title: 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.
abstract: 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.
authors: Department of Medicinal Chemistry and Molecular Pharmacology and the Purdue Cancer Center, School of Pharmacy and Pharmaceutical Sciences, Purdue University, West Lafayette, Indiana 47907, USA.
authors: Alexandra
authors: A
authors: Ioanoviciu
authors: Smitha
authors: S
authors: Antony
authors: Yves
authors: Y
authors: Pommier
authors: Bart L
authors: BL
authors: Staker
authors: Lance
authors: L
authors: Stewart
authors: Mark
authors: M
authors: Cushman
mesh_terms: D000970:Antineoplastic Agents / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D045744:Cell Line, Tumor; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry*; D004264:DNA Topoisomerases, Type I / Q000737:chemistry; D004354:Drug Screening Assays, Antitumor; D006801:Humans; D007546:Isoquinolines / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D008958:Models, Molecular; D013329:Structure-Activity Relationship; D059004:Topoisomerase I Inhibitors
chemical_list: C502983:2,3-dimethoxy-8,9-methylenedioxy-11H-indeno(1,2-c)isoquinoline; D000970:Antineoplastic Agents; D007546:Isoquinolines; D059004:Topoisomerase I Inhibitors; D004247:DNA; D004264:DNA Topoisomerases, Type I