Investigation of the Lactam Side Chain Length Necessary for Optimal Indenoisoquinoline Topoisomerase I Inhibition and Cytotoxicity in Human Cancer Cell Cultures

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Abstract
Indenoisoquinolines with lactam substituents such as ethylamino, propylamino, and butylamino have previously demonstrated potent biological activity, but an optimal length has never been established. In the present study, a series of simplified indenoisoquinoline analogues possessing a linker spacing of 0−12 carbon atoms between the lactam nitrogen and the terminal amino group have been prepared, determining that 2−4-atom lengths are optimal for topoisomerase I inhibition and cytotoxicity. Using these lengths, analogues were prepared with the amino group and portions of the linker replaced by a pyridine ring. A three-carbon spacer within the pyridine series still demonstrated potent topoisomerase I inhibition.