Cytotoxic effect and induction of sister chromatid exchange in exponentially growing rat 9L gliosarcoma cells after brief exposure to BrdU

Abstract. The magnitude of DNA modulation in rat 9L gliosarcoma cells after a brief exposure to bromodeoxyuridine (BrdU) was studied by assaying colony-forming efficiency (CFE) and the number of sister chromatid exchanges (SCEs) per metaphase. The CFE assay showed that a 1-hr exposure to BrdU, at concentrations ranging from 10 to 1000 μ M, produced a maximum cell kill of 5%. After a 2-hr exposure to 20 μ M BrdU, the surviving fraction was 0.99, and even at a BrdU concentration of 1000 μ M, 77% of the 9L cells survived. Compared with control cultures, the relative number of SCEs per metaphase in treated cultures was increased after a 1-hr exposure to BrdU at concentrations of 100 μ M or more and after a 2-hr exposure to concentrations of 20 μ M or more; no increase was observed in cells treated for 30 min with BrdU at concentrations up to 1000 μ M. When the treated cells were allowed to grow in BrdU-free growth medium, the number of SCEs per metaphase returned to the control level within 24 hr, even after exposure to BrdU at concentrations as high as 1000 μ M. These results demonstrate that exposure to BrdU at concentrations of up to 1000 μ M for 30 min, 100 μ M for 1 hr, and 20 μ M for 2 hr causes little modulation of DNA.