DNA Binding and Cleavage Modes of Shishijimicin A

Although shishijimicin A and its extreme potencies against an array of cancer cell lines have been known for more than a decade, its assumed DNA-cleaving mechanism has not been substantiated as yet. Herein we report studies that reveal binding and scission of double-stranded DNA by shishijimicin A. The results of these studies support the proposed hypothesis that DNA strand scissions are caused by 1,4-benzenoid diradicals formed by Bergman cycloaromatization of the enediyne core of shishijimicin A upon activation by thiols. In addition, double-stranded supercoiled DNA-cleavage experiments with shishijimicin A in competition with known minor groove binders, UV spectroscopic studies, and electrophoretic analysis were utilized to clarify the binding mode of the molecule to DNA. These investigations indicate that shishijimicin A binds to the minor groove of double-stranded DNA and that its β-carboline moiety plays a role in the binding through intercalation. In addition, due to the fact that naked linker regi...