PLATINUM-INDUCED MUTATIONS TO 8-AZAGUANINE RESISTANCE IN CHINESE-HAMSTER OVARY CELLS

6 platinum (Pt) compounds were compared in suspension cultured Chinese hamster ovary (CHO-S) cells with respect to their inhibition of growth, their reduction of cloning efficiency, and their induction of mutants resistant to 200 μM (30 μg/ml) 8-azaguanine (8-AG) and 3 mM ouabain (OUA), respectively. The toxicity of these compounds can be ranked by the medium concentrations which decrease suspension growth/or cloning efficiency by 50%: cis-Pt(NH3)2- Cl2 (0.9/1.5 μM)> Pt(SO4)2 + methylcobalamin (MeB-12) methylation product (20/10μM) > K2PtCl4 (32/50 μM) = K2PtCl6 (34/50 μM) = MePtCl-23 (60/50μM) > Pt(SO4)2 (66/105 μM). Following 20 h exposures to concentrations which resulted in relative survivals of 80-2%, none of the foregoing compounds increased consistently the frequency of OUAR mutants above the spontaneous frequency 6.0 X 10-6. Parallel treatments with 800 μM (100 μM/ml) ethyl methanesulfonate (EMS) increased the OUAR mutant frequency 10-12-fold. Using 8-AG for mutant selection, dose-dependent increases of 5-7-fold above the spontaneous frequency (3-8 X 10-5 were obtained with cis-Pt-(NH3)2Cl2, Pt(SO4)2, and the product from Pt(SO4)2 + MeB-12. Identical 20 h exposures to varying amounts of K2PtCl4, K2PtCl6, and MePtCl23 did not induce 8-AGR mutants. Optimal detection of Pt-induced 8AGR mutants required 7 post-treatment, expression doublings in suspension culture. Under our selection conditions 8/8 spontaneous and 24/24 Pt-induced 8-AGR variants contained reduced hypoxanthine-guanine phosphoribosyl transferase (HGPRT) specific activities (means ranging from 3 to 11% of the parental CHO-S cells). © 1979.