Metabolizing systems in cell culture cytotoxicity tests.

1. The addition of 9000 g supernatant of rat liver homogenate (S9) or rat liver microsomal fractions to a cytotoxicity test system using BCL-D1 cells has been investigated. 2. The choice of culture medium influenced the intrinsic cytotoxicity of the metabolising system to the BCL-D1 cells. Use of Ham's F10 nutrient mixture resulted in greater cytotoxicity compared with several other media. 3. Microsomal fractions provided greater cytochrome P-450 dependent activation of cyclophosphamide and were less cytotoxic than S9. 4. Direct-acting toxic compounds, such as p-aminophenol, were less toxic in the presence of a metabolising system. This was due to protein-binding rather than enzymic detoxification.