[Induction of sister chromatid exchange (SCE) and incorporation of BUdR in mouse cells treated with methotrexate].

MTX (approx. DI 50) induced an approx. 140% increase in SCE over controls. Increasing the BUdR concentration from 10(-5) to 10(-4) M an approx. 135% increase in SCE over controls was also obtained. The quenching of the H33258 dye fluorescence, measured microspectrofluorimetrically, suggested an increased in corporation of BUdR in MTX treated cells, roughly compatible with almost a doubling of the SCE control level in absence of MTX. Thus, at least a large fraction of the MTX induced SCE increase appeared to be dependent from an enhanced BUdR incorporation.