Selective effects of selenium selenite on 7,12-dimethylbenz(a)anthracene-DNA binding in fetal mouse cell cultures.
Sodium selenite inhibits the binding of 7,12-dimethylbenz(a)anthracene (DMBA) to DNA in tertiary cultures of fetal mouse cells in a rather selective fashion. Inhibition can be demonstrated at 6 but not at 3 h after DMBA addition to the cells. Inhibition is seen after treatment of the cells with DMBA concentrations of 0.05 or 0.1 micrograms/ml but not after treatment at 0.01 micrograms/ml. Furthermore the inhibition seen with up to 1 microgram selenium/ml is selective in that products from the anti bay region dihydrodiol epoxide metabolite (where the epoxide oxygen is trans to the 4-hydroxy group) are suppressed while those from the syn-dihydrodiol-epoxide (where the epoxide oxygen is cis to the 4-hydroxy group) are not affected. In the absence of selenite, it was found that syn-dihydrodiol epoxide-DNA adducts are formed in a roughly linear fashion with time over a range of DMBA concentration. In contrast, the capacity of the cells to generate anti-dihydrodiol-epoxide adducts in a 3-h interval is saturated at concentrations of DMBA above 0.025 micrograms/ml and after the initial 3-h period the cells generate these adducts at up to a 6-fold greater rate than during the initial 3 h. This increase in rate of formation of anti-dihydrodiol-epoxide products is inhibited by actinomycin D and appears to be a consequence of DMBA inducing an enzyme activity which selectively generates the anti-dihydrodiol-epoxide and not the syn-dihydrodiol-epoxide. The selective action of sodium selenite in inhibiting only anti-dihydrodiol-epoxide product formation and doing this only at certain times and at certain doses of DMBA is a result of the fact that it inhibits the induction process. Once induction has occurred, sodium selenite is no longer inhibitory of DMBA-DNA binding. The chemopreventive action of selenium in chemical carcinogenesis could be partially attributable to effects such as those described herein on carcinogen-DNA binding. It is also possible, however, that the chemopreventive actions of selenium might be attributable to effects on the expression of genes other than those involved in carcinogen metabolism.
D015127:9,10-Dimethyl-1,2-benzanthracene / Q000378:metabolism*; D000818:Animals; D001711:Biotransformation / Q000187:drug effects; D002478:Cells, Cultured; D004247:DNA / Q000378:metabolism*; D003609:Dactinomycin / Q000494:pharmacology; D051379:Mice; D020887:Selenious Acid; D012643:Selenium / Q000494:pharmacology*; D013997:Time Factors
D003609:Dactinomycin; D015127:9,10-Dimethyl-1,2-benzanthracene; D004247:DNA; D020887:Selenious Acid; D012643:Selenium