Platinum-induced mutations to 8-azaguanine resistance in Chinese hamster ovary cells.

Abstract 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%: ci s-Pt(NH 3 ) 2 - Cl 2 (0.9/1.5 μM)> Pt(SO 4 ) 2 + methylcobalamin (MeB-12) methylation product (20/10μM) > K 2 PtCl 4 (32/50 μM) = K 2 PtCl 6 (34/50 μM) = MePtCl −2 3 (60/50μM) > Pt(SO 4 ) 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 OUA R mutants above the spontaneous frequency 6.0 X 10 -6 . Parallel treatments with 800 μM (100 μM/ml) ethyl methanesulfonate (EMS) increased the OUA R 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-(NH 3 ) 2 Cl 2 , Pt(SO 4 ) 2 , and the product from Pt(SO 4 ) 2 + MeB-12. Identical 20 h exposures to varying amounts of K 2 PtCl 4 , K 2 PtCl 6 , and MePtCl 2 3 did not induce 8-AG R mutants. Optimal detection of Pt-induced 8AG R mutants required 7 post-treatment, expression doublings in suspension culture. Under our selection conditions 8/8 spontaneous and 24/24 Pt-induced 8-AG R variants contained reduced hypoxanthine-guanine phosphoribosyl transferase (HGPRT) specific activities (means ranging from 3 to 11% of the parental CHO-S cells).