DNA repeat length in chromatin from murine bone marrow and L1210 leukaemia cells

Previous studies have suggested that 1-(4-amino-2-methylpyrimidine-5-yl)-methyl-3-(2-chloroethyl) -3-nitrosoureahydrochloride (ACNU) and 1,(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) bind specifically to the nucleosomal DNA of murine bone marrow and L1210 leukaemia cells whereas the glucose nitrosoureas, 2-(3-(2-chloroethyl)-3-nitrosoureido)-2-deoxy-D-glucopyranose, (chlorozotocin, CLZ) and 1-(2-chloroethyl)-3-(-D-glucopyranosyl)-1-nitrosourea (GANU), bind preferentially to the linker DNA of bone marrow but not tumour cell chromatin. In order to provide an explanation for this differential, the DNA repeat and linker lengths in murine bone marrow and L1210 leukaemia cells were measured using electrophoresis of micrococcal nuclease-digested DNA. The linker length of bone marrow chromatin was approximately 22% longer than that in L1210 leukaemia cells from mouse ascites. The linker length of L1210 cells maintained in suspension culture was 27% less than in those from ascites fluid. The tissue-specific toxicity of sugar nitrosoureas and the differential binding of these drugs to chromatin does not appear to correlate quantitatively with differences in DNA linker length.