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  • Title: The significance of DNA damage, its repair and cell proliferation during carcinogen treatment in the initiation of pancreatic cancer in the hamster model.
    Author: Kokkinakis DM, Subbarao V.
    Journal: Cancer Res; 1993 Jun 15; 53(12):2790-5. PubMed ID: 8504421.
    Abstract:
    N-Nitroso(2-hydroxypropyl)(2-oxopropyl)amine (HPOP) is a complete pancreatic carcinogen in female hamsters at a dose of 210 mg/kg given via an Alzet 2001 pump implanted s.c. Ultimate carcinogenic metabolites of HPOP target DNA to yield 7-and O6-methylguanines (7-mGua, O6-mGua) and 7- and O6-hydroxypropylguanines (7-HpGua, O6-HpGua). During continuous administration of HPOP, levels of DNA alkylation increase linearly with time of exposure and reach a maximum at the end of treatment. Such levels are markedly lower in pancreas or in its component duct or acinar cells than in liver or in other extrahepatic organs examined, indicating that the organotropy of HPOP does not directly correlate to its extent of activation by various tissues. After continuous treatment with HPOP, all major DNA adducts with the exception of 7-mGua in liver are repaired at rates slower than those measured after a single injection of the carcinogen. Half-lives for the repair of O6-mGua are 240 h in liver and considerably longer in extrahepatic tissues. Half-lives for the removal of 7-mGua are 46, 55, 72, and 96 h in liver, kidney, lung, and pancreas; while respective values for 7-HpGua are 216, 216, 132, and 140 h. No significant repair is observed for O6-HpGua for at least 8 days. The above differences in half-lives result in the gradual increase of 7-HpGua and O6-HpGua relative to their methyl counterparts. DNA synthesis progressively increases during HPOP infusion in all the tissues examined, and reaches maximum levels 3 to 4 days after termination of treatment. In pancreas, such levels are up to 5 times greater in HPOP treated animals than in controls. The increase in DNA synthesis during carcinogen treatment is due to the greater number of cells entering S phase rather than to an increase in the rate of proliferation of a certain population of cells. The mitogenic effect of HPOP in the pancreas and the persistence of highly promutagenic hydroxypropyl adducts are postulated to contribute to the initiation of pancreatic cancer in the hamster model.
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