Transplantable pancreatic carcinoma of the rat

Using functional nanomaterials to target and regulate the tumor microenvironment: diagnostic and therapeutic applications

Malignant tumors remain a major health burden throughout the world and effective therapeutic strategies are urgently needed. Cancer nanotechnology, as an integrated platform, has the potential to dramatically improve cancer diagnosis, imaging, and therapy, while reducing the toxicity associated with the current approaches. Tumor microenvironment is an ensemble performance of various stromal cells and extracellular matrix. The recent progress in understanding the critical roles and the underlying mechanisms of the tumor microenvironment on tumor progression has resulted in emerging diagnostic and therapeutic nanomaterials designed and engineered specifically targeting the microenvironment components. Meanwhile, the bio-physicochemical differences between tumor and normal tissues have recently been exploited to achieve specific tumor-targeting for cancer diagnosis and treatment. Here, the major players in the tumor microenvironment and their biochemical properties, which can be utilized for the design of multifunctional nanomaterials with the potential to target and regulate this niche, are summarized. The recent progress in engineering intelligent and versatile nanomaterials for targeting and regulating the tumor microenvironment is emphasized. Although further investigations are required to develop robust methods for more specific tumor-targeting and well-controlled nanomaterials, the applications of tumor microenvironment regulation-based nanotechnology for safer and more effective anticancer nanomedicines have been proven successful and will eventually revolutionize the current landscape of cancer therapy.

Inhibition of mammary tumor growth using lysyl oxidase-targeting nanoparticles to modify extracellular matrix

A cancer nanotherapeutic has been developed that targets the extracellular matrix (ECM)-modifying enzyme lysyl oxidase (LOX) and alters the ECM structure. Poly(d,l-lactide-co-glycolide) nanoparticles (∼220 nm) coated with a LOX inhibitory antibody bind to ECM and suppress mammary cancer cell growth and invasion in vitro as well as tumor expansion in vivo, with greater efficiency than soluble anti-LOX antibody. This nanomaterials approach opens a new path for treating cancer with higher efficacy and decreased side effects.

PPARα Agonist-Induced Rodent Tumors: Modes of Action and Human Relevance

Widely varied chemicals--including certain herbicides, plasticizers, drugs, and natural products--induce peroxisome proliferation in rodent liver and other tissues. This phenomenon is characterized by increases in the volume density and fatty acid oxidation of these organelles, which contain hydrogen peroxide and fatty acid oxidation systems important in lipid metabolism. Research showing that some peroxisome proliferating chemicals are nongenotoxic animal carcinogens stimulated interest in developing mode of action (MOA) information to understand and explain the human relevance of animal tumors associated with these chemicals. Studies have demonstrated that a nuclear hormone receptor implicated in energy homeostasis, designated peroxisome proliferator-activated receptor alpha (PPARalpha), is an obligatory factor in peroxisome proliferation in rodent hepatocytes. This report provides an in-depth analysis of the state of the science on several topics critical to evaluating the relationship between the MOA for PPARalpha agonists and the human relevance of related animal tumors. Topics include a review of existing tumor bioassay data, data from animal and human sources relating to the MOA for PPARalpha agonists in several different tissues, and case studies on the potential human relevance of the animal MOA data. The summary of existing bioassay data discloses substantial species differences in response to peroxisome proliferators in vivo, with rodents more responsive than primates. Among the rat and mouse strains tested, both males and females develop tumors in response to exposure to a wide range of chemicals including DEHP and other phthalates, chlorinated paraffins, chlorinated solvents such as trichloroethylene and perchloroethylene, and certain pesticides and hypolipidemic pharmaceuticals. MOA data from three different rodent tissues--rat and mouse liver, rat pancreas, and rat testis--lead to several different postulated MOAs, some beginning with PPARalpha activation as a causal first step. For example, studies in rodent liver identified seven "key events," including three "causal events"--activation of PPARalpha, perturbation of cell proliferation and apoptosis, and selective clonal expansion--and a series of associative events involving peroxisome proliferation, hepatocyte oxidative stress, and Kupffer-cell-mediated events. Similar in-depth analysis for rat Leydig-cell tumors (LCTs) posits one MOA that begins with PPARalpha activation in the liver, but two possible pathways, one secondary to liver induction and the other direct inhibition of testicular testosterone biosynthesis. For this tumor, both proposed pathways involve changes in the metabolism and quantity of related hormones and hormone precursors. Key events in the postulated MOA for the third tumor type, pancreatic acinar-cell tumors (PACTs) in rats, also begin with PPARalpha activation in the liver, followed by changes in bile synthesis and composition. Using the new human relevance framework (HRF) (see companion article), case studies involving PPARalpha-related tumors in each of these three tissues produced a range of outcomes, depending partly on the quality and quantity of MOA data available from laboratory animals and related information from human data sources.

Rodent carcinogenicity of peroxisome proliferators and issues on human relevance

A variety of substances such as hypolipidemic drugs, phthalate ester plasticizers, pesticides, and industrial solvents have been shown to increase the size and number of peroxisomes in rats and mice. They are grouped under the generic term peroxisome proliferators (PP) because of their unique property of inducing peroxisome proliferation. There are marked species differences in response to PP. Rats and mice are most sensitive, and hamsters show an intermediate response while guinea pigs, monkeys, and humans appear to be relatively insensitive or non-responsive at dose levels that produce a marked response in rodents. Out of over 100 PP identified to date, about 30 have been adequately tested and shown to be carcinogenic, inducing tumors (primarily in the liver) upon chronic administration to rats and/or mice; hence, chemicals which induce the proliferations of peroxisomes have formed a unique class of chemical carcinogens. It is not well documented that activation of the "peroxisome proliferator-activated receptor alpha" (PPARalpha) is involved in PP-induced liver growth and carcinogenesis in rodents. PPARalpha is also present in human cells; however, the levels reported are about 10% of those found in the liver of rodents. The human relevance of rodent tumors induced by PP has been the subject of debate over the last decade. Review of the existing evidence on PPAR-alpha agonists by a recent International Life Science Institute (ILSI) workgroup following a human relevance mode of action (MOA) framework has concluded that despite the presence of similar pathways in humans, it is unlikely that the proposed MOA for rodent tumors is plausible in humans, taking into account kinetic and dynamic factors. The data, however, did not permit a definitive conclusion that the animal MOA is not plausible in humans. While these agents appear unlikely to be hepatocarcinogens in humans at expected levels of human exposure, it remains uncertain to some experts in the field whether there is no possibility of carcinogenic potential under any circumstances of PP exposure, and if the potential human carcinogenicity of these chemicals can be summarily ignored. A number of remaining issues on human relevance of rodent tumors induced by PP are discussed.

Mechanisms of extrahepatic tumor induction by peroxisome proliferators in male CD rats

Wyeth-14,643 (WY) and ammonium perfluorooctanoate (C8) belong to a diverse class of compounds which have been shown to produce hepatic peroxisome proliferation in rodents. From previous work, WY, but not C8, has been shown to produce hepatocellular carcinoma in rats, while C8 has been shown to produce Leydig cell adenomas. In addition, based on a review of bioassay data a relationship appears to exist between peroxisome-proliferating compounds and Leydig cell adenoma and pancreatic acinar cell hyperplasia/adenocarcinoma formation. To further investigate the relationship between peroxisome-proliferating compounds and hepatic, Leydig cell, and pancreatic acinar cell tumorigenesis, a 2-year feeding study in male CD rats was initiated to test the hypothesis that peroxisome proliferating compounds induce a tumor triad (liver, Leydig cell, pancreatic acinar cell), and to examine the potential mechanism for the Leydig cell tumors. The study was conducted using 50 ppm WY and 300 ppm C8. The concentration of WY in the diet was decreased to 25 ppm on test day 301 due to increased mortality. In addition to the ad libitum control, a second control was pair-fed to the C8 group. Interim sacrifices were performed at 1- or 3-month intervals. Peroxisome proliferation measured by beta-oxidation activity and cell proliferation were measured in the liver and testis at all time points and in the pancreas beginning at the 9-month time point (cell proliferation only). Serum hormone concentrations (estradiol, testosterone, LH, FSH, and prolactin) were also measured at each time point. Increased relative liver weights and hepatic beta-oxidation activity were observed in both the WY- and C8-treated rats at all time points. In contrast, hepatic cell proliferation was significantly increased only in the WY-treated group. Neither WY nor C8 significantly altered the rate of Leydig cell beta-oxidation or Leydig cell proliferation when compared to the control groups. Moreover, the basal rate of beta-oxidation in Leydig cells was approximately 20 times less than the rate of hepatic beta-oxidation. There were no biologically meaningful differences in serum testosterone, FSH, prolactin, or LH concentrations in the WY- and C8-treated rats when compared to their respective controls. There were, however, significant increases in serum estradiol concentrations in the WY- and C8-treated rats at 1, 3, 6, 9, 15, 18, and 21 months. At 12 months, only the C8-treated rats had elevated serum estradiol concentrations when compared to the pair-fed control. Histopathological evaluation revealed compound-related increases in liver, Leydig cell, and pancreatic acinar cell tumors in both WY- and C8-treated rats. The data support the hypothesis that the peroxisome-proliferating compounds induce the previously described tumor triad. In addition, both C8 and WY produced a sustained increase in serum estradiol concentrations that correlated with the potency of the 2 compounds to induce Leydig cell tumors (i.e., WY caused a more consistent sustained increase in serum estradiol throughout the entire study, and more specifically at the end of the study, than did C8). This study suggests that estradiol may play a role in enhancement of Leydig cell tumors in the rat, and that peroxisome proliferators may induce tumors via a non-LH type mechanism.

Four-week repeated inhalation study of HCFC 225ca and HCFC 225cb in the common marmoset

Four male and three female marmosets in each group were exposed to air only, 1000 ppm of HCFC 225ca or 5000 ppm of HCFC 225cb, for 6 h per day for 28 consecutive days. HCFC 225ca caused a slight reduction in body weight. HCFC 225cb occasionally caused somnolence during exposure and vomiting on the first day of exposure. Clinical chemistry findings included a mild reduction of triglyceride, cholesterol and phospholipid levels and increased GOT level in the HCFC 225ca exposure group. HCFC 225cb also caused a reduction of triglyceride levels in some animals. HCFC 225ca caused a slight increase of hepatic carnitine palmitoyltransferase (CPT) activity while HCFC 225cb slightly increased cyanide-insensitive palmitoyl CoA beta-oxidation (FAOS) activity. In the HCFC 225cb exposure group, an increase in cytochrome P-450 content was also observed. HCFC 225ca caused a fatty change in the hepatic cells. Increased incidence of lipid droplets in the hepatic cells and myelin-like bodies in hepatic cells, Kupffer's cells and hepatic blood vessels were observed electron microscopically in the HCFC 225ca exposure group. A proliferation of smooth endoplasmic reticulum was observed in the HCFC 225cb exposure group. Decreased peroxisome volume density in the HCFC 225ca group, and increased volume density in the HCFC 225cb exposed females were seen. However, organ weight measurement and histopathological examination did not reveal hepatomegaly or hypertrophy with either substance. Although slight changes were noticed in peroxisome volume density and in some of the peroxisomal enzyme activities, the changes related to peroxisome proliferation with HCFC 225ca and 225cb were minimal in marmosets compared to those seen in rats. Histopathological examination and hormonal analysis did not reveal any abnormalities in the pancreas or testes.

Mechanisms for the pancreatic oncogenic effects of the peroxisome proliferator Wyeth-14,643

Several peroxisome proliferators have been shown to produce pancreatic acinar cell hyperplasia/adenocarcinomas in 2-year bioassays with rats: ammonium perfluorooctanoate (C8), clofibrate, methylclofenapate, HCFC-123, and Wyeth-14,643 (WY). We have used in vitro (C8, WY) and in vivo (WY) approaches to examine several possible mechanisms of pancreatic tumorigenesis by peroxisome proliferating compounds. These mechanisms include cholecystokinin receptor agonism (CCK(A)), trypsin inhibition, alterations in gut fat content, cholestasis, and altered bile flow/composition. All of these mechanisms enhance pancreatic growth either by binding to the CCK(A) receptor or by increasing plasma CCK levels. In vitro experiments using a receptor competition binding assay demonstrated that WY and C8 do not bind directly to the CCK(A) receptor. In a continuous spectrophotometric assay, WY and C8 also failed to inhibit trypsin, a common mechanism for increasing plasma CCK levels. These in vitro results suggested that WY was not acting via the two most common mechanisms for modulation of pancreas growth. Two types of in vivo experiments were conducted. The subchronic study (2-month duration) was designed primarily to detect early changes in pancreatic growth such as those mediated by compounds that inhibit trypsin or act as CCK(A) receptor agonists. The chronic study (6 months) was designed primarily to evaluate whether the pancreatic lesions were secondary to hepatic changes such as cholestasis and/or altered bile flow/composition. In the in vivo experiments, male Crl:CDBR rats were fed diets containing 0 or 100 ppm WY. In the subchronic study WY-treated rats had a twofold increase in mean relative liver weights, an eightfold increase in hepatic peroxisomal proliferation, and a fourfold increase in hepatocyte cell proliferation after 1 week which remained elevated throughout the 2 months of treatment. In contrast, no pancreatic weight effects, increases in plasma CCK, or acinar cell proliferation was seen through 2 months in the WY group when compared to the control group. Fecal fat concentrations were also measured at 2 months and demonstrated no difference between control and WY-treated animals. The absence of any early pancreas changes in the subchronic study is consistent with the in vitro data which demonstrated that WY is not a CCK(A) agonist or a trypsin inhibitor. The chronic study demonstrated increases in pancreatic weights at 3 months (6% above control) and 6 months (17% above control), as well as increased CCK plasma levels in the WY-treated group. Liver effects in the chronic study paralleled those of the subchronic time points. Clinical pathology endpoints including increased serum concentrations of bile acids, alkaline phosphatase, and bilirubin were indicative of cholestasis in the chronic WY-treated group. The cholestasis may be responsible for the downward trend in total bile acid output, both of which may contribute to the modest increases in plasma CCK levels. These results indicate that chronic exposure to WY causes liver alterations such as cholestasis, which may increase plasma concentrations of CCK. Hence, WY may induce pancreatic acinar cell adenomas/adenocarcinomas via a mild but sustained increase in CCK levels secondary to hepatic cholestasis.

Establishment and characterization of a cultured cell line derived from nitrosamine-induced pancreatic ductal adenocarcinoma in Syrian golden hamsters

Seven kinds of pancreatic ductal adenocarcinomas induced by N-nitrosobis(2-hydroxypropil)amine in Syrian golden hamsters were established as transplantable tumor lines on syngeneic animals. These tumor lines were all well or moderately differentiated adenocarcinomas, showing various velocities of growth, unrelated to the grade of histological differentiation. A cell line, designated HaP-T1, was established in continuous tissue culture from one of these homografts. The cells grew in a monolayered sheet with an approximately 17-hour population doubling time. Chromosomal analysis revealed that the modal chromosomal number of the cell line was 44. HaP-T1 cells showed apparent tumorigenicity both on syngeneic hamsters and athymic nude mice, but they grew much faster when injected into the former animals. Morphological characteristics of HaP-T1 cells and tumors induced by HaP-T1 inoculation in both animals revealed apparent epithelial characteristics resembling ductal adenocarcinoma of the pancreas. These transplantable tumor models will contribute to the further investigation in the field of pancreatic cancer.

Free calcium and calmodulin levels in acinar carcinoma and normal acinar cells of rat pancreas

Exposure of acinar carcinoma cells and normal acinar cells of rat pancreas to the muscarinic agonist drug carbamylcholine stimulated 45Ca2+ outflux from 45Ca2+-labeled cells. More rapid outflux of 45Ca2+ was detected for carcinoma cells following muscarinic stimulation than for normal cells. Direct fluorometric measurement of cytosolic Ca2+ under basal (unstimulated) conditions in quin 2-loaded cells revealed significantly lower concentration of free Ca2+ in carcinoma cells (approximately 180 nM) than in normal cells (approximately 200 nM). Stimulation with 1 mM carbamylcholine increased the cytosolic Ca2+ concentration in carcinoma and normal cells to approximately 1900 nM, after which carcinoma cells removed cytosolic Ca2+ at a faster rate to a post-stimulation plateau concentration of approximately 140 nM, in comparison to normal cells which obtained a post-stimulation plateau concentration of approximately 300 nM. Essentially identical differences between carcinoma and normal cells were detected upon stimulation with the peptidergic agonist cholecystokinin octapeptide. Finally, carcinoma cells demonstrated approximately 3 times greater calmodulin concentration than normal acinar cells. Also, the calmodulin antagonist drug W7 (N-6-(aminohexyl)-5-chloro-1-naphthalene sulfonamide) inhibited the carbamylcholine-induced release of intracellular Ca2+ in acinar carcinoma cells. These results indicate that neoplastic pancreatic acinar cells have retained mechanisms of muscarinic- and peptidergic-stimulated intracellular Ca2+ release, and implicate calmodulin as a regulatory factor in secretagogue activation of intracellular Ca2+ release. We propose that the more rapid decline of intracellular Ca2+ concentration following muscarinic or peptidergic stimulation and the increased intracellular calmodulin concentration indicate calmodulin-mediated down-regulation of free cytosolic Ca2+ in acinar carcinoma cells to levels lower than those of normal cells.

Myosin from pancreatic acinar carcinoma cells. Isolation, characterization and demonstration of heavy- and light-chain phosphorylation

Myosin has been identified in a variety of non-muscle cells, and is believed to play a role in maintenance of cell shape, locomotion, cytokinesis, exocytosis and other cellular functions. In this paper we describe the purification of myosin from a pancreatic acinar-cell carcinoma of the rat which forms solid tumours, but retains many differentiated functions. The purified myosin was composed of a 200,000 Da heavy chain and two or three classes of light chains. Electron-microscopic examination of rotary-shadowed preparations revealed that individual molecules had two globular heads and a long tail measuring approx. 149 nm. The myosin was soluble in high-salt buffers and became sedimentable as the ionic strength was lowered. Examination of negative-stained preparations showed that this sedimentable myosin consisted of short, bipolar, thick filaments which had a strong tendency to aggregate in a head-to-head manner. The ATPase activity of the purified myosin was stimulated by EDTA or Ca2+, but not by Mg2+. In low ionic strength the Mg2+-dependent ATPase activity was activated by muscle f-actin. The pancreatic myosin bound to actin and could be dissociated by the addition of MgATP. Myosin purified from cells cultured in media containing [32P]Pi was phosphorylated on one of the light chains as well as the heavy chain. Thus pancreatic acinar cells contain a typical non-muscle myosin, and the subunits of this molecule are subject to post-translational modification by phosphorylation.

Pathways of secretion in the exocrine pancreas: the status of resting secretion

In the last decade the concept of two distinct pathways of secretion in the exocrine pancreas has slowly emerged. According to this concept, one pathway is involved in stimulated (regulated) conditions and another under resting (constitutive) conditions. This hypothesis was elaborated at first from the comparison of the specific radioactivities of secretory proteins released by the gland under resting and stimulated conditions. Analysis of the protein composition of the juice released under these two physiological conditions further supported that hypothesis. More recent studies compared the kinetic of accumulation of newly synthesized proteins in zymogen granule and their release in the gland lumen. The latter results are in agreement with a model in which secretory proteins are channelled in two separate pathways, one regulated, and one constitutive. Essentially, the constitutive pathway would correspond to a paragranular route in which the proteins would be immediately secreted instead of being stored in zymogen granules. In addition, some of the proteins released in the juice under "resting" conditions are associated to microvesicles. The term "microvesicular secretion" is used to designate that type of secretion.

Purification and characterization of alpha-amylase from rat pancreatic acinar carcinoma. Comparison with pancreatic alpha-amylase

alpha-Amylase was purified to apparent homogeneity from normal pancreas and a transplantable pancreatic acinar carcinoma of the rat by affinity chromatography on alpha-glucohydrolase inhibitor (alpha-GHI) bound to aminohexyl-Sepharose 4B. Recovery was 95-100% for both pancreas and tumour alpha-amylases. They were monomeric proteins, with Mr approx. 54000 on SDS/polyacrylamide-gel electrophoresis. Isoelectric focusing of both normal and tumour alpha-amylases resolved each into two major isoenzymes, with pI 8.3 and 8.7. Tumour-derived alpha-amylase contained two additional minor isoenzymes, with pI 7.6 and 6.95 respectively. All four tumour isoenzymes demonstrated amylolytic activity when isoelectric-focused gels were treated with starch and stained with iodine. Two-dimensional electrophoresis, on SDS/10-20%-polyacrylamide-gradient gels after isoelectric focusing, separated each major isoenzyme into doublets of similar Mr values. Pancreatic and tumour-derived alpha-amylases had similar Km and Ki (alpha-GHI) values, but the specific activity of the tumour alpha-amylase was approximately two-thirds that of the normal alpha-amylase. Although amino acid analysis and peptide mapping with the use of CNBr, N-chlorosuccinimide or Staphylococcus aureus V8 proteinase gave comparable profiles for the two alpha-amylases, tryptic-digest fingerprint patterns were different. Antibodies raised against the purified pancreatic alpha-amylase and tumour alpha-amylase respectively showed only one positive band on immunoblotting after gel electrophoresis of crude extracts of rat pancreas and carcinoma, at the same position as that of the purified enzyme. More than 95% of the alpha-amylase activity in the pancreas and in the tumour was absorbed by an excess amount of either antibody, indicating that normal and tumour alpha-amylases are immunologically identical. The presence of additional isoenzymes in the carcinoma, and dissimilarity of tryptic-digest patterns, may reflect an alteration in gene expression or in the post-translational modification of this protein in this heterogeneously differentiated transplantable pancreatic acinar carcinoma.

Comparison of the cellular pharmacology of doxorubicin in resistant and sensitive models of pancreatic cancer

The cellular accumulation and retention of doxorubicin (ADR) was investigated in two models of pancreatic adenocarcinoma, which differ markedly in their sensitivity to ADR. In vitro studies revealed that the relatively resistant cell line, WD PaCa (or well-differentiated pancreatic adenocarcinoma of the Syrian hamster), actually had higher ADR cellular levels than the sensitive cell line, PD PaCa (or poorly differentiated pancreatic adenocarcinoma of the Syrian hamster). While the efflux of ADR from WD PaCa was greater, the overall retention of ADR by WD PaCa was comparable to PD PaCa. These results failed to document differences in accumulation or retention of ADR capable of explaining the difference in the sensitivity of the cell lines to ADR and indicate the need to search beyond attainable drug concentrations for mechanisms of primary ADR resistance.

Hypertrophic foci of pancreatic acinar cells in rats

A morphologically distinctive type of pancreatic acinar cell foci, different from hyperplastic nodules and adenomas, in rats has been recognized for two decades. The lesions have been observed to occur spontaneously and to be induced experimentally. They consist of enlarged acinar cells with abundant cytoplasm of altered staining characteristics and prominent nuclei. There is, however, a wide divergence of opinion among investigators regarding the nature of the lesions. As a result of different interpretations and classifications, many terms have been given to them. Based on morphologic characteristics, the author has designated the lesions as hypertrophic foci, a descriptive morphological term. The biologic significance with particular reference to age and the relationship with acinar cell neoplasia is discussed. Also included in the review are similar lesions in other rodent species.

Inhibition of growth of pancreatic carcinomas in animal models by analogs of hypothalamic hormones

Using animal models of acinar and ductal pancreatic cancer, we investigated the effect of analogs of hypothalamic hormones on tumor growth. In Wistar/Lewis rats bearing the acinar pancreatic tumor DNCP-322, chronic administration of [L-5-Br-Trp8]somatostatin-14 significantly decreased tumor weights and volume. Somatostatin-28 and the cyclic hexapeptide analog of somatostatin cyclo(Pro-Phe-D-Trp-Lys-Thr-Phe) failed to influence the growth of this tumor. The agonistic analog of luteinizing hormone-releasing hormone [D-Trp6]LH-RH also significantly decreased tumor weight and volume in this model and reduced testosterone levels and the weights of the ventral prostate and tests. In Syrian hamsters bearing ductal type of pancreatic carcinoma, chronic administration of [L-5-Br-Trp8]somatostatin diminished tumor weights and volume. The percentage change in tumor volume was significantly decreased when compared to control animals. In one experiment, cyclic hexapeptide of somatostatin also inhibited growth of this tumor. [D-Trp6]LH-RH, given twice daily or injected in the form of microcapsules for constant controlled release, significantly decreased tumor weight and volume and suppressed serum testosterone levels. Hamsters castrated 4 days after transplantation of the pancreatic tumors showed a significant decrease in weight and volume of these tumors. This suggests that pancreatic cancers may, at least in part, be sex hormone sensitive. [D-Trp6]LH-RH may decrease the growth of pancreatic carcinomas by suppressing androgens. Somatostatin analogs reduce the growth of pancreatic ductal and acinar cancers, probably by inhibiting the release or stimulatory action of gastrointestinal hormones on tumor cells (or both). Inhibition of animal models of pancreatic tumors by chronic administration of somatostatin analogs and [D-Trp6]LH-RH suggests that these compounds should be considered for the development of a new hormonal therapy for cancer of the pancreas.

Plasma membrane retrieval in neoplastic pancreatic acinar cells

The dynamics of plasma membrane retrieval has been studied in the pancreatic acinar carcinoma in order to determine if neoplastic cells exhibiting a heterogeneity of cytodifferentiation states retain the capacity to interiorize and recycle plasma membrane. To this end, the plasma membranes of neoplastic pancreatic acinar cells were labeled with radioiodinated cationic ferritin (125I-CF), and the fate of the tracer was monitored by quantitative electron microscopic autoradiography. The undifferentiated granule-deficient cells of the tumor internalized membrane-bound 125I-CF and sequestered it predominantly in lysosomes. By contrast, the differentiated granule-rich cells internalized significantly more membrane-bound 125I-CF, and the tracer was localized in secretory granules and in lysosomes. The data suggest that neoplastic cells retain the capability of retrieving plasma membrane and that the dynamics of the process is correlated with the state of cytodifferentiation of the neoplastic cells.

Comparison of secretory protein and membrane composition of secretory granules isolated from normal and neoplastic pancreatic acinar cells of rats

The diversity of cytodifferentiation in a transplantable rat pancreatic acinar carcinoma provides a biological model system for the study of regulatory molecular events that differ from those in normal acinar cells. Secretory (zymogen) granule proteins and granule membranes of neoplastic and normal pancreatic acinar cells were compared to determine the differences in gene expression between apparently well-differentiated secretory granule-containing neoplastic cells and normal cells. Nineteen proteins observed in two-dimensional polyacrylamide gels of normal secretory granule extracts were seen also in tumor granule extract profiles, with reduced but detectable amounts of lipase and four basic proteins. In addition, tumor granule extracts contained a new protein of Mr 24,000, designated p24, which was not detectable in normal extracts. Neoplastic granule membranes, while having phospholipid composition similar to that of normal membranes, lacked or contained a greatly reduced amount of a major glycoprotein of Mr 80,000 and three other proteins of Mrs 50,000, 37,000, and 36,000. The nature of p24 protein in secretory granule extracts and the significance of the reduction or absence of Mr 80,000 membrane glycoprotein in this tumor remain to be elucidated.

Intracellular transport and storage of secretory proteins in relation to cytodifferentiation in neoplastic pancreatic acinar cells

The pancreatic acinar carcinoma established in rat by Reddy and Rao (1977, Science 198:78-80) demonstrates heterogeneity of cytodifferentiation ranging from cells containing abundant well-developed secretory granules to those with virtually none. We examined the synthesis intracellular transport and storage of secretory proteins in secretory granule-enriched (GEF) and secretory granule-deficient (GDF) subpopulations of neoplastic acinar cells separable by Percoll gradient centrifugation, to determine the secretory process in cells with distinctly different cytodifferentiation. The cells pulse-labeled with [3H]leucine for 3 min and chase incubated for up to 4 h were analyzed by quantitative electron microscope autoradiography. In GEF neoplastic cells, the results of grain counts and relative grain density estimates establish that the label moves successively from rough endoplasmic reticulum (RER) leads to the Golgi apparatus leads to post-Golgi vesicles (vacuoles or immature granules) leads to mature secretory granules, in a manner reminiscent of the secretory process in normal pancreatic acinar cells. The presence of approximately 40% of the label in association with secretory granules at 4 h postpulse indicates that GEF neoplastic cells retain (acquire) the essential regulatory controls of the secretory process. In GDF neoplastic acinar cells the drainage of label from RER is slower, but the peak label of approximately 20% in the Golgi apparatus is reached relatively rapidly (10 min postpulse). The movement of label from the Golgi to the post-Golgi vesicles is evident; further delineation of the secretory process in GDF neoplastic cells, however, was not possible due to lack of secretory granule differentiation. The movement of label from RER leads to the Golgi apparatus leads to the post-Golgi vesicles suggests that GDF neoplastic cells also synthesize secretory proteins, but to a lesser extent than the GEF cells. The reason(s) for the inability of GDF cells to concentrate and store exportable proteins remain to be elucidated.

Comment on the carcinogenic potential of di(2-ethylhexyl) phthalate

Analysis of the carcinogen bioassay of di(2-ethylhexyl) phthalate (DEHP) has shown that the designated maximum tolerated dose was exceeded in the low- and high-dose groups of male rats, in the high-dose group of female rats, and in the low- and high-dose groups of female mice. Significant differences in tumor incidence among small populations of laboratory animals within the testing facility further confounded interpretation of the bioassay. Critical data on food consumption, nutritional status, clinical signs, clinical pathology, and intestinal microorganisms are lacking. This review concludes that because of major deficiencies in the available data, the studies cannot be interpreted as showing a carcinogenic effect due to DEHP alone. Epigenetic mechanisms to explain the biologic effects are examined.

Carbamylcholine stimulation of protein secretion in pancreatic acinar carcinoma of rat

Pancreatic acinar carcinoma fragments, pulse-chase labeled with [3H]-leucine, responded to carbamylcholine chloride by increased secretion of [3H]leucine-labeled protein into external buffer medium. Secretion of labeled protein by the carcinoma fragments increased in concentration-dependent fashion between 10(-8) -10(-5) M carbamylcholine, was completely inhibited at 4 degrees C, and was accompanied by an equivalent increase in the secretion of preformed amylase. A maximally effective carbamylcholine concentration of 10(-5) M was observed for both carcinoma fragments and normal pancreas lobules. However, the maximal rate of protein secretion by the carcinoma fragments was only approximately one-fifth the rate determined for the normal pancreas lobules. This modest secretory response indicates a population of partially differentiated cells in the pancreatic acinar carcinoma which secrete less enzyme than fully differentiated adult pancreatic acinar cells. Secretory responsiveness can be utilized as a quantitative acinar cell response in studies on differentiation in pancreatic carcinoma.

Role of basal lamina in neoplastic disorganization of tissue architecture

We have studied a transplantable carcinoma of the rat pancreas [Reddy, J. K. & Rao, M. S. (1977( Science 198, 78-80] that is composed of cytologically differentiated acinar cells that have lost their epithelial orientation and do not form acini. Light microscopy shows, however, consistent palisading, reorientation, and polarization of these cells in areas of contact with the vasculature. Electron microscopy reveals a normal basal lamina (BL) along the basal portions of repolarized tumor cells that is physically separate from the endothelial BL. We used indirect immunofluorescence to examine the distribution of BL constituents, laminin (Lm) and type IV collagen (type IV), within the different microenvironments of this tumor. In normal pancreas, Lm and type IV are distributed linearly, outlining acini and blood vessels. In the tumor parenchyma, type IV is not detected, whereas Lm appears in a punctate distribution outlining cells. Reorientation of tumor cells is observed only along linearly deposited Lm and type IV bordering vessels. These data indicate that this nonmetastatic tumor has lost the ability to produce or maintain a complete BL within its disorganized parenchyma, while its cells retain the capacity to produce and reorganize along liner BL when in contact with vascular adventitia. We suggest that failure to maintain a complete BL may be involved in the neoplastic disorganization of normal tissue architecture as well as in the breakdown of boundaries during the development of invasive carcinomata.

Cell surface properties of normal, differentiating, and neoplastic pancreatic acinar cells

Acinar, centroacinar, and endocrine cells of the adult rat pancreas each exhibit distinctive cell-surface glycoconjugate patterns as detected by binding of a battery of lectin-ferritin conjugates. Acquisition of these unique glycoconjugate patterns appears to be developmentally regulated, as studies on embryonic rat pancreases at days 15, 17, and 19 of gestation indicate. Further, the three cell types appear to arise from a common stem cell(s) with surface glycoconjugate properties similar to those of the adult centroacinar cell. STudies on the cell-surface properties of a rat acinar cell tumor indicate that the neoplastic acinar cells are likely to be arrested at a developmental stage equivalent to acinar cells of the day 19 embryonic pancreas and are characterized by absence of detectable basal lamina. We hypothesize that pancreatic cancers may arise from the equivalent of the undifferentiated embryonic stem cell(s) and that the morphologic features of the tumor depend on the extent of cell differentiation, including expression of cell-surface glycoproteins and extracellular matrix, prior to neoplastic proliferation.

Transplantable pancreatic acinar carcinoma

Fragments of the nafenopin-induced pancreatic acinar cell carcinoma of rat have been examined in vitro for patterns of intracellular protein transport and carbamylcholine-induced protein discharge. Continuous incubation of the fragments with [3H]-leucine for 60 minutes resulted in labeling of rough endoplasmic reticulum, Golgi cisternae, and mature zymogen granules, revealed by electron microscope autoradiography. This result indicates transport of newly synthesized protein from the rough endoplasmic reticulum to mature zymogen granules in approximately 60 minutes. The secretagogue carbamylcholine induced the discharge of radioactive protein by carcinoma fragments pulse-chase labeled with [3H]-leucine. A maximal effective carbamylcholine concentration of 10(-5) M was determined. The acinar carcinoma resembles normal exocrine pancreas in the observed rate of intracellular protein transport and effective secretagogue concentration. However, the acinar carcinoma fragments demonstrated an apparent low rate of carbamylcholine-induced radioactive protein discharge as compared with normal pancreatic lobules or acinar cells. It is suggested that the apparent low rate of radioactive protein discharge reflects functional immaturity of the acinar carcinoma. Possible relationships of functional differentiation to the heterogeneous cytodifferentiation of the pancreatic acinar carcinoma are discussed.

Secretion granules of transplantable pancreatic acinar carcinoma of rat

Secretion granules of the rat transplantable pancreatic acinar carcinoma and of normal rat pancreas were isolated by differential centrifugation. Analysis of the granule content by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and isoelectric focusing procedures combined with specific enzyme assays indicated essential qualitative similarities between normal and neoplastic secretory proteins, suggesting retention of enzymic differentiation in this pancreatic acinar carcinoma. Accordingly, this epithelial tumor should serve as an important model for examination of regulatory mechanisms in cell differentiation and neoplasia.

Transplantation of azaserine-induced carcinomas of pancreas in rats

Two pancreatic adenocarcinomas which had been induced in Wistar/Lewis rats by azaserine treatment were transplanted into rats of the same strain by subcutaneous and intraperitoneal injection of minced tumor. Subsequently, we have serially transplanted into non-radiated recipients. Transplanted tumors have maintained evidence of acinar cell differentiation including the presence of zymogen granules in tumors studied by electron microscopy, and of lipase, amylase and trypsin activity in the supernatant of tumor homogenates. Histologically, the tumors vary from poorly differentiated solid carcinomas to well differentiated variants which form acini. Transplanted tumors are locally invasive and have metastasized to lung and liver in some recipients.

The morphologic and biologic patterns of chemically induced pancreatic adenocarcinoma in Syrian golden hamsters after homologous transplantation

A pancreatic adenocarcinoma induced by N-nitrosobis(2-oxopropyl)amine in the Syrian golden hamster was successfully transplanted to a homologous host by subcutaneous inoculation through 10 successive passages. The rate of 'tumor take' increased progressively with each generation from 60% to 100%, and the latency period after inoculation was reduced simultaneously from 6 weeks to 1 week in the second and following passages. The tumors grew rapidly, ulcerated the overlying skin, and metastasized to the regional lymph nodes and lungs. The animals usually died with multiple lung metastases between the 5th and 20th weeks. All transplanted tumors and their metastases retained the pattern of the original, well-differentiated adenocarcinomas.