ras oncogene at codon 12, with GGT-to-GAT transition. CONCLUSIONS. Pancreatic carcinoma seems to occur under occult circumstances and maintain a silent course. Even in its early developmental stage, the cancer is invasive, primarily affects islets and nerves, and exhibits mutation of the c-Ki-ras oncogene. These findings call for urgency in the development of preventive modalities.

Histologic and biologic patterns of microscopic pancreatic ductal adenocarcinomas detected incidentally at autopsy

BACKGROUND

The major clinical problems with pancreatic carcinoma are its silent course and late, fatal clinical manifestation. The results of treatments of small pancreatic carcinomas (<2 cm in greatest dimension) have led to the assumption that the detection of these cancers at earlier stages would lead to better survival and possible cure. Currently, there is no information about the histologic and biologic patterns of early stage pancreatic carcinoma, and the available data on incidentally detected tumors are fragmentary. The authors observed two incidental microscopic pancreatic ductal adenocarcinomas in female patients who died of advanced gastric carcinoma (Case 1) and renal carcinoma (Case 2).

METHODS

The pancreatic lesions were examined histologically in serial sections and immunocytochemically for islet cells. Microdissection was performed so that the lesions could be examined for c-Ki-ras mutation.

RESULTS

In Case 1, the pancreatic lesion was composed of cystic and solid components. The cystic component consisted of four small cysts compatible with a mucinous cystic tumor and showed no invasion. The solid component was a well-differentiated adenocarcinoma that occupied a 4 x 2 mm area. In Case 2, the pancreatic lesion contained two small, separate cysts, one of which was surrounded by two apparently separate, invasive adenocarcinomas 2.6 x 0.7 mm and 1.2 x 0.5 mm in greatest dimension. There was invasion of pancreatic islets and perineural spaces in both cases; and in Case 2, there was invasion of peripancreatic fatty tissue. In both cases, the epithelia of the cystic components and tumors showed mutation of the c-Ki-ras oncogene at codon 12, with GGT-to-GAT transition. CONCLUSIONS. Pancreatic carcinoma seems to occur under occult circumstances and maintain a silent course. Even in its early developmental stage, the cancer is invasive, primarily affects islets and nerves, and exhibits mutation of the c-Ki-ras oncogene. These findings call for urgency in the development of preventive modalities.

Localization of galectin-3 in normal and diseased pancreatic tissue

CONCLUSION

Galectin-3 is expressed in both human and hamster pancreatic tumors and tumor cell lines and this expression is increased over normal.

BACKGROUND

Galectin-3 is overexpressed in many gastrointestinal tumors. This study examined the expression of galectin-3 in human and hamster pancreatic tumors to determine if galectin-3 could be used as a marker for pancreatic cancer.

METHODS

Membranes were prepared from human and hamster pancreatic tumor cell lines. Galectin-3 was visualized by immunoblot analysis of separated membrane proteins using the monoclonal antibody (MAb) M3/38. Paraffin-embedded sections from normal, pancreatitis, and cancerous human pancreatic tissue and normal, N-nitrosobis(2-oxopropyl)amine (BOP)-treated hyperplastic, and cancerous hamster pancreatic tissues were processed immunohistochemically for galectin-3 using the MAb M3/38.

RESULTS

Galectin-3 was heavily expressed in cytoplasmic and nuclear regions of 50% of normal human pancreatic tissue. Expression of galectin-3 in ductal cells in chronic pancreatitis and cancerous pancreatic tissue was increased over normal and was more uniform (>95% cells/duct stained). Normal hamster pancreatic ducts showed weak or no expression of galectin-3. Hyperplastic pancreatic ductal cells from BOP-treated hamsters heavily expressed galectin-3 (60-95% cells/duct stained). Galectin-3 expression in ductal cells in cancerous pancreatic lesions was increased to >95%. Galectin-3 was also detected in the pancreatic nerves in all human tissue specimens tested.

Dietary energy restriction does not inhibit pancreatic carcinogenesis by N-nitrosobis-2-(oxopropyl)amine in the Syrian hamster

Dietary energy restriction was previously shown to be effective in preventing a wide range of experimentally induced cancers. Studies were conducted to assess the influence on pancreatic carcinogenesis of dietary energy restrictions (reduced fat and carbohydrate) of 10%, 20% or 40% in comparison with control in Syrian hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). Two carcinogenesis studies were conducted. One used a single treatment with 20 mg BOP/kg body weight and followed hamsters for 102 weeks following treatment, and the other used three weekly treatments of 20 mg BOP/kg body weight and followed hamsters for 45 weeks after treatment. Hamsters were fed control or energy restricted diet beginning the week following the last BOP treatment. Pancreatic carcinomas were induced in 9-18% of the hamsters in the first experiment and in 59-66% of the animals in the second. Dietary energy restriction did not influence carcinoma incidence in either study, and in the second experiment the multiplicity of tumors was higher in the 40% energy restriction (ER) group than in control hamsters. Plasma corticosterone was suppressed by BOP treatment, particularly in the 20% and 40% ER hamsters in the second experiment, and diet or BOP treatment did not significantly alter plasma cortisol. Pancreatic protein kinase Czeta measured by Western blot was highest in the cytosol and particulate fractions of the 40% ER hamsters in the first experiment. These results indicate that dietary energy restriction is not effective in the prevention of BOP induced pancreatic carcinogenesis in the Syrian hamster.

Effects of high-fat diet and cholecystokinin receptor blockade on promotion of pancreatic ductal cell tumors in the hamster

The mechanism by which high-fat diets potentiate pancreatic cancer is not known, but pancreaticotrophic hormones such as cholecystokinin (CCK) may be involved. The effect of CCK receptor blockade on carcinogenesis during the entire promotion period was investigated in Syrian Golden hamsters fed a high- or low-fat diet and treated with N-nitrosobis(2-oxopropyl)amine (3 x 10 mg/kg at weekly intervals). One-half of the hamsters fed a high-fat diet received the CCK-A receptor antagonist devazepide (25 nmol/kg/hr) for the duration of the experiment. At 39 weeks the incidence of pancreatic malignancies was significantly higher in hamsters fed the high-fat diet than in those fed the low-fat diet (p < 0.05). Tumor incidence was not changed by CCK receptor blockade. Potentiation of pancreatic cancer by a high-fat diet in hamsters does not appear to be influenced by endogenous CCK during the tumor promotion period.

Species differences in the expression of transforming growth factor-alpha (TGF-alpha) in the submandibular gland and pancreas

CONCLUSION

Significant differences exist in the expression of transforming growth factor-alpha (TGF-alpha) in the submandibular glands (SMG) and the pancreas of different species and among cell components in the same species.

BACKGROUND

Our previous studies have shown marked differences in the expression of TGF-alpha in the pancreas of humans and Syrian hamsters. To examine whether these differences also exist in other species, we examined the expression of TGF-alpha in the pancreas of mouse, rat, Syrian hamster, guinea pig, rabbit, pig, dog, and monkey. We included the SMG of these species for comparison.

MATERIALS AND METHODS

The formalin-fixed tissues of these species (n = 3) were investigated by immuno-histochemistry using a monoclonal antibody to TGF-alpha. The SMG of rat, mouse, hamster, rabbit, pig, dog, and monkey were examined by RT-PCR to assure the specificity of the antibody.

RESULTS

Remarkable species differences were found in the expression of this peptide in both the SMG and the pancreas. In the SMG, the expression varied in different cell components, even in the same tissue of the species. Although excretory and secretory ducts of the SMG of most species reacted with the antibody, intercalated ducts were immunoreactive only in mouse and guinea pig. Acinar cells were either weakly positive or nonimmunoreactive. In the pancreas of most species, the cells of the large and medium-sized ducts expressed TGF-alpha, whereas centroacinar cells of only rat and dog reacted with the antibody. Marked differences were found in the expression of TGF-alpha in islet cells and in its spatial distribution. Differences were also found in the immunoreactivity of mesenchymal and neural cells among the species.

In vitro pancreatic ductal cell carcinogenesis

Our experiments were designed to identify initial biochemical and biological changes that occur during pancreatic carcinogenesis. TAKA-1, an immortal hamster pancreatic ductal cell line, was treated in vitro for up to 11 weeks with the pancreatic carcinogen N-nitorosobis(2-oxopropyl)amine (BOP). These treated cells were designated TAKA-1 + BOP. The growth of TAKA-1 and TAKA-1 + BOP cell lines was investigated in soft agar and in hamsters intradermally. The resulting tumor from TAKA-1 + BOP was re-cultured in vitro and designated TAKA-1 + BOP-T. Mutation of c-K-ras and p53 oncogenes, chromosomal changes, expression of transforming growth factor alpha (TGF-alpha) and epidermal growth factor (EGF) receptor and several biochemical markers were examined in all cell lines. TAKA-1 + BOP but not TAKA-1 cells grew in soft agar and produced an invasive tumor in vivo. However, there were no differences in cell growth rate, DNA flow cytometry, or immunohistochemical findings between the non-transformed and transformed cells. TAKA-1, TAKA-1 + BOP and TAKA-1 + BOP-T cells all expressed mRNA of TGF-alpha and EGF receptor in a comparable pattern. DNA sequence analysis following polymerase chain reaction showed that neither TAKA-1 nor TAKA-1 + BOP cells has a mutation of c-K-ras or p53. Karyotype analysis demonstrated that TAKA-1 + BOP cells had more chromosomal abnormalities compared with TAKA-1 cells. Mutation of c-K-ras and p53 was not essential for carcinogenesis in hamster pancreatic ductal cells in vitro. In conclusion, immortality of the TAKA-1 cells caused expression of TGF-alpha to the same extent as in malignant cells. Chromosomal and ultrastructural patterns were the only differences detected between the non-transformed and BOP-transformed cells.

The effect of streptozotocin and a high-fat diet on BOP-induced tumors in the pancreas and in the submandibular gland of hamsters bearing transplants of homologous islets

The effect of a high-fat diet (HF) and streptozotocin (STZ) was investigated in the rapid cancer induction model developed in our laboratories. Syrian golden hamsters bearing homologous islets transplanted in their right submandibular gland (SMG) received a HF or a low-fat diet (LF). Half of the animals from each dietary group received STZ (HF-STZ and LF-STZ groups) and the other half did not (HF and LF groups). One week later, all hamsters were treated with N-nitrosobis(2-oxopropyl)amine (BOP) weekly for 3 weeks and the experiment was terminated 12 weeks after the last BOP injection. Pancreatic lesions were found in many hamsters, with a lower incidence in the LF-STZ group (13%) than in other groups (35-45%). A HF diet counteracted the inhibitory effect of STZ on pancreatic tumor induction by yet unknown mechanisms. SMG tumors, all ductal-type adenocarcinomas, developed in all groups and the incidence was lowest in the HF group (6%) compared to the LF group (15%), LF-STZ group (17%) and HF-STZ group (18%). However, the difference was not statistically significant. It was concluded that a HF diet counteracts the inhibitory effect of STZ on BOP-induced pancreatic lesions but has no effect on the induction of tumors in the SMG. STZ pretreatment does not influence tumor induction of the SMG of these hamster.

The role of Langerhans islets in pancreatic ductal adenocarcinoma

An intimate relationship between the exocrine and endocrine pancreas has been convincingly demonstrated in recent years. Animal experiments have shed some light into the complex dialog between the two tissues. This interaction is pronounced in diseases of the pancreas, especially in experimentally-induced and human pancreatic cancers. New evidence highlights the importance of intact islets in the development of exocrine pancreatic cancer. Although tumors arise from large and small ducts, invasive and malignant adenocarcinomas of ductal phenotype also derive from stem cells within islets. Development of cancer within islets explains the association between pancreatic cancer and impaired glucose tolerance or diabetes. Hence, the previous epidemiological studies suggesting that diabetes is a predisposing factor for pancreatic cancer are refuted. The available evidence suggests that pancreatic cancer in a large number of pancreatic cancer patients ultimately leads to diabetes, and that removal of the tumors improves or cures the diabetes. Both in the hamster pancreatic cancer model and in patients, the development of cancer is associated with elevated plasma levels of islet amyloid polypeptide, which may be used as a tumor marker.

Experimental evidence for the origin of ductal-type adenocarcinoma from the islets of Langerhans

To investigate the role of the islets of Langerhans in pancreatic carcinogenesis, freshly isolated islets from male Syrian hamsters were transplanted into the right submandibular glands of 50 female hamsters that were or were not pre-treated with streptozotocin. Thyroid gland fragments, cellulose powder, and immortal hamster pancreatic ductal cells were injected into the left submandibular gland of the same hamsters. All recipient hamsters were then treated with the potent pancreatic carcinogen N-nitrosobis(2-oxopropyl)amine weekly at a dose of 40 mg/kg of body weight for 3 weeks. Between 3 and 8 weeks later, 18 of 75 (24%) hamsters developed large ductal-type adenocarcinomas in the submandibular gland region, where islets were transplanted, but none developed tumors in the left submandibular gland. In 9 of 18 hamsters, tumors were multiple so that a total of 31 cancers were found. Eleven of these carcinomas were in the vicinity of transplanted islets, eight of which showed intra-insular ductular or cyst formation as seen in the pancreas of hamsters during pancreatic carcinogenesis. The formation of ductular structures within islets was also demonstrated in vitro. Some tumor cells in the vicinity of these islets were reactive with anti-insulin. Y chromosome message was found by polymerase chain reaction analysis in one of the three tumors examined. Also, like the induced pancreatic tumors, all three submandibular gland tumors that were examined had the mutation of the c-Ki-ras oncogene at codon 12 and all tumors expressed blood group A antigen. These and other findings strongly suggest that some components of islets, most probably stem cells, are the origin of ductal-type adenocarcinomas in this model.

Modification of blood group A expression in human pancreatic tumor cell lines by inhibitors of N-glycan processing

Pancreatic adenocarcinomas induced in Syrian hamsters by N-nitrosobis (2-oxopropyl)amine (BOP) treatment express blood group A (BGA) antigen, which was previously shown by this lab to be expressed on multiantennary asparagine (Asn)-linked glycans attached to membrane glycoproteins. To determine if a similar expression pattern was found in humans, three human pancreatic ductal adenocarcinoma cell lines (CD18, CD11, and Capan 1) from individuals of blood type A were analyzed and shown to express BGA antigen on membrane glycoproteins similar in molecular mass to those found in hamster tumor cells. The BGA antigen was located on Asn-linked oligosaccharides in all three human cell lines, as indicated by loss of activity after peptide:N-glycosidase F (PNGase F) treatment. Also, as shown previously in hamster pancreatic tumor cells, BGA expression at the surface of the human cell lines was blocked by growth of the cells in media containing deoxymannojirimycin (dMM), an inhibitor of mannosidase I. These results demonstrate that the BGA antigen is on Asn-linked glycans in human pancreatic adenocarcinoma cells and that these glycoproteins are processed similarly to the BGA glycoproteins in hamster pancreatic adenocarcinoma.

Bombesin may stimulate proliferation of human pancreatic cancer cells through an autocrine pathway

Bombesin is trophic to normal pancreas and acinar cell adenocarcinoma, but its effects on ductal cell tumors are undetermined. The autocrine growth effects of bombesin on well-differentiated (HPAF, CD11) and poorly differentiated (CD18, PANC-1) human ductal pancreatic cancer cell lines were investigated. Receptor binding of labeled bombesin was measured in a whole-cell microplate assay. Bombesin production was measured by radioimmunoassay. Proliferative responses were quantified using the MTT assay. Messenger RNA for bombesin and its receptor were identified by primer extension analysis. A single class of high-affinity binding sites was detected on HPAF and CD18 cells. Similar affinities and high receptor densities were found on the 2 cell lines. Bombesin was secreted by all 4 cell lines during 24-hr culture in serum-free media, and its recovery was enhanced in the presence of protease inhibitors. Primer extension analysis demonstrated the presence of mRNA for both bombesin and its receptor in HPAF, CD18, CD11 and PANC-1 cells, even though no functional receptor was found in the latter 2 lines. Bombesin significantly stimulated the proliferation of HPAF and CD18 cells. This trophic effect was inhibited by the specific bombesin antagonist RC-3095. Bombesin may act as an autocrine growth factor in some human pancreatic cancer cell lines. Furthermore, other cell lines transcribe mRNA for bombesin receptors but have no functional bombesin receptors, suggesting a genetic or post-translational change in the receptor for these cells. Bombesin may be involved as a growth factor in the development of pancreatic ductal adenocarcinoma in humans. This possible autocrine growth pathway may provide an avenue for therapeutic intervention in this malignant disease.

K-ras and p53 mutations in hamster pancreatic ductal adenocarcinomas and cell lines

K-ras and p53 gene alterations are frequently found in human pancreatic carcinomas and cell lines. The aim of this study was to analyze for the presence of K-ras and p53 gene mutations in hamster pancreatic tumors and cell lines. Mutations at the first coding exon of the K-ras gene and in exons V to VIII of the hamster p53 gene were analyzed in six cell lines (H2T, PC1, PC1.2, PC1.0, WD, and PD) and in N-nitroso-bis(2-oxopropyl)amine-induced pancreatic (n = 9) and extra-pancreatic (n = 4) tumors. K-ras mutations were present in seven of the nine pancreatic tumors and in all extra-pancreatic tumors. No p53 mutations were detected in the tumors. All cell lines analyzed contained K-ras mutations. Moreover, four of the six cell lines contained single amino acid substitutions in the p53 gene. Cell lines derived from nitrosamine-induced pancreatic tumors in the hamster contained K-ras and p53 alterations similar to those found in cell lines derived from human pancreatic carcinomas.

Stimulation of islet cell proliferation enhances pancreatic ductal carcinogenesis in the hamster model

Previous studies have shown that some N-nitrosobis (2-oxopropyl)amine (BOP)-induced ductal/ductular pancreatic cancers in the hamster model develop within islets and that streptozotocin (SZ) pretreatment that caused islet degeneration and atrophy inhibits pancreatic cancer induction. Hence, it appears that in this model islets play a significant role in exocrine pancreatic carcinogenesis. To examine whether stimulation of islet cell proliferation (nesidioblastosis) enhances pancreatic exocrine cancer development, we tested the effect of the pancreatic carcinogen BOP in hamsters after induction of nesidioblastosis by cellophane wrapping. Before wrapping, hamsters were treated with SZ to inhibit pancreatic tumor induction in the unwrapped pancreatic tissues. Control groups with a wrapped pancreas did not receive SZ. Six weeks after SZ treatment, all hamsters were treated with BOP (10 mg/kg body weight) weekly for 10 weeks and the experiment was terminated 38 weeks after the last BOP treatment. Many animals recovered from their diabetes at the time when BOP was injected and many more after BOP treatment. Only nine hamsters remained diabetic until the end of the experiment. Both SZ-treated and control groups developed proliferative and malignant pancreatic ductal-type lesions primarily in the wrapped area (47%) but less frequently in the larger segments of the pancreas, including the splenic lobe (34%), gastric lobe (13%), and duodenal lobe (6%). Only a few lesions developed in the unwrapped pancreatic region of nine diabetic hamsters with atrophic islets, whereas seven of these hamsters had tumors in the wrapped area. Histologically, most tumors appeared to originate from islets, many invasive carcinomas had foci of islets, and some tumor cells showed reactivity with anti-insulin. The results show that, in the BOP hamster model, islets are the site of formation of the major fraction of exocrine pancreatic cancer and that induction of nesidioblastosis enhances pancreatic carcinogenesis.

High-fat diet blocks the inhibition of skin carcinogenesis and reductions in protein kinase C by moderate energy restriction

The aim of this investigation was to determine the impact of dietary energy restriction (ER) with control (C) and high-fat (HF) diets on two-stage skin carcinogenesis and on the expression of specific isoforms of protein kinase C (PKC). Skin carcinogenesis was initiated on SENCAR mice with 10 nmol of 7,12-dimethylbenz[a]anthracene (DMBA) in 0.2 mL of acetone and then promoted with twice weekly treatments of 3.2 nmol of 12-O-tetradecanoylphorbol-13-acetate (TPA) in 0.2 mL of acetone for 18 wk. The experimental diets fed during TPA treatment and for 10 wk after the last TPA treatment were formulated with C (10% calories from fat) and HF (42% calories from fat) levels for freely fed groups. These diets were restricted by 20% (20% ER/C and 20% ER/HF) and by 40% (40% ER/C and 40% ER/HF). Papilloma incidence was reduced in the mice fed the 20% ER/C, 40% ER/C, and 40% ER/HF diets in comparison with the C, HF, and 20% ER/HF groups. Carcinoma incidence was also reduced in these groups. PKC alpha and zeta were assessed by western blot analysis in the epidermises of mice pre-fed the six diets for 8-10 wk (without DMBA or TPA treatment). PKC alpha was reduced in the particulate fraction by 32-44% in the 20% ER/C, 40% ER/C, and 40% ER/HF groups (P < 0.005). PKC zeta was reduced by 24-31% in the cytosol of mice fed the 20% ER/C diet and in the particulate fraction of mice fed the 40% ER/C diet (P < 0.05). The HF diet was able to block the inhibition of skin carcinogenesis and the reduction in the expression of PKC in the epidermis by 20% ER but not by 40% ER.