Relationships between chromosome damage, cell cycle delay and cell killing induced by bleomycin or X-rays

The extent of mitotic delay and chromosome aberration induction by X-rays and bleomycin has been compared in normal human foetal fibroblasts at doses giving approximately equal levels of cell killing, assayed as colony-forming ability. Bleomycin induced much less G2 delay and chromosome damage than X-rays. We conclude that the major mechanism of cell killing by bleomycin does not involve chromosome damage but the cells pass through a number of division cycles before dying and a common DNA lesion is involved in G2 delay and chromosome damage.