Changes in the 32P incorporation in rat mammary tumor after chronic administration of LH-RH analogs

We studied endogenous phosphorylation in rat transplantable MT/W9A hormone-dependent mammary tumors of untreated rats and of animals treated with LH-RH analogs, the agonist D-Trp-6-LH-RH and the antagonist N-Ac-D-p-Cl-Phe1,2,D-Trp3,D-Arg6,D-Ala10-LH-RH. Incorporation of 32P from 32P-ATP was reduced significantly in tumors of rats treated with agonistic and antagonistic analogs of LH-RH or ovariectomized. The inhibition of protein phosphorylation may be related to tumor regression.     

Changes in the32P incorporation in rat mammary tumor after chronic administration of LH-RH analogs

We studied endogenous phosphorylation in rat transplantable MT/W9A hormone-dependent mammary tumors of untreated rats and of animals treated with LH-RH analogs, the agonistd-Trp-6-LH-RH and the antagonistN-Ac-d-p-Cl-Phe^1,2,d-Trp³,d-Arg⁶,d-Ala¹⁰-LH-RH. Incorporation of³²P from³²P-ATP was reduced significantly in tumors of rats treated with agonistic and antagonistic analogs of LH-RH or ovariectomized. The inhibition of protein phosphorylation may be related to tumor regression.     

Modification of nucleic acids with 1-nitropyrene in the rat: identification of the modified nucleic acid base

A modified nucleic acid base was isolated from liver DNA of rats treated with 1-nitropyrene. The structure of the modified nucleic acid base was identified as 1-(guanin-8-yl)-aminopyrene by comparison with an authentic sample.     

In vivo and in vitro binding of epichlorohydrin to nucleic acids

Epichlorohydrin (EC) binds to macromolecules of biological relevance in vivo: DNA is less labelled than RNA and proteins, rat organs interact more than mouse organs, stomach is the most labelled organ with liver, kidney and lung involved in decreasing order. Based on the Covalent Binding Index (CBI), EC is a weak-moderate oncogen, just as other chlorinated hydrocarbons such as 1,2-dichloroethane and carbon tetrachloride. An interaction of EC with nucleic acids (DNA and polyribonucleotides) occurs also in vitro. It is mediated either by chemical reactivity per se of the molecule (near-UV (NUV) irradiation does not photoactivate EC) and by enzymatic (microsomal and/or cytosolic) fractions, whose relative effectiveness is variable in relation to the organ tested. The best substrates for interaction are poly(G) and poly(A) when using microsomal and cytosolic fractions, respectively, whereas the labelling of double-stranded DNA is always lower. On the whole, the picture of enzyme (microsome + cytosol)-mediated in vitro interaction is similar to the pattern of in vivo binding, with the exception of rat stomach enzymes which are inactive in vitro.     

In vivo and in vitro binding of carbon tetrachloride with nucleic acids and proteins in rat and mouse liver

¹⁴C-labelled carbon tetrachloride binds in vivo to DNA of mouse liver and to ^rRNA of rat liver if the animals have been pretreated with 3-methylcholanthrene. A noticeable amount of radioactivity is also observed in liver proteins. In vitro carbon tetrachloride is activated by microsomes and pH 5 enzymes of 3-methylcholanthrene-treated animals to a metabolite which can react with DNA and polynucleotides; this effect is more evident if subcellular fractions from mouse liver are used.     

In vivo and in vitro binding of benzene to nucleic acids and proteins of various rat and mouse organs

Benzene binds to macromolecules of various organs in the rat and mouse in vivo. Labelling of RNA and proteins is higher (1 order of magnitude) than DNA labelling, which is low in many organs (liver, spleen, bone marrow and kidney), and negligible in lung; no difference between labelling of rat and mouse organs was found. The covalent binding index (CBI) value was about 10, i.e. typical of genotoxic carcinogens classified as weak initiators. In vitro binding of benzene to nucleic acids and proteins is mediated by hepatic microsomes, but not by microsomes from kidney, spleen and lung, or by cytosol from whatever organ. Nucleic acid binding can be induced by pretreatment with phenobarbitone (PB) and suppressed in the presence of SKF 525-A, of cytosol and/or GSH or of heat-inactivated microsomes. Labelling of exogenous DNA is low and is similar in the presence of rat or mouse microsomes in agreement with the low interaction with DNA measured in vivo.     

In vivo and in vitro covalent binding of chlorobenzene to nucleic acids

At 22 hr after ip injection into male Wistar rats and BALB/c mice, chlorobenzene was covalently bound to DNA, RNA and proteins of the liver, kidney and lung, as has been found with various weak carcinogens. A microsome-mediated interaction with DNA occurred in vitro. The interaction was enhanced by pretreatment in vivo with phenobarbitone but was suppressed by addition of 2-diethylaminoethyl-2,2-diphenylvalerate HC1 in vitro. These results indicate the involvement of cytochrome P-450. Liver microsomes were efficient bioactivators, whereas cytosol was ineffective. The extent of in vitro interaction of chlorobenzene with synthetic polyribonucleotides was of the same order as that with DNA. Finally, ultraviolet irradiation (lambda = 254 nm or lambda max = 365 nm) activated this environmental contaminant to forms capable of interacting with DNA. The results represent evidence for genotoxicity of chlorobenzene.