Application of hydroxyurea to L5 cells partially synchronized by the harvesting procedure markedly improved the degree of synchrony in the DNA synthesis phase without permitting severe unbalanced growth of cells. Using the resynchronized DNA-making cells, the two-unit replication of DNA in a single cell nucleus was revealed, the early-replicating DNA being more actively synthesized than the late-replicating DNA, as far as L5 cells are concerned. The rate of RNA and protein syntheses was not disturbed by treatment with hydroxyurea.

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The comparative carcinogenicities of 2-acetamidofluorene, 3-methylcholanthrene, and 2-acetamidofluorene plus 3-methylcholanthrene in the hamster were investigated. Unlike the case with rats, no inhibition of tumor induction was observed when 3-methylcholanthrene was fed to hamsters simultaneously with 2-acetamidofluorene. Combined feeding of 2-acetamidofluorene and 3-methylcholanthrene resulted in adenocarcinoma of the intrahepatic bile ducts, pancreatic adenocarcinoma, and mesenterial sarcomas, while benign cystadenomas of the intrahepatic bile ducts were the only tumors observed in the hamsters fed 2-acetamidofluorene alone. Analyses for urinary metabolites of 2-acetamidofluorene revealed relatively little effect of 3-methylcholanthrene when fed simultaneously with 2-acetamidofluorene. Likewise, the continuous administration of 3-methylcholanthrene in the diet simultaneously with 2-acetamidofluorene caused no increase in the hepatic Nhydroxylation activity in vitro as compared to that of hamsters fed only one of these compounds. One possible explanation of the synergistic action of the combined feeding of 2-acetamidofluorene and 3-methylcholanthrene in producing tumors in extrahepatic tissues is that dietary 3-methylcholanthrene enhances the N-hydroxylation of 2-acetamidofluorene in these tissues.

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The ability of Anthralin to induce tumors was tested on the skin of mice pretreated with intraperitoneal injections of urethan and was compared with that of croton oil. Anthralin after urethan treatment was found to be somewhat less active than croton oil in papilloma production. It was worth noting that Anthralin, as well as croton oil, was not only active as a promoter but capable of tumor production by itself. Skin papillomas were induced in two phases. The early appearance was due to the activity of the promoting agents on urethan-sensitized skin and the late appearance seemed to be due to the urethan-independent oncogenic ability of the chemicals. The regression of the tumors and the inflammatory reaction prior to papilloma production are also discussed.

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During experiments with skin papilloma production in mice, many animals died unexpectedly due to lymphomas or other tumors. Malignant lymphomas appeared in ICR mice treated with daily paintings of Anthralin (1, 8, 9-trihydroxyanthracene) in acetone. The incidence of such tumors increased by intraperitoneal injection(s) of urethan prior to the first painting; over one-half of these animals developed tumors within 28 weeks. Many superficial and some deep lymph nodes were affected, and the thymus, liver, spleen, and kidneys were infiltrated by tumor cells, extensively in some cases. Histological examination showed marked proliferation of stem-cells and/or lymphoblasts.
Thymomas and lung adenomas were also induced. Mammary carcinoma appearing frequently in CFW mice was thought to be spontaneous and not induced.

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The carcinogenic activity of 4-(dimethylamino)azobenzene (DAB) in mice of high spontaneous hepatoma strain, C3H/HeOs, and of low hepatoma strain, C57BL, was studied.
DAB which has been known as being less active carcinogen for mice successfully induced hepatomas with cirrhotic changes in the liver in both strains of mice when the experimental animals were fed 0.06% DAB in animal chow, for as long as 5 months. The induced hepatomas were indistinguishable morphologically from those of spontaneous tumors.
Animals fed 0.06% DAB chow for 1 week to 1 month did not develop hepatoma or liver change but high incidence of systemic amyloidosis was produced only in mice of C57BL strain.

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In a study on structure-activity relationship in 4(or 5)-(alkyltriazeno)imidazole-5(or 4)-carboxamides, the antitumor activity of 4(or 5)-(dialkyltriazeno)imidazole-5(or 4)-carboxamides decreased with increasing number of carbon atoms in the side-chain, while their toxicity increased. On the other hand, both antitumor activity and toxicity of 4(or 5)-(monoalkyltriazeno)imidazole-5(or 4)-carboxamides was reduced linearly with increasing length of the side-chain. In these compounds, the maximum activity was obtained when the methyl group was introduced into the side-chain.
In order to determine the cytotoxicity in vitro of these compounds, the tumor cells were exposed to 4(or 5)-(dimethyltriazeno)imidazole-5(or 4)-carboxamide or 4(or 5)-diazoimidazole-5(or 4)-carboxamide. The former was found to produce little loss of transplantability of the cells, whereas the mean survival time of mice inoculated with the cells treated by the latter was prolonged considerably.
A qualitative analysis of the degradation products with tested compounds revealed that the dialkyl derivatives gave 4(or 5)-diazoimidazole-5(or 4)-carboxamide, whereas the monoalkyl derivatives gave 4(or 5)-aminoimidazole-5(or 4)-carboxamide. The antitumor activity of the dialkyl derivatives was independent of the rate of in vitro production of the diazonium salt. The compounds studied had little or no effect on the respiration and anaerobic glycolysis of tumor cells.

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Succeeding to the previous report, it was confirmed that the primiparous age (the virginal period) as well as the litter number played some significant rôle in determining the spontaneous mammary tumor age of mice.
The relative importances of the primiparous age, litter number, and the rest factors in determining the tumor age were 27.4, 45.8, and 26.8%, respectively, in C3H/He mice and 17.2, 43.8, and 39.1%, respectively, in Swiss albino mice, indicating that the tumor age is much dependent upon both the primiparous age and the litter number at least in the groups of mice used in the present experiment.
The equation for calculating the corrected tumor age was devised by subtracting the components of variance due to the individual differences in the primiparous age and the litter number from the tumor age.
Both the simple and rank correlations between the tumor age and the corrected tumor age obtained by this equation were found to be highly significant in both groups of mice. The significance of these findings is discussed.

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When 3-methylcholanthrene is administered to the RF mouse, the quantity of 3-methylcholanthrene excreted in the urine is only about 3% of the total administered and the majority of such methylcholanthrene is excreted within 24 hours. 3-Methyl-cholanthrene concentration in various organs was measured with lapse of time after repeated oral administration and painting. In the orally administered group, a high methylcholanthrene concentration in bone marrow is extremely specific, and its accumulation is clearly recognized also in lymph nodes and thymus. In the painted group, a high accumulation of 3-methylcholanthrene was observed in bone marrow and thymus, followed by lymph nodes and spleen.
The presence of a close correlation between organ distribution of 3-methyl-cholanthrene and induction of leukemia is pointed out and the significance of these findings in chemical leukemogenesis is discussed.

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In order to obtain information on the site of amino acid binding in the polar dyes, investigations were made with polar dyes derived from 3, 5-dimethyl-4-(dimethylamino)azobenzene (I) and 4-amino-2', 3-dimethylazobenzene (II). It was found that both (I) and (II) can give rise to appreciable amounts of proteinbound dyes in spite of the facts that (I) has methyl substitutions at both 3 and 5 positions and (II) lacks an N-methyl group. The polar dyes from (I) and (II) gave evidence indicating the presence of S-containing amino acid (probably methionine) residue and of 4-amino group of a secondary type. Both polar dyes gave non-polar dyes having a primary auxochromic amino group by prolonged alkaline treatment. It was postulated that the amino acid residue may be bound to the azo dye at the site of 4-amino nitrogen in the cases of (I) and (II). On the other hand, the polar dyes derived from DAB or 3'-methyl-DAB gave non-polar dye having a secondary auxochromic amino group as major products by alkaline treatment.

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Cholangiofibrosis and cirrhosis preceded the development of well-differentiated cholangiocarcinomas in male and female hamsters given 2-acetamidofluorene or 2-diacetamidofluorene in a semi-synthetic diet. The lesions could be followed from proliferation of new bile ducts to cholangiofibrosis, cholangiofibrosis with atypical cells, small cholangiocarcinomas, and cholangiocarcinomas with metastases. Few of the early lesions progress to the stage of carcinomas; most develop degenerative changes.

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4-Nitroquinoline 1-oxide, injected subcutaneously into rats, rapidly disappeared from the injected site. The amount of 4-hydroxyaminoquinoline 1-oxide, metabolically formed from 4-nitroquinoline 1-oxide, reached the maximum after one hour, and remained in the injected site at least for 24 hours. 4-Aminoquinoline 1-oxide was detected in a very small amount.

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Thirty-three foci of primary carcinoma of the stomach, less than 5mm in the largest diameter and regarded as representing its incipient phase in development, were histologically examined, and the basis for their development was elucidated. Out of these materials, 28 foci (84.8%) arose from the epithelium of intestinal type, 4 foci (12.1%) from the ordinary mucosa, and one focus (3.0%) was ulcer-cancer. Appearance of these microcarcinomas is briefly described. The relationship of the metaplastic epithelium to carcinoma in the stomach is also discussed.

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Viral and chemical epidermal tumors of rabbits may be contaminated with the rabbit kidney vacuolating (RKV) virus either naturally or by artificial means. The RKV virus was isolated from 17 out of 28 Shope tumors, and 9 out of 23 chemical tumors. Four rabbits bearing papillomas or carcinomas negative in initial tests for RKV virus were given intravenous injections of that virus. Subsequent tests showed virus in extracts of normal skin and tumors of all four animals.

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