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The Conditional Biological Activity of the Carcinogens in Carbon Blacks, and Its Elimination^*

( Department of Pathology, The University of Chicago, Chicago 37, Ill.)

1. A carbon black from which 3,4-benzpyrene and other aromatic hydrocarbons could be eluted with benzene was carcinogenic on subcutaneous test in mice when it was injected with tricaprylin but practically inactive in pellet form. This difference in result is interpreted as showing that the subcutaneous tissues had no eluent adequate to make the chemical available for carcinogenic action on the adjacent cells. These experiments illustrate three principles in carcinogenesis, namely, (a) the existence of "natural" carcinogenic compounds; (b) the occurrence of conditional carcinogens; and (c) the importance of the solvent in the carcinogenic response.

2. A carbon black whose benzene extracts contain no recognized carcinogenic hydrocarbons was slightly carcinogenic on biological test. It is probable that adsorbed carcinogenic chemicals were present which were not eluted in vitro but which became available for carcinogenic activity in vivo, indicating that the biological test for carcinogenicity was better than the chemical.

3. When the potent carcinogenic aromatic hydrocarbon, 3,4-benzpyrene, in an amount which when tested alone gave a 95 per cent tumor yield, was added to a noncarcinogenic carbon black of small average particle diameter prior to injection, no tumors were induced by the combination. This inactivation is attributed to adsorption, and it is interpreted as signifying that in the adsorbed state this carcinogen was rendered biologically inactive.

4. The carcinogenic activity of a carbon black was eliminated by destruction and by adsorption; it was nearly eliminated by solvent extraction.

5. The phenomenon of adsorption was a more potent factor than the solvent in determining the carcinogenic response under the experimental conditions used.

6. The principles of natural and conditional carcinogens, of solvent elution, and of adsorption are advanced to explain some clinical and epidemiological observations on human skin and lung cancers, and on the role of preceding pathological lesions in predisposing to pulmonary tumors.

^* This investigation was aided by a research grant from the American Cancer Society on recommendation of the Committee on Growth.

Received 9/30/53.