Aflatoxin B1-2,3-dichloride (AFB1-Cl2) was synthesized as a model for the probable ultimate
carcinogen,
aflatoxin B1-2,3-oxide. As expected for
aflatoxin B1-2,3-oxide, AFB1-Cl2 has an electrophilic
carbon 2; it decomposed in water (half-life of 0.5 min in 10%
dimethyl sulfoxide, pH 7.4) with the formation of 3-chloro-2,3-dihydro-2-hydroxyaflatoxin B1 and 2,3-dihydro-2,3-dihydroxyaflatoxin B1. AFB1-Cl2 formed covalent adducts with
DNA and
RNA with retention of one-half of the
chlorine; the major products apparently contained glycosidic bonds between
carbon 2 of the
aflatoxin residues and
nitrogen or
oxygen atoms in the
nucleic acids. Polyguanylic
acid was the most reactive homopolymer toward AFB1-Cl2. AFB1-Cl2 was less reactive toward mononucleotides than toward
polynucleotides. The major adducts formed on incubation of AFB1-Cl2 with
protein contained little
chlorine and could have resulted from alkylation of primary amino groups or from reactions with the hydrolysis products. Similarly, incubation of AFB1-Cl2 with
amino acids apparently resulted in
Schiff base formation between primary amino groups and the dialdehyde rearrangement forms of the hydrolysis products of AFB1-Cl2. AFB1-Cl2 was much more active than
aflatoxin B1 in inducing
sarcomas at the s.c. injection site in rats, in the initiation of
papillomas on the skin of mice, and in the induction of lung
tumors in mice. AFB1-Cl2 was also highly mutagenic for Salmonella typhimurium TA 98 and TA 100.
Aflatoxin B1 and its 2,3,-dihydro- (
aflatoxin B2), 2,3-dihydro-2-hydroxy- (
aflatoxin B2a), 2,3-dihydro-2,3-dihydroxy-, and 3-chloro-2,3-dihydro-2-hydroxy- derivatives were inactive in the mutagenicity tests; and the latter four compounds were also inactive as initiators of
papillomas of the skin in mice. The structures of the macromolecular adducts of AFB1-Cl2 formed in vitro, the carcinogenicity of this electrophile, and the lack of carcinogenicity of its hydrolysis products indicate that alkylation of
nucleic acids is a critical reaction in
tumor induction with this
carcinogen and
aflatoxin B1.