Induction of neoplastic transformation and DNA single-strand breaks in C3H/10T1/2 clone 8 cells by polycyclic hydrocarbons and alkylating agents.

The standard C3H/10T1/2 clone 8 (C3H/10T1/2 CL8) cell transformation assay was tested for its ability to identify a variety of polycyclic hydrocarbons and alkylating agents. Dose-dependent morphologic transformation occurred with benzo[a]pyrene (BaP), 3-methylcholanthrene (MCA), 7,12-dimethylbenz[a]anthracene, BaP-7,8-dihydroxy-7,8-dihydrodiol (BaP-7,8-diol), as well as with the relatively weak in vivo carcinogen benzo[e]pyrene. Dibenz[a,h]anthracene yielded a relatively weak response, whereas anthracene and phenanthrene were negative. In contrast, treatment of C3H/10T1/2 CL8 cells with two directly acting alkylating agents, N-nitroso-N-methylnitroguanidine (MNNG) and styrene oxide, gave no transformation, whereas a third alkylating agent, ethyl methanesulfonate (EMS), gave a weak response. Treatment with MCA (2.5 micrograms/ml) yielded a reproducible positive response and, therefore, served as a positive control for routine use of the C3H/10T1/2 CL8 assay. When cells treated with the hydrocarbons BaP, BaP-7,8-diol, or MCA were analyzed for nonspecific DNA damage (single-strand breaks or alkaline-labile sites) by alkaline elution techniques, little if any DNA damage was observed. In contrast, the alkylating agents MNNG, styrene oxide, and EMS yielded substantial numbers of single-strand breaks.