KINETICS OF CLEAVAGE OF INTRACELLULAR AND EXTRACELLULAR SIMIAN-VIRUS-40 DNA WITH THE ENEDIYNE ANTICANCER DRUG C-1027

A kinetic analysis of cleavage of simian virus DNA (SV40 DNA) inside a nd outside green monkey BSC-1 cells by the enediyne-protein antibiotic C-1027 and its free chromophore is described. Information on rate con stants was obtained by fitting populations of forms I (closed circular DNA), II (nicked circular DNA) and III (linear DNA) of SV40 DNA as a function of drug concentration to a kinetic model which includes: cutt ing of form I to give form II with rate constant k(1), cutting of form I to give form III with rate constant k(4), and cutting of form II to give form III with rate constant k(2). The ratio of single-strand (ss ) to double-strand (ds) cutting for the holoantibiotic and the free ch romophore, k(1)/k(4), is approximately 1.8 for extracellular SV40 DNA. For intracellular DNA and extracellular DNA which has been post-treat ed with putrescine, ds cutting is much more probable, with k(4) about four times as large as k(1). This observation suggests that amine grou ps present in the cell are able to convert abasic sites opposite an as break into a ds break in SV40 chromatin. The overall rate of cleavage of form-I DNA inside the cell is much larger than the rate outside, t he sum k(1) + k(4) being about three times as large for intracellular DNA as for extracellular DNA.