Spontaneous and mitomycin-C induced sister-chromatid exchanges : Comparison of in vivo and in vitro systems

Frequencies of sister-chromatid exchanges (SCE) were measured in vitro in mouse fibroblasts and in vivo in mouse bone-marrow cells. SCE levels in these cell systems were measured in response to varying concentrations of bromodeoxyuridine (BrdU) and mitomycin-C (MMC). Although BrdU was found to induce SCE in both cellular systems, baseline SCE levels were 2- to 3-fold higher in vitro than in vivo. SCE induction was found to be a linear function of MMC concentration in vivo and in vitro; however the slope of the in vivo curve was 5-fold higher. The interaction of BrdU substituted DNA and MMC was examined by administering a fixed dose of MMC with increasing concentrations of BrdU. The induced SCE frequencies appeared to be additive. In addition to measuring drug-induced SCE, the BrdU differential staining technique allows concomitant measurement of the inhibition of cellular replication by the test drugs.