Misrepair model for carcinogenesis by 4-nitroquinoline 1-oxide based on its parallelism with mutagenesis in Escherichia coli

211 112 Knaap, Ada G.A.C., Department of Radiation Genetics and Chemical Mutagenesis, Leiden, and the Institute of Public Health, Bilthoven (The Netherlands) The simultaneous determination of induced mutant frequencies at two loci in mouse lymphoma cells L5178Y To improve the reliability of mutant frequencies for risk evaluation, the mutation induction in mammalian cells in vitro has to be determined using several genetic markers. We measured the induction of mutations simultaneously at the X-linked HGPRT (hypoxanthine--guanine-phosphoribosyl-transferase)locus and the autosomal TK (thymidine kinase)-locus in a L5178Y mouse lymphoma cell line which is heterozygous for the enzyme TK (denoted as TK÷/--). Deficiency of the purine salvage enzyme HGPRT results in resistance to the purine analogue 6-thioguanine, whereas TK-/-- mutants can be selected for using BUdR as the selective agent. The reliability of the assay systems was assured by reconstruction experiments for measuring the optimal inoculum and by expression time experiments. In contrast to the long expresssion time (7--8 days) which is necessary before all the mutants induced at the HGPRT-locus become fully expressed, a plateau of the induced mutant frequency at the TKlocus is already reached after 2 to 3 days. A linear relationship is found between the induced mutations at each of the two loci and the concentration of EMS (2.5, 5 and 10 mM, 2 h treatment), when the stable mutant frequencies are used. The induction of mutations at the TK-locus appeared to be about two times higher than at the HGPRT-locus. Experiments with other mutagenic agents are in progress.

113 Kondo, S., Department of Fundamental Radiology, Faculty of Medicine, Osaka University, Osaka 530 (Japan) Misrepair model for carcinogenesis by 4-nitroquinoline 1-oxide based on its parallelism with mutagenesis in Escbericb~ coli Evidence for mutation theory of cancer is presented by reviewing the work done by a cooperative research team of about 15 researchers headed by the author with the working hypothesis that carcinogenesis in mammals parallels mutagenesis in bacterium at the level of DNA damage and repair. 4NQO (4-nitroquinoline 1-oxide) mimics UV: 4NQO produces adducts to purine bases of DNA, the adducts are repaired by excision repair, both in E. coli and mammals as measured biochemicaUy, and the repair is error-free as measured by mutations in E. coli and malignant transformation in cultured mouse cells, suggesting that the unexcised adducts are the major cause of mutations and cell transformation. Caffeine administered after 4NQO greatly reduces mutant yields in an excisionless strain of E. coli, transformants of mouse cells and lung tumors in mice. These suggest that caffeine suppresses the action of the error-

212 prone post-replication repair responsible for patching the defect in daughter strands (induced by 4NQO--purine adducts in the template strands) with abnormal base sequences. However, caffeine is effective for suppression of tumor induction in mice as late as 5 days after 4NQO in contrast to the caffeine sensitivity of E. coli or cultured mouse cells being limited during the first-post-4NQO DNA replication. These puzzling facts can be explained by a modification of Cairns' model of immortal DNA-strand transfer to offspring stem cells alone.

114 Kortselius, M.J.H., and E. Vogel, Department of Radiation Genetics and Chemical Mutagenesis, State University of Leiden (The Netherlands) Mutation induction by indirectly acting mutagens in Drosophila larvae

Adult males of Drosophila are capable of activating a variety of indirectly acting mutagens. Since Drosophila larvae are also frequently used in chemical mutagenesis studies, the question whether larvae can execute the essential activation steps which convert a given indirect mutagen into reactive metabolites is of particular interest. The mutagen used in these experiments, DEN, requires MFO-activity for its mutagenic action. Drosophila larvae were cultured on standard food supplemented with DEN (different concentrations). This method of administration of DEN to larvae resulted in the induction of sex-linked recessive lethals, demonstrating the ability of larvae to activate this indirectly acting mutagen. When DEN was fed only at particular stages of larval development, mutation induction occurred in first, second and third instar larvae, indicating MFO-activity in all stages of larval development. The LEC for mutation induction was determined and compared with that obtained in adult feeding experiments. In males, the LEC of DEN was over one order of magnitude lower when the chemical was fed to larvae than when it was administered (by feeding) to adults. Abbreviations: DEN, N-nitroso-N,N'-diethyl-amine; LEC, lowest e f f e c t i v e c o n c e n t r a t i o n ; MFO, mix ed function oxidases.

115 Kraj~inSaniS, B., Faculty of Defectology, University of Belgrade (Yugoslavia), Z. ZuniS, Radiobiological Laboratory, Boris Kidric Institute Belgrade (Yugoslavia), and A. Lazarov, Medical Military Academy, Belgrade (Yugoslavia) Effect o f some hemiotherapeutics o n frequency o f lymphocytes chromosomal aberrations in certain systemic diseases

The aim of this study is the determination of chromosomal changes in patients suffering from systemic diseases (Lupus erythematodes and chr.