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Cellular Replication Kinetics and Persistence of Sister Chromatid Exchange-inducing Lesions in Normal and Lymphoma AKR Cells following Exposure to 1,3-Bis(2-chloroethyl)-1-nitrosourea¹

Departments of Medicine and Radiology [J. A. B., S. S. B.], School of Medicine, and Departments of Biostatistics [J. A. B., M. K. C.] and Industrial and Environmental Health Sciences [M. K. C.], Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania 15261

The present studies were designed to evaluate the role of cell cycle time and time of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) administration on the persistence of sister chromatid exchange (SCE)-inducing lesions in normal and lymphoma second- and third-division AKR bone marrow cells.

Normal second-division cells harvested from mice given injections of BCNU at the start of an 18-, 24-, or 28-hr 5-bromo-2-deoxyuridine (BrdUrd) infusion exhibited similar linear dose-dependent increases in SCE frequencies (p > 0.05). The faster-cycling lymphoma cells, harvested after 18-hr BrdUrd infusion, had significantly higher baseline (p < 0.05) and BCNU-induced increases (p < 0.001) in SCE frequencies than did normal cells.

Dose-dependent increases in SCE frequencies were demonstrated in third-division normal and lymphoma cells from mice infused with BrdUrd for 24 or 28 hr. Whereas lymphoma cells from mice treated with 3.3 mg BCNU per kg exhibited 31.2 ± 3.9 (S.E.) SCEs in second-division cells and 4.7 ± 0.4 reciprocal and 22.9 ± 2.0 nonreciprocal SCEs in third-division cells, a 5 times higher dose of BCNU was required to induce similar levels of 30.0 ± 0.8 SCEs in second-division cells and 4.4 ± 0.6 reciprocal and 22.6 ± 1.2 nonreciprocal SCEs in third-division normal cells.

BCNU dose-dependent increases in SCE frequencies were also observed following injection of BCNU 8 hr after the start of BrdUrd infusion. The unexpectedly higher levels of SCEs for both normal and lymphoma cells by this treatment protocol may be due to SCEs occurring at the same site in successive divisions in BrdUrd. Regardless of the protocol used, lower nonreciprocal SCE frequencies were observed in third-division cells relative to SCE frequencies in second-division cells; a possible consequence of the cytotoxicity of BCNU. Injection of BCNU produced significant changes in the proportions of normal and lymphoma cells completing one, two, and three or more divisions in BrdUrd.

Lymphoma cells were consistently more sensitive to the specific type(s) of BCNU-induced damage leading to SCEs and cell death than were normal cells. These studies indicated that differences in SCE response were not due to cell cycle time, time of drug administration, or potential for repair. It is therefore suggested that increased sensitivity of lymphoma versus normal cells may be due to increased cellular uptake of BCNU.

¹ Study supported in part by American Cancer Society Grant CH-101.

² To whom requests for reprints should be addressed, at RC510 Scaife Hall, University of Pittsburgh School of Medicine, Pittsburgh, Pa. 15261.

Received 12/23/81. Accepted 4/13/82.