Germ cell mutagenesis in Drosophila: multiple endpoint analysis.

Genotoxic carcinogens, able to damage DNA by alkylation reactions, represent a very diverse class of agents which are capable of producing a wide range of DNA modifications. The mechanisms leading to genetic changes as a result of exposure to alkylating agents (AAs) have been studied in male germ cells of Drosophila using a structure-activity relationship approach (SAR). The analytical tools available concern both genetic and molecular assays. The genetic tests enable to quantify excision repair and clastogenic potency of the AA after treatment of post-meiotic male germ cells and to determine the degree of germ-cell specificity, i.e., the mutagenic effectiveness in post- versus premeiotic cell stages. For a selected group of alkylating agents the molecular spectra have been studied in post-meiotic cell stages. On the basis of these descriptors clear SAR's between genotoxic activity in germ cells and physico-chemical parameters (s-values and O6/N7-alkylguanine adducts) and carcinogenic potency in rodents became apparent, resulting in five distinct classes of alkylating agents so far. These classes are: 1) SN2-type monofunctional AAs, 2) SN1-type monofunctional AAs, 3) polyfunctional AAs, 4) agents able to form etheno-DNA adducts, and 5) aflatoxin B1 (AFB1) a bulky-adduct forming agent. The recent finding that the molecular data obtained with Drosophila and data of the specific locus tests in male mice show remarkable similarities for most genotoxic agents supports the view that Drosophila is a useful model system for the study of transgenerational damage.