The angiotensin-converting enzyme (ACE) inhibitor captopril inhibits mitosis in several cell types that contain ACE and renin activity. In the present study, we evaluated the effect of the ACE inhibitors captopril and CGS 13945 (10(-8) to 10(-2) M) on proliferation and gene expression in hamster pancreatic duct carcinoma cells in culture. These cells lack renin and ACE activity. Both ACE inhibitors produced a dose-dependent reduction in tumor cell proliferation within 24 hr. Captopril at a concentration of 0.36 mM and CGS 13945 at 150 microM decreased cellular growth rate to approximately half that of the control. Neither drug influenced the viability or the cell cycle distribution of the tumor cells. Slot blot analysis of mRNA for four genes, proliferation associated cell nuclear antigen (PCNA), K-ras, protein kinase C-beta (PKC-beta) and carbonic anhydrase II (CA II) was performed. Both ACE inhibitors increased K-ras expression by a factor of 2, and had no effect on CA II mRNA levels. Captopril also lowered PCNA by 40% and CGS 13945 lowered PKC-beta gene expression to 30% of the control level. The data demonstrate that ACE inhibitors exhibit antimitotic activity and differential gene modulation in hamster pancreatic duct carcinoma cells. The absence of renin and ACE activity in these cells suggests that the antimitotic action of captopril and CGS 13945 is independent of renin-angiotensin regulation. The growth inhibition may occur through downregulation of growth-related gene expression.

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Metabolism of 14C labeled N-nitrosobis(2-oxopropyl)amine (BOP), N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine (HPOP) and N-nitrosobis(2-hydroxypropyl)amine (BHP) by pancreatic duct cells in culture involves the following two pathways: reduction or oxidation reactions at the beta-carbon which result in the inter-conversion of these nitrosamines and activation reactions which result in the decomposition of the nitrosamine, the evolution of 14CO2 and the labeling of macromolecules. Reduction of BOP to HPOP seems to contribute significantly to the metabolism of the former nitrosamine by pancreatic duct cells, however, redox reactions at the beta-carbon of HPOP or BHP are not extensive. In terms of DNA damage, all three nitrosamines yield methyl and hydroxypropyl adducts. As expected, HPOP and BHP yield higher levels of O6-hydroxypropylguanine than BOP, while the latter yields higher levels of O6-methylguanine. There is no correlation between the ability of these nitrosamines to alkylate duct cell DNA in vitro and their carcinogenic potency in vivo. Concentrations of DNA adducts induced by pancreas specific nitrosamines (PSNs) in cultured duct cells at concentrations comparable to those found in the pancreatic juice of animals treated with BOP, are almost an order of magnitude lower than those induced in the pancreas of such animals. Discrepancies between in vitro and in vivo formation of active metabolites and DNA adducts may be attributed to the decline of the cells' ability to activate PSNs during culturing. In the same vein, the ductal cell may not be the main source of active metabolites targeting its DNA in the animal model.

The tobacco specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent carcinogen in laboratory animals. In the present study, in vitro transformation of spontaneously immortal hamster pancreatic duct cells following exposure to 20 mM NNK for 1,3,5 and 7 days is described. NNK imparted a dose-dependent and time-dependent toxicity to pancreatic duct cells in vitro. After NNK treatment, duct cells were grown either in complete duct medium (CDM) or in the absence of bovine pituitary extract, epidermal growth factor and Nu-serum (incomplete duct medium, IDM). Addition of NNK to the culture for 1 and 3 days did not affect the growth of the cells, whereas exposure of the cells for 5 and 7 days was inhibitory. One and 3 day NNK-treated cells were able to grow in the absence of growth factors and serum immediately after the treatment without any inhibition of growth. Untreated cells grew as a monolayer consisting of tightly packed polygonal cells with single nuclei. NNK treated cells also grew as a monolayer with numerous mitotic figures and multi-nucleated large cells. The doubling time between the untreated (16 h) and NNK-treated cells (14 h) was not significantly different prior to injection into the nude mice. NNK treated cells grown in IDM displayed anchorage independency in soft-agar. The tumorigenicity of the untreated and NNK treated cells (5 x 10(6)) was determined in nude mice. One and 3 day NNK-treated cells grown in CDM produced well-differentiated, mucinous tumors with a lower frequency (2/4 sites) and longer duration, but produced tumors at a higher frequency (4/4 sites) and shorter duration when grown in IDM. Five and 7 day NNK-treated cells grown in CDM did not produce any tumors; however, they produced tumors when grown in CDM followed by IDM (5/8 and 6/8 sites) with a shorter duration in nude mice. Analysis of DNA for k-ras mutation at codons 12, 13 and 61 showed G-A transition at codon 12 of the k-ras oncogene in tumor cells of 1 and 3 day NNK treatment. No mutation was detected in tumor cells from 5 and 7 day treatment.