An in vitro metabolic activation assay using liver microsomes in diffusion chambers: induction of sister chromatid exchanges and chromosome aberrations by cyclophosphamide or ifosfamide in cultured human and Chinese hamster cells.

An in vitro activation assay for identifying suspected indirect mutagens and/or carcinogens is described. It involves the incubation of diffusion chambers filled with S-9 mix (S-9 fraction of rat liver and enzyme cofactors) and a compound under test with mammalian cells. The induction of sister chromatid exchanges (SCE) and/or chromosome aberrations can then be used as an indicator of mutagenicity or carcinogenicity. When a human lymphoid cell line, B35M, or Chinese hamster cell lines, V79 and CHO, are cultured with the diffusion chamber containing S-9 mix and the well-known indirect mutagen cyclophosphamide or its analog ifosfamide, a dose related increase in SCE or chromosome aberrations is observed in all the lines. The major advantages of this system over other in vitro activation assays are alleviation of cytotoxicity of S-9 mix and flexibility of treatment time.