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.