title: Further investigations into the effect of non-benzo ring bay-region methyl substituents on tumor-initiating activity of polycyclic hydrocarbons.
abstract: The effect of a methyl substituent at the non-benzo ring bay-region position of benzo[e]pyrene (B[e]P), cholanthrene (CA) and dibenz[a,j]anthracene (DB[a,j]A) on skin tumor-initiating activity was examined. A methyl substituent at the 1-carbon of B[e]P enhanced tumor-initiating activity of the parent compound (0.18 vs. 2.4 papillomas/mouse for B[a]P vs. 1-methyl-B[e]P, respectively, with an 800 nmol initiating dose). A methyl substituent at the 7- and 14-carbons of DB[a,j]A increased the activity of this weak initiator more than 13 times. The introduction of a methyl substituent at the non-benzo ring bay-region position of CA (i.e. carbon atom 6) dramatically increased tumor-initiating activity in SENCAR mice. 6-Methyl-CA was found to be a more potent skin tumor-initiator than 3-methyl-CA, and nearly as potent as 7,12-dimethylbenz[a]anthracene, one of the most potent initiators yet tested in the 2-stage initiation-promotion mouse skin model. When taken together with previous results from our laboratories, the data further support the generality of the enhancing effect of a non-benzo ring bay-region methyl substituent on polycyclic hydrocarbon tumor-initiation.
mesh_terms: D015127:9,10-Dimethyl-1,2-benzanthracene / Q000633:toxicity*; D000818:Animals; D001551:Benz(a)Anthracenes / Q000633:toxicity*; D001564:Benzo(a)pyrene / Q000633:toxicity*; D001580:Benzopyrenes / Q000633:toxicity; D002273:Carcinogens; D005260:Female; D008748:Methylcholanthrene / Q000031:analogs & derivatives / Q000633:toxicity; D051379:Mice; D010212:Papilloma / Q000139:chemically induced*; D012878:Skin Neoplasms / Q000139:chemically induced*; D013329:Structure-Activity Relationship
chemical_list: D001551:Benz(a)Anthracenes; D001580:Benzopyrenes; D002273:Carcinogens; C053715:6-methylcholanthrene; D001564:Benzo(a)pyrene; C053714:cholanthrene; D008748:Methylcholanthrene; D015127:9,10-Dimethyl-1,2-benzanthracene; C053717:7,14-dimethyldibenz(a,j)anthracene; C053716:1-methylbenzo(e)pyrene