DIFFERENTIAL INHIBITION OF REJOINING OF X-RAY-INDUCED DNA STRAND BREAKS IN NORMAL AND TRANSFORMED HUMAN FIBROBLASTS TREATED WITH 1,3-BIS(2-CHLOROETHYL)-1-NITROSOUREA INVITRO

Abstract

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 [embryo lung] fibroblasts (WI-38) and a SV 40-transformed derivative (VA-13) with the use of alkaline sucrose sedimentation. 1,3-Bis(2-chloroethyl)-1-nitrosourea [BCNU] 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. When BCNU exposure preceded X-ray by 1 h, DNA repair was inhibited to a greater extent than when BCNU followed X-ray. The inhibition of DNA repair by BCNU appeared to be complete in transformed VA-13 cells, while only partial inhibition of repair was observed in normal WI-38 cells.