Induction of Anchorage Independence in Human Diploid Foreskin Fibroblasts by Carcinogenic Metal Salts1

We studied whether arsenic, nickel, and chromium compounds that are human carcinogens could induce transformation of cultured primary human diploid foreskin cells (HFC). All nickel compounds tested, PbCrO<, K2Cr2O7, CrO3, Na2HAsO4, NaAsO2, and jV-methyl-A/'-nitro/V-nitrosoguanidine (MNNG) caused significant (p = 0.001) dose-de pendent inductions of anchorage-independent colonies in HFC. kl l.. \s( )4. CaCl2, M ii< l> and Hg(CH3CO2)2 did not induce anchorage independence. Optimal expression times for induction of anchorage independence in HFC were observed as early as 11 days following treatment with MNNC, Ni3S2, Ni(C2H]O2)2, or NiSO<. Cell strains derived from anchorageindependent colonies showed 33 to 429-fold higher plating efficiencies in soft agar than parental populations, and the anchorage-independent phenotype was stable for eight passages, at which time cells senesced. Anchorage-independent cell strains derived from metal salt-treated cells were not resistant to the cytotoxicity of metal salts, indicating metal salts induced rather than selected for anchorage independence. Nine of 10 cell strains derived from metal compoundor MNNG-induced anchorageindependent colonies displayed the same or lower saturation densities than untreated human fibroblasts. None of these cell strains escaped senescence or showed definitive morphological transformation. MNNG (1 MU/»il)induced anchorage independence and mutation to ouabain resistance and 6-thioguanine resistance in HFC, but concentrations of N'i.-Si that induced anchorage independence did not induce mutation at either locus in HFC. These results demonstrate that carcinogenic metal salts induce stable anchorage independence early in human diploid foreskin fibroblasts, and this anchorage independence is independent of other in vitro markers of fibroblast transformation, such as focus formation or immortality. Metal salt induction of anchorage independence can now be used as an assay to study mechanisms of genotoxicity exerted by carcinogenic metal com pounds in human cells.