Induction of unscheduled DNA synthesis in primary cultures of rat pancreatic cells following in vivo and in vitro treatment with genotoxic agents

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Abstract
The pancreas is a key target tissue in human and animal carcinogenesis, yet few short‐term test systems measure genotoxicity in pancreatic cells. A method has been developed for the measurement of DNA repair as unscheduled DNA synthesis (UDS) in primary cultures of rat pancreatic cells (PRP) following in vitro or in vivo exposures to chemicals. PRP were isolated from female Sprague‐Dawley (SD) or male Fischer‐344 rats by mincing the pancreas in a collagenase solution followed by digestion in dispase. For in vitro exposures, PRP were incubated with 3H‐thymidine (3H‐TdR) in the presence of genotoxic agents for 18–22 hr. For in vivo exposures, male Fischer‐344 rats were treated with genotoxic agents 2 hr prior to sacrifice of the animals, and cells were incubated with 3H‐TdR. UDS was measured by quantitative autoradiography as net grains/nucleus (NG). Solvent controls ranged from −1.0 to −2.8 NG. Cells isolated from female SD rats and treated in vitro with methylmethane sulfonate (MMS), ethylmethane sulfonate (EMS), N‐methyl‐N′‐nitro‐N‐nitrosoguanidine (MNNG), and the pancreatic carcinogen azaserine all yielded over 4.0 NG. Cells treated in vitro with the hepatocarcinogens 2‐acetylaminofluorene (2‐AAF) and dimethylnitrosamine (DMN) and with the multisite carcinogen benzo[a] pyrene (B[a]P) yielded between −1.0 and −3.3 NG. These results are consistent with the lack of carcinogenic activity of 2‐AAF, DMN, and B[a]P in the pancreas and indicate that pancreatic cells are incapable of metabolizing these compounds to genotoxic forms. In vivo treatment with MMS at 100 mg/kg yielded 1.9 NG and with azaserine at 100 mg/kg yielded 8.2 NG. This method should be useful in detecting agents that are genotoxic to the pancreas.