(CANCER RESEARCH 50, 1634-1639. March 1. 1990| Inhibition of Streptozotocin-induced Islet Cell Tumors and 7V-Nitrosobis(2-oxopropyl)amine-induced Pancreatic Exocrine Tumors in Syrian Hamsters by Exogenous Insulin1

Parviz M. Pour,2 Katherine Kazakoff, and Kim Carlson

The Eppley Institute and Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska 68105-1065

ABSTRACT in hamsters, but animals recover from their diabetes sponta The effects of streptozotocin (SZ) and /V-nitrosobis(2-oxopropyl)amine neously. This recovery was associated with increased cell rep lication in islet and duetti lar cells with a peak 14 days post-SZ (BOP), separately or in combination, on the pancreas, common duct, and treatment.4 Treatment of diabetic hamsters with insulin pre gallbladder, all target tissues of BOP, were studied in Syrian golden hamsters. Groups of hamsters were treated with either a single dose (20 vented spontaneous recovery from diabetes and inhibited the mg/kg body weight) of BOP (BOP group), or a single i.p. dose (§0mg/ SZ-induced increase in cell replication of islet and ductular kg body weight) of SZ and 14 days later with a single s.c. injection of the cells.4 same dose of BOP (SZ + BOP group). Another group of animals was In the present study we examined the effect of SZ alone or treated similarly with BOP and SZ except that they received twice daily in combination with insulin on the induction by BOP of pan injections of insulin, beginning 1 day after SZ administration and for the creatic exocrine tumors, which are morphologically and biolog duration of the experiment (52 weeks) (SZ + insulin + BOP group). The ically similar to the human disease (11, 12). If cell proliferation control group consisted of hamsters treated with a single dose of BOP and daily doses of insulin (insulin + BOP group). Hamsters treated with in diabetic hamsters renders pancreatic cells more vulnerable SZ recovered spontaneously from their diabetes, although the mortality to the carcinogenic action of BOP, more tumors would be was high (86%). BOP treatment inhibited the diabetogenic effects of SZ expected in diabetic than in nondiabetic hamsters. On the other in both SZ + BOP and SZ + insulin + BOP groups and reduced the hand, insulin would counteract the enhancing effect of SZ on mortality to 43 and 74%, respectively. SZ pretreatment inhibited the exocrine pancreatic cancer induction because of its suppressive incidence of BOP-induced pancreatic ductal/ductular cell carcinomas in effects on cell replication. We also examined the common duct the SZ + BOP group (P< 0.01); this protective effect of SZ on carcinoma and the gallbladder, other target tissues of BOP. development was potentiated by additional treatment with insulin (SZ + insulin + BOP group, P < 0.001). Although the frequency of BOP- induced tumors in the gallbladder (all polyps) was not altered by either MATERIALS AND METHODS SZ or insulin, the frequency of the common duct polyps was significantly lower in the SZ + insulin + BOP group than in the BOP group (P < Male Syrian hamsters from the Eppley colony were housed in groups 0.005). Hamsters in the SZ, SZ + BOP, and SZ + insulin + BOP groups of 5 in plastic cages on granular cellulose bedding [Bed-O-Cobs; The developed islet cell adenomas (insulomas). However, the SZ + insulin + Anderson Cob Division, Maumee, OH], kept under standard laboratory BOP group had significant!) fewer insulomas than in the SZ + BOP conditions [room temperature, 21 ±3°C;12-h light/12-h dark cycle; group (/' < 0.0005). The overall data confirm the inhibitory effect of SZ relative humidity, 40 ±5% (SD)], and given Wayne Lab Blox (Allied on BOP-induced pancreatic cancer and suggest that this effect is related Mills, Chicago, IL) and water ad libitum. to the diabetic condition of hamsters rather than insulin deficiency and Hamsters were divided into 5 groups, 50 each, and were treated as that intact islets appear to be prerequisite for exocrine pancreatic cancer follows: BOP alone (BOP group); BOP plus twice daily insulin (see induction by BOP. On the other hand, the inhibitory action of insulin on below) for life (insulin + BOP groups); BOP plus SZ (SZ + BOP insuloma induction by SZ and on ductal/ductular cancer induction by BOP seems to be related to the suppressive effect of this hormone on />'- group); BOP plus SZ plus daily insulin for life (SZ + insulin + BOP group); SZ alone (SZ group; Table 1). The dose of BOP was 20 mg/kg cell and ductal/ductular cell replication, respectively. body weight and that of SZ was 50 mg/kg body weight. All animals were 8 weeks old when the treatment began. Surviving INTRODUCTION hamsters were sacrificed by CO2 inhalation. Blood glucose levels were Epidemiological studies suggest that diabetes presents a pre determined once before the treatment, every 8 weeks thereafter until disposing factor for pancreatic cancer (1-6) and that the risk of 28 weeks, and at the termination of the experiment at 52 weeks. At autopsy, all organs were examined grossly. The pancreas, with pancreatic cancer development remains for years after the di attached gallbladder and common duct, were fixed in Bouin's solution, agnosis of diabetes (1). Moreover, histopathological studies processed for histology by conventional methods, and stained with have revealed hyperplastic changes in the pancreatic ducts of hematoxylin and eosin. From 10 hamsters each from the SZ and SZ + deceased diabetics more often than in those of nondiabetics (7). insulin + BOP groups, the tissues were examined immunohistochemi- Reasons for the particular predisposition of diabetics toward cally for demonstration of ß-,«-,and á-cellsby using the appropriate pancreatic cancer could include perpetual proliferation of duc- antibodies as described.4 tular cells in diabetic patients (8, 9), a condition known to BOP was synthesized as reported ( 13) and was given once s.c. SZ (Sigma Chemical Co., St. Louis, MO), was prepared immediately increase the risk for carcinogenesis in many tissues, including before use as a 10-mg/ml solution in 0.1 M citrate buffer (pH 4.5) and the pancreas (10). was given i.p. as described.4 Our previous study has shown that SZ3 causes severe diabetes Insulin (Eli Lilly and Co., Indianapolis. IN) was prepared in normal Received 5/12/89; revised 8/7/89, 11/13/89; accepted 11/15/89. saline and injected s.c. twice a day during the experiment. Hamsters The costs of publication of this article were defrayed in part by the payment received 4 units Lente and 1 unit regular insulin/kg body weight 2 h of page charges. This article must therefore be hereby marked advertisement in before the dark cycle began (at 4 p.m.) and then received 4 units Lente accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1Supported by Grant CA38922. Laboratory Core Grant CA36727. National and 4 units Ultra Lente/kg body weight 16 h later (at 8 a.m. the Cancer Institute/NIH. and S1G-16. American Cancer Society. following day). Injection of each insulin type was given by separate 2To whom requests for reprints should be addressed, at The Eppley Institute syringe. This treatment schedule was found to be optimal in controlling for Research in Cancer, University of Nebraska Medical Center, 42nd and Dewey Avenue. Omaha. NE 68105-1065. 4 P. M. Pour. W. Duckworth, K. Carlson, and K. Kazakoff. Insulin therapy ' The abbreviations used are: SZ, streptozotocin; BOP. A'-nitrosobis(2-oxopro- prevents spontaneous recovery from streptozotocin-induced diabetes in Syrian pyl)amine. hamsters, submitted for publication. 1634 Downloaded from cancerres.aacrjournals.org on September 29, 2021. © 1990 American Association for Cancer Research. INSULIN EFFECTS ON SZ AND BOP CARCINOGENESIS

Table I Effective number of animals (ENA), survivals and final body weights (bw), type and incidence of tumors induced in Syrian hamsters with BOP and/or SZ with or without insulin treatment Given p values correspond to the data comparison between the groups with the same letters, i.e., a with a. b with h, etc. ductpolypsno. +SD)48 bw(g)130 bw(g)127 (%)Oa1 (%)14(42)°-*14(41)'-''9(21)4(%)1 (%)18(54)°16(47)*19(54)*14(33)'o°-*-r•(%)14(42)°-*13(38)°'*9(32)3 BOPGroupInsulin ±745 ±11132 ±11136± 1(33)°-*-'7 +BOPSZ ±1048 ±13124 32135 (3)"22 (20)"3(7)*1 +SZ ±642 ±13120 ±21126 (52)0-*-''4(9)''7(21)'° +SZBOPinsulin+BOPENA3334424315Survival(wk±945 ±10118 ±22138 (9)°-'o*-"° (2)°-"Of'c"P< (8)°0*° ±10Initial ±21Final ±17Insulomano. P <0.0005* P <0.005* 0.001*/>< P <0.005">< P<0.025">< P < 0.05Common 0.0005Adenomano.0.025Carcinomano.0.025Gallbladderpolypsno. hyperglycemia without adverse effects.4 value at week 30. The rate of survival in hamsters from the SZ Determination of Blood Glucose. Under light ether anesthesia blood + BOP group was significantly higher (57%) than in the SZ was withdrawn from the orbital vein and glucose was determined by group. the glucose oxidase method. In hamsters treated with SZ + insulin + BOP, the blood Statistical Analysis. Data were given as mean ±SD. For statistical comparison, analysis of variance by Scheffe's method was used. For glucose levels were high and remained high until week 16, at which time they were higher than levels in SZ-treated hamsters tumor incidence, data were considered from hamsters that lived longer than 28 weeks, at which time the first tumor was detected. (P < 0.04). At weeks 8 and 16, the hyperglycemia in the SZ + insulin + BOP group was also significantly higher than in the SZ + BOP group (P < 0.0001 and P < 0.0002, respectively). RESULTS Thereafter, the levels dropped sharply to values lower than in the SZ group at weeks 30 (P < 0.02) and 36 (P < 0.002). The The average survival, the initial and final body weights, and survival rate in the SZ + insulin + BOP group was 26%. the type and incidence of tumors are listed in Table 1; blood glucose levels are shown in Fig. 1. Histology

Blood Glucose In BOP and insulin + BOP groups most islets showed normal The blood glucose levels of hamsters in the SZ group de configuration and distribution. A few or several islets in both creased gradually during the observation period and reached groups showed intrainsular ductular proliferation, some of cys the normal value at 48 weeks. Most animals in this group died tic type (Fig. 2), causing fragmentation and atrophy of endo between weeks 16 and 48, and only 14% were still alive at the crine tissue. The number of these intrainsular ductules increased experiment end. with the experimental time. Also, in these altered islets, the Although initially the blood glucose levels were equally high normal ratio of 0-, a-, and 5-cells was retained. in all three groups of hamsters treated with SZ (SZ, SZ + BOP, In SZ + BOP-treated hamsters, islets varied in size from atrophie (20-50 ^m) to hyperplastic (&500 #/m; Fig. 3) and SZ + insulin + BOP), the degree of hyperglycemia became significantly less after BOP treatment in the SZ + BOP group, contained either uniformly shaped cells, as in control hamsters, compared with the SZ group at weeks 8-30 (P < 0.0001) and or a few or several hyperplastic cells with hyperchromatic at week 36 (P< 0.03). The blood sugar level reached the normal nuclei. In addition, the number of endocrine cells, and their distribution within the islets, varied between the normal ap pearing, atrophie, and hyperplastic islets and from area to area in the same pancreas or in different animals. In 6 of 42 hamsters

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WEEK Fig. 1. Blood glucose levels of hamsters treated with BOP. BOP and strepto- Fig. 2. Intrainsular ductular proliferation in a hamster treated with insulin + zotocin (BOP + SZ) or BOP + SZ plus insulin (SZ+I + BOP). BOP was injected BOP. The pseudopapillarty structures within the cystic ductules represent rup once s.c. 14 days after SZ treatment. Insulin was given daily for life. The numbers tured ductular walls. Note the presence of small and large groups of cells refer to the number of animals at the experimental intervals. *. P < 0.05: **. immunoreactive with anti-insulin. Avidin-biotin peroxidase complex method, x P < 0.005: ***. P < 0.0005 compared with SZ-treated hamsters. 200. 1635 Downloaded from cancerres.aacrjournals.org on September 29, 2021. © 1990 American Association for Cancer Research. INSULIN EFFECTS ON SZ AND BOP CARCINOGENESIS

t \\ n Fig. 5. A degenerated islet in a hamster of the SZ + BOP group. As in Fig. 4, Fig. 3. Islels in a hamster treated with SZ + BOP are of different size but there are several "ballooned cells" surrounded by cells ¡mmunoreactive with with the regular distribution of the endocrine cells. As in the normal hamster, «- antisomatostatin. Note the irregular arrangement of the ¿-cells.Avidin-biotin- cells occupy the outer zone of islets (black in photo). There are several extrainsular peroxidase complex method, x 200. n-cells (arrows). Avidin-biotin-peroxidase complex method, x 96.

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Fig. 6. Extrainsular cells immunoreactive with antiinsulin showing long and slender cytoplasmic processes, which extend between the acinar cells. Avidin- Fig. 4. A degenerated islet in a SZ + BOP-treated hamster composed of a large number of "light, ballooned" cells intermingled with a few acinar cells (long biotin-peroxidase complex method, x 200. arrow) and unstained islet cells. There is a single cell immunoreactive with anti- insulin (arrowhead). A small islet in the vicinity of this degenerated islet shows no staining (short arrow). Avidin-biotin-peroxidase complex, x 200. of this group, varying numbers of "ballooned cells" were ob served in islets (Fig. 4). All of these hamsters had normal blood glucose levels (129 and 128 mg/dl) at the time of death, whereas they all were hyperglycémiewhen the experiment began. In some of these islets with ballooned cells, none or only a few cells immunoreactive with any of the three antihormones could be found, whereas in others, primarily «-and ¿-cellswere present (Figs. 4 and 5). Generally, the atrophie islets were composed almost entirely of «-cellswith normal or increased numbers of ¿-cells,which showed derangement of their usual peripheral position in the islets (Fig. 5). However, in some islets the normal distribution of /i-, «-,and ¿-cellswere retained. On the other hand, all but one hyperplastic islet found in these Fig. 7. An islet of a hamster treated with SZ + insulin + BOP composed hamsters were composed of 0-cells with only a few or none «- primarily of cells immunoreactive with antiglucagon. There are a large number of extrainsular cells scattered between the exocrine cells (black in photo). Avidin- and/or ¿-cells.The number of extrainsular endocrine cell foci biotin-peroxidase complex, x 200. increased remarkably, a phenomenon found consistently during pancreatic carcinogenesis with BOP (11, 14). Some of these extrainsular endocrine cells showed tiny and long cytoplasmic 386 mg/dl). The remaining hamster was normoglycemic processes extending between and around the neighboring acinar throughout the experiment. In most hamsters of this group, cells (Fig. 6). islets were depleted of ß-cellsand contained primarily «-cells In the SZ + insulin + BOP group, most hamsters showed (Fig. 7), with a normal number of ¿-cellsrandomly distributed small islets with irregular borders. Ballooned cells were found within the islets. In a few hamsters groups of 0-cells could be in the islets of 5 of 43 hamsters, 4 of which were still diabetic identified in the islets, but the number of fj-cells was low, at the time they were killed (blood glucose between 318 and ranging from 10 to 50%/islet. In this group of hamsters, many 1636 Downloaded from cancerres.aacrjournals.org on September 29, 2021. © 1990 American Association for Cancer Research. INSULIN EFFECTS ON SZ AND BOP CARCINOGENESIS extrainsular cells were immunoreactive with a-, /3-,or ¿-cells. groups. About 60% of the tumors, regardless of their size, were Histológica! findings in SZ-treated hamsters were generally composed of 0-cells with none or a few (1-20%) «-cells,fewer similar to those in the SZ + BOP group with regard to the size numbers of ¿-cells(0-10%), and various number of unstained and the cell composition of islets. In 8 of 15 hamsters, balloon cells. In the remaining 40% of the neoplasms, the 0-celIs cells were identified in a number of islets. Of these 8 hamsters, contributed to 15-50% of the cell population with only a few 7 were diabetic at the time they were euthanized and the a- or ¿-cellsand many cells that did not react with any of the remaining one was diabetic at the beginning of SZ treatment. three antibodies used (Figs. 8-10). In these adenomas, the In hamsters of this group, many islets of regular or small size immunoreactive cells were arranged either in groups within or contained none or only a few cells immunoreactive with anti- individually in random fashion between the unstained cells insulin, whereas most of these cells were of the «-celltype, (Figs. 8 and 9). In some cases the apparently newly formed fi- between and around which ¿-cellsweredemonstrable. However, almost all hyperplastic islets (>500 /¿mindiameter) were com posed of/i-cells with none or a few a- and/or ¿-cells,except in one case, in which 50% of cells were «-cellsand the remaining half were /3-cells. / •¿W.' Patterns of Tumors The incidence and type of tumors found in each group are listed in Table 1. Exocrine Tumors. Ductular proliferation (pseudoductules, tu bular complex) was seen in all groups. Higher incidences oc curred in the BOP (100%), insulin + BOP (79%), SZ + BOP (60%), and SZ + insulin + BOP (44%) groups than in the SZ (9%) group. As stated above, in many cases the ductules were found, often in cystic patterns, within the islets. Significantly, more ductular adenomas were found in ham sters treated with BOP or insulin + BOP than in the other two Fig. 8. One islet cell adenoma in a hamster treated with S7. + BOP. There groups. Ductal/ductular carcinomas occurred in all groups are only a few cells immunoreactive with somatostatin and most of these cells are treated with BOP. However, the incidence of carcinomas was in the periphery of the tumor. Insulin-containing cells were relatively larger in number, were scattered throughout the tumor, and generally showed a weak significantly lower in the SZ + insulin + BOP and SZ + BOP reactivity. Avidin-biotin-peroxidase complex method, X 90. groups than in the BOP and insulin + BOP groups. Adenocar- cinomas in the BOP and insulin + BOP groups were large (about 10 mm in diameter) and invasive, whereas in the SZ + BOP group all 3 cancers were of microscopic size. There were also many more in situ carcinomas in hamsters treated with BOP (27%) or with insulin + BOP (32%) than with SZ + BOP (12%) or with SZ + insulin + BOP (7%, P < 0.001). Although the incidence of gallbladder tumors (all polyps) did "la not differ among the BOP-treated groups, significantly fewer HK common duct tumors (all polyps) were found in SZ + insulin f H •¿ + BOP-treated hamsters. : Endocrine Tumors. Islet cell tumors were seen in hamsters ' treated with SZ, SZ -I- BOP, and insulin + BOP. (The one tumor seen in a hamster of the insulin + BOP group was most probably a spontaneously developed lesion). The tumor inci dence was significantly lower in the SZ + insulin + BOP than in the SZ + BOP group (P < 0.0005). The lower incidence of insulomas in the SZ group than in the SZ -I-BOP group could be related to the early death of many hamsters in the SZ group. The first insuloma was found at week 28 in the SZ and SZ + insulin + BOP groups and at week 27 in SZ + BOP group. The neoplasms were generally small, ranging from 2 to 4 mm in diameter; only a few of them were encapsulated. Because of the small size of insulomas and because only a few sections from each pancreas were examined histologically, the insuloma incidence could have been higher than that listed in Table 1. In fact, in some cases tumors were found only in a single section and not in the subsequent slide. For this reason, not all of these tumors could be examined by all three antibodies. Morphologically, all of the endocrine neoplasms were ade nomas (insulomas) with no differences in their patterns and sizes among the groups. The neoplasms were, in most cases, ill defined and in some regions extended into the surrounding Fig. 9. Two consecutive sections of an islet cell adenoma in a hamster treated with SZ + BOP. In both sections the immunoreactive cells with antiinsulin (a) tissue. Immunohistochemical examination did not reveal dif and antiglucagon (A) are in the center of the tumor. Avidin-biotin-peroxidase ferences in the cellular composition of adenomas among the complex method, x 200. 1637 Downloaded from cancerres.aacrjournals.org on September 29, 2021. © 1990 American Association for Cancer Research. INSULIN EFFECTS ON SZ AND BOP CARCINOGENESIS

the hyperplastic (preneoplastic) islets did not correlate with that in neoplastic islets. For example, in SZ + insulin + BOP- treated hamsters in whom hyperplastic islets were almost en tirely composed of «-cells,tumors contained a few or none o- cells, various numbers of ß-cells,and none or a few ¿-cells(Fig. 10). There was also no correlation between the severity of hyperglycemia, either at the beginning or the end of the exper iment, and the pattern and incidence of tumors. Table 2 sum marizes the initial and final blood glucose levels of hamsters in each group.

DISCUSSION In the present study, hamsters treated with SZ only developed severe hyperglycemia and surviving hamsters (14%) recovered gradually from the SZ-induced diabetes spontaneously, al though 86% of hamsters died from the consequences of diabetes between weeks 16 and 48. In our previous study, recovery from diabetes occurred in 50% of hamsters at 70 days post-SZ.4 BOP treatment (SZ + BOP) clearly reduced the diabetogenic effects of SZ in this species and prolonged the survival significantly (57% versus 14%). Although SZ + BOP-treated hamsters had blood glucose levels initially as high as in the SZ group, the glucose levels dropped rapidly after BOP treatment and nor malized much earlier than did in the SZ group. In the SZ + BOP group, none of the hamsters were hyperglycémieat the end of the experiment. A similar situation was seen in the SZ + insulin + BOP group. In the previous study, administration of insulin at the same dose and frequency as given to SZ-treated hamsters (SZ Fig. 10. Two consecutive sections of a pancreas in a hamster treated with SZ + insulin + BOP. All nonneoplastic islet cells in this case are composed of n cells + insulin group) adversely affected diabetes and caused persist (a), whereas only a few «-cellsare present in islet cell adenoma (center). On the ent severe hyperglycemia during the 70-day observation period.4 other hand most tumor cells are of d-cell type showing different staining intensity In the present experiment, BOP given to SZ + insulin-treated with antiinsulin (ft) and no insulin-containing cells are in surrounding nonneo plastic islets. Avidin-biotin-peroxidase complex method, x 90. hamsters inhibited the dramatic increase of blood sugar and its persistency. Moreover, in the SZ + insulin + BOP group, blood glucose levels dropped drastically after week 16 and reached Table 2 Initial and final blood glucose levels (in mg/dl) of hamsters with induced tumors levels lower than in the SZ group thereafter, a situation that could have as well increased survival of animals in this group GroupBOPInitialFinalInsulin value114118128110781133476341741380as compared with those in the SZ group. The reasons for the beneficiary effects of BOP on the course of SZ-induced diabetes is obscure. The pronounced formation in the SZ + BOP and SZ + insulin + BOP groups of extrain- +BOPInitialFinalSZ sular endocrine cells (nesidioblastosis), a phenomenon known (100)21 to occur consistently during BOP pancreatic carcinogenesis (11, (100)7(27)19(73)04(44)1(9)3(27)150-3000005(19)5(19)1(11)3(33)1(9)6(54)>300000014(54)2(8)8(89)2(22)9(82)2(19)Maximum14, 15), could be one explanation. Whether the number or the +BOPInitialFinalSZ functional activity of these extrainsular ßcellswas sufficient to compensate for the 0-cells destroyed by SZ or in these animals extrapancreatic sources of insulin may have existed (16) is BOPInitialFinalSZInitialFinallesions. Based on beginning 7 days after SZ treatment, no pancreatic tumors were the blood glucose levels of tumor-bearing hamsters, none of induced. In the present experiment, insulin given to normogly- these adenomas seem to be biologically active. In fact, some cemic hamsters (insulin + BOP group) did not influence the hamsters with large tumors primarily composed of 0-cells had tumor yield. Therefore, it appears that intact islet cells rather glucosuria at the time of death. The predominant cell type in than the availability of insulin are prerequisite for triggering 1638 Downloaded from cancerres.aacrjournals.org on September 29, 2021. © 1990 American Association for Cancer Research. INSULIN EFFECTS ON SZ AND BOP CARCÕNOCENESIS the neoplastic effects of BOP. In fact, intrainsular ductular lethal effect of SZ (intrainsular origin) or from the nesidioblas- proliferation, an early event in pancreatic carcinogenesis (11, tosis foci (extrainsular origin). Extrainsular endocrine cells with 14, 15), was found predominantly in hamsters whose islets remarkably long and tiny cytoplasmic processes surrounding contained many /3-cells. Whether 0-cells exert their effects by the neighboring acinar cells resembled the alterations of cen- factors other than insulin or «-cells(the numbers of which were troacinar cells during exocrine pancreatic carcinogenesis of increased significantly in these animals) act as inhibitors for BOP in this species (22). This finding may imply that the ductular proliferation remains to be seen. extrainsular cells derive from altered centroacinar cells. If this The possibility that tumor inhibition by SZ could be related is the case, it will be of extreme conceptual interest to find out to toxic effects of this compound on the liver, the suggested why the differentiation pathways of centroacinar cells, the target major site of BOP metabolism to a proximate pancreatic car cells for both BOP (causing ductal/ductular tumors) and SZ cinogen (19), seems unlikely because pancreatic cells can me (inducing endocrine cell neoplasms), are different. tabolize BOP directly (20). In the present study, tumor induc In conclusion, the results of this experiment do not support tion in other target tissues of BOP, such as gallbladder, was the concept that diabetes is a risk factor for pancreatic cancer. not altered in SZ pretreated hamsters. Alloxan, another /i-cell cytotoxic substance, in a nonhepatotoxic dose also inhibited REFERENCES pancreatic tumor induction by BOP (21). Similarly, the possibility that the inhibitory action of SZ on 1. 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Pancreatic transplantion of the pancreases of hamsters treated with SZ neoplasms in an animal model: morphological, biological and comparative into normal (host) hamsters and subsequent treatment of the studies. Cancer (Phila.). 35: 379-389. 1975. 13. Nagel. D., and Kupper. R. Synthesis of A/-nilrosobis(2-oxopropyl)aminc and hosts (bearing two pancreases) with BOP did not result in its MCanalogue. J. Labelled'Compds.. 18: 1081-1085. 1981. tumor inhibition in the donor pancreas (24). Consequently, the 14. Pour. P. M. Histogenesis of exocrine pancreatic cancer in the hamster model. diabetic status, i.e., metabolic changes associated with the dis Environ. Health Perspect., 56: 229-243, 1984. ease rather than the ß-celldeficiency may be an inhibitory 15. Pour. P. M. Islet cells as a component of pancreatic ductal neoplasms. I. Experimental study. Ductular cells, including islet cell precursors as primary factor. progenitor cells of tumors. Am. J. Pathol.. 90: 295-316. 1978. 16. Hazelwood. R. L.. and Cieslak. S. R. In vitro release of pancreatic hormones In the present study, the greater inhibitor effects of the following 99r; pancreatectomy in the chicken. Gen. Comp. Endocrinol., 73: combined SZ and insulin treatment on pancreatic cancer induc 308-317, 1989. tion by BOP could be related to the suppressive effects of 17. Bell. R. H. Jr.. and Strayer. D. S. Streptozotocin prevents development of insulin on ductular cell regeneration.4 The inhibitory action of nitrosamine-induced pancreatic cancer in the Syrian hamster. J. Surg. Oncol.. 24:258-262, 1983. SZ or insulin seems to be directed toward the initiation of 18. Pour. P. M.. and Patii, K. Modification of pancreatic carcinogencsis in the pancreatic carcinogenicity, because SZ given 7 days after BOP hamster model. X. Effects of streptozotocin. J. Nati. Cancer Inst.. 71: 1059- has failed to inhibit tumorigenesis.5 The mechanisms of this 1065. 1983. 19. Kokkinakis. D. M.. Koop. D. R.. Scarpelli. D. G., Coon, M. J., and Hollen- action are not yet known. berg, P. F. Metabolism of ,V-nilroso-2.6-dimcthylmorpholine by isozyme of rabbit liver microsomal cytochrome P-450. Cancer Res., 45: 619-624. 1985. Inhibition by insulin of insuloma induction by SZ could well 20. Lawson. T.. Nagel. D.. Kolar. C., and Gairels. R. The activation of ('H)N- have the same cause, for example suppressive action of the nitrosobis(2-oxopropyl)amine by isolated hamster pancreatic cells. Carcino hormone on islet cell regeneration.4 Remarkably, most insulo- genesis (Lond.), in press, 1990. 21. Pour. P. M.. Donnelly, K.. and Stepan. K. Modification of pancreatic mas induced by SZ contained more cells immunoreactive with carcinogenesis in the hamster model. 3. Inhibitory effect of alloxan. Am. J. antiinsulin than those reactive with antiglucagon and antiso- Pathol.. 110: 310-314. 1983. matostatin, although a-cells and, to a lesser degree, ¿-cellswere 22. Pour. P. M. Mechanism of pseudoductular (tubular) formation during pan creatic carcinogenesis in the hamster model. Am. J. Pathol., 130: 335-344, the cell types that initially proliferated and replaced the dam 1988. aged /3-cells. This observation indicates that a- and A-cells are 23. Bell. R. H.. McCullough. P. J.. and Pour. P. M. Influence of diabetes on not the target of SZ toxicity. The malignant endocrine cells susceptibility to experimental pancreatic cancer. Am. J. Surg.. 755: 159-164. 1988. seem to arise either from the /i-cells that may have survived the 24. Bell. R. H.. Savers, H. J., Pour. P. M.. Ray. M. B.. and McCullough. P. J. Importance of diabetes in inhibition of pancreatic cancer by streptozotocin. ' R. H. Bell, personal communication. J. Surg. Res.. 46: 515-519. 1989.

1639 Downloaded from cancerres.aacrjournals.org on September 29, 2021. © 1990 American Association for Cancer Research. Inhibition of Streptozotocin-induced Islet Cell Tumors and N -Nitrosobis(2-oxopropyl)amine-induced Pancreatic Exocrine Tumors in Syrian Hamsters by Exogenous Insulin

Parviz M. Pour, Katherine Kazakoff and Kim Carlson

Cancer Res 1990;50:1634-1639.

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