Oncogenic interaction of carcinogenic and non-carcinogenic polycyclic aromatic hydrocarbons in mice

To evaluate possible interactions between PAH occurring in automobile exhaust condensates with regard to their tumour forming potency, the following experiments were performed. Six different doses of benzo[a]pyrene (3-100 microgram) and of dibenzo]a,h]anthracene (2-75 microgram) and mixtures thereof were tested subcutaneously on female NMRI mice. In addition, mixtures of 10 non-carcinogenic hydrocarbons were applied: benzo[e]pyrene, benzo[a]anthracene, phenanthrene, anthracene, pyrene, fluoranthene, chrysene, perylene, benzo[ghi]perylene and coronene. Mixtures of all 12 PAH were also applied. The proportion of PAH in all mixtures used was the same as in automobile exhaust condensates; benzo[a]pyrene was used as reference substance. The most important results were as follows: 1. Small doses of dibenzo[a,h]anthracene have a greater tumour promoting effect than do comparable doses of benzo[a]pyrene. Increased doses increase the effect of benzo[a]pyrene more than that of dibenzo[a,h]anthracene. 2. The mixture of benzo[a]pyrene and dibenzo[a,h]anthracene is 1.4 time more active than dibenzo[a,h]anthracene alone. 3. The mixture of all PAH has a lower efficacy than dibenzo[a,h]anthracene alone, amounting to only 0.03 that of dibenzanthracene; however, the activity of dibenzo[a,h]anthracene within the mixture of the 12 PAH increases by a factor of 3.1. 4. The activity of a mixture of dibenzo[a,h]anthracene and benzo[a]pyrene depends to about 40% on dibenzo[a,h]anthracene; and that of 12 PAH to 30% on dibenzo[a,h]anthracene alone or to 80% on a mixture of dibenzo[a,h]anthracene and benzo[a]pyrene.