Formation of 06-Methylguanine by Alkylation of Rat Liver, Colon, and Kidney DNA Following Administration of 1 ,2-Dimethylhydrazine1

[CANCER RESEARCH 37, 4082-4087, November 1977] Formation of 06-Methylguanine by Alkylation of Rat Liver, Colon, and Kidney DNA following Administration of 1 ,2-Dimethylhydrazine1

Kenneth J. Rogers and Anthony E. Pegg2 Departmentof Physiologyand SpecializedCancerResearchCenter,TheMilton S. HersheyMedicalCenter,ThePennsylvaniaStateUniversityCollegeof Medicine, Hershey, Pennsylvania 17033

SUMMARY cinogen (3, 31). Tumors were also produced in the duo denum, small intestine, liver, and kidney by 1,2-dimethyl The alkylation of DNA in the liver, kidney, and colon was hydrazine (3, 10, 13, 31). The distribution of tumors de measured at varying times after administration of 1,2-di pended on the dosage and method of application, but even methylhydrazine to rats. DNA was alkylated to a much a single injection resulted in the formation of some tumors greater extent in the liver than in the kidney or the colon in the colon and kidney (3, 10). after a dose of 200 mg/kg body weight given either by i.p. The mechanism by which 1,2-dimethylhydrazine exerts or s.c. injection. The level of alkylation in the liver was only its carcinogenic action has been postulated to be similar to slightly affected by the route of administration, but alkyla that of cycasin and simple aliphatic nitroso compounds in tion of kidney DNA was greater after s.c. injection than that metabolism of the carcinogen leads to the formation after i.p. injection, whereas the reverse was the case in the of an active alkylating agent (3, 10, 31, 35, 36). In confirma colon. A number of methylated purines were detected in tion of this hypothesis, it has been shown that, like dimeth hydrolysates of DNA isolated from rats given [â€˜4C]-1,2-di ylnitrosamine and N-methyl-N-nitrosourea, 1,2-dimethylhy @ methylhydrazmne. These included 7-methylguanmne, drazine leads to the methylation of nucleic acids in tissues methylguanine, 3-methyladenine, 1-methyladenine, and 7- in which tumors are produced (11, 12). In these experi methyladenine. The relative amounts of these products ments, it was found that 7-methylguanine was formed in were consistent with the hypothesis that alkylation was the DNA of liver, colon, and kidney of rats and mice given mediated via the metabolism of 1,2-dimethylhydrazmne to 1,2-dimethylhydrazine by s.c. injection. For some time al an alkylating species similar to that generated by dimethyl kylation of DNA has been considered the likely means by nitrosamine and N-methyl-N-nitrosourea. 06-Methylguan which cancer is induced by cycasin and the nitroso corn me was formed in the colon DNA in substantial amounts pounds (16â€”i8,22, 23, 29). However, more recent studies after injection of the 1,2-dimethylhydrazine and was not have suggested that the 06-position of guanine rather than lost rapidly from the DNA. However, 06-methylguanmne was the 7-position may be the critical site for the alkylation (17â€” present in greater amounts in the liver than in the colon or 20, 29). The presence of 06-methylguanine, but not 7- kidney at all times examined after the 1,2-dimethylhydrazine methylguanine, causes mutation in phage (21) and miscod dose of 200 mg/kg body weight. Since the liver is not a ing by nucleic acid polymerases (8). In studies with simple target organ for 1,2-dimethylhydrazine carcinogenesis, it is aliphatic nitrosamines and nitrosamides, the formation and apparent that factors other than the production of Q6@ persistence of 06-alkylguanine in various tissues including methylguanine must be of importance in tumor initiation. brain, kidney, and liver correlated well with tumorigenesis The findings are discussed in relation to the hypothesis (9, 24, 27, 30). Conversely, the alkylating agents methyl that it is the production and persistence throughout DNA methanesulfonate and ethyl methanesulfonate, which are replication of 06-methylguanine that may be the initiator of only weakly carcinogenic, resulted in much less 0-alkyl neoplasia by those carcinogens that yield methylating guanine formation (18, 30, 33, 34). These experiments agents. support the hypothesis that the formation and persistence of 06-alkylguanine until cell replication leads to the herita ble, usually irreversible, change to neoplastic growth. There INTRODUCTION is evidence that this abnormal purine can be enzymatically removed in some organs, and it appears that persistence Shortly after the discovery that the natural plant product results from either a lack of this enzyme System or its cycasin induced cancer of the colon in rats (15), it was inhibitionorsaturation(25,28,29). found that 1,2-dimethylhydrazmne was a potent colon car Since it was not known to what extent 1,2-dimethylhydra zine alkylated DNA at the 0-position of guanine in target , This work was supported by Grants CA 18137 and 1 P30 CA 18450 awarded by the National Cancer Institute, Department of Health, Education, cells or whether cells in the colon were able to carry out and Welfare. the removal of 06-methylguanine seen in the liver (9, 24, 2 Established Investigator, American Heart Association. To whom requests for reprints should be addressed. 28, 29), the production and persistence of this methylated Received April 11, 1977; accepted August 9, 1977. purine was measured in rat colon, kidney, and liver after

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treatment with [â€˜4C]-1,2-dimethylhydrazine. Comparisons methylguanine produced by treatment with 1,2-dimethylhy were made of the extent of alkylation in these tissues after drazine were then calculated from the radioactivity present treatment by either i.p. or s.c. injection. in the fractions corresponding to the marker compounds. The levels of these methylated guanines were expressed as a function of the amount of guanine present in the DNA. MATERIALS AND METHODS The adenine:guanineratiowasdeterminedforeach hydrol ysate to avoid possible errors introduced by incomplete Adult female Sprague-Dawley rats (Charles River Breed hydrolysis of the DNA or loss of guanine due to the relative ing Laboratories, Wilmington, Mass.), weighing about 200 insolubility of this base at neutral pH. These ratios were g, were treated with [â€˜4CJ-1,2-dimethylhydrazineeither i.p. consistently around 1.50. Each measurement shown in or s.c. The [14C]-1,2-dimethylhydrazine (5.84 mCi/mmole) Tables 1 and 2, except the 48-hr colon and kidney estima was purchased from New England Nuclear, Boston, Mass., tions, consisted of the mean of at least 2 separate samples and for most injections it was diluted with unlabeled 1,2- each from 2 or more rats in the case of colon and kidney. dimethylhydrazine purchased from Aldrich Chemical These valuesagreedwithin10%. Company, Milwaukee, Wis. After injection of the [â€˜4C]-1,2-dimethylhydrazine, a rat For injection, the dimethylhydrazine was dissolved in a from each experimental group was placed in a sealed cage 0.9% (w/v) NaCI solution containing 1 .5 mg of EDTA per through which free flowing air was drawn and bubbled 100 ml. The solution was then neutralized with NaHCO3. through several wash bottles containing 1 NaOH (total The concentration of [â€˜4C]-1,2-dimethylhydrazine in the volume, 900 ml). At intervals, 1-mI samples were removed solution for injection was adjusted so that a total volume of from each of these bottles and the radioactivity was deter between 0.4 and 0.6 ml was administered. The rats were mined after addition of 4 ml of water and 10 ml of Formula killed by cervical dislocation at various times after injection 947 scintillation cocktail. Efficiency of counting was about and the livers, kidneys, and colons were rapidly removed, 45%.Only a minute fraction of the radioactivity was present frozen in liquid N2, and stored at â€”60Â°untilanalyzed. All in the final wash bottle, suggesting that all the water- and rats were starved overnight prior to being killed. alkali-soluble volatile metabolites (which include [â€˜4CO@] The DNA was extracted from the frozen tissues with and [â€˜4C]azomethane)were being counted. However, it is phenol:m-cresol:8-hydroxyqumnoline:water (100:14:0.1 :11) possible that some azomethane was not retained , as this and analyzed as previously described (24, 28). The purified gaswasefficientlytrappedonlyinethanolatâ€”72Â°orin 1N DNA was hydrolyzed in 0.1 M HCI at 70Â°for 30 mm, thus H@SO4 (5).Thecumulativetotalofvolatilelabeledproducts releasing all of the purines as free bases (19). Unlabeled 7- was expressed as a percentage of the original radioactivity methylguanine and 05-methylguanine were added to the administered and provided an estimate of the rate of metab hydrolysates as markers. The purine bases were separated olism of the 1,2-dimethylhydrazine. by chromatography carried out on SephadexG-10columns eluted with 0.5 M ammonium formate:O.02% sodium azide, pH 6.8 (17, 18). The eluate absorbance at 254 nm was RESULTS monitored and 5-mI fractions were collected. Good separa tions of guanine, adenine, and 7-methylguanine, and 0- Alkylation of DNA of liver, kidney, and colon was readily methylguanine were obtained. In some experiments, other detected 24 hr after i.p. injection of a small dose of [â€˜4CJ methylated purines were also added as markers, and the 1,2-dimethylhydrazine(4 mg/kg body weight). After hydrol radioactivity corresponding to these markers was assayed. ysis of this DNA in dilute acid to release the purine bases, Separation of these purines (1-methyladenmne, 3-methylad the liberated purines were separated by chromatography enine, 7-methyladenine, and 3-methylguanine) was not on Sephadex G-10 columns. As shown in Chart la, radio complete (see legend to Fig . 1) but was adequate to permit activity corresponding to 7-methylguanine, 06-methylguan their identification among the radioactive products. me, 1-methyladenine, 7-methyladenine, 3-methyladenine, The amounts of guanine and adenine present were deter and possibly 3-methylguanmne was present. There was also mined by measurement of the absorbance at 260 nm of the radioactivity in an early eluting peak which contains pyrim relevant fractions, assuming a molar extinction coefficient idine nucleotides and apurinic acid. The greatest amount of 7200 liters-mole' â€˜cm' for guanine and 13,000 Ii of radioactivity was present in 7-methylguanine and the @ ters mole' â€˜cm1for adenine in the ammonium formate next most extensively labeled purine was 06-methylguan buffer at pH 6.8. Occasionally, the adenine and guanine me. The amounts of these products in the DNA are given in were not completely separated, in which case the relative Table 1. Levels of alkylated bases were more than an order amounts of the 2 bases in the overlapping fractions could of magnitude greater in the liver than in the kidney and be calculated by using the known Esss:E2seratios(at neutral colon. pH) of 0.11 and 1.02, respectively. As shown in Chart ib, similar alkylated bases were Radioactivity present in each eluate fraction was deter detected with larger doses of 1,2-dimethylhydrazine, which mined after addition of 10 ml of Formula-947 scintillation are capable of inducing tumors without further treatment cocktail (New England Nuclear) via scintillation counting (3, 10). However, since the specific activity of the labeled with a Beckman LS-350. The efficiency of counting, deter carcinogen had to be reduced for economic reasons when mined via the external standard channels ratio method the higher doses were given, it was not possible to quanti with appropriate quench calibration, was found to be tate the minor products of the alkylation except for 0'- around 60%. The amounts of 7-methylguanmne and 0- methylguanine. After the higher dose, also, alkylation was

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Chart I . Separation of methylated purines present in DNA of rats treated with 1,2-dimethylhydrazine. The rats were given an i.p. injection of either 4 mg [1'C]-l 2- dimethylhydrazine (specific activity, 5.84 mCi/mmole) per kg body weight (a) or 200 mg [â€˜@C]-1,2-dimethylhydrazine (specific activity, 0.208 mCi/mmole) per kg body weight (b). They were killed 24 hr later, and liver DNA was iso @ lated and hydrolyzed in 0.1 HCI. The liberated purines were then separated by chromatography on Sephadex G 10 columns with 0.05 M ammonium formats as eluting buffer. Fractions of 5 ml were collected and assayed for radioactivity as shown. The following authentic marker purines were present in the fractions indicated: 1-methyl adenine (m'A), Fractions 19 to 25; 3-methyladenine (m3A),Fractions30to 36;3-methylguanine(m3G),Frac tions 34 to 40; 7-methyladenine (m7A), Fractions 41 to 48; 7-methylguanine (m7G), Fractions 45 to 58; 0-methyl guanine (m'G), Fractions 92 to 115. Arrows, peak fraction for these purines. Fractions 10 to 21 contained pyrimidine nucleotides, apurinic acid, and 2'-deoxyribose phos phates. Fractions 60 to 95 contained guanine (G , Frac tions 60 to 71) and adenine (A , Fractions 72 to 78) and were used for the determination of the amounts of these purines present in the hydrolyzed sample. The radioactiv ity per fraction indicated was calculated as that equivalent to a sample containing 10 @moIesofguanine. The actual FRACTION NUMBER FRACTION NUMBER samples analyzed in this and the other experiments of Tables I and 2 varied between 4 and 12 @molesofgua nine, depending on the tissue and the DNA preparation.

Table 1 about 54%. The decline of 7-methylguanine was similar Alkylation of DNA following i.p. injection of (â€˜4C1-1,2- (52%) in the kidney, but the fall in 0'-methylguanine was dimethy!hydrazine only 40% in the kidney. At least part of the fall in 7- Ratswere given i.p. injections of either 4 mg [â€˜4C]-1,2-dimethyl methylguanine levels is probably due to the loss of this 2-dimethylhydrazinehydrazine (specific activity, 5.84 mCi/mole) or 200 mg [â€˜4CJ-1 purine by spontaneous depurination (16â€”18),butsince 0'- bodyweight. (specific activity, 0.208 mCi/mmole) per kg of0-methylguanineAt the times indicated, rats were killed and the content methylguanine is stable in DNA, the loss of this base from determined.The and 7-methylguanine in DNA was the liver DNA at a rate faster than the loss of 7-methylguan agreedwithinresults shown were the mean of at least 2 samples that me must indicate an enzymatically catalyzed removal proc estimations,whichÂ±10% except for the 48-hr colon and kidney ess. Further, this process must be occurring at a faster rate from4 represented a single measurement of samples pooled rats.moles in the liver than in the kidney, ii@which tumors can be induced by a single dose of 1,2-dimethylhydrazine. This guanine/1 methylated finding is similar to that found for the formation and ,2-Dimethyl- io5 moles guanine hydrazine persistence of 0'-methylguanine in liver and kidney DNA (mg/kg body 06-Methyl- 7-Methylguan after administration of dimethylnitrosamine (27, 30). meLiverOrgan wt) Time (hr) guanine The levels of methylated bases were expressed as the 352004 24 2.5 fraction of the parent guanine present in the tissue extract 669200 6 78 dialyzed . The level of methylated bases could , therefore, 401200 24 57 show a decrease as a consequence of new DNA synthesis 307Kidney 48 30 due to cell replication or to cell death of more highly 2.62004 24 0.1 alkylated cells. In either case, a parallel loss of both 7- 74200 6 8 methylguanine and 06-methylguanine would be expected. 39200 24 7 Losses due to these causes are unlikely to be significant in 36Colon 48 5 the liver and kidney since only mild hepatic necrosis, 2.52004 24 0.1 peaking at 48 hr, is produced by this dose of 1,2-dimethyl 94200 6 9 hydrazine (12), and cell turnover in these organs is relatively 39200 24 5 slow. However, in the colon, a significant proportion of the 48 3 25 apparent loss of methylated bases may be due to cell turnover. In the colon DNA, 0'-methylguanine (69% lost much greater in the liver than in the colon and kidney, and between 6 and 48 hr after treatment) was lost at a rate 0'-methylguanine was initially present at about 10% of the similar to 7-methylguanine (73%) which is consistent with level of 7-methylguanine. The amounts of these methylated this possibility. The data therefore suggest that 0'-methyl bases that were present 6, 24, and 48 hr after i.p. injection guanine is not removed from the DNA of the colonic cells of 200 mg of [â€˜4C]-1,2-dimethylhydrazineper kg body weight as rapidly as from the liver DNA. This finding is also were as shown in Table 1. The greater content of alkylated consistent with the hypothesis that target cells are less bases was found at 6 hr in all 3 tissues, and levels declined likely to be able to remove this product from their DNA substantially over the next 42 hr. In the liver, 0'-methyl before the cell division than liver cells in which tumors are guanine levels declined by 62% and 7-methylguanine by not induced by a single dose of the carcinogen.

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Table 2 shows similar data for the alkylation of liver, kidney, and colon DNA following s.c. injection of [â€˜4C]-1,2- dimethylhydrazine at the same dose of 200 mg/kg body weight. Although the liver was alkylated to approximately the same extent as after i.p. administration, alkylation in the kidney was almost 100% higher after s.c. administra tion, whereas, in the colon it was reduced by 50%. Also, 0 the period over which alkylation occurred in the kidney -a and colon was longer following s.c. administration of the 4 hydrazine. In both the colon and the kidney, 0'-methyl U guanine levels actually increased throughout the 48-hr period, indicating that alkylation must be continuing over this time. The increase was particularly marked in the colon where production of 06-methylguanine was below the limit of detection at 6 hr after treatment. 7-Methylguanine levels in the kidney declined over the period studied, but the de dine was less than that seen after i.p. administration, and in the colon there was little change in 7-methylguanine 2 16 20 21 levels over the period from 6 to 48 hr after s.c. treatment HOURS with the carcinogen. These results suggest that the rate of Chart 2. Exhalation of radioactive volatile metabolites from [â€˜4C]-1,2-di loss of 7-methylguanine from DNA is partly offset in the methylhydrazine. A rat was given a dose of 200 mg [â€˜4C)-1,2-dimethylhydra zine per kg bodyweight s.c. (a) i.p. (b) as describedin Tables1 and 2. The kidney and balanced in the colon by continued production. exhalation of volatile radioactive metabolites was measured by trapping in It is possible that the slower rate of alkylation after s.c. NaOH and counting as described in â€œMaterialsandMethodsâ€•and the administration was due to a slower rate of absorption and/ cumulative total was shown as a function of time after injection. or metabolism of the carcinogen. There is evidence that metabolism involves the oxidation of one of the carbon the shape of the curve in Chart 2 is similar to that found by atoms of the [14C]-1,2-dimethylhydrazine leading to exhala others (5, 6, 11), and even if incomplete trapping led to an tion of â€˜4CO2and[14C]azomethane (5, 6, 11). Chart 2 shows underestimate of the total extent of exhalation of the label, the cumulative percentage of the total dose exhaled over the difference is likely to be the same for both methods of 24 hr, comparing the s.c. (Chart 2a) and i.p. (Chart 2b) administration. The data should therefore be applicable for routes of administration. The total output over 24 hr the comparison of the rate of metabolism after the different amounted to 15.4% of the total label after i.p. injection and methods of administration . There was a somewhat greater 13.2% when given s.c. rate of metabolism at early times after i.p. injection, and The latter figure is substantially less than that found by production of volatile metabolites continued to increase Fiala et a!. (6) who found that after a similar dose 4% was for a slightly longer time after s.c. treatment (Chart 2). expired as â€˜4CO2and23% as [14C]azomethane. It is possible However, the differences were small compared to the strik that our figure is lower due to inefficient trapping of ing change in alkylation in the kidney and colon when s.c. [â€˜4C]azomethane(seeâ€œMaterialsandMethodsâ€•).However, and i.p. administration were compared.

Table 2 DISCUSSION Alkylation of DNA following s.c. injection of (â€˜4CJ-1,2- dimethylhydrazine It is clear that 1,2-dimethylhydrazine requires metabolic Aats were given s.c. injections of 200 mg [14C]-1,2-dimethylhy conversion into an ultimate carcinogen since tumors were drazineweight.At (specific activity, 0.121 mCi/mmole) per kg body the times indicated rats were killed and the content of O@ not found at the site of administration (3). The pathway of methylguanmneand7-methylguanmneinDNAwasTheresults determined. this metabolic activation was postulated to involve a series agreedwithinshown were the means of at least 2 samples that of oxidations that result in the production of a methyldi Â±10%.moles azonium ion (31, 35, 36). Recent studies from Weisburger guanine/10@methylated et al. have provided strong support for this pathway. They guanineO'-Methyl-moles have identified azomethane, azoxymethane, and methylaz oxymethanol as metabolites of 1,2-dimethylhydrazine (4- 7-Methyl guanineLiverOrgan Time (hr) guanine 6). The studies in the present paper also support this activation pathway since a similar range of alkylated purines 569246 63 42348 55 was formed by 1,2-dimethylhydrazmne as by dimethylnitrca 338Kidney 48 samine and N-methyl-N-nitrosourea (27-30). The fact that these methylated purines are produced in the same relative 141246 10 proportions by all 3 of these carcinogens strongly suggests 7448 12 62Colon 15 that all react via the same alkylating species. The relative reactivities of alkylating agents with different sites in nu 43246 <1 cleic acids depends on the value of their Swain and Scott s 4748 6 factor (18). For example, methyl methanesulfonate, which 9 44 has an 5 value of 0.83, alkylates DNA at the 0'-position

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Downloaded from cancerres.aacrjournals.org on September 24, 2021. © 1977 American Association for Cancer Research. K. J. Rogers and A. E. Pegg much less extensively than N-methyl-N-nitrosourea with an direct conversion of 1,2-dimethylhydrazine to an ultimate 5 of 0.42. This nitrosamide is known to decompose to carcinogen may occur in the lower gut without prior need generate an alkyldiazonium ion or equivalent species; for metabolism by the liver (7, 11, 14, 26, 37). hence, the observations that dimethylnitrosamine (27â€”30) The present studies suggest that both direct activation in and 1,2-dimethylhydrazine produce proportions of alkylated the colon and indirect activation by the liver might occur. bases similar to those formed by N-methyl-N-nitrosourea There was a marked difference in the rate and extent of indicate that the alkylation produced by these agents is alkylation of colon DNA depending on the route of admin likelytobe mediatedby a similarintermediate. istration of the 1,2-dimethylhydrazine, but at the same time We found that 0'-methylguanine was formed in the DNA there was little change in the alkylation of liver DNA. It is of colon and kidney following a dose of 200 mg/kg body hard to reconcile this disparity with the concept that the weight, which is known to induce tumors in these tissues only pathway for alkylation of the colon involves production (3, 10). This is consistent with the hypothesis that the of methylazoxymethanol in the liver. If this were the case, a formation and persistence of this product throughout DNA close parallel between the degree of reaction in the liver replication may be responsible for the initiation of tumors and in the colon might be expected. The mechanism by by those carcinogens that are converted into alkylating which the rate and extent of alkylation varies with route of agents (9, 17-20, 27-30). administration is not clear at present. It is possible that i.p. However, as previously observed by Hawks and Magee injection results in more rapid direct diffusion into the (11), who were able to measure only 7-methylguanine levels liver, intestine, and colon, which are i.p. organs, as op (owing to the low specific activity of their [14C]-1,2-dimeth posed to the retroperitoneal kidneys. The s.c. injections ylhydrazine and the analytical method used), the most were given in the back, and a greater diffusion into the extensively alkylated organ in rats treated with 1,2-dimeth kidneys relative to the i.p. structures may have occurred. ylhydrazine was the liver. Indeed, in our experiments, liver More probably, s.c. injection causes more carcinogen to DNA was alkylated at least 5 times more than DNA of colon enter directly into the arterial circulation, thus delivering a and kidney, although liver tumors have not been reported greater percentage to the kidneys. The prolonged alkylation to be produced by a singledose of the hydrazine.The of colon DNA after s.c. injection may result from the greater ability of the liver to remove 0'-methylguanine from transport of a metabolite of the 1,2-methylhydrazine from its DNA has been postulated to explain the resistance of the liver via the bile. Although the exhalation of radioactive the liver to carcinogenesis by a single dose of dimethylnitro volatile metabolites was somewhat slower after s.c. injec samine or N-methyl-N-nitrosourea (24, 27). However, as tion than after i.p. injection (Chart 2), the difference was shown in Tables 1 and 2, even by 48 hr after giving 1,2- only slight; this might be expected since alkylation of DNA dimethylhydrazine, the amount of 0'-methylguanine pres in the liver was not much affected by the route of adminis ent in liver DNA still exceeds that found in colon or kidney tration, and presumably the majority of the metabolism DNA. It is likely, therefore, that other factors must also leading to exhalation of â€˜4C02and[â€˜4C)azomethaneoccurs come into consideration in explaining the greater sensitivity in the liver. Studies of the metabolism of 1,2-dimethylhydra of the latter organs. One important factor may be the zine by isolated tissues separating metabolites by the greater rate of cell turnover in the colon which would method of Fiala et a!. (6) and measurement of alkylation of increase the chances that DNA synthesis might occur while nucleic acids are required before a full understanding of 06-methylguanine was present in the DNA. It is known that the conversion of this carcinogen into the alkylating species hepatictumors can be induced by a singledose of the can be obtained. nitroso compounds if given in conjunction with partial hepatectomy (1, 2) although a similar experiment has not been carried out with 1,2-dimethylhydrazine. It is also quite REFERENCES possible that alkylation of DNA at the 0'-position is not 1. Craddock, V. M. Liver Carcinomas Induced in Rats by a Single Adminis related to carcinogenesis by 1,2-dimethylhydrazine. Alkyla tration of Dimethylnitrosamine after Partial Hepatectomy. J. NatI. Cancer tion at other sites such as phosphate esters and the Q4@ Inst., 47: 889-907, 1971. position of thymine must also be considered. However, the 2. Craddock,V.M.,andFrei,J. V. InductionofLiverCellAdenomatain the Rat by a Single Treatment with N-methyl-N-nitrosourea Given at objection that liver cells in which tumors are not produced Various Times after Partial Hepatectomy. Brit. J. Cancer, 30: @03-511, are more extensively alkylated would apply equally well to 1974. 3. Druckrey, H. Production of Colonic Carcinomas by 1,2-Dialkylhydrazines these alkylations. Therefore, some mechanism for tumor and Azoalkanes. In: W. J. Burdette (ed), Carcinoma of the Colon and induction other than alkylation of nucleic acids cannot be Antecedent Epithelium, pp. 267-279. Springfield, III.: Charles C Thomas, ruled out at present. Publisher, 1970. 4. Fiala,E.S. Investigationsintothe MetabolismandModeof Actionof The remarkable specificity of 1,2-dimethylhydrazine to the Colon Carcinogen 1,2-Dimethylhydrazine. Cancer, 36: 2407-2412, ward the large bowel is not yet fully understood. It has 1975. been suggested that after metabolism of 1,2-dimethylhydra 5. Fiala, E. S., Bobotas, G., Kulakis, C., and Weisburger, J. H. Inhibition of 1,2-Dimethylhydrazine Metabolism by Disulfiram. xenobiotica, 7: 5â€” zine into methylazoxymethanol in the liver, a proportion of 9, 1977. this metabolite is conjugated and secreted in the bile (35, 6. Fiala, E. S., Kulakis, C., Bobotas, G., and Weisburger, J. H. Detection and Estimation of Azomethane in Expired Air of 1,2-Dimethylhydrazine 36). Deconjugation by colonic bacterial flora to release the treated Rats. J. NatI. Cancer Inst., 56: 1271-1273, 1976. methylazoxymethanol, permitting reaction with the colon 7. Gennaro, A. A., Villanueva, R., Sukonthaman, V., Vathanophas, V., and [as occurs with cycasin (15)], could then take place (4, 35, Rosemond, G. P. Chemical Carcinogenesis in Transposed Intestinal Segments. Cancer Res., 33: 536-541 , 1973. 36). This mechanism has received some support (4, 32), 8. Gerchman, L. L., and Ludlum, D. B. The Properties of 0-Methylguanine but other investigations suggest that it is also possible that in Templates for RNA Polymerase. Biochim. Biophys. Acta, 308: 310-

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NOVEMBER1977 4087

Downloaded from cancerres.aacrjournals.org on September 24, 2021. © 1977 American Association for Cancer Research. Formation of O6-Methylguanine by Alkylation of Rat Liver, Colon, and Kidney DNA following Administration of 1,2-Dimethylhydrazine

Kenneth J. Rogers and Anthony E. Pegg

Cancer Res 1977;37:4082-4087.

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