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Differential Inhibition of the Rejoining of X-ray-induced DNA Strand Breaks in Normal and Transformed Human Fibroblasts Treated with 1,3-Bis(2-chloroethyl)-1-nitrosourea in Vitro¹

Laboratory of Molecular Pharmacology, Division of Cancer Treatment, National Cancer Institute, NIH, Bethesda, Maryland 20014

The effects of 1,3-bis(2-chloroethyl)-1-nitrosourea on the rejoining of X-ray-induced DNA strand breaks were examined in normal human fibroblasts (WI-38) and a simian virus 40-transformed derivative (VA-13) with the use of alkaline sucrose sedimentation. 1,3-Bis(2-chloroethyl)-1-nitrosourea was capable of partially inhibiting repair of X-ray-produced DNA strand breaks in both cell types when the drug was added to the culture medium immediately after X-irradiation. However, when 1,3-bis(2-chloroethyl)-1-nitrosourea exposure preceded X-ray by 1 hr, DNA repair was inhibited to a much greater extent than it was when 1,3-bis(2-chloroethyl)-1-nitrosourea followed X-ray. The inhibition of DNA repair by 1,3-bis(2-chloroethyl)-1-nitrosourea appeared to be complete in the transformed VA-13 cells, while only partial inhibition of repair was observed in the normal WI-38 cells.

¹ Presented in part at the 68th Annual Meeting of the American Association for Cancer Research (6).

² To whom requests for reprints should be addressed.

Received 8/24/77. Accepted 12/12/77.