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On the Sulfate Ester of N-Hydroxy-N-2-fluorenylacetamide as a Key Ultimate Hepatocarcinogen in the Rat¹

Experimental Pathology Branch, National Cancer Institute, NIH, Bethesda, Maryland 20014

The problem of the biochemical activation steps required to elicit carcinogenicity to rat liver by N-2-fluorenylacetamide was investigated by bioassay, competitive inhibition, and biochemical techniques. Acetanilide inhibits not only the hepatocarcinogenicity of N-2-fluorenylacetamide but also that of the carcinogenic N-hydroxylated metabolite. With the parent compound, the inhibition was traced chiefly to competition at the N-hydroxylation step, which should not apply to the N-hydroxy derivative. With the latter, the addition of sodium sulfate to the diet restores the hepatocarcinogenicity of N-hydroxy-N-2-fluorenylacetamide in the presence of inhibitory acetanilide. However, sulfate addition fails to return carcinogenicity in the system N-2-fluorenylacetamide plus acetanilide, wherein the inhibition lies at the N-hydroxylation step. The combined results provide evidence that sulfate ester formation constitutes a required second activation step for the expression of carcinogenicity to the liver of rats of N-hydroxy-N-2-fluorenylacetamide, obtained by a first activation step. The required sulfotransferase enzyme system is found mainly in liver cytosol, but attempts to locate it in rat liver nuclear fractions resulted in the detection of only questionable amounts.

¹ Presented in part at the 61st Annual Meeting of the American Association for Cancer Research, Philadelphia, Pa., April 9 to 11, 1970 (36).

² Visiting Scientist, NIH, 1968 to 1971, Permanent address: Division of Biochemistry, National Cancer Center Research Institute, Tokyo, Japan.

Received 8/31/71. Accepted 11/19/71.

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