Synthesis and Mechanism of Action Studies of a Series of Norindenoisoquinoline Topoisomerase I Poisons Reveal an Inhibitor with a Flipped Orientation in the Ternary DNA−Enzyme−Inhibitor Complex As Determined by X-ray Crystallographic Analysis
journal contributionposted on 28.07.2005, 00:00 by Alexandra Ioanoviciu, Smitha Antony, Yves Pommier, Bart L. Staker, Lance Stewart, Mark Cushman
Any type of content formally published in an academic journal, usually following a peer-review process.
Several norindenoisoquinolines substituted with methoxy or methylenedioxy groups have been prepared and their anticancer properties evaluated in cancer cell cultures and in topoisomerase I inhibition assays. 2,3-Dimethoxy-8,9-methylenedioxy-11H-indeno[1,2-c]isoquinoline hydrochloride (14) is a strong topoisomerase I inhibitor and also displays very high cytotoxicity in the NCI cancer cell culture screen (mean graph midpoint of 50 nM). The X-ray crystal structure of norindenoisoquinoline 14 in complex with topoisomerase I and DNA has been solved, providing insight into the structure−activity relationships within this class of new anticancer agents. The number and position of the norindenoisoquinoline substituents have a significant influence on biological activity and demonstrate that substitution on the nitrogen atom is not an absolute requirement for the antitumor effect of the indenoisoquinolines. Removal of the 11-keto group from the lead compound 1 and replacement of the N-alkyllactam with an unsubstituted pyridine ring causes the indenoisoquinoline ring system to flip over in the DNA−enzyme−inhibitor ternary complex. This allows the nitrogen atom to assume the hydrogen bond acceptor role of the 11-keto group, resulting in hydrogen bonding to Arg364.