Elna T. Kuhlmann

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.

Inhibition of pancreatic and liver carcinogenesis in rats by retinoid- and selenium-supplemented diets

Chemoprevention by a synthetic retinoid. selenium. and these agents in combination during the postinitiation stages of carcinogenesis induced in rats by azaserine was evaluated. Male Lewis rats were given three weekly injections of 30 mg/kg azaserine while being fed a purified diet. One week after completion of carcinogen treatment, groups of rats were switched to the purified diet supplemented with either a retinoid, N-(2-hydroxyethyl)retinamide, at a level of 0.5 or 1 mmol/kg diet, or with 5 ppm sodium selenite, or with a combination of retinoid and selenium. One year after the diet change, the incidence of pancreatic and other neoplasms was determined by autopsy and histologic study. The incidence of pancreatic carcinoma (including carcinoma-in-situ, CIS) among nonretinoid-treated controls was 68%. Since the dietary supplements were fed after completion of exposure to the carcinogen, the effects on both pancreatic and liver carcinogenesis were exerted during the postinitiation phase of carcinogensis. As in previous studies, the retinoid inhibited the progression of pancreatic carcinogenesis in a dose-related fashion. Selenium alone had no effect. However, the combination of retinoid plus selenium was more effective than retinoid alone, although the increase in inhibition was not large. The retinoid was also found to inhibit liver carcinogenesis induced by azaserine. Selenium, either alone or in combination with retinoid, was ineffective. Finally, testicular atrophy, noted as a toxic effect of retinoids in other studies, was not observed in this work.

Mutated c-K-ras in small pancreatic adenocarcinomas

The objective of this study was to determine whether small human pancreatic adenocarcinomas contain activated c-K-ras as an approach to answering the question of whether c-K-ras mutation is an early change in this disease. Eight pancreatic adenocarcinomas in the range 1.2-3 cm were analyzed for c-K-ras mutation at codon 12 by amplifying the c-K-ras gene around codon 12 out of paraffin-embedded tissue sections using the poly-merase chain reaction. c-K-ras mutations were detected by allele-specific oligonucleotide hybridization. Six of the eight small pancreatic adenocarcinomas contained mutated c-K-ras at codon 12, position 2, and two of the six tumors had an additional mutation at position 1 of codon 12. Our results indicate that small pancreatic adenocarcinomas are similar to large, late-stage pancreatic adenocarcinomas in that 75% of the tumors analyzed contain mutated c-K-ras at codon 12, position 2. These data suggest that c-K-ras mutation occurs early and may therefore have a role in initiation of human pancreatic adeno-carcinoma.

Studies of pancreatic nodule induction and DNA damage by D-azaserine

The ability of the D-isomer of azaserine to induce atypical acinar cell nodules (AACN) in pancreas and to cause DNA damage in pancreas and liver was evaluated. Rats were injected with equivalent doses of D- or L-azaserine and numbers of AACN were counted after 4 months. DNA damage in pancreas and liver of rats treated in vivo, and in pancreatic acinar cells treated in vitro with D- or L-azaserine was determined by alkaline elution. Results show that D-azaserine does not significantly induce AACN in pancreas, nor does it cause extensive DNA damage in comparison with L-azaserine, suggesting that the differential effect of the 2 isomers is related to stereospecificity in either transport or metabolism.

Pancreatic carcinogenesis in azaserine-treated rats: Inhibition by a solvent mixture in the diet

The growth of azaserine-induced foci and nodules in a 4-month experiment and the incidence of carcinomas in a 15-month experiment were greater in LEW/CrlBR inbred rats fed a purified diet (AIN-76A) than in rats fed a natural-ingredient diet (chow). Addition of a mixture of several solvents to either diet reduced the incidence of adenocarcinomas in the pancreas in the long-term study but failed to reduce the number or size of pancreatic atypical acinar cell foci in the experiments of 4 months and 6 months (chow only) duration. Apparently, some component of the solvent mixture inhibits a late stage in the development of pancreatic carcinoma. Glyceryl monooleate and propylene glycol are implicated as the components of the mixture most likely to be responsible for the inhibitory effect, but neither the identity of the critical component nor the mechanism of the inhibition is known. The solvent mixture also contained ethanol and trioctanoin.

Effects of retinoids in N-nitrosobis(2-oxopropyl) amine-treated hamsters

The effect of feeding four synthetic retinoids was evaluated in carcinogen-treated hamsters. Syrian golden hamsters were injected with 20 mg/kg of N-nitrosobis(2-oxopropy1)amine (BOP) and then fed retinoid-supplemented diets for 39 weeks. All retinoid-treated groups grew more slowly than controls, and average survival was shorter in female retinoid-treated groups. A significant incidence of testicular atrophy was noted in male hamsters fed 2-hydroxy-ethylretinamide or 4-carboxyphenylretinamide. The incidence of pancreatic carcinomas was lower in 12 of 14 retinoid-fed groups than in the corresponding control groups, although the differences approached significance only in groups fed two of the retinoids—male hamsters fed N-4-propionyloxyphenylretinamide and those fed retinylidene dimedone. A low incidence of carcinoma in the control groups limits the conclusions that can be drawn from this study, but it is of note that there was no evidence of promotion.