In vitro repair synthesis of BCNU-induced DNA damage.

The nitrosoureas including BCNU are potent chemotherapeutic drugs and have been used extensively for treatment of brain tumors and other neoplasias but the mechanisms of action for the DNA lesions created and their repair are still unclear. We have recently determined the in vitro repair of BCNU-treated DNA with cellular extracts and with DNA modifying enzymes. BCNU not only caused an increase in breaks in plasmid DNA, but an increase in cross-linked DNA was also observed after restriction enzyme digestion followed by gel electrophoresis. When HeLa cell-extracts were incubated with BCNU-treated DNA, 5-10 fold increases in DNA repair synthesis were observed as compared with untreated control. Substantial increases in 5'OH and 3'OH sites of the breaks were also found in BCNU-treated DNA as determined by the 10-20 fold increases in labeling with T4-DNA kinase and by endogenous polymerases, while the amount of ligatable sites were at a minimal. When the repair capacity of two glioma cell lines (UWR1 and UWR3) with differential BCNU sensitivity, and cells from a chromosomal breakage disease, Bloom's syndrome (BS), were assessed, the activities of the two glioma cells were about 20-30% of the normal lymphoblastoid cells and HeLa cells, whereas no difference was observed in BS cells. However, differential patterns of DNA bands were observed in the glioma samples suggesting cell-type specific capacities of repair synthesis. These data are in accordance with the concept that BCNU creates multiple DNA lesions and suggests different cell types may develop a variety of repair capabilities.