Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences , Nanyang Technological University , 21 Nanyang Link , Singapore 637371 , Singapore.
Department of Chemistry, BioScience Research Collaborative , Rice University , 6100 Main Street , Houston , Texas 77005 , United States.
J Am Chem Soc. 2019 May 15;141(19):7842-7852. doi: 10.1021/jacs.9b01800. Epub 2019 May 3.
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 regions of DNA in the interphase and metaphase of eukaryotic cells are unprotected by histone proteins during entire cell cycles and because these unprotected regions of DNA are vulnerable to attack by DNA binders, it was concluded that the observed double-strand DNA cleavage and very low sequence selectivity by shishijimicin A may account for its extraordinary cytotoxicity.
尽管石蒜裂菌素 A 及其对多种癌细胞系的极端抗癌活性已为人所知十余年，但它假定的 DNA 切割机制尚未得到证实。本文报道了石蒜裂菌素 A 结合和切割双链 DNA 的研究。这些研究结果支持了以下假设：即 DNA 链的断裂是由石蒜裂菌素 A 的烯二炔核心通过 Bergman 环芳构化形成的 1,4-苯并二自由基引起的，而这种环芳构化是在巯基的激活下发生的。此外，还利用双链超螺旋 DNA 切割实验、与已知的小沟结合物竞争、紫外光谱研究和电泳分析，阐明了该分子与 DNA 的结合模式。这些研究表明，石蒜裂菌素 A 结合到双链 DNA 的小沟中，其β-咔啉部分通过嵌入作用参与结合。此外，由于真核细胞的有丝分裂和间期中 DNA 的裸露连接区在整个细胞周期中不受组蛋白的保护，并且这些未受保护的 DNA 区域易受到 DNA 结合物的攻击，因此可以推断，观察到的双链 DNA 切割和石蒜裂菌素 A 极低的序列选择性可能是其具有非凡细胞毒性的原因。
