Unscheduled DNA synthesis detection and metaphase analysis in a common test system in vivo — in vitro

Abstract The induction of clastogenic events in vivo is easily detected by using bone marrow metaphase analysis. We have previously shown that it is possible to detect unscheduled DNA synthesis (UDS) by culturing the lymphocytes of animals treated in vivo in the presence of 3H‐thymidine ([3H]dThd). Rats were treated orally with cyclophosphamide (25, 50 and 75 mg kg−1) or 2‐acetamidofluorene (10, 20 and 30 mg kg−1) suspended in Methocel® K4M Premium or with vehicle (10 ml kg−1). Five rats per group received a single dose, and peripheral blood obtained from each rat was maintained in culture with [3H]dThd. Radioautography was used as the indicator system for UDS, and bone marrow cells arrested at metaphase were examined for clastogenic events. The slides were coded and read blind to eliminate bias. A minimum of 500 cells and 50 cells were scored per rat for UDS and clastogenicity, respectively. A significant, dose‐related increase in UDS was observed in animals from both test groups and there was a significant increase in clastogenicity in the cyclophosphamide‐treated animals. The utility of one test animal for several mutagenicity tests to incorporate in situ metabolic biotransformation and yield more comparable data is supported by this work. We feel the combination of UDS and metaphase analysis in a common test animal will enable investigators to measure more closely several types of genotoxic activity induced by a single compound.