Novel Indenoisoquinolines NSC 725776 and NSC 724998 Produce Persistent Topoisomerase I Cleavage Complexes and Overcome Multidrug Resistance

Abstract

Camptothecin (CPT) derivatives are effective anticancer drugs, especially against solid tumors. As CPTs are chemically unstable and have clinical limitations, we have synthesized indenoisoquinolines as novel topoisomerase I (Top1) inhibitors. We presently report two indenoisoquinoline derivatives, NSC 725776 and NSC 724998, which have been selected for therapeutic development. Both are potent Top1 inhibitors and induce Top1 cleavage at unique genomic positions compared with CPT. Consistent with Top1 poisoning, protein-linked DNA breaks were detected in cells treated with NSC 725776 and NSC 724998 at nanomolar concentrations. Those druginduced protein-linked DNA breaks persisted longer after drug removal than those produced by CPT. Studies in human cells in culture show that NSC 725776 and NSC 724998 exert antiproliferative activity at submicromolar concentrations. Furthermore, NSC 725776 and NSC 724998 show crossresistance in cells deficient or silenced for Top1, which is consistent with their selective Top1 targeting. Similar to other known Top1 inhibitors, NSC 725776-treated and NSC 724998-treated cells show an arrest of cell cycle progression in both S and G 2 -M and a dependence on functional p53 for their cytotoxicity. Dose-dependent ;-H2AX foci formation was readily observed in cells treated with NSC 725776 and NSC 724998. These ;-H2AX foci were detectable at pharmacologically relevant doses for up to 24 h and thus could be used as biomarkers for clinical trials (phase 0). [Cancer Res 2007; 67(21):10397-405]

Activity of Indenoisoquinolines against African Trypanosomes

“…Relative to mammalian cells, African trypanosomes have a unique heteromultimeric topoisomerase IB (7) and a substantially more AT-rich genome (6) that is packaged differently (15). Thus, decreased affinity for the topoisomerase-DNA bi- (1,20), the greater-than-expected killing activity against T. brucei makes it formally possible that cleavable complexes detected in the K-SDS assay may contain DNA adducts with other topoisomerases. Additionally, while the N-6-polyamine substituent may well enhance transport into the trypanosome, the demonstrated activity of other polyamine analogs against T. brucei (31) permits speculation that these N-6-substituted indenoisoquinolines may also interfere with the polyamine metabolic pathway, a proven drug target in these parasites (3).…”

Tyrosyl-DNA Phosphodiesterase 1 (TDP1) Repairs DNA Damage Induced by Topoisomerases I and II and Base Alkylation in Vertebrate Cells

“…One nanomolar labeled DNA substrates in a 10-l reaction volume were incubated with the indicated concentration of recombinant human TDP1 (52) or cell lysate for the indicated time at 25°C in a buffer containing 80 mM KCl, 2 mM EDTA, 1 mM dithiothreitol (DTT), 40 g/ml bovine serum albumin, 50 mM Tris-HCl, pH 7.5, and 0.01% Tween 20. Reactions were terminated by adding 1 volume of gel loading buffer (96% (v/v) formamide, 10 mM EDTA, 1% (w/v) xylene cyanol, and 1% (w/v) bromphenol blue).…”

Targeting the c-Kit Promoter G-quadruplexes with 6-Substituted Indenoisoquinolines

“…Indenoisoquinoline derivatives have previously shown antiproliferative properties in various human cancer cell lines and have been considered to be topoisomerase 1 inhibitors. [27][28][29] Herein, we present the design, synthesis, and biophysical and primary biological evaluation of 6-substituted indenoisoquinolines as a new class of G-quadruplex stabilizing ligands. We have synthesized indenoisoquinolines 1a-e from commercially available indeno[1,2-c]isochromene-5,11-dione (2) with excellent yields (Scheme 1) (generally >90%, see the Supporting Information for details).…”