Toxic effect of 7,12‐dimethylbenz‐α‐anthracene on neoplastic cells grown in mixed cultures with normal fibroblasts

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Abstract
Neoplastic L fibroblasts grown in isolated cultures are highly resistant to the toxic effects of carcinogenic hydrocarbons. However, these cells become very sensitive to the toxic effect of 7,12‐dimethylbenz‐α‐anthracene (DMBA) if they are grown on the surface of the monolayer of normal mouse fibroblasts. The density of L cells grown on the glass surface in the same mixed cultures was not significantly changed by DMBA. L cells seeded in the culture of normal fibroblasts 3 days after the removal of DMBA from the medium were not damaged. These experiments indicate that normal fibroblasts exposed to DMBA transmit some toxic factor to L cells placed in their immediate vicinity. It is suggested that this factor may be some short‐lived metabolite of DMBA formed within the normal cells. It is possible that such a “lethal metabolic cooperation” with normal cells may considerably change the sensitivity of neoplastic elements in vivo to various toxic substances.