International Agency for Research on Cancer (IARC) - Summaries & Evaluations

For definition of Groups, see Preamble Evaluation.

VOL.: 56 (1993) (p. 211)
CAS No.: 77500-04-0
Chem. Abstr. Name: 3,8-Dimethyl-3H-imidazo[4,5-f]quinoxalin-2-amine

5.1 Exposure data

MeIQx (2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline) has been found in cooked meat and fish at concentrations of up to 12 ng/g. A few determinations indicated that the levels of MeIQx were lower than those of PhIP and higher than those of IQ and MeIQ.

5.2 Human carcinogenicity data

No data directly relevant to an evaluation of the carcinogenicity to humans of MeIQx were available. Studies on the consumption of cooked meat and fish are summarized in the monograph on IQ.

5.3 Animal carcinogenicity data

MeIQx was tested for carcinogenicity by oral administration in the diet in one experiment in mice and in one experiment in rats. In mice, it produced hepatocellular carcinomas in animals of each sex, lymphomas and leukaemias in males and lung tumours in females. In rats, it produced hepatocellular carcinomas in males, squamous-cell carcinomas of the Zymbal gland in animals of each sex, squamous-cell carcinomas of the skin in males and squamous-cell carcinomas of the clitoral gland in females.

Intraperitoneal injection of MeIQx to newborn male mice increased the incidence of hepatic adenomas.

A single oral treatment of rats with MeIQx followed by phenobarbital, combined with further modulating procedures, stimulated development of foci of altered hepatocytes. Sequential administration of MeIQx after N-nitrosodiethylamine enhanced the appearance of foci of altered hepatocytes in rats.

5.4 Other relevant data

No data were available on the genetic and related effects of MeIQx in humans.

MeIQx bound to DNA in several tissues of rodents dosed in vivo, and, in single studies, it induced chromosomal anomalies. It induced sister chromatid exchange in human cells in vitro and DNA damage, gene mutation and sister chromatid exchange in rodent cells in vitro. It induced gene mutation in insects and gene mutation and DNA damage in bacteria.

MeIQx can be metabolized by human microsomes to a species that damages bacterial DNA.

5.5 Evaluation

There is inadequate evidence in humans for the carcinogenicity of MeIQx.

There is sufficient evidence in experimental animals for the carcinogenicity of MeIQx.

Overall evaluation

MeIQx (2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline) is possibly carcinogenic to humans (Group 2B).

For definition of the italicized terms, see Preamble Evaluation.

Previous evaluation: Suppl. 7 (1987) (p. 65)

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       Toxicological Abbreviations