Activation of cyclophosphamide for in vitro testing of cell sensitivity

Two methods are described for the activation of cyclophosphamide by a liver microsome preparation. These procedures were applicable to an assay in vitro which tests the sensitivity of tumor cells to the drug. Satisfactory results were obtained either by pretreatment of the cyclophosphamide and removal of the microsomes before testing or by the somewhat simpler procedure of mixing drug, microsomes, and test cells for the assay. Microsome treatment of bleomycin gave a smaller increase in activity, and much smaller effects were seen on some other drugs.