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Kinetics and Extent of Repair of Bleomycin-induced Chromosome Damage in Quiescent Normal Human Fibroblasts and Human Mononuclear Blood Cells¹

Department of Developmental Therapeutics, The University of Texas M.D. Anderson Hospital and Tumor Institute at Houston [P. S., W. N. H.], and the University of Texas Graduate School of Biomedical Sciences [W. N. H.], Houston, Texas 77030

The kinetics of chromosome damage repair after belomycin treatment was studied in quiescent mononuclear human blood cells and human fibroblasts using the technique of premature chromosome condensation. Quiescent cells were treated with bleomycin for 30 min, washed free of drug, and fused with mitotic HeLa cells after various repair times. The amount of chromosome damage remaining was assayed in the G₁ prematurely condensed chromosomes. The chromosome repair kinetics profile exhibited fast- and slow-repair components. The fast chromosome repair component was apparent within 2 hr after bleomycin treatment, with a significant amount of repair having occurred within 30 min. The absolute rate of chromosome repaire then significantly slowed beyond 2 hr after treatment. The rate of chromosome repair was slightly dependent on dose with a higher rate observed at a higher dose. Interestingly, while quiescent fibroblasts were more sensitive to bleomycin than were mononuclear blood cells, both cell populations exhibited similar repair kinetics. These results suggest the following: (a) quiescent human fibroblasts and mononuclear blood cells show similar chromosome repair kinetics after bleomycin treatment; (b) there exist both fast- and slow-repair components after bleomycin treatment; and (c) the rate of chromosome repair is dependent on the degree of initial damage.

¹ Supported in part by NIH Grants CA 27931 and CA 28153.

² To whom requests for reprints should be addressed.

Received 5/16/83. Accepted 11/ 7/83.